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. 2021 Oct 26;21(21):7084.
doi: 10.3390/s21217084.

A Robust Observer-Based Control Strategy for n-DOF Uncertain Robot Manipulators with Fixed-Time Stability

Anh Tuan Vo  1 , Thanh Nguyen Truong  1 , Hee-Jun Kang  1 , Mien Van  2
Affiliations

A Robust Observer-Based Control Strategy for n-DOF Uncertain Robot Manipulators with Fixed-Time Stability

Anh Tuan Vo et al. Sensors (Basel). .

Abstract

In this paper, a robust observer-based control strategy for n-DOF uncertain robot manipulators with fixed-time stability was developed. The novel fixed-time nonsingular sliding mode surface enables control errors to converge to the equilibrium point quickly within fixed time without singularity. The development of the novel fixed-time disturbance observer based on a uniform robust exact differentiator also allows uncertain terms and exterior disturbances to be proactively addressed. The designed observer can accurately approximate uncertain terms within a fixed time and contribute to significant chattering reduction in the traditional sliding mode control. A robust observer-based control strategy was formulated, according to a combination of the fixed-time nonsingular terminal sliding mode control method and the designed observer, to yield global fixed time stability for n-DOF uncertain robot manipulators. The proposed controller proved definitively that it was able to obtain global stabilization in fixed time. The approximation capability of the proposed observer, the convergence of the proposed sliding surface, and the effectiveness of the proposed control strategy in fixed time were fully confirmed by simulation performance on an industrial robot manipulator.

Keywords: fixed-time control; nonsingular terminal sliding mode control; robot manipulators; uniform robust exact differentiator.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Block diagram of the proposed control system.
Figure 2
Figure 2
3D Description of a 3-DOF manipulator based on SOLIDWORKS.
Figure 3
Figure 3
Measured value of velocity x2 and observed value of velocity x^2 at each Joint.
Figure 4
Figure 4
Supposed value of the lumped uncertainty and observed value of the lumped uncertainty at each Joint.
Figure 5
Figure 5
Specified path and actual path of the end effector of the robot under three control strategies in 3-dimensional space (XYZ).
Figure 6
Figure 6
Path of the control errors in 3-dimensional space (XYZ).
Figure 7
Figure 7
Path of the control errors at each joint.
Figure 8
Figure 8
Control torque of the three different control strategies and comparison of chattering phenomena at each Joint.
See this image and copyright information in PMC

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