GB2182979A - Improvements in or relating to fluid-pressure-operated actuators - Google Patents

Abstract

A fluid-pressure-operated actuator has a housing 11, at least one piston 13 reciprocable in the housing. a rotatable output shaft 18, stop structure 28, 28 mounted on the housing, and a stop element 31 associated with the shaft for engaging the stop structure to limit rotary movement of the shaft, the stop element being located in a peripheral recess in the shaft and having angularly spaced ends providing part-spherical surfaces 34 engageable with said stop structure to reduce side loads on the stop structure. The recess may be a groove and the stop structure may be two spaced threaded stops respectively mounted in a wall of the housing. A further stop 42 in the form of a rotary ball may engage in the groove to provide axial restraint to the shaft. <IMAGE>

Description

SPECIFICATION Improvements in or relating to fluid-operated actuators This invention relates to fluid-pressure-operated actuators.

One form of fluid-pressure operated actuator comprises a housing, at least one piston reciprocable within the housing, a rotatable output shaft having a portion thereof within the housing, and a linkage operatively connecting the piston or pistons to said portion of the output shaft. In operation, fluid under pressure is introduced into the housing and moves the piston or pistons in one direction or the other.

This movement of the piston or pistons is transmitted by the linkage to the output shaft so that the latter is rotated to operate, for example, a fluid control valve to which the actuator is connected.

In such actuators, it is desirable to provide means to limit the rotational stroke of the output shaft in an adjustable manner, so that the rotational stroke of the output shaft can be matched exactly to equipment operated by the actuator. For example, where the actuator operates a fluid control valve including a valve member and a valve seat, the output shaft should reach one end of its stroke just as the valve member comes into engagement with the valve seat.

British specification No. 2102887 describes an actuator in which two stops are adjustably mounted in the housing and engage abutments formed by a cut-out in the output shaft.

According to this invention a fluid-pressureoperated actuator comprises a housing, at least one piston reciprocable in the housing, a rotatable output shaft having a portion in the housing, means operatively connecting the piston and the output shaft portion, stop means mounted on the housing, and a stop element associated with the shaft portion for engaging the stop means to limit rotary movement of the shaft, the stop element being located in a peripheral recess in the shaft portion and having angularly spaced ends providing partspherical surfaces engageable with said stop means.

The peripheral recess may be a peripheral groove.

The stop means may be adjustable.

The stop means may comprise two spaced threaded stops respectively mounted in a wall of the housing. The stops may be spaced by substantially the lateral dimension of the shaft in the region of said groove.

The shaft portion may comprise a pinion, said operative connection comprises racks respectively connected to two said pistons and cooperable with the pinion.

The actuator may comprise means within the housing for restricting axial movement of the output shaft. These means may comprise a stop mounted in the housing and engageable in said recess. The stop may be adjustable. The inner end of the stop may comprise a rotatable ball.

The stop may extend radially of the output shaft portion. The stop may be mounted to permit some radial movement of the stop.

The stop may be of circular cross-section and said peripheral recess have radial axially spaced surfaces between which the stop is engaged.

The invention may be performed in various ways and two specific embodiments with possible modifications will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a partly-exploded perspective view of a fluid-pressure operated actuator according to the present invention; Fig. 2 is a section through part of the actuator shown in Fig. 1 with part omitted; Fig. 3 is a side view of Fig. 2 with part omitted; Fig. 4 is a side view of a stop element; Fig. 5 is a schematic view of a further actuator; and Fig. 6 shows a modification.

Referring first to Fig. 1, the actuator 10 shown therein comprises a tubular casing or housing 11 whose open ends are closed in a fluid-tight manner by end caps 12. A pair of pistons 13 are slidably located for axial reciprocatory movement within the housing 11.

Each piston 13 has an offset axial extension 14 (not shown in Fig. 2) on which are formed rack gear teeth 15, the piston extensions being disposed such that the racks 15 face one another across the width of the housing.

Each piston includes a peripheral O-ring seai 16 engaging the casing 11. Disposed between and meshed with the two racks 1 5 is a pinion gear 1 7 formed on output shaft 18, which is rotated by movement of the two pistons 13 in opposite directions. A fluid supply port 19 is provided in the casing 11 whereby fluid, for example air, under pressure can be supplied between the pistons 13 to move them apart and rotate the pinion in one sense. A return spring 26 is housed within each end cover 12 and biasses the pistons towards the pinion.

