| 摘要 |
A nut runner for tightening screwed objects comprising: a driving motor, a driving shaft to be coupled to the screwed objects for driving the same, a reduction gear mechanism provided for transferring the revolution power of the driving motor to the driving shaft, a torque for detecting a torque applied to the driving shaft, and a control circuit for controlling the driving motor by the use of the detected output of the torque detector. In accordance with the present invention, a two-phase induction motor is employed as the driving motor. The control circuit is formed to control the magnitudes, periods and phases of intermittent currents supplied to the field coils of the two-phase induction motor so that the torque of the two-phase induction motor is controlled by the control of the magnitude of the intermittent currents, so that the revolution speed of the two-phase induction motor is controlled by the control of the periods of the intermittent currents, and so that the forward and backward driving directions are switched by the switching of phase relations of the intermittent currents.
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