| 摘要 |
1,058,789. Control of several D.C. motors. RUSTON-BUCYRUS Ltd. Oct. 18, 1965 [Oct. 23, 1964], No.44005/65. Heading H2J. [Also in Division G3] Each of the three movements of an excavator. namely hoist -lower, crowd-retract, and swing, are effected by a Ward-Leonard set having an individual control unit. The hoist generator has reversing field windings supplied through separate silicon-controlled rectifiers, a firing control device being in the form of a magnetic amplifier comprising reference control, loadcurrent responsive and voltage-responsive windings. As the voltage of the generator increases, the degree of saturation of the magnetic amplifier is decreased to retard the firing time of the controlled rectifier and reduce the generator field current. When the load current reaches a predetermined value, a Zener diode, forming part of a discontinuous gating circuit, breaks down to energize the current-responsive windings on the magnetic amplifier. This has a limiting effect upon the firing control device to reduce the generator field current. The crowdretract control is similar to that described, the control units for the two movements having the same construction and each comprising circuit components mounted on a panel. The components for the swing control are also mounted on a single panel, and the mounted components are the same as for the other panels. In the case of the swing control generator, however, a discontinuous gate is inserted in the circuit for the voltage-responsive windings and is removed from the current feedback circuit. Each control panel comprises a flat metal base for mounting in a cabinet, and carries the silicon-controlled rectifiers together with the firing control devices as well as full wave rectifiers which supply the generator field windings through the controlled rectifiers. Smaller components carried on the base include diodes in the circuit of the reference control windings, the discontinuous current gates which comprise potted assemblies embedding the Zener diodes, and harmonic suppressing chokes. The base also supports a board for mounting resistors which have a hinged cover. A panel is replaced by removing a terminal block which is then secured on the substitute panel so that the block correctly positions the conductors for ready attachment to a terminal strip. Thus, the new panel is wired for crowd, swing or hoist control. Conductors making internal connections in the panel are mounted in the terminal block. |
