GB2161992A - Rotary actuator - Google Patents

Abstract

A rotary actuator 10 comprises one or more actuation units, the or each unit consisting of a rotor 16 mounted within a stator 20. The rotor 16 and stator 20 are each provided with at least one pole member 34a, 34b, (18, 19) Fig. 4 which is so positioned that the stator pole members 34a, 34b confront the rotor pole members (18, 19) in spaced apart relationship. The stator pole members 34a, 34b are surrounded by an electrically energisable coil 35 and are circumferentially tapered so that when said coil 35 is electrically energised, a magnetic circuit is created which causes the rotor 16 to rotate relative to the stator 20 to increase combined areas of the instant confronting stator and rotor pole members 34a, 34b, (18, 19) to a maximum value. <IMAGE>

Description

SPECIFICATION Rotary actuator This invention relates to rotary actuators and in particular to rotary actuators of the type which provide rotary actuation in one direction only.

Rotary actuators, such as step per motors, which provide rotary actuation in one direction only are well known. They usually include mechanical means, such as a sprag clutch mechanism, in order to ensure that reverse rotation does not take place. However the use of sprag clutch mechanisms increases costs and also introduces the possibility of reverse rotation in the event of a failure of the mechanism.

A further problem which sometimes arises with rotary actuators is that in certain situations it is desirable for the actuator to function in such a manner that the force of actuation varies over the actuation duration. Conventional rotary actuators are not easily adaptable to provide such an effect.

It is an object of the present invention to provide a rotary actuator which provides rotary actuation in one direction only , which does not rely on the provision of mechanical means to prevent inadvertent reverse rotation and which has the facility to alter the force of actuation thereof in a predetermined manner over the actuation duration.

According to the present invention, a rotary actuator comprises one or more actuation units, the or each actuation unit comprising a stator and a rotor mounted adjacent each other, and an electrically energisable coil, each of said stator and rotor being provided with a circumferentially extending pole member which is so disposed that said pole members respectively provided on each stator and rotor confront each other in spaced apart relationship, at least one of said pole members being of circumferentially tapered configuration so that upon the rotation of said rotor relative to said stator, the combined areas of the pole members of said rotor and stator which confront each other at any one instant progressively increases from a minimum value to a maximum value, said coil, when electrically energised, providing a magnetic circuit, part of which extends between and is generally normal to the instant confronting surfaces of said pole members, so as to cause said rotor to rotate to increase said instant combined pole area to a maximum value.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a side view on section line B-B of Fig. 2 of a rotary actuator in accordance with the present invention.

Figure 2 is a view on section line A-A of Fig. 1.

Figure 2a is similar to Fig. 2 with the exception that the rotor of the actuator is shown in a different position.

Figure 3 is a view on section line A-A of Fig. 1 which depicts an alternative configuration for a rotary actuator in accordance with the present invention.

Figure 4 is a perspective view of the rotor of the rotary actuator shown in Fig. 1.

Figure 5 is a developed view of one of the stator pole members of the actuator shown in Fig. 1.

Figure 6 is a sectional side view of an alternative form of rotary actuator in accordance with the present invention.

Figure 7 is a perspective view of one of the rotors of the rotary actuator shown in Fig. 6.

With reference to Fig. 1, a rotary actuator generally indicated at 10 comprises two support members 11 and 1 2 which carry a shaft 1 3 by way of two plain bearings 14 and 1 5 respectively. The shaft 1 3 in turn carries two similar axially spaced apart rotors 1 6 and 1 7.

The rotors 1 6 and 1 7 may be integral with the shaft 1 3 as shown in Fig. 1 or they may be merely attached to the shaft 1 3 by suitable attachment means. Each of the rotors 1 6 and 17, which can be seen more clearly in Fig. 4, is of circular cross-sectional shape but with two similar diametrically opposed segments missing so that each rotor is left with two diametrically opposed part-circular pole members 1 8 and 19, the radially outer surface of each of which substends an angle of 90 at the axis of rotation of the shaft 1 3. The rotors 1 6 and 1 7 are angularly displaced with respect to each other so that they are 90 out of phase.

The rotors 1 6 and 1 7 are respectively mounted for rotation within two stator members 20 and 21 as can be seen in Fig. 1. The stator members 20 and 21, which are supported by means not shown, are generally similar. Each of the stator members 20 and 21 is respectively constituted by a pair of adjacent plates 26a and 27a, and 26b and 27b respectively. The plate pairs 26a and 27a, and 26b and 27b are each maintained in axially spaced apart relationship by a magnetically conductive bridging piece 29. A further bridging piece 30 maintains the stator members 20 and 21 in axially spaced apart relationship. The bridging pieces 29 and 30 and the plates 26a, 27a, 26b and 27b are all held together by four bolts 31 which pass through appropriate holes therein.

The plates 26a, 27a, 26b and 27b are respectively apertured with similar sized circular apertures 32a b c and d. The apertures 32a b C and d are aligned and coaxial with the axis of rotation of the shaft 1 3 so as to accommodate the rotors 1 6 and 1 7 as shown in Fig. 1. The radially inner surfaces 33a b c and d of the plates 32a b C and d respectively each have two circumferentially extending pole members 34a and 34b attached thereto.

