| 摘要 |
PURPOSE:To improve the workability for any of high and low speed sewing machines by switching the frequency of a clock pulse from a variable frequency oscillator. CONSTITUTION:A tachometer generator 2 outputs a pulse signal train through a waveform shaper 3 in the state that a sewing machine 1 is rotated. This pulse signal train is divided in frequency in response to the set amount from a speed setter 5 from a frequency divider 4. A counter 6 counts a clock pulse from a variable frequency oscillator 7 over one period of a frequency-divided pulse PD, latched to a latch 8, the actually measured period TP is outputted to a subtractor 9, thereby controlling the drive unit 12 of the motor. Even if the frequency dividing times are equal, the speed can be varied by altering the frequency of the clock pulse of a variable frequency oscillator 7. Accordingly, the ratio of the set speeds of the stages for the depression of a pedal can be varied to obtain the prescribed reduction gear shifting curve. |
