Parallel and rectilinear spring movements

This paper discusses the design of instrument movements in which the moving member is held by two equal and parallel leaf springs; the member can be moved parallel to itself by pushing it normally to the springs. In a constructed specimen the parallelism was maintained to within ± 3.5 sec of arc over 6 mm of travel by a simple method of balancing the springs. Arrangements are described for combining two or more spring systems to develop a rectilinear movement. Performances are quoted for three constructions, the best of which held a straight line within about ± 0.25 μ over 5 mm of travel, and ± 1 μ over 10 mm. In some applications spring movements are superior to kinematic slides.