Geometry-based pneumatic actuators for soft robotics

Rui Chen; Daniele Leonardis; Domenico Chiaradia; Antonio Frisoli

cs.ROFeb 27, 2026

Geometry-based pneumatic actuators for soft robotics

Authors: Rui Chen, Daniele Leonardis, Domenico Chiaradia, Antonio Frisoli

Organizations: Institute of Mechanical Intelligence, School of Advanced Studies Sant’Anna (SSSA), 56127 Pisa, Italy.

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 & tables

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.

Figure 6: Multi-gait bipedal robot demonstrates autonomous locomotion capabilities. (A)–(B) Dual GPAs leg architecture with integrated friction control. (C)–(D) Pneumatic control logic enabling three-state leg operation. (E)–(F) Synchronous forward gait and retrograde crawling patterns. (G)–(H) Unilateral turning gaits for precise navigation control.

Soft Pneumatic Actuators

See all 25 papers

Soft Pneumatic Actuators for Soft Robotics: A Motion-Based Review of Actuation Mechanisms and Performance Trade-offs
May 24, 2026Mohammed AbboodiSoft Pneumatic Actuators Soft Robotics
A Reconfigurable Fabric Based Pneumatic Actuator with Button Fastened Constraint Modules for Multi Mode Actuation
Oct 8, 2026Kentaro Kimura, Hiroki Ishizuka, Yusuke Sakaue +2Soft Pneumatic Actuators Soft Robotics
Graduate School of Engineering Science, Osaka University, Osaka 560-0043, Japan
Elastomeric Strain Limitation for Design of Soft Pneumatic Actuators
Apr 3, 2026Gregory M. CampbellSoft Pneumatic Actuators Soft Robotics
Mechanical Engineering and Applied Mechanics Presented to the Faculties of the University of Pennsylvania

May 24, 2026J/K move · Enter open · S save

Soft Pneumatic Actuators for Soft Robotics: A Motion-Based Review of Actuation Mechanisms and Performance Trade-offs

Mohammed Abboodi

Soft Pneumatic Actuators Soft Robotics Pneumatic Actuation

Open paper AskPDF arXiv

Soft pneumatic actuators are widely used in soft robotics because they can produce large motions while remaining compliant enough to interact safely with objects, environments, and the human body. However, their performance is not solely determined by pressure. Instead, the response depends on the way the actuator is built, including the shape of its chambers, the placement of reinforcements, the use of folds, material stiffness, and the constraints that guide its deformation. As the literature has expanded, it has become more difficult to determine which mechanism is most suitable for a given application and which reported results can be compared across studies. This review examines soft pneumatic actuators according to the design strategies used to generate four motion classes: linear, bending, twisting, and omnidirectional actuation. For each class, it analyzes the structural features that define the deformation path, including braid angle, fold geometry, fiber orientation, chamber arrangement, structural asymmetry, and internal constraint layers. It then discusses how the design choice affect motion output, force generation, air demand, repeatability, durability, fabrication difficulty, and robotic integration. The review further identifies key conditions that must be considered when selecting or comparing actuators, including pressure, loading condition, actuator size, pneumatic supply, and hysteresis This approach helps explain why actuators with similar motion outputs may differ substantially in design requirements, pneumatic demand, and practical suitability. It also highlights the design priorities needed for compact, efficient, repeatable, and deployable soft pneumatic systems in wearable, biomedical, and mobile robotic applications.

Abstract

Soft Pneumatic Actuators

Explore similar work

Soft Pneumatic Actuators for Soft Robotics: A Motion-Based Review of Actuation Mechanisms and Performance Trade-offs

A Reconfigurable Fabric Based Pneumatic Actuator with Button Fastened Constraint Modules for Multi Mode Actuation

Elastomeric Strain Limitation for Design of Soft Pneumatic Actuators