Safety mechanism for hoisting drums

A safety system in a hoist having an input motor, a gear reduction unit, a drum, a safety brake drivingly operatively coupled to the drum, comprising:

• a mechanical out-of-sync detector,
• a safety brake actuator responsive to an output from the out-of-sync detector for applying said safety brake,
• said detector including a mechanical differential having a first input shaft drivingly coupled to said motor, a second input shaft drivingly coupled to said drum, a brake actuator output shaft, a differential gear set coupled to said first and second input shafts and operable upon relative angular velocity changes between said input shafts in a predetermined direction and amount to rotate said output shaft in an out-of-sync condition, and
• means operatively coupling the output shaft to said safety brake actuator for applying the brake in said out-of-sync condition, said means coupling the output shaft to the safety brake actuator including a wedge ring, one-way clutch means allowing said wedge ring to remain stationary in a brake-open position during one direction of rotation of said output shaft but operable to rotate into a brake-set position during rotation in the opposite brake-setting direction of said output shaft, and linkage means coupled to said wedge ring for triggering the safety brake actuator to set the brake in response to said brake-setting rotation of said output shaft, and means releasing said wedge ring for free rotation on said one-way clutch means when said brake is set.

A method of detecting a failure or hazard condition in a hoisting machine of the type having a motor, a motor shaft driving a power transmission main drive train and thence a drum, and wherein rotational deviations between the motor shaft and drum can occur, and wherein a safety brake is provided operatively coupled to the drum to stop the drum upon detection of a failure or hazard, comprising:

• monitoring the rotational speed and direction of the motor,
• monitoring the rotational speed and direction of the drum,
• introducing a deviation correction rotation velocity component to one of said monitored speeds and directions to produce a first unidirectional relative rotation therebetween in excess of the rotational deviation,
• such hazard or failure condition producing a large differential in relative speed or direction between said monitored speeds and directions,
• detecting such large differential between the monitored speeds and directions in said hazard or failure condition, and producing a second unidirectional rotation opposite said first unidirectional rotation, and
• triggering the safety brake in response to such detected second unidirectional rotation.

A safety system in a load-carrying hoist in which there is defined a last high-speed load-carrying component and a last low-speed load-carrying component and a drive motor with a motor shaft, a power transmission main drive operatively connected 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 operatively coupled to the 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, comprising a mechanical out-of-sync detector, said detector including a monitoring secondary drive train having a first input shaft drivingly coupled to the last high-speed load-carrying component, a second input shaft drivingly coupled to the drum, means for detecting a change in the angular position of one input shaft relative to the other input shaft in one predetermined direction only and producing an emergency brake-setting rotation output to set said emergency safety brake, wherein said emergency safety-brake-setting rotation output is always unidirectional, said detecting means being unresponsive to a change in the relative angular position of said input shafts in a direction opposite said one predetermined direction and not producing said unidirectional emergency safety-brake-setting rotation output.

A safety system in a hoist having a motor with a motor shaft, a power transmission main drive, a drum, and a safety brake drivingly coupled on an operating element to the drum, said system having an accumulative angular error produced between the relative angular position of the drum and the motor shaft, comprising:

• a mechanical out-of-sync detector,
• a safety brake actuator responsive to an output from the out-of-sync detector for applying said safety brake,
• said detector including a monitoring secondary drive train having a first input shaft drivingly coupled to said motor, a second input shaft drivingly coupled to said drum, means for sensing a change in the angular position of one input shaft relative the other input shaft in one predetermined direction only and producing a brake-setting rotational output, and
• correction means for producing a predetermined, limited change in the angular position of said one input shaft relative to the other input shaft in a direction opposite said one predetermined direction in an amount greater than said accumulative angular error for compensating for such relative angular accumulative error.