Patent GB-1101297-A (GB)
Title: Speed and positioning control apparatus for power driven machines
IPC: D05B69/22
Filed: 1966-04-20
Abstract: 1,101,297. Controlling electromagnetic clutches and brakes. WARNER ELECTRIC BRAKE & CLUTCH CO. 20 April, 1966 [26 April, 1965], No. 17341/66. Headings F2D, F2E and F2L. [Also in Divisions D1 and H1] A machine tool or sewing-machine driven by an electric motor (35), Fig. 2 (not shown), through an electromagnetic friction clutch (38), and stopped by a manual control (FT), Fig. 1 (not shown), which de-energizes the clutch and energizes an electromagnetic friction brake (64), has means controlled by a position sensor switch (122) whereby, if the machine stops in other than a preselectable position, e.g. needle up or needle down, the brake is automatically deenergized and the clutch re-energized intermittently under control of an output driven speed-sensing centrifugal switch (76) which alternately energizes and de-energizes the clutch as its output speed respectively falls below or rises above a predetermined speed, such action continuing until the machine reaches the preselected stop position, whereupon the clutch is automatically de-energized and the brake energized. The same speed sensing switch (76) is also used during continuous running and has three stages of action giving three manually selectable speeds by intermittent clutch action. In a sewing-machine, the needle is driven from the motor (35), Fig. 2 (not shown), through a shaft (36), clutch (38) having axially engageable elements (49), (54) drawn together on energization of a coil (62), a shaft (31) and a belt drive (28-30) and shaft (19), a brake (64) comprising discs (65), (66) being actuated by energizing coil (72) to stop the needle when the clutch is disengaged. The output driven speed sensing centrifugal switch (76), Fig. 1 (not shown), is mounted on shaft 31 and comprises two seriesconnected centrifugally-operated switches 77, 77<SP>1</SP> opened at different speeds, the degree of depression of foot treadle FT closing switches S2, S3 to short out the switches 77, 77<SP>1</SP>. The switches 77, 77<SP>1</SP> are manually adjustable to open at any predetermined speed. The rotary position sensor switch 122 comprises a conductive segment 132, rotatable with shaft 19, having two exposed areas ND, NU of insulating material corresponding to needle down or needle up, and co-operating with wipers W1, W3, a further wiper W2 engaging segment 132. The wipers are positioned around the segment 132 with areas ND, NU in the same radial plane. To permit an operator to selectively stop the needle " up " or " down," a knee-operated lever (136), (138), Fig. 7 (not shown), is provided to close a switch PSS, energize a relay NR and open normally closed contacts NR2 and close contacts NR1 to include wiper W3 and not wiper W1 in the control means to change from stopping in " needle down " to " needle up." Further movement of lever (136) lifts the presser foot (20) through a linkage against a spring bias. Operation.-Main switch S4 is closed to drive the motor 35, the clutch being disengaged, and energizes transformer T1 which supplies a source of voltage for the clutch control circuit and a stop position control circuit via rectifier R.E. Depression of treadle FT closes the RUN contacts of switch S1 to initiate an operation cycle, the brake control circuit including the STOP contacts of switch S1 being broken to release the brake, and current being permitted to flow in the circuit including resistor R4, switches 77, 77<SP>1</SP> and switch S1 producing a voltage drop across resistor R4 which lowers the voltage level at the base b of the clutch control transistor TC rendering the transistor conductive and permitting current flow in the circuit including resistors R1, R2, the emittercollector circuit of transistor TC, clutch coil 62 and resistor R3, thereby engaging the clutch. Current will flow in the circuit including resistor R4 until the speed of shaft 31 exceeds the level set for switch 77, when the switch will open, current flow stops, and the transistor turned OFF, thus de-energizing the clutch coil. As the shaft speed falls, the switch 77 recloses and the transistor is again turned ON. The speed of the shaft is thus kept substantially constant. Further depression of the treadle closes switch S2 shorting out switch 77, and the speed of shaft 31 is then controlled by the switch 77<SP>1</SP> until switch S3 is closed by further depression of the treadle, and the machine runs at maximum speed. By " heeling " the treadle, the STOP contacts of switch S1 are closed, breaking the clutch control circuit to release the clutch, and permitting current flow in a circuit including resistors R6, R7 and the STOP contacts of switch S1 providing a voltage drop across resistor R6 and turning the brake control transistor TB ON, and permitting current flow in a circuit including resistors R1, R2, the emittercollector circuit of transistor TB, brake coil 72 and resistor R3, thereby energizing the brake to stop the needle. Diodes D1, D2 are provided to present high inductive voltages damaging transistors TB, TC, as the circuits are deenergized. If the needle stops in the desired position then the operating cycle is complete. Needle stopped out of predetermined position.- To inhibit the needle positioning controls until the machine 10 comes to a complete stop, a relay DR and a capacitor C2 are energized during running of the machine when the RUN contacts of the switch S1 are closed. When the RUN contacts of switch S1 open, the capacitor discharges through relay DR for a predetermined time interval during which normally closed contacts DR1, which connect wiper W2 with the STOP contacts of switch S1 remain open deactivating the needle position sensor and allowing the machine to stop. Assuming the machine is preset to stop the needle in the " down " position, and the needle is not in this position, when the contacts DR1 controlled by the delay relay DR close, a circuit is completed through resistors R8, R9, normally closed contacts NR2 controlled by a needle positioning relay NR, wiper W1, conductive segment 132, wiper W2, relay contacts DR1, and the STOP contacts of switch S1 the resultant voltage drop across resistor R8 turning a control transistor T3 ON, which turns transistor TB OFF, thereby de-energizing the brake coil 72. Simultaneously, current flows in the circuit including resistor R4, switches 77, 77<SP>1</SP>, normally closed contacts NR<SP>1</SP>, wipers W1, W2, conductive segment 132, normally closed contacts DR1, and the STOP contacts of switch S1, the resultant voltage drop across resistor R4 turning transistor TC ON to energize the clutch coil 62. The machine runs at a speed controlled by switch 77, until wiper W1 comes in contact with the non-conductive portion ND turning transistors TC, T3 OFF and transistor TB ON to brake the machine in the predetermined position. Single stitching.-Closure of switch FS adjacent the treadle FT completes a short circuit around the contacts NR1 and NR2 and the switch 122, so that current flows through resistors R1, R8 and R9 to step the needle through one or more single stitch operations. To remove material from the machine.-To shift the needle from a stopped needle-down position to a needle-up position, the knee pad 136 is shifted laterally, and since the contacts DR2 are closed, the needle relay NR will be energized, thus deactivating the needle-down sensor ND, W1, and activating the needle-up sensor NU, W3, again de-energizing the brake coil 72 and energizing the clutch coil 52 to index the needle to the desired " up " position.