| 摘要 |
Antifrictional screws are used to permit the resetting of safety brakes of the type used in hoists. As in prior brakes, centrifugally operated dogs connect braking members, but in the present brakes the dogs also engage actuating members of the antifrictional screws, the screws being rotatable independently of their respective braking members. The dogs can be disengaged from the actuating members by merely operating the usual controls to raise cages of the hoists. The antifrictional screws in one embodiment are then free to be turned automatically independent of the rate of rotation of a braking member by force of usual spring washers disposed between the screws and respective braking members until the brakes are normally released. In modified types, dogs or pawls for controlling the amount of braking continue to engage respective actuating members for controlling rate of rotation of the screws until the cages have been raised sufficiently to release the brakes. For testing purposes, the dogs have easily operated rods associated with them for pushing outwardly the dogs at speeds below the usual speeds required for operation. In heavy-duty hoists, second dogs positioned to clear the actuating members are included to provide a moderate amount of braking in an ascending direction. |
