Buttonhole sewing machine has a control unit which sets the operation of the cutter drive motor according to the fabric position with monitors to register abnormal cutter movements for an accurate cutting action

摘要

The buttonhole sewing machine has a mechanism to move the fabric workpiece into the position where the buttonhole is to be stitched. A motor (8) moves the cutting blade or the blade holder to and fro between a start and a cutting position. The motor (8) is operated by a control (7) to move the cutter or its holder from the start into the cutting position, and back. The control (7) can direct the motor (8) to move the blade or holder into an intermediate setting between the start and cutting positions. The control (7) gives the motor (8) commands to move the blade or its holder, between its three positions, while the fabric is being moved at the sewing machine. The control (7) gives the motor (8) a blade movement command to shift the blade or its holder into an intermediate position while the fabric workpiece is being moved into place, and then directions to move the blade into the cutting position when the fabric is correctly placed and is static. After cutting the buttonhole, the blade is returned to the start position at a slower speed than its movements into the intermediate and cutting positions. The intermediate blade position is set within a range between the start and cutting settings so that the blade is not in contact with the fabric. Drive sensors (61,62) register an abnormal cutting blade movement when the blade or holder is shifted into the cutting position, for the control (7) to repeat the blade movements through the intermediate position if there is an abnormality. The sensors (61,62) also register the rotary position of the blade drive motor (8) or the position of the blade or its holder. A time control establishes if the timing of the blade movements deviate from a standard value, which would show an abnormal blade movement pattern. Speed monitors determine the rotary speed of the blade drive motor (8) and/or the movement speed of the cutting blade or its holder, to establish if the blade action is abnormal. The speed monitor (102) measures the current supply to the blade drive motor (8), for comparison with the current used in normal buttonhole cutting operations. The cutting operation gives cuts to the left and right of the buttonhole, with the control (7) giving the operating commands to the blade drive motor (8).