Simultaneous Measurement of Tightening Tensions of Needle Thread and Bobbin Tensions of Needle Thread and Bobbin Thead in a Lock Stitch Sewing Machine

摘要

In our previous paper, a method and a system to measure the strain of the tension spring produced by the bobbin thread in a lock stitch sewing machine was proposed. In the experiments, the latch of the bobbin case had been removed in order to establish two pairs of intermittent brush-terminal contacts on the limited space of a bobbin case. However, this caused an inevitable factor of unstable sewing at speeds higher than 700 r/min. In this paper, to attain sewing speeds up to 1900 r/min, the system was modified, adopting another type of bobbin case which has a hole at the body to set the terminals, and a latch as usual, although it is imposible to keep the bridge circuit as `closed' during the needle thred tread traveling between the intermittent brust-contact and the terminals for current signals. By the measurement of the tranisent response of the brush-contact structure, and of a false signal as a significant noise caused due to the opening of the bridge circuit, the modified system showed the possibility of attaining 3000 r/min sewing speed. Different cablibration curves are obtained, depending on the fastening torque at the regulating screw for the tension spring.