SEWING MACHINE CONTAINING THREAD TIGHTENER WORKED BY OPEN LOOP CONTROL MODE OR CLOSED LOOP CONTROL MODE SELECTIVELY

摘要

PURPOSE: A sewing machine contains a thread tightener worked selectively by an open loop control mode or a closed loop control mode. The thread tightener increases quality of a seam. CONSTITUTION: On a sewing machine, at lease two materials(24,25) are sewed with upper yarn(23) and lower yarn(26) supplied to the materials and a knot is formed by the upper yarn(23) and the lower yarn(26). The sewing machine comprises: an arm shaft; an electric motor driving the arm shaft at variable speed; a controller of the sewing machine; a needle rod containing a needle(8) and being capable of being driven by the arm shaft; a thread-tightening arrangement(29) which is contacted with the upper yarn(23), containing a thread tightener, forming yarn tightening force in the upper yarn(23) by a solenoid charged with electric current and changing the electric current in accordance with speed of the arm shaft in accordance with a curve of the yarn tightening force against speed setting the knot between the materials(24,25); and an operating device for the thread tightener.