GB2140871A - Piston and cylinder actuator control - Google Patents

Abstract

A control arrangement for a pneumatic powered piston and cylinder actuator comprises a control unit 22 for controlling inlet and outlet valves 16, 18 of the opposite ends of the cylinder 10 to control the differential pressure between the opposite sides of the piston 12 and hence move the piston to or maintain the piston at any desired position. The valves are preferably of an oscillatory type, their frequency and/or amplitude of oscillation being controlled by the unit 22, which for this purpose is responsive to a detector 20a, 20b of the piston position, to detectors of the air pressure in the opposite ends of the cylinder and to a positional demand signal. <IMAGE>

Description

SPECIFICATION Piston and cylinder actuator control This invention relates to a control arrangement for a fluid-powered (e.g. pneumatic) piston and cylinder actuator. By way of example, the invention is applicable to pneumatic control system including simple robots.

Hitherto in pneumatic cylinder actuators, the stroke has been fixed and determined for example by mechanical shock absorbers acting as stops for the piston movement. We have now devised an actuator control arrangement having much increased versatility in that the piston can rapidly and accurately be moved to any desired position within its range of movements.

Thus, in accordance with this invention, there is provided a control arrangement in or for a fluidpowered piston and cylinder actuator, comprising means for controlling inlet and outlet valves of the opposite ends of the cylinder to control the differential pressure between the opposite sides of the piston and hence move the piston to or maintain the piston at any desired position.

Preferably the valves are of an oscillatory type, the control exercised on them being their frequency and/or amplitude of oscillation.

An embodiment of this invention will now be described, by way of example only, with reference to the accompanying drawing, the single Figure of which is a schematic diagram of a pneumatic piston and cylinder actuator with its control arrangement.

Referring to the drawing, there is shown an actuator having a cylinder 10 of plastics material and a piston 12 carried by a shaft 14. Each end of the cylinder is provided with oscillatory-type inlet and outlet valves 16, 18. A detector of the actual position of the piston is provided, and is shown in the form of an emitting device 20a carried by the piston and a sensor or pick up 20b carried by the cylinder.

Detectors are also provided for sensing the air pressure in the respective ends of the cylinder.

A position control unit 22 is further provided, responsive to the actual position detector 20 and to the two pressure detectors and employing a microprocessor. The microprocessor is further responsive to a signal representing a desired (e.g. new) position required for the piston in orderto issue command signals controlling the frequency and/or amplitude of oscillation of the valves 16, 18 and hence the rates of flow of air through the respective parts of the cylinder.

In order for example to move the piston from one steady position to another, initially the pressure is equal either side of the piston and firstly the requirement is to maximise the pressure on one side and minimise the pressure on the opposite side of the piston in order to promote maximum acceleration. On approaching the new, desired position, deceleration is required and is achieved by reversing the sense of the pressure differential and progressive variation of this differential is required until the piston arrives at its new position and (in order to maintain that position) the pressure differential is zero. The microprocessor serves to monitor the rate of change of the piston position and the rate of change of the pressure differential, using the information which it receives from the pressure and positional detectors.

Particularly where the actuator is run repeatedly through a program of position changes (which program is stored in a memory for the microprocessor), a memory may be arranged to store certain data monitored throughout each run and to utilise this for the next run in order to improve the control of the actuator in respect of the corresponding position change. This data may comprise the value control frequency and amplitude and the rate of change of position of the piston and rate of change of the pressure differential due to those frequency and amplitude values.

1. A control arrangement in or for a fluidpowered piston and cylinder actuator, comprising means for controlling inlet and outlet valves of the opposite ends of the cylinder to control the differential pressure between the opposite sides of the piston and hence move the piston to or maintain the piston at any desired position.

2. Acontrol arrangement as claimed in claim 1, in which the inlet and outlet valves are of an oscillatory type, their frequency and/or amplitude of oscillation being controlled.

3. A control arrangement as claimed in claim 1 or 2, comprising a detector for sensing the actual position of the piston.

4. A control arrangement as claimed in claim 3, comprising detectors for sensing the fluid pressure in the respective ends of the cylinder.

5. A control arrangement as claimed in claim 4, comprising a position control unit responsive to signals from said detectors and to an applied positional demand signal for controlling said valves.

