GB2574590A - Fluid pressure apparatus with axially opposed pistons - Google Patents

Abstract

An assembly including a fluid pressure actuator with axially opposed pistons is provided. The fluid pressure actuator 1 comprises axially opposed first and second pistons 30, 20 slidably arranged in a common casing 10. A first component 100 is fixed to or part of the casing 10 while a second component 200 is fixed to or part of the second piston 20. The first piston 30 is fixed to a support 2. The actuator is operable via a control system 300 to restrain either of the first and second components 100, 200 in a fixed position while moving the other. The movement of the first component 100 is restricted by limit stops L1 & L3, and the movement of the second component 200 is restricted by limit stops L2 & L4. A method of controlling movement in such an assembly is also disclosed.

Description

Fluid pressure apparatus with axially opposed pistons

Technical field

This disclosure relates to hydraulic or pneumatic systems comprising axially opposed pistons arranged in a common chamber.

Background

It is known to arrange two pistons in opposed relation in a common chamber. For example, EP 1 350 960 Al discloses a fluid pressure actuator with independently moveable, first and second drive elements, which may be configured as pistons with a pressurised fluid channel extending through one of the piston rods.

Such arrangements make it possible to move two components mounted on the respective pistons simultaneously or sequentially, and so may be useful for example where the components are configured as clamps and work in opposed relation to apply an inwardly or outwardly directed clamping force to a workpiece. However, the configuration of the pistons limits the range of applications, particularly in situations where space is limited.

Summary

In accordance with the present disclosure there are provided: in a first aspect, an assembly as defined in the claims, and in a second aspect, a method for controlling movement in the assembly, as defined in the claims.

The assembly comprises an actuator including first and second pistons having heads which slide in axially opposed relation in a common chamber defined by a casing. A first component is fixed to or part of the casing, while a second component is fixed to or part of the second piston. The first piston is fixed to the support while the casing and the second piston are operable to move the first and second components, each independently of the other in opposite, inward and outward directions relative to the support.

A control system is arranged and operated to control a flow of pressurised fluid to and from the chamber, either (A) to move the first component and the casing to a first limit position, and then to restrain the first component and the casing in the first limit position while moving the second component and the second piston selectively in the inward and outward directions; or (B) to move the second component and the second piston to a second limit position, and then to restrain the second component and the second piston in the second limit position while moving the first component and the casing selectively in the inward and outward directions.

Brief Description of the Drawings

Further features and advantages will become apparent from the following description wherein various illustrative embodiments are set forth, purely by way of example and without limitation to the scope of the claims, and with reference to the accompanying drawings, in which:

Fig. 1 shows an actuator with four limit stops, and with the supply of pressurised fluid in 20 a first pump/drain configuration Cl;

Figs. 2, 3 and 4 show three alternative configurations for proportional control of the flow of pressurised fluid to and from the chamber;

Figs. 5, 6, 7 and 8 show the actuator respectively in four different states SI, S2, S3 and S4 defined by the abutment of the first and second components with respective ones of 25 the four limit stops;

Figs. 9, 10, 11 and 12 show the movement of the actuator respectively in four different pump/drain configurations Cl, C2, C3 and C4;

Fig. 13 shows an example control system comprising a time delay valve arrangement and a flow reversing control for accomplishing the four alternative pump/drain configurations Cl, C2, C3 and C4; and

Figs. 14,15 and 16 show an example assembly comprising the actuator, respectively in states SI (Fig. 14), S2 (Fig. 15), and S3 (Fig. 16).

Reference numerals and characters appearing in more than one of the figures indicate the same or corresponding parts in each of them.

Detailed Description

Referring to Fig. 1, an assembly comprises an actuator 1 having a first piston 30, a second piston 20, and a cylinder or casing 10 defining a chamber 11. The first piston comprises a first piston head 31 fixed to a first piston rod 32, while the second piston comprises a second piston head 21 fixed to a second piston rod 22.

The piston heads are slidably and sealingly received in axially opposed relation in the chamber 11 with the piston rods extending slidably and sealingly through the axially opposed end walls 12,13 of the casing so that the chamber 11 is divided into three volumes VI, V2, V3. The first volume VI is defined between the first piston head 31 and the adjacent end wall 12, the third V3 between the second piston head 21 and the adjacent end wall 13, and the second V2 between the two piston heads 31, 21. The actuator may be of generally conventional design with the casing, chamber and pistons being cylindrical as well known in the art, and the two piston heads and piston rods being of equal diameter as shown.

The piston rod 32 of the first piston 30 is fixed to a support 2 which defines the frame of reference for the system so that all movement takes place relative to the support 2.

The assembly further includes a first component 100 which is fixed to or part of the casing 10, and a second component 200 which is fixed to or part of the second piston 20, for example, being fixed to a distal end of the second piston rod 22 as shown schematically in Fig. 1. It will be understood of course that the first and second components may comprise any functional parts and may be arranged in any position as required by the particular application of the assembly.

