Trajectory Tracking Control Research For Floating Space Robot System With Driving Torque Constraints

Due to constraints of drive motor size, dimensions, weight, power, and other physical conditions, most previous studies have not taken into account the existence of inevitable and unfavorable input constraints phenomenon for space robot control technology. In practical use of control technology of floating space-based robot system, if the drive motor constraints occur, the system will likely worsen the trajectory tracking performance, causing joint tremors, and leading to mechanical control failure, eventually losing stability. Based on the above background, the control problem of floating space-based robot system with driving torque constraints to track a desired trajectory in joint space and in inertial space are proposed, which is supported by National Natural Science Foundation of China.For difficult to measure feedback speed signal for actual trajectory tracking control of space robot system, a kind of position output feedback control algorithm based on first-order linear velocity filter is designed. The control algorithm can be implemented to generate a pseudo error rate signal measured by the position error of the system, which effectively eliminated measurement errors caused by the true velocity signal and improved trajectory tracking performance. However, there are some insufficiencies, as follows:the system does not consider the presence of the driver input torques are limited; compared with conventional control algorithm based on velocity measurements, the magnitude of required input torque is too large; the stability analysis too complicated and cumbersome.In response to shortcomings of the control algorithm, a class of improved control algorithm (Improved position output feedback control algorithm based on saturated function) is designed, which is applied to floating space-based robot system with driving torque constraints. The notable characteristics of the improved control algorithm, as follows:the smooth saturated arctangent function or the smooth saturated hyperbolic tangent function is introduced; the augmented error gain coefficient matrix and augmented pseudo velocity error gain coefficient matrix are also introduced. The improved control algorithm not only retains the advantage of control algorithm based on first-order linear velocity filter, but also avoids its shortcomings, which prompts the improved control algorithm more conform to the actual requirements of floating space-based robot system.Due to the influence of the small parameter perturbation, the actual conditions which considered the drive torque constraints may lead to increased difficulties of stability analysis, and may even lead to closed-loop control system divergence. Therefore, the closed-loop error system is decomposed into reduced-order model and boundary-layer model based on the singular perturbation system, and the exponentially stable of state origin is proved by using Lyapunov function respectively, which simplified the process of stability analysis and proof.The improved control algorithm is applied to trajectory tracking control of single arm space robot system in working space and dual-arm space robot system in joint space. Numerical simulation analysis and comparison show the improved control algorithm can not only control the system to track a desired trajectory quickly and asymptotically, but also can significantly reduce driver input torque value of the joint hinges, and ensure the amplitude of driver torques is within a given range.