Controlling the interaction forces between a human and an exoskeleton is crucial for providing transparency or adjusting assistance or resistance levels. However, it is an open problem to control the interaction forces of lower limb exoskeletons designed for unrestricted overground walking. For these types of exoskeletons, it is challenging to implement force/torque sensors at every contact between the user and the exoskeleton for direct force measurement. Moreover, it is important to compensate for the exoskeleton's whole-body gravitational and dynamical forces, especially for heavy lower limb exoskeletons. Previous works either simplified the dynamic model by treating the legs as independent double pendulums, or they did not close the loop with interaction force feedback. The proposed whole-exoskeleton closed-loop compensation (WECC) method calculates the interaction torques during the complete gait cycle by using whole-body dynamics and joint torque measurements on a hip-knee exoskeleton. Furthermore, it uses a constrained optimization scheme to track desired interaction torques in a closed loop while considering physical and safety constraints. We evaluated the haptic transparency and dynamic interaction torque tracking of WECC control on three subjects. We also compared the performance of WECC with a controller based on a simplified dynamic model and a passive version of the exoskeleton. The WECC controller results in a consistently low absolute interaction torque error during the whole gait cycle for both zero and nonzero desired interaction torques. In contrast, the simplified controller yields poor performance in tracking desired interaction torques during the stance phase.

中文翻译：

---

下肢外骨骼的触觉透明度和交互力控制

控制人类和外骨骼之间的相互作用力对于提供透明度或调整辅助或阻力水平至关重要。然而，控制专为不受限制的地面行走而设计的下肢外骨骼的相互作用力是一个悬而未决的问题。对于这些类型的外骨骼，在用户与外骨骼之间的每次接触处安装力/扭矩传感器来直接测量力是一项挑战。此外，补偿外骨骼的全身重力和动力也很重要，特别是对于重型下肢外骨骼。以前的工作要么通过将腿视为独立的双摆来简化动态模型，要么没有通过相互作用力反馈来闭合回路。所提出的整体外骨骼闭环补偿（WECC）方法通过使用髋膝外骨骼的全身动力学和关节扭矩测量来计算整个步态周期期间的相互作用扭矩。此外，它使用约束优化方案来跟踪闭环中所需的相互作用扭矩，同时考虑物理和安全约束。我们评估了三个受试者的 WECC 控制的触觉透明度和动态交互扭矩跟踪。我们还将 WECC 的性能与基于简化动态模型和被动版本外骨骼的控制器进行了比较。对于零和非零期望交互扭矩，WECC 控制器在整个步态周期内产生始终较低的绝对交互扭矩误差。相反，简化的控制器在跟踪站立阶段所需的相互作用扭矩方面表现不佳。