The actuator 1 is operable to move each of the first and second components 100, 200 independently of the other and relative to the support 2 in an inward direction DI towards the support 2 and in an opposite, outward direction D2 away from the support 2. In the following description, all movements are to be understood as taking place along the common central axis of the chamber and pistons in either the inward direction DI or outward direction D2, although it should be understood of course that 10 the system may have other degrees of freedom (for example, it may be angularly adjustable via a pivotable attachment to the support 2) as required by the particular application.

The assembly further comprises a control system 300 which is arranged to control a 15 flow of pressurised fluid 3 to and from the chamber 11 to cause relative movement between each of the first and second pistons and the chamber.

Generally in this specification the actuator is taken to be a hydraulic actuator, with the pressurised fluid being a substantially incompressible liquid such as any conventional 20 hydraulic fluid, and the assembly is described and illustrated accordingly. Alternatively however the actuator may be a pneumatic actuator, the pressurised fluid being a compressed gas having sufficient pressure to restrain the respective system components in their limit positions, in which case the system components including the control system may be adapted mutatis mutandis as known in the art.

Fig. 1 schematically illustrates three fluid connections 301, 302, 303 respectively to each of the three volumes VI, V2, V3 of the chamber, wherein the three fluid connections 301, 302 and 303 are configured by the control system in accordance with a first pump/drain configuration Cl.

In this specification, a pump/drain configuration means a configuration in which one of the respective volumes VI, V2, V3 is connected to a drain or tank so that when the fluid 3 contained therein is pressurised by an external force applied to the second piston or the casing it can relieve the pressure in that volume by flowing to the drain or tank, while another one of the respective volumes VI, V2, V3 is supplied with pressurised fluid 3 from a pump so as to urge the second piston or casing in motion against an external force. The fluid connection to the other one of the three volumes VI, V2, V3 may be closed so that the fluid contained therein cannot escape under pressure and so may be placed in compression by an external applied force and so resist movement of the second piston or casing responsive to that force. These three possible fluid connection states are selectively established by the control system and are referred to hereinafter as drain, closed, and pump.

In the illustration of Fig. 1 the fluid connection 301 to the first volume VI represents the drain; the fluid connection 302 to the second volume V2 is closed; and the fluid connection 303 to the third volume V3 represents the pump. This configuration is reproduced as configuration Cl in Fig. 9, with some other possible permutations of the same three fluid connections (drain, closed, pump) being shown respectively in Figs. 10 -12.

For clarity, the schematic illustration of Fig. 1 shows all three fluid connections as entering the chamber via the cylindrical wall of the casing. However, other arrangements are possible. In particular, the fluid connection 303 to the central volume V2 may extend through one of the pistons, conveniently the first piston 30, as illustrated in the example arrangement of Figs. 14 -16, which makes it possible for the range of movement of each of the pistons relative to the casing to overlap with that of the other piston, as illustrated in Figs. 5 - 8.

Fig. 1 also shows four limit stops, i.e. abutments, LI, L2, L3 and L4. Each limit stop may be arranged as a fixed part of the assembly or as a movable or removable part which has at least one use position in which it is fixed at least in the inward or outward direction DI or D2 relative to the support 2 so as to mechanically restrain the movement of the casing or second piston in that respective direction.

For clarity, in the schematic arrangement of Fig. 1 the limit stops are shown as abutting respectively the first or second component 100, 200 to define limit positions as shown in Figs. 5 - 8.

It should be understood however that each of the limit stops may be operatively engaged, respectively by the first component or the casing or by the second component or the second piston, without direct abutment - for example, via a series of functionally interdependent, intermediate components which react the motion of the respective first component/casing or second component/second piston against the respective limit stop. Equally, each of the limit stops may be configured as another functional part of the assembly. For example, limit stops L2 and L3 may be internal to the chamber, being defined respectively by the abutment of the second piston head against the fixed, first piston head, or the abutment of the first end wall 12 of the chamber against the fixed, first piston head.

For simplicity hereafter, the first component 100 and casing 10 will be referred to together as the first element 1000, and the second component 200 and second piston 20 will be referred to together as the second element 2000.

The control system 300 is arranged to control the flow of pressurised fluid 3 to and from the three volumes VI, V2, V3 of the chamber to move the first element 1000 and second element 2000 independently of each other and relative to the first piston 30 and support 2.

The first and second elements may be moved to define any or all of four possible states, represented respectively in Figs. 5 - 8 in which:

Ί limit stop LI defines a first limit position of the first element 1000 in the inward direction DI;

limit stop L2 defines a second limit position of the second element 2000 in the inward direction DI;

limit stop L3 defines a third limit position of the first element 1000 in the outward direction D2; and limit stop L4 defines a fourth limit position of the second element 2000 in the outward direction D2.

