GB2152622A - Pneumatic switching devices and linear feed motors incorporating such devices - Google Patents

Abstract

An automatic pneumatic switching device for allowing alternate supplies of pressure to a pneumatic device comprises, an attachment to a supply of pressure, a two position valve for allowing the alternate supply of pressure to two points of a pneumatic device, two reservoirs to which pressure is bled alternately from the supply to said two points depending on the valve position, two pipe connects, one from each reservoir, arranged so that pressure from the reservoir to which pressure is bled acts upon the valve in such a way as to move the valve to its other position when a threshold pressure level is reached, a combined throttle and non return valve for each reservoir to control the air bled into the reservoir and allowing it to freely vent to atmosphere through the valve when the threshold pressure has been reached and the valve moved to its other position. The device is used in a linear motor for driving a pig in a stepwise movement or for pulling a draw line for a communication cable. <IMAGE>

Description

SPECIFICATION Improvements relating to pneumatic switching devices and to linear feed motors incorporating such devices This invention relates to pneumatic switching devices and to linear feed motors incorporating such devices. The invention is especially applicable to duct motors for pulling draw ropes or for propelling probes through a pipe.

A known form of a duct motor comprises a linear actuator carrying an inflatable bladder element at each end; when actuated, the actuator is alternately extended and retracted to move the bladders alternately away from and towards each other. The motor operates by firstly inflating the bladder at the trailing end so that it grips against the wall of the duct then, the actuator is extended to advance the bladder at the leading end, next the leading end is inflated to grip against the wall so completing the cycle of movement. Such linear feed motors possess considerable disadvantages, such as their size, slowness of operation, and liability to be damaged.

To reduce these disadvantages, it has also been proposed to replace the bladders by flexible diaphragms. The actuator itself usually comprises a cylinder and piston mechanism operated by compressed air and the alternate flow of compressed air both for the cylinder and the bladders may be controlled by a pneumatic switching device which relies on pneumatic pressure differential sensors; such switching system give rise, however, to a variety of problems in operation additional to those indicated. For example the operation of the switching device requires a full stroke of the piston for each reciprocation and so it is difficult to travel round sharp bends. The problem of negotiating bends is also encountered when the linear feed motor is being used to pull or push a probe even when the probe head is attached by a universal or flexible coupling.

The object of the present invention is to help overcome the problems associated with the switching devices and motors.

According to the present invention there is provided an automatic pneumatic switching device for allowing alternate supplies of pressure to a pneumatic device comprising; an attachment to a supply of pressure, a two position valve for allowing the alternate supply of pressure to two points of a pneumatic actuator, two reservoirs to which pressure is bled alternately from the supply to said two points depending on the valve position, two pipe connects, one from each-reservoir, arranged so that pressure from the reservoir to which pressure is bled acts upon the valve in such a way as to move the valve to its other position when a threshold pressure level is reached, a combined throttle and non return valve for each reservoir to control the air bled into the reservoir and allowing it to freely vent to atmosphere through the valve when the threshold pressure has been reached and the valve moved to its other position.

According to another aspect of the present invention there is provided a linear feed motor adapted to travel along the inside of a pipe comprising flexible members adapted to a engage the walls of the pipe, an actuator for manipulating the flexible members to cause the motor to travel step wise along the pipe a rod like flexible coupling member connected at one end to a linear feed motor by means of a universal coupling and at the other end to the ancillary module via another universal coupling.

Further according to the invention to reduce problems associated with coupling a probe to the motor, the flexible coupling member is preferably in the form of a tightly coiled tension spring connected at one end of the motor and at the other end to the ancillary module by means of universal joints.

In order that the invention may be more readily understood and carried into effect it will now be described with reference to the accompanying drawings.

Figure 1 shows an example of the linear feed motor with the coupling member fitted to a probe head.

Figure 2 shows diagrammatically the controller of the motor, illustrating the working of a shuttle valve.

In operation this form of invention consists of a linear feed motor, which moves along a pipe or other paths by means of an actuator and deformable diaphragms. An ancillary module may be joined to the feed motor by means of a rod-like flexible coupling member.

The power for the movement of the linear feed motor is provided pneumatically by an automatic switching device which allows the flow of compressed air to alternate ends of the actuator.

