Automatic sewing machine capable of executing stitch back operation

An automatic sewing machine capable of executing a stitch back operation, comprising:

• a needlebar reciprocably provided in a vertical direction and holding a needle at a lower end thereof;
• needlebar driving means for reciprocating said needlebar;
• workpiece holding means for holding a workpiece;
• workpiece moving means for moving said workpiece holing means relative to said needlebar in a plane perpendicular to the vertical direction;
• stitch data storing means for storing stitch data representing stitch positions at which stitches of a stitch pattern are to be formed;
• control means for controlling said needlebar driving means and said workpiece moving means for executing a sewing operation based on the stitch data stored in said stitch data storing means to form the stitch pattern on the workpiece;
• thread breakage detecting means for detecting a breakage of a thread;
• stopping means for stopping the sewing operation of said control means upon a detection of the breakage of the thread by said thread breakage detecting means;
• stitch back position setting means for setting a stitch back position corresponding to a stitch position of the last complete stitch formed before the breakage of the thread is detected by said thread breakage detecting means;
• nonfraying stitch forming position setting means for setting a nonfraying stitch forming position at a distance from the stitch back position set by said stitch back position setting means;
• nonfraying stitch forming means for executing a nonfraying stitch forming operation at the nonfraying stitch forming position set by said nonfraying stitch forming position setting means by controlling said needlebar driving means and said workpiece moving means;
• and
• sewing operation resuming means for resuming the sewing operation executed by said control means at the stitch back position set by said stitch back position setting means.