In the first state SI, the first element 1000 is operatively engaged with limit stop LI in the first limit position, and the second element 2000 is operatively engaged with limit stop L4 in the fourth limit position.

In the second state S2, the first element 1000 is operatively engaged with limit stop LI in the first limit position, and the second element 2000 is operatively engaged with limit stop L2 in the second limit position.

In the third state S3, the first element 1000 is operatively engaged with limit stop L3 in the third limit position, and the second element 2000 is operatively engaged with limit 20 stop L2 in the second limit position.

In the fourth state S4, the first element 1000 is operatively engaged with limit stop L3 in the third limit position, and the second element 2000 is operatively engaged with limit stop L4 in the fourth limit position.

For simplicity hereafter, the two possible limit positions of the first element 1000 defined respectively by limit stops LI and L3 will be referred to, respectively as LI and L3, and the two possible limit positions of the second element 2000 defined respectively by limit stops L2 and L4 will be referred to, respectively as L2 and L4.

It should be understood that in this specification, the terms first, second, third and fourth are used as the context demands and do not necessarily indicate limit positions LI, L2, L3, L4 respectively; thus, for the avoidance of doubt, the respective limit positions are best identified by their respective numbers LI - L4 with reference to Figs. 5 - 8.

The control system may be operable in a first mode A to move the first element 1000 to a first limit position, e.g. LI or L3, and then to restrain the first element 1000 in the first limit position LI or L3 while moving the second element 2000 selectively in the inward and outward directions DI, D2.

Alternatively or additionally, the control system may be operable in a second mode B to move the second element 2000 to a second limit position, e.g. L2 or L4, and then to restrain the second element 2000 in the second limit position L2 or L4 while moving the first element 1000 selectively in the inward and outward directions DI, D2.

In the illustrated examples, the control system is operable selectively in both the first mode A and the second mode B.

It will be appreciated that either one of the first and second elements 1000, 2000 may be restrained in a respective limit position without being under an external applied load; which is to say, as long as no external force is applied to it, the restrained element will remain in a static position while the other respective element is urged in motion by the pressurised fluid 3.

It is further possible to restrain the respective one of the first and second elements 1000, 2000 in this way under load - which is to say, while it is loaded by an external force in the inward or outward direction DI or D2.

It will be understood of course that even where the working fluid 3 is substantially incompressible, an external load may cause the first or second element 1000, 2000 to move if the load is applied in a direction to reduce a respective volume VI, V2, V3 of the chamber which is connected to drain, and if there is no mechanical abutment (limit stop LI, L2, L3 or L4) to constrain movement in that direction. In this case, where the movement acts to increase another volume of the chamber which is pressurised by the pump or closed, the respective element 1000 or 2000 will be restrained only by ambient (atmospheric) pressure and so will yield when the load exceeds this value.

Therefore, in this specification, to restrain under load (or when loaded) in a particular direction, means that the respective component is restrained in a fixed position when loaded in the indicated direction by the working fluid placed in compression by the load, and/or by mechanical abutment of the solid assembly parts. Thus, the working fluid will prevent movement in response to the applied load up to a limit imposed by the fluid pressure or (for a substantially incompressible working fluid) the failure limit of the system components.

As further described below, the assembly may be arranged to restrain either or both of the first and second elements 1000, 2000 in a selected limit position while under load, either by means of one or more limit stops such as limit stops LI, L2, L3, L4, or without the use of limit stops.

Figs. 2, 3 and 4 illustrate various arrangements of the control system 300 which make it possible to restrain the first or second element 1000, 2000 under load in a selected limit position without the use of limit stops. In each example, the control system is arranged to restrain the flow of pressurised fluid 3 from the chamber 11 in proportional relation to the flow of pressurised fluid 3 to the chamber 11. Thus, fluid 3 leaving a respective volume VI, V2, V3 of the chamber is arranged to urge a proportional volume of fluid 3 to enter another respective volume VI, V2, V3.

In the example of Fig. 2, this is achieved by a pump 40 which receives the fluid 3 from

VI and supplies it to V3, while V2 is closed. The fluid drives the first element 1000 in the outward direction D2 while the second element 2000 is restrained.

If an external force F is applied to the second element 2000 it is reacted against the end wall 13 of the first element 1000 via the incompressible fluid 3 in V3, which is prevented by the pump or a check valve from flowing out of V3, thus urging the first element 1000 in the outward direction D2. This in turn urges fluid in VI via the pump into V3 which opposes the motion. Thus, by controlliing the rotation of the pump 40, the rate of movement of the first element 1000 is restrained, while the second element 2000 is restrained in its fixed position by the fluid in V3 acting in compression.

