EP2231924A1 - Method for dealing with faults occurring during the manufacture of a material web - Google Patents
Method for dealing with faults occurring during the manufacture of a material webInfo
- Publication number
- EP2231924A1 EP2231924A1 EP08863004A EP08863004A EP2231924A1 EP 2231924 A1 EP2231924 A1 EP 2231924A1 EP 08863004 A EP08863004 A EP 08863004A EP 08863004 A EP08863004 A EP 08863004A EP 2231924 A1 EP2231924 A1 EP 2231924A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- roll
- pressure
- nip
- digital valve
- digital
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
- D21G1/00—Calenders; Smoothing apparatus
- D21G1/002—Opening or closing mechanisms; Regulating the pressure
- D21G1/004—Regulating the pressure
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
- D21G1/00—Calenders; Smoothing apparatus
- D21G1/002—Opening or closing mechanisms; Regulating the pressure
- D21G1/004—Regulating the pressure
- D21G1/0046—Regulating the pressure depending on the measured properties of the calendered web
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F7/00—Other details of machines for making continuous webs of paper
- D21F7/04—Paper-break control devices
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F7/00—Other details of machines for making continuous webs of paper
- D21F7/06—Indicating or regulating the thickness of the layer; Signal devices
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
- D21G9/00—Other accessories for paper-making machines
- D21G9/0009—Paper-making control systems
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
- D21G9/00—Other accessories for paper-making machines
- D21G9/0009—Paper-making control systems
- D21G9/0045—Paper-making control systems controlling the calendering or finishing
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B11/00—Servomotor systems without provision for follow-up action; Circuits therefor
- F15B11/02—Systems essentially incorporating special features for controlling the speed or actuating force of an output member
- F15B11/04—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed
- F15B11/042—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed by means in the feed line, i.e. "meter in"
- F15B11/0426—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed by means in the feed line, i.e. "meter in" by controlling the number of pumps or parallel valves switched on
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B2211/00—Circuits for servomotor systems
- F15B2211/40—Flow control
- F15B2211/405—Flow control characterised by the type of flow control means or valve
- F15B2211/40576—Assemblies of multiple valves
- F15B2211/40592—Assemblies of multiple valves with multiple valves in parallel flow paths
Definitions
- the invention relates to a method as set forth in the preamble of claim 1 for dealing with faults occurring during the manufacture of a material web.
- the invention relates also to an apparatus for implementing the method set forth in the preamble of claim 1.
- the invention involves the use of digital valve units for controlling the action of fiber machine sections operated by hydraulic or pneumatic actuators.
- the fiber machine sections operated by hydraulic or pneumatic actuators refer to machine sections whose operation can be controlled by adjusting the flow rate and/or pressure of a fluid supplied to said sections.
- the fluid in turn, refers to a liquid, such as oil or water, or to a gas, such as air.
- the digital valve unit refers to a valve unit, including at least one digital valve group which in turn comprises a number of digital valves connected in parallel with respect to a fluid flow passing through the digital valve group.
- the volume flow of a fluid passing through a digital valve group is determined by an aperture of the digital valve group, i.e. a total valve opening area of the digital valves presently in an open position in a digital valve group.
- the digital valve refers to a valve, which is intended for adjusting the volume flow of a fluid and which has 2 - N different stepwise discrete adjustment positions, preferably 2 different discrete adjustment positions (open/shut), and the control signal delivered thereto from a control system being preferably digitalized.
- the control of a volume flow proceeding through a digital valve group occurs on the basis of a pressure difference between the fluid arriving at the digital valve group and that discharging from the digital valve group, which difference in turn depends on an aperture established by digital valves presently in an open position. Knowing the pressure difference of a fluid across a digital valve and the aperture of a digital valve group enables anticipating precisely the fluid volume flow proceeding through the digital valve group, which can be utilized in various high speed feed-forward adjustments. In the concept of feed-forward adjustments, the connection combinations of fluid- passing digital valves are selected in such a way that the desired action takes place in a pneumatic or hydraulic actuator coupled with the digital valve group.
- the analog valve refers in this application to a valve, in which the rate of volume flow through the valve (throttling, valve opening degree) depends on the magnitude of a control signal.
- Typical analog valves include servo and proportional valves.
- the fiber web refers to a web containing a fibrous material of at least partially natural origin, such as wood fibers.
- the employed fibrous material may also consist of straw, bagasse, grass, etc., among others.
- each slide valve must be specifically designed for a particular flow channel (the nominal size of a valve, i.e. the maximum volume flow through a valve, as well as the size of a valve's various flow ports within the size range, and the like details of a valve). This increases considerably the designing work for systems involving analog valves.
- -Analog valves are largely manufactured in individual pieces or in small series, which increases their manufacturing costs.
- -Analog valves exhibit fluctuation in adjustment, especially if there are major discrepancies between the initial adjustment position and the final adjustment position regarding the volume flow of a fluid passing through the valve.
- the fluctuation of adjustment leads to a slower control and a higher energy consumption.
- Another control slowing factor is the internal feedback of a slide valve, which is used for adjusting the position of a slide valve in the process of driving the valve from volume flow A to volume flow B.
- the invention relates to a method as set forth in claim 1 and to an apparatus capable of implementing said method.
- Replacing an analog regulation valve with a group of digital valves provides a considerable benefit in the control of hydraulic actuators used in paper machines and enables discarding the foregoing prior art problems:
- -Similar digital valves and digital valve groups can be used for a variety of applications, i.e. digital valves are multi-function valves.
- the operation and usability of a digital valve group depend on its control, because there is no disparity between digital valve groups in terms of the design of digital valves included therein.
- -Digital valves are inexpensive mass production articles, being needed in just a few sizes irrespective of the intended use, i.e. the design and operation of a hydraulic actuator controlled by digital valves.
- -A digital valve group is fault tolerant in operation, as when one of the digital valves develops a fault, other valves are able to make up for its operation, i.e. the fault is "circumvented".
- a digital valve group With a digital valve group, on the other hand, the same procedure can be performed in a feedforward mode of adjustment rapidly and accurately without delay and fluctuation, because the adjustment is applied to a volume flow passing through a plurality of smaller side-by-side arranged digital valves, the rate of a total volume flow proceeding therethrough (and also a pressure difference across the valve) being well predictable for each combination of currently open digital valves.
- the adjustment instruction (control signal) arriving at a digital valve group is digital, such as binary, in character. According to the adjustment instruction, an adjustment is made on a volume flow discharging from the digital valve group and on a flow-inflicted pressure by opening a particular valve combination in the digital valve group in view of achieving a desired aperture and volume flow rate of fluid for the digital valve group.
- each parallel- connected digital valve can only have a limited number of adjustment positions, i.e. the digital valve only has certain discrete flow positions.
- the digital valve has three positions: open / shut / high-speed opening.
- the positions of each digital valve are simply just on/off; the valve allows in its open position a certain volume flow to pass through, in its shut position it totally blocks the passage of a fluid flow therethrough.
- the digital valve group consists of digital valves with two positions (on/off).
- the volume flow proceeding through the valve with a higher nominal volume flow in its open position is always twice as high as the volume flow of the valve with a lower nominal volume flow.
- a digital valve group can be supplied with a binarized control signal, in which the control signal has its magnitude converted into a binary number.
- a digital valve group established by five on/off digital valves parallel- connected in an inlet flow, is controlled by means of a 12-unit control signal (adjustment instruction) of the same magnitude, wherein the sizes of volume flows admitted by digital valves 1 , 2, 3, 4, 5 are respectively 1 , 2, 4, 8 and 16 units
- figs. 1A and 1B show the effect of the number of digital valves included in a digital valve group on the attainable number of volume flows and on the accuracy of adjustment.
- Figs. 1A and 1B show the effect of the number of on/off digital valves included in digital valve groups on the attainable accuracy of adjustment as the digital valve group has 4 (fig. 1A) and 6 (fig. 1 B) digital valves in parallel connection.
- the graph shows a proportional volume flow for a digital valve group as a function of control, when the volume flow proceeding through the larger one of two valves with successive nominal volume flow rates among the group's digital valves is typically twice as high as that of the preceding valve (it is also possible to organize the volume flows of two valves with consecutive nominal volume flows in ratios other than multiples of two).
- the digital valve group has its control response approaching rapidly the response attainable by an analog slide valve as the number of valves is increased in the digital valve group, since each digital valve added to the group enables the number of possible opening combinations to be approximately doubled.
- the roll nip refers to a roll nip between two rolls, or also to a roll nip present between a roll and a belt, unless otherwise indicated.
- the belt can be e.g. a metallic, polymeric, felt type or wire type belt.
- Figs. 1 A and 1 B show the effect of the number of digital valves included in a digital valve group on the attainable number of volume flows and on the accuracy of adjustment.
- Fig. 2A shows schematically a multi-roll calender in a view directly to the calender's end face.
- Fig. 2B shows a pressure load adjustment for a supporting lever present at the end of two intermediate rolls by means of hydraulic actuators controlled by a digital hydraulic unit.
- Fig. 2C shows diagrammatically data and fluid flows for the control of another hydraulic actuator according to fig. 2B.
- Fig. 2D shows a synchronized control by means of two separate digital valve units for a hydraulic actuator coupled with supporting levers present at the ends of two intermediate rolls.
- Fig. 3A shows schematically the formation of a relief and reset pulse for a roll present in a multi-roll calender's roll nip by using a digital valve unit as the roll nip is about to receive an fault of fig. 3B; the figure shows the flows of a hydraulic fluid in the hydraulic actuator, as well as a pressure load for the roll.
- Fig. 3B shows, in a view directly to the end face, a roll nip between two rolls, which is about to receive a splice between two fiber webs.
- Fig. 3C shows a steady-state condition control for the supporting lever of an intermediate roll by means of a digital valve unit prior to the formation of a relief and reset pulse of fig. 3A.
- Fig. 3D shows a control for the supporting lever of an intermediate roll by means of a digital valve unit during a relief pulse of fig. 3A.
- Fig. 3E shows a control for the supporting lever of an intermediate roll by means of a digital valve unit during a reset pulse of fig. 3A.
- Fig. 3F shows, in a view directly to the end face, a roll nip between two rolls, which is about to receive a web break present in a fiber web.
- Fig. 3G shows the flows of a hydraulic fluid in a hydraulic actuator, existing in the high-speed opening of a multi-calender's roll nip established by digital hydraulic units, as well as a respective roll position in the roll nip being opened.
- Fig. 3H shows pressure and flow conditions existing in the high-speed opening process according to fig. 3A of a roll nip between a multi-calender's two intermediate rolls, in the control by a hydraulic cylinder for the pressure load of a supporting lever, on the piston head side and piston rod side of the cylinder.
- Fig. 4A shows schematically a long-nip calender in a view directly to the calender's end face.
- Fig. 4B shows in an enlarged scale a long-nip zone for the calender of fig. 4A.
- Fig. 5 shows schematically a control process for an oil-water heat exchanger by means of a digital hydraulic unit.
- Fig. 6 shows schematically a pressure load adjustment mode for one loading element based on a closed control system according to the prior art.
- Fig. 7 shows schematically a pressure load adjustment mode for an active roll loading element based on an open control system according to the invention.
