GB2154071A - Actuating device - Google Patents

Abstract

An actuating device for moving a member 10 through a range of movement includes a further member 16 also movable through said range of movement, a double acting solenoid device 27 positioned between the two members and brake means 17 operable to hold the further member 16 relative to a support. In use with the brake means locked the solenoid device is energised in one direction following which the brake is released and the solenoid device energised in the opposite direction following which the brake means is applied and the process repeated until the member has moved to the required position. <IMAGE>

Description

SPECIFICATION Actuating device This invention relates to a method and apparatus for moving a member th rough a range of movement using an electromagnetic device.

One way of effecting the required movement of the member would be to use an electric motor coupled to the member using a screw and nut mechanism. The disadvantage with this arrangement arises because of an additional operational requirement that the member once at the required position in the range of movement should be capable of being vibrated at a frequency of about 1 KHZ backwards and forwards from the required position. The range of movement required is small in the particular example, about 3 mm, and it has been proposed to use a device which includes an armature and a pair of solenoids which when energised move the armature in opposite directions.

The armature or the stator would be coupled to the member with the other component to a fixed support and by energising the two solenoids to appropriate levels the member could be moved to the desired position and also vibrated. The disadvantage with this arrangement is that the armature must have a range of movement relative to the stator at least equal to the desired range of movement of the member which means that the maximum air gap between the armature and the halves of the stator must also be at least equal to the range of movement. The effect is that even for the small range of movement required in the particular example considerable electrical power has to be expended in order to move the member.

The object of the present invention is to provide a method and apparatus for the purpose specified in a simple and convenient form.

According to the invention a method of moving a member through a range of movement comprises providing a further member in spaced relation to said first mentioned member and movable through said range of movement, providing a double acting solenoid device between said members, providing releasable brake means whereby said further member can be held relative to a fixed support, energising said solenoid device to achieve maximum relative movement of said members in one direction, releasing said brake means and energising said solenoid device to achieve maximum relative movement in the opposite direction, said further member moving relative to the support a distance less than the relative movement of the members, reapplying said brake means and repeating the process until the first mentioned member attains the desired position.

According to the invention an apparatus for the purpose specified comprises a further member spaced from said first mentioned member and movable through said range of movement, a double acting solenoid device including a stator and an armature coupled to said members respectively, releasable brake means by means of which said further member can be held relative to a fixed support, and means for energising said solenoid device whereby the device can act to move said members apart or draw the members towards each other.

One example of an apparatus in accordance with the invention will now be described with reference to the accompanying drawing and with reference to the drawing there is shown a beam member 10 which is balanced about a pivot 11.

The pivot 11 is defined at one end of a post 13 which itself is pivotally mounted on a further pivot 14 mounted on a fixed support 15 relative to which the member 10 is required to be moved. The post is rigidly connected to a second member 16 which is spaced from the member 10, the second member also being balanced about its pivot. It is required to pivot the member 10 about the pivot 14through a small range of angular movement which corresponds to a generally linear movement along the line 12, of 3 mm.

The support 15 carries a releasable brake generally indicated at 17 and which comprises a pair of friction elements 18 one of which is carried on the support 15 and the other of which is carried on a spring loaded component 19 slidable in a bearing in the support. Located between the friction elements 18 is a tongue 20 which is secured to the member 16. The tongue extends in the direction of required movement of the member 10 and under the action of the spring loading of the component 19, is held against movement. The brake is released by supplying electric current to an actuator 21. The actuator comprises a stator structure 22 which defines a plurality of circumferentially axially axially spaced pole pieces 23.Grooves are defined between the pole pieces and are occupied by windings 24 which conveniently are connected in series and are arranged so that when electric current is passed therethrough, adjacent pole pieces assume opposite magnetic polarity. The diameters of the pole pieces decrease towards the component 19. A!so forming part of the actuator is an armature 25 formed from magnetic material. The armature is hollow and has stepped internal surface which defines pole faces 26 facing the pole faces of the pole pieces 23.

Conveniently the aforesaid component 19 is integra: with the armature and the spring which biases the component is disposed between the end of the stator and the component. In the de-energised condition as shown, air gaps exist between the pole faces 26 and the pole faces of the pole pieces but when the winding is energised the armature moves to take up the air gaps and the grip of the elements 18 upon the tongue 20 is relaxed thereby allowing the member 16 to pivot.

