GB2340664A

GB2340664A - An electromagnetic device using a spring and dynamic core arrangement

Info

Publication number: GB2340664A
Application number: GB9817715A
Authority: GB
Inventors: Ludovic Chauvet; Philippe Drumel; Stephane Chauvet
Original assignee: Draftex Industries Ltd
Current assignee: Laird Holdings Ltd
Priority date: 1998-08-15
Filing date: 1998-08-15
Publication date: 2000-02-23
Also published as: GB9817715D0; EP0981138A2; EP0981138A3

Abstract

An electromagnetic device comprises a coil 14, a core 8, spring means 18 and an output linkage 6, 24. The device is arranged such that on energizing the coil 14 the core 8 and the output linkage 6, 24 are moved in a first direction A against the action of the spring 18. On de-energizing of the coil 14 the core 8 is moved in a second direction B, opposite to that of the first direction A, by the energy stored by the spring means 18. During the movement in the second direction B the core 8 accumulates kinetic energy over a predetermined distance 32 before engaging with the surface 26 of the output linkage 6, 24. The core 8 then transmits energy into the movement of the output linkage 6, 24. The output member 6 may be connected to a control rod 24 which slidably extends through the core 8. The control rod 24 may have an enlarged head 27 against which a further coil 28 acts. The device may be arranged to provide an initial pulse of force at the beginning of movement of the output linkage 6, 24 in the first and second directions A, B.

Description

1 2340664 ELECTROMAGNETIC ARRANGEMEN= The invention relates to

electromagnetic arrangements.

According to the invention, there is provided an electromagnetic arrangement, comprising a core movable in a first direction against the action of spring means in response to electromagnetic energisation of a coil and movable in a second, opposite, direction in response to stored energy in the spring means as the latter resiles, an output member mounted for movement in directions corresponding to the first and second directions, first force transmitting means for transmitting a force from the core to the output member as the core moves in the f irst direction whereby to cause movement of the output member in the corresponding direction, and second force transmitting means for transmitting a force from the core to the output member as the output member moves in the second direction whereby to move the output member in the corresponding direction, the second transmitting mean s including means defining a predetermined amount of play whereby to permit accumulation of kinetic energy in the core before transmission of the force to the output member.

According to the invention, there is further provided an 2 electromagnetic arrangement, comprising an armature carrying an electrically energisable coil and having wall means defining a space in which an electromagnetic field is developed when the coil is energised, a core mounted within the space and movable therein in a first direction from a first datum position of the core to a second datum position of the core against the force of a first spring in response to the magnetic field and movable in the second, opposite, direction from the second datum position to the first datum position in response to the stored energy in the first spring when the latter resiles upon de-energisation of the coil, an output member mounted adjacent to the core for movement in directions corresponding to the first and second directions, first force transmitting means responsive to movement of the core in the first direction for exerting a pulling force on the output member, and second force transmitting means responsive to movement of the core in the second direction for exerting a pushing force on the output member, the second force transmitting means including means defining a predetermined amount of play when the core is in the second datum position for delaying the exertion of the pushing force on the core until the core has moved through this predetermined amount of play.

Electromagnetic arrangements embodying the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which:

3 Figure 1 is a cross-section through one of the arrangements in the state where it is electrically de-energised; Figure 2 corresponds to Figure 1 but shows the arrangement in the state in which it is electrically energised; and Figure 3 is a graph showing the force produced by the arrangement compared with the air gap within the assembly.

The electromagnetic arrangement shown in Figures 1 and 2 comprises a housing 5 containing an electromagnet which, in a manner to be described, moves an output rod 6 to and fro in the direction of the arrows A and B. Rod 6 slides in a guide 7 and is connected to a mechanism (not shown) which is to be actuated by the electromagnetic arrangement. The electromagnet comprises a core 8 slidable to and fro in the direction of the arrows A and B in a cylindrical space 10 which is defined within an armature 12 wound with an electrical coil 14. The core 8 has two end faces 15 and 16, with a cylindrical recess 17 formed in end 16. A compression spring 18 is located in the recess 17 and acts between the base 20 of the recess 17 and the closed end 22 of the cylindrical space 10.

