CA2314958A1 - Pressure fluid actuator with damping and speed control device - Google Patents
Pressure fluid actuator with damping and speed control device Download PDFInfo
- Publication number
- CA2314958A1 CA2314958A1 CA002314958A CA2314958A CA2314958A1 CA 2314958 A1 CA2314958 A1 CA 2314958A1 CA 002314958 A CA002314958 A CA 002314958A CA 2314958 A CA2314958 A CA 2314958A CA 2314958 A1 CA2314958 A1 CA 2314958A1
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- Prior art keywords
- piston
- damping
- chamber
- actuator according
- bush
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- 238000013016 damping Methods 0.000 title claims abstract description 70
- 239000012530 fluid Substances 0.000 title claims abstract description 54
- 238000007789 sealing Methods 0.000 claims description 5
- 230000002093 peripheral effect Effects 0.000 claims description 4
- 238000007599 discharging Methods 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000000284 resting effect Effects 0.000 description 1
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
- F15B15/00—Fluid-actuated devices for displacing a member from one position to another; Gearing associated therewith
- F15B15/20—Other details, e.g. assembly with regulating devices
- F15B15/22—Other details, e.g. assembly with regulating devices for accelerating or decelerating the stroke
- F15B15/222—Other details, e.g. assembly with regulating devices for accelerating or decelerating the stroke having a piston with a piston extension or piston recess which throttles the main fluid outlet as the piston approaches its end position
-
- 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
- F15B15/00—Fluid-actuated devices for displacing a member from one position to another; Gearing associated therewith
- F15B15/20—Other details, e.g. assembly with regulating devices
- F15B15/22—Other details, e.g. assembly with regulating devices for accelerating or decelerating the stroke
- F15B15/223—Other details, e.g. assembly with regulating devices for accelerating or decelerating the stroke having a piston with a piston extension or piston recess which completely seals the main fluid outlet as the piston approaches its end position
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Fluid Mechanics (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Actuator (AREA)
- Vibration Prevention Devices (AREA)
Abstract
The pressure fluid actuator comprises a tubular body and closing heads to define a piston chamber in which a piston may reciprocate. The piston, at both ends, is provided with a damping bush which may protrude into a flow damping chamber in each closing head connected to a fluid inlet/outlet port; a conduit comprising a flow throttling valve is branched between each side of the piston chamber and the damping chamber in each closing head. The flow damping bush comprises a longitudinally extending fluid supply duct provided with a pressure actuated unidirectional flow control valve which prevent the pressure fluid to flow from the piston chamber into the damping chamber during damping at the end of a piston stroke, while allowing flow circulation into the piston chamber when the bush is within the damping chamber at the beginning of a piston stroke.
Description
PRESSURE FLUID ACTUATOR WITH DAMPING AND SPEED CONTROL DEVICE
BACKGROUND OF THE INVENTION
The present invention relates to pressure fluid actuators comprising a reciprocable piston member into a piston chamber, and more particularly relates to a hydraulic, pneumatic or hydro-pneumatic cylinder provided with a flow damping device acting at the end of each working stroke of the piston, and to achieve a rapid starting movement of the same piston upon each reversal of its stroke.
PRIOR ART
As is known, in many applications for hydraulic and pneumatic cylinders or similar actuators, it is required to use suitable damping devices to absorb most of the kinetic energy of the load, while gradually decreasing the piston speed at the end of each working stroke; in this way the piston is prevented from striking abruptly against the head pieces which close the piston chamber of the actuator.
Generally, the damping systems used in hydraulic or conventional pneumatic cylinders require a small-diameter spigot at each end of the piston, to penetrate into a damping chamber in a corresponding closing head, or alternatively require a tubular member having a restricted path for discharging the fluid, which extends from each head to tightly penetrate into a corresponding dead hole in the piston; linear actuators provided with damping systems of this kind are described, for example, in EP-A-0,005,407, EP-A-0,082,829 and EP-A-0,648,941.
Systems of the above mentioned type generally do not allow an immediate and rapid starting of the piston, since the pressure fluid initially supplied to the inlet port of the cylinder, is impinging on an extremely small thrust surface along a substantial long portion at the beginning of the piston stroke, until the spigot has been substantially withdrawn from the damping chamber. Moreover, on the side of the piston rod, the situation is extremely unfavorable since the thrust surface is correspondingly reduced by the cross-sectional area of the same piston rod.
In the conventional hydraulic cylinders these results in a damping and starting modes for the piston, which are different from each other and which negatively affect on the controlled load.
In other words, with the use of the damping systems presently known, initially the piston begins to move slowly at the starting owing to the inadequate thrust exerted by the pressure fluid on the spigot inside the damping chamber, and then suddenly speed up when the spigot has been substantially withdrawn and the load connected to the cylinder is already moving.
In many applications, however, a fast starting movement of the piston is required at each reversal of the piston stroke so as to avoid sudden speed variations to the load, once it has started to move.
