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Modeling and Parameter Estimation of Robot Manipulators using Extended Flexible Joint Models
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. (RT)
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. (RT)
Royal Institute of Technology, Department of Solid Mechanics.
ABB AB, Sweden.
2014 (English)In: Journal of Dynamic Systems Measurement, and Control, ISSN 0022-0434, Vol. 136, no 3, 031005- p.Article in journal (Refereed) Published
Abstract [en]

This paper considers the problem of dynamic modeling and identification of robot manipulators with respect to their elasticities. The so-called flexible joint model, modeling only the torsional gearbox elasticity, is shown to be insufficient for modeling a modern industrial manipulator accurately. The extended flexible joint model, where non-actuated joints are added to model the elasticity of the links and bearings, is used to improve the model accuracy. The unknown elasticity parameters are estimated using a frequency domain gray-box identification method. The conclusion is that the obtained model describes the movements of the motors and the tool mounted on the robot with significantly higher accuracy. Similar elasticity model parameters are obtained when using two different output variables for the identification, the motor position and the tool acceleration.

Place, publisher, year, edition, pages
2014. Vol. 136, no 3, 031005- p.
Keyword [en]
Modeling, flexible arms, calibration and identification, motion control, robot manipulator.
National Category
Control Engineering
URN: urn:nbn:se:liu:diva-61667DOI: 10.1115/1.4026300ISI: 000333588100005OAI: diva2:370692
Available from: 2010-11-17 Created: 2010-11-17 Last updated: 2014-05-06
In thesis
1. Modeling and Control of Flexible Manipulators
Open this publication in new window or tab >>Modeling and Control of Flexible Manipulators
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Industrial robot manipulators are general-purpose machines used for industrial automation in order to increase productivity, flexibility, and product quality. Other reasons for using industrial robots are cost saving, and elimination of hazardous and unpleasant work. Robot motion control is a key competence for robot manufacturers, and the current development is focused on increasing the robot performance, reducing the robot cost, improving safety, and introducing new functionalities.  Therefore, there is a need to continuously improve the mathematical models and control methods in order to fulfil conflicting requirements, such as increased performance of a weight-reduced robot, with lower mechanical stiffness and more complicated vibration modes. One reason for this development of the robot mechanical structure is of course cost-reduction, but other benefits are also obtained, such as lower environmental impact, lower power consumption, improved dexterity, and higher safety.

This thesis deals with different aspects of modeling and control of flexible, i.e., elastic, manipulators. For an accurate description of a modern industrial manipulator, this thesis shows that the traditional flexible joint model, described in literature, is not sufficient. An improved model where the elasticity is described by a number of localized multidimensional spring-damper pairs is therefore proposed. This model is called the extended flexible joint model. The main contributions of this work are the design and analysis of identification methods, and of inverse dynamics control methods, for the extended flexible joint model.

The proposed identification method is a frequency-domain non-linear gray-box method, which is evaluated by the identification of a modern six-axes robot manipulator. The identified model gives a good description of the global behavior of this robot.

The inverse dynamics problem is discussed, and a solution methodology is proposed. This methodology is based on the solution of a differential algebraic equation (DAE). The inverse dynamics solution is then used for feedforward control of both a simulated manipulator and of a real robot manipulator.

The last part of this work concerns feedback control. First, a model-based nonlinear feedback control (feedback linearization) is evaluated and compared to a model-based feedforward control algorithm. Finally, two benchmark problems for robust feedback control of a flexible manipulator are presented and some proposed solutions are analyzed.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2010. 101 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1349
Modeling, identification, control, robot manipulator, DAE, flexible multibody dynamics, inverse dynamics, benchmark
National Category
Control Engineering
urn:nbn:se:liu:diva-60831 (URN)978-91-7393-289-9 (ISBN)
Public defence
2010-12-03, Sal Visionen, Hus B, Campus Valla, Linköping University, Linköping, 10:15 (English)
Available from: 2010-11-18 Created: 2010-10-27 Last updated: 2010-11-18Bibliographically approved

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