Adaptive Integral Sliding Mode Control for Flexible Joint Space Manipulators
ObjectiveAccurate trajectory tracking control is critical for space robotic arms to perform on-orbit service missions. However, nonlinear joint friction and external load disturbances in complex space environments lead to significant degradation of the tracking performance of flexible joint space ma...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Editorial Department of Journal of Sichuan University (Engineering Science Edition)
2025-01-01
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| Series: | 工程科学与技术 |
| Subjects: | |
| Online Access: | http://jsuese.scu.edu.cn/thesisDetails#10.12454/j.jsuese.202400882 |
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| Summary: | ObjectiveAccurate trajectory tracking control is critical for space robotic arms to perform on-orbit service missions. However, nonlinear joint friction and external load disturbances in complex space environments lead to significant degradation of the tracking performance of flexible joint space manipulators (FJSM). An adaptive integral sliding mode controller (AISMC) based on the singular perturbation with a two-state observer is proposed to address the issue.MethodsFirstly, the rigid-flexible coupled system is decomposed by using singular perturbation theory to yield two second-order subsystems with distinct time scales, of which one is slow subsystem and the other one is fast subsystem. The concept of integral manifold is introduced to reconfigure the decoupled system, and the control strategy design of the two low-order subsystems is transformed into the tracking control strategy design: in the slow subsystem, the controller is designed so that the joint angle tracks the desired joint position; in the fast subsystem, the controller is designed so that the joint elastic torque tracks the desired elastic torque , which simplifies the design of the sub controllers and ensures the overall stability of the system and the control accuracy. Subsequently, an adaptive integral sliding mode controller is elaborated to accomplish the desired tracking performance. The control strategy is based on a two-state observer to construct an integral sliding mode surface, which avoids the requirement of measuring velocity and acceleration in the FJSM system and thus effectively reduces the chattering phenomenon. In addition, an adaptive law for switching gain is proposed for the slow and fast subsystems in the FJSM, which eliminates the requirement of knowing the upper limit of the external perturbation. The closed-loop stability of the whole FJSM system is verified by Lyapunov's theorem. Finally, simulation experiments are conducted with a planar three-link flexible joint space manipulators as the controlled object, aiming at verifying the effectiveness of the proposed controller in tracking and controlling the system in the presence of joint nonlinear friction as well as external load perturbations. In addition, the adaptive integral sliding mode controller (AISMC) in this paper is compared with the integral sliding mode controller (ISMC), where the switching gain adaptive law is not included in the ISMC.Results and DiscussionsInitially, the three joints of the robotic arm are tasked with tracking step signals while neglecting joint friction and external disturbances. As shown in Fig. 3(a), the tracking performance of the third joint position reveals that the adaptive integral sliding mode controller (AISMC) exhibits superior performance compared to the integral sliding mode controller (ISMC). Specifically, AISMC achieves a shorter tuning time, a faster transient response, and enables the joint angle to closely follow the desired trajectory more rapidly. In Fig. 3(b), it is evident that the sliding mode surface of AISMC converges to zero faster than that of ISMC. Furthermore, Figs. 3(c) and 3(d) indicate that the adjustable switching gain stabilizes at 0.02 seconds as the sliding mode surface reaches zero, effectively preventing gain overestimation and enhancing the system's overall control performance. Next, friction and disturbance signals are introduced at the joints, and the tracking errors for the three joint positions of the robotic arm are shown in Fig. 4(a)–(c). These results demonstrate that the proposed adaptive integral sliding mode control (AISMC) scheme provides a faster transient response and smaller tracking error compared to the traditional controller ISMC. For a more comprehensive comparison of control performance, quantitative evaluations of regulation time, root mean square error (RMSE), and steady-state tracking error are conducted. As shown in Table 3, the AISMC outperforms the ISMC in ideal trajectory tracking, largely due to the adaptive law for switching gain, resulting in a shorter regulation time, reduced tracking error, and lower RMSE in the steady-state phase. Finally, to evaluate the disturbance rejection capability and inverse actuation of the proposed control method, an impulsive disturbance load is introduced into the control input of the flexible joint space manipulator (FJSM), while the reference signal is set to zero. As shown in Fig. 6(a), the AISMC exhibits a smaller deviation from the zero horizontal position and demonstrates rapid reverse actuation in response to the disturbance, performing notably better than the comparison controller. Additionally, Fig. 6(b) illustrates that the AISMC requires less control torque to counteract sudden load disturbances. This indicates that the proposed controller possesses strong robustness to abrupt loads, whereas the comparison controller, which lacks an adaptive law, struggles to manage the effects of these sudden disturbances effectively.ConclusionsAn adaptive integral sliding mode control scheme based on singular perturbation is proposed to accomplish the angular position tracking of a flexible joint space manipulator under joint nonlinear friction and external disturbance conditions. The method introduces an integral sliding mode surface to ensure asymptotic convergence of the tracking error of the FJSM system. A power convergence law with adaptive gain adjustment is proposed to reduce chattering and decrease the dependence on the disturbance upper bound. Compared with the conventional ISMC scheme, the proposed controller shows significant improvement in tracking performance and disturbance robustness. Simulation results show that the proposed controller possesses higher tracking accuracy, stronger disturbance suppression capability, and better robustness than other controllers. |
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| ISSN: | 2096-3246 |