In order to partly overcome this drawback, it has been proposed to supply the pressurised fluid directly into the piston chamber, via an additional duct, on one side of each closing head of the piston chamber.
Such a solution, although on the one hand it helps to solve the starting problem, on the other hand is disadvantageous both from a constructional point of view and with regard to operation of the same actuator.
In fact, the arrangement of an additional supply duct, together with an associated control valve, on one side of each closing head, results in higher manufacturing costs, a greater risk of leakage for the fluid and, frequently, the impossibility of arranging the cylinder in a desired working position since it could hinder the connections to the fluid supply and discharge ducts or the additional supply ducts, or preventing access to the needle valves along the fluid throttling paths which are part of the damping device.
Finally, conventional damping devices or those of the type described in the cited publications, which require the use of suitable seals, although they may be suitable in pneumatic cylinders, where the involved pressures are of the order of a few bar, proved to be entirely inadequate in hydraulic cylinders where the fluid reaches high pressure values of the order of a few hundred bar.
OBJECTS OF THE INVENTION
The main object of the present invention is to provide a linear pressure fluid actuator provided with a suitable damping system which subsequently allows a rapid movement of the piston at the starting of each working stroke.
A further object of the present invention is to provide a linear actuator of the above mentioned kind, provided with a damping system for achieving damping and fast starting movement, suitable for universal use, in both hydraulic and pneumatic cylinders, i.e. independently of the type of fluid used.
Yet another object of the present invention is to provide a linear actuator as defined above, in particular for double-acting hydraulic or pneumatic cylinders, provided with a damping system for damping and achieving a fast starting movement of the piston, of the same type on both side ends of the piston stroke.
Yet another object of the present invention is to provide a linear actuator as defined above which is constructionally simplified, more cost-effective and easy to assemble, such that it may be sold in disassembled condition and packaged in kit form.
BRIEF DESCRIPTION OF THE INVENTION
According to the invention, a pressure fluid actuator has been provided with flow damping device, the actuator comprising:
a tubular body and a head member at each end of the tubular body to define a piston chamber, each head member provided with a damping chamber opening towards the piston chamber and comprising a fluid inlet/outlet port;
a piston member reciprocable into the piston chamber, the piston member being provided with a damping bush at each side end to tightly penetrate the damping chamber of a head member at the end of the piston stroke;
and a fluid supply duct longitudinally extending in each damping bush, said fluid supply duct comprising a pressure-actuated unidirectional flow-control valve to S allow pressurised fluid to flow from the damping chamber to the piston chamber when the damping bush is within the damping chamber at the beginning of a piston stroke.
According to the invention it is therefore possible to control the deceleration and the speed of the piston at the end of each working stroke, as well as to control the starting of the piston member at the beginning of each working stroke.
BRIEF DESCRIPTION OF THE DRAWINGS
These and further features of a pressure fluid actuator, according to the present invention, will emerge more clearly from the following description with reference to the examples in the accompanying drawings in which:
Fig. 1 is a longitudinal sectional view of a double acting cylinder, with the piston at the right end of its stroke;
Fig. 2 is an enlarged detail of the right-hand end of the cylinder according to Figure 1, at the time the piston has started its return stroke;
Fig. 3 is an enlarged view of the left-hand end of Figure 1 with the piston approaching the end of the stroke;
Fig. 4 is a cross-sectional view along the line 4-4 of Fig. 1, relating to a first embodiment;
Fig. 5 is a cross-sectional view, similar to that of the preceding figure, relating to a second embodiment;
Fig. 6 is an enlarged view, similar to that of Figure 2, relating to a further embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
As shown in Figure 1, the actuator denoted in its entirety by reference 10, comprises a tubular body 11 and two closing heads 12 and 13 to define a chamber 14 inside which a piston 15 reciprocates.
Each closing head 12 and 13 is provided with an inlet/outlet port 16, 17, for supplying and discharging a pressurised fluid, for example oil or air, which communicates with a damping chamber 18 and 19 coaxially arranged inside each head 12, 13 and opening towards the piston chamber 14, as shown.
The left-hand head 13 in Figure 1 also comprises a guide sleeve 20 for the rod 21 of the piston 15, suitable seats being provided for annular seals 22, for example of the lip type, as shown.
Each end head 12 and 13, on the side opposite to the inlet/outlet port 16 and 17, is provided with a branched duct 24A, 24B comprising a needle valve 23 - also called a flow throttling valve - which defines a restricted path for discharging the fluid, which on the side 24A opens into the piston chamber 14, while on the opposite side 24B opens into the damping chamber 18 or the damping chamber 19, respectively.
The two needle valves 23, the narrow passages 24A, 24B
and the damping chambers 18 and 19 in both end heads 12 and 13 form part of a damping system for damping the speed of the piston 15, at each end of a working stroke, and for controlling the starting speed of the piston at the beginning of each working stroke.
