Classifications

• • 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
• • 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
  • F15B11/044—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed by means in the return line, i.e. "meter out"
• • 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
  • F15B19/00—Testing; Calibrating; Fault detection or monitoring; Simulation or modelling of fluid-pressure systems or apparatus not otherwise provided for
• • 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
  • F15B2211/40507—Flow control characterised by the type of flow control means or valve with constant throttles or orifices
• • 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
• • 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
  • F15B2211/41—Flow control characterised by the positions of the valve element
  • F15B2211/411—Flow control characterised by the positions of the valve element the positions being discrete

Definitions

• the invention relates to a control system for controlling the rate and/or position of an actuator operating by a pressurized medium, according to the preamble of claim 1.
• the invention also relates to a method for controlling the rate and/or position of an actuator operating by a pressurized medium, according to the preamble of claim 12.
• hydraulics is used to transfer energy by means of a pressurized medium, wherein a pressurized volume flow produced by pumping means is controlled by valve means and utilized in actuator means, such as cylinders and engines, to produce a linear motion, a force, a moment, or a rotational motion.
• actuator means such as cylinders and engines
• Known pressurized media include hydraulic oil, pressurized air and water or water-based hydraulic fluids (HFA, HFB, HFC, HFD).
• proportional control valves are used in a known manner, one example being presented in US patent 5,785,087.
• the disclosed valve is a slide-type valve, in which the position of the slide is controlled by means of a proportional magnet to choke the pressurized medium and simultaneously to control the quantity and direction of the volume flow.
• the valve is controlled by an external electric set signal which is proportional to the desired volume flow.
• the valve is used to provide stepless control of the volume flow.
• control system is suitable for controlling the rate of an actuator, but it can also be applied in position control when continu- ously monitoring a desired or set position dependent on the moment of time.
• US patent 2,999,482 discloses the control of an on/off system on the pressure side, to transfer the cylinder to a desired extent.
• US patent 4,590,966 discloses one version of the on/off system, i.e. a kind of a digital valve block which is coupled to the pressure and return sides of a valve.
• a corresponding block type is also presented in US patent 4,518,011.
• the number of control steps can be decreased and increased according to the need and the use, wherein the same valve system can be applied in a more efficient way in different situations.
• the need of few control steps will also reduce the number of on/off valves, which will cut down the costs.
• the operation of valves, particularly the change in the control always involves a response time which, in the case of a slide valve, depends on the length of the distance that the slide must move. If necessary, the on/off valves will operate simultaneously, wherein the delay of operation is substantially constant with all the changes in the control of the volume flow, because the valves only move between the open and closed positions.
• Fig. 1 is a schematic diagram showing the characteristic curve of a proportional valve of prior art
• Fig. 2 is a schematic diagram showing the characteristic curve of a valve system according to the invention, with respect to one set of valves,
• Fig. 3 is a block chart showing the structure of a valve system according to a preferred embodiment of the invention.
• Figs. 4a to 4d show different possibilities to couple the valve system of Fig. 3,
• Fig. 5 is a schematic view showing a circuit applying an on/off valve system in the control of a cylinder
• Fig. 6 shows the rates of the cylinder in the system of Fig. 5 with different combinations of valve openings
• Fig. 7 shows the rates of Fig. 6 in an order of magnitude
• Fig. 8 shows pressure variations in the system of Fig. 5 with different combinations of valve openings.
• Figure 1 shows the characteristic curve of a proportional directional valve according to prior art, wherein the transmission capacity of the volume flow Q of the valve is linearly dependent on a control signal V.
• the rate of the characteristic curve is also dependent on the pressure difference effective over the valve, that is, the pressure loss in the directional valve.
• the control signal used is a voltage signal V, but it is also possible to use a current signal /.
• the level selected for the control signal / is used as a set value V S ET, wherein maximum control V MAX corresponds to the maximum of the volume flow QMAX, and, respectively, the other levels of the curve cor- respond to the volume flow Q SET , wherein no volume flow is obtained when the control is zero.