Each of the stator pole members 34a and 34b extend around approximately one half of the radially inner surface 33a b c or d so that circumferentially adjacent stator pole members 34a and 34b define a complete circular pole as can be seen in Fig. 2. Each of the stator pole members 34a and 34b is additionally of circumferentially tapered form as can be seen in Fig. 5. Moreover each pair of stator pole members 34a and 34b is so disposed that the end of the broadest portion of each of the stator pole members is in series abutment with the narrowest portion of its circumferentially adjacent stator pole member. Each pair of stator pole members 34a and 34b on each of the stators 20 and 21 is aligned with the other pole member pair on its particular stator. Moreover the stator pole member 34a and 34b pair on one of the stators are in phase with the other stator pole member 34a and 34b pair.

The rotors 1 6 and 17, and the stators 20 and 21 and their respective stator pole members 34a and 34b are so dimensioned that the rotors 1 6 and 1 7 may freely rotate within the stators 20 and 21. Moreover the partcircular rotor pole members 1 8 and 1 9 of the rotors 1 6 and 1 7 are arranged to be aligned with and are in radially spaced apart relationship with the stator pole members 34a and 34b as shown in Figs 1 and 2.It will be seen therefore that upon the rotation of the rotors 1 6 and 1 7 in the appropriate direction, the stator pole members 34a or 34b surface which is adjacent to and confronts the rotor pole member 1 8 or 1 9 will progressively increase in width. Thus upon rotation of the rotors 1 6 and 1 7 in the appropriate direction, the combined areas of the rotor and stator pole members 18,19 and 34a, 34bwhich confront each other at any one instant progressively increases from a minimum value to a maximum value.

The axially spaced apart stator plate pairs 26a and 27a, and 26b and 27b each provide axial location for a coil 35. The coil 35 extends around each of the stator 20 and 21 and may be of the conventional wound wire type. However we prefer that it should consist of a wound conductive tape in view of the improved penormance benefits which such tape brings.

If the coil 35 of the stator 21 is electrically energised, it provides a toroidally shaped magnetic circuit shown in interrupted lines 36 in Fig. 1 which extends axially within the bridging piece 29 and the rotor 1 7 and radially within the plates 26a and 26b, the stator pole members 34a b c and d and across the gaps between and normal to the confronting surfaces of the rotor and stator pole members 18, 1 9 and 34a, 34b respectively.If the rotor 1 7 and stator 21 are in the relative positions shown in Fig. 2 in which the combined area of the confronting surfaces of the rotor pole members 18, 1 9 and the stator pole members 34a and 34b is at a minimum value, then the magnetic attraction between the rotor and stator pole members 18, 1 9 and 34e and d respectively causes the rotor 1 7 to rotate in a clockwise direction (when viewed in Fig. 2) so as to increase the combined pole area to a maximum value. That maximum value is reached when the rotor 1 7 has rotated through 90 to the position shown in Fig. 2a.

Thus energising the coil 35 results in the rotation of the rotor 17, and hence the shaft 1 3 and the rotor 1 6 through an angle of 90 .

This in turn brings the rotor 1 6 into a position in which the combined confronting areas of its rotor pole members 1 8 and 1 9 and the stator pole members 34a and 34b is at a minimum value. Consequently if the current to the coil 35 of the stator 21 is switched off and a current is applied to the coil 35 of the stator 20 the resultant toroidal magnetic circuit causes the rotor 1 6 to rotate through an angle of 90 to increase the confronting combined areas of the rotor pole members 1 8 and 19, and the stator pole members 34a and 34b to a maximum value.This in turn results in the rotor 1 7 being returned to its original position in which the combined confronting areas of its probe members 1 8 and 1 9 and the stator pole members 34a and 34b are at a minimum value.

It will be seen therefore that alternate electrical energisation of the coils 28 of the stators 20 and 21 results in the rotors 16 and 1 7 alternately providing stepwise rotation of the shaft 1 3 in 90 increments. It will be appreciated however that rotational increments of more or less that 90 could be provided by altering the circumferential lengths of the pole members of the rotor 16, 17 and stator units 20, 21. Moreover if complete rotation is not required, only one unit need be employed, the configuration of which determines the degree of rotation of its rotor and associated shaft.

The provision of curcumferentially tapered stator pole members 34a and 34b provides the capacity for accurate control over the force/stroke relationship of the rotors 1 6 and 1 7. Thus the rotor 1 6 and 1 7 force/stroke relationship may be readily fixed by ensuring that the degree of taper of the stator pole members 34a and 34b is in accordance with the appropriate rate of change of confronting pole member area with stator pole member circumferential extend.

It is envisaged that even greater control of the rotor force/stroke relationship may be achieved by configuring the rotor or stator pole members in such a manner that the radial gap between them varies with stator pole member circumferential extent. The arrangement would be such that the stator starts at a position in which the radial gap is large and rotates to a position in which the gap is small, the magnetic attraction between the rotor and stator pole members causing the rotor to rotate to reduce the gap to a minimum value. Such an arrangement is shown in Fig. 3 in which the stator pole members 34a and 34b are of progressively decreasing radial thickness.