In this connection, as shown in the cross-section of Figure 1 and in the enlarged details according to Figures 2 and 3, each side of the piston 15 is provided with a damping bush 25 having an external cone-shaped surface so as to tightly close each of the two damping chambers 18 and 19, causing a gradual sealing action during the insertion into the damping chamber 18, 19 at the end of each stroke of the piston 15.
Each damping bush 25, as shown for the left-hand bush in Figure l, has a thick end wall 26 bearing against the end face of the piston 15 and having a peripheral wall 27 delimited by a cylindrical internal surface having a diameter greater than the diameter of the rod 21 so as to form an annular space 28 open towards the piston chamber _7_ 14.
The piston rod 21 also has an extension 22A of smaller-diameter which passes through axially aligned holes in the end walls 26 of two bushes 25 and in the central piston 15, and provided with a threaded end for screwing engagement with a nut 29 which keeps the assembly consisting of the piston 15, the rod 22 and the two damping bushes 25 in the assembled condition shown in Figure 1.
As shown, each damping bush 25 has one or more longitudinal holes or flow passages 30 which extend from the rear end of the bush, i.e. the end facing the central piston 15, towards the internal cavity 28.
Both ends of each passage 30 open to the chamber 14 via one or more recesses 31, at the rear side and directly at the front side.
Each longitudinal passage 30 in the bushes 25 comprises a pressure actuated unidirectional valve, for example consisting of a ball valve 32 having a diameter smaller than that of the hole defining the passage 30 and designed to seal against a conical seat 33 on the side facing the annular space 28 in each bush 25. The ball valve 32 has the function of preventing the fluid from flowing from the piston chamber 14 into the damping chamber 18 and 19 when the said damping bush 25 extends inside the respective damping chamber 18 and 19, so as to gradually reduce the speed of the piston 15 in an usual manner at the end of its stroke, as shown for example in the enlarged detail according to Figure 3, and to allow the fluid to flow in the opposite direction, as shown in the enlarged detail of Figure 2 and as explained further below.
The accompanying drawings illustrate the use of a unidirectional valve of the ball type, although within the scope of the present invention it is possible to use any other type of non-return valve provided that it is suitable for the purpose. Similarly, with regard to the restricted passage 24A and 24B use of a needle valve 23 has been shown since it allows the speed of the piston to be adjusted by _g_ setting the same valve; however, other solutions are possible as regards the type and arrangement of the ball valve 32 and flow throttling valve 23 or the restricted passage, depending on the requirements.
As mentioned above, each passage 30 in the damping bush 25 on one side leads into the front-open cavity 28 inside the bush and on the other side communicates with the piston chamber 14, via a recess 31 on the end face of the piston 15; however, it is also possible to form this recess on the rear end face of the bush.
The recess 31 may be formed in any manner; for example it may consist of a simple radial slot or having a circular shape as shown in the cross-sectional view according to Figure 4, or a helical shape or other suitable shape as shown in the cross-sectional view of Figure 5.
The various solutions offer varying degrees of effectiveness since the circular shape of~the recess 31 according to Figure 4, compared to a simple radial slot, allows an increase in the thrust surface at the start of each piston stroke, in particular on the more critical side where the rod 22 is located.
Similarly, the solution according to Figure 5 tends to increase further the thrust surface, compared to the solution according to Figure 4, since the helical recess 31' extends as far as the peripheral edge of the piston 15 so that most of the front surface of the latter is immediately acted on by the pressurised fluid, increasing the thrust so as to impart a fast starting movement of the piston.
Unlike the previously known solutions, according to the present invention it is possible to vary the initial thrust acting on the piston 14 by providing each sealing bush 25 with several longitudinal passages 30, each with its own non-return valve, so as to increase the quantity of fluid supplied at the start of each working stroke, thereby increasing the initial thrust and the starting speed of the piston 15 depending on the load to be controlled or the work requirements envisaged.
The operating principle of the device for damping and controlling the starting speed of the piston may be understood from the details shown in Figures 2 and 3.
With reference to Figure 2, it is assumed that the piston 15 has reached the end of its return stroke towards the right, with the piston 15 resting against the end head 12; the sealing bush 25 will be fully inside the damping chamber 18.
Starting from these conditions, when the movement of the piston 15 must be reversed, the port 17 in the head 13 is connected to the discharge, while fluid under pressure is supplied through the inlet port 16 of the head 12.
In these conditions the fluid under pressure fills the damping chamber 18, exerting a thrusting action on the bush and at the same time immediately flows through the passage 30, opening the ball valve 32, as shown in Figure 2. Therefore, the fluid under pressure, via the passage 30 which is now open, enters into the slot 31 and, via the 20 latter, immediately flows into the piston chamber 14, exerting on the piston 15 a strong thrusting action which will move it with the maximum speed permitted by the load connected to rod 21 of the cylinder.
