Field of the Invention
This invention relates, in general, to sewing machines and, in particular, to a new and useful device for automatically guiding the workpiece on a sewing machine particularly to produce a curved edge parallel seam.
Such a device is known through German Patent Application DE-OS No. 25 22 422. The drive device of the plunger, a pneumatic cylinder, is actuated by the edge scanning device at the convex work edge areas deviating from a straight line via a solenoid valve, so that the plunger is lowered onto the work for the production of a curved edge-parallel seam laterally spaced from the cloth feed and presses it against the work support. The cloth feed, meanwhile, continues to operate, so that the work is rotated about the plunger as an axis of rotation. The pressing force must be so great that also narrow radii can be controlled exactly to obtain an edge-parallel seam. Due to the braking, the cloth feed set to a certain stitch length cannot fully transmit its feed action to the work, resulting in much shorter stitches than on the seam sections to be sewn without the plunger; this not only impairs the good appearance of the work but also is not acceptable because of the fragment piercing and hence weakening of the material and because of the conspicuous stitch accumulation in the curved areas.