Relative movement of the members 10 and 16 can be effected by a double acting electromagnetic device 27. This comprises an inner stator portion 28 coupled to the member 16, an armature 30 coupled to the member 10 and an outer stator portion 29 coupled to the member 16. The inner stator portion 28 and the armature 30 are constructed in the same manner as the stator and armature of the device 21.

The outer stator portion 29 surrounds the armature and has axially spaced annular pole pieces 31 positioned relative to the pole pieces on the inner stator portion so as to allow limited axial movement of the armature. The limited axial movement is substantially less than the required movement of the member 10 and as a result the maximum air gap is small. The outer stator portion is also provided with windings which when energised cause movement of the armature in the opposite direction to that caused by energising the windings on the inner stator portion 28. The axis of the device 27 lies on the line 12.

It is convenient for the total mass of each member 10 and 16 to be substantially equal although this is not essential.

The windings of the electromagnetic devices are connected to individual control circuits whereby they can be energised in sequence as will now be described.

As shown the windings of the outer stator portion 29 are energised and this has resulted in the two members being moved about their pivots, their maximum distance apart. If now the brake is released and the windings of the inner stator portion energised with those of the outer stator portion being de-energised, the two members will move towards each other by an amount equal to the stroke of the armature 28. However, if the masses of the member are substantially equal they will each move by the same distance and in particular the member 16 will move away from the support by half the stroke of the armature 30. The brake is then reapplied by de-energising the device 21. The windings of the inner stator portion 28 are then deenergised and those of the outer stator portion 29 energised and the members are moved apart by a distance equal to the stroke of the armature.The process is then repeated and each of the members moves in the desired direction of movement one half of the stroke of the armature 30 per cycle. Some additional movement of the member 10 beyond that as explained above can be obtained by releasing the brake just before the member 10 has completed its movement. Movement in the opposite direction is achieved by braking the movement of the tongue and hence the member 16 while the windings of the inner stator portion are energised.

The sequence of operation as described is repeated until the member 10 reaches a position such that one more cycle will take it beyond the desired position. Atransducer is provided to provide an indication of the position of the member.

The final position of the member 10 is attained by pulsing the current flow in the windings of the stator portions 28 and 29 and by controlling the magnitude of the current flowing in each winding. The pulsing of the current produces in the example, a movement of the member + 2.5 microns. The total movement of the member along the line 12 is 3 mm and the armature travel 0.125 mm. The small airgap means that the power consumption of the device 27 is very much smaller than would be the case if the device had a stroke of 3 mm. This makes it easier to cool the device and also simpiifies the design of the control circuits.

Since the two members are moving about the pivot 14 the tongue 20 should be curved having its centre of curvature at the pivot 14. Moreover, the surfaces of the elements 18 which engage the tongue should be curved in a complementary manner. The range of relative movement of the armature 30 and the stator portions 28 and 29 is so small that it is possible to mount the armature and stator portions directly on the members respectively.

Claims (8)

1. A method of moving a memberthrough a range of movement comprises providing a further member in spaced relation to said first mentioned member and movabie through said range of movement, providing a double acting solenoid device between said members, providing releasable brake means whereby said further member can be held relative to a fixed support, energising said solenoid device to achieve maximum relative movement of said members in one direction, releasing said brake means and energising said solenoid device to achieve maximum relative movement in the opposite direction, said further member moving relative to the support a distance less than the relative movement of the members, reapplying said brake means and repeating the process until the first mentioned member attains the desired position.

2. An apparatus for moving a memberthrough a range of movement comprises a further member spaced from said first mentioned member and movable through said range of movement, a double acting solenoid device including a stator and an armature coupled to said members respectively, releasable brake means by means of which said further member can be held relative to a fixed support, and means for energising said solenoid device whereby the device can act to move said members apart or draw the members towards each other.

3. An apparatus according to Claim 2 in which said members are pivotally mounted relative to each other about a first pivot, said double acting solenoid device being positioned to cause relative movement of said members about said first pivot.

4. An apparatus according to Claim 3 in which said further member is pivotally mounted about a second pivot carried by said support.

5. An apparatus according to Claim 4 in which said releasable brake means includes resilient means acting to effect actuation of said brake means, and a single acting solenoid device which can be energised to release said brake means.

6. An apparatus according to Claim 5 in which said brake means includes a tongue and a pair of friction elements between which the tongue is lated, said tongue being secured to said further means.

7. An apparatus according to Claim 3 in which said first pivot is defined by a part secured to said further member.

8. An apparatus for moving a memberthrough a range of movement comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawing.