Orekhov Greg, Luque Jason, Lerner Zachary F
Mechanical Engineering Department, Northern Arizona University, Flagstaff, AZ 86011 USA.
Mechanical Engineering Department, Northern Arizona University, Flagstaff, AZ 86011 USA, and also with the Department of Orthopedics, The University of Arizona College of Medicine-Phoenix, Phoenix, AZ 85004 USA.
IEEE Robot Autom Lett. 2020 Oct;5(4):6025-6032. doi: 10.1109/lra.2020.3011370. Epub 2020 Jul 22.
Lower-limb exoskeletons are widely researched to improve walking performance and mobility. Low-level sensor-less exoskeleton motor control is attractive for consumer applications due to reduced device complexity and cost, but complex and variable transmission system configurations make the development of effective open-loop motor controllers that are responsive to user input challenging. The objective of this study was to develop and validate an open-loop motor control framework resulting in similar or greater performance vs. closed-loop torque control. We used generalized linear regression to develop two open-loop controllers by modeling motor current during exoskeleton-assisted walking; a "complex" model used desired torque and estimated ankle angular velocity as inputs, while a "simple" model used desired torque alone. Five participants walked at 1.0-1.3 m/s on a treadmill with closed-loop and both open-loop controllers providing ankle exoskeleton assistance. Both open-loop current controllers had similar root-mean-squared torque tracking error (p=0.23) compared to the closed-loop torque-feedback controller. Both open-loop controllers had improved relative average torque production (p<0.001 complex, p=0.022 simple), lower power consumption (p<0.001 for both), and reduced operating noise (p=0.002 complex, p<0.001 simple) over the closed-loop controller. New control models developed for a different ankle exoskeleton configuration showed similar improvements (lower torque error, greater average and peak torque production, lower power consumption) over closed-loop control during over-ground walking. These results demonstrate that our framework can produce open-loop motor controllers that match closed-loop control performance during exoskeleton operation.
下肢外骨骼已得到广泛研究，以改善行走性能和活动能力。低级别无传感器外骨骼电机控制因设备复杂性和成本降低而对消费应用具有吸引力，但复杂且可变的传动系统配置使得开发响应用户输入的有效开环电机控制器具有挑战性。本研究的目的是开发并验证一种开环电机控制框架，使其在性能上与闭环转矩控制相当或更优。我们通过对辅助外骨骼行走过程中的电机电流进行建模，利用广义线性回归开发了两种开环控制器；一种“复杂”模型将期望转矩和估计的踝关节角速度作为输入，而“简单”模型仅使用期望转矩。五名参与者在跑步机上以1.0 - 1.3米/秒的速度行走，闭环控制器和两种开环控制器均提供踝关节外骨骼辅助。与闭环转矩反馈控制器相比，两种开环电流控制器的均方根转矩跟踪误差相似（p = 0.23）。与闭环控制器相比，两种开环控制器的相对平均转矩产生均有所改善（复杂模型p < 0.001，简单模型p = 0.022），功耗更低（两种模型p < 0.001），运行噪声更小（复杂模型p = 0.002，简单模型p < 0.001）。为不同的踝关节外骨骼配置开发的新控制模型在地面行走过程中与闭环控制相比也有类似的改善（转矩误差更低、平均和峰值转矩产生更大、功耗更低）。这些结果表明，我们的框架能够产生在操作外骨骼期间与闭环控制性能相匹配的开环电机控制器。
