Synthesis of a Force Generator using Two-Fold Tape Loops

Abstract

Normal linear springs have spring characteristics that are often too simplistic for complex applications. For instance in balancing applications, constant force or negative stiffness mechanisms are required. A tape loop, which consists of a two-fold tape spring, is a compliant shell mechanism which can act as a force generator with theoretically any force-displacement behavior by adjusting the tape spring’s cross-section.

In this thesis, a synthesis method is developed to determine the required tape spring geometry for obtaining the desired force-displacement behavior. Fifteen force-displacement curves are defined which all describe a unique characteristic behavior. These fifteen force-displacement curves are used as input to synthesize fifteen tape spring geometries. The resulting geometries are simulated in a finite element model to validate the synthesis method. The geometry with a non-zero constant force characteristic, is optimized, produced and tested in an experiment.

It is shown that a tape loop can generate all fifteen force-displacement curves by varying its cross-section and thereby can act as an all-purpose force generator. The production of tape loops however is challenging.