Patent GB-196411-A (GB)
Title: Improvements relating to safety devices for winding or hoisting apparatus
IPC: B66B5/10
Filed: 1922-02-11
Abstract: 196,411. Raeburn, C. E., Taylor, W. E., and Metropolitan-Vickers Electrical Co., Ltd. Feb. 11, 1932. Overwinding, preventing; emergency power cut-off gear.-In winding or hoisting apparatus fitted with brakes which are applied automatically in the event of overwinding or of excessive speed during the run, electrically - controlled means are provided to apply the brakes gradually in the event of excessive speed during the run, and to apply them rapidly in the event of overwinding. For example, the overwinding mechanism may comprise a valve 34, Fig. 2, which is operated electrically by the opening of a switch by the moving cage, depth indicator, or the like, and serves to cut off supply fluid from the brake cylinder 30 and open the latter to exhaust, thereby allowing a piston to fall quickly and apply the weighted brakes. Overspeeding during the run may operate two valves 28, 29 of which the valve 28 cuts off the supply fluid without moving the valve 34, while the valve 29 affords a limited opening to exhaust allowing the piston to fall gradually. Fig. 1 shows one means of actuating and controlling these valves automatically. A three-phase motor 3 drives the winding drum (not shown). A movement of the controlling handle 10 to the left or right establishes one or other of the circuits 8, 8<a> between the mains, thereby energizing the coils of one or other of the auxiliary switches 6 and closing the switch. This closes a circuit which energizes the coil of a corresponding main motor switch 5, so that the motor is driven in one direction or the other, in accordance with the particular switch 5 operated. The two circuits 8, 8<a> both pass through one branch of a double switch 9 which is normally closed, the other branch of the switch being in circuit with a relay 18. A self-exciting serieswound direct-current generator 11 is driven by the winding drum so that its speed is proportional to the speed of the cage. A rheostat 15 and the actuating-coil of the relay 18 are in series with the field-winding 12 of the generator. The movable arm of the rheostat is connected mechanically with the depth indicator or the winding gear so that its speed of rotation is proportional to the speed of the cage. The rheostat varies the resistance in series with the field-winding 12 so as to maintain the voltage of the generator approximately constant for all speeds of the cage up to the safe limiting speed. Excessive speed opens the relay 18 and breaks the circuit 20, thereby deenergizing the coil controlling the switch 21 and opening the latter. This breaks the energizing circuit of a three-phase solenoid 22 and allows the weighted core 22<a> to fall, which movement is communicated by linkages to the controlling valves 28, 29. The switch 21 is connected mechanically with the double switch 9 so that the latter is opened with the former, thus cutting off power from the motor. When the speed decreases, the relay 18 recloses automatically, but in order to restart the motor it is necessary to re-close the switches 9, 21 by operating a push button 24, which re-establishes the circuit 20 through a branch in parallel with these switches. On overwinding occurring, the depth indicator 19 operates a switch 32 which opens a main-supply switch 33 and thus actuates the valve 34 to apply the brakes quickly, independently of the speed of the cage. As an alternative means of control, both overwinding and excessive speed may operate the valve 34 in the same way, and the gradual application of the brakes on excessive speed be secured by partly throttling the normal exit from a dash-pot cylinder 31, thereby slowing the movement of the piston. Specifications 12436/11 and 28747/13 are referred to.