| 摘要 |
PURPOSE:To stabilize motor drive at the time of overload or start by varying an oscillating frequency to always set an electric input to a piezoelectric element to a set value or less. CONSTITUTION:When a motor has no malfunction, the outputs of a phase limiter 63 and a current limiter 66 are 0V. Accordingly, a VCO (variable oscillator) 44 is controlled by the addition of the outputs of a constant phase circuit 67 and a constant current circuit 68 (voltages at points G, H). If a malfunction such as an overload, an excess input to a piezoelectric element at the time of start occurs, the output level of a phase difference detector 37 exceeds a lower phase limit value or the output level of a current detection level 51 exceeds an upper current limit. Thus, 5V is output to a point I or J by the operation of the limiter 63 or 66, the addition of voltages of the points G, H, I, J by an adder 70 exceeds 5V, and the oscillating frequency of the VCO momentarily becomes high, thereby preventing an excess input from momentarily being applied to the piezoelectric element. |
