GB2309747A - Fluid-pressure-operated actuators - Google Patents

Abstract

A fluid-pressure-operated actuator 10 has a housing 11 containing axially reciprocable pistons 14, 14a biassed inwards by springs 19, 19a and moved outwards by air pressure to rotate output shaft 18. Nuts 38, 38a on rotatable shafts 30, 30a are co-operable with the respective piston and can be adjusted axially by rotation of the shafts to limit the movement of the pistons to a selected extent between zero and maximum and to position the selected extent at a selected position within the maximum extent. The shafts 30, 30a are long enough to permit full relaxation of the springs before full disassembly of end caps 13, 13a from central housing body 12 and in association with nuts 38, 38a provide manual override for positioning the shaft 18.

Description

FLUID PRI5EURE-OPERATED ACIUATORS THIS INVENTION relates to fluid-pressure-operated actuators.

Part-turn pneumatic actuators are used in a wide range of industries and uses. Most operate by the action of a piston or pistons on a rotating member.

Many uses require accurate adjustment of the actuator travel to ensure optimum efficiency of the mechanism operated by the actuator. Adjustable travel stops are fitted to actuators to achieve this function. An example of these is described in GB-A2102887 in which stops act directly on a rotating member of the actuator and limited adjustment of the end limits of movement is available in both directions of rotation.

Many pneumatic actuators for fail-safe use are fitted with springs which act in one direction and which are compressed by air pressure in the opposite direction. These springs are precompressed on assembly to yield a residual spring load at the end of the spring-operated stroke. The energy in the pre-compressed springs has to be released when the actuator is dis-assembled and this requires arrangement to ensure the safety of the person performing the operation. Often these arrangements require special equipment which may not readily be available and in consequence a dangerous situation may arise.

Spring-loaded pneumatic actuators are used as fail safe devices to operate in the case of a failure of control systems and/or a failure of air or electrical supplies. The nature of their function depends upon a pre-loading of the springs to fulfil their designed purpose. The springs are contained in the pre-loaded state by end cap closures mechanically secured to a centre housing. However, in some designs the mechanical securement of the end closures is achieved by pre-loading before they dis-engage.

Many designs approach the problem of containing the spring load by the provision of a retractor cap at the bottom of the spring which cap may be engaged by a retaining bolt inserted through the end closure. This is used to contain the spring between the retractor cap and the end closure before the mechanical securement of the end closure in the actuator body is removed. However the spring is still compressed in the unit of cap, spring and end closure.

With such a design it is difficult to design a screwretained end closure which guarantees that a retaining bolt for the end closure is fitted before the screws are removed.

Instead of a screw-retained end closure, the end closure may be held to the centre housing by a helical wire coil key as described in GB-A-2123517.

In many uses consideration is given to a possible failure of control supplies and this requires the provision of a means of manually positioning the controlled mechanism or locking it in a safe position until normal operations are resumed.

In many cases this is overcome by the additional fitment of a mechanical device such as a gear box or a lockable lever arrangement.

According to one aspect of the invention a fluid-pressure operated actuator comprises a housing, piston means movable in the housing for an extent of movement between first and second limit positions, a rotary output shaft operatively connected to the piston means and extending to the exterior of the housing, means defining said first and second limit positions, and means for adjusting the defining means for varying the extent continuously between zero and a maximum.

The defining means may be adapted to locate a selected extent at any position within said maximum extent.

There may be first limit defining means defining the first limit and second limit defining means defining the second limit, and means for adjusting both the first and the second limit defining means.

The limit-defining means may comprise an axially movable non-rotatable member threadedly connected to a rotary member.

The rotary member may be rotatable from outside the housing. The rotary member may comprise an axial member.

There may be two pistons each operatively connected to the output shaft and each having axially inner and outer faces selectively co-operable with axially inner and outer faces on a respective one of the first and second limit defining means.

Each piston may be biassed towards the other by spring means.

According to another aspect of the invention a fluid pressure operated actuator comprises piston means movable in a housing, spring means engageable between the piston means and a detachable part of the housing, and means preventing detachment of the housing part until the spring means is relaxed.

