| 摘要 |
A method of sewing the corners of a double seam, employing a two-needle machine the two needle rods of which each may be mutually independently engaged and disengaged. The method uses control means to arrive at the corner point of the inner seam, disengaging the internal needle rod, furthersewing to the corner point of the outer seam, stopping the sewing machine with the outer needle penetrating the workpiece, then rotating the workpiece, sewing the thus rotated outer seam, and engaging the inner needle rod. The sewing machine comprises at least one adjustable feed dog means, at least one sensor which is disposed ahead of the needles and which triggers the process of positioning the respective needle at the corresponding corner point, said triggering occurring when the edge of the workpiece passes said sensor, a pulse generator coupled to the main shaft of the sewing machine, which pulse generator provides counting pulses for a pulse counter, a microcomputer which controls the operation of the feed dog means in accordance with pulses emitted by the sensor and the pulse generator. To avoid a shortened stitch in the outer seam when forming stitches with the two needles in the region of the corner point of the inner seam, the stitch formation is carried out in two stitch forming cycles, in the first cycle stitch formation by the outer needle rod is prevented, and the advancing is reduced to the stitch length required to reach the corner point of the inner seam, and in the second cycle the inner needle rod is disengaged and the advancing is reduced to the distance comprising the difference between the normal stitch length (as set) and the stitch length executed in the first cycle.
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