On release of pressure at port 19 the springs move the pistons towards each other and rotates the pinion in the opposite sense. The cover 12 includes a peripheral O-ring seal 21 sealingly engaging the inner surface of the housing 11. A circlip 22 is received in confronting peripheral recesses in the cover and housing and may take the form of a stainless steel flexible coiled spring cut to the appropriate length; this minimises stress concentration, and cannot be pre-stressed unlike nuts and bolts. The output shaft 18 is mounted in the housing 11 for rotation about an axis 23 transverse to the direction of movement of the pistons 13 and has at its ends respective dogs 24, 25, by means of which it can be coupled to the equipment (such as a fluid flow control valve) to be operated by the actuator.

The pinion gear 17 is provided on a portion of the shaft 18 which is disposed within the casing 11, and may be formed as an integral part of the output shaft or may be a separate component which is keyed to the shaft for rotation therewith.

In order to limit the rotational stroke of the output shaft 18 in both directions, a pair of adjustable stops 26, 27 are provided which engage angularly spaced abutments on the part of the shaft 18 located within the housing 11 for limiting rotary movement of the shaft in two opposed senses. In the embodiment shown in Figs. 1 to 4 the adjustable stops 26, 27 are constituted respectively by a pair of threaded bolts 28 which are received with lock nuts 29 and seals (not shown) through threaded apertures in the housing wall 30 and the abutments are formed respectively by the ends of a stop element 31 located in an annular groove 32 machined in the shaft 18.

The bolts 28 are beyond one end of the gear teeth 17 and are substantially supported along their length by the housing wall on an enlargement which in this region extends across the cylinder.

The stop element 31 is a length of wire cut to a suitable length and whilst the wire is straight the cut ends are formed in a lathe to provide part-spherical, preferably hemi-spherical, end surfaces 34.

The rotational stroke of the output shaft 18 in each direction is limited by engagement of the end of a respective one of the bolts 28 with a respective one of the surfaces 34, such as is illustrated in Fig. 2, and each limit can be adjusted simply by screwing the appropriate bolt 28 in one direction or the other.

The bolts 28 are located so as not to obstruct movement of the pistons.

The groove 32 can be machined at the same time as the pinion profile is turned and the wire is bent to lie in the groove 32. The diameter of the wire 31 is such that the wire is contained within the groove 32 and does not stand proud of the surface 35 of the shaft 18. The groove may as shown have a flat base 36 and outwardly diverging flat side walls 37. The element 31 is welded at 38 to the shaft, the weld material being in the groove.

The inner ends of the bolts 28 have flat end surfaces 39 respectively engageable with the surfaces 34.

The part-spherical surfaces 34 ensure that there are substantially no side loads on the stop bolts 28 regardless of the angular position of the piston, within the design range of angular movement of the piston.

The arcuate position of the stop element 31 in the groove 32 is selected as desired, for example in relation to the pinion teeth and the dogs 24, 25. Thus a stock of pinions with a groove 32 but no stop element, can be kept and an appropriate stop element welded into place at short notice to meet particular requirements.

Means are also provided for locating the pinion in the direction of the axis 23.

There are two forces which act axially on the pinion in addition to the need to retain the pinion in position.

First, the design of pinions normally results in a pneumatic end load which in most actuators is resisted by a circlip at the top of the pinion outside the housing. This circlip can interfere with the mounting of other items on the actuator. Second, when actuators are badly mounted the pinion may be forced axially in the opposite direction which can interfere with the functioning of the actuator.

In the present case the groove 32 can be used to restrain the pinion against both these forces and locate it accurately in the housing without the circlip.

A third tapped aperture 40 is provided in wall 30 between those for the stop bolts or screws 28. A bolt or screw 41 with a suitably formed inner end is inserted into the groove 32 which is designed to provide a suitable bearing surface.

This screw 41 has a steel ball 42 peened into its inner end to reduce the rolling friction.

The ball 42 can rotate in the end of the bolt 41.

The ball 42 could be omitted and the inner end of bolt 41 engage in the groove.