- Typical operations for adjusting the hydraulic actuators of a calender by means of analog slide valves include: -pressurization of hydraulic cylinders coupled with the bottom and/or top roll of a multi-roll calender's roll set, which are used for adjusting pressure in the roll set's roll nips, as well as the opening process of roll nips in faults such as web breaks;
- the multi-roll calender can be lever-loaded, i.e. the roll nips are loaded by means of hydraulic cylinders coupled with supporting levers present at the ends of intermediate rolls or by means of loading elements operated by intra-roll hydraulic actuators.
- Each slide valve must be designed specifically for a particular flow channel (the nominal size of a valve and additionally the size of a valve's flow ports within the size range), which increases considerably the designing work for systems involving hydraulic components;
- the controls of hydraulic actuators executed by slide valves are fault-sensitive and, in addition, the electronics of control components for slide valves is susceptible to heat aging and faults caused by high temperatures; Slide valves are designed in individual pieces with the result that their spare parts will probably be expensive;
- hydraulic actuators are controlled by the digital valve groups of a digital valve unit, all or some of the previously used slide valves being replaced thereby.
- the digital valves included in digital valve groups are structurally identical, the only difference between the parallel-connected digital valves lying in a volumetric flow rate allowed through thereby as the valves are in an open position.
- the volume flows allowed by the digital valves of a group to pass through are planned correctly, it is possible, in practice, to compensate for a failure of one valve by changing appropriately the volume flows proceeding through the other valves.
- -Control of a hydraulic actuator with a digital valve group provides considerably more fault tolerance than hydraulic actuator control effected by a slide valve, because the failure of a single valve is not enough to significantly impair the operation of a digital valve group;
- -A digital valve group contains hardly any control electronics, whereby the resistance of its electronic components to heat aging, and to temperature as well as to vibration, shall not become a problem;
- Fig. 2A shows schematically a multi-roll calender 500 in a view directly to the calender's end face.
- the multi-roll calender 500 of a per se known design comprises alternating heatable thermo rolls and polymer-coated rolls.
- the number of such thermo rolls and polymer-coated rolls in a multi-roll calender is typically 6 to 16 examples, e.g. the so-called Optiload calender used by the Applicant features typically 6 to 12 rolls, 2 to 5 of which are thermo rolls and 4 to 7 are polymer- coated rolls.
- the multi-roll calender's 500 roll set 50 shown by way of example in the figure, comprises 6 rolls, said rolls being provided with internal loading elements for changing the line pressure profile zone by zone in a roll nip N between two rolls.
- At least a top roll 5; 5c and a bottom roll 5; 5b of the roll set 50 are heatable thermo rolls, having also hydraulic actuators (hydraulic cylinders) 2; 20; 202, 201 coupled therewith for pressurizing the roll set in vertical direction.
- Between the top roll 5; 5c and the bottom roll 5; 5b are set four deflection compensated intermediate rolls 5; 5a, at the ends of which are supporting levers 3 linked to a calender body 55.
- the supporting levers 3 are used for adjusting a deflection of the intermediate rolls 5a, which is caused by the own weight of these rolls 5a as well as by bearing loads existing at the ends of the rolls.
- the pressure load applied for example on the supporting lever 3 of one of the intermediate rolls 5a in fig. 2A, included for example in the multi-roll calender 500 of fig. 2A and established by means of the hydraulic cylinder 20, is controlled by an analog slide valve regulating the flow and/or pressure on either side of the hydraulic cylinder's piston (both on the piston rod side and the piston head side), the adjustment strategy must be based on a feedback adjustment of the volume flow (and hence the pressure) on the cylinder's piston side.
- the method according to the invention by using a digital valve group, provides a capability of regulating precisely and rapidly both the fluid pressure existing on the hydraulic cylinder's 2; 20 pressure side (piston head side) and the volume flow of a hydraulic fluid, as well as also the back pressure of a hydraulic fluid existing on the hydraulic cylinder's working side (piston rod side) and the volume flow.
- This is achieved by virtue of the digital valve group having a high-speed adjustment response to a digital adjustment instruction and by means of a non-feedback adjustment of the volume flow proceeding through the digital valve groups included in a digital valve unit.
- the digital valve group comprises a plurality of small digital valves, the volume flow proceeding therethrough being always constant in an open position, whereby the pressure difference between a fluid arriving at the valve and a fluid discharging from the valve is highly predictable for each aperture of the digital valve group.
- the pressure of a hydraulic cylinder working on the supporting lever of a calender's intermediate roll is adjusted by means of at least one digital valve group connected to both the pressure and working sides of a hydraulic cylinder, regulating both the pressure side for its volume flow and pressure and the working side for its volume flow and pressure.
- the hydraulic cylinders applying load on each supporting levers of one roll are controlled by their own digital valve units, which are synchronized functionally at a control system level.
- the operation of a hydraulic cylinder applying load on the supporting lever of a roll is regulated by means of two digital valve groups coupled with the cylinder's pressure side and by means of two digital valve groups coupled with the cylinder's working side.
- the digital valve groups coupled with the pressure side of a hydraulic cylinder are used for performing a high-speed opening of the hydraulic cylinder.
- the pressurization of a multi-roll calender's roll nips is changed rapidly by means of digital valve groups coupled with the pressure and working sides of a hydraulic cylinder by changing the ratio of fluid pressures existing on the pressure and working sides of said hydraulic cylinders.
- a digital-valve controlled adjustment according to the invention for regulating the pressure load for a calender's supporting levers provides multiple benefits over the above-described prior art:
- -A digital valve group provides a capability of controlling rapidly the fluid pressure and the volume flow both on the pressure and the working side of a hydraulic cylinder, which enables an active and high-speed adjustment of the pressure existing on a first side and the back pressure existing on a second side of the cylinder's piston.
- the position of a hydraulic cylinder's piston and hence the pressure load applied by a hydraulic cylinder on supporting levers at the ends of a roll can be rapidly adjusted as desired, because the ratio of volume flow on various sides of the piston lends itself to a rapid adjustment.
- the pressure load adjustment for the supporting lever of an intermediate roll provides a means of controlling the pressure and working side fluid flow (and thereby also the fluid pressure) in a hydraulic actuator working actively on the loading of a lever, the resulting control process will be high-speed and good in terms of its efficiency and energy consumption both in changes of the pressure load at the start and end of a calendering process and in the high-speed opening of a roll nip, as well as in a steady-state condition during calendering, in which the objective is to maintain a certain equilibrium pressure state in the hydraulic actuator.
- the hydraulic actuator adjustment mode according to the invention based on digital hydraulic valve units, is capable of achieving an energy saving of about 30 to 50%.
- the adjustment mode of the invention is practically non-fluctuating, because it involves controlling the fluid flow and the fluid pressure on both sides of a hydraulic cylinder by means of digital valve groups with a high-speed opening capability and by means of a feed-forward mode of adjustment.
- the pressure load adjustment for a roll supporting lever implemented by means of digital valve groups receiving a digital adjustment instruction is more versatile than the respective adjustments implemented by means of slide valves subjected to analog control. This is due to the fact that a digital valve group provides a capability of operating effectively over a considerably more extensive operating range than what is possible by means of a slide valve; one and the same digital valve group makes it possible to operate within the range of both a minor and a major volume flow delivered into a hydraulic actuator.
- each digital valve group consists of 2...n examples of separate parallel-connected digital valves, the rate of volume flow passing therethrough in an open position being known exactly and providing a possibility of freely selecting those of said valves that have a fluid flow passing through.
- flow engineering type restrictions laminar vs turbulent flow
- delays caused by intra-valve feedback delays caused by intra-valve feedback
- technical restrictions in terms of valve materials and increasing investment costs.
- the adjustment of hydraulic actuators, carried out by digital valve groups is practically non-fluctuating, which is why it is considerably more stable and quicker than that carried out by means of slide valves of the prior art.
- Fig. 2B shows schematically a control of hydraulic actuators 3 used for loading the supporting levers 3 of one intermediate roll in a multi-roll calender, performed by a single digital valve unit 100.
- Fig. 2C shows schematically data and fluid flows for the control of one of the hydraulic actuators of fig. 2B.
- Fig. 2D shows likewise schematically a control of hydraulic actuators 2 used for loading supporting levers 3 present at the ends of one intermediate roll in a multi- roll calender, performed by specified digital valve groups 100; 100' and 100; 100", and a synchronization of operation for the thus controlled hydraulic actuators 2.
- Fig. 2B visualizes the adjustment of pressurization for supporting levers 3 present at each end of an intermediate roll (not shown in the figure) by means of a digital hydraulic unit 100 containing four digital valve groups 10.
- the adjustment of pressure load for the supporting lever 3 present at each end of an intermediate roll by means of a hydraulic actuator 2; 20; 20' and 2; 20; 20" coupled therewith is performed with identical systems, which is why the following discussion relates more closely to the pressure load adjustment of only the left-hand side supporting lever 3.
- the inlet flow proceeding to a pressure side 20b of the hydraulic actuator 2; 20 passes by way of a valve unit 30, which includes high-speed opening and safety valves; these can be implemented either by traditional slide valve engineering or alternatively by one or more digital valve groups.
- a digital valve unit 100 which is coupled with the hydraulic cylinder 20 functioning as a hydraulic actuator 2 used for loading the supporting lever 3, and which replaces a commonly employed 4/2-way valve (slide valve).
- the presented digital valve unit 100 enables a concurrent control of two flow channels 6; 61 , 62, which extend to pressure and working sides 20b, 20a of the hydraulic cylinder 20, respectively.
- the digital valve unit 100 comprises 20 on/off digital valves divided into four digital valve groups 10; 10a, 10b, 10c, 10d, comprising two digital valve groups 10c, 10d regulating actively the pressure side (piston head side) 20b of the hydraulic cylinder and two digital valve groups 10, 10b regulating actively the working side (piston rod side) 20a of the hydraulic cylinder.
- the digital valve groups 10b and 10c regulate an inlet flow v s of pressurized hydraulic fluid from a supply line 7; 71 respectively to the working side 20a of the cylinder 20 as well as to the cylinder's pressure side 20b along respective flow lines 6; 61 and 6; 62.
- the digital valve groups 10d and 10a regulate respectively a hydraulic fluid outlet flow from the cylinder's pressure side 20b and working side 20a to a tank line 7; 72.
- the fluid flow pressurized to a certain known pressure, arrives by way of the same supply line 7; 71 across a throttle valve at the digital valve groups 10c, 10b which control the inlet flow v s to be delivered both to the pressure and the working side 2Ob 1 20a of the hydraulic cylinder 20.
- the pressure of inlet flow along the supply line 7; 71 is established for example by a pump (not shown in the figure).
- the hydraulic fluid discharges from the respective digital valve groups 10d and 10a, which regulate the fluid flow coming out of the pressure and working sides of the hydraulic cylinder, proceeding into the tank line 7; 72 which carries the fluid into a storage tank (not shown in the figure) by way of a counter-valve.
- Each digital valve group 10 of the digital valve unit 100 includes 5 on/off digital valves 1 , the flow rates passing therethrough in an open position being proportioned in such a way that the first valve has a flow rate of 1 unit, the second has 2 units, the third has 4 units, the fourth has 8 units, and the fifth valve has 16 units, whereby the digital valves 1 of each digital valve group have a capability of providing 31 different valve combinations 1 A of open-state digital valves, corresponding to 31 flow rate combinations or different opening degrees for the digital valve group 10.
- the pressure and working sides 20b, 20a of the hydraulic cylinder 20 have their respective flow lines 6; 61 and 6; 62 connected to respective pressure measuring devices M; M", M', each of which comprises a bellows type equalizer as well as a pressure gauge.
