GB777394A - Variable resistance instrument - Google Patents

Abstract

777,394. Variable resistors. BENDIX AVIATION CORPORATION. April ], 1955 [April 19, 1954], No. 9572/55. Class 37. A variable resistance device comprises a resistance element such as wire or strip helically wound along the thread of an insulating screw member which is slidably engaged by a contact element mounted on a nut moved along the screw, the nut being restrained from rotation relative to the screw. Figs. 1 and 2 show a variable resistance in which an elongated resistance element 14 is wound in a groove cut in the flattened top of a thread 12 formed on a cylindrical core of insulating material 11. The core is rigidly mounted on an end-plate 15 of insulating material and the ends of the resistance element 14 are brought out through suitable bores extending within the core to the outer surface of end-plate 15, Fig. 4, not shown. Suitable tapping connections to the resistance element may also be provided as shown by tapping leads 16 and 20. A contact sliding along resistance element 14 and rotating on threads 12 is provided by means of a head plate 27 of insulating material having a ball-bearing 28 in which a drive frame 29 is rotated, the frame 29 includes a shaft 30 mounted in bearing 28 and connected to a drive-plate 31 carrying a drive ring 32, metal cage rods 33 are mounted at one end in bushing 31a in ring 32 and are fixed at the other end to take off contact plates 34. A cylindrical follower block 37 of insulating material slidably fixed to rod 33 and the contact ring 39 of spring metal has its opposite ends located in slots 40 in block 37, the spring is shaped so it maintains frictional engagement with rods 33. It is electrically connected by slidable contact arrangements via compression spring 43 bearing against strip 39 which also bears against a metal contact button 45 pressing against the resistance element 14 by means of spring 44. Block 37 is provided with drive threads 46 which mesh with the thread 12 on the core 11 and take off contact springs 47 bear against contact plate 34 and are connected by leads 48 to the outer face of the plate 15. When shaft 13 rotates drive frame 29 rotates and member 37 moves along the screw-thread of the insulating core 11. In a modification, Fig. 5, not shown, the thread 12 is rectangular in crosssection and the resistance element is let into the outer face of the rectangular cross-section, the threads of the follower block 37 being similarly contoured. In a further modification, Fig. 6, not shown, the rectangular resistance element is located in a recess in the space between turns of the thread. Bushings 31a which hold cage rods 33 in position are advantageously made of nylon.