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A Novel Virtual Sensor for Estimating Robot Joint Total Friction Based on Total Momentum

State Key Laboratory of Robotics and System, School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150080, China
Authors to whom correspondence should be addressed.
Appl. Sci. 2019, 9(16), 3344;
Received: 12 July 2019 / Revised: 8 August 2019 / Accepted: 12 August 2019 / Published: 14 August 2019
(This article belongs to the Special Issue Artificial Intelligence for Smart Systems)
PDF [3016 KB, uploaded 14 August 2019]


Robot joint friction is an important and complicated issue in improving robot control performance. In this paper, a virtual sensor based on the total generalized momentum concept is proposed to estimate the total friction torque, including both the motor-side and link-side friction, of robot joints without joint torque sensors. The proposed algorithm only requires a robot joint dynamics model and not a complex friction model dependent on factors such as time and velocity. By compensating for the estimated friction torque with a robot joint controller, the trajectory tracking performance of the controller, especially the velocity tracking performance, can be improved. To verify the effectiveness of the developed algorithm, 2-DOF planar manipulator simulations and single-joint system experiments are conducted. The simulation and experimental results show that the designed virtual sensor can effectively estimate the total joint friction disturbance and that the controller trajectory tracking performance is improved after observed friction compensation. However, the position tracking performance improvement of the controller is less than that for the velocity tracking performance improvement during the experiments. In addition, the velocity step response ability and velocity tracking performance of the controller are improved more at low velocities than that at high velocities in the experiments. The proposed algorithm has engineering and theoretical significance for estimating robot joint friction and improving the performance of robot joint controllers.
Keywords: robot joint total friction estimation; total momentum; observer; robot dynamics model robot joint total friction estimation; total momentum; observer; robot dynamics model
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Xu, T.; Fan, J.; Fang, Q.; Wang, S.; Zhu, Y.; Zhao, J. A Novel Virtual Sensor for Estimating Robot Joint Total Friction Based on Total Momentum. Appl. Sci. 2019, 9, 3344.

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