GB1157831A - Load Lifting Devices incorporating Brake means - Google Patents

Abstract

1,157,831. Brakes for winding drums. EATON YALE & TOWNE Inc. 27 Jan., 1967 [21 Feb., 1966], No. 7416/66. Heading B8B. [Also in Division F2] A load lifting device includes brake linings 16, 17, Fig. 1, resiliently urged into engagement with a brake drum 13 to hold a load in a fixed position, the linings being movable about the drum axis between first and second extreme positions, a linkage 35 permitting engagement of the linings with the drum in a first condition and holding them out of engagement in a second condition so that a lifting movement when the linkage is in its first condition (as in Fig. 1) causes the linings to rotate toward their second extreme position whilst moving the linkage to an intermediate position permitting brake drum slippage and subsequent movement of the drum moves the linkage to its second condition. The brake mechanism is applied to a mechanical hoist using a recirculating ball screw and has a shaft 12, splined to an electric motor, which passes through a plate 11 forming part of a gearbox casing. In the position shown in Fig. 1 the brake drum 13 is initially prevented from rotating. When the electric motor control lever (not shown) is moved in the lifting direction the motor torque increases until the brake drum 13 and brake shoes 14, 15 are rotated clockwise causing pivot pin 18 to actuate microswitch 47 thereby causing a solenoid 44 to be energized to withdraw armature 45 against spring 46. Further rotation causes cam surface 37d to contact outer ball bearing race 39 and the reaction causes link 37 to be lifted thereby straightening toggle linkage 35 to partially release the brake shoes 14, 15 against the force of spring 25. As drum 13 rotates a pin 10 strikes member 38, which engages pin 43 to move the toggle linkage overcentre until surface 36a engages adjusting screw 54. During lifting friction pads 33, 34 are spring-loaded against drum 13. The drag caused by the latter, when the motor torque has been reduced, rotates the brake shoes counter-clockwise until the pivot pin 18 actuates microswitch 47 to de-energize the solenoid 44. Spring 46 then moves the toggle linkage 35 back overcentre allowing the brake linings to be applied by spring 25 to hold the load in the raised position. To lower the load the motor control lever is moved towards the " lower" position and switch 61, Fig. 2, is closed. Further movement increases the motor torque to slightly lift the load so that microswitch 47 energizes the solenoid as described and microswitch 48, when actuated by pin 18 energizes coil B. This causes the motor torque to fall with further movement of the control lever. As the load is lowered microswitch 48 opens but coil B remains energized through coil B1 whilst microswitch 47 returns to the position shown to energize relay coil A, the solenoid 44 remaining energized through contact B5. Energization of relay coil A causes energization of relay coil C which opens contact C2, relay coil B remaining energized through contact A1. Lowering is stopped when the control lever is moved towards the neutral position and the load is lifted slightly to operate microswitch 47 whereby relay coils A, B are de-energized but relay coil C remains energized through contact C1. When the load is lowered microswitch 47 breaks the circuit to solenoid 44 because contact B5 is now open but completes a circuit to energize coil D, which de-energizes coil C, which in turn de-energizes coil D to return the circuit components to their original condition.