CONTROLLING FLUID ACTUATED PISTON AND CYLINDER DEVICES

Abstract: A fluid actuably piston and cylinder device arranged to act as an electrical switch so that the device can be controlled or monitored comprising a piston (2) and piston rod (3) which is electrically insulated from the cylinder (1) while the piston is spaced from the ends of the cylinder and which is electrically connected to at least a portion of the cylinder when the piston is at an end position in the cylinder, the electrical connections associated with the piston and with the said portion of the cylinder enabling an electrical voltage to be applied across the piston and cylinder.

Description: CONTROLLING FLUID ACTUATED PISTON AND CYLINDER DEVICES TECHNICAL FIELD The invention relates to fluid actuated piston and cylinder devices. More particularly, but not exclusively, the invention relates to the control of compressed air actuat.ed piston and cylinder devices. BACKGROUND ART It is known to control such " devices pneumatically by means of control valves. ounted at each end of the cylinder. Such an arrangement doubles or trebles the number of fluid lines associated with the device and an . ' automatic machine employing several such devices therefore requires a large and unwealdy number of such lines. More importantly devising the circuitry necessary for correct sequential control of the various operations of the piston and cylinder devices of the automatic machine, using fluid actuated switches operating in "cascade", involves many hours of skilled labour. This problem is particularly acute where "one-off" automatic machines are involved since for each different machine a unique circuit will need to be devised. This problem can be mitigated by controlling all of the piston and cylinder devices of the machine by means of any one of a number of known multi-channel, electrical or pneumatic programmers. Such an arrangement requires however the use of piston and cylinder devices provided with means for sensing when the piston is in an end position in the cylinder. It is known to provide piston and cylinder devices with micro-switches or micro-valves for this purpose but such devices are too expensive for many applications. DISCLOSURE OF INVENTION We have now discovered that it is possible to make a fluid actuated piston and cylinder device operate as an electrical switch without the necessity of separate micro- switches. According to the invention there is provided a fluid actuable piston and cylinder device comprising a piston and piston rod which is electrically insulated from the cylinder while the piston is spaced from the ends of the cylinder, and which is electrically connected to at least a portion of the cylinder when the piston is in an end position in the cylinder, and electrical connections associated with the piston and with the said portion of the cylinder enabling an electrical voltage to be applied across the piston and cylinder. Preferably the cylinder is electrically connected to the associated machine frame which is maintained at a known (e.g. earth) potential while the piston is connected to a voltage source. For this latter purpose an electrical contact may be provided on the cylinder body, but insulated therefrom, for sliding contact with the piston rod. Alternatively the piston may be connected to the voltage source via a flexible (preferably insulated) lead connected to the piston rod at its end remote from the piston. Such arrangements will of course require the piston and rod to be electrically interconnected, but this is usually the case in practice. One convenient way of electrically insulating the piston and rod from the cylinder is by employing conventional plastics seals. However, in most cylinder devices the nose bearing which supports the piston rod is electrically connected to the cylinder. It is necessary for the purpose of this BVRE OMPI invention that this nose bearing is insulated from the cylinder body e.g. by being mounted in a plastics bush. It will usually be necessary in addition to insulate the piston rod from the part of the machine to which it is connected and further it may be desirable to enclose the piston rod, e.g. in a flexible gaiter, to avoid unintentional earthing of the piston rod. BRIEF DESCRIPTION OF DRAWINGS Typical embodiments of piston and cylinder device are illustrated by way of example in the accompanying drawings in which:- Fig. 1 is a longitudinal section through a piston and cylinder device, and Fig. la is a scrap view of part of a piston and cylinder device. BEST MODE OF CARRYING OUT THE INVENTION In Figure 1 of the drawings a pneumatic piston and cylinder device comprises a cylinder 1 provided with end caps 12 and 13 respectively and in which a piston 2 is slidingly mounted. The piston is connected to a piston rod 3 which extends outside the cylinder and which is sealed to the cylinder by means of a plastics bush 4 in the end cap 13. The piston 2 and rod 3 are electrically conductive but are insulated from the cylinder 1 and end caps 12 and 13 by the bush 4 and by piston seals 7. The cylinder 1 and end caps 12 and 13 are electrically conductive. A flexible wire 9 which is insulated from the cylinder and end caps is connected to the piston rod so that when the piston is in a limiting position at either end of the cylinder 1 an electrical circuit between the cylinder and the wire 9 is completed. The part of the piston rod protruding from the cylinder is covered by an insulating gaiter 5 to 'prevent unwanted earthing of the piston rod and the free end of the piston rod is connected to a machine part to be actuated by the piston and cylinder device by means of an electrically insulating coupling 6 e.g. of plastics. The end cap 12 of the cylinder is provided with an adjustable stroke limiting device in the form of a screw threaded bolt the bolt being electrically conductive. In Figure la of the drawings there is shown a modified piston and cylinder device generally similar to that described with reference to Figure 1 except that the flexible electrically conductive insulated wire 9 has been replaced by an electrical contact which makes sliding engagement with the piston rod and which comprises an electrically conductive spherical member 10 which is resiliently urged into contact with the piston rod 3 by means of a spring 11 which is preferably mounted in the end cap 13 but electrically insulated therefrom the spherical member 10 being electrically connected to an electrical pickup 9 by means of which the circuit can be completed. Where it is desired to sense separately when the piston is at one or other end of the cylinder this can be achieved by insulating one end of the cylinder from the other, e.g. by providing a plastics seal between the body of the cylinder and one end cap thereof, both parts of the cylinder having electrical connection to the control circui It may be advantageous in this case to maintain the piston at earth potential and to apply the voltage to the cylinder and end cap. INDUSTRIAL APPLICABILITY By means of the invention, fluid actuated piston and cylinder devices may be controlled by an electrical or pneumatic programmer the steps of which are initiated by signals from the said devices which arise whenever such said devices move from one end position to the opposite end position, it being unnecessary for the programmer to 'know' which of the two end positions has been reached, but merely that a change of position has taken place. The movement of the piston from one end of the cylinder to the other breaks a circuit and then re-makes it. It is this break and remake of a switch (i.e. the piston/cylinder) that can be used directly or indirectly to operate a stepping relay.

Claims: CLAIMS 1. A fluid actuable piston and cylinder device comprising a piston and piston rod which is electrically insulated from the cylinder while the piston is spaced from the ends of the cylinder, and which is electrically connected to at least a portion of the cylinder when the piston is in an end position in the cylinder, and electrical connections associated with the piston and with the said portion of the cylinder enabling an electrical voltage to be applied across the piston and cylinder. 2. A fluid actuable piston and cylinder device according to claim 1, comprising an electrical contact on the cylinder body, but electrically insulated therefrom, for sliding contact with the piston rod. 3. A fluid actuable piston and cylinder device according to claim 1, wherein the piston is connected to the voltage source via a flexible lead connected to the piston rod at its end remote from the piston. 4. A fluid actuable piston and cylinder device according to any preceding claim, wherein one end of the cylinder is electrically insulated from the other, both parts of the cylinder having electrical connections. 5. A fluid actuable piston and cylinder device according to any preceding claim, wherein one end of the cylinder carries an electrically conductive adjustable stop member arranged to contact the piston to limit movement thereof in one direction. 6. A fluid actuable piston and cylinder device substantial as hereinbefore described with reference to, and as illustrated in, the accompanying drawings. - 0MPI

Inventors: CINIGLIO A, ELLEFSEN A, HADFIELD R
Applicants: CINIGLIO A, ELLEFSEN A, HADFIELD R, ROTAWINDER LTD
Application year: 1979
Main classification: F15B15
IPC codes: F15B15