Hoist having worm safety device

A safety system in a load-carrying hoist in which there is defined a last low-speed, load-carrying component, a last high-speed, load-carrying component including a main drive motor, a power transmission main drive operatively coupled to the motor, a drum operatively coupled to the main drive and to the last low-speed, load carrying component, a secondary drive including substantially irreversible gearing having a first portion with gear teeth driven by one power source and a second portion with gear teeth in mesh with the gear teeth of the first portion driven by the drum at a speed slower than the gear teeth of said first portion and wherein the drum cannot substantially back drive the first portion, thus holding the drum in the event of a hazard condition, positioning means for automatically engaging the first portion power source for accelerating the gear teeth of the first portion of the irreversible gearing to said gear tooth speed faster than the gear teeth of the second portion and in a direction out of interference with the gear teeth of the second portion of the irreversible gearing during normal operations, but allowing interference to lock the gear teeth of the second portion when a hazard condition occurs.

A hoist comprising a drive motor, a main gear reduction drive unit driven by the motor, a drum driven from the drive unit, normally irreversible drive means continuously drivingly engaged for stopping the drum in a hazard condition, said irreversible drive means including a worm wheel drivingly coupled to the drum, a worm having teeth meshed with teeth on the worm wheel, means responsive to pushing contact of a worm wheel tooth against a worm tooth only when both are moving in the same direction as in normal operation for increasing the speed of the worm relative to the worm wheel to advance the worm tooth out of engagement with the worm wheel tooth for substantially synchronizing the speeds of the worm and worm wheel teeth, said speed-increasing means becoming operative to lock the worm wheel with the worm when said directions of the worm wheel and worm teeth are opposite to one another in an abnormal hazard condition, shock-absorbing means allowing axial movement of the worm to absorb part of the kinetic energy of the motor drive unit and drum during an emergency stop, torque-limiting means in the drive unit for absorbing the remainder of the kinetic energy during an emergency stop, and overspeed protection means for automatically triggering a lock-up between the teeth of the worm and worm wheel for an emergency stop when the drum runs beyond its rated normal speed.

A safety system for a hoist of the type comprising a main drive motor, a main drive train coupling the motor to the drum, and a control for reversing the direction of the main drive motor, the improvement comprising a worm wheel coupled to the drum, a worm having teeth meshing with teeth on the worm wheel, means for automatically accelerating the worm to give a tooth on the worm a speed greater than the speed of a tooth on the worm wheel to move a tooth on the worm away from a tooth on the worm wheel during reversal of the main drive motor and at a torque sufficient to overcome frictional contact between the meshing teeth of the worm and worm wheel.