Patent GB-957471-A (GB)
Title: Improvements in or relating to electric potentiometers
IPC: H01C10/24
Filed: 1961-04-06
Abstract: 957,471. Variable resistors. LITTON INDUSTRIES Inc. April 6, 1961 [April 7, 1960], No. 12391/61. Heading H1S. [Also in Division F2] A potentiometer with a helical resistance element includes a first guide helix which guides a wiper along and around the element in one direction, a second guide helix for returning the wiper in the opposite direction, and means, such as a cam, which disconnects the wiper from the element for the duration of its return passage, whereby continuous rotation of the potentiometer driving shaft produces a repetitive variation of its resistance from the minimum to the maximum value. Shaft 12, Fig. 1, is rotatable within a stationary helicallywound resistance element 44 and left and righthanded helical guide grooves 52 and 50, the carriage 30, Figs. 1 and 5, being slidingly mounted, with the interposition of a lubricating lining 56, upon an arm 22 which is fixed to and rotatable by shaft 12. Carriage 30 carries a resilient metal wiper 28 and a cam-shaft 38 which presses the wiper into contact with the element when it is rotated through 45 degrees from the Fig. 5 position, such that an edge of its central square portion engages in a V-groove 42. One of the follower elements 34 and 36, which are displaced with respect to one another by 45 degrees is always engaged with its corresponding guide helix, such that continuous rotation of shaft 12 causes the wiper 28 to move leftwards along and around the helical element until the abutment of follower 34 against stop 54 rotates shaft 38, disengaging follower 36, allowing wiper 28 to spring away from the resistance element, and engaging follower 34 with its guide helix 50 so that the disengaged wiper is moved back to the other end of the element for a repetition of the cycle. Wiper 28 is electrically connected to arm 22 by a wiper 58 mounted on the carriage 30 and projecting through a hole therein, a brush and slip ring connection being made between arm 22 and output lead 14. In a further embodiment, Figs. 3 and 8, a shaft 146, with counter-wound helical guide grooves 150 and 152 formed thereon, is rotatably mounted on an arm 122 which is fixed to and rotatable by shaft 112. Wiper 128 and the follower and cam assembly 134, 138, Fig. 8, are slidably mounted on the rods 126 supported in arm 122, the planet gear 184 and stationary sun gear 186 causing shaft 146 to rotate about its own axis, with consequent sliding of the wiper and cam assembly along rods 126, when it is rotated bodily around the helix by shaft 112. In a modification (Figs. 9 to 11, not shown), the counter-wound guiding helices are formed on the inner surface of the potentiometer housing. In any of the embodiments the pitch of the two guide helices may be arranged to produce a return of the disengaged wiper faster than its forward movement, and a continuous output may be obtained by the use of two ganged potentiometers, or by the use of two wipercam assemblies mounted about the same resistance helix at opposite ends of the arm 22 or 122 (Figs. 2 and 4, not shown). The resistance element may be wound to provide an exponential or sinusoidal output, and the use of a pair of helical guide grooves of different depths for moving the wiper in and out of contact with the resistance element during its opposite traverses is referred to.