The use of robotic limb exoskeletons is growing fast either for rehabilitation purposes or in an aim to enhance human ability for lifting heavy objects or for walking for long distances without fatigue. The paper proposes a nonlinear optimal control approach for a lower-limb robotic exoskeleton. The method has been successfully tested so far on the control problem of several types of robotic manipulators and this paper shows that it can also provide an optimal solution to the control problem of limb robotic exoskeletons. To implement this control scheme, the state-space model of the lower-limb robotic exoskeleton undergoes first approximate linearization around a temporary operating point, through first-order Taylor series expansion and through the computation of the associated Jacobian matrices. To select the feedback gains of the H-infinity controller an algebraic Riccati equation is solved at each time-step of the control method. The global stability properties of the control loop are proven through Lyapunov analysis. Finally, to implement state estimation-based feedback control, the H-infinity Kalman Filter is used as a robust state estimator.

中文翻译：

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一种下肢机器人外骨骼的非线性最优控制方法

机器人肢体外骨骼的使用正在快速增长，无论是出于康复目的，还是为了增强人类举起重物或长距离行走而不疲劳的能力。本文提出了一种下肢机器人外骨骼的非线性最优控制方法。迄今为止，该方法已成功地在多类机器人机械臂的控制问题上进行了测试，本文表明，它还可以为肢体机器人外骨骼的控制问题提供最优解。为了实现这种控制方案，下肢机器人外骨骼的状态空间模型通过一阶泰勒级数展开和相关雅可比矩阵的计算，在临时操作点周围进行第一次近似线性化。为了选择 H-infinity 控制器的反馈增益，在控制方法的每个时间步求解代数 Riccati 方程。通过李雅普诺夫分析证明了控制回路的全局稳定性。最后，为了实现基于状态估计的反馈控制，H-infinity Kalman 滤波器被用作鲁棒状态估计器。