GB2115227A - Rotary actuator - Google Patents

Abstract

A rotary actuator (10) comprises one or more units, each of which consists of a rotor (16) (17) mounted for rotation within a stator (20). Each stator (20) (21) has semi-circular cross-section surfaces (24, 25), the axes of which are spaced apart and parallel. Each rotor (16) (17) has two part circular cross- section surfaces (18, 19) which confront the semi-circular cross-section surfaces (24, 25) of the stator and an axis of rotation of which is parallel with coplanar with and situated mid-way between the axes of the two semi- circular cross-section surfaces (24, 25). The arrangement is such that upon rotation of the rotor the gaps between the confronting surfaces (18, 19, 24 and 25) of the rotor and stator progressively decrease from a maximum value to a minimum value. A coil (28) is contained within each Stator (20) (21) and when electrically energised, creates a magnetic field which causes the rotor (16) (17) to rotate to reduce the gaps from the maximum to minimum values. <IMAGE>

Description

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

Rotary actuators, such as stepper motors, which permit rotary actuation in one direction only are well known. They are usually provided with a sprag clutch mechanism in orderto ensure that reverse rotation does nottake place. However, the use sprang clutch mechanisms increases costs and also introduces the possibility of inadvertent reverse rotation in the event of a failure of the mechanism.

It is an object of the present invention to provide a rotary actuator which provides rotary actuation in one direction only and which does not not rely on the provision of mechanical means to prevent inadvertent reverse rotation.

According to the present invention, a rotary actuator comprises one or more units, the or each unitcomprisingastatoranda rotormountedfor rotation about an axis of rotation within said stator, said stator and rotor having confronting surfaces which are radially spaced apartfrom each other and so configured that upon rotation of said rotor in the direction of actuation of said actuator, the radial gap between said confronting surfaces progessively decreases from a maximum valueto a minimum value, said stator having a coil associated therewith which, when electrically energised, provides a toroidally shaped magnetic path extending axially within said rotor and stator and radially across the gap between said confronting surfaces thereof, said radially extending component of said magnetic path causing said rotor to rotate to reduce said gap to said minimum value.

The rotorofthe or each unit may be provided with two dametrically opposed surfaces to confront said stator, said stator being provided with corresponding confronting surfaces each of which is so configured thatthe radial gap between it and its corresponding rotor surfaces progessively decreases from a maximum to a minimum value upon rotation of said rotor in the direction of actuation of said actuator.

Said rotary actuator may consist of two of said units, the rotors of which are coaxially mounted and so positioned as to be 90" out of phase with each other, the stators of said phases being in phase with each other.

Said rotary actuator may alternately comprise on of said units in combination with a further unit compris ing a rotor and stator ofthe same configuration as i saidpreviousphase,therotorofsaidfurtherunit being 90" out of unit with the rotor of said first unit, the stator of said further unit being in phasewith said stator of said first unit, eitherthe rotor or stator of said further unit being provided with a permanent magnet in in the magnetic path thereof, the coils of said units being electrically connected in series or in parallel to be simultaneously actuated.

The rotor of each of said units is preferably of circular cross-section with segments thereof missing so thatthe remainder defines said confronting surfaces.

The confronting surfaces of each said unit stators are preferably constituted by at least two semicircular cross-section opposed surfaces, the axes of which are spaced apartfrom each other and from the axis of rotation of said rotor, the axes of said at least two semi-circular cross-section sufaces and said rotor being coplanar and parallel.

Said coil may be formed from a wound conductive tape.

The invention will now be described, byway of example, with reference to the accompanying draw ings in which Figure lisa sectional side view of section line A-A of Figure 3 of a rotary actuator in accordance with the present invention.

Figure 2 is a perspective view of the rotor ofthe rotaryactuatorshown in Figure 1.

Figure3 is a sideviewon section line B-B of Figure 1 showing the rotor ofthe rotary actuator in a non-actuated position.

Figure 4 is a sideviewon section line B-B of Figure 1 showing the rotor of the rotary actuator in an actuated position.

