GB2162248A

GB2162248A - Fluid-powered linear actuator

Info

Publication number: GB2162248A
Application number: GB08518063A
Authority: GB
Inventors: Kurt Stoll
Original assignee: Festo SE and Co KG
Current assignee: Festo SE and Co KG
Priority date: 1984-07-27
Filing date: 1985-07-17
Publication date: 1986-01-29
Also published as: DE3427690A1; JPS6145106A; GB8518063D0; GB2162248B

Abstract

An actuator cylinder for fluid power operation has a cylinder tube (26) with a piston (22) running therein, a cylinder cover (9) at one end of the cylinder and having an axially adjustable abutment member (4) therein surrounding the piston rod (1). Near the piston (2) there is a cushioning sleeve (3) which is engaged by a sealing ring (5) when it is moved into a cushioning chamber (14) inside the abutment member and around the piston rod (1). It is now not possible for fluid to flow out of the chamber past the sealing ring (5) and it is forced to flow instead through a choke duct (11) with an adjustable choke (13). This ensures that the impact of the piston (2) on the abutment member (4) is cushioned. <IMAGE>

Description

SPECIFICATION An actuator cylinder The present invention relates to cylinder actuators more particularly of the sort comprising a cylinder tube, a reciprocating piston arranged therein, a cylinder cover shutting off one end of the cylinder tube, an abutment member running axially through the cover, means for adjusting the abutment member in the axial direction, one end of the member facing into the cylinder tube taking the form of an abutment face, a sensor such as a valve having a valve member extending from said abutment face into cylinder, a control duct consisting of channel system in the abutment member and in the cylinder cover and of peripheral grooves fashioned in an interface between the abutment member and the said cover, and an axially moving piston rod fitting into the abutment member, that takes the form of a sleeve, said piston rod having an end face that is joined to the axially moving piston, whose piston rod runs axially in an abutment member.

The abutment member extends axially through a cylinder cover, with which it is connected so that it may be adjusted and set in relation thereto. The control valve located in the abutment member functions for example to reverse the motion to the piston as caused by a pneumatic or hydraulic fluid.

In the terminal position the piston engages the end abutment face of the abutment member actuating the control valve. Owing to the impact of the pis ton on the abutment face there is heavy wear; and more especially the abutting face will be damaged.

Furthermore the piston impinges onto the plunger of the control valve without being braked so that the control valve will cease to operate accurately and has to be replaced.

One object of the present invention is therefore to remedy these shortcomings.

A further aim of the invention is to produce a braking or cushioning effect on the piston.

A still further objective of the invention is to make it possible for the abutment member of the cylinder to be adjusted while maintaining such a possibility of cushioning the impact of the piston.

In accordance with a further purpose, the inven tion is to make possible a variation in the degree of cushioning with respect to duration and inten sity.

In order to achieve these or further objects that will appear during the course of the following ac count, an actuator cylinder designed for operation with fluid, is characterized by comprising: a cylin der tube, a piston adapted to move axially in said cylinder tube, a cylinder cover placed at one end of said cylinder tube, an abutment member extending through said cylinder cover and having means for adjusting it in an axial direction in relation to said cover, said abutment member having an abutment face adjoining a cylinder space between said pis ton and said cover, a control sensor set within said abutment face, said sensor including a driving plunger projecting towards said cylinder space, said sensor being included in a control line composed of a duct system within said abutment member and said cylinder cover, and of corresponding peripheral groove means between said cylinder cover and said abutment member, a piston rod attached at one end to said piston, said piston rod running through said abutment member, a cushioning sleeve on said piston rod for producing a cushioning effect shortly before said piston abuts said abutment face, said sleeve being adjacent said piston, a cushioning seal ring at an end of said abutment member nearest said piston, said abutment member being made with a cushioning chamber between it and said piston rod, to receive said cushioning sleeve, said sleeve then cooperating with said seal ring, said cushioning chamber being connected by a first passage in said abutment member with outer peripheral groove means, which is connected via a second passage in the cylinder with an inlet connection port for fluid, and with the cylinder space between the piston and the cylinder cover, by way of a choke duct with an adjustable choke means therein.

