Detachable drive for sewing machine trimming knife

Abstract

A sewing machine comprises a rotatable main shaft which drives a needle upwardly and downwardly over a sewing station to sew through material which is moved thereover and which includes a trimming knife mounted adjacent the needle for upward and downward movement for selectively and periodically cutting the material. The trimming knife is driven by a linkage mechanism from an eccentric drive and the eccentric drive is detachably connected between the main shaft and the linkage mechanism and permits the knife to be driven with the mainshaft of the sewing machine or by an independent drive through a separate detachable drive mechanism. In one embodiment a positioning motor is connected to the drive through a hand wheel and an engageable and disengageable clutch so that it may drive a linkage mechanism including an eccentric to move the knife upwardly and downwardly for cutting the material being sewn during the operation of the sewing machine or separately when the sewing machine drive is discontinued. The drive is defined from the positioning motor to the hand wheel and through a clutch to the main shaft of the sewing machine which drives an eccentric for operating the linkage mechanism to reciprocate the knife. Another embodiment includes a separate trimming drive including two free wheel clutch arrangements permitting the knife to be driven synchronously with the sewing machine needle drive as well as its separate drive.