| 摘要 |
1,261,550. Electromagnetic brakes. SOC. "POTAIN". 22 Jan., 1969 [23 Jan., 1968], No. 3524/69. Heading F2E. A control circuit to provide gradual release and application of an eddy-current brake 3, 4 to the motor shaft 1 of a crane effects a required brake actuation in a time equal to that required to discharge or charge a capacitor, 14. In use, to initiate swinging of a tower crane, a contactor 7 or 8 is closed by a respective switch 5, 6 to swing the crane in a required direction which closure connects the point 10 to supply line 9 to discharge the capacitor 14 thus turning off transistors 17 and 20 and releasing the brake due to reduction of current in the coil 4, the reduction of current following a similar law to that governing the discharge of the capacitor. When the motor is required to stop the switch is opened so that the capacitor charges through resistors 11, 16 causing current to flow through the coil to re-apply the eddy-current brake. A locking brake applied to a turning part is provided. In an alternative embodiment, Fig. 2, (not shown), a rheostat (25) is included in series with the capacitor to provide manual adjustment of charging time, the remainder of the circuit being as above. |
