Armature for an actuator

1. An armature for an actuator for applying vibration to a body along an axis, the armature comprising:

at least two parallel wound helical windings on the axis, and a terminal arrangement connected to the ends of the windings for selective connection of the windings to two external A.C. drivelines, the terminal arrangement being switchable between a relatively low impedance mode, with at least two of the windings connected electrically in parallel, and a relatively high impedance mode, with two of the windings or two groups of parallel-connected windings connected in series.

2. The armature according to claim 1 , in which there are two windings, and the terminal arrangement connects them in parallel or in series in the low and high impedance modes respectively.

3. The armature according to claim 1 , in which there are four windings, and the terminal arrangement connects them all in parallel, or two parallel-connected pairs in series, in the low and high impedance modes respectively.

4. The armature according to claim 1 , in which there are eight windings, and the terminal arrangement connects them all in parallel, or parallel-connected pairs in series, in the low and high impedance modes respectively.

5. The armature according to claim 1 , in which at least one of the windings is wound in two concentric overlapping helices, in the same rotational sense over both helices.

6. The armature according to claim 1 , in which at least two of the windings are adjacent in the direction of the axis and are wound together in a helix on the axis.

7. The armature according to claim 1 , in which the terminal arrangement comprises terminals for the ends of corresponding windings, and conductive connectors which are movable between the terminals for the ends of the windings to provide selective electrical connections.

8. The armature according to claim 7 , in which the conductive connectors are bars which are connectable manually and removably to the terminals.

9. The armature according to claim 8 , in which the bars are connectable by nuts and bolts.

10. The armature according to claim 8 , in which the bars are permanently interconnected by a non-conductive arm to form a switch assembly.

11. The armature according to claim 10 , in which the switch assembly is mounted on the actuator and is pivotable between two positions at which the bars are aligned respectively with different terminals for establishing the different impedance modes.

12. The armature according to claim 10 , in which the switch assembly comprises terminals for connection to the external A.C. drivelines, those terminals being permanently connected to the ends of at least two different windings.

13. The armature according to claim 1 , in which the actuator has a stator body and the terminal arrangement is mounted on the stator body.

14. The armature according to claim 1 , wherein the actuator is electromagnetic and includes a stator.

15. The armature according to claim 14 , comprising a power supply connected to the terminal arrangement by external A.C. drivelines.

16. A method of altering an impedance of windings of an armature having a plurality of windings wound in parallel, comprising changing interconnections between ends of the windings to provide at least one of selectively parallel winding connection, series connection of two windings, and of two groups of parallel-connected windings.

17. The method according to claim 16 , in which the process of changing the interconnections comprises manually removing and re-applying electrical conductors between terminals connected to the winding ends.

18. An armature for an actuator for applying vibration to a body along an axis, the armature comprising:

at least two parallel wound helical windings on the axis, and means for selective connection of the windings to two external A.C. drivelines, the selective connection means being switchable between a relatively low impedance mode, with at least two of the windings connected electrically in parallel, and a relatively high impedance mode, with two of the windings or two groups of parallel-connected windings connected in series.

19. The armature according to claim 18 , wherein the actuator is electromagnetic and includes a stator.

20. The armature according to claim 18 , wherein at least one of the windings is wound in two concentric overlapping helices, in the same rotational sense over both helices.