Abstract
An adaptive model-free control with nonsingular terminal sliding-mode (AMC-NTSM) is proposed for high precision motion control of robot manipulators. The proposed AMC-NTSM employs one-sample delayed measurements to cancel nonlinearities and uncertainties of manipulators and to subsequently obtain sufficiently simple models for easy control design. In order to maintain high gain controls even when the joint angles are close to the reference target values and accordingly achieve high precision and fast response control, a nonlinear sliding variable is also adopted instead of a linear one, asymptotically stabilizing controls by guaranteeing even a finite-time convergence. In addition, sliding variables are reflected on control inputs to support fast convergence while achieving uniform ultimate boundedness of tracking errors. The control gains of the proposed AMC-NTSM are adaptively adjusted over time according to the magnitude of the sliding variable. Such adaptive control gains become high for fast convergence or low for settling down to steady motion with better convergence precision, when necessary. The switching gains of the proposed AMC-NTSM are also adaptive to acceleration such that inherent time delay estimation (TDE) errors can be suppressed effectively regardless of their magnitudes. The simulation and experiment show that the proposed AMC-NTSM has good tracking performance.
Highlights
For a long time, robot manipulators have been successfully developed to achieve high-precision control performance
This paper proposes an AMC-nonsingular terminal sliding-mode (NTSM) for achieving high precision and fast response, and applies it to robot manipulators
ADAPTIVE MODEL-FREE CONTROL WITH NONSINGULAR TERMINAL SLIDING-MODE We propose an adaptive model-free control with nonsingular terminal sliding-mode (AMC-NTSM) as follows: τ t = Mt [−qt−L + M −t 1τ t−L ]
Summary
Robot manipulators have been successfully developed to achieve high-precision control performance. As in the control gains, the nonlinear sliding variables of the existing MC-NTSMs have an inherent trade-off between tracking performance and noise effects arising from the derivative of tracking errors. The switching gains of the proposed AMC-NTSM are adjusted in proportion to the magnitude of acceleration that is associated with the upper bound of TDE errors. Sliding variables are directly reflected on the proposed AMC-NTSM to support fast convergence with moderate gains while achieving uniform ultimate boundedness of tracking errors This plays a role in resolving the aforementioned trade-off arising from nonlinear sliding variables of existing MC-NTSMs. In summary, the proposed AMC-NTSM is aimed at reinforcing an existing MC-NTSM with adaptive schemes, flexible TDE error suppression, and responsive practical control in order to achieve better tracking performance while reducing undesirable side effects.
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