GB2233711A

GB2233711A - Rodless piston/cylinder unit

Info

Publication number: GB2233711A
Application number: GB8912058A
Authority: GB
Inventors: Douglas Cecil Clarke
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-05-25
Filing date: 1989-05-25
Publication date: 1991-01-16
Also published as: GB8912058D0; DE4016867A1

Abstract

A rodless, fluid pressure operated piston/cylinder unit comprises a cylinder 10, a piston 11 reciprocable in the cylinder, a fluid reservoir 12, 13, having a fluid port 25, at each of the two ends of the cylinder, a return passage 14 between the reservoirs, a rotatable drive member 29 in the reservoir 12 and a guide member 34 in the reservoir 13, a flexible drive element 36 connected to one end of the piston and extending around the rotatable drive member and into the return passage, and a flexible tensioning element 37 connected to the other end of the piston and extending around the guide member and into the return passage where it is joined to the flexible drive element. The tensioning element passes through a sealing block 39 positioned between the reservoir 13 and the return passage 14, or the tensioning element is joined to the flexible drive element by a seal (not shown) movable in the return passage. <IMAGE>

Description

Rodless Piston/Cylinder Unit This invention relates to rodless, fluid

pressure operated piston/cylinder units.

Rodless piston/cylinder units have many applications as they are little more than half the length of conventional piston/cylinder units, and therefore afford a significant saving in space. Known rodless piston/cylinder units comprise a casing having a fluid operable piston within the casing and a take-off element mounted on the casing for rectilinear movement therealong. In most cases, the movement of the piston is transmitted to the take-off element via a drive which moves rectilinearly with the piston and which passes through the casing. As may be expected, this creates considerable sealing problems which adds significantly to the cost of the unit.

According to the present invention, there is provided a rodless, fluid pressure operated piston/cylinder unit comprising a cylinder, a piston reciprocable in the cylinder, a fluid reservoir, having a fluid port, at each of the two ends of the cylinder. a return passage between the reservoirs, a rotatable drive member in one of the reservoirs and a guide member in the other reservoir, a flexible drive element connected to one end of the piston and extending around the rotatable drive member and into the return passage, and a flexible tensioning element connected to the other end of the piston and extending around the guide member and into the return passage where it is joined to the flexible drive element, the tensioning element passing through sealing means positioned between the said other reservoir and the return passage, or the tensioning element being joined to the flexible drive element by sealing means movable in the return passage.

Preferably, the flexible drive element and rotatable drive member are in positive driving engagement with one another. In this case, the flexible drive element may be a toothed or apertured belt, or a drive chain.

If the flexible tensioning element passes through sealing means between said other reservoir and the return passage, the flexible tensioning element is smooth so that an effective seal is provided between the tensioning element and the sealing means, and may, for example, be in the form of a spring steel strip or nylon coated wire. It is not, however, essential to provide a perfect seal between the tensioning element and the sealing means as a small amount of leakage past the seal will not significantly impair the operation of the unit.

Preferably, the return path is arranged alongside the cylinder.

Advantageously, means are provided to cushion the piston at its end of stroke positions.

Conveniently, the position of the guide member is adjustable in order to tension the flexible drive element and flexible tensioning element.

The rotatable drive member will normally include a shaft extending to the outsiae of the said one reservoir.

The unit may serve as a rotary actuator or a linear actuator. In the latter case, the shaft may be connected by a further flexible drive element to a takeoff element mounted for slidable movement externally of the unit.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a diagrammatic, perspective view, partly broken away, of a linear actuator including one embodiment of a rodless, fluid pressure operated piston/cylinder unit according to the present invention, Figure 2 is a section taken along the line II-II of Figure 1 Figure 3 line III-III of Figure Figure 4 is a section taken along the 2, is a section taken along the line IV-IV of Figure 2, and Figure 5 is a section taken along the line-V-V of Figure 2.

Referring to the drawings, the linear actuator shown therein comprises a cylinder 10, a piston 11 reciprocable in the cylinder 10, fluid reservoirs 12 and 13 at opposite ends of the cylinder 10, a return passage 14 extending alongside the cylinder 10 and between the reservoirs 12 and 14, and a slideway 15.

The actuator is basically made up from two aluminium extrusions 16 and 17 (see Figure 2), two aluminium blocks 18 and 19, and two die cast end caps 20 and 21. The cylinder 10 and return passage 14 extend parallel to one another in the extrusion 16, the slideway is formed by the extrusion 17, and the end caps 20 and 21 define the two reservoirs 12 and 13, respectively. The extrusions 16 and 17 are connected together in side-by-side parallel relationship and the blocks 18 and 19 are disposed between opposite ends of the two extrusions and the two end caps 20 and 21, respectively.

