GB2203492A

GB2203492A - Piston/cylinder monitor

Info

Publication number: GB2203492A
Application number: GB08808952A
Authority: GB
Inventors: Arnold Dossler
Original assignee: Schwaebische Huettenwerke Automotive GmbH
Current assignee: Schwaebische Huettenwerke Automotive GmbH
Priority date: 1987-04-16
Filing date: 1988-04-15
Publication date: 1988-10-19
Anticipated expiration: 2008-04-15
Also published as: IT8820209A0; IT1217422B; GB2203492B; GB8808952D0; DE3713021A1; DD268742A5

Description

1 Piston/Cylinder Monitor 2203492 This invention relates to a

piston/cylinder monitor for monitoring travel and position of a piston in an hydraulic or pneumatic cylinder.

For monitoring travel and position of a piston of an hydraulic or pneumatic cylinder it is known to provide terminal-switch controls with corresponding detector elements. However, such control and detector elements involve corresponding space requirements for inlet and outlet piping. This often gives rise to problems. This is particularly true in cases where there is but little space available at a location of the cylinder to be monitored or where such additional elements would be troublesome. This is especially the case with robot machinery. On the other hand, in order to avoid damage or accidents, it is frequently desirable to provide such elements to ascertain whether an hydraulic or pneumatic cylinder operates faultlessly.

Therefore, the task underlying the present invention is one of constructing a piston/cylinder monitor which monitors travel and position of a piston in a hydraulic or pneumatic cylinder and this without any troublesome effects or spatial problems.

According to the present invention, there is provided a piston/cylinder monitor for monitoring travel and position of a piston in an hydraulic or pneumatic cylinder characterised in that the monitor comprises a cylinder adapted to be mounted in a feed conduit of the cylinder to be monitored and a piston movable longitudinally of the cylinder, wherein an inner wall of the cylinder at terminal positions of the piston is 2 29 provided with annular cavities such that when the piston is located at a said terminal position communication is established between passageways at opposite end portions of the cylinder and in that the monitor comprises detector elements for determination of position of the piston at the terminal positions.

According to the inventionr the cylinder which is to be modified remains free of troublesome fittings. Rather, the monitoring function is located in the region of the feed pipe of the cylinder to be monitored, and can take place at a location where it is not bothersome and/or where no spatial problems arise, while nevertheless providing a precise monitor-ing. This is achieved substantially enabling pressure or leakage losses to be compensated, because a refill flow takes place through the annular cavities according to the invention in the inner cylinder wall, in the required amounts.

Inversely, that is to say, during the return stroke, the pressure medium can be wholly displaced by the piston to the reservoir, the piston then coming to rest in the other terminal position in Which a connection is provided through further annular cavities, according to the invention in the cylinder wall. in this manner, the residual pressure in the system is zero in the inactive state.

A further very great advantage of the invention consists in that by means of the control cylinder according to the invention even very short strokes of the cylinder to be monitored can be controlled, which is either fraught with problems or cannot be achieved at all with known terminal switches, for example. Thus. for example, dimensions of the piston space in the control cylinder can be varied at will relative to the cylinder to be monitored. This means, that a piston space of large c 3 W 35 axial dimensions but 9f small diameter is provided, whereby correspondingly longer trajectories result. The only provision to be observed is that the volume of the piston space in the control cylinder,, relative to that of the cylinder to be monitored. remains the same as a whole.

In an advantageous further development of the inventiont provision may be made for arranging a pressure monitor between the control cylinder and the hydraulic or pneumatic cyliner.

By means of the pressure monitor according to the invention it is ensured that larger leakages, due to which the plant fails to pressurise in spite of a refill with pressure medium through the annular cavities according to the invention, can be detected so that corresponding safety measures can be taken.

In an advantageous manner it is furthermore provided that the piston space of the control cylinder has a slightly smaller volume than the piston space of the hydraulic or pneumatic cylinder to be monitored.