The preventing means may comprise a threaded member rotatable in the housing part and threadedly connected to the piston or to a member for engaging the piston.

The preventing means may comprise connector means for preventing movement of the housing part relative to the remainder of the housing until spring pressure on the connector means is relieved.

The connector means may comprise a flexible elongate member in confronting annular grooves on the housing part and the remainder of the housing. The elongate member may be a helical coil.

According to a further aspect of the invention a fluid pressure-operated actuator comprises a housing, piston means movable in the housing operatively connected to a rotary output shaft, and means within the housing for holding the output shaft in a selected position within the extent of movement.

The holding means may comprise means for holding the piston means.

The holding means may comprise an axially movable member mounted for axial movement on a rotatable member operable from outside the housing. The rotatable member does not move axially.

The axially movable member may be within the piston means.

The piston means may comprise two pistons each with a holding means and spring means biassing the pistons towards each other.

An actuator according to the invention may comprise two or more of the above aspects.

The invention may be performed in various ways and some specific embodiments with possible modifications will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1A is an axial section through an actuator in one position; Fig. 1B shows the actuator in another position; Fig. 2 shows part of the actuator during disassembly; Figs. 3A to 3D show part of the actuator in other operating conditions; Figs. 4 is a view of part of a further actuator similar to part of Fig. 1A; Fig. 5 shows part of the further actuator in a position similar to Fig. 1B; Figs. 6A to 6D are views similar to Figs. 3A to 3D of the further actuator; Figs. 7, 8 and 9A to 9D) are views similar to Figs. 4, 5, 6A to 6D of a modified actuator; Fig. 10 shows part of another actuator in one condition; Fig. 11 shows the part in another condition; ; and Fig. 12 shows the assembled actuator.

An air pressure-operated actuator 10 has a housing 11 having a central cylindrical hollow body 12 and hollow end caps 13, 13a. The end caps and associated parts are generally similar and will be referenced accordingly.

Axially reciprocable in the body 12 are opposed pistons 14, 14a each with a respective axially inner extension 15, 15a each having on its radially inner face a toothed rack 16, 16a (shown schematically) engaging diametrically opposite parts of a gear wheel 17 secured on an output shaft 18 sealingly rotatably mounted in the body 12 and extending to the exterior of the body 12 for operative connection to a mechanism (e.g. a valve or a damper) for movement of the mechanism between a first position (e.g open) and a second position (e.g closed). The rotation of shaft 18 between first and second positions is typically less than 360".

Fig. 1A shows one axial limit of movement of the pistons and Fig. 1B the other axial limit, corresponding respectively to the first and second positions of shaft 18.

The pistons 14, 14a are biassed axially inwards by respective helical springs 19, 19a engaged between the respective end cap 13, 13a and an axially outer radial face 20, 20a of the pistons 14, 14a.

The piston 14 has a central passage 21 which at its axially inner end has a threaded portion 22 engaged with an externally threaded plug 23 having an axially outer radial end face 24. A central recess 25 is formed in the axially outer face of the plug.

The passage 21 is partly formed in an axial extension 26 of the piston 14 extending axially outwards from the radially inner part of the piston 14 which receives the plug 23 in an air-tight manner.

The end cap 13 has a central bore receiving a two-part liner 27 defining an inner surface 28 in which is rotatable an unthreaded portion 29 of an axial shaft 30 which has externally screw threaded portion 31 axially inwards of the portion 29 and bolt head 32 outwards. Inner and outer bearings 33, 34 are provided and nut 35 on portion 31 and head 32 against the bearings hold the shaft 30 in axial position whilst permitting rotation of the shaft 30 in the end cap 13.

Seals are provided as required e.g. at 37.

An internally threaded nut 38 is mounted on portion 31 and has an axially inner radial end face 39 and an axially inner external flange 40 providing an axially outwards facing radial surface 41. The axially outer end of the extension 26 has a radially inward part 42 providing an axially inwards face 43.

The nut 38 can move axially with respect to the piston 14 but not rotatably. For example the radially outer surface 44 of the flange 40 and the radially inner face 45 of the extension 26 are non-round and generally mating or, as shown, flange 40 may have an external radially extending key 46 axially slidable in but non-rotatable in an axial keyway 47 in extension 26.