These features ensure that when the piston is moved along the last part of its stroke towards the cover and abutment member there is cushioning effect which is dependent on the length of the buffer sleeve, since the displacement of the driving fluid into the cushioning passage is shut off and the fluid then has to flow through the choke duct.

The level of the cushioning effect may be adjusted by the setting of the abutment member and a choke setting screw.

The construction in accordance with the invention offers the advantage that the impact of the piston on the abutment face of the abutment member is cushioned, this to a substantial extent reducing the stresses inflicted on the material of the piston and the abutment member; furthermore the length of life of the valve is extended. Moreover the cushioning effect is not dependent on the position of the abutment member and is equally produced, since the main part of the cushioning system is coaxially integrated in the axially adjustable abutment member, there being a further contribution in this respect from the peripheral groove, which conducts the fluid in the uncushioned condition on the outer periphery of the abutment member.

A further advantage of the invention is that the inertia of the piston when it strikes the abutment surface may be adjusted by setting the choke in accordance with specific requirements. At the same time however it is possible for the duration of the piston stroke also to be adjusted by changing the setting of the choke, something which offers the particular advantage that no additional devices have to be provided in order to set the du ration of the stroke of the said piston. By way of an adjustment of the choke it is furthermore possible, as an additional advantage, to variably set the point in time at which the control valve generates a reversing pulse.

A further beneficial effect obtainable with the present invention is that by changing the setting of the abutment member the commencement of the choking effect may be set, and furthermore the length of the piston stroke and the time elapsing between two consecutive control pulses generated by the control valve. By a combination of the adjustment of the choke and abutment member there is the further useful effect that the possibilities noted may be substantially extended.

The feature of forming the cushioning chamber between the abutment member and the piston rod leads to the advantage of simple manufacture, as for example by drilling.

The advantageous further feature that the breadth of the gap constituting the cushioning chamber is equal to approximately the radial thickness of the cushioning sleeve is conducive of a compact manner of construction, since the breadth of the gap only has to be made large enough to allow for a sufficient rate of drain of the fluid into the non-cushioned condition. If only a minimum thickness of the discharge gap is needed in the cushioning chamber, it will suffice, in accordance with a further advantageous feature of design, to adapt the gap breadth to the radial thickness of the cushioning sleeve to that length of the cushioning space which is equal to at least the length of the cushioning sleeve.

A further advantageous simplification of the invention is to be achieved if the cushioning sealing ring is so designed that its assumes the function of a check means. By using only one single component it is thus simultaneously possible to produce a satisfactory cushioning effect and also to ensure unimpeded flow of the driving fluid in the noncushioned condition of the piston motion.

In the event of the cushioning ring seal being set in a peripheral groove located in the inner or bore face of the abutment member, this will provide a secure seat for the sealing ring.

In order to ensure that the actuator in accordance with the invention is particularly simple to produce, while at the same time producing an optimum seat for the cushioning sealing ring, the latter is best only mounted in the end face of the inner part of the abutment member, the sealing edge or lip possibly projecting out clear of the abutment face.

The feature of designing the cushioning sealing ring with two sealing lips, of which the one surrounds the cushioning sleeve in the piston after moving into the abutment member and the other lip makes contact with the abutment member, when used in conjunction with the advantageous feature of having at least one axial passage between the cushioning sealing ring abutment member placed therearound so as to connect the space in the cylinder with the cushioning chamber, leads to the more particularly significant benefit that dynamic cushioning is produced on moving the cushioning sleeve into the cushioning chamber, while in the case of the reverse movement an unimpeded flow of the driving fluid into the cylinder space will be possible.

If the peripheral groove placed in circuit between the cushioning chamber and the connection port for the driving fluid, is made with at least the same axial length as the peripheral grooves of the control duct, the result will be a very large range of adjustment of the abutment member.