With reference to Figure 1, a rotary actuator generally indicated at 10 comprises two support members 11 and 12which carry a shaft 13 byway of plain bearings 14 and 15 respectively. The shaft 13 in turn carriestwo similar axially spaced apart rotors 16 and 17.The rotors 16 and 17 may beintegralwiththe shaft 13 as shown in Figure 1 orthey may be merely attached to the shaft 13 by suitable attachment means. Each of the rotors 16 and 17, which can be seen more clearly in Figure 2, is of circular crosssection shape with two similar diametrically opposed segments missing so that each rotor is left with two diametrically opposed part-circular outer surfaces 18 and 19.The rotors 16 and 17 are angularly displaced with respect to each other so that they are 90" out of phase with each other.

The rotors 16 and 17 are respectively mounted for rotation within two stator members 20 and 21 scan be seen in Figure 1. The stator members 20 and 21, which are supported by means not shown, are similar and in phase with each other. Each ofthestator members 20 and 21 is constituted by two pairs of abutting plates 26a and 27a, and 26b and 27b. The plate pairs 26a and 27a, and 26b and 27b are maintained in axially spaced apart relationship by a magnetically conductive bridging piece 29. Afurther bridging piece maintains the stator members 20 and 21 in axially spaced apart relationship. The briding pieces 29 and 30 and the plates 26a and band 27a and bare all held together by four bolts 31 which pass through appropriate holes therein.

The plates 26a and 26b respectively define similar coaxial semi-circular cross-section surfaces 24a and 24b. The plates 27a and 27b also respectively define similarcoaxia I semi-circular cross-section surfaces The drawing(s) originally filed were informal and the print here reproduced is taken from a later filed formal copy.

25a and 25b so that the semi-circular cross section surfaces 24a and b respectively oppose the semicircular cross-section surfaces 25a and b. However the axes ofthe semi-circular cross-section surfaces 24a and b, and 25a and bare spaced apart and parallel so that the semi-circular cross-section surfaces 24a and band the semi-circular cross-section surfaces 24a and band the semi-circular cross-section surfaces 25a and bare displaced as can be seen more clearly in Figures 3 and 4. The stator members 20 and 21 are so positioned with respect to the rotors 16 and 17 thatthe axis of rotation ofthe rotors 16 and 17 is coplanar and parallel with the axes of the semicircular cross-section stator surfaces 24a and band 25a and band is also located mid-way between those axes.The rotors 16 and 17 and stators 20 and 21 are so dimensioned that the rotors 16 and 17 may freely rotate within the stators 20 and 21. However since the axis of the rotors 16 and 17 is not coaxial with the axes of the semi-circular cross-section stato r surfaces 24a and band 25a and bthe radial gaps between rotor surfaces 18 and 19 and the statorsurfaces 24aand b and 25a and ovary upon rotation of the rotors 16 and 17. More specifically, the radial gaps between rotor andstatorsurfaces 18 and 24aand b, and 19 and25a and b progressively decrease from a maximum value when the rotor 16 and stator 20 are in the relative positions shown in Figure 3, to a minimum value when the rotor 16 and stator 20 are in the relative positions shown in Figure 4.The same progessive decrease in value ofthe gaps between the rotor and statorsurfaces 18 and 24a and b, and 19 and 25a and b occurs on the rotor 17 and stator 21. However since the rotor 17 is 90" out of phase with the rotor 16 when the radial gaps between the rotor and stator surfaces 18 and 24a and b, and 19 and 25a and b on the rotor 16 and stator20 are at their maximum value, the radial gaps between the rotor and statorsurfaces 18 and 24a and band 19 and 25a and b on the rotor 17 and stator 21 are attheirminimum values and vice versa.

The axially spaced apart plates 26a and band 27a and b provide axial location for a coil 28. The coil 28 extends around each of the stators 20 and 21 and may be of the conventional wound wire type butwe prefer that it should consist of a wound conductive tape so that it provides improved performance.

If the coil 28 of the stator 20 only is electrically energised, it provides a toroidally shaped magnetic path shown in interrupted lines at 33which extends axially within the bridging piece 29 and the rotor 16 and radially within the plates 26a and band 27a and b and across the gaps between the rotor and stator surfaces 18and 24aand b. If the rotor16and stator20 are in the relative positions shown in Figure 3, the resultant magnetic attraction between them causes the rotor 16 to rotate in a clockwise direction (when viwed in Figure3) to reduce 24aand band 19 and 25a and bto a minimum value. Thusthe rotor 16 rotates through 90" until it reaches the position shown in Figure 4, and then stops.Since the rotors 16 and 17 are 90D out of phase with each other, when the rotor 16 is in the position shown in Figure 4, the rotor 17 is in the position with respect to its stator 21 in which the gapsbetweentheirsurfaces 18and24aand b,and 19 and 25a and bare at a maximum value.Thus if the currentto the coil 28 ofthe stator 20 is switched off and the coil 28 of the stator 21 is then electrically energised, then a similartoroidaly shared magnetic field 34 in the stator31 causes the rotor 17 to rotate through 90 until the gaps between the surfaces 18 and 24a and band 19and 25aand bare attheir minimu m value, whereu pon it stops. Subsequent alternate electrical energisation of the coils 28 of the stators 20 and 21 results in the rotors 16 and 17 alternately providing stepwise rotation of the shaft 13 in 900 increments.It will be appreciated, however, that rotational increments of more or less than 90 could be provided by altering the configuration of the two units which are defined by the rotor 16 and stator 20 and the rotor 17 and stator 21 and/or by the use of additional similar units. Moreover if complete rotation is not required only one unit need be employed, the configuration of which determines the degree of rotational actuation of its rotor and associated shaft.

In an alternative form of the present invention, one of the two units defined by the rotor 16 and stator 20 and the rotor 17 and stator 21 could be modified by the incorporation of a permanent magnet( which is of the magnetically indestructible type) into its magne- tic circuit, for instance in the axial magnetic path part ofthe rotor. If the two coils were connected in series or parallel via a single switch, the shaft 13 would rotate through 900 when the coils are electrically energised and then through a further 90 when the current is switched off. Moreover the permanent magnet would ensure that the shaft 13is locked against rotation when the current is switched off.

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

Claims (8)

1. A rotary actuator comprising one or more units, the or each unit comprising a statorand a rotor mounted for rotation within said stator, said stator and rotor having confronting surfaces which are radially spaced apart from each other and so configured that upon rotation of said rotor in the direction of actuation of said actuator, the radial gap between said confronting surfaces progressively decreases from a maximum valueto a minimum value, said stator having a coil associated therewith which, when electrically energised, provides a toroidally shaped magnetic path extending axially within said rotor and stator and radially across the gap between said confronting surfaces thereof, said radially extending component of said magnetic path causing said rotor to rotate to reduce said gap to said minimum value.

2. A rotary actuator as claimed in claim 1 wherein the rotor of the or each unit is provided with two diametrically opposed surfaces to confront said stator, said stator being provided with corresponding confronting surfaces, each of which is so configured thatthe radial gaps between it and its corresponding rotor surFace progressively decrease from a maximum to a minimum value upon rotation of said rotor inthedirection of actuation of said actuator.

3. A rotary actuator as claimed in claim 1 or claim 2 wherein said rotary actuator consists of two if said units, the rotors of which are coaxially mounted and so positioned as to be 90c out of phase with each other, and the stators of which are in phase with each other.

4. A rotary actuator as claimed in claim 1 orclaim 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 rotor of said further unit being 90 out of phase with the rotor of said first unit,the stator of said further unit being in phase with said of said first unit, eitherthe rotor or stator of said further unit being provided with a permanent magnet in the magnetic path thereof, the coils of said units being electrically connected in series or in parallel to be simultaneously actuated.

5. Arotaryactuator as claimed in anyone preceding claims wherein the rotor of each of said units is of circular cross-section with segments thereof missing so that the remainder defines said confronting surfaces.

6. A rotary actuator as claimed in any one preceding claim wherein the confronting surfaces of each of said stator units are constituted by at leasttwo semi-circular cross-section opposed surfaces, the axes of which are spaced apart from each other and from the axis of rotation of said rotor, the axes of said at least two semi-circular cross-section surfaces and of said rotor being coplanar and parallel.

7. Arotaryactuatorasclaimedin anyone preceding claim wherein said coil is formed from a wound conductive tape.

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