| 摘要 |
1. A system for controlling a rotatable device, the system comprising a controller and a rotary device, which has a stator and rotor, wherein the controller is connected to the rotary device to control rotation of the rotary device, and wherein the controller is adapted to periodically energise at least one energising coil of the device to create a magnetic field of a polarity which induces the rotor to rotate in a single direction and wherein the controller is switched off so as to de-energise the energising coil when other forces, being forces other than those resulting from the energised energising, coil produce a resultant force which induces rotation of the rotor in the single direction. 2. The system as claimed in claim 1 wherein the controller's adapted to energise the at least one energising coil for a period during which the resultant force from the other forces acts to rotate the rotor in the opposite direction, whereby the force applied by the at least one energising coil is greater than the resultant force. 3. The system as claimed in claim 2 wherein the controller is adapted to switch off input current to the energising coil before the resultant force is zero. 4. The system as claimed in claim 3 wherein the controller is adapted to switch off the at least one energising coil for a period before the resultant force is zero and to allow back EMF to urge the rotor to rotate in the single direction before the resultant force is zero. 5. The system as claimed in claim 4 wherein the at least one energising coil is adapted to be energised by the controller through one or more predetermined angles of a complete revolution of the motor. 6. The system as claimed in claim 4 wherein the energising coil is adapted to be energised by the controller for one or more predetermined periods of time for each revolution of the rotor. 7. The system as claimed in claim 5 or 6 wherein the at least one energising coil is adapted to be energised more than once during a single revolution of the rotor. 8. The system as claimed in claim 7 wherein at least one of the energising coil is energised each time the resultant force applies a force to the rotor in the opposite direction. 9. The system as claimed in claim 8 wherein at least one energising coil is energised by a periodic pulse applied by the controller. 10. The system as claimed in claim 9 wherein the periodic pulses are all of the same sign. 11. The system as claimed in claim 10 wherein the at least one of the coils is energised whenever the resultant force is in the opposite direction to the single direction and then for a period less than the predetermined period during which the resultant force changes from zero to a maximum. 12. The system as claimed in claim 11 wherein the rotor has at least one magnetic field generating means which is able to generate a magnetic field which interacts with the magnetic field generated by the energising coil when energised to apply a force to rotate to the rotor in one direction. 13. The system as claimed in claim 12 wherein the energising coil includes a magnetic interaction means which is adapted to either repel or attract the magnetic field generating means. 14. The system as claimed in claim 13 wherein the magnetic interaction means comprises an iron core of the or each energising coil and the magnetic field generating means comprises at least one permanent magnet. 15. The system as claimed in any one of the preceding claims including a switching circuit which is adapted to switch off the controller and connect the energising coils to an output whereby induced current in the energising coils can be used. 16. The system as claimed in any one of the preceding claims wherein the controller comprises a rotary switch. 17. The system as claimed in claim 16 wherein the rotary comprises contacts having a cross-sectional width which varies with height.
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