• V SE ⁇ may also be negative, wherein the direction of the flow and the position of the valve are changed as well.
• a proportional magnet In a directional proportional valve, a proportional magnet has an effect on the control slide which is normally centered by means of springs.
• the proportional magnet in turn, is normally a direct current (DC) magnet, whose output is an armature force or a range of motion which is proportional to the level of the input electric control signal.
• the valve control means are provided on a circuit board which is electrically coupled to the valve. To the circuit board, in turn, it is possible to couple a control system for controlling the valve and the larger apparatus.
• the control signal with a certain level and obtained from the control system can thus be used to control the volume flow through the valve and further the actuator coupled to the valve.
• the pressurized volume flow can further be used to control the speed and direction of motion of the cylinder actuator.
• the direction of motion of the cylinder i.e., the position of the valve slide
• the set signal can also be, for example, a signal from 0 V to 20 V, wherein the limit value is 10 V.
• Figure 1 also shows the graphic symbol of the directional proportional valve and the ports therein.
• Figure 2 shows the stepped characteristic curve of one set of valve in an on/off valve system, wherein the volume flow Q is only changed stepwise when the control signal V is changed.
• the volume flow Q S£T of the valve system is changed stepwise when the set signal V SET exceeds or goes below the limits set for the steps.
• the controllability of the volume flow of the pressurized medium is the better, the smaller the size dQ of the step is in relation to the maximum volume flow Q MAX , that is, the greater the number of valves.
• an advantageous valve system 100 intended for the control of an actuator, comprises at least ports P, T, A, and B.
• the inlet port P is arranged for coupling a pressure line in the system to receive a volume flow of a pressurized medium normally from a pump.
• the outlet port T is arranged to couple a return line in the system, the return line being a tank line or a line with a lower pressure level than the pressure line.
• the first working port A is arranged to couple an actuator, such as the piston side of a cylinder, in the system.
• the second working port B is arranged to couple an actuator, such as the piston rod side of a cylinder, in the system.
• the volume flow is input in the actuator through one working port, and simultaneously the volume flow is received from the actuator through the other working port.
• the system 100 comprises electrically controllable coupling means 101 which are arranged to form at least a first connection 1 (between the inlet port P and the first working port A) and simultaneously a second connection 2 (between the outlet port T and the second working port B).
• the coupling means 101 are also arranged to form at least a third connection 3 (between the inlet port P and the second working port B) and to form simultaneously at least a fourth connection 4 (between the outlet port T and the first working port A).
• the different coupling alternatives are also illustrated by means of graphic symbols in Fig. 4c.
• the desired coupling alternatives can be implemented, for example, by means of an electrically controlled 4/2 valve, which is an on/off valve V of the slide type as shown in Fig. 3.
• connections can be implemented by means of two parallel electrically controlled 3/2 valves.
• the coupling means 101 may thus vary to a great extent, and they can be connected to the system 100 also separately.
• the system 100 comprises only the first connection 1 between the inlet port P and the first working port A, as well as the separate second connection 2 between the outlet port T and the second working port B.
• the coupling means 101 are thus coupled to the working ports A and B, when necessary. For example, in connection with the control of an engine, the means 101 will not be needed, if the engine only rotates in one direction.
• valve means 102 comprise two sets of valves 103 and 104. Each set comprises several electrically controllable on/off valves which are coupled in parallel and whose mutual pressurized medium throughput capacity is arranged as a stepped series.
• the minimum capacity of the volume flow of the pressurized medium in the whole valve system 100 is determined by the capacity of the smallest valve in the set, and the maximum capacity by the sum capacity of all the valves.
• a set 103 (in the port P) is used to control the volume flow in the connections 1 and 3
• a set 104 in the port T) is used to control the volume flow in the connections 2 and 4.
• valve sets 103 and 104 can also be assembled in another way to form a desired stepped characteristic curve, wherein the set may comprise several valves of the same size.
• the valve sets may also be different from each other.
• the valve set in the example system in turn, can be easily represented mathematically, and its number of valves is as small as possible in relation to the number of the steps.