It is furthermore possible for the length of the peripheral groove to to be at least twice the range of adjustment of the abutment member and for the passage to be connected with the peripheral groove in all positions of the abutment member intermediate its end settings. Such features lead to an unhindered utilisation of the full range of adjustment of the abutment member.

In accordance with a further feature of the invention the choke mounted in the choke passage may have a choke screw that is able to be adjusted from the outside. This allows a stepless adjustment of the degree of the cushioning effect even while the actuator is in operation.

In accordance with further useful features of the invention, the cover of the cylinder tube may have a supply passage which connects the connection port for driving fluid with the space inside the cylinder tube. A check valve may be mounted in this passage with opens in response to a pressure coming from the connection port for the driving fluid. The cushioning sealing ring may have but one sealing lip, which sealingly surrounds the cushioning sleeve in the in-cylinder position thereof. These further features of the invention are conducive of a simple design of the cushioning sealing ring without a check valve lip, since the driving fluid may flow into the cylinder space via a feed passage which is shut off by a check valve when the fluid is flowing in the opposite direction.

A more detailed account of the invention will now be given on the basis of the accompanying drawings, in the course of which description still further advantages of the invention will become apparent.

Figure I shows a section through a cylinder actuator in keeping with the invention.

Figure 2 shows a section of part of a form of the actuator with a single feed passage.

Figure 3 shows a section of part of an actuator in accordance with the invention as taken on the line A-A of figure 2.

Figure 4 is a section as taken on the line B-B of figure 3.

In figure 1 the reader will see a cylinder actuator having a cylinder tube 26 shut off at its end by a cylinder cover 9. The cylinder cover 9 has an abutment member 4 running through it axially with a gas-tight joint between the member 4 and the cover. For its part, the abutment member 4 surrounds an axially moving piston rod 1 like a sleeve. One end of the piston rod 1, which is within the cylinder space 12, has a piston 2 attached to it. The piston cooperates with the cylinder tube 26 in a conventional manner. The cylinder cover 9 possesses a radial collar extension 27, same having a connection port 10 for driving fluid.

A passage extends from this fluid connection port, such passage preferably being in the form of a axial, drilled hole running as far as the inner face 28 of the cylinder cover, in which the abutment mem ber 4 runs. Furthermore a choke passage 11 is connected with the connection port 10 to provide a connection between the said driving fluid connection port 10 and the cylinder space 12. This choke passage 11 is preferably in the form of an axially drilled hole and has a choke 13 therein which may be adjusted from the outside using a choke screw 23, not described her in detail. It is best if the choke screw 23 runs in a radial hole that is machined at a right angle to the choke passage 11.At a different position on its periphery the cylinder tube cover 9 has at least two further passage systems 29 and 39, not described in detail, which are connected with the surface 28 of the cylinder tube.

At its outer end furthest from the cylinder tube the cylinder cover 9 furthermore possesses a clamp or nut 31 screwed onto a threaded axial extension 32 of the abutment member 4. It is by means of this thread that the abutment member 4 may be screwed in and out of the threaded cover and locked in any such setting with the lock nut 31. The abutment member 4 is therefore able to be steplessly adjusted and locked after such alteration in its axial position. The abutment member 4 possesses a guide and sealing insert 42, that is preferably coaxially locked in place within the threaded extension 32 so that the piston rod 1 is free to run axially within it.

At its cylinder end 19 the cylinder tube 26 possesses an abutment face 16 for the piston 2 so that the piston rests against the face 16 in its initial po- sition. A control valve 33 is mounted in this end of the abutment member so that the actuating plunger 34 of the valve projects out through the abutment face 16, preferably in an axial direction.

