| 摘要 |
<p>1,132,967. Preventing grabs from swinging. DAVY & UNITED INSTRUMENTS Ltd. 7 Dec., 1965 [8 Dec., 1964], No. 49910/64. Heading B8B. The travelling crab 4 of an ore unloader is accelerated and decelerated during traversing movements by a control device in such a manner that at the end of the periods of acceleration or deceleration the grab 3 is moving at zero angular velocity, thereby avoiding swinging relative to the crab. The movements of the grab during unloading are automatically controlled by the control system described in Specification 1,083,132. In practice acceleration and deceleration are effected in two bursts separated by a period of running at a constant velocity, or accelerating or decelerating at a different rate. The pre-selected programme is calculated and final adjustments are made by observations on the movements of the grab in use. In Fig. 4, (not shown), a motor 30 of the cross traverse winch has coupled to it a position transducer which applies to a comparator circuit 33 a position signal. This is compared with a reference signal, applied along a line 29, which represents the terminal position of the grab. An error signal representing the difference between the actual and required positions is applied by circuit 33 through contacts 34 to a swing control unit 35. The latter controls the cross traverse speed according to the preselected pattern. The output from unit 35 is applied to a control unit 36 for the winch motor 30. A similar system controls the height of the grab. A circuit for the control of acceleration and deceleration is illustrated in Figs. 5A, 5B (not shown).</p> |
