Patent GB-950437-A (GB)
Title: High speed clutch and brake actuating circuit
IPC: H03K17/54
Filed: 1962-09-28
Abstract: 950,437. Controlling clutch-brake combinations; electromagnetic brakes. SPERRY RAND CORPORATION. Sept. 28, 1962 [Oct. 10, 1961], No. 36886/62. Headings F2C, F2E and F2L. [Also in Division H3] A control circuit for clutch-brake mechanism having clutch and brake engaging solenoids 234, 206, Fig. 2, comprises a first bi-stable conducting device 202 connected to the clutch solenoid, a second bi-stable conducting device 200 connected to the brake solenoid, means for selectively switching one of the devices to its high conducting state, and a condenser 210 coupled to the conducting devices in such a way that it is charged or discharged in accordance with the conducting device rendered conducting, so as to provide the associated clutch and brake energizing solenoid with a current which has an initial peak magnitude, followed by a lower steady state magnitude. In the form shown, the bi-stable conducting devices 200, 202 are thyratrons, but alternatively silicon controlled rectifiers may be used. The circuit is controlled by a flip-flop 218. A negative potential - E 2  is applied to the first grids of the two thyratrons 200, 202. On initiating a cycle of operations, the flip-flop 218 fires the brake control thyratron 200, so that current flows through the brake-engaging solenoid 206. At the moment of firing of the thyratron 200, a surge of current passes from a positive terminal + E 1  through the condenser 210 to the solenoid 206, but as charging of the condenser is completed, the current falls to a limit determined by a rheostat 208 in parallel therewith. A bias circuit 220, 222, associated with the thyratron 200, acts through a rectifying diode 224 and a condenser 230 to hold the clutch control thyratron 202 non-conducting. If the flip-flop 218 now fires the clutch control thyratron 202, the charged condenser 210 immediately discharges through the clutch-engaging solenoid 234, thus giving a surge of current, which is continued by a steady flow of reduced magnitude through a rheostat 236. When the clutch control thyratron 202 fires, the change of potential applied through a resistor and condenser 256, 258 quenches the brake control thyratron 200, which is now held in its non- conducting state by the potential of a bias circuit 244, 246 of the clutch control thyratron, applied through a rectifying diode 248 and a condenser 254. When the flip-flop 218 again fires the thyratron 200, the cycle is repeated, re-charging of the condenser 210 producing an initial surge of current for brake engagement. Clutch-brake combination.-A driven shaft 100, Fig. 1, rotating a tape drive capstan, carries a clutch disc 102 engaged on one side by a brake member 104 and on the other side by a clutch member 132. The brake member 104 is fast with an armature 114 biased in the brakeengaging direction by a spring 124 and cooperating with a brake-engaging solenoid 110, a connection 116, 122 permitting relative axial movement but not rotary movement between the armature and a surrounding fixed frame 126. A motor shaft 156 is coupled by a connection 144 permitting axial movement to an armature 138 fast with the clutch member 132 engageable with the driven clutch disc 102, a compression spring 152 biasing the clutch member towards the driven clutch disc. A stationary clutch-engaging solenoid 130 surrounds and journals an extension of the clutch member 132. The surge of current supplied to one of the solenoids 110, 130, on initiation of brake or clutch engagement, causes rapid cessation or commencement of rotation of the shaft 100, the holding current of relatively small magnitude then supplied maintaining the brake or clutch in engagement.