Automatic work guiding apparatus for sewing machines

A fabric-guiding apparatus for a sewing machine having a table, a seam forming mechanism and a fabric feed mechanism for sewing two superposed layers of work fabric, comprising:

• a detector member disposed ahead of said seam forming mechanism in a direction of work feed, and including a pair of detector elements sensing side edges of said two layers of work fabric, respectively and each generating a detection signal indicative of the sensing of the respective side edge;
• a separator-plate disposed ahead of said seam forming mechanism in said work feed direction and separating said two layers so as to position the side edge of one of said two layers on said separator plate and that of the other below said separator plate;
• a first guiding wheel rotatable about an axis parallel to a line of said work feed direction and engageable with the upper surface of the upper layer above said separator plate;
• a second guiding wheel rotatable about another axis parallel to said line of the work feed direction and engageable with the lower surface of the lower layer below said separator plate;
• a pair of drive motors operative in response to said detection signals to rotate said first and second guiding wheels independently of each other selectively in forward and reverse directions for positively positioning said side edges of the two layers on said detector elements respectively;
• first pressure exerting means for exerting a first contact pressure urging said first guiding wheel into engagement with said upper surface of the upper layer, said first pressure exerting means having a first adjusting mechanism and a first electric motor operative in response to command signals to actuate said first adjusting mechanism for adjusting said first contact pressure;
• second pressure exerting means for exerting a second contact pressure urging said second guiding wheel into engagement with said lower surface of the lower layer, said second pressure exerting means having a second adjusting mechanism and a second electric motor operative in response to command signals to actuate said second adjusting mechanism for adjusting said second contact pressure;
• a memory for storing command data relating to said command signals and representative of said first and second contact pressures;
• a pair of drive circuits operating said pair of drive motors according to said command signals, respectively, until optimum levels of said first and second contact pressures have been established;
• and
• control means for automatically establishing the optimum levels of said first and second contact pressures, said control means (a) supplying to said pair of drive circuits predetermined numbers of said command signals for changing said first and second contact pressures in steps of a predetermined amount prior to a normal operation of the fabric-guiding apparatus, (b) outputting rotation signals to operate said pair of drive motors for laterally moving said two superposed layers when said predetermined numbers of command signals are supplied to said said pair of drive circuits, (c) checking according to said detection signals from said detector elements whether or not said two layers have been moved into position by said first and second guiding wheels, (d) updating said command data each time said predetermined numbers of the command signals have been supplied to said pair of drive circuits, and (e) stopping the updating of said command data when said detection signals indicate that said two layers have been moved into position, whereby said command data stored in said memory when said detection signals have been generated represent said optimum levels of first and second contact pressures.