In the assembled condition shown in Figs. 1A, 1B, the radial inner face 59 of the body 12 at the ends engages an outer face 51 of the respective end cap and the axial end face 52 of the body 12 engages an axially inner face 53 of an external flange 54 on end cap 13, the parts 13, 12, 13a being held together axially by various methods including an internal key design or screws through the flange of the end cap 13 into the end face of the body 12 or tie rods extending through the flanges 54 of the end caps on each end so as to hold the body 12 under pressure. Suitable seals (not shown) are provided between the confronting faces.

One suitable key is an elongate helical coil 60 received in confronting circumferential grooves in overlapped surfaces 51, 59 of the end cap and the body 12; an example is described in specification GB-A-2253459.

The pistons 14, 14a are moved from the first position Fig. 1A to the second position Fig. 1B by air pressure supplied to the space 58 between the pistons through a supply port 61 in the body 12 from a supply 62 which may be a solenoid-operated valve 63 connected to a source of pressure air and operated by a control signal. On operation of another control signal the valve 63 connects the space 58 to exhaust and the springs 19, 19a move the pistons axially inwards. Axial inward movement (Fig. 1B) of the pistons 14, 14a is limited by engagement of face 43 of either one of the piston extensions 26 with the face 41 of the respective nut 38 (nut 38 as shown). The face 43 can be provided by an integral part of the piston as shown or by an inserted plug secured into the end of the piston extension 26 and provided with a hole for the shaft 30 to pass through.

Axial outward movement (Fig. 1A) of the pistons 14, 14a is limited by engagement of the face 24 of a plug 23 fitted to either one of the pistons 14, 14a with the face 39 of the respective nut 38 (nut 38A as shown). The face 24 can be provided by a plug as shown or by an integral part of the piston. Each limit position can be independently adjusted by rotating the respective shaft 30 or 30a to cause the associated nut 38 or 38a to move axially. One nut 38 can set both limit positions or either of the two limit positions can be set respectively by the two nuts 38. The extent of movement of the pistons (and shaft 18) can be adjusted continuously in a range from zero to a maximum, and an actual selected extent of permitted movement can be located at any selected position in the range, if both nuts 38 are used to effect the selection.The valve need not be closed or fully open in either limit position of the shaft 18 and the pistons can be spaced apart in the inner limit positions differently than shown in Figs. 1A and 1B. This adjustment feature can be used in an actuator in which the springs 19, 19a are omitted and the pistons are moved inwards by air pressure supplied to the end closures in known manner.

During dis-assembly (and assembly) the force exerted by the springs 19, 19a can be safely taken up by rotation of shaft 30 so that the spring force is contained between the end cap, nut and the piston. The end cap retention key 60, or the housing screws or bolts, can then be safely removed without any load being exerted on them by the springs. Once this force has been contained, the end cap can be permitted to move away from the body 12 by rotation of the shaft 30 to a position (Fig. 2) in which the springs are not stressed whilst the end cap remains connected via the connection between the shaft 30 and the axial face 41 of nut 38 and the piston extension face 43.

Further rotation of the shaft 30 disconnects shaft 30 from nut 38 and allows disassembly of the unit with unstressed springs. In the outermost position, the inner-end of shaft 30 is received in recess 25 of plug 23. In general and in particular in the case where the supply of pressure air fails, the actuator can be manually adjusted to any desired position by rotation of one or both bolts 32, 32a, e.g. by a spanner or handwheel, to rotate the shaft 30 or 30a. Thus in Fig. 3A the actuator is in the position of Fig. 1A, and in Fig. 3B is in the position of Fig. 1B.

One way of locking a shaft 30 is to provide a ring with angularly spaced apertures around the head 32 and fixed to the end cap and another apertured ring embracing the head 32 and secure the rings together with a releasable lockable padlock. Another way is to embrace the head 32 by a member and prevent the member rotating by screw means extending through the member into an external boss on the end cap. This is indicated schematically at 70. The locking can be at any desired position of shaft 30 and override any supply signal.

