Design, Manufacturing and Open-Loop Control of a Soft Pneumatic Arm

TL;DR

This work presents PAUL, a modular soft pneumatic arm comprised of three silicone segments with embedded bladders, designed to achieve five independent DOFs in space and nine actuator inputs. An open-loop, data-driven approach based on a large vision-guided dataset enables direct and inverse kinematic predictions via a table-based model, circumventing some complexities of PCC and FEM methods. The study demonstrates PAUL’s bending capabilities (up to ~40° per segment), a measurable workspace, and light-load carrying performance, validating its potential for inspection in cluttered environments while highlighting tradeoffs between redundancy, accuracy, and fabrication. Future work targets closed-loop control, sensor integration, and more automatic parameterization to enhance precision and reliability in real-world deployments.

Abstract

Soft Robots distinguish themselves from traditional robots by embracing flexible kinematics. Because of their recent emergence, there exist numerous uncharted territories, including novel actuators, manufacturing processes, and advanced control methods. This research is centred on the design, fabrication, and control of a pneumatic soft robot. The principal objective is to develop a modular soft robot featuring with multiple segments, each one of three degrees of freedom. This yields to tubular structure with five independent degrees of freedom, enabling motion across three spatial dimensions. Physical construction leverages tin-cured silicone and a wax casting method, refined through iterative processes. 3D-printed PLA moulds, filled with silicone, yield the desired model, while bladder-like structures, are formed within using solidified paraffin wax positive moulds. For control, an empirically fine-tuned open-loop system is adopted. The project culminates in rigorous testing bending ability and weight carrying capacity and possible applications are discussed.

Figures (21)

• Figure 1: PAUL robot. The figure shows the arm, with its three segments and the trihedron that allows its position and orientation to be known, as well as the pneumatic actuation bench (at the top), the compressor (on the right) and the two cameras and the calibration grid, which make up the vision system. Source: authors.
• Figure 2: Bladder cores. (a) CAD Model. (b) Dimensioned drawing. All dimensions are in m m. Source: authors.
• Figure 3: Final design of PAUL's segments. All dimensions are in m m. Source: authors.
• Figure 4: 3D printed connection between segments. Source: authors.
• Figure 5: Complete PAUL manufacturing process. (a) Bladder manufacturing. (b) Mould assembly. (c) Mould assembled with the three bladders in place, ready for pouring the silicone. (d) Curing of the silicone. (e) Removal of excess parts. (f) Melting of the wax in the oven. (g) Bathing of the segment in boiling water. (h) Sealing the bottom of the mould. (i) Placement of the tubes. Source: authors.