GB2154282A

GB2154282A - Fluid pressure actuators

Info

Publication number: GB2154282A
Application number: GB08403884A
Authority: GB
Inventors: William Brian Holmes; Jack Schofield; Brian John Cave; William Vincent Hammonds
Original assignee: H C H MANUFACTURING Ltd
Current assignee: H C H MANUFACTURING Ltd
Priority date: 1984-02-14
Filing date: 1984-02-14
Publication date: 1985-09-04
Also published as: GB8403884D0

Abstract

The cylinder has a piston 2 within a body 1 constrained to move along a screw by means of a pressure such as pneumatic or hydraulic pressure. The linear motion of the constrained piston imparts a rotary motion to the screw 4 which in turn operates a signal generator 5. This can give the relative position of the piston within the cylinder to a high degree of linear accuracy at any time. When stationary the piston 2 is locked in position by the brake piston 8 and cone 7. The stiffness of the locking system can give controlled operating conditions plus a fail-safe device in the event of loss of operating pressure. <IMAGE>

Description

SPECIFICATION Intelligent cylinders precise control, indication and iodizing in position of fluid operated pistons within cylinders We, H.C.H. Manufacturing Ltd., a Company registered in the United Kingdom at 30 Exchange Street East, Liverpool 2, do hereby declare the invention, for which we pray a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a method and apparatus that enables a piston operating within a cylinder to be positioned at any point within that cylinder, the position of the piston and its rod may also be indicated to a device that records that position. A further device provides locking of the piston and rod in any particular position, during, or at either end of the stroke.This locking action may be internally or externally controlled or be automatic, so if necessary providing a safety factor giving a locked position if the fluid pressure drops to ambient conditions. The device will lock the piston and rod and maintain equilibrium despite the influence of external forces acting upon the apparatus.

The speed of motion of the piston and rod assembly in the cylinder may also be controlled by the application of the braking mechanism or control signal which may be incorporated in this device.

Conventionally linear motion may be imparted to a piston attached to a rod within a cylinder by fluid flowing into the cylinder under the influence of pressure. The fluid may be either gaseous or liquid.

The invention improves this conventional device so extending its use. The apparatus described below gives added capabilities to the system so enabling more versatile functions to be used, particularly in relation to automated systems, usually with digital control.

In cases where the actuating fluid is gaseous, an added disadvantage with conventional devices is that outside forces greatly influence the position of the piston and rod, as the gas is resilient and imparts this property to the device.

Any two or more pistons and cylinders moving in a common system fed from a common pressure source do not stay in unison unless linked directly by mechanical means or by sophisticated control devices.

The signal emanating from the described apparatus may be used to control the motion so giving the desired speed or position of the pistons and rods within the cylinders.

We have examined the requirements for either pneumatic or hydraulic cylinders and propose in this description to show how the apparatus which is the subject of this invention overcomes the deficiencies in conventional systems. Description of a typical application: A piston with rod attached is free to move to either end of a cylinder under the influece of fluid pressure. This may be liquid or gas.

For this example air is chosen as the typical gas application.

In the piston is held a recirculatory ball nut, as the piston is actuated in either linear direction within the cylinder the piston is prevented from rotating by internal or external restraint.

The linear motion so imparted causes the ball screw to rotate.

The screw itself is located longitudinally, but is inheritantly free to rotate either clockwise or anti-clockwise, unless some restraint is applied. This screw carries either a device for imparting a signal or a braking device, or both simultaneously. In this typical example both are taken as being carried on the rotating screw.

A braking piston is actuated in one direction which takes off the braking action and in the opposite direction which applies a braking action to the rotary motion of the screw. The cessation of this rotary motion will cause the piston motion to be arrested, through the action of the nut upon the piston.

By this means the piston can be stopped at any point in its position in the cylinder.

The actuation of the piston in taking off the brake is by a fluid pressure acting on either a circular area or an anulus that preferably are equal to each other, but not necessarily so.

The actuation of the piston to apply the brake is by pressure over the full area or part of the area or by a spring load applied to the piston. The piston itself is restrained from rotating, in this typical case by a dowel in the end cover.

The rotary motion of the screw is imparted to a brake disc or cone upon which the piston acts to give the braking capability to the system. This braking action can, if so desired, override the tendency of the piston to move when air pressure is applied to either side of the piston.

Rotation of the screw imparts a rotary motion to a disc or other device that will generate a signal, in this case digital, to some external or internal apparatus to either record the speed, or amount of motion or position of the piston within the cylinder.

The actuation of braking system can also be by spring load either solely or in conjunction with pressure. This will give a desirable safety device in case of failure of the air pressure.