Differently from the prior art and the solutions 25 proposed in the previously cited documents, there will be no sudden variation now in the speed of the piston 15, once it has started its movement, nor any gradually increase since the piston will start to move immediately with the maximum allowed speed.
When the piston has reached the end of its forwards stroke, towards the left, as shown in Figure 3, and as soon as the damping bush 25 on the left-and side of the piston 15 starts to enter and close the damping chamber 19, the pressure difference which is created between the fluid remaining inside the chamber 14 and the fluid inside the damping chamber 19 will immediately close the non-return valve, preventing the fluid inside the chamber 14 directly reaching the outlet port 17 in the end head 13.
Therefore the remaining fluid in the piston chamber 14 will be forced to flow through the restricted passage 24A, 24B, slowing down in a controlled manner the speed of the piston 15 so as to prevent the said piston striking the end head 13.
When the movement of the piston 15 is to be reversed again, the fluid supplied to the port 17 of the head 13 will impinge on the thrusting surface formed by the damping bush 25, less the cross-section of the rod 21, which would be insufficient to produce the required thrusting force.
However, owing to the pressure of the fluid, the ball valve 32 of the left-hand bush in Figure 3, will open, allowing the fluid to impinge on the surface of the piston and develop fully the required thrust and speed, also in view of the fact that the number of branched fluid supply holes or passages in each sealing bush 25 may vary from that shown, depending also on the variation in the internal diameters of the chambers 14, 18 and 19 and the diameters of the respective unions or apertures 16 and 17 for connection to a pressurised fluid source.
Figures 4 and 5 show two different solutions as regards the form and arrangement of the slots or recesses 31, 31' in the piston 15 or in the said bush 25.
In particular Figure 4 shows a single circular slot 31 which is coaxial with the piston 15 and into which two passages 30 in the damping bush lead, while Figure 5 shows the use of two helical slots 31' which extend from a respective passage 30 in the bush 25 to the peripheral edge of the piston 15. In both cases the same reference numbers, if necessary with the addition of an apiece, have been used in order to indicate parts which are similar or equivalent to those shown in the preceding figures.
Figure 6 in the drawings shows a further solution which differs from that of Figure 1 as regards the formation of the fluid supply path in the two damping bushes 25 and the piston 15, together with the associated non-return valve. The cylinder according to Figure 6, which is only partially shown, is substantially similar to that shown in Figure 1; therefore, in this case also, the same reference numbers have been used to indicate similar or equivalent parts.
The solution according to Figure 6 differs from the solution according to Figure 1 in that now the non-return valve consists of an annular element 35 seated in a corresponding annular recess 36 at the rear end of each bush 25, leading both into the cavity 28 inside the said bush by means of a plurality of holes 37 and to the piston 15; as regards the rest, the cylinder according to Figure 6 is similar to and operates in a manner entirely identical to that of the cylinder according to Figure 1.
From the above description and illustrations in the accompanying drawings it is therefore obvious that the invention provides a linear actuator actuated by a fluid under pressure, in particular a hydraulic or pneumatic cylinder or an air-hydraulic cylinder provided with a system for damping and controlling the speed of deceleration and initial movement of the piston, which uses a non-return valve actuated so as to open and close by the same pressurised fluid which flows into the piston chamber and by means of which it is possible to achieve the desired objects.
It is understood that, however, that the above description and illustrations in the accompanying drawings have been provided purely by way of example of the general features of the actuator according to the invention and that other modifications or variations are possible without thereby departing from that claimed.
BACKGROUND OF THE INVENTION
The present invention relates to pressure fluid actuators comprising a reciprocable piston member into a piston chamber, and more particularly relates to a hydraulic, pneumatic or hydro-pneumatic cylinder provided with a flow damping device acting at the end of each working stroke of the piston, and to achieve a rapid starting movement of the same piston upon each reversal of its stroke.
PRIOR ART
As is known, in many applications for hydraulic and pneumatic cylinders or similar actuators, it is required to use suitable damping devices to absorb most of the kinetic energy of the load, while gradually decreasing the piston speed at the end of each working stroke; in this way the piston is prevented from striking abruptly against the head pieces which close the piston chamber of the actuator.
Generally, the damping systems used in hydraulic or conventional pneumatic cylinders require a small-diameter spigot at each end of the piston, to penetrate into a damping chamber in a corresponding closing head, or alternatively require a tubular member having a restricted path for discharging the fluid, which extends from each head to tightly penetrate into a corresponding dead hole in the piston; linear actuators provided with damping systems of this kind are described, for example, in EP-A-0,005,407, EP-A-0,082,829 and EP-A-0,648,941.
Systems of the above mentioned type generally do not allow an immediate and rapid starting of the piston, since the pressure fluid initially supplied to the inlet port of the cylinder, is impinging on an extremely small thrust surface along a substantial long portion at the beginning of the piston stroke, until the spigot has been substantially withdrawn from the damping chamber. Moreover, on the side of the piston rod, the situation is extremely unfavorable since the thrust surface is correspondingly reduced by the cross-sectional area of the same piston rod.