The two end caps 20 and 21 are each divided into two chambers 22 and 23. The chamber 22 of each end cap communicates with the cylinder 10 via a through bore 24 in a respective block 18, 19, and has a f luid port 25 for connection to a supply of compressed fluid, generally air or low pressure hydraulic fluid, or exhaust/drain. The chamber 23 of each end cap communicates with the slideway 15.

A shaft 26 is mounted in roller bearings 27 for rotation in the chamber 22 of the end cap 20 and this shaft 26 extends through a rotary seal 28 in the dividing wall of the end cap 20 into the chamber 23.

Toothed wheels 29 and 30 are fixed to the shaft 26 for rotation therewith, the wheel 29 being mounted on the shaft 26 in the chamber 22 and the wheel 30 being -5 mounted on the shaft 26 in the chamber 23.

A shaft 31 is fixedly mounted in a tensioning device 32 in the chamber 22 of the end cap 21, and a shaft 33 is mounted in the chamber 23 of the end cap 21 5 and is fixed to the dividing wall of the end cap 21.

Idler wheels 34 and 35 are mounted for rotation on the shafts 31 and 33, respectively, through the intermediary of sleeve bearings. The wheel 34 has a smooth peripheral surface, whereas the wheel 35 has a toothed peripheral surface.

A flexible toothed drive element 36 is connected to one end of the piston 11 and a smooth, flexible tensioning element 37 in the form of a spring steel strip is connected to the other end of the piston.

The drive element 36 extends through the bore 24 in the block 18, around the toothed wheel 29 in the chamber 22 of the end cap 20, and into the return passage 14 via a comparatively large opening 38 in the block 18. The tensioning element 37 extends through the bore 24 in the block 19, around the idler wheel 34 in the chamber 22 of the end cap 21, and into the return passage 14 through a sealing block 39 securely located in a stepped opening 40 in the block 19.

The sealing block 39 is preferably self- lubricating and may, for example, be formed of graphite impregnated nylon. In any event, the sealing block 39 co-operates with the smooth tensioning element 37 to provide a reasonably effective seal between the tensioning element 37 and the block 39, although, as mentioned previously, a perfect seal is not essential as a small amount of leakage past the sealing block 39 will not significantly impair the operation of the actuator.

The flexible drive element 36 is joined to the flexible tensioning element 37 in the return passage 14 by a connector 41, which moves in the return passage 14 with a substantial clearance.

Thus, if pressurised fluid is applied to the fluid port 25 in the end cap 20, and the fluid port 25 in the end cap 21 is connected to exhaust/drain, the piston 11 will move to the right, and if the connections to the ports 25 are reversed, the piston will move to the left.

The flexible drive element 36 and the flexible tensioning element 37 are connected to the piston 11 by connectors 42 and 43, respectively. The connector 42 comprises a plug 44 in a sleeve 45 having an annular step in its outer surface. The smaller diameter end of the sleeve 45 is externally threaded for engagement with an internal thread in a blind bore 46 in the piston 11. The plug 44 has a head 47 which abuts the end of the sleeve 45 in the blind bore 46 to hold the plug captive relative to the sleeve 45. The plug 44 has a slot 48 extending towards the head 47 from the other end of the plug and diametrically across the plug. The slot 48 is shaped to correspond to the shape of the toothed drive element 36. To connect the drive element 36 to the piston 11, the drive element 37 is f irst slotted into the plug 44. The sleeve 45 is then slid over the plug 44, and the sleeve 45 is then screwed into the blind bore 46.

The connector 43 likewise comprises a plug 49 and a sleeve 50. The sleeve 50 is identical to the sleeve 45, but the plug 49 differs from the plug 44 in that it has a slot 51 of different shape. The slot 51 is generally T-shaped and has a thin neck portion leading from the outer end of the plug 49 to an enlarged head portion which is circular in cross-section and which receives a pin 54 around which an end of the tensioning member 37 is wrapped.

The sleeves 45 and 50 are arranged to enter respective throughbores 24 in the blocks 18 and 19 as the piston 11 approaches respective ends of stroke positions. As the sleeve 45, 50 enters its respective throughbore 24, a cushion seal 55, located in an annular groove in the sleeve 45, 50, seals against the wall of the throughbore 24 to prevent further displacement of fluid through the throughbore 24. Fluid trapped between the piston 11 and each of the blocks 18. 19 will flow into respective reservoirs 12, 13 through a variable restricted passage 56 (see Figure 1) provided in each block 18, 19, but at a very much slower rate, and this will have the effect of cushioning the piston 11 at its end of stroke positions.

