Time delay armshaft positioning control system for sewing machine

Abstract

Abstract A CIRCUIT IS DISCLOSED FOR AUTOMATICALLY, DRIVING A SEWING MACHINE TO A PREDETERMINED POSITION OF THE ARMSHAFT RESPONSIVELY TO THE NORMAL RELAXATION OF THE FOOT CONTROLLER. TWO SILICOAN CONTROLLED RECTIFIERS (SCR''S) ARE EMPLOYED. ONE SCR CONTROLS THE RANGE OF MOTOR SPEEDS BY VARIABLE GATE VOLTAGES SUPPLIED THERETO BY A FOOT CONTROLLER-ACTUATED RESISTANCE. A SWITCH SUPPLYING A.C. LINE VOLTAGE TO THE SPEED CONTROL CURCUIT IS NORMALLY OPEN IN THE RELAXED POSITION OF THE CONTROLLER BUT IS CLOSED RESPONSIVELY TO INITIAL ACTUATION OF THE CONTROLLER. THIS SWITCH IS CONNECTED IN SHUNT WITH THE ANODE-CATHODE CIRCUIT OF A SECOND SCR WHICH MAY BE MAINTAINED CONDUCTIVE ONLY FOR A PREDETERMINED TIME AFTER THE SWITCH IS OPENED. THIS CONDUCTIVE TIME IS ESTABLISHED BY A TIMING CAPACITOR WHICH IS CHARGED THROUGH A DIODE ONLY WHEN THE SWITCH IS CLOSED, AND IS DISCHARGED INTO THE GATE OF THE SECOND SCR WHEN THE SWITCH IS OPENED. A NORMALLYOPEN REED SWITCH IS POSITIONED TO BE INFLUENCED BY A SMALL PERMANENT MAGNET MOUNTED ON THE HANDWHEEL WHICH IS COUPLED TO THE ARMSHAFT AND CLOSURE OF THIS SWITCH IS THUS EFFECTED IN A PREDETERMINED POSITION OF THE HANDWHEEL. THE REED SWITCH IS CONNECTED ACROSS THE GATECATHODE CIRCUIT OF THE SECOND SCR AND, WHEN CLOSED, REMOVES THE GATE VOLTAGE TO TURN OFF THE SCR AND STOP THE MOTOR. THE RELAXED POSITION OF THE FOOT CONTROLLER PROVIDES A MINIMUM RESISTANCE FOR ESTABLISHING A FIXED LOWSPEED HIGH-TORQUE POSITIONING DRIVE FOR THE MOTOR. THE TIMING CAPACITOR IS CHOSEN WITH RESPECT TO ITS DISCHARGE RESISTANCE TO PROVIDE A LIMITED CONDUCTIVE TIME FOR THE SECOND SCR AT LEAST LONG ENOUGH TO ALLOW THE LOW-SPEED DRIVE TO FIND THE DESIRED STOP POSITION OF THE ARMSHAFT AFTER WHICH THE SECOND SCR IS RENDERED INOPERATIVE BECAUSE THE CAPACITOR HAS DISCHARGED BELOW THE FIRING VOLTAGE. THUS THE HANDWHEEL CAN BE READILY ROTATED MANUALLY TO REPOSITION THE ARMSHAFT WITHOUT DANGER OF INTERFERENCE FORM THE POSITIONING DRIVE WHICH HAS BEEN RENDERED INOPERATIVE UNTIL THE NEXT ACTUATION OF THE FOOT CONTROLLER.

Inventors

• 👤 James W Mais
• 👤 George M Nicholayeff
• 👤 Donny V Lee

Bibliographic Details