Design Optimization of Wire Arrangement with Variable Relay Points in Numerical Simulation for Tendon-driven Robots (2401.02730v1)

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.

• The paper introduces a novel multi-objective optimization framework that integrates variable relay points to improve tendon-driven robot designs.
• It employs the NSGA-II algorithm within the Optuna framework to effectively handle both continuous and discrete optimization parameters.
• Comparative experiments demonstrate that variable relay point configurations significantly boost operational force and velocity compared to constant moment arm setups.

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

This paper discusses a novel approach to design optimization for wire arrangements in tendon-driven robots, focusing on configurations that allow for variable relay points. The flexibility inherent in tendon-driven robots—where wire paths can be freely chosen without the constraints typical of axis-driven robots—serves as a key advantage. This paper aims to enhance that flexibility by introducing a multi-objective optimization framework that can handle complex wire routing through variable relay points and achieve desired operational force and velocity spaces.

Background and Motivation

Previous work in tendon-driven robot design has often simplified wire arrangements by assuming constant moment arms or neglecting wire configurations that span multiple joints. These simplifications limit the potential for optimizing the robot's physical capabilities. This paper seeks to overcome these limitations by incorporating variable relay points in the wire arrangement optimization problem, thus broadening the design search space and enabling the consideration of more complex robot configurations.

Methodology

The optimization problem is formulated such that each wire within the robot is characterized by a start point, multiple relay points, and an end point. The optimization aims to achieve specified physical performance goals using black-box optimization techniques. The objective functions are designed to account for both feasible operational force spaces (OFS) and operational velocity spaces (OVS), thus addressing the multi-faceted nature of the robot's operational demands.

The paper employs the NSGA-II algorithm, implemented within the Optuna framework, to perform the multi-objective optimization. This approach facilitates the handling of both continuous and discrete parameters within the optimization problem, allowing for the exploration of a diverse set of potential configurations.

Results and Observations

Experiments demonstrate that the performance of wire arrangements can be significantly enhanced by allowing for variable relay points. Comparative results suggest that variable relay point configurations potentially outperform those relying on constant moment arm settings, particularly when relay points are strategically increased. Such flexibility allows the robot to achieve superior force and velocity capabilities, suggesting that a more nuanced control of the body's physical properties is attainable with this method.

Furthermore, the optimization framework was shown to be adaptable to varying demands imposed by gravity and target OFS and OVS geometries. This adaptability points to the potential for broader applications where robots need to operate in varied environments with distinct physical constraints.

Implications and Future Directions

The implications of this work are substantial for the design and optimization of tendon-driven robots. By allowing more complex wire arrangements, designers can better tailor robots to specific tasks, taking full advantage of the configurability offered by tendon-driven designs. This could lead to advancements in robotic applications requiring precise manipulation and interaction with complex environments—domains that are increasingly relevant in industrial automation and service robotics.

Future research could expand on the current framework by integrating three-dimensional wire routing considerations, optimizing joint structures alongside wire arrangements, and incorporating additional objective functions that reflect real-world task requirements more closely. Experiments could also validate the proposed methods on physical prototypes to assess the practical viability of the optimized designs.

Overall, this paper provides a foundation for more adaptable and efficient design strategies in tendon-driven robotics, broadening the potential applications and capabilities of such robots in various fields.