Pedal-operated electronic speed controller for sewing machine - has manual adjustment for selection of maximum motor speed

摘要

Sewing machine has an electronic speed-control circuit of the drive motor whereby the max. speed of the motor can be adjusted by means of a manual pre-selector dial, whilst the machine is operated by a variable-control pedal which allows the motor speed to be varied normally up to the pre-set max. The circuit elements comprise a 4-diode full-wave rectifier; a thyristor to control the motor current; a potentiometer circuit for selecting the maximum speed of the motor; a compensating circuit which corrects for the effect of the load on the motor speed; and the control pedal. Device permits more accurate speed control for operations requiring a steady, slow speed than can be achieved by the use of conventional pedal-operated rheostats. The pedal remains effective for varying the motor speed up to the selected maximum, and the form of the pedal is circular, allowing it to be operated easily from any angle.