| 摘要 |
The motor assembly comprises a bidirectional stepping motor having a coil, a stator provided with a central opening in which is mounted for rotation about an axis a rotor including a permanent magnet which is magnetized along an axis of magnetization, and positioning means for defining two rest positions of the rotor in which the axis of magnetization of the magnet is directed along an axis of static equilibrium. The stator is formed of two pole pieces which partly surround the rotor and are interconnected by two intermediate parts and by four isthmuses in such a manner that the intermediate parts are intersected by the axis of static equilibrium and that two isthmuses which are opposite each other in relation to the axis of rotation of the rotor are located in one direction making with the axis of static equilibrium an angle of between 30 DEG and 60 DEG . Two of these isthmuses which are located in the same direction have a width such that they are very rapidly saturated with magnetic flux when the coil produces in the stator, in response to a driving pulse, a magnetic field which enables the rotor to be made to turn in one direction, while the other two isthmuses have a width two to four times greater so that, when the coil generates a magnetic field which causes the rotor to turn in the other direction, the wide isthmuses, or, in this case again the narrow isthmuses become saturated, but less rapidly, so as to obtain a difference in the form of the current in the coil which enables a control device associated with the motor to determine the direction in which the rotor prepares to turn in response to a driving pulse and to avoid any unintentional reversal of the direction of rotation of the motor. |