It is ensured in this manner that the detector piston. at the end of a stroke, always bears against the stop so as to be able to monitor the two terminal positions.

A simple and very effective solution for the communication between the piston space of the control cylinder and the feed conduit to the piston can be monitored and the return conduit to the reservoiri respectively. may consist in providing the detector piston in its middle region with seal elements and by having grooves, incisions or the like projecting from 4 both front faces as far as the central seal region and by arranging in the inner cylinder wall radial grooves which are larger or wider than the packing region of the detector piston.

In this manner, the pressure medium can flow in each of the end positions over the packing and. along the longitudinal grooves in the piston either to the consumer or into the reservoir.

As detector elements there may be employed inductive switches.

A very simple embodiment of the control cylinder according to the invention is to constitute it from a hose.

Due to the flexibility of the hose, it can be used even in a restricted space and fitted accordingly.

A simple solution for the detector cylinder may consist of this being embodied as a sphere.

Following is a description, by way of example only and with reference to the accompanying drawing, which is a cross section, of one method of carrying the invention into effect.

In the drawings there is shown a piston/cylinder monitor comprising a high-strength aluminium tube 1. the two front faces of which are sealed by plugs 2 and 3 with passage bores 4 and 5. The passage bore 4 is connected to a return conduit here not shown to the reservoir and to a pump conduit. while the passage bore 5 with a feed conduit 6 leads to a hydraulic cylinder here not shown, which is to be monitored. From the feed conduit 6 derives a side conduit 7. in which a pressure monitor 8 is arranged. Such pressure monitors are generally known for which reason shall not be described in detail.

In the interior of the aluminium tube ll which forms the cylindert a detector piston 9 is arranged, made of brass, for example. In the frontal bore 10 of the detector piston 9.a magnetic disc 11 is seated. From both front faces of the detector piston 9, several peripherally spaced axial grooves 12 originate, which terminate in a packing region 13 in the middle of the detector piston 9. The packing region 13 also contains a packing 14.

In the inner peripheral wall 15 of the aluminium tube 1 annular grooves are arranged, which communicate with the grooves 12 in the detector piston 9. The arrangement of the annular grooves 16 in the aluminium tube 1 is so selected, that the packing region 13 of the detector piston 9 is bypassed when thp detector piston 9 applies with the appropriate front face against the closure plug 2 or 3, respectively. As is appapent from the drawing, the annular grooves 16 are larger, respectively wider than the length of the packing region 13, owing to which in the two terminal positions a communication is established from the two front faces of the detector piston 9 inwards to the axial grooves 12 extending within the packing region 13. In order to achieve a continued conveying of the pressure medium to the passage bores 4 or 5, respectively, the two front faces of the detector piston are provided with radial groove 17y through which a communication is established between the axial grooves 12 and the passage bores 4 or 5, respectively. The radial grooves 17 open on one front face into the frontal bore 10, in which the 6 magnetic disc 11 is arranged, whilst on the other side, for this same purposei' a pocket bore 18 is provided, into which the radial bores 12 open.

on the outside about the aluminium tube 1 two electronic proximity switches 19 are arranged. which are magnetically activated. This activation is effected by way of the magnetic disc 11, the proximity switches 19 and the magnetic disc 11 are so positioned relative to each other that at all times the end positions of the detector piston 9 are indicated, that is to say, the position of the detector piston 9 when it applies against the plugs 2 or 3.

