A Passively Adaptive Rotary-to-Linear Continuously Variable Transmission

In this paper, we present the synthesis and design of a rotary-to-linear continuously variable transmission with the ability to passively change gear ratio as a function of the output load. The primary mechanism involves variable-pitch rollers whose angle changes as a function of the output load due to the compliance properties of their housing. By changing spring stiffness, the relationship between the linear output load and transmission ratio can be tuned to optimize drive motor operating conditions over the entire range of output loads. After laying out the working concept, we show the performance analysis for such a transmission applied to a 6-W DC motor and present an example design analysis for tuning to maximize power output over the entire range of operating conditions. A prototype system was used to measure key parameters such as rolling resistance and lateral slip coefficients and to evaluate the transmission performance in a target application.