| 摘要 |
A dynamic braking system for a motorized lifting mechanism such as a crane, hoist or the like allows the load to be lowered at a controlled rate during a power failure. An auxiliary power source is activated to apply an excitation current to the stator windings, creating a static magnetic field. When the brake is released the rotor rotates in the static magnetic field, generating an A.C. voltage that is rectified and applied to the stator, thereby increasing the strength of the static magnetic field. An equilibrium is reached, and the load is lowered at a controlled rate. In the preferred embodiment the A.C. voltage is supplied through an adjustable resistor, allowing the lowering rate to be selectively controlled.
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