In the conventional hydraulic cylinders these results in a damping and starting modes for the piston, which are different from each other and which negatively affect on the controlled load.
In other words, with the use of the damping systems presently known, initially the piston begins to move slowly at the starting owing to the inadequate thrust exerted by the pressure fluid on the spigot inside the damping chamber, and then suddenly speed up when the spigot has been substantially withdrawn and the load connected to the cylinder is already moving.
In many applications, however, a fast starting movement of the piston is required at each reversal of the piston stroke so as to avoid sudden speed variations to the load, once it has started to move.
In order to partly overcome this drawback, it has been proposed to supply the pressurised fluid directly into the piston chamber, via an additional duct, on one side of each closing head of the piston chamber.
Such a solution, although on the one hand it helps to solve the starting problem, on the other hand is disadvantageous both from a constructional point of view and with regard to operation of the same actuator.
In fact, the arrangement of an additional supply duct, together with an associated control valve, on one side of each closing head, results in higher manufacturing costs, a greater risk of leakage for the fluid and, frequently, the impossibility of arranging the cylinder in a desired working position since it could hinder the connections to the fluid supply and discharge ducts or the additional supply ducts, or preventing access to the needle valves along the fluid throttling paths which are part of the damping device.
Finally, conventional damping devices or those of the type described in the cited publications, which require the use of suitable seals, although they may be suitable in pneumatic cylinders, where the involved pressures are of the order of a few bar, proved to be entirely inadequate in hydraulic cylinders where the fluid reaches high pressure values of the order of a few hundred bar.
OBJECTS OF THE INVENTION
The main object of the present invention is to provide a linear pressure fluid actuator provided with a suitable damping system which subsequently allows a rapid movement of the piston at the starting of each working stroke.
A further object of the present invention is to provide a linear actuator of the above mentioned kind, provided with a damping system for achieving damping and fast starting movement, suitable for universal use, in both hydraulic and pneumatic cylinders, i.e. independently of the type of fluid used.
Yet another object of the present invention is to provide a linear actuator as defined above, in particular for double-acting hydraulic or pneumatic cylinders, provided with a damping system for damping and achieving a fast starting movement of the piston, of the same type on both side ends of the piston stroke.
Yet another object of the present invention is to provide a linear actuator as defined above which is constructionally simplified, more cost-effective and easy to assemble, such that it may be sold in disassembled condition and packaged in kit form.
BRIEF DESCRIPTION OF THE INVENTION
According to the invention, a pressure fluid actuator has been provided with flow damping device, the actuator comprising:
a tubular body and a head member at each end of the tubular body to define a piston chamber, each head member provided with a damping chamber opening towards the piston chamber and comprising a fluid inlet/outlet port;
a piston member reciprocable into the piston chamber, the piston member being provided with a damping bush at each side end to tightly penetrate the damping chamber of a head member at the end of the piston stroke;
and a fluid supply duct longitudinally extending in each damping bush, said fluid supply duct comprising a pressure-actuated unidirectional flow-control valve to S allow pressurised fluid to flow from the damping chamber to the piston chamber when the damping bush is within the damping chamber at the beginning of a piston stroke.
According to the invention it is therefore possible to control the deceleration and the speed of the piston at the end of each working stroke, as well as to control the starting of the piston member at the beginning of each working stroke.
BRIEF DESCRIPTION OF THE DRAWINGS
These and further features of a pressure fluid actuator, according to the present invention, will emerge more clearly from the following description with reference to the examples in the accompanying drawings in which:
Fig. 1 is a longitudinal sectional view of a double acting cylinder, with the piston at the right end of its stroke;
Fig. 2 is an enlarged detail of the right-hand end of the cylinder according to Figure 1, at the time the piston has started its return stroke;
Fig. 3 is an enlarged view of the left-hand end of Figure 1 with the piston approaching the end of the stroke;
Fig. 4 is a cross-sectional view along the line 4-4 of Fig. 1, relating to a first embodiment;
Fig. 5 is a cross-sectional view, similar to that of the preceding figure, relating to a second embodiment;
Fig. 6 is an enlarged view, similar to that of Figure 2, relating to a further embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
As shown in Figure 1, the actuator denoted in its entirety by reference 10, comprises a tubular body 11 and two closing heads 12 and 13 to define a chamber 14 inside which a piston 15 reciprocates.
Each closing head 12 and 13 is provided with an inlet/outlet port 16, 17, for supplying and discharging a pressurised fluid, for example oil or air, which communicates with a damping chamber 18 and 19 coaxially arranged inside each head 12, 13 and opening towards the piston chamber 14, as shown.