• the control curve achieved with the example system makes a precise, almost linear control possible, particularly at high speeds.
• the sets 103 and 104 are implemented with four electrically controlled 2/2 valves (solenoid controlled on/off valves), as shown in Fig. 3.
• the mutual pressurized medium volume flow throughput capacities of the valves V1 to V4 are arranged according to table 1. For the control, at least two valves are needed.
• each set comprises four (number indicated as N) valves 15 to achieve a control step.
• the throughput capacity of the first valve (V1) is 0.5 l/min (indicated as Q)
• the throughput capacities of the following valves (V2, V3, V4) are 1.0 l/min, 2.0 l/min and 4 l/min, respectively, that is, according to the calculatory rule 2 (n"1) *Q, in which the variable n is the serial number of the valve.
• the size dQ obtained for a step is Q, and the maximum number of steps will be 15 (that is, according to the calculatory rule 2 N -1), excluding step 0.
• the minimum capacity of the system is Q and the maximum capacity is 7.5 l/min (that is, according to the calculatory rule Q » (2 N -1)).
• the required number N of valves can be calculated on the basis of the desired maximum capacity and dQ desired. In a corresponding manner, three valves will be needed to provide seven steps, and six valves to provide 63 steps. Typically, the number of valves ranges from 3 to 7.
• Figs. 4a and 4b graphic symbols are used to illustrate the coupling possibilities of the sets 103 and 104, respectively.
• the coupling to the port A or B will depend on the position of the coupling means 101.
• the presented sets are identical, but they may differ from each other as desired.
• the connection 1 to 4 can be closed, and if only one valve V1 to V4 in the set is opened, a connection is made, wherein the volume flow passed through the valve system will depend on the valves being open at the time.
• the controllability of the volume flow Q in the coupling is indicated with a lineation.
• the valve system is found to be capable of providing, in addition to the couplings of a normal 4/3 valve, also couplings in which one connection is closed at a time. This is possible, because the sets 103 and 104 can be controlled separately, if necessary. Furthermore, the separation also means that pressure losses can also be controlled separately in simultaneous connections.
• the valve system 100 also comprises electrical control means 105 for controlling the valve means 103, 104 by control signals 106.
• the control means 105 consist of a programmable microcontroller which is coupled by control conductors to the valves of the sets 103, 104 and the valve V of the means 101.
• the controller 105 implements the control by means of a control algorithm stored in its memory means, under a system program controlling the device.
• the control algorithm is formed to provide the desired control.
• the controller 105 receives, when necessary, one or more set signals 107 and 108 from the outside, on the basis of which the valves of the sets are opened and closed, or the valve of the means 101 is shifted, when necessary.
• the controller 105 is also used to automatically adjust the rate at which the volume flow of the connections in the valve system 100 is changed, that is, to adjust the acceleration and deceleration ramps of the actuator.
• the asymmetry of the transmission of the volume flows of the sets is also adjusted in each situation; for example, the transmission of the set 104 on the return side is guided to a higher level than the transmission of the set 103 on the pressure side, to reduce pressure losses. Alternatively, to avoid cavitation, the transmission of the set 103 is guided to be higher than that of the set 104.
• control signal 107, 108 to be input to the controller 105 such as a set signal (for example, a voltage signal from -10 V to +10 V or a current signal), is applied in a control algorithm to compute the level shown in Fig. 2 and the direction of motion of the actuator, followed by the control of the valves of the sets 103 and 104 and the means 101.
• the control of the valves V, V1-V4 may be implemented, for example, by relays of the control means 105, through which the operating voltage is input to the valves.
• Parameters related to the computing of the control algorithm of said controller 105 are preferably input to the controller 105, for example, by means of a programming device or a control system 109, such as a computer system, which forms the control system of the upper level. At least some of the parameters can be set by means of control screws or control buttons connected directly to the controller 105. It may even have a display and a keypad for manual input of the parameter values.
• Said control system 109 can be used simultaneously to control also other valve sys- terns or devices to which the valve system 100 is connected.