6. A control arrangement as claimed in claim 5, in which the position control unit includes a microprocessor responsive to signals from said detectors and serving to monitor the rates of change of the piston position and of the pressure differential for generating signals controlling said valves.

7. A control arrangement in or for a fluid powered piston and cylinder actuator, substantially as herein described with reference to the accompanying drawings.

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

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Piston and cylinder actuator control This invention relates to a control arrangement for a fluid-powered (e.g. pneumatic) piston and cylinder actuator. By way of example, the invention is applicable to pneumatic control system including simple robots. Hitherto in pneumatic cylinder actuators, the stroke has been fixed and determined for example by mechanical shock absorbers acting as stops for the piston movement. We have now devised an actuator control arrangement having much increased versatility in that the piston can rapidly and accurately be moved to any desired position within its range of movements. Thus, in accordance with this invention, there is provided a control arrangement in or for a fluidpowered piston and cylinder actuator, comprising means for controlling inlet and outlet valves of the opposite ends of the cylinder to control the differential pressure between the opposite sides of the piston and hence move the piston to or maintain the piston at any desired position. Preferably the valves are of an oscillatory type, the control exercised on them being their frequency and/or amplitude of oscillation. An embodiment of this invention will now be described, by way of example only, with reference to the accompanying drawing, the single Figure of which is a schematic diagram of a pneumatic piston and cylinder actuator with its control arrangement. Referring to the drawing, there is shown an actuator having a cylinder 10 of plastics material and a piston 12 carried by a shaft 14. Each end of the cylinder is provided with oscillatory-type inlet and outlet valves 16, 18. A detector of the actual position of the piston is provided, and is shown in the form of an emitting device 20a carried by the piston and a sensor or pick up 20b carried by the cylinder. Detectors are also provided for sensing the air pressure in the respective ends of the cylinder. A position control unit 22 is further provided, responsive to the actual position detector 20 and to the two pressure detectors and employing a microprocessor. The microprocessor is further responsive to a signal representing a desired (e.g. new) position required for the piston in orderto issue command signals controlling the frequency and/or amplitude of oscillation of the valves 16, 18 and hence the rates of flow of air through the respective parts of the cylinder. In order for example to move the piston from one steady position to another, initially the pressure is equal either side of the piston and firstly the requirement is to maximise the pressure on one side and minimise the pressure on the opposite side of the piston in order to promote maximum acceleration. On approaching the new, desired position, deceleration is required and is achieved by reversing the sense of the pressure differential and progressive variation of this differential is required until the piston arrives at its new position and (in order to maintain that position) the pressure differential is zero. The microprocessor serves to monitor the rate of change of the piston position and the rate of change of the pressure differential, using the information which it receives from the pressure and positional detectors. Particularly where the actuator is run repeatedly through a program of position changes (which program is stored in a memory for the microprocessor), a memory may be arranged to store certain data monitored throughout each run and to utilise this for the next run in order to improve the control of the actuator in respect of the corresponding position change. This data may comprise the value control frequency and amplitude and the rate of change of position of the piston and rate of change of the pressure differential due to those frequency and amplitude values. CLAIMS

1. A control arrangement in or for a fluidpowered piston and cylinder actuator, comprising means for controlling inlet and outlet valves of the opposite ends of the cylinder to control the differential pressure between the opposite sides of the piston and hence move the piston to or maintain the piston at any desired position.

2. Acontrol arrangement as claimed in claim 1, in which the inlet and outlet valves are of an oscillatory type, their frequency and/or amplitude of oscillation being controlled.

3. A control arrangement as claimed in claim 1 or 2, comprising a detector for sensing the actual position of the piston.

4. A control arrangement as claimed in claim 3, comprising detectors for sensing the fluid pressure in the respective ends of the cylinder.

5. A control arrangement as claimed in claim 4, comprising a position control unit responsive to signals from said detectors and to an applied positional demand signal for controlling said valves.

6. A control arrangement as claimed in claim 5, in which the position control unit includes a microprocessor responsive to signals from said detectors and serving to monitor the rates of change of the piston position and of the pressure differential for generating signals controlling said valves.

7. A control arrangement in or for a fluid powered piston and cylinder actuator, substantially as herein described with reference to the accompanying drawings.