GB2302708A

GB2302708A - Rotary Actuators

Info

Publication number: GB2302708A
Application number: GB9513038A
Authority: GB
Inventors: David Ralph Mooney; Lemos John Newman Cedric De
Original assignee: Worcester Controls AG; Worcester Controls UK Ltd
Current assignee: Worcester Controls AG; Worcester Controls UK Ltd
Priority date: 1995-06-27
Filing date: 1995-06-27
Publication date: 1997-01-29
Also published as: GB9513038D0; WO1997001712A1; GB2302708A8; AU6012596A

Abstract

A pneumatically operated rack-and-pinion type actuator for ball valves and the like comprises a piston and cylinder device in which the outward loads generated by the rack and pinion are taken by the cylinder itself via bearing elements 50 on the pistons and air transfer to the actuating chambers between and behind the pistons is effected by non-structural air transfer tubes 68,70 on which the pistons freely slide. By avoiding the need for structural piston guide rods and associated structures, the actuator is greatly simplified. End caps are fixed by circlips 62 arranged to be carried into grooves in cylinder 48 by sloping end surfaces on the caps.

Description

2302708 1 ROTARY ACTUATORS This invention relates to rotary actuators and

more particularly but not exclusively to pneumatically operated rotary actuators for ball and the like valves. A main aspect of the invention is concerned with the inter- related questions of the loads arising from the use of a rack and pinion type or other linear-to-rotary motion convertors, and the communication of pneumatic or other fluid pressure to the actuating chambers of such devices and thus these aspects of the invention are concerned with actuators comprising such devices. Further aspects of the invention are concerned with the related question of the mounting and location of an end cap or plug for a fluid pressure operated actuator, and thus are applicable to such fluid pressure operated actuators more generally.

There are disclosed in GB 11 71 618 and GB 1251805 (Norbro Engineering Ltd) pneumatically operated piston-rack rotary actuators comprising twin pistons carrying rack portions, an associated rotary pinion, and a cylinder assembly provided by cylinder portions clamped together by substantial structural guide members on which the pistons slide. These guide members serve as load taking means to resist the outward ly-d i rected forces generated by the rack and pinion assembly during use. Accordingly, there is provided for sliding engagement between each piston and the associated guide rod, an extended bearing sleeve. Notably also, there is provided clearance between the pistons and their associated cylinder (see items 36 and 37 in Fig 1) which is sealed by an O-ring 35.

Notably also in GB 11 71 618 the structural guide 2 rods also serve as air transfer tubes for feeding air or other gas internally within the actuator to the piston actuating chambers at opposite ends of the device and between the pistons.

Shortcomings of the above-discussed prior proposal are principally its relatively complex construction and consequential relatively high cost. There is a considerable need to achieve simplification and cost reduction while retaining the satisfactory operating characteristics.

An object of the present invention is to provide an actuator suitable for use in relation to ball and the like valves, and which may have application more widely, offering improvements in relation to simplicity of construction and/or reduced manufacturing cost and/or performance characteristics with respect to the above-mentioned state of the art, or generally.

According to the invention there is provided an actuator as defined in the accompanying claims.

In an embodiment an actuator comprises a cylinder portion and associated pistons together with rack and pinion means for converting linear to rotary motion. In place of the internal load taking means of the prior GB 1618 specification mentioned above, the embodiment provides for the pistons to transfer load directly to their associated cylinder portion, by means of axial ly-extended bearing means. Moreover, the pistons slide on air transfer tube means not forming part of the load taking means for the pistons. The air transfer tube means is sealed to the piston or pistons by non load-bearing sealing means.

By this means there is provided a simple construction utilising a cylinder and an associated block without the requirement for rods for assembly purposes. Moreover, the end caps of the cylinder 3 assembly take the axial loads which in the prior proposal were retained within the integral assembly held together by the mounting rods. Additionally, no bearing sleeves are needed between the pistons and their associated tubes. Also the tubes are a relatively simple and inexpensive construction.

In the embodiment, the extended bearing means on the pistons is located generally radially outwardly of the respective rack portion of the piston so that the outward ly-directed load is transferred direct to the cylinder.

Also in the embodiment, the end caps or plugs of the piston and cylinder assembly are located in use by circlip means so as to be releasable in a simple manner. The circlip is adapted to resist the repetitive loadings by virtue of features of its shape and the profile of the corresponding surface on the end cap, as more fully described below.

The air transfer tubes in the embodiments comprise a tube fixed to the end cap or plug to feed air from that end of the assembly to the chamber between the pistons. There is also provided a second tube extending between the head side chambers of the device to interconnect these chambers for actuation purposes. The air tube fixed to the actuator end cap is thus-fixed by means of a profiled ferrule which is inserted into the tube for mounting purposes.