In a further alternative form of the present invention, one of the units defined by the rotor 1 6 and stator 20, and the rotor 1 7 and stator 21 could be modified by the incorporation of a permanent magnet (which is of the magnetically indestructable type) into its magnetic circuit, for instance in the axial magnetic circuit path part of the rotor. If the two coils 35 are connected in series or parallel via a single switch, the shaft 1 3 rotates through 90 when the coils are electrically energised, and then through a further 90 when the current to the coils is switched off. Moreover the permanent magnet ensures that the shaft 1 3 is locked against rotation when the current is switched off.

An alternative form of rotary actuator in accordance with the present invention is shown in Figs. 6 and 7. The actuator, which is generally indicated at 37 comprises a circular cross-section stator 38 which is provided with a sleeve 39 along its longitudinal axis which receives a shaft 40 for rotation therein.

The shaft 40 carries two identical rotors 41, which, as can be seen more clearly in Fig. 7 are disc shaped and are provided with two diametrically opposed axially extending integral pole members 42. The rotor pole members 42 confront circumferentially tapered pole members 43 which are provided on each end of the stator 38.

The stator 38 is provided with two cut-out portions 44 which respectively accommodate two conductive tape wound coils 45. The coils, when electrically energised, provide toroidal magnetic circuits 46 which, inter alia, pass across the gap between the stator and rotor pole members 42 and 43 as indicated by the interuppted lines 47.

The rotary actuator 37 functions in a manner similar to that of the actuator described with reference to Figs. 1-5 in that the coils 44 are alternately actuated so that the rotors 41 rotate to increase the combined areas of the confronting portions of the rotor and stator pole members 42 and 43 respectively to a maximum value. It differs from the previously described actuator however in that the pole members 42 and 43 confront each other axially rather than radially. This may be desirable if, for instance, it is desirable to provide some degree of axial loading on the shaft 40.

Although the present invention has been described with respect to embodiments which are provided with tapered stator pole members and circumferentially separated rotor pole members, it will be appreciated that tapered rotor pole members and circumferentially separated stator pole members could be utilised if so desired.

It will be seen therefore that the present invention provides rotary actuators which are capable of single or multi-step rotation and which are of extremely simple and therefore cheap, construction. Moreover, when energised, they are capable of rotation in one direction only and therefore do not require any mechanical device to prevent reverse rotation. Electrical control is also simple since the electrical supply to the actuator does not have to carry any "direction of rotation" information.

Claims (9)

1. A rotary actuator comprising one or more actuation units, the or each unit comprising a stator and a rotor mounted adjacent each other, and an electrically energisable coil, each of said stator and rotor being provided with a circumferentially extending pole member which is so disposed that said pole members respectively provided an said stator and rotor confront each other in spaced apart relationship, at least one of said pole members being of circumferentially tapered configuration so that upon the rotation of said rotor relative to said stator, the combined areas of the pole members of said rotor and stator which confront each other at any one instant progressively increases from a minimum value to a maximum value, said coil, when electrically energised, providing a magentic circuit, part of which extends between, and is generally normal to, the instant confronting surfaces of said pole members so as to cause said rotor to rotate to increase said instant combined pole area to a maximum value.

2. A rotary actuator as claimed in claim 1 wherein said stator and rotor pole members confront each other in radially spaced apart relationship.

3. A rotary actuator as claimed in claim 1 or claim 2 wherein said rotary actuator consists of two of said actuation units, the rotors of said units being coaxially mounted so that the pole member on one of said rotors is 90 out of phase with the pole member on the other of said rotors, the pole members on said stators being in phase with each other.

4. A rotary actuator as claimed in claim 1 or claim 2 wherein said rotary actuator comprises one of said units in combination with a further unit comprising a rotor and a stator of the same configuration as said previous unit, the pole member on the rotor of said further unit being 90 out of phase with the pole member on the rotor of said first unit, the pole member on the stator of said further unit being in phase with the probe member of said first unit, either the rotor or stator of said further unit being provided with a permanent magnet in the magnetic circuit thereof, the coils of said units being electrically connected in series or in parallel to be simultaneously actuated.

5. A rotary actuator as claimed in any one preceding claim wherein the rotor of the or each actuation units if of circular cross-section with segments thereof missing so that the remainder defines the pole members thereof.

6. A rotary actuator as claimed in any one preceding claim wherein said rotor and stator pole members are additionally so configured that upon the rotation of said rotor in the direction of actuation of said actuator, the gap between rotor and stator pole members progressively decreases from a maximum value to a minimum value.

7. A rotary actuator as claimed in any one preceding claim wherein said actuation unit comprises a stator having two of said pole members which are circumferentially adjacent so that the widest portion of one of said pole members is situated adjacent the narrowest portion of the other of said pole members.

8. A rotary actuator as claimed in any one preceding claim wherein said coil is formed from a wound conductive tape.

9. A rotary actuator substantially as hereinbefore described with reference to and as shown in the accompanying drawings.