Sewing machine drive
AssigneeFritz Gegauf Aktiengesellschaft Bernina-Nachmaschinenfabrik
InventorOtmar Stillhard
Life of this patent
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Abstract
A sewing machine drive having a mains rectifier (1) which, via a chopper (2) operating at a relatively high frequency, supplies direct current pulses to the driving motor (3). The duty ratio of these driving pulses is controlled as a function of a nominal value transmitter (11) and a current limiting circuit (14) controlled by the motor speed. This produces a smooth quiet, vibration-free operation of the motor (3) or the driven machine with a high degree of motor efficiency. Moreover, a speed-dependent current limitation occurs in such a manner that at high speeds a limited maximum current flows, which at the same time results in an output limitation.
Claims7
A sewing machine drive for connection to an a.c. power supply, comprising:
- a d.c. motor;
- a rectifier coupled to the a.c. power supply and delivering a d.c. voltage for said motor;
- a chopper connected to said motor and receiving said d.c. voltage, said chopper being controlled by a pulse modulator which is connected to an oscillator and to a control circuit delivering a control voltage for adjusting the duty ratio of pulses produced by said pulse modulator in dependence upon the speed of said motor so as to maintain said speed of said motor substantially constant;
- and
- a current limiting circuit connected to said pulse modulator and controlled by a voltage proportional to current in said motor for limiting said control voltage to a maximum value, said value being continuously variable in proportion to said current in said motor, any further increase of said motor current above a predetermined value resulting in a decrease in said speed of said motor such that motor output power is substantially constant for all motor speeds.
Dependencies are inferred from the claim text.