GB2100473A

GB2100473A - Fluid-governed servosystem

Info

Publication number: GB2100473A
Application number: GB8102863A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-01-30
Filing date: 1981-01-30
Publication date: 1982-12-22
Also published as: GB2100473B

Abstract

A pulse modulated servosystem comprises a fluid-actuated, double-acting piston-cylinder unit (11) and two on-off valves (3, 4) for governing the supply of fluid to said unit (11). Each valve (3, 4) is governed by pulses from a controller (19) and is arranged between a pump (7) and a reservoir (6). Two conduits (9, 15) for supplying fluid to opposite sides of the piston-cylinder unit (11) are branched off from respective fluid connections (5, 8 and 5, 16) between the pump (7) and the valves (3, 4) after respective restrictions (101, 102). Each of the valves (3, 4) is governed by a separate amplifier output signal via a connection (21, 22) from the common controller (19) and any limitation of the accuracy due to inertia of the valves is eliminated by influencing both chambers (10, 14) of the piston-cylinder unit (11). In another embodiment, Fig. 1, not shown, additional electromagnetic valves (1), (2) take the place of restrictions (101), (102), valve (1) being actuated by line (21) and valve (2) by line (22). <IMAGE>

Description

SPECIFICATION Fluid-governed servosystem This invention relates to a servosystem of the type comprising a fluid-actuated, double-acting pistoncylinder unit and two on-off valves for governing the supply of fluid to said unit, in which each valve is pulse-governed and arranged between a high pressure source and a low pressure reservoir for said fluid, two conduits for supplying fluid to the said pistoncylinder unit being branched off from a fluid connection between the said high pressure source and the said valves.

In the known servosystems ofthis type the timelag of the onsff valves causes problems which may be solved by using series connected valves in conduits for the fluid, said valves being governed to partly overlap each other e.g. by phase modulation.

The present invention aims to provide a servosystem which is accurate and reliable in operation and utilises a minimum amount of valves and electronic equipment.

According to the invention, there is provided a servo-system of the type comprising a fluidactuated, double-acting pistoncylinder unit and two on-off valves for governing the supply of fluid to said unit, in which each valve is pulse-governed and arranged between a high pressure source and a low pressure reservoir for said fluid, two conduits for supplying fluid to the said pistoncylinder unit being branched off from a fluid connection between the said high pressure source and the said valves, wherein each of the said conduits for supplying fluid to the said pistoncylinder unit is branched off after restriction means and wherein each of said valves is governed by a separate amplifier output signal from a common controller.

By means of the invention, the pistoncylinder unit can be continuously influenced by pulse trains in both directions so that not only is the time-lag of the valves eliminated, but also the servosystem will operate without friction and react with accuracy during any performance.

The invention will now be further described, by way of example, with reference to the drawings, in which: Fig. 1 shows one embodiment of a servosystem according to the invention; Fig. 2 is a graph showing a valve governing pulse train; Fig. 3 is a graph showing a corresponding pulse train of valve operations; and Fig. 4 shows a second embodiment of a servosystem according to the invention.

In the drawings, like parts are denoted by like reference numerals.

Referring first to the embodiment of Fig. 1,the reference numerals 14 designate four solenoid governed valves, all of them being shown in the "off" position. The valves 1 and 3 form a pair of valves being series connected between a high pressure source - indicated as conduits 5 - and a low pressure reservoir 6 for a fluid. Said fluid is oil in the embodiment shown, but could alternatively be e.g. com- pressed air. The pressure is provided by a pump 7.

The valves 1 and 3 are interconnected by a conduit 8 from which a conduit 9 is branched off and connected to a first variable volume chamber 10 of a double-acting piston-cylinder unit 11. Said unit comprises a piston 12 rigidly connected to a piston rod 13. A second variable volume chamber 14 is connected to a conduit 16 via a conduit 15, the conduit 16 connecting the valves 2 and 4.