- a pressure load P k of the hydraulic cylinder 20 refers to the pressure applied by the hydraulic cylinder 20 (piston 22) on the supporting lever 3.
- Such an active adjustment proceeds substantially faster than with a slide valve, in which the adjustment of the hydraulic cylinder's 20 working side 20a cannot be effected quickly and actively because of delays caused by the internal feedback of a slide valve and because of the slowness of a feedback adjustment to be carried out by a slide valve.
- the fluid flow arrives under the certain pressure p s at the digital valve unit 100 by way of the supply line 7; 71 closable by a throttle valve and proceeds to the cylinder's pressure side 20; 20b or working side 20; 20a through the fluid-flow controlling, respective digital valve group 10; 10c or 10; 10b.
- the supply side digital valve group 10; 10c or 10; 10b there has been opened a digital valve combination 1 A ; 120b tai 1 A ; i20a.
- V 6 which provides a desired volume flow V 6 ; V 62 in the flow line 6; 62 extending from the digital valve group 10; 10c to the cylinder's 20 pressure side 20b or a volume flow V; V 6 i in the flow line 6; 61 extending from the digital valve group 10b to the cylinder's working side 20a.
- the volume flow V 6 discharging from each digital valve group 10; 10b, 10c to the hydraulic cylinder 2; 20 along the flow line 6 and the volume flow V 2 o; V 2 oa > V 2 Ob established on the various sides 20a, 20b of the cylinder's piston 22, respectively, can be anticipated accurately from a pressure difference dp existing between an inlet pressure p s of the fluid arriving at the digital valve group (10b or 10c) along the supply line 71 and a pressure P 6 ; P ⁇ 2, P ⁇ i existing in the respective flow line 6; 62, 61 extending downstream of the digital valve group 10 to the cylinder's 20 pressure or working side (the pressure Pe of the flow line 6 is P 6 i in the flow line 6; 61 extending to the cylinder's working side 20a or P 62 in the flow line 6; 62 extending to the pressure side 20b), as well as from a current aperture 1 A of the digital valve group 10 (for example 1 2 o a in the digital valve group 10b controlling a flow proceeding to
- the pressure difference dp between a flow V 6 , which has proceeded through any digital valve group 10 into the flow line 6, and an inlet flow v s , which has arrived at this particular digital valve group 10, depends in turn on the aperture 1 A of this digital valve group 10.
- the volumetric flow rates V 20 b ja V 2 o a arriving in the hydraulic actuator's 20 pressure side 20b and working side 20a are changed by modifying an aperture 120 b or 1 20a of the respective digital valve groups 10c or 10b controlling the inlet side flow of a hydraulic fluid.
- the volume flow V 6 ; V 62 or V 6 ; V 6 i discharging from the inlet side digital valve group 10; 10c and/or 10; 10b into the flow line 6; 62 or 6; 61 and/or the respective fluid pressure P 6 ; P 62 or P 6 ; P 61 existing in said flow lines result in a certain volume flow and fluid pressure on various sides 20a and 20b of the hydraulic cylinder's 20 piston.
- a modification of the aperture 1A ;i20b or 1A ; 1 20 a for the digital valve group 10c or 10b can be effected on the basis of a new volumetric flow rate level V 2 o; V 20b and/or V 20 ; V 20a and/or a new respective pressure and back pressure level P 20 ; P2ob and/or P 20 ; P 2 Oa desired for the hydraulic cylinder's 20 pressure side 20b and/or working side 20a, when said volume flow or pressure resulting in the cylinder's 20 various sides 20a or 20b is known by calculation or empirically on the basis of a volume flow V 6 ; V 6 i or V 6 ; V 62 of the flow line 6; 61 or 6; 62 and/or on the basis of a fluid pressure P 6 ; P 6 i or P 6 ; P 62 existing in the flow line.
- the respective outlet side digital valve group 10a or 10d controlling the outlet flow of the pressure or working side, has all of its digital valves in a closed position (the aperture 1A of the group 10a or 10d is 0).
- the pressure downstream of a digital valve group 10 can also be monitored by a pressure measuring device M and adjustment operations can be checked on that basis as necessary.
- the pressure displayed each time by a pressure gauge M coupled with the respective flow line 62/61 of the pressure/working side 20b/20a and the new pressure desired for the hydraulic cylinder's pressure/working side are used as a basis for selecting the appropriate digital valves to be opened in the outlet- flow controlling digital valve group 10a or 10d.
- the respective digital valves of the inlet side digital valve group 10b or 10c are closed for the purpose that the pressurized fluid flow coming from the supply line 71 be prevented from migrating into the flow line 6; 62 or 6; 61 leading to the cylinder's 20 pressure or working side 20b or 20a.
- the fluid flow proceeds from the hydraulic cylinder's 20 pressure or working side 20b or 20a along the respective pressure- or working- side flow line 6; 62 or 6; 61 to the discharging flow (outlet flow) controlling digital valve groups 10d or 10a.
- the appropriately opened digital valves 1 of these digital valve groups 10a and 10d enable adjusting a flow rate V 6; V 6 i or V 6 ;V 62 proceeding from the discussed digital valve groups to a tank line 7; 72 along the flow line 61 or 62, and thereby adjusting the rate of outlet flow and the magnitude and rate of pressure fall on the cylinder's 20 pressure or working side 20b or 20a.
- Fig. 2C shows schematically data flows traveling between a control system 4 and a digital valve unit 100 in the process of changing and maintaining a pressure load
- a control unit 42 included in the control system 4 receives information continuously or at specific intervals from pressure gauges M; M' and M; M" regarding fluid pressures P 6 ; P 62 , P ⁇ ; P ⁇ i existing at a particular instant in the flow lines 6; 62 and 6; 61 leading from the digital valve unit 100 to the piston head side (pressure side) 20b and the piston rod side (working side) 20a of the hydraulic cylinders 20.
- the control system 4 On the basis of this pressure data P 6 measured by measuring gauges and on the basis of a pressure load P k ; P k - as well as P k ; PK to be applied on the supporting levers 3; 3' and 3; 3", the control system 4 is able to determine an appropriate anticipating adjustment strategy for changing processes of a roll nip load or for holding a roll nip at a steady-state load.
- control systems 4 decides, on the basis of a previously programmed anticipating adjustment strategy, which way to change the ratio of fluid pressures P2 0 ; P ⁇ oa and P 20 ; P 20b on the hydraulic cylinders' 20 working and pressure sides, to which extent and over which time period, such that a nip pressure for the roll nip, and at the same time pressure loads P k ; P k 1 , P k acting on the hydraulic cylinders' nip pressure, are established as desired.
- the control system's 4 control unit 42 works out volume flows V 2 o; V 20a and V 2 o; V 2Ob of fluid desired at a particular instant for each hydraulic cylinder's 20; 20' or 20; 20" piston rod side (working side) 20a and piston head side (pressure side) 20b, and possibly also respective fluid pressures P 20 ; P 2 Oa and P 20 ; P 2 Ob-
- the volume flows V 20 ; V 20a and V 20 ; V 20b of each cylinder's working side and pressure side are matched by certain volume flows V 6 ;V 6 i and V 6 ; V 62 as well as pressures P ⁇ iP ⁇ i ja P 6 ; P 62 in flow lines 6; 61 and 6; 62 extending to the hydraulic cylinder's 20 working and pressure sides 20a and 20b downstream of the digital valve groups.
- the control system's 4 control unit 42 supplies a calculator unit 41 with information about these new flow rates of the cylinder's 20 working and pressure sides, the calculator unit 41 working out as to which aperture 1A of each digital valve group 10 is needed in order to reach desired volumetric flow rates and transmitting a respective adjustment instruction to each digital valve group.
- the adjustment instruction transmitted to each digital valve group 10; 10a, 10b, 10c, 10d is a binary-mode adjustment instruction, which comprises a volume flow adjustment function F(V) for hydraulic fluid or a position adjustment function F(X) for a hydraulic cylinder's piston and contains information regarding at least which valves 1 in each digital valve group 10; 10a, 10b, 10c, 10d will be open and which ones will be closed (opening of a digital valve group) and for how long.
- each digital valve group 10 has an ability to provide a large number of unequal discrete volume flows in the flow lines 6; 61 and 6; 62, resulting in an equally large number of volume flow/pressure states for the hydraulic cylinders' 20 pressure and working sides, it is possible to use one and the same digital valve group to implement both gradual volume flow and pressure modifications taking place in the steady-state condition and also major pressure and volume flow changes taking place at the starting and finishing stage of a calendering process.
- the synchronization of two or more hydraulic actuators 2 has been traditionally implemented in papermaking industry either by using flow distributors, by connecting the actuators in series or by controlling each actuator independently with servo/proportional valves featuring a positional or flow-related feedback.
- actuator-specific control effected by means of control circuits containing servo/proportional control valves, is the high cost of such circuits.
- a drawback with such control valves is a substantial pressure loss, and in order to implement synchronization, there is needed a special position adjustment control as well as a feedback of adjustment.
- Such synchronization for the operation of two hydraulic actuators is possible to carry out in a traditional manner by means of digital valve units 100, both by using a series connection of the actuators 2 and by using flow distributors, whereby a volume flow discharging from one and the same digital valve group is distributed for various hydraulic actuators.
- the system depicted in figs. 2B and 2C uses the same digital valve groups 10 of the digital valve unit 100 to control synchronically two hydraulic actuators 2; 20' and 2; 20" present at each end of a roll.
- the flows emerging from each digital valve group are branched at an appropriate point for various hydraulic actuators, as displayed in fig. 2B.
- each actuator is adjusted separately by means of its own digital valve unit and the operation of these digital valve units is synchronized at a control system level.
- Each digital valve group of the digital valve unit 100 is supplied as an adjustment instruction with a time-linked flow instruction F (V) or a position adjustment function F (X) (see fig. 2C), and this is followed by the digital valve group adjusting accurately, without delay, a volume flow bound for the actuator / arriving from the actuator.
- the digital valve group regulates accurately the speed of a hydraulic actuator.
- the accuracy of adjustment carried out by the digital valve unit 100 results a) from the fact that the operation of each digital valve group 10 of a digital valve unit can be controlled accurately in a feed-forward mode of adjustment, the adjustment taking place without feedback and without time delay, and b) from the fact that the adjustment accuracy of a digital valve unit is directly proportional to the number of digital valve units contained in a system and to the nominal volume flow of each valve, as indicated above in relation to the description of figs. 1A and 1B. Even a very minor increase in the number of on/off digital valves results in a remarkable improvement in the accuracy of adjustment.
- the embodiment shown schematically in fig. 2D illustrates a control for the operation of two parallel-connected identical hydraulic actuators 2, said control being implemented by means of two digital valve groups 100; 100' and 100; 100" which are separate, yet functionally interconnected by means of a control system.
- the hydraulic actuators 2 are hydraulic cylinders 20, which are used for controlling the position of relief levers present, for example, at the ends of a common roll the same way as presented in figs. 2B and 2C.
- Each of both hydraulic cylinders 20; 20' and 20; 20" is controlled by its own specific digital valve group 100; 100' and 100; 100".
- Each digital valve unit 100' or 100" contains four digital valve groups 10; 10a, 10b, 10c, 10d.
- the digital valve units 100' and 100", as well as the digital valve groups 10 contained therein, are structurally and operationally identical to each other, which is why like structural components of said digital valve units are designated with like reference numerals.
