GB906445A - Miniature variable resistance device - Google Patents

Abstract

906,445. Variable resistors. GLOBE-UNION Inc. Dec. 14, 1959 [Jan. 2, 1959], No. 42465/59. Class 37. A compact variable resistor comprises a base, with a resistance element in a groove, having flat terminals and a conductive shaft moulded integrally to it, with a movable assembly rotatable by a cover about the shaft causing a contact to move over the element. Shaft 2 and terminals 4, 5, 6, Figs. 2 and 3, are moulded into a base 1, terminal 4 having collar 34 in which the shaft 2 is staked. The inner ends 9 and 10 of terminals 5 and 6 underlie an annular groove 7, Fig. 5, in which the resistance element 8, comprising a phenolic strip with resistance paint on its upper surface is located. The ends of the element 8 are coated with silver paint and silver laden epoxy is used to cement it into the groove 7, thus providing good electrical contact with the terminals 5 and 6. The moving elements consist of a cover 22, a contact spring 16 and take-off spring 24 all secured to a headed bushing 11 rotatable about the shaft 2, opposed slots 12 on the bushing, Fig. 4, receiving tabs from each of the elements to prevent relative rotation. The cover 22 has a flange 31 riding on the inner face of the base to form a dust seal and a broad bearing prevents wobble of the moving elements with respect to the shaft. The contact spring 16 is circular in shape, having a C-shaped slot 17 dividing it into an outer ring 18 and inner disc 19. The disc 19 seats against the inner walls of the cover 22 and has a central opening which fits tightly on the bushing 11, and the ring 18 is biased out from the plane of the disc to give a spring-pressed sliding engagement between the nipple 21 and the resistance element 8. To give a satisfactory electrical contact between the contact spring 16 and the terminal 4, the shaft 2 is provided with an annular shoulder 3 against which the take-off spring 24 has a spring-biased sliding contact. The spring 24 has a C-shaped portion 25 and a circular portion 26 joined by a U-shaped bridge 28. The portion 26 rests flatly against the inner disc 19 and the C-shaped portion 25 is outwardly biased from 26 and has its ends provided with dimples 29. The cover 22 and spring assembly is rotatably held on the shaft 2 by a retaining ring 30, the walls of the cover being slightly deformed to maintain a sliding bearing between the edge of the flange 31 and base 1. The terminals 4, 5 and 6 are blanked out on a metal strip (Figs. 7 and 9, not shown) and are moulded to the base using a jig and die.