In the example of Fig. 3, a similar effect is achieved by two pumps 41, 42 connected together by a common shaft and driven in rotation by a motor. The external force F urges fluid 3 from VI via pump 41 to the tank 50, which in turn drives pump 42 in rotation to urge a proportional volume of fluid 3 from the tank 50 into V3.

Each pump may be a positive displacement pump. It will be understood that the pump connections and closed connection can be connected to the three volumes VI, V2, V3 as required to obtain the desired relative movement of the two elements 1000, 2000 in either direction DI or D2. If one of the connected volumes contains a piston rod and the other does not, or if the piston rods are of different diameters, then the two pumps 41, 42 can be configured with different positive displacement volumes which are matched to the displacement of each respective volume of the actuator for the same linear movement of the system elements 1000, 2000.

Fig. 4 shows how a similar arrangement can be obtained using a separate actuator 60 comprising a chamber 61 and piston 62 which is driven axially under power to transfer the pressurised fluid 3 between the two volumes on either side of the piston head 63 and the respective volumes VI, V2 or V3 of the chamber 11. The piston 62 may comprise one or two piston rods to match the volumes of the chamber 61 to the respective volumes VI, V2, V3 of the chamber 11. By restraining the axial movement of the piston 62, either of the two elements 1000, 2000 can be restrained under an external load F in either direction while the other is moved independently in the desired direction DI or D2. The fluid connections between the two chambers 61, 11 can be selectively defined by the control system to obtain the desired motion.

An arrangement such as that shown in any of Figs. 2, 3 and 4 may be used to restrain the flow of pressurised fluid 3 from the chamber 11 in proportional relation to the flow of pressurised fluid 3 to the chamber 11, with the fluid connections to the three chamber volumes VI, V2, V3 configured suitably:

- to restrain the first element 1000 in a first limit position, when under load in the inward direction DI, while moving the second element 2000 selectively in the inward and outward directions DI, D2, and

- to restrain the first element 1000 in a first limit position, when under load in the outward direction D2, while moving the second element 2000 selectively in the inward and outward directions DI, D2, and

- to restrain the second element 2000 in a second limit position, when under load in the inward direction DI, while moving the first element 1000 selectively in the inward and outward directions DI, D2, and

- to restrain the second element in a second limit position, when under load in the outward direction D2, while moving the first element 1000 selectively in the inward and outward directions DI, D2.

In each case, the first limit position may correspond to the limit positions LI or L3, while the second limit position may correspond to the limit positions L2 or L4. However, since no limit stops LI, L2, L3, L4 are required, each limit position may be selectively variable so that it can be freely selected at any position of each of the elements 1000, 2000 along their range of movement in the direction DI or D2. For example, an operator of the system could select a limit position at which to stop (limit) the movement of the respective element 1000, 2000 during one stroke of the element, and restrain the element in that limit position while moving the other respective element, and then select a different limit position during the next movement. Alternatively the limit position could be defined before the respective element 1000, 2000 reaches it, for example, by a position sensor forming part of the control system, perhaps providing an array of alternative positions of the element from which the desired limit position may be selected by a selector switch or the like. Thus, each element 1000, 2000 can be moved to a selected limit position anywhere in its range of movement and then restrained in that position under load while moving the other respective element 1000 or 2000 in either direction DI, D2.

Optionally, a compensating means such as an accumulator may be provided to compensate for a difference in the volume displacement of the two sides of the system (respectively, urging fluid to flow into the chamber 11, and allowing fluid to flow out of the chamber 11). For example, if the two pump rotor volumes are not exactly matched, the compensating means may deliver or accumulate a small volume of fluid 3 on one side of the circuit relative to the other, so as to maintain freedom of movement without developing excessive fluid pressure. The volume of the compensating means may be adjustable or continuously variable and may correspond to a small degree of freedom of movement of the respective elements 1000, 2000, which may be regarded as a linear range within which each limit position is defined in the direction DI or D2.

Alternatively, by employing limit stops as described above to define the respective limit positions, it is also possible to restrain a respective one of the elements 1000, 2000 under load while moving the other respective element 1000, 2000 in the desired direction, using a simple pump/drain circuit configuration which does not require accurately matched positive displacement volumes on each side of the pumped circuit.

Table 1 indicates how the novel mechanism including none, one, or more than one of the respective limit stops (indicated by their respective number LI, L2, L3, L4) can restrain each of the casing and the second piston in a fixed position when loaded in the indicated inward or outward direction, while the respective other one of the casing and the second piston is moved by a fluid circuit in which one side of the circuit is connected to drain substantially without resistance as indicated respectively in circuit configurations Cl, C2, C3 and C4..

As mentioned above, generally in this specification, including in the further embodiments described below, it is not necessary for the limit stops LI, L2, L3, L4 to be arranged externally of the casing to engage the elements 1000, 2000 in direct abutment as illustrated for the sake of simplicity and ease of understanding in Figs. 5 - 8. However, as an exception and purely for the purposes of Table 1, the limit stops LI, L2, L3, L4 are taken to be external to the casing as illustrated, while the abutment of the first piston head 31 against the inward end wall 12 of the casing is taken into account as equivalent to limit stop L3, and the abutment of the second piston head 21 against the first piston head 31 is taken into account as equivalent to limit stop L2. Thus, in Table 1, the second and third limit positions are taken to be present even if the limit stops L2 and L3 are not present.

Table 1: Restraint of each moving part in a fixed position under load while the other part is moved in a pump/drain circuit configuration

X Restrained in a fixed position when loaded in this direction

O Not restrained in a fixed position when loaded in this direction

LIMIT STOP(S) L-	CASING IS RESTRAINED IN FIXED POSITION WHEN LOADED IN DIRECTION	SECOND PISTON IS RESTRAINED IN FIXED POSITION WHEN LOADED IN DIRECTION
INWARD	OUTWARD	INWARD	OUTWARD
when second piston is moved	when second piston is moved	when casing is moved	when casing is moved
INWARD C3	OUTWARD C4	INWARD C3	OUTWARD C4	INWARD C2	OUTWARD Cl	INWARD C2	OUTWARD Cl
None	O	O	X	X	X	X	O	O
1	X	X	X	X	X	X	O	O
2	0	0	X	X	X	X	O	O
3	0	0	X	X	X	X	O	O
1+2	X	X	X	X	X	X	O	O
1+3	X	X	X	X	X	X	O	O
2+3	0	0	X	X	X	X	O	O
1+2+3	X	X	X	X	X	X	O	O
4	0	0	X	X	X	X	X	X
1+4	X	X	X	X	X	X	X	X

It can be seen that when a first limit position is defined by a first abutment or limit stop LI to limit movement of the first element 1000 in the inward direction DI, the control system is operable in a simple pump/drain configuration C3, C4:

- to restrain the first element 1000 in the first limit position LI (states SI, S2), when under load in the inward direction DI, while moving the second element 2000 selectively in the inward and outward directions, and

- to restrain the first element 1000 in the first limit position LI (states SI, S2), when under load in the outward direction D2, while moving the second element 2000 selectively in the inward and outward directions.

It can further be seen that when a second limit position is defined by a second abutment or limit stop L4 to limit movement of the second element 2000 in the outward direction D2, the control system is operable in a simple pump/drain configuration Cl, C2:

- to restrain the second element 2000 in the second limit position L4 (states SI, S4), when under load in the inward direction DI, while moving the first element 1000 selectively in the inward and outward directions DI, D2, and

- to restrain the second element 2000 in the second limit position L4 (states SI, S4), when under load in the outward direction D2, while moving the first element 1000 selectively in the inward and outward directions DI, D2.

Referring particularly to Fig. 13, by providing a combination of three limit stops or abutments, it is possible to arrange the control system to selectively reconfigure the fluid connections 301, 302, 303 in each of the four pump/drain fluid configurations Cl, C2, C3 and C4 responsive to sensing a change in the pressure or flow rate of the pressurised fluid 3 to define a repeatable and reversible sequence of movement of the first and second elements 1000, 2000 between the four states SI, S2, S3, S4.

In this arrangement three limit positions are defined as follows:

- A first limit position is defined by a first abutment LI or L3 which limits movement of the first element 1000 in the inward or outward direction DI or D2.

- A second limit position is defined by a second abutment L2 or L4 which limits movement of the second element 2000 in the inward or outward direction DI or D2.

- A third limit position is defined by a further, third abutment LI, L2, L3 or L4, wherein either:

(A) the third abutment LI or L3 limits movement of the first element in the inward or outward direction DI or D2 to define a range of movement in the inward and outward directions DI, D2 between the first and third limit positions LI and L3, in which case the first element 1000 is defined as a constrained component, and the second element 2000 is defined as a free component; or (B) the third abutment L2 or L4 limits movement of the second element 2000 in the inward or outward direction DI or D2 to define a range of movement in the inward and outward directions DI, D2 between the second and third limit positions L2 and L4, in which case the second element 2000 is defined as a constrained component, and the first element is defined as a free component.

In this arrangement, the control system is arranged:

- to direct the flow of pressurised fluid 3 to and from the respective volumes VI, V2, V3 of the chamber 11 to move a respective one of the free component and the constrained component in a first movement to a respective one of the limit positions LI, L2, L3, L4, and then

- to sense a change in a pressure or flow rate of the pressurised fluid 3 consequent on the respective one of the free component and the constrained component reaching the respective one of the limit positions LI, L2, L3, L4, and

- responsive to sensing said change, to direct the flow of pressurised fluid 3 to and from the respective volumes VI, V2, V3 of the chamber 11 to move the other respective one of the free component and the constrained component in a second movement to a respective one of the limit positions LI, L2, L3, L4.

Optionally in this arrangement, as illustrated by Fig. 13, the control system 300 may include a valve arrangement 310 and a flow reversing control which in the illustrated example is formed by a valve 350. The flow reversing control is operable (e.g. by an electrical switch, not shown, connected to a solenoid 351, as shown) to supply the flow of pressurised fluid 3 to the valve arrangement 310, selectively in opposite, first and second flow directions, represented in Fig. 13 by the two possible states of the valve 350. The valve arrangement 310 is arranged:

responsive to receiving from the flow reversing control 350 the flow of pressurised fluid 3 in the first flow direction, to direct the flow of pressurised fluid to and from the chamber 11 to move the free component and the constrained component sequentially in a first sequence comprising the first and second movements; and then, responsive to receiving from the flow reversing control 350 the flow of pressurised fluid 3 in the second flow direction, to direct the flow of pressurised fluid 3 to and from the chamber 11 to move the free component and the constrained component sequentially in a second sequence in which each of the first and second movements is reversed in direction with respect to the first sequence.

In the example of Fig. 13, referring also to Figs. 5 - 7, the valve arrangement 310 is arranged:

- responsive to receiving from the flow reversing control 350 the flow of pressurised fluid in the first flow direction, to direct the flow of pressurised fluid to and from the chamber 11 to move the first and second elements 1000, 2000 from an initial state SI to a second state S2 and then to a third state S3; and then,

- responsive to receiving from the flow reversing control 311 the flow of pressurised fluid 3 in the second flow direction, to direct the flow of pressurised fluid 3 to and from the chamber 11 to reverse the sequence of movements to move the first and second elements 1000, 2000 from state S3 back to state S2 and then back to the initial state SI.

The valve arrangement 310 includes two time delay valves 320, 330 and functions as follows.

When the reversing control 350 is arranged to establish the forward flow direction as illustrated, V3 is fed by the pump and retracts the second element 2000 in the inward direction DI to limit position L2.

Fluid pressure in V3 urges the first element 1000 in the outward direction D2, generating fluid pressure in VI which is applied to time delay valve 330. This initiates the timer function of time delay valve 330 which then opens after a period determined by the volume of its accumulator 331, allowing fluid in VI to flow to the tank or drain 50 so that the first element 1000 moves in the outward direction D2 to limit position L3.

The solenoid 351 is then operated to reverse the flow direction from valve 350, applying fluid pressure to time delay valve 320 and activating its timer function. Fluid 3 also flows to VI and applies fluid pressure to time delay valve 330, activating its timer function.

Since the second element 2000 is restrained in the inward direction DI by limit stop L2, fluid pressure in VI urges the first element 1000 to move in the inward direction DI to limit position LI, urging fluid 3 to flow out of V3.

The time delay setting of time delay valve 320 is shorter than than of time delay valve

330, so that time delay valve 320 opens first, allowing pressurised fluid 3 to flow to V2.

Valve 315 is then activated, preventing fluid 3 from flowing to VI and to time delay valve 330 which has not yet reached the end of its time delay period and so remains closed.

The fluid pressure in V2 urges the second element 2000 to move in the outward direction D2.

Valve 314 is also closed when time delay valve 320 has opened, closing VI and so preventing the first element 1000 from moving in the outward direction D2.

Referring now to Figs. 14 -16, the assembly is configured by way of example to control the transmission of shaft power between three shafts 400,401,402. In this example it can be seen that the pressurised fluid 3 is arranged to flow through a flowpath 302 which extends through the first piston 30 and opens through the first piston head 31 into the second volume V2 within the region of the chamber 11 between the first and second piston heads 31, 21 so that the respective ranges of movement of the first and second elements 1000, 2000 overlap.

The first shaft 400 comprises a shoulder LI which defines a first limit stop to limit movement of the first element 1000 in the inward direction DI. The first component 100 comprises a splined sleeve 101 rotating in a bearing 102 and slidable between a first limit position (Fig. 14) defined by the abutment of the sleeve 101 against the shoulder LI, and a third limit position (Fig. 16) defined by the abutment of an internal stop 410 of the casing 10 against the first piston head 31 which defines the third limit stop L3 to restrain movement in the outward direction D2.

The second piston rod 22 is extended to support a gear 403 mounted on a rotary bearing 404 which together define the second component 200. The rod 22 slides through an axial bearing 405 which forms the fourth limit stop L4, limiting movement of the second element 2000 in the outward direction D2 by abutment of the bearing 404 against the bearing 405 in a fourth limit position (Fig. 14). A second limit stop L2 is defined by an internal stop 406 mounted on the first piston head 31, the second piston head 21 engaging the internal stop 406 in to limit its movement in the inward direction DI in a second limit position (Fig. 15).

The first and second elements are moved axially to selectively couple and decouple the three transmission shafts as described above and as shown in sequence in Figs. 14,15, and 16.

Industrial applicability

The novel assembly may be used to provide controlled, independent movement of two functionally related components at the distal end of an outwardly extending assembly, wherein both ranges of movement are defined relative to a single support at a proximal end of the assembly, and thus on the same side of the support.

Since the chamber is common to both pistons, the ranges of the first and second elements 1000, 2000 may be arranged to overlap by providing a flowpath for the pressurised fluid to flow through the first piston and first piston head into the central volume of the chamber.

Each of the first and second elements 1000, 2000 may be restrained in a limit position while under load in one or both directions, while moving the other respective element independently and reversibly in the desired direction. Where the restraint is accomplished by a proportional fluid flow to and from the chamber, the limit position may be selected freely at any point in the range of motion of the respective component. Alternatively, by providing limit stops or abutments in selected positions, a simple pump/drain circuit configuration may be adopted, which may further provide a repeatable sequence of movements which is reversible simply by reversing the direction of flow from the pump.

In summary, a fluid pressure actuator comprises axially opposed first and second pistons slidably arranged in a common casing. A first component is fixed to or part of the casing while a second component is fixed to or part of the second piston. The first piston is fixed to a support. The actuator is operable to restrain either of the first and second components in a fixed position while moving the other independently and relative to the support.

In alternative embodiments the first and second components may be coaxial or collinear.

Many further possible adaptations within the scope of the claims will be evident to those skilled in the art.

In the claims, reference numerals and characters are provided in parentheses purely for ease of reference and are not to be construed as limiting features.

Claims (13)

1. An assembly comprising:

a first component (100),

5 a second component (200), and a support (

2);

each of the first and second components being moveable independently of the other and relative to the support in an inward direction (DI) towards the support and in an opposite, outward direction (D2) away from the support;

10 the assembly further comprising an actuator (1) for moving each of the first and second components relative to the support, the actuator comprising:

a first piston (30) comprising a first piston head (31), a second piston (20) comprising a second piston head (21), and a casing (10) defining a chamber (11), the first and second piston heads being

15 slidably received in axially opposed relation in the chamber;

the assembly further comprising a control system (300) arranged to control a flow of pressurised fluid (3) to and from the chamber to cause relative movement between each of the first and second pistons and the chamber; wherein the first component (100) is fixed to or part of the casing (10),

20 the second component (200) is fixed to or part of the second piston (20), and the first piston (30) is fixed to the support (2); and the control system is operable to control the flow of pressurised fluid to and from the chamber, either:

(A) - to move the first component and the casing to a first limit position, and then

25 - to restrain the first component and the casing in the first limit position while moving the second component and the second piston selectively in the inward and outward directions;

or:

(B) - to move the second component and the second piston to a second limit

30 position, and then

- to restrain the second component and the second piston in the second limit position while moving the first component and the casing selectively in the inward and outward directions.

5 2. An assembly according to claim 1, wherein the first limit position is defined by a first abutment (LI), the first abutment being connected to the support, the first component or the casing being arranged to operatively engage the first abutment to limit movement of the first component and the casing in the inward direction (DI), and the control system is operable to control the flow of pressurised fluid to and from

10 the chamber:

- to restrain the first component and the casing in the first limit position, when under load in the inward direction, while moving the second component and the second piston selectively in the inward and outward directions, and

- to restrain the first component and the casing in the first limit position, when

15 under load in the outward direction, while moving the second component and the second piston selectively in the inward and outward directions.

3. An assembly according to claim 1 or claim 2, wherein the second limit position is defined by a second abutment (L4), the second abutment being connected to the

20 support, the second component or the second piston being arranged to operatively engage the second abutment to limit movement of the second component and the second piston in the outward direction (D2);

and the control system is operable to control the flow of pressurised fluid to and from the chamber:

25 - to restrain the second component and the second piston in the second limit position, when under load in the inward direction, while moving the first component and the casing selectively in the inward and outward directions, and

- to restrain the second component and the second piston in the second limit position, when under load in the outward direction, while moving the first component

30 and the casing selectively in the inward and outward directions.

4. An assembly according to claim 1, wherein the control system is operable to control the flow of pressurised fluid to and from the chamber, both:

(A) - to move the first component and the casing to a first limit position, and then

- to restrain the first component and the casing in the first limit position while moving the second component and the second piston selectively in the inward and outward directions;

and:

(B) - to move the second component and the second piston to a second limit position, and then

-to restrain the second component and the second piston in the second limit position while moving the first component and the casing selectively in the inward and outward directions.

5. An assembly according to claim 1, wherein the control system is arranged to restrain the flow of pressurised fluid from the chamber in proportional relation to the flow of pressurised fluid to the chamber.

6. An assembly according to claim 1, wherein the control system is arranged to restrain the flow of pressurised fluid from the chamber in proportional relation to the flow of pressurised fluid to the chamber:

- to restrain the first component and the casing in the first limit position, when under load in the inward direction, while moving the second component and the second piston selectively in the inward and outward directions, and

- to restrain the first component and the casing in the first limit position, when under load in the outward direction, while moving the second component and the second piston selectively in the inward and outward directions, and

- to restrain the second component and the second piston in the second limit position, when under load in the inward direction, while moving the first component and the casing selectively in the inward and outward directions, and

- to restrain the second component and the second piston in the second limit position, when under load in the outward direction, while moving the first component and the casing selectively in the inward and outward directions.

7. An assembly according to claim 1, wherein:

the first limit position is defined by a first abutment (LI; L3), the first abutment being connected to the support, the first component or the casing being arranged to operatively engage the first abutment to limit movement of the first component and the casing in the inward or outward direction; and the second limit position is defined by a second abutment (L2; L4), the second abutment being connected to the support, the second component or the second piston being arranged to operatively engage the second abutment to limit movement of the second component and the second piston in the inward or outward direction; and a third limit position is defined by a third abutment (LI; L2; L3; L4), the third abutment being connected to the support, and either:

(A) the first component or the casing is arranged to operatively engage the third abutment to limit movement of the first component and the casing in the inward or outward direction to define a range of movement in the inward and outward directions between the first and third limit positions, wherein the first component and the casing are defined together as a constrained component (1000), and the second component and the second piston are defined together as a free component (2000); or (B) the second component or the second piston is arranged to operatively engage the third abutment to limit movement of the second component or the second piston in the inward or outward direction to define a range of movement in the inward and outward directions between the second and third limit positions, wherein the second component and the second piston are defined together as a constrained component (2000), and the first component and the casing are defined together as a free component (1000);

and wherein the control system is arranged:

- to direct the flow of pressurised fluid to and from the chamber to move a respective one of the free component and the constrained component in a first movement to a respective one of the limit positions, and then

- to sense a change in a pressure or flow rate of the pressurised fluid consequent on the respective one of the free component and the constrained component reaching the respective one of the limit positions, and

- responsive to sensing said change, to direct the flow of pressurised fluid to and from the chamber to move the other respective one of the free component and the constrained component in a second movement to a respective one of the limit positions.

8. An assembly according to claim 7, wherein the control system (300) includes a valve arrangement (310) and a flow reversing control (350), the flow reversing control being operable to supply the flow of pressurised fluid to the valve arrangement, selectively in opposite, first and second flow directions;

and the valve arrangement is arranged:

responsive to receiving from the flow reversing control the flow of pressurised fluid in the first flow direction, to direct the flow of pressurised fluid to and from the chamber to move the free component and the constrained component sequentially in a first sequence comprising the first and second movements; and then, responsive to receiving from the flow reversing control the flow of pressurised fluid in the second flow direction, to direct the flow of pressurised fluid to and from the chamber to move the free component and the constrained component sequentially in a second sequence in which each of the first and second movements is reversed in direction with respect to the first sequence.

9. An assembly according to claim 1, wherein the pressurised fluid is arranged to flow through a flowpath (302) which extends through the first piston (30) and opens through the first piston head into a region (V2) of the chamber between the first and second piston heads.

10. A method for controlling movement in an assembly, the assembly comprising: a first component (100), a second component (200), and

5 a support (2);

each of the first and second components being moveable independently of the other and relative to the support in an inward direction (DI) towards the support and in an opposite, outward direction (D2) away from the support;

the assembly further comprising an actuator (1) for moving each of the first and second 10 components relative to the support, the actuator comprising:

a first piston (30) comprising a first piston head (31), a second piston (20) comprising a second piston head (21), and a casing (10) defining a chamber (11), the first and second piston heads being slidably received in axially opposed relation in the chamber;

15 the assembly further comprising a control system (300) arranged to control a flow of pressurised fluid (3) to and from the chamber to cause relative movement between each of the first and second pistons and the chamber;

the method comprising:

arranging the assembly such that:

20 the first component (100) is fixed to or part of the casing (10), the second component (200) is fixed to or part of the second piston (20), and the first piston (30) is fixed to the support (2); and operating the control system to control the flow of pressurised fluid to and from the chamber, either:

25 (A) - to move the first component and the casing to a first limit position, and then

- to restrain the first component and the casing in the first limit position while moving the second component and the second piston selectively in the inward and outward directions;

or:

(B) - to move the second component and the second piston to a second limit position, and then

- to restrain the second component and the second piston in the second limit position while moving the first component and the casing selectively in the inward and 5 outward directions.

Intellectual Property Office