- the digital valve groups 10a, 10b, 10c, 10d contained in each digital valve unit 100; 100', 100" are used for adjusting a flow arriving in the pressure or working side of whichever hydraulic actuator 20' or 20" or discharging therefrom.
- Each digital valve group 10 comprises n pieces of digital valves, fig. 2D only displaying the first and last digital valves 1 in each digital valve group 10.
- the digital valve groups are used for adjusting the inlet and outlet flows for each hydraulic actuator's pressure side (piston head side) 20b by way of a flow line 6; 62.
- the digital valve groups, designated by reference numerals 10c and 10d, are in turn used for adjusting the inlet and outlet flows for each hydraulic actuator's 20 working side (piston rod side) 20a by way of a flow line 6; 61.
- the hydraulic fluid flow v t ; v t - or v t ; v t - discharges from each hydraulic cylinder's 20; 20' or 2; 20" pressure or working side 20b or 20a by way of the flow line 62 or 61 to the digital valve groups 10a or 10d and further to a tank line 7; 72.
- the establishment of a volume flow of desired magnitude for each hydraulic cylinder's 20; 20' or 20; 20" pressure or working side 20b or 20a is performed in a manner analogous with the system shown in figs.2B and 2C, yet bearing in mind that each hydraulic cylinder 20; 20' or 20; 20" has its own digital valve unit 100; 100' or 100; 100" controlling the same.
- the inlet flows v s ; v s - ja v s ; v s - arriving at the hydraulic cylinders20* and 20" from the supply line 7; 71 or the outlet flows v t ; v r ja v t ;v t - discharging from the hydraulic cylinders 20' and 20" to the tank line 7; 72 are in no contact whatsoever with each other before reaching the respectively common supply line 7; 71 or tank line 7; 72.
- the mutual synchronization for the operation of the digital valve units 100' and 100", and at the same time that of the hydraulic actuators 20 is handled in terms of control engineering through the intermediary of a control system (not shown in the figure) issuing adjustment instructions thereto.
- each hydraulic actuator's 20' and 20" volume flow with a certain delay time is conducted by a feed-forward mode of adjustment by supplying each digital valve unit 100' or 100" with a desired volume flow instruction F(V)' and F(V)" at a specific time interval, said volume flow instructions F(V)' and F(V)" being identical.
- the digital valve units could just as well be only supplied with a position adjustment instruction F(X) regarding the hydraulic actuator's 20 piston as a result of knowing the pressures existing at the position of the hydraulic actuator's 20 piston and on the hydraulic actuator's working and pressure sides.
- servo and proportional valves are used for adjusting the pressure of hydraulic actuators acting on supporting levers at the ends of intermediate rolls or from inside a roll on the roll shell and/or for adjusting a loading cylinder which lifts or lowers the top or bottom roll of a multi-roll calender.
- slide valves only work effectively over a narrow volume flow/pressure range and have a relatively long delay in the performance of adjustment; if the pressure load of a hydraulic cylinder must be changed quickly and at the same time the volume flow into the hydraulic cylinder's working and pressure side undergoes a considerable change, there will be problems because of a delay resulting from the feedback adjustment of a slide valve's stem and because of a fluctuation of adjustment resulting from the feedback adjustment strategy, even if the hydraulic actuator itself were to operate instantly and accurately.
- the slide valves are capable of performing neither the high-speed relief of a calender's roll nip load nor the quick instant opening and closing of a roll nip while maintaining the calender's running speed.
- an objective of the invention is to provide an apparatus and method, which enable the nip load of a roll nip to be instantly relieved and to reset the original nip load in such a way that the loading-relieving-reloading cycle of a roll nip becomes as rapid as possible, yet at the same sufficiently precise in terms of the roll nip's pressure load variation.
- Another objective of the invention is to provide the high-speed opening and re- closing of a roll nip while the running speed of a calender remains unchanged.
- This embodiment of the invention is based on the fact that the hydraulic actuators, such as hydraulic cylinders 20, which act on levers 3 present at the ends of intermediate rolls 5 or from inside a roll on the roll shell, and/or on a loading cylinder which applies pressure directly on the top or bottom roll of a calender, are controlled by means of a digital valve unit 100 for creating a relief pulse for the pressure load of a roll nip N and thereafter a reset pulse for the pressure load of the roll nip N.
- the position of a joint included in a fiber web arriving at a multi-roll calender is identified and the time of its arrival at the calender's each roll nip and its passage therethrough is estimated or calculated.
- the successive roll nips of a multi-roll calender 500 are subjected to a roll nip relief pulse and reset pulse in an appropriate synchronism with each other for conveying a joint H; W 8 between two fiber webs in a controlled manner through the multi-roll calender's roll nips.
- the pressure load in the roll nip N is reduced by using the digital valves of an appropriate digital valve group 10 for instantly cutting back the volume flow into the pressure side (piston side) of a hydraulic cylinder 20 with respect to the volumetric fluid flow existing on the hydraulic cylinder's 20 working side in the state of equilibrium.
- the pressure load applied by the hydraulic actuator to a roll nip shall be returned to a level existing prior to the relief pulse.
- the pressures of a hydraulic actuator such as a hydraulic cylinder 20, shall be equalized with each other.
- Another embodiment of the invention is in turn based on subjecting roll-loading elements, which are coupled with hydraulic actuators (e.g. hydraulic cylinders), to a stepwise, accelerated opening pulse by means of digital valve units linked to the hydraulic actuators.
- the reduction of load for the roll-loading elements takes place in a feed-forward based adjustment mode by modifying a volume flow arriving at the hydraulic actuators (and at the same time a pressure existing therein) according to a certain, previously determined volume flow modification profile.
- This embodiment of the invention is viable for example during a fiber web breaking incident occurring in the process of calendering; the fiber web break point on a fiber web arriving at the calender is identified and the time of its arrival at the calender's roll nip is estimated and calculated.
- Fig. 3A shows schematically the provision of a relief and reset pulse for a roll nip in a multi-roll calender as said roll nip receives an fault present on a fiber web.
- Fig. 3B shows one roll nip in a multi-roll calender, which is about to receive an fault present on a fiber web.
- Figs. 3C-3E illustrate the changes of volume flow and fluid pressure taking place during the relief and rest pulse of fig. 3A in a hydraulic cylinder loading the supporting lever of a roll.
- Fig. 3F shows one roll nip in a multi-roll calender, which is about to receive a web break.
- Fig. 3G shows in turn the instant opening of a multi-roll calender's roll nip by a method of the invention as said roll nip is about to receive a web break present on a fiber web.
- Fig. 3H illustrates the changes of volume flow and fluid pressure taking place during the roll nip opening of fig. 3E in a hydraulic cylinder loading the supporting lever of a roll.
- a relief and reset pulse for a roll nip shown in figs. 3A-3E, as well as the instant opening of a roll nip shown in figs. 3F-3H will be illustrated by way of example as applied to the multi-roll calender 500 of fig. 2A, whose control system 4 for the supporting lever 3 of an intermediate roll 5; 5a and whose digital valve unit 100 controlling the supporting lever are consistent for example with those of fig. 2D.
- the control of loading cylinders used for lifting the bottom roll 5; 5b and pressing the top roll 5; 5b of the calender's 500 roll set can be implemented with an at least partially similar digital valve unit 100 and its control system 4.
- Figs. 3A-3E illustrate the provision of a relief and reset pulse, controlled by a digital valve unit 100, for a hydraulic cylinder 20 acting on a supporting lever present at the end of a multi-roll calender's intermediate roll as the roll nip is traversed by an fault H, such as a joint H; W 8 between two fiber webs as shown in fig. 3B.
- the relief and rest pulse provides a means for changing a pressure load K p applied by the hydraulic cylinder's 20 piston 22 to the supporting lever while the fault passes through the roll nip.
- Fig. 3B visualizes two superimposed rolls 5, leaving a roll nip N therebetween.
- the rolls comprise for example two rolls of fig. 2A, included in a multi-roll calender.
- the roll nip is traversed by a fiber web W to be calendered.
- the figure shows a condition, in which the roll nip N is just about to receive a joint W 8 between two different fiber webs W; W1 and W; W2.
- the figure visualizes the changes during a roll nip relief and reset pulse in a volume flow V20b of hydraulic fluid into the hydraulic cylinder's 20 pressure side (piston head side) 20b over a certain time t, and the bottom part of the figure shows the changes that have taken place over the same time t in a pressure load K p applied on the supporting lever.
- This embodiment of the invention has its basis on a feed-forward control of the pressure load K p implemented by a digital valve unit 100 both during the roll nip's N pressure load relief pulse and during the roll nip's N pressure load reset pulse.
- Figs. 3C-3F illustrate the actions of a hydraulic cylinder's piston 22, which take place during a roll nip relief and reset pulse and which are used for controlling the changes of a pressure load K p for the supporting lever of a roll located at the roll nip.
- figs. 3B-3D visualize hydraulic fluid flows V 2O a and V 2 Ob delivered from a digital valve unit 100 into various sides 20a and 20b of the hydraulic cylinder's 20 piston 22, as well as a fluid pressure P2 0 a.P2 0 b established by the hydraulic fluid flow.
- Figs. 3C-3F illustrate the digital valve unit 100 schematically and it can be for example similar to what is shown in fig. 2D, comprising four digital valve groups 10a, 10b, 10c, 10d, two of which are used for controlling a fluid flow into the piston head side 20b of a hydraulic cylinder and two of which do the same for the piston rod side 20a.
- Fig. 3F visualizes two superimposed rolls 5, leaving a roll nip N therebetween.
- the rolls comprise for example two rolls of fig. 2A, included in a multi-roll calender.
- the roll nip is traversed by a fiber web W to be calendered.
- the figure shows a condition, in which the roll nip N is just about to receive a web break W k present on the fiber web W.
- Fig. 3G shows the instant opening of a roll nip N by a method of the invention as a web break H; W k shown in fig. 3F is arriving at the roll nip.
- the top view shows the change over a certain time period t in a volumetric fluid flow V 2 Oa to be delivered into the hydraulic cylinder's 20 pressure side 20b, and the bottom view shows schematically the positional change of a roll 5 in vertical direction (e.g. in a roll nip between two rolls, the positional change of the bottom roll's highest point in vertical direction) over the same time.
- V 2 Oa volumetric fluid flow
- V 2 Oa to be delivered into the hydraulic cylinder's 20 pressure side 20b
- the bottom view shows schematically the positional change of a roll 5 in vertical direction (e.g. in a roll nip between two rolls, the positional change of the bottom roll's highest point in vertical direction) over the same time.
- 3E shows the positional change of a roll 5 in a calender's roll nip N, the change in the relative position of a piston 22 loading the roll by way of a supporting lever 3 with a pressure load K p will be similar in a longitudinal direction of the hydraulic cylinder 20.
- the changes of the piston's 22 position in the opening of a roll nip and those of a relevant roll supporting lever's pressure load K p are shown in more detail in fig. 3H.
- a volume flow V2 0 and a pressure P2 0 of the fluid to be supplied into a hydraulic cylinder 20 are controlled by a digital valve unit 100 containing a plurality of digital valve groups 10, as specified in connection with the description regarding the control of a roll supporting lever 3 in figs. 2B-2D, the volume flow passing through a particular digital valve group 10 in the digital valve unit 100 will be known beforehand within all the volume flow ranges of a hydraulic cylinder 20.
