RI: Small: A New Mechanical Coupling Metric to Enable Effective Biped Locomotion Control

腿式运动已经进化成为陆地哺乳动物（包括人类）的主要运动方式。虽然高度结构化或人工环境可能会给它们提供替代方法，但腿部运动仍然是穿越许多地方的最有效方式。其中包括不平坦的自然地形，以台阶和楼梯为特色的人为设计的环境，以及由自然和/或人为元素组成的灾害废墟。因为它们模仿人类的结构，双足机器人在人类设计的环境中操作和与人类同行一起执行人类辅助任务特别有趣。几十年的研究努力试图将双足机器人移出实验室，使它们能够在现实环境中执行更广泛的实际任务。然而，在这一愿景完全实现之前，仍然存在一个根本性的挑战，即如何使机器人能够像人类一样动态而高效地移动，同时保持人类所表现出的出色稳定性。大多数现代双足机器人要么移动得相对缓慢，从而消耗过多的能量，要么移动得更快、更有效，但太容易因为轻微的干扰而摔倒。该项目旨在开发两足机器人，使其在效率和稳健性方面更像人类。它制定并应用了一种新的、更通用的动态机器人控制和稳定性度量，该度量利用了类人运动的潜在力学，展示了其在实验室机器人实验中的实用性。更广泛的影响集中在通过强调机器人与儿童自己的主要运动方式——步行之间的工程联系，鼓励K-12学生在STEM学科中接受高等教育。该项目旨在制定和实验验证一种基于非驱动自由度控制权限的分析措施的双足运动控制的新方法。腿式运动系统本质上是欠驱动的，因为在脚和地面之间的接触点没有驱动器。本项目中的方法展示了通用动态控制权威度量的四个特征，这些特征将使控制器设计产生既鲁棒又高效的步态，其特点是1)适用于一系列运动的普遍性；2)灵活使用，具有多种机械设计；3)与自然动力学保持一致，产生节能步态；4)分析性使系统的机械和控制设计成为可能。基本的方法是，在任何状态下，将系统速度分解成与输入对齐的方向，称为控制速度，以及与输入正交的方向（相对于动能度量），称为正交速度。控制速度和正交速度之间耦合的可计算度量量化了系统对非驱动自由度的控制权限，是新的动态控制度量的基础。在受控速度方向和正交速度方向之间存在完全解耦的构型被称为动态奇点。强耦合有利于系统具有良好的抗干扰性能，弱耦合则有利于系统具有良好的抗干扰性能。因此，该项目研究了如何彻底了解干扰的性质，以利用动态双足步态控制中的动态奇异性。

Legged locomotion has evolved to provide the primary means of locomotion for land-based mammals, including humans. While highly-structured or artificial environments may lend themselves to alternative means, legged locomotion still provides the most effective way to traverse many locales. These include uneven natural terrains, human-designed environments featuring steps and staircases, and disaster rubble consisting of natural and/or human-made elements. Because they mimic the human structure, biped robots are of particular interest for operation in human-designed environments and performing human-assistive tasks alongside their human counterparts. Several decades of research efforts have sought to move biped robots out of laboratories and enable them to perform a wider range of practical tasks in real-world environments. A fundamental challenge that remains before this vision is fully realized, though, is how to enable robots to move in the very dynamic and efficient manner of humans while still maintaining the excellent stability that humans exhibit. Most modern biped robots either move relatively slowly and thus expend an excessive amount of energy or else move more rapidly and efficiently, but are too susceptible to falls caused by only minor disturbances. This project seeks to enable the development of biped robots that move more like humans, in terms of both efficiency and robustness. It formulates and applies a new, more general metric of dynamic robot control and stability that exploits the underlying mechanics of human-like locomotion, demonstrating its utility in laboratory robot experiments. The broader impact centers around encouraging K-12 students to pursue higher education in the STEM disciplines by highlighting engineering connections between robots and children¹s own primary means of locomotion -- walking.This project seeks to formulate and experimentally validate a novel approach to biped locomotion control based on an analytical measure of the control authority over the unactuated degrees of freedom. Legged locomotion systems are inherently underactuated because there are no actuators at the points of contact between the feet and the ground. The approach in this project exhibits the four characteristics of a universal dynamic control authority metric that would enable the design of controllers to produce gaits that are both robust and efficient, characterized by 1) generality of application to a range of movements; 2) flexibility for use with a variety of mechanical designs; 3) consistency with the natural dynamics to yield energy efficient gaits; and 4) analyticity to enable systematic mechanical and control design. The basic approach is, at any state, to decompose system velocities into directions that are aligned with the inputs, termed the controlled velocities, and directions orthogonal (with respect to the kinetic energy metric) to the inputs, termed the orthogonal velocities. A computable measure of coupling between the controlled and orthogonal velocities quantifies the control authority of the system over the unactuated DOFs and is the basis for the new dynamic control metric. Configurations where there is complete decoupling between the controlled and orthogonal velocity directions are referred to as dynamic singularities. Strong coupling is advantageous for the system to have good disturbance rejection properties, while weak coupling is desirable for the system to have good disturbance isolation properties. Thus, the project examines how a thorough understanding of the nature of the disturbances can be used to exploit dynamic singularities in the control of dynamic biped gaits.