JPS6464686A - Sewing machine performing automatic adjustment of thread by phase control - Google Patents

Abstract

PURPOSE: To facilitate the fine control of tension by controlling peak tension at the time of the elevation of a needle thread take-up corresponding to a sewing condition and releasing the clamp of a needle thread before and after a needle thread take-up upper dead center corresponding to an upper shaft phase. CONSTITUTION: The needle thread 3 pulled out by a thread drum 2 is hooked to a needle thread guide 4, a needle thread tension device 5 and an intermittent pressurizing device 6, passed through the needle thread take-up 7 and passed through a needle 8. By the operation of this sewing machine, signals are outputted to the driver 57 of the intermittent pressurizing device 6 at the time of an operation phase θ stored in the storage device 62 of an intermittent operation phase corresponding to input from the detection means 58 of the upper shaft phase, the solenoid of the intermittent pressurizing device 6 is operated and pressurization to the needle thread 3 is released. For instance, in the case of the release at the phase θ1 , needle thread tension is elevated from fixed tension T0 by the needle thread tension device by the elevation of the needle thread take-up 7, turned to the tension T1 at the phase θ1 , released at the time and turned to a tension curve like a dotted line in the diagram thereafter and the thread tightening of the tension T1 is performed at the phase θ1 .