- the volume flow is known from the aperture 1A of each digital valve group 10, as well as from a pressure difference between a fluid pressure p s existing in the supply line arriving at a digital valve group or a fluid pressure p t existing in the tank line 7; 72 departing from this digital valve group and a fluid pressure P 6 running in the flow line 6 extending to the hydraulic cylinder 20.
- a digital valve group 10b of the digital valve unit 100 shown for example in figs. 3C-3F is supplied with an inlet flow V 8 along the supply line 7; 71 , the average pressure applied thereby to the walls of the supply line being p s , the rate of a volume flow V 62 departing along a flow line 6; 62 from this particular digital valve group 10b to the pressure side 20b of a hydraulic cylinder 20 will be determined on the basis of a fluid pressure P 62 existing in the flow line 62 leading to the loading cylinder 20 and a current opening of the digital valve group 10b.
- the fluid pressure P 62 is precisely predictable on the basis of the digital valve group's 10b opening, i.e.
- a total flow port established by currently open-state digital valves i.e. on the basis of a throttling degree provided by the digital valve group. Because the volume flow V 62 departing from the digital valve unit's 100 digital valve group 10b into the flow line 6; 62 (and further into the hydraulic cylinder's pressure side 20b), and the pressure P 62 existing in the flow line 62, are precisely predictable, a fluid pressure P 2Ob and a fluid flow V 2O b developing on the hydraulic cylinder's 20 piston head side 20b are predictable even without a feedback adjustment, resulting in a high-speed and accurate adjustment.
- the delivery of a relief and reset pulse is performed by reducing first a volume flow into the hydraulic cylinder's piston head side 20b to a certain extent and by restoring thereafter the volume flow into the piston head side 20b to its former level after a certain time period t.
- the load reset pulse is delivered by increasing first the volume flow into the hydraulic cylinder's piston head side 20b to a certain extent and by restoring thereafter the volume flow into the piston head side 20b to its former level after a certain time period t.
- the roll nip pressure load K p applied by the hydraulic cylinder's piston 22 on a supporting lever is reduced, as displayed in the bottom view of fig. 3A, from a pressure level A to a pressure level B over a time period t1.
- the volume flow into the piston head side 20b of a hydraulic cylinder is reduced by means of that/those digital valve group/groups of a digital valve unit 100, which is/are used for regulating a volume flow V 6; 62 and thereby also a fluid pressure P 6; Q 2 in the flow line 6; 62 extending to the hydraulic cylinder's 20 piston head side.
- the adjustment of a volume flow V 62 is performed, as already previously explained in connection with figs. 2B and 2D, by selecting an appropriate opening for the digital valve group 10b for providing the reduced volume flow V 62 . This is followed by restoring the digital valve group's 10b opening to what it was before the opening was changed.
- 3C is a condition just before the delivery of a relief pulse, for example in the situation of fig. 3B, during the course of fiber web calendering in a steady state of equilibrium.
- a digital group is supplied by the control system with an equilibrium-sustaining adjustment instruction F(V); F(VT), according to which the digital valve group 10b presents an opening 1 A ; I2ot > ⁇ and the digital valve group 10c presents an aperture 1 A ; 12OaT-
- the hydraulic cylinder 20 has both its piston head side 20b and its piston rod side 20a supplied from the digital valve group 100 through the intermediary of the digital valve groups 10b and 10c with a certain equilibrium-state volume flow V 2 ot > ⁇ and V 2 oa ⁇ .
- the digital valve unit After the lapse of an appropriate time t2, measured from the inactivation of a relief pulse (pulse 1), the digital valve unit is supplied as an adjustment instruction (for the load K p ) 20 with a reset pulse (pulse 2) F(V); F(V 2 ) by momentarily increasing a volume flow supplied into the hydraulic cylinder's 20 piston side 20b (pressure side) with respect to a volume flow supplied into the cylinder's working side 20a (piston rod side).
- This is preferably implemented by modifying first in an appropriate manner the aperture of a digital valve group 10b controlling the flow supplied into the piston side 20b from an aperture 1 2 o b ⁇ to an aperture 1 2 ob2.
- the calender is a multi-roll calender 500 with a certain number of roll nips N (e.g. a calender shown in fig. 2A)
- the load relief and rest pulses of consecutive roll nips are phased in such a manner that the joint between two fiber webs proceeds through all roll nips N involved in a calendering process without changing the calendering speed.
- the exact effect and effect delay of a load relief and reset pulse issued by the digital valve unit 100 on hydraulic cylinders 20 acting on supporting levers 3 present at the ends of each intermediate roll may fluctuate slightly, depending on pressure losses in tube and pipe systems, as well as on structural differences in the hydraulic cylinder 20 and in the supporting levers 3 coupled therewith and other such roll-specific factors (regarding the bottom roll and the top roll, the cylinder 20 is a loading cylinder with a direct effect on the vertical position of the roll).
- the phasing of load relief and reset pulses with respect to the calender's 500 each running speed can be performed for example in such a way that the effect and delay of relief and reset pulses issued by the digital valve unit
- the hydraulic cylinder 20 controlled by a digital unit, for instantly opening a roll nip N between two rolls, for example when a web break H; W k of fig. 3F passes through the roll nip, the high-speed relief of a nip pressure in the roll nip is performed by modifying the ratio between volume flows V 20 b, V 20a arriving in the pressure and working sides 20b, 20a of hydraulic cylinders 20 applying pressure on the supporting levers of a roll present at the roll nip.
- 3G visualizes a volumetric flow profile of the fluid being supplied into the piston head side of one hydraulic cylinder applying pressure on a supporting lever, while the volume flow for the hydraulic cylinder's working side remains more or less unchanged.
- the roll's vertical position is first changed with a quick initial acceleration (step 1 in fig. 3G) by rapidly reducing the fluid pressure existing on the piston head side of a hydraulic cylinder with respect to the fluid pressure existing on the piston rod side.
- a quick initial acceleration step 1 in fig. 3G
- the volume flow (and fluid pressure) proceeding through a digital valve group 10b supplying fluid into the cylinder's 20 pressure side 20b is reduced, according to fig.
- the volume flow is reduced by limiting the size of a flow port 1A established by the digital valve group 10b, by selecting an appropriate aperture 1A; I 2 ot > i of the relevant digital valve group 10c for providing said lower volume flow rate V 2 ot>i-
- the volume flow V 2 Oa to be supplied into the piston rod side 20a of a cylinder 20 can be momentarily increased from an equilibrium-state volume flow V 2O aT to a new higher volume flow rate V 2 o a i in order to increase a back pressure P 2 o a existing on the piston rod side with respect to a fluid pressure P 2 ot. ⁇ existing on the cylinder's pressure side (piston side) 20b in the state of equilibrium (P 20a i >P2 0 bi)-
- the loading effect of a piston 22 on an element (in this case, an intermediate roll supporting lever) pressurizing the roll present in a roll nip N is reduced and the roll changes its vertical position, as depicted in fig.
- the pressure difference between fluid pressures P20b and P 20 a existing in the hydraulic cylinder's 20 piston head side 20b and piston rod side 20a is equalized gradually by increasing the volume flow V 2Ob supplied into the piston head side 20b, and the stepwise control of the roll's vertical position and at the same time the opening of the roll nip N are stopped prior to roll end blocks by adapting the fluid pressures on the hydraulic cylinder's 20 piston side 20b and rod side 20a to become equal, whereby also the volume flows for the piston side and the rod side have a ratio which is the same as before the opening of the roll nip.
- the fluid pressures P2ot > ⁇ n and P 2 OaTn are lower than the fluid pressures P2 0 b ⁇ and P 20a ⁇ of the state of equilibrium existing at the start of the roll nip N opening process.
- the control of a roll nip's N high-speed opening process is effected as a direct control of the volume flow proceeding through various digital valve groups 10 of a digital valve unit according to a pre-established volume flow profile and the tuning of a high-speed opening is effected on each roll nip of a calender as the roll/calender is used for the first time. If necessary, profile changes for volume flows supplied into various sides of a loading cylinder can be performed on the basis of verifying measurements.
- fig. 3H Depicted schematically in fig. 3H is another supporting-lever pressurizing hydraulic cylinder 20, which is present at the end of a multi-roll calender's intermediate roll and the control of which is effected by a digital valve controlled system similar to that illustrated earlier in figs. 2D as well as 3B-3D.
- a state of equilibrium a steady-state condition
- prevailing prior to the high-speed opening during the course of continuous calendering while the pressure load is constant, there exists an equilibrium-state pressure load K p ⁇ .
- a fluid pressure P20a ⁇ which is established by a volume flow V 2 OaT-
- a volume flow V 2 OaT- Respectively, on the hydraulic cylinder's pressure side, i.e. on the piston rod side 20b in the figure, exists an equilibrium- state fluid pressure P2 0 b ⁇ , which is established by a volume flow V 2Ob T-
- the digital valve unit is controlled by an adjustment instruction F(V); F(VT), which may be of a feedback type.
- the digital valve unit is supplied with an adjustment instruction F(V); F( ⁇ ), on the basis of which the volume flow (and fluid pressure) proceeding through a digital valve group 10b delivering fluid into the cylinder's 20 pressure side 20b is reduced by the digital valve unit from an equilibrium-state volume flow V 2 o t> ⁇ and a matching fluid pressure P 2 ObT down to a predetermined V 2 ObI and a matching fluid pressure P 2 obi. resulting in a quick reduction of the hydraulic-cylinder established pressure load K p from an equilibrium-state pressure load K pT to a lower pressure load K p i.
- the volume flow supplied into the cylinder's 20 piston rod side 20a is increased from an equilibrium-state volume flow V 2Oa T to a new higher-rate volume flow V 2 oai for increasing a counter pressure P 2 o a existing on the piston rod side with respect to a fluid pressure P 20b ⁇ existing on the cylinder's pressure side (piston side) 20b in the state of equilibrium.
- This is followed by a stepwise equalization of the pressure difference between fluid pressures P20b and P20a existing on the hydraulic cylinder's 20 piston head side 20b and piston rod side 20a as shown in fig. 3E.
- the digital valve unit is given a string of adjustment instructions (F(V); F(V 2 ), F(V 3 )... F(V n ), which are used for increasing a volume flow V 20b supplied into the piston head side 20b and possibly for simultaneously reducing a hydraulic fluid volume flow V 20a supplied into the piston rod side 20a as the pressure load K p is falling in a stepwise manner Kp2, Kp3..K pn .
- the high-speed opening of a roll nip is executed by a so-called hybrid control, wherein the major changes in a loading cylinder concerning a volumetric fluid flow in the initial acceleration stage of a roll opening process (e.g. step A in fig. 3E) are implemented quickly by means of a digital valve group with a feed-forward adjustment strategy.
- a slower stepwise continued opening of the roll wherein the changes of a volume flow on various sides of the loading cylinder are less dramatic, can be implemented thereafter with traditional slide valves by using a feedback mode of adjustment.
- the paper machine In response to moving machine parts, the paper machine develops resonance vibrations in several components, which may damage paper machine equipment and reduce the running speed of a paper machine.
- the multi-roll calenders may experience a so-called barring effect with the successive rolls of a calender developing resonance vibration.
- the barring effect is often a result of md-directed faults present on the fiber web. The barring effect is detrimental to the coating of polymer-coated rolls.
- Film transfer technique is currently one of the most popular coating, surface-sizing, and pigmenting methods for paper and board.