• the set value and the parameters can be input to the controller 105 in digital format, for example through a bus 107 or 108, but in some embodiments, also in analog formats by a set signal 107 or 108.
• Each parameter may also be provided with a separate signal line.
• control is performed simply by one set value (for example, a voltage signal from -10 V to +10 V or a current signal), and the con- troller takes care of the more precise control of the system 100 in an optimal way by means of the control algorithm.
• the set value may also be entered under manual control, for example by means of a control stick controlled by the operator to achieve the desired rate.
• the desired rate is thus, for example, slow or fast, depending on the position of the control stick.
• the valve system 100 consists of separate valves V and V1-V4 which are preferably fixed to a joint base plate which is also provided with the necessary drillings and channel- lings to form said connections.
• the system becomes a uniform and compact unit.
• the base plate is also provided with some of the ports (P, T, A, B) of the valve system 100, for example for a tube fastening or a bed plate fastening.
• the necessary connections may also be formed by means of tubes and hoses by joining the valves.
• the valve system may also be provided with other ports to form special connection in addition to the presented connections 1 to 4.
• the valve V could be used to close the ports A and B and to set up a connection between the ports P and T via said sets 103 and 104.
• Figure 5 shows a typical circuit applying an on/off valve system for the control of a cylinder 200.
• the tank pressure used in the calculation is the value 0 bar, and the pressure losses of the valve 101 are assumed to be insignificant, and the volume flows Q selected for the valves (V1 , V2, V3 and V4) are 0.5, 1 , 2 and 4 l/min, respectively, when the pressure difference over the valve is 5 bar.
• the series may be, for example, 2, 4, 8 and 16 l/min.
• the proportion of the tank pressure and the pressure losses may also be considered a sepa- rate factor.
• KVP 1 Volume flow coefficient of the smallest valve in the valve set on the pressure side [m 3 /(s-Pa 0-5 )]
• K VT 1) Volume flow coefficient of the smallest valve in the valve set on the return side [m 3 /(s-Pa 0,5 )] n P 1) Number of valves on the pressure side n ⁇ 1) Number of valves on the return side av P 2) Opening of the valve set on the pressure side (integer from 0 to 2 (n p 1) ) av ⁇ 2) Opening of the valve set on the return side (integer from 0 to 2 (n ⁇ 1) ) r Area ratio of the cylinder Ap A B z Auxiliary variable av P Kvp/(av ⁇ Kv ⁇ )
• the required computation is implemented in the control algorithm of the control means 105, in which the invariable parameters describing the system (marked above with the reference 1) ) are input.
• the computation is implemented with different combinations of the variable parameters (marked above with the reference 2) ), which results in the outputs (marked above with the reference 3) ).
• the control means 105 After optimization and the selection of the combination, the control means 105 generate control signals 106 to guide the valve means 102, i.e. the valves, to the desired position.
• the desired set value is changed, the operations are performed again.
• the set value can be continuously changed and monitored by the control algorithm. In the following, the procedure of the control algorithm will also be presented to achieve the desired set value.
• the computation of the combinations can also be performed separately, within or outside the control system 109.
• the computation is made, for example, with a computer device, and the control means 105 are used to store, for example in a table, the computed rate values and the values of said parameters which were used for the computation (the pressures, the opening combination used, the forces, etc.).
• the values of the table can be placed in an optimation algorithm to find out the order of supremacy of the opening combinations.
• the desired combination is selected for use, and on the basis of the table, the valves are guided to the corresponding position. The arrangement reduces and accelerates the computation of the control means 105.
• the control means 105 may also comprise a unit which is easy and ready to use, including the calculation of the opening combinations, wherein the data about the actuator and valve set to be used is first input therein.
• the control means 105 may already comprise several alternative models on the pressure medium circuits 100 to be used, or they can be defined for example by means of parameters or by modelling.
• the control means 105 take care of the computation and storage of the necessary computation algorithms.
• the negative direction can also be processed in a similar way by taking it into account in the above-mentioned formulas.
