IMBALANCE DETECTOR FOR ROTOR

PURPOSE:To shorten the imbalance detection time, by supplying an excitation current to a magnet coil so as to generate a relatively large magnetically energizing force when a rotational speed is low and a relatively small magnetically energizing force when it is high. CONSTITUTION:A shaft 19 of a rotor 18 is pivoted rotatably on a V groove 17 of a pair of hooks 16. A pair of magnets 20 is fastened at the upper end of a slide member 15 at a specified interval and a magnet coil 21 is arranged thereabove. When the rotational speed of the rotor 18 is low, a large magnetically energizing force is generated in such a direction that a member 15 is returned to a neutral position to make the member 15 equivalent to a heightened rigidity thereof with a natural frequency of the member 15 in transit to a high frequency area. When the rotational speed is high, a relatively small magnetically energizing force is generated to make the member 15 equivalent to a lowered rigidity thereof with the natural frequency thereof in transit to a low frequency area. Then, with an increase in the rotational speed, the natural frequency of the member 15 moves in the direction opposite to the increase therein, thereby preventing greater resonance of the member 15.