- the film transfer technique comprises forming a film on a roll with an application device and transferring the film onto the surface of a fiber web in a roll nip between the roll and its counter-roll.
- the faults of a roll surface may develop resonance vibrations in the roll nip between the roll and the application bar, which cause clouding of the coating or surface size and/or uneven spreading of the film on the roll and thereby on the fiber web.
- the process of winding a paper web on a storage reel generally involves the use of a winding unit, wherein the paper web proceeds onto a storage reel by way of a roll nip between the storage reel and a breast roll and at the same time the storage reel is supported from below by means of a metal belt driven between two rolls.
- the paper wound up on the storage reel develops faults, which are likely to cause further disturbances in paper feeding as the breast roll and/or the storage-roll supporting endless metal belt begins to resonate with the fault present in a roll of paper carried by the storage reel.
- the method according to the invention is based on the procedure that the location of an fault H causing vibrations be identified on the surface of a roll or on a fiber web about to arrive at a roll nip, for example by means of a pressure measurement linked with the roll nip, and the arrival moment of an fault at a roll nip and the dwell time of an fault in a roll nip be estimated or calculated. After this, as the trouble spot arrives at a roll nip, the pressure in the nip is reduced momentarily by means of an anticipating feed-forward adjustment.
- the pressure reduction is effected by diminishing the bearing/pressurization action of a roll and/or its counter-roll bearing/pressurizing element through the intermediary of a hydraulic actuator, which is coupled with one or more digital valve groups used for controlling a volume flow to the hydraulic actuator.
- a hydraulic actuator which is coupled with one or more digital valve groups used for controlling a volume flow to the hydraulic actuator.
- the momentary relief of a load applied on a supporting element 3 by a hydraulic actuator 2 coupled with a digital valve group 100 and the reset of said load in a roll nip take place for example in a manner similar to what has been earlier illustrated in figs. 3A-3E when describing the establishment of a relief pulse and a rest pulse for the pressure load of a roll nip in a multi-roll calender.
- One type of calender used today for the soft calendering of a fiber web is a so-called shoe calender, wherein the fiber web to be calendered is conveyed to a long nip established between a hard-surfaced counter roll (usually a heatable thermo roll) as well as a shoe roll opposite thereto and provided with an endless belt.
- a hard-surfaced counter roll usually a heatable thermo roll
- the endless belt extending around a shoe roll used in a shoe calender or the surface of a counter roll opposite to the shoe roll becomes in certain areas thinner than the rest of the structure as a result of wearing, the material web W may become calendered in a long nip to a lesser thickness every time the thinner spot of the endless belt or the counter roll arrives at the roll nip.
- the part of a shoe calender commonly subjected to wearing is the endless belt (e.g. a fabric-reinforced polyurethane belt) rotating on top of the shoe element of a shoe roll,
- the uneven calendering of the material web W can be precluded by a method of the invention and by an apparatus used therein.
- the hydraulic actuators such as hydraulic cylinders applying a load on the shoe element of a shoe calender
- the method is based on the procedure that every time a thinner spot present in the endless belt of a shoe calender or in its counter roll rotates into the long nip, the load of hydraulic cylinders pressurizing the shoe element will be relieved and, after the thinner spot has passed the long nip, the load of hydraulic cylinders pressurizing the shoe element will be reset to its former level.
- Fig. 4A shows schematically a shoe calender in view directly to an end face.
- Fig. 4B shows the long-nip zone of fig. 4A in an enlarged scale.
- Depicted schematically in fig. 4A is a typical shoe calender 800 without its lubrication system.
- Fig. 4B 1 in turn, shows an endless belt 8a on a shoe roll 8 in a long-nip zone N 1 on top of which lies a reduced-thickness spot of the fiber web W, such as a paper web.
- the shoe roll 8 consists of a loadable shoe element 8b, hydraulic actuators 2 applying a load on the shoe element in a roll nip N between the shoe roll 8 and a counter roll 80 opposite thereto, an endless belt 8a rotating on top of the shoe element, as well as a lubrication system (not shown in the figures) provided between the shoe element 8b and the belt 8a.
- the hydraulic actuators 2 visualized in the figures consist of two side-by-side rows of hydraulic cylinders 200; 200' and 200; 200", the rows extending from one end of the shoe element to the other in a direction (CD-direction) perpendicular to a machine direction (MD-direction).
- Each hydraulic cylinder row 200; 200' and 200; 200" is controlled by its own digital valve unit 100; 100' or 100; 100". Operation of the digital valve units 100 is synchronized by a control system 4.
- the design of the digital valve units 100' and 100', the operation control of each hydraulic cylinder row 200' and 200" by these digital valve units, and the synchronization of said digital valve units for mutual operation by the control system 4 can be analogous with respect to the previously described working example according to fig. 2D.
- the shoe roll 8 has its counter roll 80 comprising a heated thermo roll 80 used in the soft calendering of a material web, whereby the shoe calender 800 has its long nip N established between the shoe element 8b, as well as the endless belt 8a running on top of the shoe element, and the thermo roll 80, the fiber web W to be calendered being conveyed into said nip.
- Monitoring deformations in the endless belt 8a can be conducted by measuring continuously, on-line, a pressure load P1 established by the hydraulic cylinders 200 loading the shoe element 8b, as well as a surface pressure P2 of the endless belt in the long nip N.
- Measuring the surface pressure P2 of an endless belt in a long nip can be conducted by using for example the method described in the patent document FI-20055020.
- the control system 4 takes into consideration at least a rotating speed of the endless belt 8a, a length of the long nip N in machine direction, and a thickness and surface area of the endless belt's reduced-thickness spot H t .
- the nip pressure is relieved and reset again by supplying the hydraulic actuators 2, such as the hydraulic cylinders 200, loading the shoe element 8b and coupled with the digital valve group/groups 100, with an appropriately timed and proper-duration load relief pulse and a load reset pulse, as explained in more detail in connection with the description of figs. 3A-3D.
- the relief pulse and the load reset pulse enable first the pressure load of the hydraulic cylinders 200 on the shoe element 8b and thereby on the roll nip N to be reduced and, after an appropriate time period has lapsed from the commencement of the relief pulse, the nip loading pressure is reset to its original value by means of the reset pulse.
- the relief pulse for the hydraulic actuators 200 is given by changing (reducing) the volume flow of a fluid passed into the hydraulic actuators' piston side from the digital valve groups 100; 100' or 100; 100" with respect to the volume flow passed into their rod side from the digital valve unit, as depicted in figs.
- the flow relief pulse issued by the valves of a digital valve group leads to a reduction of the pressure applied by the hydraulic cylinders' 200 piston on the shoe element 8b and further on the shoe element's endless belt 8a having rotated into the long nip's N zone; since the endless belt 8a rotated into the range of the long nip N has its part H t reduced in thickness, the pressure load applied by the endless belt 8a on the fiber web W nevertheless remains in the long nip N at its previous level.
- the actions aimed at resetting the pressure load of the shoe element 8b are commenced with the digital valve units 100.
- the fluid flow passed into the hydraulic actuators' 200 piston side is increased with respect to the flow passed into their rod side and momentarily the ratio of flows is reset to its original value by means of an appropriate aperture of a digital group in the digital valve unit, as described in connection with the specification of fig. 3A, (and, at the same time, the fluid pressures existing on various sides of each hydraulic cylinder's piston are reset to equal fluid pressures existing in a steady-state condition).
- the load reset pulse given by the digital valve units 100 the pressure load of the hydraulic actuators 200 on the shoe element 8b present within the long nip's N zone will be reset to the level of a steady-state condition existing prior to the relief pulse.
- the control system 4 of the digital valve units 100 is supplied with data regarding at least a running speed of the fiber web W and/or a rotation speed of the endless belt 8a, a length of the long nip N in machine direction, and a length of the endless belt's 8a reduced- thickness spot H t in machine direction.
- the control system 4 is supplied with data regarding a pressure load applied by the hydraulic actuators 200 on the shoe element and changes of the endless belt's 8a load profile in the long nip N.
- the long nip's N length, the fiber web's W running speed, and the endless belt's 8a rotation speed can be obtained by measuring and/or are otherwise previously known.
- the length of the endless belt's 8a reduced-thickness spot H t and the thickness of said reduced-thickness spot with respect to the other thickness of the endless belt, as well as a length of the reduced-thickness spot in a lengthwise direction of the long nip N (in machine direction), are obtained on the basis of measurements as described earlier.
- the degree of relieving the compression force P1 applied by the hydraulic actuators' 200 pistons on the shoe element 8b, required in a method of the invention, depends on how much the endless belt has thinned with respect to the non-reduced thickness of the rest of the endless belt. Because changes in the flow rates of a hydraulic fluid into the hydraulic actuators' 200 pressure and working sides result in a certain change in the compression force applied by the hydraulic actuators' 200 pistons on the shoe element 8b and thereby on the endless belt 8a, the required changes of compression force can be used as a basis for finding out empirically and/or by calculation and/or by table lookup the parameters needed by the adjustment program for changing the volumetric hydraulic fluid flow in the digital valve units 100 coupled with the hydraulic actuators 200.
- the flow rate passing through each digital valve group depends on the aperture 1A of a digital valve group, i.e. on the total area of open-state digital valves' ports and on the pressure difference between a fluid arriving at a particular digital valve group and a fluid having passed through the same (see fig. 2D and related specification).
- the pressure difference across the aperture 1A of a particular digital valve group is obtained by measurements or it is otherwise readily predictable.
- the control system 4 enables working out a rapid feed-forward adjustment instruction for a particular time period according to a particular adjustment profile (see fig.
- control system 4 selects, on the basis of flow rates to be conducted on the pressure and/or working side of desired hydraulic cylinders 200, those hydraulic elements' volume-flow adjusting digital valve groups of the digital valve units 100; 100' or 100; 100" which enable producing the load relief and reset pulses consistent with the adjustment instruction, and thereafter, on the basis of a desired degree of change, selects from among these digital valve groups those digital valves which are open at specific times.
- the time lapse between relief and reset pulses for the load of the shoe element 8b and thereby the endless belt 8a depends on a length of the endless belt's reduced-thickness spot (H; H t ) and a length of the long nip N.
- One embodiment of the invention is based on a lubricating oil circulation for bearings implemented by means of one or more digital valve groups.
- lubrication is performed by having oil circulate in the bearing systems of rolls both in wet, dryer, and finishing sections.
- Other bearing systems of paper machines' equipment and motors such as the bearing systems of fans, barking drums, refiners, mixers, coaters, winders and slitters, can be provided with lubrication by circulating oil.
- the lubrication by circulating oil is used in paper machines principally for extending the longevity of bearing systems, because it is the degree of purity of lubricating oil which is most critical for the longevity of a bearing.
- -suction rolls which are located in a wire section of the wet end and have a rotating roll shell and which are driven by means of a planetary gear.
- the most common bearing used both in suction and driving sides for suction rolls comprises roller ball bearings and oil is generally conducted to the center of bearings.
- the fiber web travels, while supported by felts, in roll nips between press rolls and most of the water still contained in the web is removed in compression.
- the press rolls are provided with roller ball bearings on both service and driving sides.
- the oil is typically conducted to the center of a bearing and removed from either side of the bearing into an oil-collecting chamber and then out of a bearing housing by way of an outlet formed in the bearing housing.
- the dimensioning of oil circulation is most of all influenced by temperature planned for the bearing system and by the grade of lubricating oil.
