Sewing machine equipped for producing shaped seams

A device for producing shaped seams in a sewing machine having a main shaft, at least one needle engaged with the main shaft for forming stitches, workpiece feed means for feeding the workpiece in a feed direction passed the needle, and stitch length setting means for setting the length of each stitch, the device comprising:

• a control switching circuit;
• a pulse generator operatively coupled to the main shaft for generating pulses during the movement of the workpiece by the feed means;
• a first sensor positioned ahead of the needle in the workpiece feed direction for sensing the passage of a trailing edge of the workpiece, the workpiece having a guiding edge extending at an angle to the trailing edge thereof;
• a second sensor for sensing the passage of the trailing edge aligned with said first sensor in the feed direction of the workpiece;
• and
• a third sensor spaced laterally of said second sensor in the feed direction of the workpiece, said second and third sensors connected to said controlled switching circuit for supplying respective signals with the passage of the trailing edge of the workpiece to the controlled switching circuit which, with pulses from said pulse generator, is operable to calculate the angle between the trailing and guiding edges of the workpiece;
• said controlled switching circuit being connected to said first sensor and operative with pulses from said pulse generator and a signal from said second sensor to determine an actual feed distance for the workpiece along the feed direction thereof, and to compare the actual feed distance with a desired feed distance.