GB2291475A

GB2291475A - Pneumatic Hydraulic Cylinders

Info

Publication number: GB2291475A
Application number: GB9414586A
Authority: GB
Inventors: Edward Fullerton
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-07-20
Filing date: 1994-07-20
Publication date: 1996-01-24
Also published as: GB9414586D0

Abstract

A pneumatic or hydraulic cylinder comprises a cylinder (1) and a piston (4) adapted to move to and fro within the cylinder (1) between the ends (2 and 3) thereof. A stop (8) is situated between the piston (4) and one end (3) of the cylinder (1). The position of the stop (8) relative to the end (3) of the cylinder (1) is adjustable and signalling means (12) are provided for signalling when the piston (4) comes into contact with the stop (8). <IMAGE>

Description

DESCRIPTION PNEUMATIC HYDRAULIC CYLINDERS The present invention relates to pneumatic and hydraulic cylinders. More especially, the present invention relates to pneumatic and hydraulic cylinders in which the stroke length of the piston is adjustable.

Pneumatic cylinders are used extensively in machinery and in process equipment because they are both relatively inexpensive and easy to use.

It is a requirement of many types of machinery and process equipment that the pneumatic cylinder used is one in which the stroke length of the piston is easily and accurately adjustable. Filling and depositing machines such as are used in the food industry exemplify this requirement.

In conventional pneumatic cylinders it has always been necessary to increase the length of the cylinder to twice and some times more than twice the original length of the cylinder to achieve the required stroke adjustment.

The extra length demanded by the introduction of a stroke length adjustment mechanism introduces a number of distinct disadvantages, all of which add to the cost of the equipment. In the case of filling machines in particular it results in an out of proportional increase in the cost of the ancillary equipment and especially of the extensive conveyor systems used with filling and depositing machines. This is especially so when a number of filling machines are fitted in line on conveying systems.

In many cases filling machines are used as free standing units without the addition of conveyor systems. In such cases the extra length of the stroke adjustment means that the frame of the machine and supporting brackets, stands etc. are all of larger construction and are therefore more expensive to manufacture. In addition the machine takes up more floor space resulting in extra cost and further inconvenience.

It is an object of the present invention to provide a pneumatic cylinder in which the stroke length of the piston is adjustable, which obviates or at least mitigates the disadvantages of the conventional pneumatic cylinders referred to hereinabove.

It is a further object of the present invention to provide an hydraulic cylinder in which the stroke length of the piston is adjustable.

According to the present invention there is provided a pneumatic or an hydraulic cylinder comprising a cylinder and a piston adapted to move to and fro within the cylinder between the ends thereof, wherein the pneumatic or hydraulic cylinder further comprises a stop situated between the piston and one end of the cylinder, means for adjusting the position of the stop relative to the said end of the cylinder and signalling means for signalling when the piston comes into contact with the stop.

It will be seen that the stroke length of the piston is determined by the distance between the other end of the cylinder and the adjustable stop.

Preferably, the stop and the stop adjustment means together comprise a stop nut which is non-rotatably mounted on a rotatable screw threaded rod extending the length of the cylinder. By rotating the screw threaded rod the stop nut is caused to travel along its length in the direction of rotation.

Conveniently, the screw threaded rod is spring biased away from the said end of the cylinder such that when the piston contacts the stop nut the screw threaded nut is pushed rearwards against the spring biasing to actuate the said signalling means.

The rotatable screw threaded rod may be accommodated within a hollow piston rod as the piston travels along it between the said other end of the cylinder and the stop nut. However, it is envisaged that the screw threaded rod may equally simply extend through an offcentre aperture in the piston and be supported between the ends of the cylinder. In this case the stop nut can be trapped against the inner wall of the cylinder to prevent it from rotating as the screw threaded rod is rotated.

Where the piston rod is hollow to accommodate the screw threaded rod it is generally of a larger diameter than normal.

This significantly reduces the volume capacity of the cylinder in the area through which the piston rod passes, effectively reducing air consumption on the inlet stroke where a reduced pressure is desirable.

This can save on the running costs of the machine.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing which shows a schematic crosssectional side elevation of a pneumatic cylinder in accordance with the present invention. For the sake of clarity and ease of understanding details of the pneumatic cylinder such as oil seals, brackets and retaining bolts have been omitted.

Referring to the drawing the pneumatic cylinder comprises a cylindrical outer casing 1 which is closed at each end by a front end cap 2 and a rear end cap 3 respectively. A piston 4 is slidably mounted within the outer casing 1 and is connected to a piston rod 5 which is slidably supported within an aperture in the front end cap 2. As will be readily understood the piston 4 can travel back and forth within the outer casing 1 between the end caps 2 and 3 under the influence of pneumatic pressure and this in turn causes the end of the piston rod 5 to reciprocate to and fro to drive a mechanism connected thereto. In this respect the pneumatic cylinder of the present invention is like a conventional pneumatic cylinder.