- the bearing system temperature is influenced by the diameter, rotation speed and weight of the roll.
- the multi-roll calenders used for the soft calendering of a fiber web include several superimposed deflection compensated polymer-coated rolls, as well as heated thermo rolls, while the roll nips used for fiber web calendering are made up by a pair of rolls, including a thermo roll and opposite thereto a polymer- coated roll.
- the actual calendering process is influenced, among other factors, by a nip load existing in each roll nip, temperature of the thermo roll, and moisture of the fiber web.
- the roll nips present in the roll set of a multi-roll calender may have unequal existing nip loads, it is necessary, when designing bearing systems for the rolls, to consider the position of a roll in the roll set and the nip load existing in the roll nip. Because the roll set of even one and the same multi- roll calender often has its rolls in unequal operating conditions, it may also be required that the flow rate of a circulating oil lubrication brought to each bearing and removed from the bearing housing be dimensioned in a roll- and bearing- specific manner, whereby the bearing system for a multi-roll calender's roll set is likely to become laborious in terms of its design work. Typically, the quantitative adjustment of lubricating oil for each bearing must indeed be implemented as a feedback through the intermediary of an oval wheel or a turbine measurement. In multi-roll calenders as well, the most common type of bearing comprises roller ball bearings.
- the circulation of lubricating oil is currently implemented with analog regulating valves in several parts of a paper machine, such in the bearing systems of press and calender rolls, but also in other bearing systems of a paper machine's equipment and motors.
- the rolls of paper machines are generally provided with spherical roller ball bearings, while typical rolls include the deflection compensated rolls of wet end calenders.
- analog valves it is required that the feedback adjustment of oil supply for each bearing be dimensioned and planned separately, whereby the bearing system and its lubrication are likely to become complicated and expensive. Controlling the lubricating oil circulation with one or more digital valve groups of a digital valve unit results in a substantial advantage over the circulation control effected by means of analog valves.
- the lubricating oil is dispensed by way of a digital valve unit, composed of one or more digital valve groups, to bearings housed in an apparatus such as a multi-roll calender.
- each bearing has a specific valve unit assigned thereto for dispensing the amount of lubricating oil required by the bearing at a particular time.
- the volumetric circulation flow of lubricating oil needed by various bearing systems in paper machines and the extent of change in the volumetric flow are such that the digital valve group of a digital valve unit serving each bearing has conveniently 3 to 6 digital valves in parallel connection.
- the dosage of lubricating oil to a bearing is suitably conducted by changing the aperture of a digital valve group supplying oil to the bearing.
- the supply of oil to the digital valve units can be conducted in a manner equivalent to fig. 2D, i.e. by way of the inlet line 7; 71 common to the digital valve units.
- the digital valve unit itself does not include a dosage control for lubricating oil, but it only functions as a dosage dispenser. If the control is applied for example to a lubricating oil circulation for the rolls of a multi-roll calender, the amount of oil needed by all bearings of the calender can be controlled in a centralized manner with a separate control system coupled with the digital valve units by using a feedforward based adjustment strategy.
- the control system is used for calculating the amount of lubricating oil required for each bearing at a particular instant e.g. on the basis of acquired bearing-related measuring data and for opening appropriate digital valves included in a digital valve group of the digital valve unit supplying oil to the bearing in order to provide a desired volumetric lubricating oil flow to the bearing system.
- the control system is quick. Accordingly, the control system can be apparatus-specific, such as calender-specific, because there is no need to design a specific lubricating oil circulation for each bearing. As the lubricating oil circulation control system is apparatus-specific instead of being bearing-specific, the control system becomes simpler and more attractive in terms of its costs. If desired, the lubricating oil circulation implemented by means of digital valve units can also have a feedback coupled therewith, for example by the intermediary of presently used flow measurements, but the lubricating oil circulation is very well viable even without feedback.
- the invention relates to the adjustment of the blasting output of compressed air, especially in web feeding, when exchanging a paper grade to be processed in a paper machine.
- Web feeding as regards a fiber web, is particularly needed in the process of conveying the end of a fiber web across unsupported spaces in calendering, coating, pressing, and reeling.
- adjusting the output of an air blast is conducted by using resistance valves, which are practically fan-specific in the sense of only enabling the output of blasting air to be adjusted over a specific narrow range of volumetric flow at a time. In a resistance valve, the air proceeds through a short throttle passage.
- the amount of flow passed through a valve port depends on a pressure difference on either side of the valve port, as well as on a surface area of the port.
- the amount of flow and at the same time the air pressure existing on either side of the port are regulated in a resistance valve by adjusting the size of the throttle passage. Adjustment of a high-output air blast with such an analog resistance valve is inaccurate, wasteful in terms of energy, and expensive.
- the invention has an objective of providing a method and apparatus for adjusting the output of a compressed air blast, especially in the process of fiber web feeding.
- the method and apparatus according to the invention enable achieving the foregoing objectives.
- the method according to this embodiment of the invention relies on conveying the compressed air through a digital valve group, which is present in a compressed air flow channel and which comprises 2 to 8, generally 3 to 6 digital on/off valves side by side.
- the sizes of valves included in a digital valve group are preferably selected in such a way that the amount of air per unit time passing through the larger one of two open-state valves with consecutive flow rates is twice as much as that having passed through the smaller valve.
- the size of an aperture established by a digital valve group is adjusted by opening and closing appropriate on/off digital valves in the digital valve group. The area of this aperture determines a pressure difference between the air flow supplied to a digital valve group and the air flow having passed through the digital valve group.
- the volume flow of compressed air having passed through a digital valve group is in turn determined on the basis of an aperture area and the above-mentioned pressure difference.
- the digital valve apertures with consecutive diameters have the size thereof appropriately selected, the digital valve group will be capable of providing the effective adjustment of a compressed air flow in fiber web feeding and, at the same time, a valve unit to be fitted in the air flow channel enables adjusting the compressed air flow over an extensive flow range.
- the adjustment of a compressed air flow output implemented as described, reduces considerably the number of necessary compressed air flow regulating valve units.
- the adjustment of air output with a digital valve group is remarkably more precise than with throttle valves, the energy saving being as much as 30 to 50% in the web feeding process of a large-scale paper machine.
- Heat exchangers are necessary in various parts of a paper machine.
- One of the required services thereof involves the cooling of lubricating oil arriving from the process.
- the heat exchangers used for various services in a paper machine are often oil- water heat exchangers with oil moving on the primary side and cooling water on the secondary side.
- the regulation of a cooling water circulating rate is implemented by means of a pneumatic throttle valve supplied by the manufacturer, which is nevertheless expensive in terms of its purchase costs.
- the cooling water regulating valve makes up an excessive portion of the total costs of a heat exchanger, necessitating the use of valves adapted to this particular heat transfer device.
- the regulation of cooling water circulation is implemented by adapted valves not originally designed for this particular heat exchanger, such valves are often inferior in terms of energy and water efficiency to those specifically designed for the discussed actuator.
- the invention is aimed at eliminating the drawbacks appearing in the prior art.
- the heat exchanger should provide an exact adjustment over the entire adjustment range for the amount of fluid traveling on the secondary side.
- the heat transfer fluid such as water
- the heat transfer fluid to be supplied into the secondary side of a heat exchanger is delivered by way of a digital valve group.
- the digital valve group has 2 to 8, preferably 3 to 6 on/off digital valves connected in parallel, depending on a volume flow required for the secondary side.
- a digital valve group on the supply side of a heat exchanger enables providing the heat exchanger with a regulation which is accurate at both low and high flow rates.
- the on/off digital valves are externally identical and only differ from each other in terms of the diameter of their fluid passage apertures, whereby the investment costs of a digital valve group are substantially lower than those incurred by formerly used actuator-specific regulating valves.
- a heat exchanger of the invention it should be noted that one and the same heat exchanger can be used for a variety of projects, because the heat exchanger has its secondary side flow adjustable within an extensive range.
- the heat exchanger according to the invention is described more closely with reference to fig. 5.
- Fig. 5 shows schematically an oil-water heat exchanger of the invention.
- FIG. 5 Visible in fig. 5 is an oil-water heat exchanger 9, wherein the oil circulating on a primary side 92 is for example oil flowing in a lubricating oil circulation.
- the cooling water supply on a secondary side 9; 91 of the heat exchanger is integrated with a digital valve unit 100, comprising one digital valve group 10 which includes 6 parallel-connected on/off digital valves 1.
- the oil circulating on the primary side 92 is cooled with water, the cooling capacity (volumetric flow) of which must be dimensioned in such a way that one and the same water circulation of the secondary side 91 enables both the cooling of hot oil, with a temperature of about 200 0 C, and the slight heating of oil in connection with cold starting the apparatus lubricated by the primary side. Therefore, the water circulation 92 must have a very extensive volumetric flow range.
- the number of digital valves 1 contained in a digital valve group 10 and the volume flow passing therethrough are adapted to match the required cooling capacity.
- the supplied cooling water is regulated by a digital valve group 10, which includes 6 pieces of on/off digital valves 1 disposed in a parallel relationship in the cooling water supply flow.
- the volume flow passing through the digital valves 1 is selected such that, in two valves of consecutive volume flows, the valve with a larger flow port has a volume flow which 2 x that of the smaller valve.
- Open or partially open adjustment systems based on digital valve units are viable for replacing current closed feedback type adjustment systems, which are based on analog adjustment valves for example in the process of calendering or spreading a fiber web with so-called active rolls.
- the active rolls refer here to rolls, which are provided with roll-engaged internal or external loading elements enabling a surface profile to be modified in a longitudinal direction of the roll
- Fig. 7 visualizes the pressure adjustment with a digital valve unit 100 for a loading element, which is applying load on a roll and coupled with the piston rod of a hydraulic cylinder 20.
- the roll is for example a so-called Sym-roll provided with several intra-roll loading elements, or a roll with whose stub shafts is coupled a hydraulic cylinder having a loading element on its piston head.
- fig. 6 illustrates a corresponding traditional system for adjusting a pressure Kp for a loading element applying load on a roll surface from inside.
- the adjustment system comprises the use of a closed (feedback type) adjustment system for controlling the pressure load Kp for a loading element coupled with a hydraulic cylinder's 20 piston 22, wherein changing of the pressure load is performed by using a prior art analog adjustment valve and a pressure regulator.
- the pressure regulator is given a target pressure value Pref, for example by way of a potential message.
- a pressure P 6 existing in a line 6 leading to the hydraulic cylinder 20 is measured continuously or at specific intervals, for example by means of an electronic sensor or optionally in a hydromechanical manner, by conducting the pressure to an end face of the valve's slide.
- the pressure regulator receives continuously or at specific intervals information about a difference between the target pressure value Pref and a pressure Ptot measured from the line 6 and applies on that basis an adjustment instruction Pinstruction for correcting all the time the adjustment valve's slide to such a position at which the measured pressure Ptot is as close as possible to the target pressure Pref.
- the adjustment of the slide's position can be executed either by an electronic adjuster and actuator or hydromechanically, for example by means of springs.
- a problem with such a traditional adjustment system is a risk of its instability. The question is about a so-called closed adjustment system, the stability of which depends, among other things, on a pressure regulator and its tuning parameters, as well as on the dynamic behavior of a loading element, a pipe system, and an adjustment valve.
- the instability manifests itself as a fluctuation of the loading element's pressure load Kp, a vibration which deteriorates for example the quality of paper surface as paper is calendered in a roll nip provided with a roll whose surface is pressurized from inside with such a loading element.
