D3-ARM: High-Dynamic, Dexterous and Fully Decoupled Cable-driven Robotic Arm

TL;DR

The paper addresses precision and robustness challenges in cable-driven arms where motors are remote from the end-effector, particularly for harsh environments. It proposes a fully decoupled, lightweight design (D3-Arm) with two decoupling mechanisms and a cable-pretension module to minimize friction and cable slack, while keeping all electrical components at the base. The authors present a DH-based kinematic model with rolling constraints, an improved Jacobian solution for inverse kinematics, and experimental validation showing 1.29 mm repeatability and 2.0 kg payload capability, along with high-speed dynamic performance. The work demonstrates that decoupled, base-mounted cable transmission can achieve high precision and dynamic capability, enabling safer operation in environments requiring electrical isolation, such as underwater or high-radiation settings, with potential future improvements via tension-aware control and stiffness modulation.

Abstract

Cable transmission enables motors of robotic arm to operate lightweight and low-inertia joints remotely in various environments, but it also creates issues with motion coupling and cable routing that can reduce arm's control precision and performance. In this paper, we present a novel motion decoupling mechanism with low-friction to align the cables and efficiently transmit the motor's power. By arranging these mechanisms at the joints, we fabricate a fully decoupled and lightweight cable-driven robotic arm called D3-Arm with all the electrical components be placed at the base. Its 776 mm length moving part boasts six degrees of freedom (DOF) and only 1.6 kg weights. To address the issue of cable slack, a cable-pretension mechanism is integrated to enhance the stability of long-distance cable transmission. Through a series of comprehensive tests, D3-Arm demonstrated 1.29 mm average positioning error and 2.0 kg payload capacity, proving the practicality of the proposed decoupling mechanisms in cable-driven robotic arm.

Figures (10)

• Figure 1: D3-Arm: a fully decoupled cable-driven robotic arm with all its electrical components located at the base.
• Figure 2: Proportion and joint composition of D3-Arm. Pairs of lines in the same color indicate a group of cables that drive the same joint. The side view shows the cable routing of the decoupling cable aligner mechanism arranged in Joint1. The front view shows the cable routing of decoupling rolling pair mechanism arranged in Joint2 and Joint3.
• Figure 3: Schematics of the motion coupling problem and decoupling way during a pitching motion. (a) Normal routing of cables in two adjoining joints. (b) Motion coupling in normal routing. (c) Decoupled routing of cables in two adjoining joints. (d) Motion situation after decoupling.
• Figure 4: Detailed design of decoupling cable aligner Mechanism. The mechanism consists of fixed pulleys and movable pulleys, ensuring that the driving cables remain aligned with the motion axis of Joint1.
• Figure 5: Detailed design of decoupled rolling pair Mechanism. (a) cable routings in joint motion. (b) cable routings in decoupling way. (c) Relationship between the cable motion and joint angle. (d) Cable displacement during joint movement.