Abstract
The variable stiffness joint (VSJ) has the characteristics of independent and controllable position and stiffness. The variable stiffness characteristics and inherent flexibility make the VSJ suitable to be used as the actuation joint of the physical human-robot interaction application robot, so as to improve the task adaptability of the robot and physical human-robot interaction safety. The VSJ based on equivalent lever mechanism has the advantages of low energy consumption in stiffness adjustment, so there are many researches on this type of VSJ. The tracking control of output link angular position and joint output stiffness are two basic control targets of the VSJ. For the system dynamic model of the VSJ based on equivalent lever mechanism, considering the unknown parametric perturbations, the unknown friction torques acting on the drive units, the unknown external disturbance acting on the output link and the control input saturation constraints, a robust tracking controller based on feedback linearization, disturbance observer with anti-windup measures, sliding mode control and estimation error compensator is designed to improve the tracking control accuracy of the position and stiffness of the VSJ. The simultaneous tracking control of position and stiffness of the VSJ can be achieved by the designed controller, and the simulation results show the effectiveness and robustness of the proposed controller. Moreover, the simulation results show that the proposed estimation error compensator for the disturbance observer with fixed preset observation gain can effectively reduce the system output tracking error and improve the anti-disturbance characteristics of the controller.
Highlights
In the current research field of the flexible robot, variable stiffness joint (VSJ) is a kind of flexible robot actuation joint with independent and controllable characteristics of position and stiffness [1]
For the commonly used disturbance observer (DOB) with fixed preset observation gain [20], [22]–[24], [31]–[35] as shown in equation (26), a novel robust tracking control scheme based on feedback linearization (FL), DOB, sliding mode control (SMC) and disturbance estimation error compensator (DEEC) is designed to improve the tracking accuracy of the position and stiffness of the VSJ based on the equivalent lever mechanism
The dynamic model of the CompAct-VSA [14] developed by the Italian Institute of Technology is chosen as the study object in this article, and it is a representative VSJ in the type of VSJs with series configuration based on equivalent lever mechanism
Summary
In the current research field of the flexible robot, variable stiffness joint (VSJ) is a kind of flexible robot actuation joint with independent and controllable characteristics of position and stiffness [1]. In this article, 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. For the system dynamics model of the VSJ based on the equivalent lever mechanism with parametric uncertainties, unknown friction torques, unknown external disturbance and control input saturation constraints, we design a robust tracking controller to realize the simultaneous robust tracking control of the position and stiffness of the VSJ to the desired trajectories. In the design process of the controller, we introduce a novel estimation error compensator for the traditional DOB with fixed preset observation gain to improve the tracking control accuracy and anti-disturbance performance of the controller
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