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Inverse Dynamics of Robot Manipulators Using Extended Flexible Joint Models
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology. (RT)
Department of Solid Mechanics, Royal Institute of Technology, Stockholm, Sweden.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

High performance robot manipulators, in terms of cycle time and accuracy, require well designed control methods, based on accurate dynamic models. This work investigates different methods for the inverse dynamics of a general manipulator model, called the extended flexible joint model. This model can describe elasticity in all directions, unlike the traditionally used robot models. The inverse dynamics solution is needed for feedforward control, which is often used for high-precision robot manipulator control. The inverse dynamics of the extended flexible joint model can be computed as the solution of a high index differential algebraic equation (DAE). The obtained DAE is analyzed, and solvers for both minimum phase and nonminimum phase systems are suggested. The solvers are evaluated by simulation, using a manipulator with two actuators and five degrees-of-freedom. Finally, the suggested concept for inverse dynamics is experimentally evaluated using an industrial robot manipulator. In this experimental evalution, an identified model is used in the inverse dynamics computation. Simulations using the same identified model are in good agreement with the experimental results. The conclusion is that the extended flexible joint inverse dynamics method can improve the accuracy for manipulators with significant elasticities,

Keyword [en]
Modeling, flexible arms, calibration and identification, motion control, robot manipulator
National Category
Control Engineering
URN: urn:nbn:se:liu:diva-61594OAI: diva2:370555
Available from: 2010-11-17 Created: 2010-11-17 Last updated: 2010-11-18
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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