The axial position of the piston rod 13 will influence a position indicator 17 giving a signal via a wire 18 to a controller 19. In said controller 19 the signal obtained from the indicator 17 is compared with a governing signal supplied through a wire 20 and corresponding to a desired axial position of the rod 13.

The controller 19 emits two trains of pulses - one through a wire 21 to the solenoids of the valves 1 and 4 and another through a wire 22 to the solenoids of the valves 2 and 3.

Each pulse train is of the type shown in Fig. 2. Here the voltage V is shown as a function of the time t.

During equal periods T the voltage is v, during part to of each period, while it is zero during the remaining part of the period - i.e. T-t1. A solenoid activated valve being influenced by the pulse train of Fig. 2 will perform opening and closing movements as shown in Fig. 3. Here the valve travel is designated by S and a fully opened valve is obtained after a travel distance si. It appears that due to reactance and inertia of a solenoid governed valve, complete opening will be dependent on obtaining a certain proportion between t1 and T.

The servosystem of Fig. 1 is influenced in both directions-in one direction by the pulsesthrough the wire 21 and in the other direction by the pulses through the wire 22. Thus, it will be the difference between the pulse width t1 of the two pulse trains and not the actual width which will determine the function of the servosystem. As the piston 11 is always influenced in both directions the friction in the piston-cylinder unit is eliminated. The most simple system will use the same frequency 1/Tin both pulse trains -one through the wire 21 and the other through the wire 22. The pulses may be emitted alternately through the two wires.

The embodiment shown in Fig. 4 differs from the embodiment shown in Fig. 1 in that the valves 1 and 2 have been replaced by restrictions 101 and 102 connected in series with non-return valves 103 and 104.

This embodiment is cheaper to manufacture, but is somewhat slower in operation. In many applications the slower operation is of no importance. The non-return valves are not necessary for the function of the servosystem, but make it possible to retain the system locked in any desired position by closing the valves 3 and 4.

1. A servosystem of the type comprising a fluidactuated, double-acting piston-cylinder unit and two on-offvalves for governing the supply of fluid to said unit, in which each valve is pulse-governed and arranged between a high pressure source and a low pressure reservoir for said fluid, two conduits for supplying fluid to the said piston-cylinder unit being

