GB1199256A - Safety Device Primarily for Machine Guards - Google Patents

Abstract

1,199,256. Transformers. DONOVAN ELECTRICAL CO. Ltd. 4 Oct., 1967 [6 Oct., 1966], No. 44653/66. Heading H1T. [Also in Divisions F2, H3 and H4] A device for providing a signal when two relatively movable members are in a predetermined positional relationship comprises a primary head 10, for attachment to one of said members and for generating a varying field, and a secondary head 11, for attachment to the other of said members, in which is induced an output signal when said heads are in juxtaposition. As described, with particular reference to a machine tool provided with a guard, one head being attached to the guard and the other to the body of the machine, the heads each comprise a C-shaped laminated core 13 or 14, Fig. 2, of magnetic material in which the separation between the limbs of the core (w) is equal to the length of the said limbs (d). Each limb carries a coil and these may have equal turns, or those of the secondary head 11 may exceed those of the primary head 10. The assemblies of coils and laminations are embedded in epoxy resin contained in metal casings 17 or 18. The pole faces of the cores are also covered with a thin layer of the resin. Wires to the coils are led out of the casings through flexible armoured cables 19. An arrangement is described (Fig. 3, not shown) in which there is no cable appendant to the guard, which may then be wholly removed. Two pairs of co-operating heads are provided and the two heads on the guard are interconnected. One head on the machine body is connected as a primary head, and the other as a secondary head. Means are also described for ensuring that the guard is replaced the right way round (Figs. 4 and 5, not shown). One head is provided with a projecting tongue at one end, and the cores of both heads are asymmetrically arranged within their casings. A circuit arrangement is described in which the signal from the secondary head when it is properly aligned with the primary head is utilized to operate a relay which closes a contact allowing the machine tool to be used (Fig. 1, not shown).