Nonlinear Friction Compensation of a Flexible Robotic Joint with Harmonic Drive

Abstract

To suppress the abrupt and unexpected turning velocity fluctuation of the industrial robot under the condition of trajectory tracking, a flexible robotic joint experimental setup with the harmonic drive was established. The measured friction with Stribeck effect and velocity were modeled by a simple polynomial fit method. Two friction compensation control strategies of feedforward and feedback were designed. The friction compensation experiments were carried out on the dSPACE system, the good restraint effect of fluctuation on the turning velocity was verified and the control accuracy of feedback compensation control strategy proved better.

Friction torque field distribution of a permanent‐magnet spherical motor based on multi‐physical field coupling analysis

“…The simplified Stribeck model is shown in Figure 6. In the low‐speed motion stage, the friction torque decreases with increasing angular velocity from to , which is called the Stribeck effect [24]. From this, the friction torque expression can be established as where is the empirical constant, is the maximum static friction torque, is the Coulomb friction torque, and B is the viscous friction coefficient.…”

“…The simplified Stribeck model is shown in Figure 6. In the low-speed motion stage, the friction torque decreases with increasing angular velocity from ω th1 to ω th2 , F I G U R E 5 Simplified support structure of the permanent-magnet spherical motor, including upper frictionless support mandrels and lower frictional support mandrels F I G U R E 6 Three stages of the simplified Stribeck friction torque model which is called the Stribeck effect [24]. From this, the friction torque expression can be established as…”

Friction Compensated Force Control of Electro-Hydraulic System Using Fuzzy Controller

“…Friction affects the system performance, no matter the system is under position, velocity or force control. The mostly used method to counteract friction problems was to implement a model-based friction compensation [10][11][12][13][14][15][16][17] because of its less complexity compared to friction model-free compensation method. Implementing of a steady state friction compensation is straight forward and was effectively implemented in various applications [10][11][12][13].…”

“…The mostly used method to counteract friction problems was to implement a model-based friction compensation [10][11][12][13][14][15][16][17] because of its less complexity compared to friction model-free compensation method. Implementing of a steady state friction compensation is straight forward and was effectively implemented in various applications [10][11][12][13]. In the neural network training process of the five-axis milling center process force estimation, friction on each axis of the machine was estimated by Stribeck friction model with the use of velocity data on that axis [10].…”

“…A proposed reaction observer consisted of a disturbance observer working in combination with compensations of static friction, backlash and oil leakage, could effectively estimate reaction force acting on a hydraulic actuator [12]. Steady state friction model of a flexible robot joint was constructed by curve fitting of piecewise continuous polynomial functions, and robot joint velocity control performance was improved with the friction compensation in the PI controller compared to the controller without compensation [13].…”