Description of mechanical construction of a typical pneumatically operated apparatus: The piston (2) moves in cylinder (1) under the influence of air being fed into either port A or B.

When air pressure is applied to port A this pressure is also applied to area X. This actuates the brake piston (8) so clearing it from contact with the brake cone 7. The main piston is then free to move in direction E carrying with it piston rod (18). This motion is imparted through the ball nut (3) to the bail screw (4). The ball screw is located longitudinally, but free to rotate, by means of bearings (14) located in housing (6).

If the pressure is released from port A the piston movement can be stopped by application of the brake by either pressure acting on the brake piston over area Z, or the influence of the spring (13). This application of braking effort has a considerable mechanical advantage over the effort of any influence to move the main piston by either air pressure or influence of external forces on the piston rod.

The same principle applies to motion in the opposite direction, direction W. Air pressure is applied to port B1 and simultaneously to port B2. This pressure is felt over anulus area Y which has a similar effect to applying pressure to area X in that the brake piston is freed from contact with the brake disc or cone. As area Z is, in this particular case, double that of either area X or anulus area Y, the same pressure applied to Z will exert double the force on the brake piston. This means the rotary motion of the ball screw can be stopped by applying a pressure to area Z so stopping the main piston at any particular point and mechanically locking it if thk pressure on area Z is sustained or the spring is loading the brake piston onto the brake cone or disc.

The brake piston is prevented from turning by the dowel (9).

The disc (5) is attached to the ball screw (4) and rotates with it. By any suitable means or as in this case a light sensitive device with a light omission device picks up a signal from the disc so giving a suitable signal to indicate motion or position. This signal can be used either to control the apparatus or to give an indication of its position or state.

The amount of force imparted to the braking system is determined by the pressure balance in relation to area across the brake piston.

This means that the apparatus can be controlled in various states for example, the piston can be stopped from moving or decelerated, varying amounts of stiffness can be applied, so controlling the force of locking or controlling the speed of rotation, and hence the speed of travel of the main piston. General application of the Principle: Any fluid actuated piston within a cylinder may be precisely positioned or controlled during its travel or locked at any point in its stroke or at either end of its stroke In general use this would mainly apply to piston and cylinder assemblies actuated by either a hydraulic fluid or in an air system operated pneumatically.

It will be particularly useful in conjunction with computer controlled systems with the added advantage or the fail safe property imparted by the ability to lock the system either during use or on a system pressure failure.

The braking effort may be applied to the shaft of the ball screw assembly by disc or cone or cylinder.

The sensing of the rotary motion of the ball screw in this case is by recording light variations through a disc, but this may be done by other methods, e.g. magnetic flux changes.

In some cases it may be desirable to incorporate the sensing in with the brake assembly using the rotary part to impart the signal.

The signal so provided may be used to control its speed of motion or to control its speed of motion or to indicate its position within the cylinder.

Claims

1. Apparatus incorporating mechanical devices as described in the foregoing description allows the piston within a cylinder to be precisely controlled by internal or external signals.

2. The piston speed may be controlled by either utilising the signals emanating from the system itself or from an external source.

3. The position of the piston within the cylinder may be determined or indicated, or both, by using the signal so described, or by the influence of the braking system.

4. The piston and rod assembly may be locked at any linear position in the cylinder by means of the braking system which may be actuated by a pressure or a spring load applied to the system.

5. A fluid operated intelligent cylinder which can be made in varying sizes in which the operation of the system is not influenced by mass effect.

5. The apparatus so described enables the piston to be moved in varying or fixed increments in any direction along the length of the cylinder.

6. The system can operate in an hostile environment, e.g. temperature, positive or negative pressure.

7. Size of apparatus is not limited by mass effect.

CLAIMS Amendments to the claims have been filed, and have the following effect: Claims 1 to 7 above have been deleted or textually amended.

New or textually amended claims have been filed as follows:

1. A fluid operated intelligent cylinder allowing a piston movement within a cylinder to be precisely determined, the signal also be used during motion to determine piston speed and direction of travel.

2. A fluid operated intelligent cylinder, in which the position of the piston may be controlled by means of restraining by a brake mechanism and a ball screw and nut, these giving the required mechanical properties to meet its service requirements. This enables the piston to be moved at fixed or varying length along its stroke in either direction.

3. A fluid operated intelligent cylinder which can be positively locked at any point in its stroke, the influence of the brake system being greater than the forces available for movement of the piston within the cylinder, and upon any failure of the fluid pressure a device which may be incorporated would lock safely in its last position the piston within the cylinder.

4. A fluid operated intelligent cylinder which may operate in a hostile environment which may be variations of external temperature or pressure.