快速二阶终端滑模控制及其在下肢外骨骼的应用

为了提高传统二阶终端滑模控制的全局收敛性,提出一种快速二阶终端滑模控制算法.设计一种二阶趋近律,将绝对值函数隐藏在积分项里,并增加线性项以提高全局收敛性.当系统状态未到达滑模面时,采用二阶趋近律,并通过调整参数避免奇异问题;当系统状态到达滑模面时,采用不含不连续符号项的指数趋近律,以保证控制误差有限时间收敛.采用Lyapunov直接法证明快速二阶终端滑模控制算法的稳定性,及其比super twisting算法具有更优良的收敛特性.以下肢外骨骼为研究对象,建立动力学模型.在考虑建模误差和外部干扰的情况下,将该算法应用于下肢外骨骼的姿态控制.仿真结果表明,所提出的控制算法能够有效抑制抖振,并且比super twisting算法具有更良好的跟踪性能,验证了该算法的有效性.

Fast second-order terminal sliding mode control and its application in exoskeleton of lower extremities

In order to improve the global convergence rate of traditional second-order terminal sliding mode control, a fast second-order terminal sliding mode control algorithm is proposed in this paper.Compared to the traditional second-order terminal sliding mode control, a new second-order approximation law is designed with absolute value functions hidden in the integral term, also a linear term is included to improve the global convergence rate.A second-order approaching rule is initially used with the possibility to avoid singularity via parameter tuning until the state has reached the sliding manifold, then a continuous exponential approaching rule is adopted instead to guarantee finite time convergence.Lyapunov direct method is used to prove the stability of fast second-order terminal sliding mode control algorithm and has better convergence properties than that of the super twisting algorithm.A lower extremity exoskeleton is taken as the research object, and its dynamics model is established.The algorithm is applied to the attitude control of the lower extremity exoskeleton with modeling errors and additive disturbance.Simulation results show that the proposed control algorithm can effectively alleviate the chattering effect, and outperforms than that of the super twisting algorithm, which verifies the effectiveness of the proposed algorithm.