Interaction Forces of Soft Fiber Reinforced Bending Actuators

TLDR

Soft‑bending actuators are compliant, compact, and lightweight, making them attractive for robotic tasks, yet their nonlinear material behavior and complex motions make characterization difficult. This study investigates a single‑chamber, fiber‑reinforced soft‑bending actuator and its bending and force‑exertion characteristics during environmental interaction. The actuator incorporates a sensing layer for real‑time bending angle measurement, and the authors develop a quasi‑static analytical model based on internal pressure and material stretch, complemented by a finite‑element model, to analyze fiber reinforcement and validate experiments. Experiments confirm that the analytical model accurately predicts the relationship between air pressure, bending angle, and tip force, and that the integrated bend‑angle sensor enables real‑time force estimation without a dedicated force sensor.

Abstract

Soft-bending actuators are inherently compliant, compact, and lightweight. They are preferable candidates over rigid actuators for robotic applications ranging from physical human interaction to delicate object manipulation. However, characterizing and predicting their behaviors are challenging due to the material nonlinearities and the complex motions they can produce. This paper investigates a soft-bending actuator design that uses a single air chamber and fiber reinforcements. Additionally, the actuator design incorporates a sensing layer to enable real-time bending angle measurement for analysis and control. In order to study the bending and force exertion characteristics when interacting with the environment, a quasi-static analytical model is developed based on the bending moments generated from the applied internal pressure and stretches of the soft materials. Comparatively, a finite-element method model is created for the same actuator design. Both the analytical model and the finite-element model are used in the fiber reinforcement analysis and the validation experiments with fabricated actuators. The experimental results demonstrate that the analytical model captures the relationships of supplied air pressure, actuator bending angle, and interaction force at the actuator tip. Moreover, it is shown that an off-the-shelf bend angle sensor integrated to the actuator in this study could provide real-time force estimation, thus eliminating the need for a force sensor.