The left-hand head 13 in Figure 1 also comprises a guide sleeve 20 for the rod 21 of the piston 15, suitable seats being provided for annular seals 22, for example of the lip type, as shown.
Each end head 12 and 13, on the side opposite to the inlet/outlet port 16 and 17, is provided with a branched duct 24A, 24B comprising a needle valve 23 - also called a flow throttling valve - which defines a restricted path for discharging the fluid, which on the side 24A opens into the piston chamber 14, while on the opposite side 24B opens into the damping chamber 18 or the damping chamber 19, respectively.
The two needle valves 23, the narrow passages 24A, 24B
and the damping chambers 18 and 19 in both end heads 12 and 13 form part of a damping system for damping the speed of the piston 15, at each end of a working stroke, and for controlling the starting speed of the piston at the beginning of each working stroke.
In this connection, as shown in the cross-section of Figure 1 and in the enlarged details according to Figures 2 and 3, each side of the piston 15 is provided with a damping bush 25 having an external cone-shaped surface so as to tightly close each of the two damping chambers 18 and 19, causing a gradual sealing action during the insertion into the damping chamber 18, 19 at the end of each stroke of the piston 15.
Each damping bush 25, as shown for the left-hand bush in Figure l, has a thick end wall 26 bearing against the end face of the piston 15 and having a peripheral wall 27 delimited by a cylindrical internal surface having a diameter greater than the diameter of the rod 21 so as to form an annular space 28 open towards the piston chamber _7_ 14.
The piston rod 21 also has an extension 22A of smaller-diameter which passes through axially aligned holes in the end walls 26 of two bushes 25 and in the central piston 15, and provided with a threaded end for screwing engagement with a nut 29 which keeps the assembly consisting of the piston 15, the rod 22 and the two damping bushes 25 in the assembled condition shown in Figure 1.
As shown, each damping bush 25 has one or more longitudinal holes or flow passages 30 which extend from the rear end of the bush, i.e. the end facing the central piston 15, towards the internal cavity 28.
Both ends of each passage 30 open to the chamber 14 via one or more recesses 31, at the rear side and directly at the front side.
Each longitudinal passage 30 in the bushes 25 comprises a pressure actuated unidirectional valve, for example consisting of a ball valve 32 having a diameter smaller than that of the hole defining the passage 30 and designed to seal against a conical seat 33 on the side facing the annular space 28 in each bush 25. The ball valve 32 has the function of preventing the fluid from flowing from the piston chamber 14 into the damping chamber 18 and 19 when the said damping bush 25 extends inside the respective damping chamber 18 and 19, so as to gradually reduce the speed of the piston 15 in an usual manner at the end of its stroke, as shown for example in the enlarged detail according to Figure 3, and to allow the fluid to flow in the opposite direction, as shown in the enlarged detail of Figure 2 and as explained further below.
The accompanying drawings illustrate the use of a unidirectional valve of the ball type, although within the scope of the present invention it is possible to use any other type of non-return valve provided that it is suitable for the purpose. Similarly, with regard to the restricted passage 24A and 24B use of a needle valve 23 has been shown since it allows the speed of the piston to be adjusted by _g_ setting the same valve; however, other solutions are possible as regards the type and arrangement of the ball valve 32 and flow throttling valve 23 or the restricted passage, depending on the requirements.
As mentioned above, each passage 30 in the damping bush 25 on one side leads into the front-open cavity 28 inside the bush and on the other side communicates with the piston chamber 14, via a recess 31 on the end face of the piston 15; however, it is also possible to form this recess on the rear end face of the bush.
The recess 31 may be formed in any manner; for example it may consist of a simple radial slot or having a circular shape as shown in the cross-sectional view according to Figure 4, or a helical shape or other suitable shape as shown in the cross-sectional view of Figure 5.
The various solutions offer varying degrees of effectiveness since the circular shape of~the recess 31 according to Figure 4, compared to a simple radial slot, allows an increase in the thrust surface at the start of each piston stroke, in particular on the more critical side where the rod 22 is located.
Similarly, the solution according to Figure 5 tends to increase further the thrust surface, compared to the solution according to Figure 4, since the helical recess 31' extends as far as the peripheral edge of the piston 15 so that most of the front surface of the latter is immediately acted on by the pressurised fluid, increasing the thrust so as to impart a fast starting movement of the piston.
Unlike the previously known solutions, according to the present invention it is possible to vary the initial thrust acting on the piston 14 by providing each sealing bush 25 with several longitudinal passages 30, each with its own non-return valve, so as to increase the quantity of fluid supplied at the start of each working stroke, thereby increasing the initial thrust and the starting speed of the piston 15 depending on the load to be controlled or the work requirements envisaged.
The operating principle of the device for damping and controlling the starting speed of the piston may be understood from the details shown in Figures 2 and 3.
With reference to Figure 2, it is assumed that the piston 15 has reached the end of its return stroke towards the right, with the piston 15 resting against the end head 12; the sealing bush 25 will be fully inside the damping chamber 18.
