Design and Validation of a Variable Stiffness Spiral Cam Actuator

This study presents the design and validation of a variable stiffness actuator incorporating multiple cam mechanisms. The actuator is intended for use in walking assistance, focusing on assisting individuals with diminished ankle function. This study highlights the advantages of variable stiffness actuators over traditional and other modern actuators in mobility assistance. The working principles of the proposed Variable Stiffness Spiral Cam Actuator (VS-SCA) are described, focusing on the cantilever beams with adjustable supports, main cam mechanism, and symmetric support positioning architecture utilizing an Archimedean spiral cam. The design and fabrication process are discussed, considering system design considerations, cantilever beam design, cam design, and spiral cam design. The analytical methodology used for validation is also presented, which connects the subsystems of the actuator and allows for the determination of effective torsional stiffness. The experimental validation showed that the VS-SCA provides a range of stiffness from 20 to 75 Nm/rad for dorsiflexion, necessary for providing ankle assistance during the push-off phase of walking, while maintaining low stiffness (4 - 12 Nm/rad) for plantarflexion not to hinder natural ankle motion in the swing phase.