Title: Stepping motor

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Abstract: A stepping motor for use in an electronic timepiece which has a permanent magnet rotor and a stator provided with a driving coil. The stator is comprised of stator pole pieces each having assymetric portions which provide primary and secondary magnetic paths, respectively, whereby two static equilibrium positions are provided. The rotor may be stable at either one of these static equilibrium positions by controlling the supply of two-phase pulses to the driving coil so that the rotor may be rotated in normal or reverse direction. Su This invention relates in general to stepping motors and, more particularly, to a reversible stepping motor for use in an electronic timepiece. As is well known, stepping motors, also called pulse motors, are becoming increasing employed in industrial applications due to the introduction of digital pulse techniques. Typical one of these applications involves electronic timepieces having electro-mechanical timekeeping movements which are driven by the stepping motors. Such motors are unidirectional and typically 180.degree. per input pulse. The stepping motor is usually comprised of a rotor and a stator provided with a driving coil. The stator has two pole pieces which are displaced or offset from each other with respect to a central axis between the pole pieces. With this arrangement, it is difficult to assemble the stator pole pieces so as to provide a stable operation of the rotor. In another expedient, the stator pole pieces are integrally formed with one another and shaped by stamping. This requires the provision of a complicated die for the specific stator pole pieces. In addition, the stepping motor of this type can not be driven in the reverse direction due to its inherent construction. It has heretofore been proposed to provide various types of reversible stepping motors for use in the electronic timepieces. Each of these stepping motors is usually comprised of more than three stator pole pieces and two driving coils which provide a larger construction, and is not suited for the electronic timepieces in which a minimum spacing for the stepping motor is required. Since, further, the stepping motor of this type is driven by four-phase pulses, a driver circuit is necessarily complicated in construction. It is, therefore, an object of the present invention to provide an improved stepping motor which overcomes the shortcomings encountered in the prior art. It is another object of the present invention to provide an improved stepping motor which is specifically suited for use in an electronic timepiece. It is another object of the present invention to provide an improved stepping motor which is simple in construction and easy to assemble. It is still another object of the present invention to provide an improved stepping motor which can be driven in a normal or reverse direction. It is still another object of the present invention to provide an improved stepping motor which has a single driving coil by which a rotor is rotated in a normal or reverse direction in a simple manner. It is a further object of the present invention to provide an improved stepping motor which has a single driving coil and a driver circuit arranged to apply two-phase pulses to the driving coil so as to rotate a rotor in a normal or reverse direction. It is a further object of the present invention to provide an improved stepping motor which has a single driver circuit comprised of a control switch means to control the supply of two-phase pulses to a driving coil.


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