As shown most clearly in Figure 2, the output rod 6 is rigid with a control rod 24. The control rod 24 is of lesser diameter than 4 the output rod 6 so as to define an annular end face 26 of the output rod 6 which extends around the control rod 24. The control rod 24 is freely slidable within a bore through the core 8. The control rod 24 has an enlarged head 27, and a second compression spring 28 acts between the base 20 of the cylindrical recess 17 and the underside of this head 27, so as to urge the control rod to the left (as viewed in Figures 1 and 2) relative to the core 8.

Figure 1 shows the configuration of the electromagnet assembly when the coil 14 is de-energised. The core 8 is urged outwardly of the cylindrical space 10 by the compression spring 18 so that its end face 15 abuts against the housing 5 around the guide 7. The core 8 thus abuts against the end face 26 of the output rod 6 and forces the latter outwardly of the housing 5 to its maximum extent. In this position of the core 8, the air gap 30 has its maximum size.

When the coil 14 is electrically energised, the core 8 is electromagnetically attracted in the direction of the arrow A and moves inwardly of the cylindrical space 10, towards the end face 22, compressing the spring 18 and also compressing the spring 28. The force exerted by the compressed spring 28 thus drags the control rod 24 in the direction of the arrow A, thereby drawing the output rod 6 in the same direction. Movement of the core 8 in the direction of the arrow A stops when it abuts against the end face 22 of the cylindrical space 10, and the relative configuration shown in Figure 2 is achieved. However, the movement of the output rod 6 in the direction of the arrow A is limited by external means (not shown) so that, with the core 8 fully attracted by the electromagnetic field, a predetermined amount of play 32 exists between the end face 15 of the core 8 and the end face 26 of the output rod 6. The external means for limiting the travel of the output rod 6 can take any suitable form which is arranged so that the maximum travel of the output rod 6 in the direction of arrow A is less than the maximum travel of the core 6. The strength of the spring 28 is selected so that the core 6 can continue its travel after the movement of the output rod 6 has stopped but with the necessary force still being applied to the output rod.

The electromagnetic arrangement preserves the configuration shown in Figure 2 for so long as the coil 14 is electrically energised. When the coil 14 is de-energised, the core 8 starts to move in the direction of the arrow B under the action of the energy stored in the compression spring 18. Initially, the control rod 24 (and thus, also, the output rod 6) does not move, as the spring 28 resiles, or only moves slowly under the resiling action of spring 28. However, the core 8 freely moves in the direction of the arrow B, gaining kinetic energy as it travels through the 6 play 32. When the core has travelled through a distance corresponding to the play 32, it will sharply impact strike the end face 26 of the output rod 6 thus instantaneously producing a substantial increase in the force applied to the output rod. This impact force will persist only momentarily, but the output rod 6 will continue to be moved thereafter in the direction of the arrow B by the force in the spring 18, until the end face 16 of the core 8 abuts against the housing as shown in Figure 1.

The operation is explained in more detail with reference to the graph of Figure 3.

In Figure 3, curve I shows the electromagnetic force developed during energisation of the coil 14. When the air gap 30 is a maximum, corresponding to Figure 1, the electromagnetic force is at a minimum. If desired, however, it is possible to provide a momentary increase in the electromagnetic force by temporarily augmenting the current flowing through the coil. This may be carried out electronically and produces a peak in the applied force as shown at 34 in Figure 3 when the core 8 begins to move on its inward stoke. This momentary increase in force helps to overcome the effect of inertia on the output rod 6, such as the inertia caused by its load (not shown). After this momentary increase in current, the applied force then decreases but thereafter increases as the air gap 30 is reduced, rising to a 7 maximum force just before the air gap 30 is reduced to zero.

Curve II shows the operation during the return stroke of the core 8 under the action of the spring 18. The force exerted by the spring 18 will be relatively high when the air gap 30 is zero. As explained in conjunction with Figure 2, this initial force causes the core 8 to accelerate as the core travels through the extent of the play 32 (Figure 2). When the core 8 abuts against the end face 26 of the output rod 6, there will be a momentary and substantial increase in force applied to the output rod 6 as shown at 36 in Figure 3. Again, this will help to overcome the effects of any inertia acting against movement of the output rods 6. This peak force then falls, and thereafter the force applied to the output rod 6 reduces gradually as the spring 18 resiles.

