Soft pneumatic grippers: Topology optimization, 3D-printing and experimental validation

TL;DR

The paper tackles the challenge of designing soft pneumatic grippers whose actuation loads depend on geometry by introducing a topology-optimization framework that couples Darcy-based pneumatic loading with a drainage term in a robust blueprint-eroded formulation, solved by MMA. The 2D optimized PneuNet unit is extruded into a 3D arm composed of 10 units, and FEM validation using an Ogden material model alongside 3D printing demonstrates improved bending and reliable grasping of objects across shapes and weights. The study provides a full pipeline from topology optimization to experimental realization, including a detailed 3D printing workflow and close agreement between FE predictions and measured deformations. Overall, the approach enables automatic geometry discovery for SPGs and demonstrates practical, scalable gripping performance validated by both simulations and experiments.

Abstract

This paper presents a systematic topology optimization framework for designing a soft pneumatic gripper (SPG), explicitly considering the design-dependent nature of the actuating load. The load is modeled using Darcy's law with an added drainage term. A 2D soft arm unit is optimized by formulating it as a compliant mechanism design problem using the robust formulation. The problem is posed as a min-max optimization, where the output deformations of blueprint and eroded designs are considered. A volume constraint is imposed on the blueprint part, while a strain-energy constraint is enforced on the eroded part. The MMA is employed to solve the optimization problem and obtain the optimized soft unit. Finite element analysis with the Ogden material model confirms that the optimized 2D unit outperforms a conventional rectangular design under pneumatic loading. The optimized 2D unit is extruded to obtain a 3D module, and ten such units are assembled to create a soft arm. Deformation profiles of the optimized arm are analysed under different pressure loads. Four arms are 3D-printed and integrated with a supporting structure to realize the proposed SPG. The gripping performance of the SPG is demonstrated on objects with different weights, sizes, stiffness, and shapes.

Figures (9)

• Figure 1: (a) Numerically simulated gripping action (Sec. \ref{['Sec:3DSPG']}) (b) Functional demonstration of a 3D-printed SPG for gripping ball (Sec. \ref{['Sec:3DSPG']}) (c) 3D CAD model of one arm of the SPG with optimized pressure chambers. A SPG arm is constituted by 10 optimized pressure chambers. Iso, bottom and top views are also depicted of one of the optimized pressure chambers.
• Figure 2: (a) A 2D schematic diagram for SPG arm. Symmetric half design domain (SHDD) is shown in the left with pneumatic and fixed boundary conditions. $k_{s}$ indicate the output spring stiffness. $L_x$ and $L_y$ denote dimensions in $x$ and $y$ directions, respectively. Non-design solid (NDS) and non-design void (NDV) regions are also shown. (b) Optimized unit
• Figure 3: 2D CAD models are displayed. (\ref{['fig:2DoptCAD']}) 2D CAD model: Optimized chamber, and (\ref{['fig:2DrecCAD']}) 2D CAD model: Rectangular chamber.
• Figure 4: Objective and volume fraction convergence plots for the blueprint design
• Figure 5: Performance comparison of conventional rectangular and optimized chambers. (\ref{['fig:2D_rec_result']}) and (\ref{['fig:2D_opt_result']}) depict the undeformed and deformed profiles for conventional and optimized pressure chambers, respectively. The finite element analyses are performed in ABAQUS with geometric and material nonlinearity. The optimized chamber provides 86.98% more deformation compared to the conventional chamber at $10kPa$ pressure load. U2 indicates deformation in $y$ direction.