The valve 33 has a valve space 35 having a valve passage 36 leading from it into a peripheral groove 37 let into the outer face of the abutment member 4. A further valve passage 39 runs from a second valve connection 38, such passage 39 not falling in the plane of the drawing and therefore not being visible. It runs to a second peripheral groove 40 on the abutment member. The abutment member also has a third peripheral groove 7, which has a passage 6 running from it, preferably in a radial direction, to a cushioning chamber 14 between the surface 41 of the piston rod 1 and the inner face 17 of the abutment member 4, said chamber 14 being sealed off by a packing 42 in the threaded abutment member 4 at the end of the chamber nearest the threaded axial extension 32.The peripheral grooves 7, 37 and 40 are separated from each other by seals 51 set in lands therebetween i. e. set in the outer cylindrical surface of the abutment member between the said grooves. They engage the bore surface of the cylinder so that the grooves 7, 37 and 40 are sealed off from each other. The grooves 7, 37 and 40 are best designed with the same length and their spacing is preferably in accord with the amount of length of possible axial adjustment in the position of the abutment member 4.

On the bore face of the abutment member 4 there is a cushioning sealing ring 5 placed in a peripheral groove 18. This sealing ring 5 possesses two sealing lips 21 and 22, respectively, of which the one sealing lip 21 is directed in an axial and radial direction towards the cylinder chamber 12 and towards the piston 2, whereas the other sealing lip 22 has generally the opposite direction and contacts the shoulder 43 forming the limit of the peripheral groove 18. The cylindrical surface 48 of the peripheral groove 18 has at least one axial passage 20, preferably in the form of an axial groove, with a length equaling the length of the groove 18. A cushioning sleeve 3 is force fitted or clamped on the piston rod 1 adjacent to the piston 2.The length of this sleeve is made equal to the desired cushioning action or stroke and is preferably chamfered or the like at its end nearer the cylinder cover. Instead of being force fitted on the piston rod 1, the cushioning sleeve may be made integrally with the piston 2 or screwed on the piston.

The outer surface 49 of this cushioning sleeve acts as a running sealing face cooperating with the sealing lip 21 on motion of the sleeve into the cushioning space 14.

Starting in the position of the piston rod in which the sleeve is to the left of the abutment member, in accordance with the invention, the piston 2, the piston rod 1 secured thereto and the cushioning sleeve 3 move through and towards the cover 9. The motion of the piston is for instance caused by fluid under pressure supplied to the active piston side 50 opposite to the piston rod side.

In the present context a detailed account of the supply of the driving fluid to the actuator would not be relevant for the invention. In the initial phase of such piston motion the cushioning sleeve 3 on the piston rod 1 will be clear of the cushioning chamber 14 and consequently still out of engagement with the cushioning sealing ring 5. The fluid present in the cylinder space 12 is displaced, it flowing via the cushioning chamber 14, the passage 6, the peripheral groove 7 and the passage 8 into the connection port 10, whence it is suitably led off via a duct, not illustrated. If now the piston 2 reaches a position in which the cushioning sleeve 3 is engaged by the cushioning sealing ring 5, the path for the fluid between the cylinder space 12 and the cushioning chamber 14 will be interrupted.Consequently the fluid will now be obliged to flow via the choke passage 11 through the choke 13 into the connection port 10. By suitable setting of the choke screw 23 the speed of flow of the fluid may be varied and thus also the intensity of the cushioning effect, since the speed of motion of the piston depends on the possible rate of flow of the driving fluid in the choke passage 11. The motion of the piston towards the cylinder cover will come to an end when the piston engages the abutment face 16, the control valve 33 being actuated owing to the face so that the valve plunger 34 is pushed inwards. This control valve 33 may for example be called upon to function as sensor or pick up responding to the piston motion and producing a control pulse for controlling the direction of motion of the piston, i. e. to reverse it.

The passage system 30 is linked via the peripheral groove 37 and the valve passage 36 with the valve chamber 35 of the control valve 33 and may for example be connected with a control pressure.