- the adjustment system may also respond unnecessarily to an intermittent impulse resulting from the rotation of a roll.
- Fig. 7 shows an adjustment method by a digital valve unit 100 for a pressure load Kp applied on a roll surface by one loading element included in a roll member, such as a roll provided with internal loading elements.
- the digital valve unit 100 comprises two digital valve groups 10.
- the flow supplied by way of a flow line 6 to a hydraulic cylinder's 20 pressure side 20b has its flow rate V 6 and flow pressure P 6 regulated by a digital valve group 10; lOpressure.
- the flow proceeding from the hydraulic cylinder's pressure side 20b to a tank line 7; 72 has its flow rate and pressure regulated by a digital valve group 10; lOreturn.
- Both the digital valve group 10; lOpressure, regulating pressure and flow rate in the flow line 6, and the digital valve group 10; lOreturn, regulating the pressure P 6 and the flow rate V 6 of a fluid conveyed into the tank line include N examples of parallel- connected on/off digital valves with an unequal flow-through in the on-position. Each digital valve can be either totally open or totally closed. The number N of digital valve can be unequal in the digital valve group 10; lOreturn, controlling a flow from the flow line 6 to the tank line 7; 72, and in the digital valve group 10; lOpressure, controlling a flow from the supply line 7; 71 to the flow line 6.
- the number of on/off digital valves with a flow- through unequal relative to each other is N.
- the aperture 1 A of a digital valve group 10 is a total sum of digital valves controlled at specific times in the digital valve group to an open position and may only attain specific discrete values.
- the aperture 1 A ; lApressure can achieve 2 N unequal opening combinations and discrete apertures.
- lApressure- Because each digital valve in a digital valve group can be either totally open or totally closed, each aperture 1A can achieved at high accuracy. The advantage achieved thereby is that a digital valve group enables eliminating the uncertainties, such as hysteresis and zero creep, associated with analog adjustment valves.
- the flow rate of a fluid passing at a particular time by way of a digital valve group into the line 6 depends on the supply pressure Ps of a fluid arriving at the digital valve group by way of the supply line 7; 71 and on the digital group's aperture 1 ; lApressure at a particular time.
- a pressureN is then matched by a specific pressure load Kp; Kp1 , Kp2..KpN of the loading element, because the pressure load Kp sets at such a pressure that the volume flow that has passed through the digital valve group 10; lOpressure is equal to the volume flow proceeding through the head of a piston 22 coupled with the loading element.
- These pressure loads can be worked out by two optional models: -a mathematical model, in which a mathematical model is developed between a digital valve group and a loading element and the model is used for working out the loading element's pressure loads Kp matching various apertures 1A; lApressure of the digital valve group 10; lOpressure, or
- Both the mathematical model and the empirical model actually provide a model describing an adjustment system made up by a hydraulic cylinder and a digital valve unit 100, enabling the definition of a pressure load Kp obtained with various apertures 1 A ; lApressure ; lApressurei . iApaine2 • • 1 ApressureN of the digital valve group 10; IOpressure controlling a fluid flow into a hydraulic cylinder's pressure side 20b.
- the pressure load Kp can be adjusted by selecting such an aperture 1A; lApressure by which the aperture-defined pressure load Kp is close to a target pressure.
- the pressure load adjustment can be conducted without the feedback of pressure, i.e.
- each aperture 1A of a digital valve group is attainable in such a repeatable manner that a pressure load provided by the model matches sufficiently well the real pressure load.
- a correct aperture 1 A ⁇ pressure .
- the above-described adjustment system does not consider variations of a supply pressure P 8 in the inlet flow V 6 , P 6 , which pressure variations have an effect on the rate of volume flow passing through each aperture of a digital valve group as the volume flow depends on the supply pressure P s and on the aperture 1 A ;
- ⁇ pressure- Variation of the supply pressure P 8 can be compensated for by measuring a supply pressure and presuming, for example, that the ratio of a loading element's pressure load Kp to a supply pressure remains constant.
- the pressure adjustment system for a roll member's loading element established by means of a digital valve unit can also be used as part of a closed or feedback type adjustment system.
- the target value for a loading element's pressure load Kp is first used as a basis for selecting an appropriate aperture 1A; l A pr e s s ure for a digital valve group, as described above.
- a measurement is conducted on the pressure load and, based on the difference between a measured pressure load and a target pressure load, the target value of a pressure load Kp is changed by means of a closed adjustment system which comprises an analog adjustment valve in coupling with a pressure regulator.
- the load element's pressure loads Kp or the hydraulic cylinder's working side pressures matching the apertures 1A of a digital valve group passing a fluid into the hydraulic cylinder's pressure side.
- the optimal aperture l A op t of a digital valve group establishing, in a line leading to the hydraulic cylinder, a specific volume flow and pressure matched by a desired pressure load Kp or a pressure of the hydraulic cylinder's working side.
- the optimal aperture "Uopt of a digital valve group establishing, in a line leading to the hydraulic cylinder, a specific volume flow and pressure matched by a desired pressure load Kp or a pressure of the hydraulic cylinder's working side.
- the adjustment system is a hybrid adjustment system, which contains a closed adjustment system and an open one and which involves changing the pressure of a loading element's pressure load Kp or that of that of the hydraulic cylinder's working side with a closed adjustment system, including for example an analog slide valve, and thereafter adjusting the flow with a digital valve unit to match new target values set for the pressure load Kp or for the hydraulic cylinder's working side pressure
- a hybrid adjustment system which contains a closed adjustment system and an open one and which involves changing the pressure of a loading element's pressure load Kp or that of that of the hydraulic cylinder's working side with a closed adjustment system, including for example an analog slide valve, and thereafter adjusting the flow with a digital valve unit to match new target values set for the pressure load Kp or for the hydraulic cylinder's working side pressure
- the optimal aperture iA O p t of a digital valve group establishing, in a line leading to the hydraulic cylinder, a specific volume flow and pressure matched by a desired new pressure load Kp or a pressure of the hydraulic cylinder's working side.
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Abstract
Description
Claims
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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FI20070984A FI120317B (en) | 2007-12-14 | 2007-12-14 | Method of treating deviations during manufacture of a material web and plant for carrying out the procedure in a calender |
PCT/FI2008/050734 WO2009077650A1 (en) | 2007-12-14 | 2008-12-12 | Method for dealing with faults occurring during the manufacture of a material web |
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EP2231924A1 true EP2231924A1 (en) | 2010-09-29 |
EP2231924B1 EP2231924B1 (en) | 2011-06-01 |
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EP08863004A Not-in-force EP2231924B1 (en) | 2007-12-14 | 2008-12-12 | Method for dealing with faults occurring during the manufacture of a material web |
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EP (1) | EP2231924B1 (en) |
CN (1) | CN101903594B (en) |
AT (1) | ATE511574T1 (en) |
FI (1) | FI120317B (en) |
WO (1) | WO2009077650A1 (en) |
Families Citing this family (15)
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DE102009026606A1 (en) * | 2009-05-29 | 2010-12-02 | Metso Paper, Inc. | Digital hydraulic controller |
DE102009055308A1 (en) * | 2009-12-23 | 2011-06-30 | Metso Paper, Inc. | Arrangement for controlling the position of a roll or the nip pressure of a nip in a fibrous web machine |
DE102010000833A1 (en) * | 2010-01-12 | 2011-07-14 | Metso Paper, Inc. | Paper machine for manufacturing fibrous material web, has fluid pressure-driven actuators provided for controlling nip pressure in gap between air pressure devices, and switching valves controlling movement of actuators |
FI121896B (en) * | 2010-02-05 | 2011-05-31 | Metso Paper Inc | BOMBABLE ROLL AND SYSTEM |
WO2012041536A1 (en) | 2010-09-27 | 2012-04-05 | Metso Paper, Inc. | Fluid pressure control system |
DE102010042780A1 (en) | 2010-10-21 | 2012-04-26 | Metso Paper, Inc. | Fluid system for e.g. paper or paperboard machine for producing fibrous material web, has calculation device computing calibration value of valves, on basis of detected piston travel or path between acquisition locations and travel time |
DE102010043168A1 (en) | 2010-10-29 | 2012-05-03 | Metso Paper, Inc. | Method for filling pressure reservoir with e.g. oil, in fluid system of fibrous material web manufacturing machine e.g. paper manufacturing machine, involves controlling moving velocity of piston by selection of pressure chambers |
EP2543890B1 (en) * | 2011-07-04 | 2018-09-05 | Valmet Technologies, Inc. | Safety component |
DE102012218146A1 (en) | 2012-10-04 | 2014-04-10 | Metso Paper, Inc. | Calibration method for system of fluid used in paper machine, involves calculating discharge coefficient value of supply valve based on determined differences in pressure and discharge coefficient of drain valve |
DE102013200857A1 (en) | 2013-01-21 | 2014-07-24 | Valmet Technologies, Inc. | Device for determining position of actuator i.e. hydraulic piston, in actuator cylinder of hydraulic system in fibrous material web manufacturing machine i.e. paper machine, has detection device detecting impulse response of actuator |
WO2018161147A1 (en) * | 2017-03-06 | 2018-09-13 | Honeywell Limited | Method and apparatus for designing model-based control having spatial robustness for multiple-array cross- direction (cd) web manufacturing or processing systems or other systems |
CN108179585B (en) * | 2018-03-05 | 2024-05-28 | 博路威机械江苏有限公司 | Y-shaped double-nip deflection controllable roller |
CN113174773B (en) * | 2021-05-06 | 2022-07-15 | 山东明源智能装备股份有限公司 | Complex multi-information processing method for papermaking equipment |
CN113515046B (en) * | 2021-07-19 | 2023-05-16 | 西安理工大学 | Winding tension control method of web coating machine based on feedforward control |
CN114215804B (en) * | 2022-02-22 | 2022-04-29 | 中国空气动力研究与发展中心高速空气动力研究所 | Electro-hydraulic servo system for driving curved knife supporting mechanism |
Family Cites Families (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FI115144B (en) * | 1999-10-13 | 2005-03-15 | Metso Paper Inc | calendering |
FI113794B (en) * | 2002-11-14 | 2004-06-15 | Metso Paper Inc | Method and arrangement for controlling the position and / or force of an elongated roller assembly |
FI114647B (en) * | 2003-07-02 | 2004-11-30 | Metso Paper Inc | An arrangement for controlling the web with a press section of a paper or board machine |
-
2007
- 2007-12-14 FI FI20070984A patent/FI120317B/en not_active IP Right Cessation
-
2008
- 2008-12-12 AT AT08863004T patent/ATE511574T1/en active
- 2008-12-12 EP EP08863004A patent/EP2231924B1/en not_active Not-in-force
- 2008-12-12 WO PCT/FI2008/050734 patent/WO2009077650A1/en active Application Filing
- 2008-12-12 CN CN2008801213224A patent/CN101903594B/en not_active Expired - Fee Related
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See references of WO2009077650A1 * |
Also Published As
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FI120317B (en) | 2009-09-15 |
FI20070984A0 (en) | 2007-12-14 |
CN101903594A (en) | 2010-12-01 |
WO2009077650A1 (en) | 2009-06-25 |
EP2231924B1 (en) | 2011-06-01 |
CN101903594B (en) | 2012-07-18 |
ATE511574T1 (en) | 2011-06-15 |
FI20070984A (en) | 2009-06-15 |
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