In the embodiments, the air tubes are sealed to their respective pistons by means of O-rings.

The air transfer tubes may be of a number of different materials including plastics and stainless steel. The air transfer tube which moves with its respective piston may be arranged to actuate a micro switch for a control system of the apparatus.

A further factor in relation to the provision of means for transferring actuating air within the 4 actuator concerns the requirement that the actuator shall be able to co- operator in a simple face-to-face manner with the associated valve structure. This requirement precludes the possibility of providing a simple external air transfer duct, which might otherwise represent a simple and direct manner of achieving the necessary operating characteristics.

Considering now the second aspect of the invention concerning the location of the cap or end plug of the assembly by a circlip, this aspect of the invention is characterised by the feature that the circlip is adapted to be loaded inwards with respect to its locating groove, in use.

As a result, in the embodiment, the advantage is provided that despite the endless cycles of loading of the circlip each time the actuator is energised, the possibility that such repetitive cycles of the device will ultimately cause wear of the loaded surfaces and corresponding, increased tolerances until at last the circlip will be disengaged, is greatly reduced, moreover, this result is achieved in a simple manner by adoption of appropriate profiles on the relevant surface of the end cap or plug and/or on the circlip itself and its locating groove.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

Fig 1 shows a plan view of assembly; Fig 2 shows a section on the line II-II in Fig 1; Fig 3 shows a side elevation view of the actuator of Fig 1, the direction of viewing being shown by arrow III in Fig 1; Fig 4 shows a section on the line IV-IV in Fig 1; and an actuator Fig 5 shows a vertical section on the line V-V in Fig 3; Fig 6 shows an end elevation view of the actuator of Fig 3, as indicated by arrow VI in Fig 3; and Fig 7 shows an enlarged portion of the end cap and cylinder assembly of Fig 2.

As shown in the drawings an actuator 10 comprises a main body 12 having body halves 14 and 16, and located therein and extending through the main body a tube or cylinder 18 having end plugs 20 and 22.

Actuator 10 has a drive output shaft 24 adapted to transmit drive to the complementary drive input formation of a ball or other type of valve (not shown). The valve assembly is adapted to mount faceto-face with the flat end face 26 of body half 14. As shown in Fig 3, threaded bores 28 are provided in face 26 for mounting purposes in relation to the ball valve assembly to be controlled.

Turning now to the internal structure of actuator 10, and referring to Fig 2 of the drawings, it can be seen that actuator 10 further comprises pistons 30 and 32 slidable within cylinder 18, and each formed with a part-cylindrical axially-inwardly extending extension portion 34, 36, each extension portion being of corresponding part-cylindrical form and thus being arcuate as viewed in the axial direction. Each extension portion is formed with an array of rack teeth 38 to co-operate with complementary pinion teeth 40 formed on the inner portion of drive output shaft 24, which is journalled in bearings (not shown) provided in main body 12.

It will be understood that the rack-and-pinion device, 38, 40 causes linear relative motion of the pistons lengthwise of the axis 42 of actuator 10 to be converted to rotary motion about the axis 44 of shaft 24 to effect controlled actuating motion of up to 90 degrees of a valve actuating member (not shown).

6 It will be noted that drive output shaft 24 is formed with a slot-form drive output formation 46 for drive transmission purposes. It will also be noted that the interaction of rack and pinion teeth 40, 38 results in generally outwardly-directed forces F being applied to piston extension portions 34, 36 causing these to be loaded outwards against the internal surface 48 of cylinder 18. The extension portions 34 and 36 are accordingly provided with axially lengthwise-extending bearing elements 50 of bearing materials such as PTFE whereby friction and wear is reduced. The bearing elements are provided in the form of discreet bearing inserts of appreciable axial length as shown in Fig 2 and relatively narrow width, at spaced intervals across the arcuate extent of the piston extensions 34 and 36.

Accordingly, it can now be seen that the generally outward ly-d irected f orces generated by the rack and pinion device 38, 40 are transferred direct through the piston extensions 34 and 36 and bearing elements 50 to cylinder 18 during use.

Pistons 30 and 32 have respective sealing rings 52 and are freely slidable within cylinder 18. A central chamber 54 is defined between the pistons to receive actuating air to cause relative outward movement of the pistons. End chambers 56 and 58 are defined between pistons 30 and 32 and their respective end caps or plugs 22 and 20 respectively. The end plugs 20 and 22 are sealed to cylinder 18 by respective sealing rings (not shown) received within ring grooves 60 formed in cylinder 18. The end plugs are retained in their working positions, in a 62 in cylinder 18, and to be more fully described below.