• the feeding pressure p s and the force F effective on the cylinder 200 should be known or measured.
• the above formulas can be used to calculate the pressures of the balanced state and the rate for all the possible opening combinations of the on/off valves on the P and T sides. Of these values, the best possible one can be selected by using a desired criterion.
• a desired penalty function J is used here, which is for example a function on the pressures and rate of the bal- anced state, and possibly also on the change in the pressure, wherein:
• Figure 6 shows the speed v of the cylinder 200 of Fig. 5 with different combinations of openings of the valve set 103 on the P side and the valve set 104 on the T side, wherein a large number of separate, discontinuous or discrete values are obtained, because of the on/off valves.
• the stepped chart of Fig. 7 is obtained, in which each step represents a given combination.
• a particular advantage of the invention is that substantially the same rate is represented by several different combinations whose pressure levels may be very different and of which it is then possible to select the most suitable one, as long as for example the rate error is within allowed limits. Pressure variations on the piston side in the example system are illustrated in Fig. 8. As a selection criterion, for example a minimum change in the pressure is used, compared with the prevailing pressure level. Also other criteria can be used in the selection of the combinations to be used next.
• one of the two valve sets is normally fully open.
• V max thus corresponds to the outermost combination of the T or P valve set, which is parallel to either the T-axis or the P-axis.
• the present invention is not limited to these steps, but all the steps will be taken into account. It is also possible to move on the same rate level by means of different combinations, because equal columns denote various combinations (and also different pressure levels) but substantially the same rate.
• v re f is the desired cylinder rate.
• the variable X is the desired exponent, for example 2, and the coefficient K 0 is a weight coefficient.
• To compute the rate one must also know the force F effective on the cylinder.
• these different values p A , P B and the rate v of the balanced state with all the possible opening combinations.
• these different values p A , p B , v
• p A , p B , v are used to compute the value of the penalty function J.
• That combination of the valve sets for example, 103 and 104 which best meets the criteria of the penalty function J.
• that opening combination will be selected, for which the function J has the lowest value, wherein the rate error is the smallest.
• a maximum value can be set for the rate error, wherein it is possible to select any suitable opening combination, for which the function J is smaller than it.
• the selection of the suitable opening combination may also be based on other criteria.
• the penalty function J is, for example:
• the value set for the penalty function J is a very large number (or this alternative can be excluded from the further processing), if there is a risk of cavitation with this opening combination, wherein this combination is clearly not included in those to be selected.
• target pressures p A ⁇ ref and p B , ref are set for the pressures p A and p B , not to deviate from them more than desired.
• the magnitude of the deviation will depend on the coefficients of the penalty function.
• the target pressures are used to influence energy savings, wherein the pressure should be kept as low as possible, but by avoiding cavitation.
• the aim at the target pressure can be combined with the need to keep the rate approximately within a desired range and represented with the formula (without conditions for preventing cavitation, which may be added in the formula):
• the on/off valves operate in a stepped manner, and with different combinations it is possible to select a set of discrete steps, wherein great variations in the pressure level, as a counter-balance for good rate control, is not always acceptable.
• changes in the pressure level i.e. pressure jumps
• p A>ed and p ⁇ , ec are the pressures selected in the previous computation round, that is, the discrete step used by the control, from which the aim is to move on to the next one to implement cylinder control and a change in the rate.
• the penalty function may be supplemented with the optimization of the target pressures, wherein the variation takes place in the range of a given pressure value.
• the maximum of the feeding pressure p s should be kept as low as possible.
• the aim is achieved by requiring that the low- est pressure in the system must be relatively low and constant. Normally, the lowest pressure is on the return side, when the force is resistant.
• the aim is to keep p B as desired (p B , r e f ) within the set limits (p B , r e f - PB), and p A is allowed to vary freely.
• the simplest case is open control, in which the desired rate v re is obtained directly from the control means 105, 109 or from the operator, for example by means of a control stick.
• the rate error is the smaller, the better the loading force F and the feeding pressure p s are known.
• precise rate control will only be achieved, if the loading force is accurately known or measured.
