Patent GB-1526401-A (GB)
Title: Slip-ring assembly
IPC: H01R39/08
Filed: 1975-10-28
Abstract: 1526401 Slip-ring assembly WILLIAM McGEOCH & CO (BIRMINGHAM) Ltd 28 Oct 1975 [29 July 1974] 33308/74 Heading H2E A slip-ririg assembly has a plurality of conductive rings 1, e.g. twenty spaced apart axially on, and secured to a central insulating support, with a gap between rings, wherein the surfaces of adjacent rings, forming the sides of the gap have insulating coatings. In an embodiment the insulating support is made of a cylindrical body 1 having in its periphery twelve, equally spaced grooves 2 extending parallel to its longitudinal axis and each receiving a supporting rod 3; the body 1 and rods 3 can be made of a fabric or glass fibre reinforced epoxy resin or high grade dielectric and the rods are secured to the grooves 2 by an adhesive, e.g. epoxy resin adhesive. Slip rings 5, 6 are fitted in slots 4, the rings being coaxial with body 1 and having an inner diameter greater than the maximum diameter of the insulating support. Each of the rings 5, 6 has on its inside a plurality of lugs 10, which fit closely in slots 4, the number of lugs being half the number of rods 3 so that adjacent rings engage alternate rods. Rings 5, 6 are made of brass and each is provided with a terminal pin 11 extending inside the body 1, for connection to a conductive lead inside the body. The surfaces 4a, 4b may be planar or have recesses 12, and. a local recess 13 may be provided on each lug 10. Alternatively the recesses 12 may be replaced by local recesses in the sides of the lugs 10, and/or the recesses 3 may be replaced by local recesses in the bases of slots 4. Both methods result in the adhesive layer being locally thickened, to provide key-like formations 12a, 13a which act as reinforcements to secure the rings against turning relatively to the support. The sides 9 of the rings are covered by a layer of insulant 15 which is compatible with the adhesive used to secure the rings to the support. With some adhesives, e.g. epoxy resins, it is desirable to apply to the lugs a priming coating which ensures a good bond between the ring and the adhesive and insulant. The outer contact surfaces of the rings are coated with a layer of silver 4, e.g. by silver plating over a nickel-plate base, or spraying. To prevent conductive slivers from entering the gaps between rings the outer surfaces of rings, after the silver layer has been applied, are subjected to fine machining and silversmith's "pithing". During the fine machining operation the gaps may be filled with a removable packing, e.g. plastics foam to reduce the entry of fine slivers in the gaps. The purpose of securing the rings to alternate rods, for adjacent rings, is to maximize the lengths of leakage paths between rings. Alternatively, since the insulating coatings 15 increase the leakage paths considerably, each ring may be provided with sufficient lugs so that it can be secured to every rod, thus increasing the rigidity of the assembly. The rings may be made by cutting from a cylindrical blank and the lugs formed by machining the insides of the rings. The silver layer 15 may be replaced by any noble metal or any suitable conductive corrosion resistant material.