Automatic buttonhole apparatus for use with sewing machine

摘要

A presser bar has a presser attachment for holding fabric placed on a machine bed and a shoe is attached to the presser attachment in such a manner as to be slidable in the fabric feed direction. A first slidable variable resistor is fixed to a lateral surface of the shoe, with its slider connected to the presser bar so as to be displaced. A recess is formed in the machine arm or bed at a certain position and a second slidable variable resistor is mounted in the recess, with its slider projecting therethrough. This slider of the second variable resistor is adapted to be displaced, for example, by a button inserted in the recess and confined between the slider and a wall of the recess. The first variable resistor provides a voltage substantially corresponding to the amount of fabric feed, while the second variable resistor provides a voltage corresponding to the button size. Thus, the length of the buttonhole to be stitched is determined by comparing the fabric feed related voltage with the button size related voltage.