Lin Jianping, Divekar Nikhil V, Thomas Gray C, Gregg Robert D
Robotics Institute, University of Michigan, Ann Arbor, MI 48109 USA.
Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109 USA.
IEEE Open J Control Syst. 2022;1:15-28. Epub 2022 Apr 12.
Task-specific, trajectory-based control methods commonly used in exoskeletons may be appropriate for individuals with paraplegia, but they overly constrain the volitional motion of individuals with remnant voluntary ability (representing a far larger population). Human-exoskeleton systems can be represented in the form of the Euler-Lagrange equations or, equivalently, the port-controlled Hamiltonian equations to design control laws that provide assistance across a continuum of activities/environments by altering energetic properties of the human body. We previously introduced a port-controlled Hamiltonian framework that parameterizes the control law through basis functions related to gravitational and gyroscopic terms, which are optimized to fit normalized able-bodied joint torques across multiple walking gaits on different ground inclines. However, this approach did not have the flexibility to reproduce joint torques for a broader set of activities, including stair climbing and stand-to-sit, due to strict assumptions related to input-output passivity, which ensures the human remains in control of energy growth in the closed-loop dynamics. To provide biomimetic assistance across all primary activities of daily life, this paper generalizes this energy shaping framework by incorporating vertical ground reaction forces and global planar orientation into the basis set, while preserving passivity between the human joint torques and human joint velocities. We present an experimental implementation on a powered knee-ankle exoskeleton used by three able-bodied human subjects during walking on various inclines, ramp ascent/descent, and stand-to-sit, demonstrating the versatility of this control approach and its effect on muscular effort.
外骨骼中常用的基于任务特定轨迹的控制方法可能适用于截瘫患者，但它们过度限制了具有残余自主能力的个体（代表了更大的群体）的自主运动。人体-外骨骼系统可以用欧拉-拉格朗日方程的形式表示，或者等效地用端口受控哈密顿方程来设计控制律，通过改变人体的能量特性在连续的活动/环境中提供辅助。我们之前引入了一个端口受控哈密顿框架，该框架通过与重力和陀螺项相关的基函数对控制律进行参数化，这些基函数经过优化以适应不同地面坡度上多种步行步态的归一化健全关节扭矩。然而，由于与输入-输出无源性相关的严格假设，这种方法没有灵活性来再现更广泛活动集的关节扭矩，包括爬楼梯和从站立到坐下，这种无源性确保了人类在闭环动力学中对能量增长保持控制。为了在日常生活的所有主要活动中提供仿生辅助，本文通过将垂直地面反作用力和全局平面方向纳入基集来推广这种能量塑造框架，同时保持人体关节扭矩和人体关节速度之间的无源性。我们展示了在三名健全人类受试者使用的动力膝-踝外骨骼上进行的实验，该实验涵盖了在各种坡度上行走、坡道上升/下降以及从站立到坐下的过程，证明了这种控制方法的通用性及其对肌肉努力的影响。