The magnitude of the shock force produced when the core 8 comes into abutment with the end face of the output rod 6 depends on the amount of the play 32, the pre-stress in the spring 18, the strength of the spring 18, and the mass of the core 8. Each of these parameters can be adjusted to obtain a desired shape for the curves shown in Figure 3.

In this way, an electromagnetic arrangement can be produced which produces a substantial and momentary increase in applied force during the return stroke of the core movement. If combined with 8 means for temporarily augmenting the current through the coil at the beginning of the inward stroke (as explained in conjunction with Figure 3), the electromagnetic arrangement produces a substantial and momentary increase of force at the beginning of each of its two strokes. In this way, any inertial effect in the mechanism being controlled by the electromagnetic arrangement is overcome. The arrangement remains monostable and therefore has a safety position if the coil becomes defective.

The maximum force exerted by the arrangement can be changed by adjusting the strengths of the two springs 18 and 28. The springs enable the return force (direction B) to be adjusted to be different from the output force (direction A).

In the electromagnetic arrangement described, the coil 14 can be sealed within the housing 5, enabling a waterproof structure.

Claims

9 CLAIMS

1 An electromagnetic arrangement, comprising a core movable in a first direction against the action of spring means in response to electromagnetic energisation of a coil and movable in a second, opposite, direction in response to stored energy in the spring means as the latter resiles, an output member mounted for movement in directions corresponding to the first and second directions, first force transmitting means for transmitting a force from the core to the output member as the core moves in the first direction whereby to cause movement of the output member in the corresponding direction, and second force transmitting means for transmitting a force from the core to the output member as the output member moves in the second direction whereby to move the output member in the corresponding direction, the second transmitting means including means defining a predetermined amount of play whereby to permit accumulation of kinetic energy in the core before transmission of the force to the output member.

2. An arrangement according to claim 1, in which the core is constrained for sliding movement in the first and second directions and the output member is constrained for movement in the corresponding directions colinearly with the core, the predetermined play being defined between one end of the core and an adjacent end of the output member when the core has moved to a limit position in the first direction in response to the electromagnetic energisation of the coil.

3. An arrangement according to claim 2, in which the spring means comprises a compression spring which is compressed by movement of the core in the first direction.

4. An arrangement according to claim 3, in which the compression spring acts between the other end of the core and a fixed member with respect to which the core moves in the first and second directions.

5. An arrangement according to any preceding claim, in which the first force transmitting means includes second spring means.

6. An arrangement according to claim 5, in which the output member is connected to a control member which is movable through and relative to the core in the first and second directions, and in which the second spring means acts between the control member and the other end of the core.

7. An electromagnetic arrangement, comprising an armature carrying an electrically energisable coil and having wall means defining a space in which an electromagnetic field is developed 11 when the coil is energised, a core mounted within the space and movable therein in a first direction from a first datum position of the core to a second datum position of the core against the force of a first spring in response to the magnetic field and movable in the second, opposite, direction from the second datum position to the first datum position in response to the stored energy in the first spring when the latter resiles upon deenergisation of the coil, an output member mounted adjacent to the core for movement in directions corresponding to the first and second directions, first force transmitting means responsive to movement of the core in the first direction for exerting a pulling force on the output member, and second force transmitting means responsive to movement of the core in the second direction for exerting a pushing force on the output member, the second force transmitting means including means defining a predetermined amount of play when the core is in the second datum position for delaying the exertion of the pushing force on the core until the core has moved through this predetermined amount of play.

8. An arrangement according to claim 7, in which the second force transmitting means comprises one end of the core which exerts the pushing force on the output member by abutting the latter, and in which the predetermined amount of play exists between that end of the core and the output member.

12 9. An arrangement according to claim 8, in which the f irst spring acts between the other end of the core and part of the wall means defining the space.

10. An arrangement according to any one of claims 7 to 9, in which the second force transmitting means comprises a second spring acting between the core and the output member.

11. An arrangement according to claim 10, in which the second spring acts between the other end of the core and a control member mounted for sliding movement through the core and through the one end thereof and connected to the output member.

12. An electromagnetic arrangement, substantially as described with reference to the accompanying drawings.