Patent GB-567017-A (GB)
Title: Variable resistance devices
IPC: H01C10/20
Filed: 1943-07-19
Abstract: 567,017. Variable-contact resistances; casings for resistances ; combinations and sets of resistances. PLESSEY CO., Ltd. July 19, 1943, No. 11704. Convention date, Nov. 12, 1942. [Class 37] A variable resistance element adapted for interconnection with other similar elements or with end plates comprises a case having integral attaching means at one end and complementary interfitting integral attaching means at the other end whereby the element may be connected to a similar element by placing the elements together end to end with the attaching means of one element interfitting with the complementary attaching means of the other element. Fig. 1 shows two volume control sections 18, 19 attached together to provide a tandem control assembly, each section of which has a separate control shaft. The volume controls are housed in similar cylindrical metal cases 20, 21. The case 20 has a front end wall 22 with a central aperture in which is secured a cylindrical fixed bushing 23 extending axially through the case 20. A flat contact ring 24 is mounted on the bushing 23, but insulated therefrom by an insulating ring 25. The ring 24 has an integral terminal lug 26 projecting through an aperture in the case, from which it is insulated by a strip of irisulating material 27. The resistance element comprises a ring 28 of insulating material with a carbonaceous surface layer 29. Terminal lugs connected to the ends of the resistance layer extend out through apertures in the wall of the case. A floating bushing 32 is held within the stationary bushing 23 and adapted to rotate within it. The bushing 32 has a retaining shoulder 33 at its front end and a plate 34 of insulating material secured to its rear end. Fixed to the plate 34 is a control arm 35 carrying at one end a cylindrical metal contact 36 sliding on the resistance layer 29 and at the other end an integral contact 37 sliding on the terminal ring 34. Externally each of the cases 20, 21 is provided around the periphery of its closed end with two pairs of raised rim sections 40 at diametrically opposed positions, as shown in Fig. 2. The open ends of the cases are provided with corresponding integrally formed spring flanges 41 for connecting the cases together. Between each pair of flanges 41 is a short locking tongue 42. The casings are assembled with the flanges 41 in the wide spaces between the pairs of rim sections 40 and are relatively rotated through 90 degrees so that the flanges 41 fit over the sections 40 and the tongues 42 snap into the notches between the pairs of raised rims. A front end mounting plate 43 provided with flanges 51 and' tongues 52 is similarly fastened to the front case 20 and carries a bushing 44 threaded to receive a nut for mounting the assembly on a panel. A snap-acting switch 45 is mounted on a rear end plate 46 with rim portions 50 which are held in the flanges 41 of the case 21. The switch 45 has an actuating arm 47 with a pair of spaced parallel flanges between which engages a pin 39 formed on the rivet 38 which secures the control arm 35 to the plate 34. A tubular control shaft 48 having a splined end section 49 fitted within the floating bushing 38, which has complementary internal splinings provides control means for the resistance section- 18. A solid shaft 58 concentrically mounted within the shaft 48 and having a splined end section 59 within the bushing of section 19 provides a control for that section. The shafts 48, 58. are initially formed with a plurality of splined sections 49, 49a, 49b, Fig. 3, and 59, 59a, 59b, Fig. 4, separated by notches to facilitate breaking off the splined sections not required for a particular assembly. Small flat metal rings 56, 66 are tightly fitted on the shaft between the plain section and the first splined section, and may be permanently secured by upsetting the shaft. In a modification, Fig. 6, the casing 60 is open at both ends, the front ends being formed with integral tongues 61. 'The resistance unit has a base disc 63 of insulating material provided with notches 64 which engage with the tongues 61. A metal clamping disc 68 has an integral central bushing 69 which passes through a central aperture 70 in the disc 63. The edge of the disc 68 is formed with rolled-over flanges 71 corresponding to the run sections 40, Figs. 1 and 2. The discs 63, 68 are clamped to the casing 60 by bending down the tongues 61. In another modification, Fig. 8, three resistance element sections 80, 81, 82 are fitted together and are ganged under control of a single control shaft 83. The casing of each section has an integral pressed-up rim 84 adjacent to the front end wall and a series of flanges at its open end. One of these flanges 85 extends for about one-third of the circumference of the casing and a set of three shorter flanges 86 are uniformly spaced about the remainder of the circumference. To assemble two units together, the rim 84. of one unit is set into the flange 85 of the other unit and the flanges 86 snapped over the rim 84 to secure the cases together. The shaft, shown in Fig. 11, comprises a plain section 91 and a series of splined end sections 92, 92a, 92b, 92c alternated with a series of 'short reduced sections 93 having small tapered flanges 94 thereon. The shaft is originally provided with the largest number of splined sections that will ever be required and then the sections not required for any particular application are cut off, as shown at 92c. The shaft is held in place by a wire hairpin clip 95 engaging the groove 93.