Design and Nonlinear Modeling of a Modular Cable Driven Soft Robotic Arm (2401.06377v2)

Abstract: We propose a novel multi-section cable-driven soft robotic arm inspired by octopus tentacles along with a new modeling approach. Each section of the modular manipulator is made of a soft tubing backbone, a soft silicon arm body, and two rigid endcaps, which connect adjacent sections and decouple the actuation cables of different sections. The soft robotic arm is made with casting after the rigid endcaps are 3D-printed, achieving low-cost and convenient fabrication. To capture the nonlinear effect of cables pushing into the soft silicon arm body, which results from the absence of intermediate rigid cable guides for higher compliance, an analytical static model is developed to capture the relationship between the bending curvature and the cable lengths. The proposed model shows superior prediction performance in experiments over that of a baseline model, especially under large bending conditions. Based on the nonlinear static model, a kinematic model of a multi-section arm is further developed and used to derive a motion planning algorithm. Experiments show that the proposed soft arm has high flexibility and a large workspace, and the tracking errors under the algorithm based on the proposed modeling approach are up to 52$\%$ smaller than those with the algorithm derived from the baseline model. The presented modeling approach is expected to be applicable to a broad range of soft cable-driven actuators and manipulators.

• The paper presents a novel design and nonlinear static model that accurately predicts cable-induced bending in soft robotic arms.
• It integrates a modular, low-cost fabrication method with decoupled cable actuation for enhanced flexibility and control.
• Experimental results demonstrate reduced tracking errors and an expanded workspace, confirming its potential for diverse soft actuator applications.

Introduction

The development of soft robotic manipulators has made significant strides in recent years. In contrast to their rigid counterparts, these robots offer advantageous properties such as inherent compliance and safe interaction with humans and their surroundings. Building upon such advancements, in the field of cable-driven soft robotic arms, a novel multi-section design inspired by the agility and versatility of octopus tentacles is introduced. This work encompasses a novel design approach supplemented by a sophisticated nonlinear kinematic modeling strategy that captures the distinct nonlinear effects characteristic of these systems.

Design and Fabrication

Fundamental to this work is the modular design of the robotic arm, constructed with a soft tubing backbone, a body of soft silicone, and two rigid endcaps per section, facilitating low-cost production through casting and 3D printing. Each module's design facilitates a decoupling of cable actuation between sections, permitting focused control and compliance. Deviating from traditional designs that include rigid guides, this model forgoes these components to embrace greater flexibility and nonlinear interaction of cables and soft arm body.

Mathematical Modeling and Algorithms

Central to the operational efficacy of such robotic arms is the understanding and modeling of their nonlinear physical behavior. Previous approaches to this challenge have often relied on piecewise constant curvature (PCC) models or more complex finite element method (FEM) and Cosserat rod models. This paper introduces a novel analytical static model that explicitly accounts for the transverse deformation of cables within the silicon arm body, a phenomenon previously unaddressed.

Furthermore, the paper presents a kinematic model for multi-section arms and formulates a motion planning algorithm. The model efficiently maps the actuation cable lengths to the resultant bending configuration, crucial for executing precise maneuvers. Experimental validation demonstrates a superior prediction performance of this model as opposed to the baseline standard, particularly under conditions of significant bending.

Experimental Validation and Outcomes

The superiority of the proposed model is evident through comparative experiments against a baseline model. The soft robotic arm's high flexibility and large workspace are confirmed, with reduced tracking errors noted under the new modeling approach. These experimental results suggest that the modeling techniques proposed may find broad applicability in a variety of soft cable-driven actuator systems.

In conclusion, the paper under discussion unifies novel design, innovative fabrication techniques, and advanced nonlinear modeling to significantly progress the field of soft robotics. This modular, cable-driven soft robotic arm has potential applications across a gamut of sectors where delicacy, adaptability, and safety are paramount. Future work includes enhancing the model for dynamic interactions and integrating sensors for efficient real-time feedback control.