Sewing machine lower thread monitor - uses two-position sensor with signal trip if broken thrread allows a third position

摘要

The appts. registers a break in the lower thread of a sewing machine, when executing a chain stitch seam. The sensor is pivoted in a reciprocating motion, and has two sections. The first section moves between two settings, if the sensor is turned, where the lower thread follows its normal pat between these two points, with a drive to operate the sensor. The second section is used to trigger an output signal if the sensor moves past the normal point where the lower thread would be, on moving from the first to the second point, thus indicating a thread break. This allows the lower thread to be monitored positively, while occupying little space below the lower plate of the sewing machine.