Starting at the valve port 38, the valve passage 39 extends via the peripheral groove 40 to the passage system 29 in the cylinder cover 9. If the control valve 33 is not actuated, the connection between the two passage systems 29 and 30 is interrupted for the valve chamber 35 will be cut off from the valve port 38 by means of a valve spring 44. This valve spring 44 urges the valve member 45 towards a seal 46. If now, as mentioned above, the piston 2 impinges on the valve plunger 34, the valve member 45 will be moved clear of the seal 46 and the two systems of passages will be connected so that it is then possible for example for the fluid to be moved from the passage system 30 into the passage system 29 in the way described above.A pulse may now be produced in the passage system 29 which reverses the direction of flow of the driving fluid so that fluid flows into the fluid connection port 10. The driving fluid may now make its way via the passage 8, the peripheral groove 7 and the passage 6 into the cushioning chamber 14 from where it passes past the sealing lip 22 of the cushioning sealing ring 5, through the opening 20 and into the cylinder space 12. The sealing lip 22 therefore more or less has the function of a sort of check valve, and while it is possible for the driving fluid to pass from the cushioning chamber into the cylinder space, motion thereof in the opposite direction is not possible.

The piston 2 will now move in a direction away from the cylinder cover 9.

It will be clear from this account that the choke does not only function to regulate the level of cushioning or damping, but furthermore makes it possible to vary the time between two consecutive engagements of the piston on the abutment face 16 so that the piston may be utilized as a timer or timing switch. The fact that in addition to the setting of the choke it is also possible to adjust the position of the abutment member 4 in the cylinder cover 9 constitutes a further possible way of increasing this time interval.

The placement of the passage 8, in relation to the peripheral groove 7 and of the passage systems 29 and 30 in relation to the peripheral grooves 40 and 37, is such that the passages have generally the same position in relation to the corresponding peripheral groove. In the design of figure 1 the abutment member 4 has been screwed as far as possible into the cylinder cover 9 so that the passages are opposite the grooves adjacent that axial edge, which is directed in the opposite direction to that of piston motion. The maximum available range of adjustment of the abutment member is therefore controlled by the axial extent of the grooves.

A further possible embodiment of the actuator cylinder in keeping with the invention will be seen in figures 2, 3 and 4. Between the cylinder space 12 and the connection port 10 for the driving medium there is a further supply passage 24. This passage is marked in broken lines in figure 2 and is outside the plane of the figure. It is best for this passage to be placed near the choke passage 11 and more especially parallel thereto The supply passage 24 will be seen from figure 4 to have a check valve 25, that is best of conventional design and which is not described here in detail. The check valve 25 is so mounted that there is a possibility of flow from the connection port 10 into the cylinder space 12, but not the other way round. In the case of this form of the invention it is possible to dispense with a cushioning sealing ring 5, which has two sealing lips.It is sufficient to have a plain sealing ring with a single sealing lip which makes sealing engagement with the cushioning sleeve when same is driven inwards. The cushioning sealing ring 5 does not need to have any check valve function. The manner of operation of the actuator cylinder is the same in this form of the invention as in the working example to be seen in figure 1.

The check valve shuts and the driving fluid passes from the cylinder space 12 via the cushioning space 14 into the connection port 10 for the driving fluid. After the piston 2 has engaged the abutment face and after reversal of the direction of flow of the driving fluid, it flows, taking the path of the least resistance, through the supply passage 24 through the check valve 25 into the cylinder space 12. More especially this form of the invention offers a simple seal on the cushioning sleeve, for a simple cushioning sealing ring lends itself to this application and it is furthermore feasible to dispense with the above-noted passages 20.

If the supply duct 24 is fitted with a choke, not described here in detail, it is then furthermore possible to vary the supply rate of the fluid so that the velocity of travel of the piston to a given axial position may be varied in another way as well.

