| 摘要 |
PURPOSE:To prevent a switching element from damaging due to the stepout of a motor or the overcurrent of an inverter by providing frequency suppressing means for suppressing the increase in the output frequency of the inverter. CONSTITUTION:In an inverter 1 for driving the induction motor 2 of a sewing machine 3, discriminating means 8 operates frequency suppressing means 9 when the output of a pedal detector 5 becomes larger than the set value as compared with the output of a tachometer generator 7. Thus, even if the peal 6 is pressed at any high speed, if the rotating speed of the motor 2 does not rise in response thereto, the means 9 operates on the basis of the output of the means 8 to control to allow the inverter controller 4 to suppress the increase in the output frequency of the inverter. Accordingly, it can prevent a switching element from damaging due to the stepout of the motor 2 or the overcurrent of the inverter 1. |