The inner end of the piston rod 5 defines an open ended tube within which is received a screw threaded rod 6. The internal diameter of the tubular piston rod 5 is such that it and the piston 4 can travel freely back and over the screw threaded rod 6. The opposite end of the screw threaded rod 6 extends through an aperture in the rear end cap 3 and is connected to a knob or handle 7 which enables the screw threaded rod 6 to be manually rotated. Mounted on the screw threaded rod 6 is a stop nut 8. This is prevented from rotating with the screw threaded rod 6 by an elongate rod 9 which extends the length of the outer casing 1, through apertures in the stop nut 8 and in the piston 4, and is supported at each end in a blind hole in a respective one of the end caps 2 and 3.As the screw threaded rod 6 is rotated it causes the stop nut 8 to move either backwards or forwards along its length depending on the direction of rotation.

Also mounted on the screw threaded shaft 6 is a spring 10 which serves to bias the screw threaded shaft 6 away from the rear end cap 3 and an externally mounted disc 11 which, in use, serves to actuate a signalling device 12, such as a micro-switch, when the piston 4 has reached the end of its travel within the outer casing 1 towards the rear end plate 3. Another signalling device 13 is provided adajcent the front end cap 2. This signalling device 13 is actuated by a pin 14 which extends through the front end cap 2 when the piston 4 has reached the end of its travel towards the front end plate 3.

As will now be explained, the screw threaded rod 6 and the stop nut 8 together allow the stroke length of the pneumatic cylinder, that is to say the distance through which the piston 4 travels back and forth within the outer casing 1, to be adjusted. In this regard it will be seen that as the stop nut 8 is wound along the screw threaded rod 6 towards the front end cap 2 the distance through which the piston 4 can travel is restricted. As the piston 4 reaches the stop nut 8 it pushes against it and forces the screw threaded rod 6 to move rearwardly against the spring bias of spring 10. This in turn causes the externally mounted disc 11 to move against the signalling device 12. In conventional fashion the signalling device 12 reverses the direction of travel of the piston 4 and causes it to proceed towards the front end cap 2.When the piston 4 reaches the front end cap 2 it pushes against the pin 14 which actuates the other signalling device 13 to again reverse the direction of travel of the piston 4 and initiate a new stroke cycle, again in conventional fashion.

It will be seen that the pneumatic cylinder in accordance with the present invention enables the stroke length to be adjusted without requiring any change in the overall length of the cylinder itself as is the case with conventional pneumatic cylinders having an adjustable stroke length. Not only does this help keep the cost of the pneumatic cylinder itself to the minimum, but, owing to the reduced length of the pneumatic cylinder, it also helps keep the costs of associated ancillary equipment down as this is not required to accommodate the extra length of a conventional pneumatic cylinder.

In the embodiment of the present invention as shown in the accompanying drawing the stroke length of the pneumatic cylinder is adjusted by means of a knob mounted on the screw threaded rod. In some applications access to the pneumatic cylinder itself may be somewhat restricted. It is therefore envisaged that the screw threaded rod may be adjusted remotely from the pneumatic cylinder through an arrangement of gears and chains or even by a remotely controlled solenoid motor.

It is also envisaged that a scale of some sort will be provided to show the actual stroke length.

Claims

1. A pneumatic or hydraulic cylinder comprising a cylinder and a piston adapted to move to and fro within the cylinder between the ends thereof, wherein the pneumatic or hydraulic cylinder further comprises a stop situated between the piston and one end of the cylinder, means for adjusting the position of the stop relative to the said end of the cylinder and signalling means for signalling when the piston comes into contact with the stop.

2. A pneumatic or hydraulic cylinder according to claim 1, wherein the stop and the stop adjustment means together comprise a stop nut which is non-rotatably mounted on a rotatable screw threaded rod extending the length of the cylinder such that by rotating the screw threaded rod the stop nut is caused to travel along its length in the direction of rotation.

3. A pneumatic or hydraulic cylinder according to claim 2, wherein the screw threaded rod extends through an aperture in the said end of the cylinder and is connected to a handle which enables the rod to be manually rotated.

4. A pneumatic or hydraulic cylinder according to claim 2 or 3, wherein the screw threaded rod is spring biased away from the said end of the cylinder such that when the piston contacts the stop nut the screw threaded nut is pushed rearwards against the spring biasing to actuate the said signalling means.

5. A pneumatic or hydraulic cylinder according to claim 2, 3 or 4, wherein the rotatable screw threaded rod is accommodated within a hollow piston rod as the piston travels along it between the said other end of the cylinder and the stop nut.

6. A pneumatic or hydraulic cylinder according to claim 2, 3 or 4, wherein the screw threaded rod extends through an off-centre aperture in the piston and is supported between the ends of the cylinder.

7. A pneumatic or hydraulic cylinder according to claim 6, wherein the stop nut is trapped against the inner wall of the cylinder to prevent it from rotating as the screw threaded rod is rotated.

8. A pneumatic or hydraulic cylinder substantially as hereinbefore described with reference to the accompanying drawing.