GB2188984A - Fluid-operable piston and cylinder - Google Patents

Abstract

A fluid-operable cylinder has at each end a signalling port (17) to a respective one of which a fluid pressure signal is applied only when the piston (6) is at the end of a stroke, the fluid pressure signal being obtained from the pressurised working fluid, for example compressed air, through respective passageways (22, 23) extending between the opposite end faces (7, 8) of the piston (6). The passageways (22, 23) and the ports (17) are valved by respective pairs of poppet valves (30, 20) that are normally closed but the appropriate pair of which is opened when the piston reaches the end of a stroke, whereby the fluid pressure signal is fed to the appropriate port (17). The signal may be used to effect reversal of the piston and/or to effect a sequencing operation in an automatic cycle. <IMAGE>

Description

SPECIFICATION Fluid-operable cylinder The invention relates to a fluid-operable cylinder of the kind comprising a cylinder and a piston movable therein alternately to each end of the cylinder by the application of a pressurised working fluid to one or other end of the cylinder, while permitting fluid to be exhausted from the opposite end of the cylinder and also including means providing fluid pressure signals to indicate the position of the piston in its stroke.

It is known in fluid-operable cylinders of this kind to provide tapping ports at different positions in the length of the cylinder to provide pressure signals responsive to internal pressure within the cylinder at the respective positions to indicate the position of the piston within the cylinder at any instant. However in known cylinders when the piston has reached the end of its stroke, the fluid pressure at a tapping adjacent the end of the cylinder is of necessity equal to the exhaust pressure or is at zero pressure.An object of the invention is to provide a cylinder in which the signalling pressure at an end signalling port for indicating when the piston is at the end of its stroke adjacent that end of the cylinder is derived from the working fluid pressure at the pressure end of the piston, whereby the end position pressure signal is at a pressure greater than exhaust pressure and is therefore of sufficient magnitude to effect, for example, a sequencing signal to reverse the stroke of the piston where an automatically repeated cycle is required.

According to the invention, a fluid-operable cylinder of the aforesaid kind includes at least one end-of-stroke signalling port to which a fluid pressure signal is applied only when the piston is at the respective end of its stroke, the fluid pressure signal being obtained from the pressurised working fluid in the opposite end of the cylinder through a passageway extending from one end face to the other end face of the piston and controlled by valve means, said valve means being normally closed and only open when the piston is at said respective end of its stroke.

Preferably there is an end-of-strolte signalling port at each end of the cylinder and the valve means comprises a first poppet valve in each of a pair of end walls of the cylinder in a passageway extending between the interior of the cylinder and the respective end-of-stroke signalling port, each first poppet valve being normally closed to the interior of the adjacent end of the cylinder and having an operating plunger engageable by the piston when the piston has reached the respective end of its stroke, thereby to open said first poppet valve to permit the respective end-of-stroke signalling port to communicate with the interior of the respective end of the cylinder, and a pair of oppositely-acting second poppet valves, each positioned in a passageway extending between the end faces of the piston and having an operating plunger extending from opposite end faces of the piston and each engageable with a respective end wall of the cylinder when the piston has reached one or other end of its stroke, both second poppet valves being closed except when the piston has reached one or other end of its stroke, when the plunger of one of the second poppet valves will be depressed by engagement against the adjacent end wall of the cylinder, thereby to open the respective second poppet valve to permit pressurised working fluid to flow past the open second poppet valve from the pressure end of the cylinder to the exhaust end thereof and then through the adjacent first poppet valve which has also been opened by the piston having reached the respective end of its stroke.

Each end-of-stroke signalling port may have an associated exhaust or vent port to which it is arranged to be connected by the respective first poppet valve when the latter has returned to its normally-closed position with respect to the interior of the cylinder on movement of the piston from the respective end-of-stroke position towards the opposite end of the cylinder. By way of example, a fluid-operable cylinder in accordance with the invention is now described with reference to the accompanying drawing which is an axial section through the cylinder.

Referring to 'the drawing, the cylinder comprises a cylindrical wall 1 closed at each end by end closure blocks 2, 3, each having internal end faces 4, 5 respectively. A piston 6 is movable within the cylinder between the two end faces 4 and 5, that is between two endof-stroke positions in which an end face 7 or 8 of the piston 6 is engageable with or is closely adjacent the respective cylinder end face 4 or 5 respectively. The piston has axial extensions 9, 10 which are slidable within 0ring seals 11, 12 in the end blocks 2, 3 respectively to open or close the respective internal end space of the cylinder to working fluid and exhaust ports 13, 14 in each end block 2, 3 to enable the piston to be reciprocated between its end-of stroke positions.

The piston 6 and its axial extensions 9, 10 are mounted on a co-axial piston rod 15 which extends through the end block 2 to provide an external end portion 16 by which the piston rod 15 is connectable to an external member to be driven linearly.

Each end block 2, 3 has an end-of-stroke signalling port 17 (also indicated E and F re spectively). Alongside each signalling port 17, there is a corresponding signal exhaust port or vent 18 (also indicated H and G respectively).

