| 摘要 |
<p>Provided is a variable speed hoist using an electric motor equipped with a pull rotor brake and capable of conducting current by which the pull rotor brake can be reliably released at an operation starting time, even in the variable speed hoist such as, for example, an electric chain block having a short acceleration time, without decreasing an output frequency when starting applying an excess voltage to the electric motor. The variable speed hoist includes an inverter and an electric motor equipped with a pull rotor brake and controls the speed of the electric motor to be gradually increased. In the variable speed hoist, the inverter is set so as to operate in a predetermined voltage-to-frequency (V-F) pattern, and when the motor is activated, the acceleration (output frequency increase rate) until frequency reaches from f1 to f2 is set smaller than the acceleration (output frequency increase rate) until frequency reaches from f2 to f3, thereby supplying power sufficient to be able to release the pull rotor brake.</p> |
