A nonlinear transmission that increases piezo-stack work output

A non-linear motion transmission mechanism for improving the mechanical work output of an active material drive element is presented. This improvement is achieved by addressing the typical mismatch between the characteristics of a driven load, such as a constant force or spring load, and the active material's force-displacement behavior; this behavior is described, at a constant drive level, by a linear decrease in the possible force with increasing displacement. The motion transmission mechanism consists of a simple linkage that couples the active material to the load. As the active material does work on the load, the linkage changes the mechanical advantage or leverage of the active material with respect to the load, thereby tailoring the load to best exploit the active material's force-displacement behavior. A kinematic model is used to predict the maximum quasi-static mechanical work output that can be obtained. Optimization of the model geometry results in a transmission with a theoretical work enhancement of 36.9% for a constant load and a theoretical work enhancement that approaches 100% for a spring load. The possibility of work enhancement is verified in an experiment that demonstrates a work output improvement of 27.1% for the constant load case.