Sewing machine has electro-magnetically controlled thread tensioning unit, operated on the basis of empirical experience

摘要

A process to join two items by sewing uses a sewing machine (1) with an electro-magnetic (34) thread-tensioning unit (29). The current flowing through the coil (33) in the electro-magnet (34) is varied by the sewing machine (1) motor speed in accordance with an empirically-established graph profile. An Independent claim is also included for a sewing machine where the upper thread (23) is synchronized with the lower thread at different speeds, with the knot placed essentially between the two items. The sewing machine has a microprocessor (55) with a memory chip (56) holding the graph curve parameters which link electrical current and motor speed. The microprocessor regulates a potentiometer.