Each pair of signalling and signal exhaust ports 17, 18 communicate with a duct 19 in the respective end block 2, 3 and containing a three-port, two-way poppet valve 20 (also indicated as J and C respectively). Each of the poppet valves 20 has a spring-biased operating plunger 21 which normally projects from the respective end face 4, 5 except when it has been depressed by the respective piston end face 7, 8 when the piston 6 is in one or other of its end-of-stroke positions. When the plunger 21 of a valve 20 is not depressed, the signalling and exhaust ports 17, 18 communicate with each other and the duct 19 is closed with respect to the interior of the cylinder, as shown for the left-hand poppet valve J.When the piston 6 is in an end-of-stroke position and the plunger 21 of a valve 20 is depressed, the exhaust port 18 is closed to the adjacent signalling port 17 and the signalling port 17 communicates through the duct 19 with the interior of the cylinder, as shown for the right-hand poppet valve C.

The piston 6 contains two parallel passageways 22, 23 each extending between the opposite end faces 7, 8 of the piston 6 and terminating in a pair of annular galleries 24, 25 defined between 0-rings 26, 27 and 28, 29 located in grooves in the end faces 7, 8.

The passageways 22, 23 each contain an oppositely-acting two-port, two-way poppet valve 30 each having an operating plunger 31 extending one from each of the piston end faces 7, 8. These two valves 30 are also indicated as poppet valves B and D. The valves 30 are normally maintained closed by springs 32; but in one or other of the end-ofstroke positions of the piston 6, one of the plungers 31 is depressed to open the respective passageway 22, 23. In the drawing, the valve B is closed and the valve D is open.

When the piston is in an intermediate postion between the end-of-stroke positions, all four poppet valves B,D,C,J are closed with respect to the interior of the cylinder and each signalling port E,F communicates with its adjacent exhaust port G,H. Therefore no signalling pressures are present at the ports E,F.

When the piston 6 is in the right-hand endof-stroke position as illustrated, the valves D and C are open and thus pressurised working fluid in the cylinder at the left-hand end of the piston 6 passes through the open valve D and passageway 23 in the piston 6 into the annular gallery 25 to the open duct 19 of the valve C and then to the signalling port F. The valve C, in this position, is closed to the exhaust port G. The valve B is closed. Also the valve J is in its closed position in which the signalling port E communicates with the exhaust port H. Therefore no signalling pressure is present at the port E.

When the piston 6 is in the left-hand endof-stroke position, opposite to that illustrated, the valves B and J are open and thus pressurised working fluid in the cylinder at the righthand end of the piston 6 passes through the open valve B and passageway 22 in the piston 6 to the open duct 19 of the valve J and then to the signalling port E. The valve J, in this position, is closed to the exhaust port H.

The valve D is closed. Also the valve C is in its closed position in which the signalling port F communicates with the exhaust port G.

Therefore no signalling pressure is present at the port F.

Therefore in both end-of-stroke positions of the piston, working fluid from the pressure end of the piston is passed through the piston from one end thereof to the other and applied to the opposite signalling port. This high pressure signal may be used to effect reversal of the piston or to effect movement of another valve, thereby, where required, to effect a sequencing operation in an automatic cycle.

The fluid-operable cylinder may be used with any required working fluid, e.g., a hydraulic fluid or compressed air. The cylinder may be any kind of actuator having a reciprocatable piston e.g., a linear piston actuator, as shown, a rotary actuator, a cable-operating cylinder or a rod-less cylinder.

Although the cylinder illustrated has an endof-stroke signalling port at each end, the endof-stroke signalling port may be provided at one end only. In thse case, there would be only one valve 20 and only one passageway 22 or 23 in the piston containing only one valve 30.

Claims (6)

1. A fluid-operable cylinder comprising a cylinder and a piston movable therein alternately to substantially each of the cylinder by feeding a pressurised working fluid into one or other end of the cylinder while permitting fluid to exhaust from the opposite end of the cylinder, characterised in that the cylinder includes at least one end-of-stroke signalling port to which a fluid pressure signal is applied only when the piston is at the respective end of its stroke, the fluid pressure signal being obtained from the pressurised working fluid in the opposite end of the cylinder through a passageway extending from one end face to the other end face of the piston and being controlled by valve means, said valve means being normally closed and only open when the piston is at said respective end of its stroke.

2. A fluid-operable cylinder as claimed in claim 1 wherein the valve means comprises a first poppet valve located in said passageway in the piston, the poppet valve being normally closed and having an operating plunger engageable with a respective end wall of the cylinder when the piston substantially reaches the respective end of its stroke, thereby to open the poppet valve.

3. A fluid-operable cylinder as claimed in claim 2 wherein the valve means further comprises a second poppet valve located in a passageway extending between the interior of the cylinder and the signalling port, said second poppet valve normally being closed and having an operating plunger engageable by the piston when the piston substantially reaches the respective end of its stroke, thereby to open the second poppet valve.

4. A fluid-operable cylinder as claimed in claim 3 wherein the signalling port has an associated exhaust port to which it is arranged to be connected by the second poppet valve when the latter is returned to its normally closed position on movement of the piston from the respective end-of-stroke position towards the opposite end of the cylinder.

5. A fluid-operable cylinder as claimed in any one of claims 1 to 4 wherein there is an end-of-stroke signalling port at each end of the cylinder, to which ports an end-of-stroke fluid pressure signal is alternatively applied during reciprocating movement of the piston within the cylinder.

6. A fluid-operable cylinder substantially as herein before described with reference to and as illustrated in the accompanying drawing.