The illustrated actuator is designed primarily for operating fluid flow control valves of the ball, butterfly or plug type, and accordingly the stops provided by the bolts 28 and the abutments provided by the surfaces 34 are arranged to give a rotational stroke of approximately 90 for the output shaft 18. However, the stops and abutments may be suitably arranged to provide any desired angular stroke for the output shaft, depending upon the intended use of the actuator. It will be noted from Fig. 2 that the heads of the bolts 28, 41 are disposed closely adjacent one another on the housing exterior substantially within the diameter of the shaft 18, which greatly facilitates the adjustment operation, at one side of the actuator, so that the adjusting bolts are clear of the dogs 24, 25 and the equipment operatively connected to the dogs.

The invention can also be employed in a fluid-operated actuator shown in Fig. 5. In this on the power stroke, pressure fluid is supplied at 50 and moves the pistons apart, as shown, to one limit of movement, fluid pressure in passage 51 moves valve 52 against spring 53 to connect the interior of the casing 11 outside the piston heads to exhaust through passages 54, valve 52 passages 55, 56. Also, fluid pressure opens non-return valve 57 to raise the pressure in cap 58 to supply pressure.

Should the fluid supply at 50 fail, valve 57 closes, the spring 53 moves the valve 52 to connect the air in cap 58 to passages 55, 56 through valve passage 59, and passage 54 is connected to exhaust. Thus each piston receives full supply pressure from cap 58 and the pistons move towards each other up to the other limit stop, rotating shaft 18 to open or close the associated valve.

It will be understood that the actuator may have a single piston. For example the left-hand piston of Fig. 2 may be omitted.

In the modified arrangement of Fig. 6 the annular groove 50 in the piston is of square or rectangular section and axial restraint of the pinion 17 is provided by a circular cross-section dowel 51 having squared off ends. The dowel 51 may be of hardened steel and is supported with a running fit in a radial reamed recess 52 in the wall of housing 11 and its inner end is received in the groove 50. A threaded sealing plug 53 is removably located in a tapped hole and has its inner end engaged by the outer end of the dowel, and is positioned to permit a degree of radial floating movement of the dowel. The stop wire 31 and stops 26, 27 are present as in Fig. 2.

The housing 11 extends close to the pinion and in one form a bush 54 with low coefficient of friction forms a local thickening of housing 11.

The material of housing 11 may be a hard anodized aluminium having a lower coefficient of friction than the steel on steel contact of the dowel and the pinion.

Claims (13)

1. A fluid-pressure-operated actuator comprising a housing, at least one piston reciprocable in the housing, a rotatable output shaft having a portion in the housing, means operatively connecting the piston and the output shaft portion, stop means mounted on the housing, and a stop element associated with the shaft portion for engaging the stop means to limit rotary movement of the shaft, the stop element being located-in a peripheral recess in the shaft portion and having angularly spaced ends providing part-spherical surfaces engageable with said stop means.

2. An actuator as claimed in Claim 1, in which the peripheral recess is a peripheral groove.

3. An actuator as claimed in Claim 1 or Claim 2, in which the stop means is adjustable.

4. An actuator as claimed in Claim 1 or Claim 2 or Claim 3, in which the stop means comprises two spaced threaded stops respectively mounted in a wall of the housing.

5. An actuator as claimed in Claim 4, in which the stops are spaced by substantially the lateral dimension of the shaft in the region of the groove.

6. An actuator as claimed in any preceding Claim, in which the shaft portion comprises a pinion, and said operative connection comprises racks respectively connected to two said pistons and cooperable with the pinion.

7. An actuator as claimed in any preceding Claim, which comprises means within the housing for restricting axial movement of the output shaft.

8. An actuator as claimed in Claim 7, in which the means within the housing comprises a stop mounted in the housing and engageable in the recess.

9. An actuator as claimed in Claim 8, in which the stop is adjustable.

10. An actuator as claimed in Claim 8 or Claim 9, in which the inner end of the stop comprises a rotatable ball.

11. An actuator as claimed in Claim 8, or Claim 9 or Claim 10, in which the stop extends radially of the output shaft portion.

12. An actuator as claimed in Claim 11, in which the stop is of circular cross-section and said peripheral recess has radial axially spaced surfaces between which the stop is engaged.

13. A fluid-pressure-operated actuator substantially as hereinbefore described with reference to Figs. 1 to 4, or Fig. 5, or Fig. 6, of the accompanying drawings.