存在关节死区的空间机器人无扰快速终端滑模控制

针对机械臂一般操作过程中运动学的非完整特性进行运动规划时没有考虑机械臂与待抓取目标之间的关系与关节的实际特性, 研究了存在关节死区的漂浮基平面三连杆空间机械臂拦截目标前最后阶段的载体无扰动空间规划与控制. 首先根据拉格朗日第二类方程, 建立存在关节死区的载体位姿均不受控的漂浮基平面三连杆空间机械臂的动力学模型, 推导出三连杆空间机械臂反作用零空间的数学模型, 并对反作用零空间进行向量范数约束算法研究; 进而提出了一种具有抗干扰性与高收敛性的非奇异快速终端滑模控制算法实现系统的姿态无扰控制, 该方法采用变系数双幂次趋近率与非奇异快速终端滑模面相结合的方式, 提高系统状态收敛速度与抗干扰性. 为了消除机械臂关节存在的死区特性, 设计了自适应死区补偿器, 通过自适应控制来逼近死区特性的上界, 以消除关节死区对系统带来的影响, 确保跟踪控制的有效执行. 最后基于Lyapunov函数法证明了系统的稳定性, 并通过系统数值仿真结果验证了存在死区情况下机械臂的各关节角跟踪上无反应空间下的期望轨迹的同时载体的姿态处于稳定状态, 验证了所提方法的有效性. 

REACTIONLESS TERMINAL SLIDING MODE CONTROL OF SPACE ROBOT WITH JOINT DEAD-ZONE

As the present reaction null space planning for the incomplete kinematic properties of the space manipulator during the general operation involvesn either the impact of joint dead-zones on the system nor the relationship between the manipulator and the target to be grasped, it can not ensure the effectiveness of the tracking control in the presence of joint dead-zone. In this paper, the study of reaction null space planning and control in the final period before intercepting a target of a free-floating three-link space manipulator with joint dead-zone is focused. First, the dynamic model of a free-floating three-link space manipulator with joint dead-zone is established by the second Lagrange equation, in which the position and attitude of the carrier are uncontrolled. Then, the reaction null space mathematical model of the free-floating three-link space manipulator with joint dead-zone is derived, and the vector norm constraint algorithm of the reaction null space is studied. Furthermore, a nonsingular fast terminal sliding mode control algorithm with anti-interference and high convergence is proposed, in which it combines the double power reaching rate of variable coefficient with the nonsingular fast terminal sliding mode surface to improve the convergence speed and interference immunity. The dead-zone of the joint may reduce the control accuracy of the space robot system. In order to eliminate the influence of the free-floating three-link space manipulator’s joint dead-zone, an adaptive dead-zone compensator is designed. This compensator can approach the upper bound of dead-zone characteristics by self-adaptive control to eliminate the effect of the joint dead-zone on the system and to ensure the effectiveness of the tracking control. Finally, based on the Lyapunov function method the stability of the system is proved, and numerical simulation is carried out. The simulation results show the desired reactionless trajectories are tracked with the base’s attitude reactionless and the effectiveness of the proposed planning and control algorithm is demonstrated.