Sewing machine input signal waveshaping

Abstract

In an electronically controlled sewing machine, new stitch position coordinate information is retrieved from a solid state memory and transferred to the sewing machine servo system one bit per some proportional clock period, at either a fast stepping rate or a slow stepping rate depending upon the speed of the sewing machine. By use of suitable logic gates, a low speed condition will initiate a slow stepping rate of some fraction of a predetermined clock period, whereas a high speed condition will initiate a fast stepping rate of once every clock period. The new data from the solid state memory is fed to a comparator wherein it is compared to the immediately prior stitch position coordinate information transferred to the servo system and retained in an up/down counter. The comparator determines whether the new data requires an up or a down count of the counter. The signal from the up/down counter is transferred to a pulse width modulator, the output of which is fed to a digital to analog converter for the appropriate bight or feed servo system of the sewing machine. In effect, the pulse width modulated signal transferred to the servo system is a ramp signal of steep or shallow slope dependent on whether the sewing machine is operating above or below a predetermined speed.