This paper introduces a compliant actuator design that achieves both equilibrium position control and stiffness modulation using a single motor unit. The actuator combines a passive positive feedback (negative stiffness) mechanism with an actively tunable positive stiffness mechanism, enabling two modes of operation: wide-range stiffness tunability and controllable equilibrium positioning. A prototype prosthetic limb demonstrates the actuator’s ability to vary stiffness from highly compliant to rigid behavior while maintaining low power input.
Why it matters: Traditional compliant actuators require two motors to control stiffness and equilibrium position, increasing complexity and energy use. This design simplifies the architecture and enhances efficiency, offering a promising solution for prosthetics, rehabilitation devices, and robotic locomotion where adaptable stiffness is critical.