Optimized Design of a Soft Actuator Considering Force/Torque, Bendability, and Controllability via an Approximated Structure

TL;DR

This work presents a model-based, multi-objective design strategy for soft pneumatic actuators by approximating the actuator as a cantilever beam. It derives nonlinear kinematic and dynamical models that link input pressure to torque, bending, and natural frequency, and then formulates an optimization to maximize normalized torque and bending angle under geometry and controllability constraints. Experimental validation with fabricated prototypes confirms improvements in torque (up to ~0.359 Nm), bending (around 206–232 degrees depending on material), and controllability using an LQR controller achieving ~0.8 s settling time. The approach demonstrates how geometry-driven tuning of dynamical properties can be integrated into the design process to achieve enhanced performance in SPAs while maintaining desirable dynamic behavior.

Abstract

This paper introduces a novel design method that enhances the force/torque, bendability, and controllability of soft pneumatic actuators (SPAs). The complex structure of the soft actuator is simplified by approximating it as a cantilever beam. This allows us to derive approximated nonlinear kinematic models and a dynamical model, which is explored to understand the correlation between natural frequency and dimensional parameters of SPA. The design problem is then transformed into an optimization problem, using kinematic equations as the objective function and the dynamical equation as a constraint. By solving this optimization problem, the optimal dimensional parameters are determined. Six prototypes are manufactured to validate the proposed approach. The optimal actuator successfully generates the desired force/torque and bending angle, while its natural frequency remains within the constrained range. This work highlights the potential of using optimization formulation and approximated nonlinear models to boost the performance and dynamical properties of soft pneumatic actuators.

Figures (11)

• Figure 1: The soft pneumatic is analyzed mechanically by approximating its intricate structure as a cantilever beam.
• Figure 2: The mechanical analysis of the Pressure-to-Force/Torque model involves the following steps (a)-(d). (a) Segmenting a chamber from the actuator for analysis. (b) Both ends of the segmented chamber are open. (c) Treating the open chamber as a closed volume, as the air pressure within the chamber is evenly distributed and balanced across the open areas. (d) The supplied air pressure inflates the chamber and generates torques. The bending geometric of the soft actuator for analyzing the Pressure-to-Bending model is shown in (e).
• Figure 3: (a) The segmented chamber is halved to obtain the free-body diagram. (b) The free-body diagram showcases the pressures, $P$ and $P_w$, acting on it. (c) The cross-sectional view of the chamber is presented, where the neutral surface is depicted by a dashed black line and the embedded flex sensor is indicated by a purple line. (d) The dimensional parameters of the cross-section are established.
• Figure 4: The approximated structure of the soft actuator generates a bending angle θ with a load F(P).
• Figure 5: Premilinarily verification of force/torque of optimal dimensional parameters by using the Pressure-to-Force/Torque model and the finite element analysis(FEA). The results are compared with the experimentation, Optimal(exp).

Theorems & Definitions (2)

• Remark 1
• Remark 2