Referring to Figure 1, the linear feed motor 20 comprises two pair of closely spaced, resiliently deformable, disc shaped diaphragms 22 and 23 which are clamped between sets of flanges 24 and 25. Each diaphragm is of slightly greater diameter than the inside diameter of the pipe in which it is working. The diaphragms are held in the correct spaced relationship by means of rods 27 and 28, which also couple them to front and rear guide plates 29 and 30, which may be made of a plastic material. The guide plate 29 is rigidly connected to a cylinder 31 and the flanges 25 of the outer of the diaphragms 25 is connected to the piston 32 which slides in the cylinder 31. The cylinder 31 and the piston 32 constitute the linear actuator of the feed motor.Pipe connects 33 and 34 are provided at the ends of the cylinder 31 to allow compressed air to be supplied automatically to opposite sides of the piston 32 in the cylinder by the automatic pneumatic switching device.

When the linear feed motor is pushed into the pipe the diaphragms deform against the wall of the pipe to adopt the profiles shown, which are generally concave as viewed from the trailing end of the motor. As the actuator extends the trailing diaphragms 22 react against the wall and resist return movement whilst the leading diaphragm 23 move forward quite freely. Then as the actuator retracts the leading diaphragm 23 react against the wall and resist return movement whilst the trailing diaphragms are brought up quite freely towards the leading diaphragms. The linear feed motor therefore proceeds in 'stepwise' manner.

The motor may be used for taking a draw line through the pipe; this draw line can then be used for drawing a communication cable through a pipe. A flexible tube may be provided to pass cables through the motor, one end of this tube being fixed to one set of diaphragms and free to slide through the other.

The guide plates 29 and 30 are provided in the motor to assist in directing the motor round a curve in the pipe by sliding along the wall.

The diaphragms may be removed and replaced by one of different sizes dependent upon the pipe in which the motor is working.

In this example the diaphragms are disc shaped but they could be different shapes, for example flexible fingers. The resilience of the diaphragms may be enhanced by spring loading them.

The flanges may be of any rigid material or alternatively the diaphragms may be arranged to be rigid themselves over the central region and flexible over the outer regions, for example by thickening of the material at the central region.

The rod-like coupling member for attaching an ancillary module to the linear feed motor is also shown in Figure 1. A coupling member 35 is rigidly connected to flanges 25 of the outer diaphragm 23 and this passes through an aperture in the protecting plate 30. This forms one member of a universal coupling 36, the other member of which is connected to an elongated rod-like coupling 37. At the end remote from the linear feed motor the rod-like coupling member is connected to the ancillary module 21 via a second universal coupling 39.

The ancillary module may be in the form of a small television pick up tube or some other suitable device or an automatic pneumatic switching device. As shown, the ancillary module is provided with wheels 38 which are adapted to support it centrally in the inside of the pipe. In normal situations the rod-like coupling member 37 acts as a strut and pushes or pulls the ancillary module 21 along the pipe without flexing but if a sharp bend should be encountered in the pipe it will flex under the pressure imparted to it and assist the ancillary module to negotiate the corner. It has been found that where the coupling member 37 is used very sharp bends can be successfully negotiated. In this example the rod-like coupling 37 is formed from a tightly coiled tension spring but other strut-like, flexible members may be used.

The actuator in the linear feed motor can be powered by any convenient agency but in this example it is pneumatic. It might alternatively be hydraulic. Figure 2 shows a convenient switching device for providing the power for a pneumatic actuator and this will now be discussed with reference to figure 2.

Figure 2 a) and b) shows the working of a known component called a 5/2 shuttle valve, a brief description of which follows. The valve runs through a sleeve 8 which has ports 5, 6, 7, and the valve has ducts 9. 10. 11, 12 running through it. The position of the valve within the sleeve 8 determines which ducts are open to the ports. In Figure 2 a) the valve is shown in this first position in which the valve supplies pressurised air to one port A of the work cylinder (cylinder 31 of Figure 1), and the other port B is vented to the atmosphere. The piston 32 in the cylinder 31 is then forced towards B. The shuttle valve is moved some time later over to the second position whereupon cylinder port B is supplied with the pressurised air, therefore the piston is pushed back towards A.The valve is moved to its alternate position by pilot air, but in an alternate imbodiment may be moved to its second position by pilot air and returned to its original position by the action of a spring.

