Robust Tracking Control Of The Variable Stiffness Actuator Based On The Lever Mechanism

Abstract

This paper is concerned with the design of a robust adaptive tracking control scheme for a class of variable stiffness actuators (VSAs) based on the lever mechanisms. For these VSAs based on the lever mechanisms, the AwAS‐II developed at Italian Institute of Technology (IIT) is chosen as the study object, and it is an enhanced version of the original realization AwAS (actuator with adjustable stiffness). Firstly, for the dynamic model of the AwAS‐II system in the presence of parametric uncertainties, unknown bounded friction torques, unknown bounded external disturbance and input saturation constraints, by using the coordinate transformations and the static state feedback linearization, the state space model of the AwAS‐II system with composite disturbances and input saturation constraints is transformed into an uncertain multiple‐input multiple‐output (MIMO) linear system with lumped disturbances and input saturation constraints. Subsequently, a combination of the feedback linearization, disturbance observer, sliding mode control and adaptive input saturation compensation law is adopted for the design of the robust tracking controller that simultaneously regulates the position and stiffness of the AwAS‐II system. Under the proposed controller, the semi‐global uniformly ultimately bounded stability of the closed‐loop system has been proved via Lyapunov stability analysis. Simulation results illustrate the effectiveness and the robustness of the proposed robust adaptive tracking control scheme.

Research on Angle and Stiffness Cooperative Tracking Control of VSJ of Space Manipulator Based on LESO and NSFAR Control

“…Combined with the feedback linearization method, in the case of input saturation constraints, the system's control input variables is shown in (10).…”

“…OWAIS et al [9] derived a Lagrangian-based dynamic model which lies in consideration of both viscous damping and gravity and proposed two Control algorithms based on Linear Quadratic Regulator (LQR) and nonlinear backstepping, respectively. Guo et al [10] established the dynamic model in the presence of parametric uncertainties, unknown bounded friction torques, unknown bounded external disturbance, and input saturation constraints, by using the coordinate transformations and the static state feedback linearization, and designed a robust tracking controller by a combination of a disturbance observer, sliding mode control, and an adaptive input saturation compensation law.…”

Robust Tracking Control of Variable Stiffness Joint Based on Feedback Linearization and Disturbance Observer With Estimation Error Compensation

“…A neural network adaptive control strategy based on feedback linearization is proposed for the position and stiffness tracking of the SVSA, and the feasibility of the proposed approach is verified by simulation results [19]. A robust tracking controller based on feedback linearization, disturbance observer (DOB) and sliding mode control is designed for the simultaneous tracking control of the position and stiffness of the AwAS-II, and the effectiveness of the controller has been illustrated by simulation results [20]. A robust tracking control scheme based on linear extended state observer with estimation error compensation is proposed for the tracking control of the antagonistic VSJ based on equivalent nonlinear torsion spring and the serial VSA based on the equivalent lever mechanism, and the effectiveness of the proposed controller is verified by simulation results [21].…”

“…Many control strategies [11][12][13][14][15][16][17][18] focus on the studies of the control characteristics and applications of the VSJs, but not on the robustness of the position and stiffness tracking control of the VSJ. Although the DOBs have been used in the tracking control of the VSJs to improve the robustness of tracking control, the DOBs in these control schemes [20,[22][23][24] have fixed preset observation gain, and the estimation errors of the DOBs are not considered in the design of controllers. There are also some controllers for the position tracking control of multi-DOF robot system driven by the VSJ based on equivalent lever mechanism [24,25], but these controllers do not focus on the implementation of simultaneous position and stiffness tracking control of the VSJ.…”

“…In the robust tracking control schemes of the VSJs [20,[22][23][24] or non VSJ systems [31][32][33][34][35], the DOB is a widely used technique to improve the robustness of system tracking control. In this paper, considering the possible model parameter perturbations, the unknown friction torques acting on the driving units, the unknown external disturbance acting on the output link and the control input saturation constraints in the system dynamics of the VSJ based on the equivalent lever mechanism, a novel robust tracking control scheme is designed to realize the simultaneous position and stiffness tracking control of this type of VSJ.…”