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Fluid-governed servosystem This invention relates to a servosystem of the type comprising a fluid-actuated, double-acting pistoncylinder unit and two on-off valves for governing the supply of fluid to said unit, in which each valve is pulse-governed and arranged between a high pressure source and a low pressure reservoir for said fluid, two conduits for supplying fluid to the said pistoncylinder unit being branched off from a fluid connection between the said high pressure source and the said valves. In the known servosystems ofthis type the timelag of the onsff valves causes problems which may be solved by using series connected valves in conduits for the fluid, said valves being governed to partly overlap each other e.g. by phase modulation. The present invention aims to provide a servosystem which is accurate and reliable in operation and utilises a minimum amount of valves and electronic equipment. According to the invention, there is provided a servo-system of the type comprising a fluidactuated, double-acting pistoncylinder unit and two on-off valves for governing the supply of fluid to said unit, in which each valve is pulse-governed and arranged between a high pressure source and a low pressure reservoir for said fluid, two conduits for supplying fluid to the said pistoncylinder unit being branched off from a fluid connection between the said high pressure source and the said valves, wherein each of the said conduits for supplying fluid to the said pistoncylinder unit is branched off after restriction means and wherein each of said valves is governed by a separate amplifier output signal from a common controller. By means of the invention, the pistoncylinder unit can be continuously influenced by pulse trains in both directions so that not only is the time-lag of the valves eliminated, but also the servosystem will operate without friction and react with accuracy during any performance. The invention will now be further described, by way of example, with reference to the drawings, in which: Fig. 1 shows one embodiment of a servosystem according to the invention; Fig. 2 is a graph showing a valve governing pulse train; Fig. 3 is a graph showing a corresponding pulse train of valve operations; and Fig. 4 shows a second embodiment of a servosystem according to the invention. In the drawings, like parts are denoted by like reference numerals. Referring first to the embodiment of Fig. 1,the reference numerals 14 designate four solenoid governed valves, all of them being shown in the "off" position. The valves 1 and 3 form a pair of valves being series connected between a high pressure source - indicated as conduits 5 - and a low pressure reservoir 6 for a fluid. Said fluid is oil in the embodiment shown, but could alternatively be e.g. com- pressed air. The pressure is provided by a pump 7. The valves 1 and 3 are interconnected by a conduit 8 from which a conduit 9 is branched off and connected to a first variable volume chamber 10 of a double-acting piston-cylinder unit 11. Said unit comprises a piston 12 rigidly connected to a piston rod 13. A second variable volume chamber 14 is connected to a conduit 16 via a conduit 15, the conduit 16 connecting the valves 2 and 4. The axial position of the piston rod 13 will influence a position indicator 17 giving a signal via a wire 18 to a controller 19. In said controller 19 the signal obtained from the indicator 17 is compared with a governing signal supplied through a wire 20 and corresponding to a desired axial position of the rod 13. The controller 19 emits two trains of pulses - one through a wire 21 to the solenoids of the valves 1 and 4 and another through a wire 22 to the solenoids of the valves 2 and 3. Each pulse train is of the type shown in Fig. 2. Here the voltage V is shown as a function of the time t. During equal periods T the voltage is v, during part to of each period, while it is zero during the remaining part of the period - i.e. T-t1. A solenoid activated valve being influenced by the pulse train of Fig. 2 will perform opening and closing movements as shown in Fig. 3. Here the valve travel is designated by S and a fully opened valve is obtained after a travel distance si. It appears that due to reactance and inertia of a solenoid governed valve, complete opening will be dependent on obtaining a certain proportion between t1 and T. The servosystem of Fig. 1 is influenced in both directions-in one direction by the pulsesthrough the wire 21 and in the other direction by the pulses through the wire 22. Thus, it will be the difference between the pulse width t1 of the two pulse trains and not the actual width which will determine the function of the servosystem. As the piston 11 is always influenced in both directions the friction in the piston-cylinder unit is eliminated. The most simple system will use the same frequency 1/Tin both pulse trains -one through the wire 21 and the other through the wire 22. The pulses may be emitted alternately through the two wires. The embodiment shown in Fig. 4 differs from the embodiment shown in Fig. 1 in that the valves 1 and 2 have been replaced by restrictions 101 and 102 connected in series with non-return valves 103 and 104. This embodiment is cheaper to manufacture, but is somewhat slower in operation. In many applications the slower operation is of no importance. The non-return valves are not necessary for the function of the servosystem, but make it possible to retain the system locked in any desired position by closing the valves 3 and 4. CLAIMS

1. A servosystem of the type comprising a fluidactuated, double-acting piston-cylinder unit and two on-offvalves for governing the supply of fluid to said unit, in which each valve is pulse-governed and arranged between a high pressure source and a low pressure reservoir for said fluid, two conduits for supplying fluid to the said piston-cylinder unit being branched off from a fluid connection between the said high pressure source and the said valves, wherein each of the said conduits for supplying fluid to the said pistoncylinder is branched off after restriction means wherein each of said valves is governed by.a separate amplifieroutputsignal from a common controller.

2. Aservosystem according to claim 1,wherein non-return valves are connected in series with said restriction means.

3. A servosystem according to claim 1, wherein said restriction means consist of onoff valves.

4. A servosystem according to claim 3, wherein one valve upstream of the branch connection of one conduit to the said pistoncylinder unit and the valve downstream of the branch connection of the other conduit to the said pistoncylinder unit are connected to a first common amplifier output for synchonous governing, and the two remaining valves are connected to a second common amplifier output.

5. A servosystem substantially as described herein with reference to the drawings.