At the first valve position Figure 2 a) a reservoir C for pilot air is charged with pressurised air via the shuttle valve port 5 through the throttle E until there is sufficient pressure in the reservoir in order to overcome the shuttle valve stiction. The shuttle valve is then actuated via pipe connect 3 to the second position Figure 2 b). In this position port 5 and therefore cylinder port A are vented to the atmosphere and connector 3 and reservoir C vent to the atmosphere via throttle non return valve E. When the shuttle valve moves into this second position then the reservoir D charges up via throttle non return valve F with air bled from the supply to port B of the cylinder 31 and the reservoir D applies pressure to the shuttle valve in a pipe connector 3, and eventually when a threshold pressure is exceeded the reverse process occurs with the shuttle valve moving back into the first position.

The venting of the reservoir D (or C if the case may be) to the atmosphere when the valve has moved to its next position ensures that there is no impedance to the travel of the shuttle when returning to that position.

The use of this switching device has the advantage that even if the stroke of the cylinder 31 is restricted by some obstruction the piston will return when the reservoir pressure reaches the threshold level.

An advantageous feature of the system comprising the linear feed motor, coupling member and switching device is that it is reversible. The motor can be made to return by pulling on a draw line so the discs are inverted and so the motor moves in the return direction and the rod-like coupling member will now pull the ancillary module rather than pushing it, Using this type of system it will also be easier to negotiate sharp bends. As the reciprocation of the cylinder is now independent of the achieved stroke the linear feed motor will be able to go round small radius bends where the cylinder stroke is limited by the pipe walls. The flexible coupling member will reduce the difficulties experienced when a probe is to be propelled round a curve.

The linear feed motor can be used to feed cables out of or along a pipe, this linear feed apparatus comprising the linear actuator with at least one diaphragm, wherein said diaphragms are rigid at their outer regions and provided in their central regions with an orifice with flexible lips; if the diaphragm at one end of the apparatus is secured to the wall of the pipe. then reciprocation of the linear actuator serves to drive the cable or the like along the pipe. It is to be understood that these devices separately or together may be applied to other situations.

Claims (8)

1. An automatic pneumatic switching device for allowing alternate supplies of pressure to a pneumatic device comprising, an attachment to a supply of pressure, a two position valve for allowing the alternate supply of pressure to two points of a pneumatic device, two reservoirs to which pressure is bled alternately from the supply to said two points depending on the valve position, two pipe connects, one from each reservoir, arranged so that pressure from the reservoir to which pressue is bled acts upon the valve in such a way as to move the valve to its other position when a threshold pressure level is reached, a combined throttle and non return valve for each reservoir to control the air bled into the reservoir and allowing it to freely vent to atmosphere through the valve when the threshold pressure has been reached and the valve moved to its other position.

2. A linear feed motor including a pneumatic switching device according to Claim 1, further comprising a pneumatic actuator for propelling the motor along a path in a step wise manner, said actuator comprising a piston and cylinder mechanism connected to said valve so as to cause the alternate supply of pressure from said source to two points at opposite ends of said cylinder.

3. A linear feed motor according to Claim 2, in which said piston and cylinder are coupled respectively to flexible diaphragms adapted to fit, flexed condition, into a pipe along which the motor is to be propelled.

4. A linear feed motor adapted to travel along the inside of a pipe comprising flexible members adapted to engage the walls of the pipe, an actuator for manipulating the flexible members to cause the motor to travel step wise along the pipe a rod-like flexible coupling member connected at one end to a linear feed motor by means of a universal coupling and at the other end to the ancilliary module via another universal coupling.

5. A linear feed motor as claimed in Claim 4, wherein the rod-like coupling member consists of a tightly coiled spring.

6. A system for propelling ancilliary modules through a pipe including; a linear feed motor, an automatic switching device comprising; a supply of pressure a two position valve for allowing the alternate supply of pressure to two points of a pneumatic device, two reservoirs to which pressure is bled alternately from the supply to said two points depending on the valve position.

two pipe connects, one from each reservoir, arranged so that pressure from the reservoir to which pressure is bled acts upon the valve in such a way as to move the valve to its other position when a threshold pressure level is reached, a combined throttle and non return valve for each reservoir to control the air bled into the reservoir and allowing it to freely vent to atmospher through the valve when the threshold pressure has been reached and the valve moved to its other position, and a rod like coupling device attached at one end to said automatic switching device by means of a universal coupling and at the other end to said linear feed motor via a second universal coupling.

7. An automatic switching device substantially as described herein.

8. A system for propelling ancillary modules through a pipe substantially as described herein.