Air for controlling actuator 10 is admitted to removable manner, by means of respective circlips received in respective grooves formed likewise 7 the actuator through ports 64, 66 formed in end plug 22, as shown in Fig 6. The arrangements for transmission of air from these ports to the chambers 54, 56 and 58 will now be described.

Broadly, to effect controlled supply of air from ports 64 and 66 to the chambers 54, 56 and 58 there are provided primary and secondary air transfer tubes 68 and 70 respectively. Primary tube 68 transfers air from port 66 to central chamber 54. Secondary air transfer tube 70 transfers air from port 64 to both of the chambers 56 and 58. Thus, transfer tube 68 is associated with outward movement of the pistons, and air transfer tube 70 with inward movement of the pistons.

The air transfer tubes extend slidingly through corresponding bores 72, 74, 76 and 78 formed in the pistons 30 and 32. The pistons freely slide on the tubes 68 and 70 and are provided with grooves 80, 82 and 84, to receive 0-rings (not shown) to effect airtight sealing as appropriate for the necessary pneumatic control. Thus, in the case of primary air transfer tube 68, the 0-ring (not shown) in ring groove 80 seals bore 72 to prevent air transfer from inner chamber 54 to outer chamber 56. The 0- rings in ring grooves 82 and 84 do likewise.

Primary air transfer tube 68 is located and mounted in position on end plug 22 by means of a tapered ferrule 86 (see Fig 7) which is inserted into the open end of tube 68 to fix same in position and to produce a fluid-tight seal. The ferrule has a f ew degrees of taper on its outer surf ace so as to produce the necessary mounting and sealing effect upon insertion into the open end of air transfer tube 68. The inner bore 88 of ferrule 86 is of uniform radius.

As shown in Fig 2, primary air transfer tube 68 extends into chamber 54 and delivers air thereto. It 8 will be noted that bore 74 in piston 32 which receives the inner end of transfer tube 68 is formed with a vent bore 92 to provide direct venting from tube 68 to chamber 54. Likewise, piston 30 has a vent bore 94.

In the case of air transfer tube 70, axial location of the tube is effected by direct engagement of the tapered ends 96, 98 with the end plugs 22, 20. Sealing of the tubes to the pistons is effected by the 0rings in ring grooves 82 and 84.

Bore 74 is closed at its outer end by an end plug 100.

It is particularly to be noted that the air transfer tubes 68 and 70 do not form any part of the load taking means with respect to the rack and pinion device 40, 38. The air transfer tube 68 and 70 are formed, for example, of a plastics material, or stainless steel and are merely sealed to the pistons by non load-bearing 0-ring seals. The air transfer tubes have no means for resisting any appreciable loads generated during use, notably outward ly-d irected loads resulting from the use of the rack and pinion device. Thus, the air transfer tubes are of relatively low strength materials and have no mountings appropriate for transfer of loads to any load resistant structure. In any case, the outwardly directed loads are transferred directly laterally outwardly through the piston extension portions 34 and 36 to the cylinder 18.

Fig 4 shows the plan view profile of the piston extension portions 34, 36 - only one of these being seen in this view. Fig 4 also shows the arrangements whereby drive output shaft 24 extends through aligned bores 102 formed in cylinder 18 and receiving corresponding complementary collars 104 formed in the upper and lower main body halves 14 and 16 and which co-operate with sealing rings 106 located against 9 central rack portion 108 of output shaft 24. Grooves 110 are provided in the main body halves 14 and 16 to receive further sealing rings (not shown) to seal between the body halves and cylinder 18.

Also shown in Figs 4 and 5 are air chambers of generally cylindrical form, formed in aligned positions in pistons 30 and 32, and in end plug 22. The purpose of these chambers is to house coiled compression springs designed to be compressed and thus to store energy and to provide a fail safe return capability in the event of power failure.

Main body halves 14 and 16 are held in clamped positional relationship by nut and bolt assemblies 114 - see Fig 3. Details of the arrangement whereby circlips 62 retain end plugs 22 and 20 in position will now be described further.

As shown in Fig 7, circlips 72 are of round cross-sectional profile and are located in corresponding circlip grooves 116 which are of complementary part-circular profile. Each circlip cooperates with its respective end plug through a contacting portion of the plug which is adapted to generate an inward force on the circlip itself. Thus, in this embodiment, the contacting portion of plug 22 seen in Fig 7 is in the form of a shoulder 118 having a corresponding 45 degree profiled or chamfered annular surface 120 adapted to contact the circlip 62 and to apply to it a force directed so as to tend to maintain the circlip within its groove 116. Thus, the resultant force is directed into the groove rather than in any direction which is axial of the actuator assembly or directed inwardly thereof.

