Control device for a sewing machine

摘要

The control device controls the sewing speed of a sewing needle automatically in a manner such that the temperature of the sewing needle, subjected to the influence of heat generated by friction with the material being sewn, does not exceed an adjustable predetermined value. Respective measuring members determine the temperature of the sewing needle and the temperature of a reference needle mounted at a location spaced from the sewing needle, and are connected to the input of a differential comparator circuit providing the differential voltage of the measuring members. A signal generator is operatively associated with the sewing needle and produces output pulses responsive to reciprocation of the sewing needle, to control connection of the output of the differential comparator circuit to the input of the sewing machine motor control. The reference needle is substantially identical with the sewing needle. A plurality of reference needles of different sizes may be provided, and brought selectively into the control circuit either mechanically or electrically in accordance with the size of the sewing needle being used.