Starting from these conditions, when the movement of the piston 15 must be reversed, the port 17 in the head 13 is connected to the discharge, while fluid under pressure is supplied through the inlet port 16 of the head 12.
In these conditions the fluid under pressure fills the damping chamber 18, exerting a thrusting action on the bush and at the same time immediately flows through the passage 30, opening the ball valve 32, as shown in Figure 2. Therefore, the fluid under pressure, via the passage 30 which is now open, enters into the slot 31 and, via the 20 latter, immediately flows into the piston chamber 14, exerting on the piston 15 a strong thrusting action which will move it with the maximum speed permitted by the load connected to rod 21 of the cylinder.
Differently from the prior art and the solutions 25 proposed in the previously cited documents, there will be no sudden variation now in the speed of the piston 15, once it has started its movement, nor any gradually increase since the piston will start to move immediately with the maximum allowed speed.
When the piston has reached the end of its forwards stroke, towards the left, as shown in Figure 3, and as soon as the damping bush 25 on the left-and side of the piston 15 starts to enter and close the damping chamber 19, the pressure difference which is created between the fluid remaining inside the chamber 14 and the fluid inside the damping chamber 19 will immediately close the non-return valve, preventing the fluid inside the chamber 14 directly reaching the outlet port 17 in the end head 13.
Therefore the remaining fluid in the piston chamber 14 will be forced to flow through the restricted passage 24A, 24B, slowing down in a controlled manner the speed of the piston 15 so as to prevent the said piston striking the end head 13.
When the movement of the piston 15 is to be reversed again, the fluid supplied to the port 17 of the head 13 will impinge on the thrusting surface formed by the damping bush 25, less the cross-section of the rod 21, which would be insufficient to produce the required thrusting force.
However, owing to the pressure of the fluid, the ball valve 32 of the left-hand bush in Figure 3, will open, allowing the fluid to impinge on the surface of the piston and develop fully the required thrust and speed, also in view of the fact that the number of branched fluid supply holes or passages in each sealing bush 25 may vary from that shown, depending also on the variation in the internal diameters of the chambers 14, 18 and 19 and the diameters of the respective unions or apertures 16 and 17 for connection to a pressurised fluid source.
Figures 4 and 5 show two different solutions as regards the form and arrangement of the slots or recesses 31, 31' in the piston 15 or in the said bush 25.
In particular Figure 4 shows a single circular slot 31 which is coaxial with the piston 15 and into which two passages 30 in the damping bush lead, while Figure 5 shows the use of two helical slots 31' which extend from a respective passage 30 in the bush 25 to the peripheral edge of the piston 15. In both cases the same reference numbers, if necessary with the addition of an apiece, have been used in order to indicate parts which are similar or equivalent to those shown in the preceding figures.
Figure 6 in the drawings shows a further solution which differs from that of Figure 1 as regards the formation of the fluid supply path in the two damping bushes 25 and the piston 15, together with the associated non-return valve. The cylinder according to Figure 6, which is only partially shown, is substantially similar to that shown in Figure 1; therefore, in this case also, the same reference numbers have been used to indicate similar or equivalent parts.
The solution according to Figure 6 differs from the solution according to Figure 1 in that now the non-return valve consists of an annular element 35 seated in a corresponding annular recess 36 at the rear end of each bush 25, leading both into the cavity 28 inside the said bush by means of a plurality of holes 37 and to the piston 15; as regards the rest, the cylinder according to Figure 6 is similar to and operates in a manner entirely identical to that of the cylinder according to Figure 1.
From the above description and illustrations in the accompanying drawings it is therefore obvious that the invention provides a linear actuator actuated by a fluid under pressure, in particular a hydraulic or pneumatic cylinder or an air-hydraulic cylinder provided with a system for damping and controlling the speed of deceleration and initial movement of the piston, which uses a non-return valve actuated so as to open and close by the same pressurised fluid which flows into the piston chamber and by means of which it is possible to achieve the desired objects.
It is understood that, however, that the above description and illustrations in the accompanying drawings have been provided purely by way of example of the general features of the actuator according to the invention and that other modifications or variations are possible without thereby departing from that claimed.
Claims (12)
1. A pressure fluid actuator provided with a flow damping device, the actuator comprising:
a tubular body and a head member at each end of the tubular body to define a piston chamber, each head member provided with a damping chamber opening towards the piston chamber and comprising a fluid inlet/outlet port;
a piston member reciprocable into the piston chamber, the piston member being provided with a damping bush at each side end to tightly penetrate the damping chamber of a head member at the end of the piston stroke;
and a fluid supply duct longitudinally extending in each damping bush, said fluid supply duct comprising a pressure-actuated unidirectional flow-control valve to allow pressurised fluid to flow from the damping chamber to the piston chamber when the damping bush is within the damping chamber at the beginning of a piston stroke.
a tubular body and a head member at each end of the tubular body to define a piston chamber, each head member provided with a damping chamber opening towards the piston chamber and comprising a fluid inlet/outlet port;
a piston member reciprocable into the piston chamber, the piston member being provided with a damping bush at each side end to tightly penetrate the damping chamber of a head member at the end of the piston stroke;
and a fluid supply duct longitudinally extending in each damping bush, said fluid supply duct comprising a pressure-actuated unidirectional flow-control valve to allow pressurised fluid to flow from the damping chamber to the piston chamber when the damping bush is within the damping chamber at the beginning of a piston stroke.
