A pneumatic particle-blocking variable-stiffness bending actuator

This study introduces a variable-stiffness pneumatic bending actuator to enhance the stiffness of flexible robots. The bending actuator combines the working principles of a pneumatic drive, a wedge structure, and particle blockage. It enables one-dimensional, bidirectional bending motion and offers pose-maintenance capabilities. The approach to variable-stiffness is both driven and antagonistic. Stiffness in both bending and opposite directions is nonlinearly correlated with air pressure values. Specifically, at 0.5 MPa of air pressure, the stiffness in the bending direction increases to 6.1 times the initial stiffness. At 0.15 MPa, the stiffness in the opposite direction is 2.1 times the initial value. When air pressure is greater than 0.15 MPa, the stiffness incrementally increases due to the wedge impedance force. A driven variable-stiffness control is simple and suitable for applications with a constant load direction, while the antagonistic approach is more suitable for occasions where the load direction changes during movement.