Design Optimization of Wire Arrangement with Variable Relay Points in Numerical Simulation for Tendon-driven Robots

Abstract

One of the most important features of tendon-driven robots is the ease of wire arrangement and the degree of freedom it affords, enabling the construction of a body that satisfies the desired characteristics by modifying the wire arrangement. Various wire arrangement optimization methods have been proposed, but they have simplified the configuration by assuming that the moment arm of wires to joints are constant, or by disregarding wire arrangements that span multiple joints and include relay points. In this study, we formulate a more flexible wire arrangement optimization problem in which each wire is represented by a start point, multiple relay points, and an end point, and achieve the desired physical performance based on black-box optimization. We consider a multi-objective optimization which simultaneously takes into account both the feasible operational force space and velocity space, and discuss the optimization results obtained from various configurations.

Figures (8)

• Figure 1: The concept of this study. We prepare design parameters of wire arrangement, calculate the evaluation value for target and feasible force / velocity regions regarding each design, and obtain the design parameter with the best performance by multi-objective black-box optimization.
• Figure 2: The design parameters of wire arrangement. The number of wires $M$, the number of relay points $N$, the position of the relay point $l^m_n$, and the link $d^m_n$ that the relay point is attached to are set as variables.
• Figure 3: The definition of variables for calculation of objective function for feasible operational force space.
• Figure 4: The experimental setup of this study. The robot configuration for $L^{\{s, e\}}_{d}$ and the evaluated joint angles are shown. The design parameters were changed to Variable or Constant, gravity configuration to w/o-Gravity or w-Gravity, and target operational force / velocity space to Target-1 or Target-2.
• Figure 5: The experiment of Target-1 w/o Gravity. For Variable with $M=\{3, 4\}$ and $N=\{2, 3\}$ and for Constant with $M=\{3, 4\}$, the sampling results and Pareto solutions are shown. For one Pareto solution with minimized $|E_{force}-E_{velocity}|$, the wire arrangement and target (blue line) and feasible (red line) operational force / velocity spaces are shown.