Realization of an Energy-Efficient Adjustable Mechatronic Spring

Although semi-active variable mechanical dampers are well-known and highly developed concepts, creating an efficient variable stiffness has remained a challenge. In this paper, a brushless dc motor combined with a mechanical motion converter is utilized to synthesize the behavior of a mechanical spring. It is shown that synthesizing resistive and inductive elements in the motor shunt circuit can create damping and stiffness behaviors, respectively. The actuator shunt is digitally controlled by a bidirectional boost converter, which uses a sliding-mode algorithm. Using the proposed approach, the actuator can exhibit independent damping and stiffness effects in real-time. Analytic studies regarding the power requirements and criteria for controller convergence are presented and verified through experimental studies.