GB568421A - Improvements in or relating to cut-outs - Google Patents

Abstract

568,421. Preventing overwinding. KING, Ltd., G. W., and KING, D. M. July 27, 1943, Nos. 12203/43 and 69/44. [Class 78 (v)] [Also in Group XXVI] Means for stopping a driven element, e.g. a hoist, when overload occurs, or the element reaches an end position, comprises a friction clutch 18 between driving and driven elements 10, 12 and members, e.g. a screw 35 and nut 38, driven by the respective elements and adapted upon variation in relative speed to stop the driving element. In the normal driving position, the screw 35 holds open the switch 48 of an electromagnetic brake on the driven element, while a micro-switch 50 controlling the electric driving motor, or micro-switches 50, 52 in the case of a reversible motor remain closed. When speed variation occurs, clutch 18 slips and the screw 35 moves, permitting switch 48 to close, thereby applying the brake, and. subsequently opening switches 50 or 52 in the motor circuit. Two switches may be used instead of three, in which case each switch controls the motor and a relay to operate the brake. After cutting out the motor in the " raise " direction it may be necessary to prevent rotation of the nut 38 when the " lower " circuit is closed until the screw returns to its normal position. This may be accomplished by using a brake strong enough to withstand the combined torques of the load and motor. Alternatively, a non- rotatable bracket 55 is provided, having pins 59 engaging ratchet teeth in the nut, whereby rotation thereof in one direction is prevented. The sleeve is moved out of engagement with the ratchet by the screw 35 when the latter reaches its normal position. The invention may be applied to electrical, mechanical or hydraulic drives for hoists in other mechanism.