| 摘要 |
PURPOSE:To drive a printer head at a substantially constant current even during operation of a number of wires by adopting such a shape and constitution that will not make any electric closed circuit in a permanent magnet, yoke and other parts which constitute the head. CONSTITUTION:A permanent magnet 12 and a yoke 13 are formed with a groove, or a permanent magnet 14 and a yoke 15 are partially cut. When a coil 5-1 is excited together with other forest coils and magnetic flux phi1 tends to pass upward through a core 1-1, an eddy current is caused in the core 1-1 but, at the same time, an eddy current ie is caused also in the permanent magnet 2 and the yoke 3. The eddy current ie flows along an inner peripheral surface 10 of the permanent magnet 2 and the yoke 3 rather than the part near the outer peripheral surface 11. Because an groove is formed in the inner periphery thereof as stated, the eddy current flowing along the inner periphery can be interrupted. Thus, the value of operating current for driving pins in the number of, e.g., 9, concurrently can be reduced down to a value not larger than 130% of the current value necessary for driving a single pin, and operating magnetic flux can be risen in a shorter time, resulting in the decreased width of a driving pulse. |
