Apparatus for detecting defective sewing by a sewing machine

摘要

An apparatus according to the present invention comprises a sensor and a control circuit. The sensor is disposed near a needle drop portion of a needle plate and detects the quantity of light transmitted through cloths passing over the needle plate. The control circuit determines defective sewing from increase and decrease of said light quantity. The control circuit comprises means for storing the averaged value of the light transmitted in a few stitches of initial sewing operation, and means for determining defective sewing continuously from the initial sewing operation by comparing the average value with the value of the light transmitted and detected each time. Thus, it is possible to immediately start the practical sewing operation without taking time for test sewing or other extra jobs even when every cloth to be sewn is different in properties.