Claims

1. An actuator cylinder designed for operation with fluid, said actuator cylinder comprising a cylinder tube, a piston adapted to move axially in the cylinder tube, a cylinder cover placed at one end of the cylinder tube, an abutment member extending through the cylinder cover and having means for adjustment thereof in an axial direction in relation to the cover, the abutment member having an abutment face adjoining a cylinder space between the piston and the cover, a control sensor set within the abutment face, the sensor including a driving plunger projecting towards the cylinder space, and being included in a control line comprising a duct system within the abutment member and the cylinder cover, and corresponding peripheral groove means between the cylinder cover and the abutment member, a piston rod attached at one end to the piston and extending through the abutment member, a cushioning sleeve on the piston rod for producting a cushioning effect shortly before the piston abuts the abutment face, the sleeve being adjacent the piston, a cushioning seal ring at an end of the abutment member nearest the piston, a cushioning chamber defined between the abutment member and said piston rod to re ceive the cushioning sleeve, the latter being co-operable with the seal ring, the cushioning chamber being connected by a first passage in the abutment member with outer peripheral groove means, the latter being connected via a second passage in the cylinder with an inlet connection port for fluid, and with the cylinder space between the piston and the cylinder cover by way of a choke duct with an adjustable choke means therein.

2. An actuator cylinder according to claim 1, wherein the choke is adjustable so as to adjust the duration of the stroke of the piston, the impact of the piston on the abutment face and the time between two consecutive control pulses generated by the sensor, and the axial position of the abutment member is adjustable so as to vary the commencement of slowing down of the piston by the choke, the piston stroke and the time between two consecutive control pulses.

3. An actuator cylinder according to claim 1 or 2, wherein the cushioning chamber is in the form of a restricted gap constituted by an axially limited space between the abutment member and the piston rod.

4. An actuator cylinder according to claim 3, wherein the radial extent of the gap is generally equal to the radial thickness of the cushioning sleeve.

5. An actuator cylinder according to claim 3 or 4, wherein the radial extent of the gap forming the cushioning chamber along an axial length running from the abutment face of the abutment body for at least a distance equal to the axial length of the cushioning sleeve, is matched to the radial thickness of the cushioning sleeve.

6. An actuator cylinder according to any of the preceding claims, wherein the cushioning seal ring is adapted to exert a check valve function in relation to the fluid, the seal ring preventing one direction of flow when the piston moves towards the cylinder cover and permitting such flow when the piston moves in the opposite direction.

7. An actuator cylinder according to claim 6, wherein between the seal ring and the abutment encompassing same, there is at least one axial passage connecting the cylinder space with the cushioning chamber.

8. An actuator cylinder according to any of the preceding claims, wherein the seal ring is located in a peripheral groove in the surface of the abutment member.

9. An actuator cylinder according to claim 8, wherein the peripheral groove is made directly in an end face of the abutment member forming the abutment face thereof.

10. An actuator cylinder according to claim 8 or 9, wherein the cushioning seal ring possesses two sealing lips, one of which is adapted to contact the cushioning sleeve in the position inside the abutment member and the other of which is adapted to contact the abutment member at a limiting face of the groove holding the seal ring on the cylinder cover side thereof.

11. An actuator cylinder according to any of claims 8 to 10, wherein the peripheral groove has an axial length at least equal to that of the peripheral groove means.

12. A cylinder actuator according to any of claims 8 to 11, wherein the peripheral groove has an axial length at least equal to the length of possible axial adjustment of the abutment member.

13. An actuator cylinder according to any of the preceding claims, wherein the passage in the cylinder cover is connected with the outer peripheral groove means in all possible settings of the abutment member.

14. An actuator cylinder according to any of the preceding claims, wherein the choke in the choke duct comprises an externally accessible screw for its adjustment.

15. An actuator cylinder according to any of the preceding claims, wherein a feed passage in the cylinder cover extends from the fluid inlet port to the cylinder space.

16. An actuator cylinder according to claim 15, comprising a check valve in the feed passage, the check valve being opened by pressure at the inlet port.

17. An actuator cylinder according to any of the preceding claims, wherein the sealing ring possesses a single sealing lip adapted to contact the sleeve when same is in said cushioning space.

18. An actuator cylinder substantially as hereinbefore described with reference to the accompanying drawings.