Mechanical Design and Experiments of a New Rotational Variable Stiffness Actuator for Hybrid Passive-Active Stiffness Regulation

To improve collision safety in robot-human collaborative applications, increasing attention has been paid to rotational variable stiffness actuators. A new rotational variable stiffness actuator, which works in two stages, is proposed for hybrid passive-active stiffness regulation. The passive stage is based on the motions of springs driven by the rack-and-pinion systems, elastically converting the shaft's rotation into the inner shell rotation fixed to the internal gear of the active stage. The active stage is designed to achieve the movement of the pivot point located on the roller actuated by the adjustment motor, providing the output angle of the output shaft. The two pairs of rack-and-pinion systems of the passive stage and the two pairs of planetary gears of the active stage are designed for side-by-side placement, improving the stability and balance of the stiffness regulation process. Two symmetrical cam-slider mechanisms acting as leverage pivots ensure the synchronous movements of the two rollers. The variable stiffness actuator is designed and validated by simulations and experiments. Strength analysis and stiffness analysis are presented. The designed actuator can obtain the range of stiffness adjustment of 35-3286 N center dot mm/deg. The range of the angle difference between the input and output shafts is +/- 48 degrees.