Clarke变换让软体机器人运动规划不再有奇点,实现高效精确控制。
Clarke Transform -- A Fundamental Tool for Continuum Robotics
- 用广义克拉克变换将多自由度关节映射到二维正交坐标空间。
- 实现无分支、闭式解、无奇点的正逆运动学与100%成功率采样。
- 适合做软体机器人控制与高维运动规划的通用框架参考。
本文介绍克拉克变换及其坐标系,为任意数量耦合位移驱动的连续体与软体机器人提供解耦方案。通过广义克拉克变换及其逆变换,可将任意数量的关节值压缩至二维空间,且不丢失关键信息。该空间构成关节空间的流形,由两个正交的克拉克坐标描述。文中展示了其在运动学、采样和控制中的应用。通过推导此前未知的、任意关节数的前向机器人依赖映射,正逆运动学均实现无分支、闭式解、无奇点。采样作为评估方法性能的代理,提出一种无分支、闭式、可向量化且成功率100%的采样方法,并支持自定义分布形状。由于基于流形结构,简单的、受约束启发的二维线性控制器始终输出可行控制量。此外,建立了克拉克坐标与连续体及软体机器人中改进表示之间的关系,证明其为这些表示的推广。克拉克变换提供有价值的几何洞察,推动在高维关节空间的二维流形上直接设计方法,确保满足约束。尽管是简单线性映射,该变换数学一致、物理解释清晰、可解释性强,有助于统一连续体与软体机器人领域的各类框架。
原文摘要 · Abstract (English)
This article introduces the Clarke transform and Clarke coordinates, which present a solution to the disengagement of an arbitrary number of coupled displacement actuation of continuum and soft robots. The Clarke transform utilizes the generalized Clarke transformation and its inverse to reduce any number of joint values to a two-dimensional space without sacrificing any significant information. This space is the manifold of the joint space and is described by two orthogonal Clarke coordinates. Application to kinematics, sampling, and control are presented. By deriving the solution to the previously unknown forward robot-dependent mapping for an arbitrary number of joints, the forward and inverse kinematics formulations are branchless, closed-form, and singular-free. Sampling is used as a proxy for gauging the performance implications for various methods and frameworks, leading to a branchless, closed-form, and vectorizable sampling method with a 100 percent success rate and the possibility to shape desired distributions. Due to the utilization of the manifold, the fairly simple constraint-informed, two-dimensional, and linear controller always provides feasible control outputs. On top of that, the relations to improved representations in continuum and soft robotics are established, where the Clarke coordinates are their generalizations. The Clarke transform offers valuable geometric insights and paves the way for developing approaches directly on the two-dimensional manifold within the high-dimensional joint space, ensuring compliance with the constraint. While being an easy-to-construct linear map, the proposed Clarke transform is mathematically consistent, physically meaningful, as well as interpretable and contributes to the unification of frameworks across continuum and soft robots.
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