The mode of functioning of the oil volume controller according to the invention is as follows:

Prior to activation of the hydraulic or pneumatic cylinder to be monitored, the detector piston 9 is located in its left-hand position, in which it 'applies with the left-hand front face against the plug 2. In the piston space 20 located in front of it unpressurized pressure medium is located. just as in the feed conduit 6 and in the cylinder to be monitored.

about by the circuiting through the annular grooves 16 in the aluminium tube 1. If now a pressure medium is introduced by a pump here not shown through the passage bore 4 into the control cylinder, the detector piston 9 moves to the right until it comes to bear on the other side with its front face against the plug 3. At the same tim e, the pressure medium in the feed conduit and in the cylinder to be monitored is correspondingly pressurized. Since - as is apparent in the drawing - in this terminal position there is likewise established a unpressurized condition is brought The short- 7 :1 short-circuit connection through the axial grooves 12 in the detector piston 9, the annular grooves 16 in the aluminium tube 1 and the radial grooves 17 to the feed conduit 6 and thus to the cylinder to be monitored, it is possible both to compensate for leakage losses and to increase the pressure at will if so required. Since at the same time a monitoring is carried out by the pressure monitor 8. ' it is also ensured that the required pressure is present in the system. otherwise, the pressure monitor-8 will respond.

By means of the monitoring with the electronic proximity switches, the terminal position of the detector piston 9 is also monitored, so that it can be detected in this manner when the cylinder to be monitored jams, because in this case as well the detector piston cannot travel to its terminal position. Howevert in order for the piston to securely reach the terminal positions, the volume of the piston space 20 must be at least equal, or better still slightly smaller than the volume of the piston space of the cylinder to be monitored.

If the passage bore 4 of the plug 2 or a corresponding feed conduit is connected to the return conduit to the reservoir, then the detector piston 9 moves to the left until its end-position catch on the other side. while it comes to bear with one front face against the plug 2. Owing to the already mentioned short-circuit connection, the system can be made pressure-free.

Y 8

Claims

1. A piston/cylinder monitor for monitoring travel and position of a piston in an hydraulic or pneumatic cylinder characterised in that the monitor comprises a cylinder (1) adapted to be mounted in a feed conduit of the cylinder to.be monitored and a piston (9) movable longitudinally of the cylinder (1), wherein an inner wall (15) of the cylinder (1) at terminal positions of the piston (9) is provided with annular cavities (16) such that when the piston (9) is located at a said terminal position communication is established between passageways (4,5) at opposite end portions of the cylinder (1) and in that the monitor comprises detector elements (11r19) for-determination of position of the piston (9) at the terminal positions.

ll

2. A monitor according to Claim 1 characterised in that between the cylinder (1) and the cylinder to be monitored there is provided a pressure monitor (8).

3 A monitor according to Claim 1 or 2, characterised in that the volume (20) swept out by the piston (9) in cylinder (1) is equal to or less than the volume swept out by the piston in the cylinder to be monitored.

4. A monitor according to any one of the preceding claims characterised in that each of the annular cavities (16) comprises a groove.

9

5. A monitor according to Claim 4 characterised in that the piston (9) is provided with a portion (13) of enlarged diameter and portions adjacent opposite sides of the enlarged diameter portion are provided.with axial passageways (12)r the enlarged diameter portion (13) containing a piston ring (14) and being of an axial dimension smaller than an axial dimension of each of the grooves (16).

6. A monitor according to any one of the preceding claims characterised in that the cylinder (1) and the piston (9) are of non-magnetic material and in that the piston carries a magnetic element (11) arranged to cooperate with electronic proximity switches (19) for magnetic actuation of detector elements arranged outside of the cylinder (1).

7. A monitor according to Claim 6, characterised in that the magnetic element is formed as a magnetic disc (11) which is located in a recess (10) in the piston (9).

8. A monitor according to Claim 6 or Claim 7 characterised in that the detector elements are induction switches.

9. A monitor according to any one of the preceding claims characterised in that the cylinder (1) is constructed as a hose.

10. A monitor according to any one of the preceding claims characterised in that the piston (9) is constructed as a sphere.

A piston/cylinder

11. monitor substantially as hereinbefore described and as illustrated in the accompanying drawing.

Publibhed 1988 at The Patent Ofnee, State House, 88/71 High Holborn, London WCIR 4TP. Further copies may be obtained from The Patent Offles, Sales Branch, St Mary Cray, Orpington, Rent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1187.