Patent GB-1083132-A (GB)
Title: Improvements in or relating to control systems for material handling devices with overhead travelling grabs
Inventor: HOLMES FRANK RICHMOND
IPC: B65G67/00
Filed: 1963-03-30
Abstract: 1,083,132. Automatically operated overhead travelling grabs. ASHMORE, BENSON, PEASE & CO. Ltd. March 31, 1964 [March 30, 1963], No. 12714/63. Heading B8B. An overhead travelling grab 21, Fig. 1, can be programmed to automatically unload material from the hold of a ship 45 and discharge it through either of shoots 99, 100. The grab is traversed, opened and closed and raised and lowered by winches in a housing 22 and cables. A runway 17 for a grab-carriage 20 may be swung up about hinges 18. An operator's cab 40 is movable both vertically and horizontally. The grab may be programmed to traverse the ship's hold transversely in a stepby-step fashion and between each step the grab may extract material once or several times from the same place at the same level or at successively lower levels. After the traverse is completed the grab may move back to its starting point in one movement or in a step-bystep manner digging as it goes. The level at which the grab digs may be determined by the grab itself without any pre-setting by introducing a load cell into the hoisting rope. Provision may also be made for the grab to travel longitudinally of the hold in a step-by-step manner after successive traversing movements so that the whole of the hold is covered. To compensate for movements of the ship in a vertical plane sensing means are provided which modify the level at which the grab digs in accordance with changes in the level of the ship. One of two or more discharge positions for the grab may be selected and this information together with the position of the grab at any time and the other variables are displayed on a panel. To compensate for slip and stretch in the operating cables independent cables may be provided for sensing the position of the grab and trolley. The position of all of the moving parts may be indicated by position switch operated either mechanically e.g. by sorew and nut mechanism, by servo-mechanisms or by selsyns. Alternatively the positions may be record d in a digital form. Multi-position switches such as uniselectors may also be used. Manual control is provided e.g. for initially positioning the grab before starting automatic operation. During unloading the grab is moved towards the discharge point before it is fully raised and is appropriately accelerated and slowed down in response to controlling signals. Interlocks are provided between the hoisting and traversing means to prevent the grab being traversed too far when insufficiently hoisted. A similar interlock prevents premature lowering of the grab. Fig. 8 shows a series of position switches 131-134 corresponding to positions of the grab-carriage 20 which are displaced by a screw and nut mechanism 137 driven by the transverse step-by-step control mechanism. These switches are operated by a member 135 moved by a screw which is driven by the means which sense the position of the grab-carriage. The switches 131-134 as a group operate outer and inner traverse limit switches 138, 139 themselves displaceable by screws. Similar devices may control the level of operation of the grab. Figs. 10, 11 (not shown) show block diagrams for the control of the grab-hoist winch and cross traverse winch respectively by means of multi-position rotary switches. With magnetic material an electromagnet may replace the grab.