CAREER: Reverse Engineering Human Leg Mechanics to Transform Control of Robotic Prostheses

近年来，机器人假体、矫形器和外骨骼等使腿部截肢患者能够行走的辅助设备取得了相当大的进展。然而，现有的系统很难在动态的、真实的环境中运行，其中包括意想不到的干扰。因此，这个职业项目的目标是满足对辅助机器人的需求，这些机器人可以通过利用人类运动的潜在动力来自然地对干扰做出反应，即通过实时提供设备来改变人类通过肌肉激活在不知不觉中调节的关节僵硬和阻尼特性。关键的想法是了解神经系统如何在行走过程中调节腿部关节僵硬和阻力，并将这些信息用于设计和控制辅助机器人的新的、受生物启发的蓝图。该项目还将提供对人体如何应对干扰的洞察。该项目的结果将显著提高仅在美国就有100多万名下肢截肢者的生活质量和生产率。在整个项目中，研究和教育的整合将产生广泛的影响，通过1)通过有针对性的活动向K-12学生推广STEM和残疾意识，展示工程学的正式和“创造者”方面，2)实施工程学学生和临床医生之间的知识转移的跨学科机制，以及3)赞助和指导学生高级设计项目，通过与临床医生的共同监督直接支持这项研究。主要研究人员的长期研究目标是推进一种变革性的方法来设计和控制包含并利用人类运动潜在动力的辅助机器人。为了实现这一目标，该项目将测量行走过程中膝关节的机械阻抗，并利用获得的信息开发新一代仿生控制系统，使辅助机器人的用户能够在包括意外干扰在内的动态环境中更自由地移动。研究将利用首席研究员实验室已经开发或正在开发的辅助设备：用于膝盖的扭矩可控外骨骼，以及为膝盖和脚踝关节提供动力的开源机械腿假体(OSL，由NSF奖励开发)。研究计划是在三个目标下组织的。第一个目标是研究利用扭矩可控外骨骼测量膝关节机械阻抗的技术，该外骨骼将在健全的受试者行走时进行量化。方法将在一个由弹簧和质量组成的被动机械系统中进行验证，这些系统的阻抗在涉及人类受试者之前是已知的。可用于确定膝关节在运动过程中的机械阻抗的数据将记录在穿戴膝关节外骨骼的受试者身上，同时在分体式皮带跑步机上行走，其中可以施加小的扰动(例如增加坡度)，并通过外骨骼测量响应扭矩。将应用扰动，以便可以在步态周期中的每个点获得阻抗的快照。点阻抗将通过将惯性、刚度和阻尼参数拟合到二阶微分方程式来量化。第二个目标是推导用于腿的生物启发的阻抗控制的控制方程，该控制方程将在用于控制OSL的开源库中实现。在目标1下获得的结果将与估计脚踝阻抗的初步工作相结合，以得出能够同时调节膝关节-脚踝动力学、运动学和机械阻抗的统一控制律。控制方程将被转换成能够命令OSL的软件库，并使得能够实时控制膝盖-脚踝阻抗，即，刚度、阻尼和平衡位置参数将作为步态相位的函数而改变，从而不被预先设置为单一速度。OSL获得所需刚度和阻尼系数的能力将在台式测试装置中得到验证。第三个目的是了解基于阻抗的控制系统对使用OSL的膝上截肢者的影响，在有/没有干扰的情况下进行行走测试。受试者将在使用阻抗控制系统和每个人指定的假体以自我选择的步速行走时进行研究。随后的研究将调查受试者在仪表式跑步机上行走时受到干扰的影响。将对不同条件下的运动学、运动学、新陈代谢和稳定性指标进行比较，以更好地了解生物启发控制方法如何影响截肢者的行动能力，以及这些措施与肢体力学的比较。尽管将会有一些干扰，但这个项目将专注于了解在斜坡和斜坡上行走的影响。这个奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Advances in assistive devices that enable individuals with leg amputations to walk, e.g., robotic prosthesis, orthoses and exoskeletons, have been considerable in recent years. However, existing systems have trouble operating in dynamic, real-world environments that include unexpected disturbances. Thus, the goal of this CAREER project is to address the need for assistive robots that can naturally respond to disturbances by exploiting the underlying dynamics of human locomotion, i.e., by providing the device, in real time, with the same abilities to change joint stiffness and damping properties that humans unknowingly regulate through muscle activations. The key idea is to understand how the nervous system regulates leg joint stiffness and resistance throughout walking, and use this information for a new, bio-inspired blueprint for design and control of assistive robotics. This project will also provide insight into how the human body responds to disturbances. The results from this project will significantly improve quality of life and productivity for over a million lower-limb amputees in the U.S. alone. Throughout the project, the integration of research and education will have broad impact through the 1) promotion of STEM and disability awareness to K-12 students through targeted events that showcase the formal and "maker" sides of engineering, 2) implementation of interdisciplinary mechanisms for knowledge transfer between engineering students and clinicians, and 3) sponsorship and mentoring of student senior design projects that directly support this research through co-oversight with clinicians.The principal investigator's long-term research goal is to advance a transformative approach to the design and control of assistive robots that embrace and exploit the underlying dynamics of human locomotion. Towards this goal, this project will measure the mechanical impedance of the knee joint during walking and use the information obtained to develop a new generation of bio-inspired control systems that will enable users of assistive robots to move more freely in dynamic environments that include unexpected disturbances. Studies will make use of assistive devices already developed or under development in the principal investigator's lab: a torque-controllable exoskeleton for the knee and an Open-Source Robotic Leg prosthesis (OSL, developed under an NSF award) that has powered knee-ankle joints. The Research Plan is organized under three aims. The FIRST AIM is to investigate techniques for measuring knee mechanical impedance using the torque-controllable exoskeleton, which will be quantified in able-bodied subjects during walking. Methodologies will be validated in a passive mechanical system of springs and masses for which impedances are known before involving human subjects. Data that can be used to determine mechanical impedance of the knee during locomotion will be recorded from human subjects wearing the knee exoskeleton while walking on a split-belt treadmill in which small perturbations (e.g. increased ramp angle) can be applied and response torques measured by the exoskeleton. Perturbations will be applied such that a snapshot of impedance can be obtained at each point during the gait cycle. Point impedances will be quantified by fitting inertia, stiffness and damping parameters to a second-order differential equation. The SECOND AIM is to derive governing equations for bio-inspired impedance control of the leg that will be implemented in an open-source library for control of the OSL. The results obtained under Aim 1 will be synthesized with preliminary work estimating the impedance of the ankle to derive a unified control law that enables simultaneous regulation of knee-ankle kinetics, kinematics and mechanical impedance. The governing equations will be translated into a software library that is able to command the OSL and enables real-time control of knee-ankle impedance, i.e., stiffness, damping and equilibrium position parameters will be altered as a function of gait phase and, thus, not predisposed to a single speed. The ability of the OSL to achieve the desired stiffness and dampening coefficients will be validated in a benchtop testing setup. The THIRD AIM is to understand the effect of the impedance-based control system in above-knee amputees using the OSL, tested during ambulation with/without disturbances. Subjects will be studied while ground walking at a self-selected pace with both the impedance-controlled system and each person's prescribed prosthesis. A subsequent study will investigate the effect of disturbances while subjects are walking on an instrumented treadmill. Kinetics, kinematics, metabolics and stability measures across conditions will be compared to better understand how the bio-inspired control approach affects amputee mobility and how these measures compare to able-body mechanics. Though several disturbances will be applied, this project will focus on understanding the effect of walking on inclines and declines.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.