| 摘要 |
PURPOSE: To reduce the nonuniformity of thrust and to make excellent thrust control possible by exciting two or more out of a plurality of coils by a current value producing means simultaneously, and calculating a current value so that the thrust generated as the result may coincide with a target thrust. CONSTITUTION: Currents are caused to flow into a plurality of coils simultaneously, and the value of a current to be caused to flow into each coil is determined so that the total sum of thrusts generated by those coils may coincide with a target thrust. When the number of poles of the permanent magnets of a needle 1 is four and the number of coils to be excited is two, currents to be caused to flow into the two coils are determined by a target current value producing means 9 on the basis of a position signal from a position detecting means 5 and a target thrust from a target thrust producing means 7. But switching of coils to be excited is performed when the current value of the coil is zero. As the result, it becomes possible to remove thrust nonuniformity to be produced on the occasion of switching coils to be excited, and to perform excellent thrust control by the reduction of thrust nonuniformity. |
