GB1183126A - Improvements in or relating to Bridge Cranes - Google Patents

Abstract

1,183,126. Preventing swinging of loads in bridge cranes. KONE OSAKEYHTIO. 25 Aug., 1967 [25 Aug., 1966], No. 39162/67. Heading B8B. [Also in Division H2] A bridge crane comprises a trolley running on the bridge and having a drum from which extends a cable or chain provided with a hook, a prime mover for moving the trolley, and synchronization means for controlling the prime mover such that when the crane operator controls the prime mover so that the trolley is accelerated or decelerated to alter its movement relative to the bridge the prime mover automatically accelerates or decelerates the trolley by the same amount and in the same direction after a time which is half the time of the period of the oscillation of a load on the hook produced by the first said acceleration or deceleration, so as to effectively cancel the said oscillation. The prime mover may be a twospeed squirrel-cage motor having the speed ratio of 1: 2, the motor speeds being used respectively for the two accelerations with the second one actuated by the synchronization means, and the operation being reversed for deceleration. In the control circuit shown in Fig. 4 movement of the drum 9 changes the setting of the potentiometer Rp to alter the charge on the condenser C to accord with the length of cable or chain unwound from the drum. When measuring of half the oscillation time begins, the switch 10 is changed over so that the condenser discharges through the resistance R 3 , and a time relay A operates the motor again when the condenser charge has reached a predetermined value. In the control circuit shown in Fig. 5 which is used for short impulse driving of the trolley, the switch A is closed when the motor is actuated by the operator, to charge the condenser C in dependence on how long the motor is actuated, the charging current passing through the diode D I and transistor Trl. When the relay A, Fig. 4, operates after the appropriate time the switch B is closed and the condenser discharges through the diode D, and the transistor Trl. The current also passes to the transistor Tr 2 to direct its collector tension to zero, and when the condenser is discharged the collector tension rises to that of the current source and this may be used as a signal for the motor to stop. If a large load causes the trolley to slip during the first actuation of the motor the discharge of the condenser may be made dependent on the distance travelled, e.g. by providing a switch controlled by a magnetic toothed wheel on the motor.