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

腿部运动已经进化为包括人类在内的陆上哺乳动物提供了主要的运动方式。虽然高度结构化或人工环境可能会提供替代方法，但腿部运动仍然提供了穿越许多地点的最有效方式。这些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/或人造元素组成的灾难瓦砾。因为它们模仿人类的结构，两足机器人特别适合在人类设计的环境中操作，并与人类同行一起执行人类辅助任务。几十年的研究努力试图将两足机器人带出实验室，使它们能够在现实世界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，仍然存在的一个根本挑战是如何使机器人能够像人类那样以非常动态和高效的方式移动，同时仍然保持人类表现出的极好的稳定性。大多数现代两足机器人要么移动相对较慢，从而消耗过多的能量，要么移动得更快、更有效率，但太容易受到仅由微小干扰引起的摔倒。该项目旨在使两足机器人的开发在效率和健壮性方面都更像人类。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指标，该指标利用了类似人类运动的基本机制，在实验室机器人实验中展示了其有效性。更广泛的影响集中在通过强调机器人与儿童之间的工程联系来鼓励K-12学生在STEM学科中继续接受高等教育？S自己的主要运动方式--行走。该项目旨在制定并实验验证一种新的方法，该方法基于对非致动自由度的控制权限的分析测量。腿部运动系统天生驱动不足，因为在脚和地面的接触点上没有致动器。本项目中的方法展示了通用动态控制权威指标的四个特征，该指标将使控制器的设计能够产生既健壮又高效的步态，其特征是：1)适用于各种运动的通用性；2)与各种机械设计一起使用的灵活性；3)与自然动力学的一致性，以产生能源效率高的步态；以及4)可分析性，以实现系统的机械和控制设计。基本方法是，在任何状态下，将系统速度分解成与输入对齐的方向，称为受控速度，以及与输入垂直(相对于动能度量)的方向，称为正交速度。可计算的受控速度和垂直速度之间的耦合测量量化了系统对非致动自由度的控制权威，是新的动态控制度量的基础。在受控速度方向和垂直速度方向之间存在完全解耦的构型称为动态奇点。强耦合有利于系统具有良好的抗扰性能，弱耦合有利于系统具有良好的干扰隔离性能。因此，该项目研究了如何通过彻底了解干扰的性质来利用动态两足步态控制中的动态奇点。

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.