Hoist drive safety system

A safety system in a hoist having a primary drive train comprising an input motor on the high-speed end of the primary drive train and a gear reduction unit drivingly connected to the motor, a drum drivingly connected to the gear reduction unit, a normal operating brake, and an emergency brake operatively coupled to the drum, comprising:

• a mechanical out-of-sync detector;
• said normal operating brake being located on the high-speed end of the primary drive train, said detector including a mechanical differential assembly having a first input element operatively coupled to said motor, a second input element drivingly coupled to said drum, an overspeed release clutch, which disconnects when rotated above a predetermined rotational speed, drivingly connected between one of said input elements and its respective motor or drum, an output element, differential means coupled to said first and second input elements and operable upon relative angular velocity changes between said input elements, including a relative velocity change caused by disconnection of the overspeed release clutch, to rotate said output element in an out-of-sync condition;
• and
• brake-applying means responsive to said detector for applying only said emergency brake.

A safety system in a hoist having an input motor, a primary drive train unit drivingly connected to the motor, a drum drivingly connected to the primary drive train unit, a normal operating brake and an emergency brake on an operating element drivingly coupled to the drum, comprising:

• a mechanical out-of-sync detector;
• brake-applying means responsive to an output from the out-of-sync detector for applying said emergency brake;
• said detector including a mechanical differential assembly having a first input element drivingly coupled to said motor, a second input element drivingly coupled to said drum, an output shaft, differential means coupled to said first and second input elements and operable upon relative angular velocity differences in either rotational direction between said input elements to rotate said output element in an out-of-sync condition;
• said primary drive train including torque-limiting transfer means operable to allow major slippage to limit torque applied between the motor and the drum for dissipating kinetic energy of the motor and primary drive train in case of a hazard condition of the type precluding upward movement of the load but causing minor slippage during normal operation, and wherein said major and minor slippage causes a relative major and minor change in angular velocity of said first and second input elements to rotate said differential output element;
• including nulling means for maintaining the output element in an in-sync condition to compensate for such minor relative angular velocity differences between said input elements;
• and
• said brake-applying means being responsive to such output element rotation for applying the brake in said out-of-sync condition, said brake-applying means including a high-force spring held in a cocked condition and, when released, capable of applying a high braking force, a trigger mechanism holding said spring in said cocked condition, a low-force trigger release mechanism for holding said trigger in said cocking condition, and means for releasing said low-force trigger release mechanism to release said trigger mechanism to thereby release said spring to set the brake, and reset means for resetting the low-force trigger release mechanism and triggering mechanism to recock said spring and thus reset said brake.

A safety system for a hoist of the type having an input motor, a primary drive train, a drum, and a brake coupled to the drum or to an element drivingly coupled to the drum, comprising:

• said primary drive train including an input motor means, said primary drive train having a first high-speed load-carrying element, a drum operatively connected to an output end of said primary drive train, a last low-speed load-carrying element operatively associated with said drum, an operating brake operatively associated with the motor to hold the load when the motor is de-energized, and an emergency brake operatively coupled to the drum;
• means for detecting a hazard condition, such as an operating brake failure, including first and second input elements drivingly coupled to the first high-speed and last low-speed load-carrying elements of the hoist, an output element that moves when a differential rotation occurs between said input elements, an electric clutch which, when electrically energized, drivingly couples one of said input elements with its respective load-carrying element and being inoperative upon being electrically de-energized to decouple the input element from its respective load-carrying element;
• and
• brake-applying means for applying the brake responsive to motion of said output element of said detecting means when said electric clutch is de-energized and said operating brake fails.

A safety system in a load-carrying hoist in which there is defined a last upstream load-carrying component and a last downstream load-carrying component and in input motor with a motor shaft, a power transmission main drive operatively coupled to the motor, an operating brake operatively associated with the motor to hold the load when the motor is de-energized, a drum and an emergency safety brake drivingly coupled to an operating element closely associated with this drum but independent of the main drive so as to provide emergency holding of the load in the event of a main drive failure, a safety brake actuator responsive to an output from an out-of-sync detector for applying said safety brake,

• a mechanical out-of-sync detector, said detector including a monitoring secondary drive train having a first input shaft drivingly coupled to the last upstream load-carrying component, a second input shaft drivingly coupled to the last downstream load-carrying component, means for detecting a predetermined variation in relative speed or direction between said two input shafts and producing an emergency brake-setting rotation output to set said emergency safety brake,
• said power transmission main drive having minor slippage producing an accumulative error between the relative rotations of the last upstream and last downstream load-carrying components, and error compensating means for compensating for such relative rotation accumulative error so that an emergency brake-setting rotation output does not occur from said accumulative error.