The pistons can be locked at any desired position within the range of movement by moving one nut 38 to lock the pistons against movement in one direction and moving the other nut 38 to lock the pistons against movement in the opposite direction. This is illustrated in Figs. 3c and 3d.

In Fig. 3C the nut 38A is at the right-hand limit of movement with the actuator in the position of Fig. 1A (preventing inward movement of the pistons by the springs) and in Fig. 3D the nut 38A is at the left-hand limit of movement with the actuator in the position of Fig. 1B (preventing outward movement of the pistons by air pressure). The end cap, and thus the actuator, is thus locked in the position of Fig. 3C or 3D.

The above arrangement provides: a) A travel limit stop arrangement which affords infinite adjustment in both directions within the full range of a partturn pneumatic actuator.

b) A travel limit stop arrangement which allows safe pre-compression and decompression of springs without the use of special equipment.

c) A travel stop arrangement which allows the use of the travel stops to act as a means of manual operation in the event of loss of supply to the actuator.

d) A travel stop arrangement which allows the adjustment of the operated mechanism to a desired position and locking the mechanism in this position.

The described arrangement has the following features: a) Limiting the action of the actuator in both directions over a continuous range within its extremes.

b) Pre-compressing and decompressing the springs safely without recourse to special equipment.

c) Adjusting the actuator manually to position the mechanism operated by the actuator in a desired position in the event of a failure of supply.

d) Locking the actuator in any desired position, overriding any supply signal.

Some aspects of the invention can be applied to both single-acting and double-acting actuators. Thus a piston can be moved in one direction by pressure fluid and in the reverse direction by spring means; or can be moved in both directions by pressure fluid.

In the arrangement of Fig. 1A above, the springs could be omitted and pressure fluid supplied as required to the end caps to move the pistons inwards. For example, a further supply port 61a can also be provided to supply air via a connecting pipe or internal passage 61B to the spaces 62A at both ends of the actuator.

In a modification (Figs. 4, 5, 6A to 6D), the plugs 23, 23a are omitted, the axially inner ends of the pistons having no aperture, and a drive-in smooth bore plug 100 is secured in the outer end of the piston extensions 26, 26a, (flange 42 being omitted) to provide shoulder 43. The nut 38, 38a has a non-round e.g. hexagonal periphery as above and is placed in the bore 21 before the plug 100.

In a further modification (Figs. 7, 8, 9A to 9D) a knuckle 110 is inserted into a slot 111 in the extension 26 and has an inner threaded base 112 which receives the shaft 31. In this case the knuckle can engage, with appropriate adjustment, a selected end face 43 or 24b of the slot 111.

A more simple arrangement is shown in Figs. 10 to 12, which may be particularly useful for positioning ball and plug valves which may not require adjustable stops for limiting the valve movement. In this example an axial extension 80 of the piston 14a has a bore 81 which receives in its outer region a drive-in plug 82 having a non-round outer periphery in a corresponding shape section of the bore 81. The plug 82 has an internal thread co-operable with a threaded bolt 83 (not shown in Fig. 12) which extends through the end cap 13.

The bolt 83 can be rotated to allow the springs 19 to fully relax (Fig. 11) whilst holding the end cap. O-ring seals are indicated at 84 and confronting grooves 60a; 60b in the end cap and cylinder 12 respectively receive key 60 of helically wound wire. In the assembled condition of Fig. 12 the bolts 83 are removed and the end cap 13 is held in place by the key 60 which is partly compressed radially by slight axial movement of the end cap and then holds the end cap against axial movement.

In order to remove the end cap and springs for maintenance, the bolt 83 is inserted into the end cap and rotated in the plug 82 to an extent sufficient to take up the axial force on the spring 19 and relieve the axial force on the key 60. The key 60 can then be removed through an aperture in the cylinder 12, through which it was initially inserted, and the bolt 83 can then be rotated in the plug 82 to allow the end cap 13 to move axially and fully allow the spring 19 to expand to the fully relaxed position (Fig. 11) when the bolt 83 can safely be removed from the plug 82.

