Patent GB-780339-A (GB)
Title: Improvements in or relating to grab mechanisms for grappling articles
Inventor: DENT KENNETH HENRY
IPC: B66C1/66
Filed: 1954-10-29
Abstract: 780,339. Lifting devices for engaging articles. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Oct. 14, 1955 [Oct. 29, 1954], No. 31389/54. Class 78 (4). A sleeve 19, Fig. 1, mounted coaxially within a sleeve 16 carried by the body of the device illustrated is rotated by a rotor 11 influenced by windings 12 to engage or release an article to be lifted. The sleeve 19, which is formed of a non- magnetic stainless steel and is bolted to the rotor 11, is formed with bayonet sockets 20 for engaging horizontal radially extending arms on a spider carried by the article to be lifted. When the winding 12 is energized the rotor 11 is turned so that the lead-in slots 21 of the bayonet slots 20 in the sleeve 19 are brought into coincidence with plain slots 22 in the outer sleeve 16; the arms of a spider may thus be introduced into the bayonet slots 20 where they are held when the winding 12 is de-energized to permit the spring 33 to return the rotor 11 and sleeve 19 to their normal position. Adjustable stops 46 co-operating with pegs on the rotor 11 define its extreme positions. A spring-biased probe 27 operated by the spider to close a switch 32, and a three position switch CS, Fig. 4, operated by a cam driven from a winch winding the cable 42, Fig. 1, by which the device is raised and lowered, permit a partly automatic operation of the device. The conductors within the cable 42 are connected into the controlling circuit by slip rings and brushes 58 ... 61. When the device is lowered to the region in which it is to grip an article, the switch CS is moved to the position PU. Thus, provided a foot-operated switch FS has been closed, the winding 12 is energized to prepare the device to engage the arms of a spider which are guided into the slots 21, 22 by fairings 23, 24. When the spider raises the probe 27 to close the switch 32, this completes the circuit of a relay A/2 which locks over contacts A1 and at contacts A2 interrupts the circuit of the windings 12 so that the sleeve 19, Fig. 1, is returned to trap the arms of the spider. The relay A/2 is subsequently released by the foot switch FS and the switch CS is moved by its cam, as the winch raises the article to the level at which it is to be released, through a position N to the position RLSE. When the article is then lowered to rest it again raises the probe 27 to close the switch 32 which, provided the switch FS has been closed, completes a circuit of the self-locking relay A/2. Contacts A2 of this relay then complete the circuit of the winding 12 which is energized to bring the slots 21, 22, Fig. 1, into coincidence so that the device may be raised from the spider. A lamp L2 indicates when the winding 12 is energized, while a further lamp L1 is controlled by a switch 31 closed by the probe 27 immediately before the switch 32. A similar device raised and lowered by a winch provided with a different cam to operate the switch CS may serve for transferring a spider from an upper level to a lower. Alternatively, a single device such as that illustrated may be employed with a reversing switch between the switch CS and the contacts A2 or, as a further alternative, the cam controlling the switch CS may be arranged so that it can be advanced or retarded and its drive reversed. Energizing the winding 12 may latch, instead of unlatching the spider.