Generalized spiral torsion spring model

A general analytical model for spiral torsion springs is presented in this work. Few works have been found about analytical design of this kind of springs, especially that take into account strip thickness, or when coils are blocked in the housing or in the shaft. However there is a wide range of work that analyses some particular characteristic of the coils or its housing, which generate specific performance on the spiral spring. An analytical model is generated from an analysis of the different variables affecting the length of the spring strip that is free or blocked on the housing or the shaft. The main design parameters are length, variation of curvature of the spiral, relationship between the curvatures of shaft and housing, strip thickness and the variation of the bending stiffness along the length of the spring strip, which allow having different types of torque–shaft rotation angle characteristic curves. Model is validated with experiments on a two-starts spiral spring prototype. A parametric study is performed with the validated model to gain insight on spiral spring design.