Similarly, the end cap, spring and piston can be brought to a pre-assembled compressed condition using bolt 83 before being assembled into the cylinder 12 whereupon the key 60 can be inserted and the bolt 83 then safely removed.

The arrangement may be used in three differing applications.

a) Once relieving force has been exerted on the springs by the retaining screw 83, the key 60 can be removed. The retaining screw can then be unscrewed until the pre-compression of the springs is totally relieved. The end closure and the springs can then be disassembled. This operation is useful for replacement of springs.

b) Retaining screws 83 are fitting to both ends of the actuator. Relieving force is exerted on the springs by the retaining screws and both keys 60 are removed. By rotating the pinion 91 the pistons are forced out of engagement and the end closure/springs/piston retaining screw assembly can be removed as a whole. This operation is useful for general maintenance and examination.

c) When an assembly as in b) is removed and examination shows a need to disassemble the springs, the retaining bolt 83 can be used as in a) safely to decompress and remove the springs.

The maximum angle of rotation of the shaft 18 can be different in different actuators e.g. 90 , 1800, 270".

Claims (20)

1. A fluid-pressure-operated actuator comprising a housing, piston means movable in the housing for an extent of movement between first and second limit positions, a rotary output shaft operatively connected to the piston means and extending to the exterior of the housing, means defining said first and second limit positions, and means for adjusting the defining means for varying the extent continuously between zero and a maximum.

2. An actuator as claimed in Claim 1, in which the defining means is adapted to locate a selected extent at any position within said maximum extent.

3. An actuator as claimed in Claim 1, comprising first limit defining means defining the first limit and second limit defining means defining the second limit, and means for adjusting both the first and the second limit defining means.

4. An actuator as claimed in Claim 3, in which each of the first and second limit defining means is adapted selectively to define either of the first and the second limits.

5. An actuator as claimed in any preceding claim, in which the limit defining means comprises an axially movable non-rotatable member threadedly connected to a rotary member.

6. An actuator as claimed in Claim 5, in which the or each rotary member is rotatable from outside the housing.

7. An actuator as claimed in Claim 5 or Claim 6, in which the or each rotary member comprises an axial member.

8. An actuator as claimed in any of Claims 3 to 7, comprising two pistons each operatively connected to the output shaft and each having axially inner and outer faces selectively co-operable with axially inner and outer faces on a respective one of the first and second limit defining means.

9. An actuator as claimed in Claim 8, in which each piston is biassed towards the other by spring means.

10. An actuator as claimed in Claim 9, in which the spring means are helical and the respective rotatable member extends through the spring means.

11. An actuator as claimed in any of Claims 1 to 8, comprising spring means engageable between the piston means and a detachable part of the housing, and means preventing detachment of the housing part until the spring means is relaxed.

12. An actuator as claimed in Claim 11, in which the preventing means comprises a threaded member rotatable in the housing part and threadedly connected to the piston or to a member for engaging the piston.

13. An actuator as claimed in Claim 12, in which the threaded member comprises a said rotary member.

14. An actuator as claimed in Claim 1 or Claim 3, including means within the housing for holding the output shaft in a selected position within the extent of movement.

15. An actuator as claimed in Claim 14, in which the holding means comprises means for holding the piston means.

16. An actuator as claimed in Claim 15, in which the holding means comprises the limit defining means.

17. An actuator as claimed in any of Claims 1 to 7, in which the piston means is biassed in one direction by spring means.

18. A fluid-pressure-operated actuator comprising piston means movable in a housing, spring means engageable between the piston means and a detachable part of the housing, and means preventing detachment of the housing part until the spring means is relaxed.

19. A fluid-pressure-operated actuator comprising a housing, piston means movable in the housing operatively connected to a rotary output shaft, and means within the housing for holding the output shaft in a selected position within the extent of movement.

20. A fluid-pressure-operated actuator substantially as hereinbefore described with reference to and as shown in Figs. 1, 2, 3A to 3D, or Figs. 4, 5, 6A to 6D, or Figs. 7, 8, 9A to 9D, or Figs.

10 to 12, of the accompanying drawings.