• very precise rate control will not be necessary.
• the force effective on the cylinder is not always known.
• a more precise rate control will be achieved by measuring the realized rate and by selecting valve combinations by minimizing the rate error. If the target rate v ref is higher than the measured rate v, one should select an opening combination which provides a higher rate.
• the problem is the loading force F, whose value may be poorly known.
• the feature which is essential for the closed control that the order of the opening combinations is independent of the loading force, wherein in the formulas (4) to (6) and (10) to (12) it is possible to use a rough estimate for the loading force, or to set the value of the loading force to zero in the calculation.
• the sets of the different opening combinations can be predetermined (penalty function J).
• the sets By means of the sets, one achieves for example a good rate control (formula (15)) and optimal pressures (formula (16)), when the loading force F is positive, negative or zero, each as a set of its own.
• the suitable opening combination can be selected directly without advancing in an order, naturally depending on the desired rate profile as a function of time. At the same time, it is possible to optimize for example the pressures.
• the rate v re required for the selection of the opening combinations is generated by a rate controller, whose input is the rate error (v ref - v) and whose control algorithm is aimed at minimizing the rate error.
• the advantage in this way of controlling is that the rate controller operates with low difference variables.
• the desired rate may vary as a function of time so that for example the desired rate ramp v ref (t) could be followed.
• the control means 105 may be arranged to continuously determine this desired rate.
• the desired rate as a function of time v ref (t) can also be stored, for example, as a function or a table, to be read by the control means.
• This desired rate value, whether constant or variable, may also be a control signal 107 and/or 108, which is generated with the same or a separate control system 109.
• the desired rate can be generated on the basis of the desired position path x r ).
• the desired path x re f(t) can also be stored, for example, as a function or a table, to be read by the control means 105.
• the system also comprises means for determining the position of the actuator, the measured position x being, in turn, compared with the desired position x ref .
• the position reference x ref (t) is used to determine the required rate, which is based, for example, on the fact that the actuator must have a given rate to reach the next position within a given time.
• the path can often be presented as a curve which is, for example, a position ramp, a rate ramp, or a polynomial of the third or fifth order, and which can, in most cases, also be derived 1 to 3 times. The derivation will result in the rate curve to be used, indicating the target rate v ref for each moment of time.
• the rate profile can also be stored to be ready in for example a table, or it is determined by computation in the control means 105, in which the position path is input.
• the loading force can be determined, for example, by the formula (3).
• the result is to achieve good rate control without feedback from the rate.
• the optimization of the pressures is also more successful, because measured information is also obtained about the pressures. It is also possible to use lower counterpressures without the risk of cavitation, because the pressures have been measured. Alternatively, it is possible to use a loadcell in a way known as such for measuring the force.
• the feeding pressure p s can be reduced.
• a pump with a fixed volume and setting the feeding pressure p s with a shut-off valve it is possible to use a lower feeding pressure than with symmetrical valves of prior art, in which the pressures on both the pressure and return sides are affected by pressure losses over the shared slide.
• the separate valve sets can be controlled individually, wherein particularly the counterpressure can be minimized, still avoiding cavitation.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Fluid-Pressure Circuits (AREA)
• Servomotors (AREA)
• Flow Control (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

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Cited By (28)

Citations (3)

• 2001
  • 2001-04-23 FI FI20010827A patent/FI118608B/fi not_active IP Right Cessation
• 2002
  • 2002-04-22 DK DK02716861T patent/DK1386083T3/da active
  • 2002-04-22 ES ES02716861T patent/ES2271235T3/es not_active Expired - Lifetime
  • 2002-04-22 EP EP02716861A patent/EP1386083B1/de not_active Expired - Lifetime
  • 2002-04-22 DE DE60214362T patent/DE60214362T2/de not_active Expired - Lifetime
  • 2002-04-22 WO PCT/FI2002/000329 patent/WO2002086327A1/en active IP Right Grant
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  • 2002-04-22 CA CA2483644A patent/CA2483644C/en not_active Expired - Lifetime

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