Geometry-based pneumatic actuators for soft robotics

Abstract

Soft pneumatic actuators enable safe human-machine interaction with lightweight and powerful applied parts. On the other side, they suffer design limitations as regards complex actuation patterns, including minimum bending radii, multi-states capabilities and structural stability. We present geometry-based pneumatic actuators (GPAs), a design and implementation approach that introduces constraint layers with configurable CNC heat-sealed chambers. The approach achieves predictable deformation, near-zero bending radii, multi-states actuation, and enables customizable and repeatable complex actuated geometries. Mathematical modeling reveals predictable linear angle transformations and validates nonlinear torque-angle relationships across diverse configurations. We demonstrate versatility of the GPAs approach through three applications: a 49 g wrist exoskeleton reducing muscle activity by up to 51%, a 30.8 g haptic interface delivering 8 N force feedback with fast response, and a 208 g bipedal robot achieving multi-gait locomotion. GPAs establish a configurable platform for next-generation wearable robotics, haptic systems, and soft locomotion devices.

Figures (6)

• Figure 1: Geometry-based pneumatic actuators overcome fundamental limitations of conventional designs.(A) Single-chamber actuators exhibit unpredictable deformation instabilities under external loading. (B) GPAs architecture integrates constraint layers with CNC heat-sealed chambers for programmable geometry control. (C) Constraint layer integration eliminates deformation instabilities, ensuring predictable actuation behavior. (D) GPAs versatility enables diverse applications: exoskeletons, haptic interfaces, and autonomous locomotion systems.
• Figure 2: Systematic characterization reveals predictable GPAs performance relationships.(A) Key geometric parameters defining GPAs behavior. (B) Torque characterization system for force-angle relationship determination. (C) Inflation pressure minimally affects final bending angle. (D)--(F) Parametric analysis demonstrating linear relationships between initial angle $\alpha_0$, final angle $\alpha_1$, and contraction factor $\lambda$. (G) Inflation of actuators with different initial angles $\alpha$. (H) Mathematical model validation of nonlinear torque-angle relationships with pressure dependence. (I) and (J) Model validation across diverse actuator configurations.
• Figure 3: Extended GPAs architectures enable specialized functionality.(A) Parallel configurations achieve compact, low-profile designs. (B) Single-chamber variants demonstrate constraint layer versatility. (C) multi-states architectures enable complex biomimetic motions. (D) Segmented designs provide independent multi-region control. (E) Bilateral configurations permit bidirectional actuation capabilities.
• Figure 4: Lightweight soft exoskeleton demonstrates therapeutic efficacy.(A)--(B) Exoskeleton design incorporating parallel GPAs architecture. (C) Linear torque-pressure relationship enables predictable assistance. (D)--(E) Bidirectional functionality for flexion and extension support. (F) Dynamic testing protocol with EMG monitoring. (G) Significant muscle activity reduction validates therapeutic potential.
• Figure 5: Kinesthetic haptic interface enables immersive force feedback.(A)--(B) Lightweight device architecture with curved GPAs. (C) Force-pressure-displacement relationships for predictable output control. (D)--(E) Dynamic characterization setup with integrated force sensing and fitted force-resistance relationship. (F)--(G) Rapid response characteristics and sinusoidal tracking performance. (H)--(I) Virtual reality integration demonstrating practical manipulation feedback.