As shown, the piston 11 is formed in two parts lia and llb, which are screw-threadably connected together with the interposition of one or more annular magnets 57 which can be used to provide magnetic signals to positional sensors or the like.

The slideway 15 has two confronting V-shaped grooves 58 and 59. A slider 60, equipped with bearing strips 61, is mounted between the V-shaped grooves 58 and 59 for slidable movement along the longitudinal extent of the slideway 15, and a take-off element 62 is secured to the slider 60. A toothed drive belt 63 is connected between opposite ends of the slider 60 and extends over toothed wheel 30 and idler wheel 35, and through a return passage 64 provided in the extrusion 17.

Thus, as the piston 11 moves under the influence of fluid pressure applied to one of the fluid ports 25, the take-off element 62 will move in unison with the piston 11 by virtue of the drive train consisting of drive element 37, wheel 29, shaft 26, wheel 30, and drive belt 63.

An encoder can be run of f the shaft 26 in order to program the operation of the actuator.

The shaft 26 could be provided with a pneumatically or electronically operated brake to hold the piston 11 in a selected position.

The actuator could have two slideways, one on either side of the cylinder 10, and each equipped with a take-off element. In this case, the two takeoff 1 1 elements could be anchored so that when f luid pressure is applied to one of the fluid ports 25, the cylinder and slideways move whilst movement of the take-off elements is arrested.

The actuator could be used as a rotary actuator by omitting the slideway(s) and taking the rotary drive from the shaft 26.

The idler wheel 34 could be in the form of a non-rotatable guide. The flexible tensioning element could, by way of example, by in the form of nylon coated wire instead of a spring steel strip.

The sealing block 39 could be omitted and the connector 41 could be in the f rom of a further piston movable along the return passage 14. In this case, there will be no clearance between the further piston and the passage 14 so that the further piston acts as a movable seal. The area of each end surface of the further piston will be less than the area of each end surface of the piston 11 so that the differential pressure applied to the two pistons will move the piston 11 in a required direction. In this particular case, there is no requirement for the tensioning element to be smooth, and consequently the tensioning element could be a toothed or apertured belt, similar to the drive element.

Claims

1. A rodless, f luid pressure operated piston/cylinder unit comprising a cylinder, a piston reciprocable in the cylinder, a fluid reservoir, having a fluid port, at each of the two ends of the cylinder, a return passage between the reservoirs, a rotatable drive member in one of the reservoirs and a guide member in the other reservoir, a flexible drive element connected to one end of the piston and extending around the rotatable drive member and into the return passage, and a flexible tensioning element connected to the other end of the piston and extending around the guide member and into the return passage where it is joined to the flexible drive element, the tensioning element passing through sealing means positioned between the said other reservoir and the return passage, or the tensioning element being joined to the flexible drive element by sealing means movable in the return passage.

2. A piston/cylinder unit as claimed in Claim 1, 20 wherein the flexible drive element and rotatable drive member are in positive driving engagement with one another.

3w A piston/cylinder unit as claimed in claim 2, wherein the flexible drive element is a toothed or apertured belt, or a drive chain.

4. A piston/cylinder unit as claimed in any one of Claims 1 to 3, wherein the flexible tensioning element passes through sealing means positioned between said other reservoir and the return passage and wherein the flexible tensioning element is smooth so that an effective seal is provided between the tensioning element and the sealing means.

5. A piston/cylinder unit as claimed in Claim 4, wherein the flexible tensioning element is in the form of a spring steel strip.

6. A piston/cylinder unit as claimed in Claim 4, wherein the flexible tensioning element is in the form of nylon coated wire.

7. A piston/cylinder unit as claimed in any one of the preceding claims, wherein the return path is arranged alongside the cylinder.

8. A piston/cylinder unit as claimed in any one 15 of the preceding claims, wherein means are provided to cushion the piston at its end of stroke positions.

9. A piston/cylinder unit as claimed in any one of the preceding claims, wherein the position of the guide member is adjustable in order to tension the flexible drive element and flexible tensioning element.

10. A piston/cylinder unit as claimed in any one of the preceding claims, wherein the rotatable drive member includes a shaft extending to the outside of the said one reservoir.

11. A piston/cylinder unit rodless, fluid pressure operated substantially as hereinbefore described with reference to the accompanying drawing.

12. An actuator including a piston/cylinder unit as claimed in any one of the preceding claims.

13. A linear actuator including a piston/cylinder unit as claimed in any one of Claims 1 to 11, wherein the rotatable drive member includes a shaft extending to the outside of said one reservoir and the shaft is connected by a further flexible drive element to a takeoff element mounted for slidable movement externally of the piston/cylinder unit.

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