High order sliding mode control of a space robot manipulator

Abstract

In this study, a high-order sliding mode controller (HOSMC) is designed for the control of a one degree-of-freedom (DOF) flexible link space robotic arm with payload. The high order sliding mode based controller is developed, which exploit the robustness properties of sliding-mode controllers (SMCs), while also increasing accuracy by reducing chattering effects. Ever increasing demand for high-speed performance and low energy consumption of space robotic systems require low-mass designs. This restriction puts a limitation on the degree of rigidity of space robot manipulators. These manipulators may posses' significant flexibility that needs to be taken consideration in the design of the control systems. Space robot manipulators have highly nonlinear and coupled dynamics. Flexible space robot arms have structural flexibilities and resulting high number of passive degrees-of-freedom. Therefore, the control of such flexible systems has significant challenges due to the highly nonlinear structure. The high performance control of a flexible link space robotic arm requires the full system dynamic structural flexibilities become of increased importance particularly when high speed, high accuracy operation of lightweight structures is aimed. In this study, a high-order sliding mode controller (HOSMC) is designed for the control of a one degree-of-freedom (DOF) flexible link space robotic arm with payload. The high-order sliding mode based controller is developed, which exploit the robustness properties of sliding-mode controllers (SMCs), while also increasing accuracy by reducing chattering effects. In most related literature, the full system dynamic structural flexibilities effects are neglected to avoid increased computational complexity at the expense of compromising the tracking accuracy of the system in the transient and steady-state. As a solution to the problem, in this study, the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> order HOSM (2-HOSM) control law is derived by including the structural flexibilities into the control design process. 2-HOSM controller is designed to achieve set-point positioning control. The performance of the designed control method is tested for the precise positioning of a space robotic arm under heavy uncertainties and external disturbances has been evaluated in real-time on an experimental setup. The proposed control method is applied for the set-point control and trajectory control of the system and has resulted in an improved precision and overall performance as demonstrated by experimental results. The improved accuracy obtained 2-HOSMC motivates the implementation of the schemes for demanding control applications under heavy uncertainties.