Controllable spiral spring, in particular with logarithmic characteristics

Abstract

An instrument has a rotatable part and a helical spring secured to the instrument casing at its outer end and to the rotatable part at its inner end. The spring characteristics are made to depart from linear, by changing the cross-sectional area of the spring progressively substantially from one end to the other of the spring. Preferably, the spring thickness is kept constant and its width varied, as by providing a tapered slot through the spring along its length. Provision is made for further selectively varying the spring characteristics, by rendering inactive selected lengths of the outer turns of the spring. In one embodiment (FIGS. 1 and 2) this is done by providing a split ring that encircles the spring and whose ends can be moved toward or away from each other to contact selected lengths of the outer turns of the spring. In other embodiments (FIGS. 3 and 4) a helical rib coaxial and coextensive with the spring is rotated relative to the spring to contact varying lengths of the inner (FIG. 3) or outer (FIG. 4) side of the outermost turns of the spring.

Dependencies are inferred from the claim text.