Design, modeling and control of a reconfigurable variable stiffness actuator

This work presents a reconfigurable variable stiffness actuator (RVSA) based on a rotational spring mechanism (torsional spring) and a group of specially designed symmetrical S-springs. The variable stiffness mechanism (VSM) enables continuous stiffness regulation from compliant to almost rigid. Besides, the stiffness can be adjusted by only rotating the spring to change its effective beam length with a simple drive chain, which contributes to easy control, fast response, and well energy efficiency. The internal friction is weakened by the combination bearing design. The spring rotation needed is almost perpendicular to the forces generated by the springs, which helps to reduce the torque required to maintain or adjust the stiffness (i.e., resistance torque). Mathematical models of stiffness were established for this novel RVSA, and its design parameters were analyzed. A prototype of the RVSA was constructed, and experiments based on a feedforward proportional derivative (PD) controller demonstrated the effectiveness of the design. A case study for the device’s energy-saving ability was presented. The test results showed that the RVSA had potential in energy efficiency in several cyclic tasks.