Trimmer potentiometer having means for lead screw misalignment compensation

Claim 1

A variable resistor comprising: A. an elongated housing member having walls defining an axially extending hollow interior cavity having an open side; B. an elongated substrate member firmly secured to said housing member, said substrate member having a resistance element disposed on a substantially flat surface thereof facing and substantially covering the open side of the interior cavity of said housing; C. an axially extending threaded lead screw member disposed in the cavity in said housing member and extending therefrom to enable manipulation of the lead screw from the exterior of the housing; D. a wiper member disposed in the cavity in said housing, said wiper member engaging said lead screw and having a wiper contact element engaging the resistance element on said substrate member; E. terminal means for making electrical contact with said resistance element and said contact element from the exterior of said housing; wherein the improvement comprises: F. said housing having a pair of axially extending substantially flat shoulders located on opposite sides of the cavity in the housing, said shoulders facing toward the substantially flat face of the substrate member and being spaced therefrom; G. said wiper member having a pair of flanges on opposite sides thereof, said flanges being disposed between the shoulders on the housing member and the flat surface of the substrate member and defining a pair of substantially flat shoulders overlying and facing the flat shoulders on the housing member, said wiper member also having a flexible spaced pair of transversely extending ribs for disengageably receiving the threaded lead screw therebetween, the sides of said wiper member being spaced from the walls of the cavity in the housing member to allow the wiper member to laterally position itself within said housing in spaced relation with the walls of the interior cavity thereof when assembled on the lead screw, thereby being enabled to accommodate some misalignment of the lead screw; H. a pair of spaced smooth runner elements on said wiper member, both of the runner elements having a surface substantially co-planar with and engaging the substantially flat face of the substrate member, said wiper contact element being disposed on said wiper member between said spaced runner elements; I. a pair of resilient smooth protuberances extending from the shoulder on one of said wiper and housing members and extending to the shoulder on the other of said members, one of said protuberances being disposed on each side of the cavity in said housing member, said protuberances having an area of contact with said other member which is relatively small with respect to the overlying area of the shoulders on said members, said protuberances having a relaxed dimension greater than the distance between the adjacent facing shoulders on said housing and said wiper members so as to be resiliently compressed therebetween, said protuberances resiliently urging said wiper runner elements into firM sliding engagement with the substantially flat surface of said substrate member to prevent tilting motion of said wiper member with respect to both the shoulders on said housing member and the flat surface of said substrate member while accommodating transverse motion of the wiper member with respect to said lead screw, so that the lead screw controls only the axial translatory motion of the wiper member in the housing and whereby a tolerance in alignment of the lead screw can be accommodated without binding or rocking of the wiper member during adjustment thereof.