BigPatents India

A sewing machine (1) is provided with a thread-tightening arrangement (29) comprising a thread tightener (32) which is operated by a solenoid (34). The current that flows through the coil (33) of the solenoid (34) is modified in dependence on the speed of the arm shaft according to a de-termined curve of the thread-tightening power over the speed such that a knot of an upper thread and an under thread lies substantially between the work pieces. The thread-tightener (32) is operated optionally in an open-loop control mode or in a closed-loop control mode, a single-knob control (50) being provided for the closed-loop control mode and the open-loop control mode. (FIG. - 2)