Industrial robot accurate trajectory generation by nested loop iterative learning control
Journal
Mechatronics
Journal Volume
74
Date Issued
2021
Author(s)
Abstract
Common error sources of industrial robot manipulators include joint servoing error, imprecise kinematics, mechanical compliance, and transmission error. In this work we present a nested loop iterative learning control (ILC) feedforward structure: an inner loop that compensates for motor dynamics, and an outer loop that corrects the deviation along the path tracked, that features practically efficient implementation. Taking advantage of industrial robot's speed reduction transmission, single-input-single-output method is demonstrated effective for the nonlinear coupled robot dynamics. Data-based inversion technique that incorporates motion constraint is used for fast inner loop convergence. The outer loop utilizes inverse Jacobian matrix for joint reference modification. For nonlinear static friction that is difficult to be compensated for with only joint command, notch filtering is utilized in the learning process to avoid exciting vibration inherently exists in the robot. The proposed nested loop ILC requires only the nominal kinematic parameters from the robot manufacturer, and can be readily implemented without modifying the existing robot controllers. The effectiveness of the proposed method is experimentally verified on a six degree-of-freedom robot manipulator. ? 2021 Elsevier Ltd
Subjects
Data-based dynamic inversion
Iterative learning control (ILC)
Robot manipulator
Trajectory tracking
Degrees of freedom (mechanics)
Errors
Flexible manipulators
Industrial robots
Inverse problems
Iterative methods
Jacobian matrices
Kinematics
Learning algorithms
Modular robots
Notch filters
Robot applications
Stiction
Transmissions
Two term control systems
Efficient implementation
Feedforward structures
Inversion techniques
Iterative learning control
Mechanical compliance
Single input single output
Six degree-of-freedom
Trajectory generation
Industrial manipulators
Type
journal article