In this paper, we present a novel model-free fractional-order adaptive back-stepping control scheme for the wearable exoskeletons with constraints on the joint angle tracking errors. Firstly, the ultra-local model based intelligent proportion integration differentiation (iPID) control is combined with time delay estimation (TDE) to realize a model-free feature, and the precise modeling process can be abandoned. Then, an adaptive back-stepping controller is introduced to handle with the estimation errors of TDE. Control behavior is greatly improved by introducing the fractional-order calculus and prescribed performance is guaranteed by the log-type barrier Lyapunov function implemented in the back-stepping approach. In addition, system stability is verified via Lyapunov stability theory. Finally, to demonstrate the effectiveness of the proposed control scheme, a 5 DOF wearable exoskeleton virtual prototype is designed in SolidWorks and transferred to MATLAB as the controlled plant for visualization simulation. Simulation results show the improved performance between the proposed method and comparison methods.

在本文中，我们提出了一种新的无模型分数阶自适应反步控制方案，用于可穿戴外骨骼，并限制关节角度跟踪误差。首先，基于超局部模型的智能比例积分微分（iPID）控制与时延估计（TDE）相结合，实现无模型特征，可以放弃精确建模过程。然后，引入自适应反步控制器来处理 TDE 的估计误差。通过引入分数阶微积分，控制行为得到了极大的改善，并且规定的性能由在反步方法中实现的对数型势垒 Lyapunov 函数保证。此外，系统稳定性通过李雅普诺夫稳定性理论得到验证。最后，为了证明所提出的控制方案的有效性，在 SolidWorks 中设计了一个 5 自由度的可穿戴外骨骼虚拟原型，并将其传输到 MATLAB 作为受控对象进行可视化仿真。仿真结果表明，所提出的方法与比较方法之间的性能有所提高。