Towards intrinsic force sensing and control in parallel soft robots
This work addresses the problem of precise force control in soft robotics for applications requiring high contact forces, representing an incremental advance by extending intrinsic sensing to hydraulic systems.
The paper tackled the challenge of intrinsic force sensing and control in hydraulic parallel soft robots, which face high actuation variability and nonlinear responses, by developing an algorithm using fluid volume and pressure data. Results showed that axial forces on a single actuator could be estimated with an accuracy of 0.56 ± 0.66 N in a quasi-static setup, and the method enabled accurate force control in both single and multi-degree-of-freedom systems.
With soft robotics being increasingly employed in settings demanding high and controlled contact forces, recent research has demonstrated the use of soft robots to estimate or intrinsically sense forces without requiring external sensing mechanisms. Whilst this has mainly been shown in tendon-based continuum manipulators or deformable robots comprising of push-pull rod actuation, fluid drives still pose great challenges due to high actuation variability and nonlinear mechanical system responses. In this work we investigate the capabilities of a hydraulic, parallel soft robot to intrinsically sense and subsequently control contact forces. A comprehensive algorithm is derived for static, quasi-static and dynamic force sensing which relies on fluid volume and pressure information of the system. The algorithm is validated for a single degree-of-freedom soft fluidic actuator. Results indicate that axial forces acting on a single actuator can be estimated with an accuracy of 0.56 +- 0.66N within the validated range of 0 to 6N in a quasi-static configuration. The force sensing methodology is applied to force control in a single actuator as well as the coupled parallel robot. It can be seen that forces are accurately controllable for both systems, with the capability of controlling directional contact forces in case of the multi degree-of-freedom parallel soft robot.