Accordingly, under conditions of use in which endless repeated cycles of the actuator are carried out, there is no tendency for the cycles of force applied by the end plug to the circlip to dislodge same.

Removal of the circlip for servicing or other purposes is carried out in the usual way by flexure out of the groove 116 after inward movement of the pistons and of the end plugs.

There is shown in Fig 2, and likewise in Figs 3 and 6 a pair of plug retaining screws 122 insertable through threaded apertures in cylinder 18 to engage in corresponding profiled recesses in plugs 20 and 22 to inhibit both inward movement of the plugs when pistons 30, 32 are retracted, and to inhibit any tendency for rotation of the plugs relative to the pistons, which would be detrimental to the air transfer tubes.

Use of the actuator is believed to be self- evident. A controlled supply of pneumatic pressure is delivered to end cap 22 and to ports 64, 66 to cause output shaft 24 to be driven. Outward forces generated by the rack and pinion device are resisted by cylinder 18. End caps 20, 22 are retained by their respective circlips 62.

Amongst other modifications which could be made in the above embodiments while remaining within the scope of the invention are the use of alternative circlip cross-sectional profiles such as a polygonal profile. Likewise, alternative arrangements for the air transfer tubes could be adopted, including the use of alternative materials and alternative dispositions with respect to the pistons.

11

Claims

CLAIMS:-

1 A pneumatically operated rotary actuator for ball and other valves comprising a cylinder portion, pistons slidable therein, rack and pinion means located within said cylinder portion and between said pistons, load taking means for f orces generated by said rack and pinion means, air input means for said actuator, and air transfer tube means for supplying said air from said air input means to said pistons, said pistons being adapted to slide with respect to said air transfer tube means, characterised by said load taking means for said rack and pinion means being provided by said cylinder portion and an associated axially-extended bearing means on said pistons, said air transfer tube means not forming part of said load taking means and being sealed to at least one of said pistons by non load- bearing sealing means.

2 A fluid pressure operator rotary actuator comprising a cylinder portion, associated pistons and linear to rotary motion conversion means characterised by fluid pressure transfer tube means adapted to transfer fluid pressure to said pistons and not forming part of the load taking means for said pistons.

3 An actuator according to claim 1 characterised by said rack of said rack and pinion means being provided on said pistons and said extended bearing means being located radially outwardly of said rack portions of said pistons.

4 An actuator according to any one of the preceding 12 claims characterised by an end cap or plug for said cylinder means located with respect thereto by circlip means.

An actuator according to any one of the preceding claims characterised by said air transfer tube means being sealed to said at least one of said pistons by an 0-ring.

6. An actuator according to any one of the preceding claims characterised by said air transfer tube means comprising a tube to feed air from one end of said actuator to a chamber located between said pistons and said tube being sealed to the one of said pistons at said one end of the actuator and being f ixed to end structure of the actuator at said end.

7 An actuator according to claim 6 characterised by said air transfer tube being fixed to said end cap or plug of said actuator by insertion of a profiled f errule into said tube to cause said tube to grip a bore formed in said cap or plug.

8 An actuator according to any one of claims 1 to 5 characterised by said air transfer tube means comprising a tube to feed air between the head side chambers of said actuator at opposite ends of the actuator.

An actuator according to any one of the preceding claims characterised by said air transfer tube means comprising a plastics material.

An actuator according to any one of claims 1 to 7 characterised by said air transfer tube means 13 comprising stainless steel.

11 An actuator according to any one of the preceding claims characterised by said air transfer tube means being adapted to actuate a micro switch for a control system of said actuator upon movement of said tube with said one of said pistons.

12 A pneumatically operated rotary actuator for ball and other valves comprising a cylinder portion, pistons slidable therein and rotary motion generating means, said cylinder portion having removable end cap or plug means together with locating means therefor, characterised by said locating means comprising a circlip adapted to be loaded inwardly into a groove therefor during use.

13 A fluid pressure operated actuator comprising a cylinder portion, associated pistons and rotary motion generating means characterised by retaining means for an end cap or plug of said cylinder portion, said retaining means comprising a circlip adapted to be loaded inwards with respect to its mounting groove in use.

14 An actuator according to claim 12 or claim 13 characterised by said circlip being adapted to be loaded inwards with respect to its groove by means of a profile on the contacting portion of said cap or plug, said profile being adapted to generate said inward force.

An actuator according to any one of claims 12 to 14 characterised by said profile on said contacting portion of said circlip being adapted to generate said 14 inward force.

16 An actuator according to any one of the preceding claims characterised by said circlip being of generally round cross-sectional profile.

17 An actuator according to any one of claims 12 to 15 characterised by said circlip being of generally polygonal cross-sectional profile.