2. Actuator according to Claim 1, wherein the fluid supply duct leads into an open cavity of the damping bush at the front side, and towards the piston chamber at the rear side.
3. Actuator according to Claim 2, wherein said fluid supply duct is connected to the piston chamber at the rear side by at least one slot.
4. Actuator according to Claim 3, wherein said slot is in the form of an annular slot on an end piston face.
5. Actuator according to Claim 3, wherein the slot extend up to the peripheral edge of the piston.
6. Actuator according to Claim 3, wherein said slot extends radially.
7. Actuator according to Claim 5, wherein said slot extends in a helical manner.
8. Actuator according to Claim 1, wherein the pressure actuated valve in the fluid supply duct is of ball type.
9. Actuator according to Claim 1, in which fluid supply duct is provided in an end wall of the sealing bush.
10. Actuator according to Claim 3, wherein said slot is formed on a front surface of the piston.
11. Actuator according to Claim 3, wherein said slot is formed on the rear surface of an end wall of the damping bush.
12. Actuator according to Claim 1, wherein said fluid actuated valve comprises an annular element, freely movable inside an annular recess provided at the end wall of the damping bush.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IT1999MI001751A IT1313145B1 (en) | 1999-08-04 | 1999-08-04 | LINEAR ACTUATOR WITH DAMPING AND SPEED CONTROL DEVICE |
| ITMI99A001751 | 1999-08-04 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2314958A1 true CA2314958A1 (en) | 2001-02-04 |
Family
ID=11383498
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002314958A Abandoned CA2314958A1 (en) | 1999-08-04 | 2000-08-03 | Pressure fluid actuator with damping and speed control device |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP1074750A3 (en) |
| CA (1) | CA2314958A1 (en) |
| IT (1) | IT1313145B1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102007003384B4 (en) * | 2007-01-23 | 2009-11-19 | Festo Ag & Co. Kg | Actuator with actuator element |
| JP6546746B2 (en) * | 2015-02-10 | 2019-07-17 | Ｋｙｂ株式会社 | Fluid pressure cylinder |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1039844B (en) * | 1957-05-23 | 1958-09-25 | Pumpenfabrik Urach | Hydraulic working cylinder with damping device |
| DE2027395A1 (en) * | 1970-06-04 | 1971-12-09 | Hennecke E | Double-acting pressurized working cylinder with end position cushioning |
| FR2410756A1 (en) * | 1977-11-30 | 1979-06-29 | Outillage Air Comprime | STARTING DEVICE FOR A CUSHIONED PISTON CYLINDER |
| FR2425008A1 (en) | 1978-05-05 | 1979-11-30 | Climax France Sa | DEVICE FOR CONTROLLING THE DECELERATION AND / OR ACCELERATION OF A MOBILE ELEMENT FOLLOWING A BACK-AND-BACK RIGGED ALTERNATIVE MOVEMENT, IN THE NEARBY OF AT LEAST ONE OF THE MOBILE ELEMENT LIMIT DEAD POINTS |
| JPS57114003A (en) * | 1980-12-29 | 1982-07-15 | Showa Mfg Co Ltd | Hydraulic shock absorber |
| SE8107724L (en) | 1981-12-22 | 1983-06-23 | Mecman Ab | DEVICE FOR A Piston Rod Loss PRESSURE CYLINDER |
| DE3712671A1 (en) * | 1987-04-14 | 1988-10-27 | Hydraulik Zubehoer Ges Fuer | PISTON-CYLINDER UNIT |
| IT1272731B (en) | 1993-10-18 | 1997-06-26 | Luciano Migliori | LINEAR ACTUATOR WITH POSITION ADJUSTABLE PNEUMATIC SHOCK |
-
1999
- 1999-08-04 IT IT1999MI001751A patent/IT1313145B1/en active
-
2000
- 2000-08-02 EP EP00116651A patent/EP1074750A3/en not_active Withdrawn
- 2000-08-03 CA CA002314958A patent/CA2314958A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| IT1313145B1 (en) | 2002-06-17 |
| EP1074750A3 (en) | 2003-06-04 |
| EP1074750A2 (en) | 2001-02-07 |
| ITMI991751A0 (en) | 1999-08-04 |
| ITMI991751A1 (en) | 2001-02-04 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |