GB2042079A - Stroke variation relay device - Google Patents

Abstract

A stroke variation relay device 1 comprises a master piston and cylinder unit 2, a slave piston and cylinder unit 3 and a housing cylinder 14 common to both, the housing cylinder 14 containing a shuttle element 20 comprising two axially spaced end walls 21, 22 connected by a cylindrical body member, the shuttle element 20 making sealing contact with the housing cylinder 14, an abutment member 18 contained within the housing cylinder 14, the shuttle element 20 being displaceable within limits with respect to the housing cylinder 14, its extent of movement from zero displacement to maximum displacement being controlled by the positioning of the abutment member 18, while a control piston 19 connected via a connecting rod 8A of the slave piston and cylinder unit 3 is housed within the cylindrical body member of the shuttle element 20, the rod 8A passing through the end wall 21 of the shuttle element 20 and porting 24, 25, 23 to facilitate external control functions. <IMAGE>

Description

SPECIFICATION Stroke variation relay device This invention relates to a stroke variation relay device for fluid powered piston and cylinder units for use in an automation system for the purpose of accurately controlling linear displacement; either between rigidly-held or progressively-reached,-stage/signal/stage positions; as may be required for example as part of the three-dimensional/multi articulation of a robot arm, in manufacturing, assembly and/or materials handling systems.

The concept of this device is based upon the premise that; where a double-acting piston and cylinder unit is locked rigidly in position its rod may be actuated into either of only two, precise, positions-fully out or fully in; end-walls being recognised not only as physical barriers but also as the agency which endows the stroke length with its inherent accuracy. A natural corollary being for example that the only way to obtained a precise, inherently accurate, 7.0474 inch outstroke mode from a 10 inch piston and cylinder unit is to reposition the complete unit 2.9526 inches further back, lock it rigidly in position and actuate to full outstroke.

Prior art proposals have involved the use of 'Positioners' acting directly on 'working' piston and cylinder units and seeking to obtain, de facto, intermediate stroke positions without reference to physical constraint. The principle is fundamentally unsound; 'accuracy' is typically no better than + 0.5% of full stroke length and frequently worse, whilst positional rigidity has involved the use of parallel oil/hydro check units; these deficiencies confine the use of such 'Positioners' to the more rudimentary of static load applications, requiring only approximate location.

The present invention is concerned with a device capable of positively and accurately controlling the extension or retraction of a piston rod, whether or not under dynamic load.

Furthermore, preferred operation will cause the piston rod to be locked, in a 'fail-safe' mode, when signal pressure fluid is exhausted, or inadvertently lost.

According to the present invention, a stroke variation relay device for fluid powered piston and cylinder units, comprises a master piston and cylinder unit, a slave piston and cylinder unit, and a housing cylinder common to both the master and the slave cylinders, the housing cylinder containing a shuttle element comprising two axially spaced end walls connected by a cylindrical body member, which shuttle element makes sealing contact with the housing cylinder, the latter also containing an abutment member connected to the piston rod of the master piston and cylinder unit, the shuttle element being displaceable within limits with respect to the housing cylinder, its extent of movement from zero displacement to maximum displacement being controlled by the positioning of the abutment member, while a control piston connected via a connecting rod to the piston rod and/or piston head of the slave piston and cylinder unit is housed within the cylindrical body member of the shuttle element and within limits is axially displaceable within the cylindrical body member, the connecting rod passing through an end wall of the shuttle element remote from the end wall adapted to engage the abutment member, and porting to facilitate external control functions and provide flow paths to admit and/or exhaust pressure fluid.

Porting is provided in both end walls of the housing cylinder and may also conveniently be provided through the latter's cylindrical body member, for example in such a position as to remain within the displaceable limits of the opposing faces of the shuttle element's end walls.

Flow paths are provided via drillings within the end walls of the shuttle element and pipes extramural to the latter's cylindrical body member; one connecting the full bore side of the control piston with the port(s) in that end wall of the housing cylinder adjacent to the slave piston and cylinder unit; a second, connecting the annulus side of the control piston with the port(s) in that end wall of the housing cylinder adjacent to the master piston and cylinder unit, via the abutment member, the latter being apertured for unrestricted fluid transmission therethrough.

Conveniently, a third flow path may be provided, in which case for example drillings and a plunger valve in each of the end walls of the shuttle element may be provided, joined by a pipe extramural to the shuttle element's cylindrical body member and by further drillings, on the downstream side of the plunger valve within that end wall of the shuttle element adjacent to the abutment member, and finally via the, otherwise isolated, annular chamber existing between the end walls of the shuttle element and extra-mural to the latter's cylindrical body member; one valve being opened by, and as, the annulus face of the control piston meets the shuttle element's annulus end wall, the other valve being opened by, and as, the outer face of the shuttle element's full bore end wall meets the abutment member; such that concurrent actuation of both plunger valves will connect the port(s) in that end wall of the housing cylinder adjacent to the slave piston and cylinder unit with the port(s) in the housing cylinder's cylindrical body member, for example to allow a line pressure signal to pass for the purposes of sequence control. Thus the housing cylinder may have three ports but preferably six are provided, the additional ports being for external control functions.

Preferably, the master and slave piston and cylinder units are both low pressure oil hydro/pneumatic systems conveniently incorporating 2-position control valves, whilst the fluid preferably employed in the housing cylinder and shuttle element is air.

Conveniently, and for monitoring seal and/or gland condition, and/or to avoid any question of pressurised air contaminating the low pressure oil systems, short-length radially-apertured coaxial spacing pieces may be fitted between the housing cylinder's end walls and the end walls of their adjacent master and/or slave piston and cylinder units; in which case the spacing pieces may have substantial internal annular clearance with the rod passing through them, whilst a short length of the latter will preferably be visible via the radial apertures, thus providing sight, sound and feel detection, in work.Where the position of the abutment member is to be varied by the direct mechanical application of an external movement to the outer rod of the master piston and cylinder unit, such unit will be double-ended, but where external movement is to be applied to the rod of a remote master piston and cylinder unit, both master units will be singleended; the relative position of the one being set up on the other by closed-circuit displacement transfer.

Where there is to be direct mechanical application of the variable movements of the outer rod of the slave piston and cylinder unit; as relayed to the latter by the control piston; the slave unit will be double-ended, but where external movement is to be provided by the rod of a remote slave piston and cylinder unit, both slave units will be single-ended; the relative position of the one being set up on the other by closed-circuit displacement transfer.

It is preferred that the ratio of the diameter of the piston rods to the diameter of the cylinder bores should be the same, both in the case of the shuttle element and the master and slave, piston and cylinder units, and any remote master and/or slave piston and cylinder unit(s), and that each of the pistons and the internal end walls of all such piston and cylinder units, should all have smooth faces at 90 to piston rod centre line. Where these parameters are met, it can be shown that the ratio of displaceable volume, per unit of stroke length, between the full bore side of a single-ended piston and cylinder unit and the annulus side of such unit will be the same, irrespective of the bore of the cylinder. For the purposes of this description, such piston and cylinder units are termed 'compatible'.

For example, single-ended piston and cylinder units of 3 inch, 6 inch and 9 inch bore, having rods of 1 inch, 2 inch and 3 inch diameter respectively, all have a rod : bore/diameter, ratio, of 1:3 and all will be found to have a 'full-to-annuíus-side-bore/volume', ratio, of 1.1 25:1, per unit of stroke length.Thus for example, (with "at 3. 1415927) 'compatible' cylinder (A), having a 6 inch bore x 2 inch rod, full bore volume is 28.274334 per inch of stroke and annular volume is 25.132742 per inch of stroke (i.e.: 1.1 25:1) and 'compatible' cylinder (B), having a 3.75 inch bore X 1.25 inch rod, full bore volume is 11.044661 per inch of stroke and annular volume is 9.817477 per inch of stroke (i.e.: also 1.1 25:1); it will be seen that: Full bore A volume Annular A volume = = 2.56 Full bore B volume Annular B volume Let (A) have a 9.25 inch stroke and (B) no greater than 23.68 inch stroke (ie.: 9.25 X 2.56 = 23.68); connect the two full-bore sides by pipe and the two annular sides by a second pipe; have both pipes pass 'through' ONE: 2-position/4-port/pilot-open/spring-close/flow valve, (pipes, valve, fittings and ports should not be less than half inch i.d.) fully extend one unit's rod and fully retract the other; fill the complete, closed-circuit, system with oil.

Let (A) be the slave piston and cylinder unit of a modular "stroke variation relay" device; conveniently one of several identical units working in synchronization from one programme source and all housed in a free-standing cabinet; and let (B) be a remote slave piston and cylinder unit, mounted to and controlling the articulation of one link of a heavy duty robot arm.

(Note however that (B) could be any 'compatible' unit, for example with bore ranging from 9 4 inch to 12 inches and with respective stroke lengths ranging down from several yards to 2 inches; these sizes being based on the assumption that (A) is 6 inches bore X 9.25 inch stroke).

Thus, with both the slave and the remote slave piston and cylinder units located and locked in a previously selected position, conveniently sustaining a designed work load, and with the housing cylinder and shuttle element at zero p.s.i.g. and their control ports open, the sequence of operation where a double-ended master unit is being used is as follows:- (a) Actuation of the controls of the master piston and cylinder unit allows an external low energy, signal source to slide the eternal piston rod of the master unit, and hence the abutment member, to the next required location; note: this may or may not displace the shuttle element but it will NOT move the control piston.

(b) De-actuation of the controls of the master piston and cylinder unit locks the abutment member in position.

(c) Actuation of the controls of the housing cylinder and shuttle element applies pressure fluid simultaneously, to both the annular outer face of the shuttle element and the full bore side of the control piston, via their port(s) and/or bores, and will either cause the shuttle element to maintain its pressure contact with the abutment member, or the control piston to maintain its pressure contact with the annulus end wall of the shuttle element; dependent upon whether the device is to relay (further) extension or (further) retraction of the slave piston rod.

(d) Actuation of the controls of the slave and remote slave piston and cylinder units unlocks the control piston whilst the uninterrupted and continued admission of pressure fluid to the housing cylinder and shuttle element will cause the (load sustaining) remote slave piston rod to be relocated by displacement transfer, directly, positively and accurately-free from any tendency to initial directional hesitation-in its new, pre-selected position.

(e) De-actuation of the controls of the slave and remote slave piston and cylinder unit locks their piston rods in their new (fail-safe) position.

(f) De-actuation of the controls of the housing cylinder and shuttle element opens their control ports and returns them to zero p.s.i.g. and completes the operating cycle.

Difficulties have been experienced in prior art proposals concerning 'displacement transfer'.

These have involved contamination of oil by pressurised air in cases where 'non-compatible' units have meant that dissimilar volumes of oil were being transferred and (air-pressurised) volume compensating reservoirs have, typically, been incorporated, in most cases with linepressure air actually in contact with the oil, inevitably resulting in aeration problems and accentuating the imbalance of liquid volumes. Furthermore, wherever an imbalance of liquid volume is allowed to occur, in such a system, unequal pressures are set up making leak-tight sealing difficult to maintain. Another source of difficulty, often overlooked, has been uneven signal response in multi-valve circuits, setting up shock pressures.

In so far as the present invention is concerned with a displacement transfer system, like volumes are being transferred at like pressures. No 'reservoirs' are required and there is no proximity of pressurised air to the oil circuits to allow of any contamination. One flow valve is used, per circuit, specifically to avoid 'shock' from uneven signal response. Finally, a 1.1 25:1 heat/expansion compensating device prevents undue pressure build-up, in work.

The master and slave piston and cylinder units and the housing cylinder may all be arranged co-axially or alternatively the overall length of the device may be reduced by a re-arrangement of the various elements. Conveniently, the end walls of the shuttle element may be secured to its cylindrical body member by a plurality of parallel tie rods extending between the end walls, in which case each end wall may carry a buffer member externally of the cylindrical body member to provide clearance for tie rod nuts.

Similarly, the housing cylinder may be provided with end walls secured by a plurality of parallel tie rods. Similarly, the master and slave units may be provided with end walls secured by a plurality of parallel tie rods.

The invention will now be described in greater detail, by way of examples, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic longitudinal sectional view through a first embodiment of stroke variation relay device in accordance with the present invention; Figure 2 is a longitudinal sectional view, to a larger scale, of the shuttle element of Fig. 1 rotated to show a third flow path; Figure 3 is an isometric view of the spacing piece of Fig. 1 with the rod omitted for clarity; Figure 4 is a front elevation of Fig. 3 showing the rod; Figure 5 is a side elevation of Fig. 3 showing the rod; Figure 6A corresponds generally to Fig. 1 but shows a second embodiment of stroke variation relay device in accordance with the present invention;; Figures 6B to 6D show various operational positions of the device of Fig. 6A to further extend the remote slave unit; Figures 7A to 7D show various operational positions of the device of Fig. 6A to partially retract the remote slave unit, and Figure 8 details part of the hydraulic circuit for the embodiment of Figs. 6A to 7D.

In both embodiments, like components are accorded like reference numerals.

A stroke variation relay device 1 comprises a master piston and cylinder unit 2 and a slave piston and cylinder unit 3, both units being oil filled. The master piston and cylinder unit 2 comprises a cylinder 4, a piston 5 slidably located within the cylinder 4, a first co-axial piston rod 6 connected to the piston 5 and extending in one direction away from the piston 5 and through an end cap 7 of the cylinder 4, and a second co-axial piston rod 8 also connected to the piston 5 but extending in the opposite direction away from the piston 5 and through an end cap 9 of the cylinder 4.Both end caps 7 and 9 are provided with ports 10 for the admission or exhaust of oil from annulus chambers 11 and 1 2 to each side of the piston 5, under the control of a valve 1 3. The slave piston and cylinder unit 3 is almost identical to the master piston and cylinder unit 2 and suffix A has been added to the reference numerals of the slave piston and cylinder unit 3.

A housing cylinder 14 is common to, and co-axial with, both master and slave piston and cylinder units 2 and 3, the housing cylinder 14 having an end cap 1 5 to which the master piston and cylinder unit 2 is attached via an interposed spacing piece 1 6 detailed in Figs. 3 to 5, and an end cap 1 7 to which the slave piston and cylinder unit 3 is attached via another interposed spacing piece 16. The piston rod 8 passes through the adjacent spacing piece 16 and through the end cap 1 5 and terminates in an abutment 1 8 slidable within the housing cylinder 14.The piston rod 8A passes through the adjacent spacing piece 16 and through the end cap 1 7 and terminates in a control piston 1 9 which is contained within a shuttle element 20 itself contained within the housing cylinder 14 and having an end wall 21 through which the piston rod 8A passes, and an end wall 22, both end walls making sealing contact with the internal periphery of the housing cylinder 14.

The end cap 1 5 has a port 23, and the end cap 1 7 has a port 24, while a port 25 through the housing cylinder 14 communicates with the annular area 26 defined between the end walls 21 and 22 of the shuttle element 20. The end wall 21 has a port 27 connected to a conduit 28 in turn connected to a port 29 in the end wall 22. The end wall 21 also has a port 30 connected to a conduit 31 in turn connected to a port 32 in the end wall 22. As shown in Fig.

2, a third fluid flow path is provided by a drilling 33 in the end wall 21 housing a plunger valve 34, and a drilling 35 in the end wall 22 housing a plunger valve 36. The valve 34 blocks or unblocks a port 37 in the end wall 21 while the valve 36 blocks or unblocks a port 38 in the end wall 22. The port 37 communicates with the area between the end wall 21 and the end cap 17, while the port 38 communicates with the area 26, both ports being connected by a common conduit 39.

Operation of the device of Figs. 1 to 5, where single-ended master and slave piston and cylinder units are shown, is as follows. Firstly, Fig. 1 is illustrated in a non-operative position, for to be operative the end wall 22 would be in contact with the abutment member 1-8 and the control piston 1 9 would be in contact with the end wall 21.From an operative position a situation in which the slave piston and cylinder unit 3 is located and locked in a previously selected position, sustaining a designed work load, and with no air pressure applied to either the housing cylinder or shuttle element, the controls of the master piston and cylinder are actuated so that by means of the valve 1 3 the master piston and cylinder unit is unlocked and thereafter an external force is applied to the piston rod 6 to displace the latter and hence the abutment member 1 8 to the next required location, which displacement may or may not displace the shuttle element 20. The head 5 is then locked in position upon deactuation of the valve 13.The controls of the housing cylinder 14 and shuttle element 20 are then actuated via port 24 firstly to act on the end wall 21 and secondly via port 27, conduit 28 and port 29, to act on the control piston 1 9. After a predetermined pressure has been applied to both the control piston 1 9 and the shuttle element 20, the controls of the slave piston and cylinder unit 3 may be actuated to unlock the latter by operation of the valve 1 3A with the continued admission of air via port 24 to both the control piston 19 and the shuttle-element 20. The control piston 19 is thereby unlocked and hence the piston rod 6A is displaced e.g. to the left of Fig. 1, as indicated in dotted line, if the abutment member 1 8 has been moved to the left.It is of course important to ensure that the slave piston and cylinder unit 3 is not prematurely locked in position prior to the control piston 1 9 and shuttle element 20 completing their displacements and the plunger valves 34 and 36 ensure this, as both must be unseated, the valve 34 by being struck by the control piston 1 9 and the valve 36 by striking the abutment member 18, before control valve 1 3A may be de-actuated to lock the slave piston and cylinder unit 3 in its new position. After this the housing cylinder 14 and shuttle element 20 are de-pressurised, the spacing pieces 16 ensuring that air/oil contamination cannot occur by any leakage through end caps 15, 17, 9 and 9A.

Considering now the embodiments of Figs. 6A to 8 where single-ended slave and remote slave piston and cylinder units are shown, the ratio of the diameter of the piston rods to the diameter of the cylinder bores are the same, both in the case of the shuttle element and the master and slave, and the remote slave, piston and cylinder units and each of the pistons and the internal end walls of the master slave and remote slave, piston and cylinder units all have smooth faces at 90 to piston rod centre line, in which case the ratio of displaceable volume, per unit of stroke length, between the full bore side of a single-ended piston and cylinder unit and the annulus side of such unit will be the same, irrespective of the bore of the cylinder and hence it is possible to employ the slave piston and cylinder unit 3 not to effect a work function by the mechanical application of piston rod 6A, as in the case of the first embodiment, but to provide this by the rod 6B, of a single-ended remote slave piston and cylinder unit 3A. As this unit is almost identical to the master and slave units 2 and 3, the suffix B has been added to the same reference numerals. It will be observed that the annulus area 40 of the slave unit 3 is connected to annulus area 41 of the remote slave unit 3A, while full bore area 42 of the slave unit 3 is connected to full-bore area 43 of the remote slave unit 3A through an enlarged control valve 1 3B, as shown diagrammatically in Fig. 8. The mode of operation of the device 1 is the same as for the first embodiment.

In Fig. 6A, both master, slave and remote slave piston and cylinder units 2, 3 and 3A respectively are all locked. In Fig. 6B the master, piston and cylinder unit 2 has been unlocked and displaced, by actuating the valve 13, to re-position the abutment member 18, re-locking of the master, piston and cylinder unit 2 being indicated in Fig. 6C. After pressure at the port 24 and in the area 26 has reached a predetermined value, the valve 1 3B can be actuated, so that the control piston 1 9 is free to be re-positioned by the air pressure acting on it. This displaces the piston 5A which in turn displaces fluid from area 42 to area 43 and from area 41 to area 40 to displace the piston rod 6B to the left as indicated in Fig. 6D in which position the plunger valves 34 and 36 will have been tripped whereby de-actuation of the valve 1 3B again becomes possible to lock the slave and remote slave piston and cylinder units 3 and 3A respectively in their new positions.

In Figs. 7A to 7D, similar movements occur, but the sequence is shown for retracting the piston rod 6B in contrast to extending this, as shown in Figs. 6A to 6D.

Claims (20)

1. A stroke variation relay device for fluid powered piston and cylinder units comprising a master piston and cylinder unit, a slave piston and cylinder unit, and a housing cylinder common to both the master and the slave cylinders, the housing cylinder containing a shuttle element.comprising two axially spaced end walls connected by a cylindrical body member, which shuttle element makes sealing contact with the housing cylinder, the latter also containing an abutment member connected to the piston rod of the master piston and cylinder unit, the shuttle element being displaceable within limits with respect to the housing cylinder, its extent of movement from zero displacement to maximum displacement being controlled by the positioning of the abutment member, while a control piston connected via a connecting rod to the piston rod and/or piston head of the slave piston and cylinder unit is housed within the cylindrical body member of the shuttle element and within limits is axially displaceable within the cylindrical body member, the connecting rod passing through an end wall of the shuttle element remote from the end wall adapted to engage the abutment member, and porting to facilitate external control functions and provide flow paths to admit and/or exhaust pressure fluid.

2. A device as claimed in Claim 1, wherein porting is provided in both end walls of the housing cylinder.

3. A device as claimed in Claim 1 or Claim 2, wherein porting is provided through the cylindrical body member of the housing cylinder.

4. A device as claimed in any preceding Claim, wherein flow paths are provided via drillings within end walls of the shuttle element and pipes extra-mural to the latter's cylindrical body member; one connecting the full bore side of the control piston with the port(s) in that end wall of the housing cylinder adjacent to the slave piston and cylinder unit; a second, connecting the annulus side of the control piston with the port(s) in that end wall of the housing cylinder adjacent to the master piston and cylinder unit, via the abutment member, the latter being apertured for unrestricted fluid transmission therethrough.

5. A device as claimed in Claim 4, wherein a third flow path is provided by drillings and a plunger valve in each of the end walls of the shuttle element, joined by a pipe extra-mural to the shuttle element's cylindrical body member and by further drillings, on the downstream side of the plunger valve within that end wall of the shuttle element adjacent to the abutment member, and finally via the, otherwise isolated, annular chamber existing between the end walls of the shuttle element and extra-mural to the latter's cylindrical body member; one valve being opened by, and as, the annulus face of the control piston meets the shuttle element's annulus end wall, the other valve being opened by, and as, the outer face of the shuttle element's full bore end wall meets the abutment member; such that concurrent actuation of both plunger valves will connect the port(s) in that end wall of the housing cylinder adjacent to the slave piston and cylinder unit with the port(s) in the housing cylinder's cylindrical body member.

6. A device as claimed in Claim 5, wherein the housing cylinder is provided with six ports.

7. A device as claimed in any preceding Claim, wherein the master and slave piston and cylinder units are both low pressure oil hydro/pneumatic systems.

8. A device as claimed in Claim 7, wherein the master and slave piston and cylinder units both incorporate two-position control valves.

9. A device as claimed in any preceding Claim, wherein the fluid employed in the housing cylinder and shuttle element is air.

1 0. A device as claimed in any preceding Claim, wherein short-length radially-apertured coaxial spacing pieces are fitted between the housing cylinder's end walls and the end walls of their adjacent master and/or slave piston and cylinder units. y

11. A device as claimed in any preceding Claim, wherein the ratio of the diameter of the piston rods to the diameter of the cylinder bores is the same, both in the case of the shuttle element and the master and slave, piston and cylinder units and any remote master and/or slave piston and cylinder unit(s).

1 2. A device as claimed in any preceding Claim, wherein each of the pistons and the internal end walls of the master and slave, piston and cylinder units and any remote master and/or slave piston and cylinder unit(s) all have smooth faces at 90 to piston rod centre line.

1 3. A device as claimed in any preceding Claim, comprising a heat/expansion compensating device for the fluid(s) involved.

14. A device as claimed in any preceding Claim, wherein the master and slave piston and cylinder units and the housing cylinder are arranged co-axially.

1 5. A device as claimed in any one of Claims 1 to 13, wherein the master and slave piston and cylinder units and the housing cylinder are arranged side by side.

16. A device as claimed in any preceding Claim, wherein the end walls of the shuttle element are secured to its cylindrical body member by a plurality of parallel tie rods extending between the end walls.

1 7. A device as claimed in Claim 16, wherein each end wall of the shuttle element carries a buffer member externally.

1 8. A device as claimed in any preceding Claim, wherein the housing cylinder is provided with end walls secured by a plurality of parallel tie rods.

19. A stroke variation relay device for fluid powered piston and cylinder units substantially as hereinbefore described with reference to Figs. 1 to 5 of the accompanying drawings.

20. A stroke variation relay device for fluid powered piston and cylinder units substantially as hereinbefore described with reference to Figs. 6A to 8 of the accompanying drawings.