liu.seSearch for publications in DiVA
Change search
ReferencesLink to record
Permanent link

Direct link
Inverse Dynamics of Flexible Manipulators
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
Royal Institute of Technology, Sweden.
2009 (English)In: Proceedings of the 2009 Conference on Multibody Dynamics, 2009, 1-20 p.Conference paper (Refereed)
Abstract [en]

High performance robot manipulators, in terms of cycle time and accuracy, require well designed control methods, based on accurate dynamic models. Robot manipulators are traditionally described by the flexible joint model or the flexible link model. These models only consider elasticity in the rotational direction. When these models are used for control or simulation, the accuracy can be limited due to the model simplifications, since a real manipulator has a distributed flexibility inall directions. This work investigates different methods for the inverse dynamics of a more general manipulator model, called the extended flexible joint model. 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). One method is to solve the discretized DAE using a constant stepsize constant-order backwards differentiation formula (BDF). This work shows that there is only a small difference between solving theoriginal high-index DAE and the index-reduced DAE. It is also concluded that scaling of the algebraic equations and their derivatives is important.

The inverse dynamics can be solved as an initial-value problem if the zero dynamics of the system is stable, i.e., minimum phase. For unstable zero dynamics, an optimization approach based on the discretized DAE is suggested. An optimization method, using a continuous DAE formulation, is also suggested and evaluated. The solvers are illustrated by simulation, using a manipulator with two actuators and five degrees-of-freedom.

Place, publisher, year, edition, pages
2009. 1-20 p.
Keyword [en]
Manipulator, Control, Differential algebraic equation, Flexible multibody dynamics, Non-minimum phase, Inverse dynamics
National Category
Control Engineering
URN: urn:nbn:se:liu:diva-61326OAI: diva2:369951
2009 Conference on Multibody Dynamics, Warsaw, Poland, 29th June - 2nd July, 2009
Swedish Research Council
Available from: 2010-11-12 Created: 2010-11-12 Last updated: 2013-09-16
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

Open Access in DiVA

No full text

Other links

Related report

Search in DiVA

By author/editor
Moberg, Stig
By organisation
Automatic ControlThe Institute of Technology
Control Engineering

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 174 hits
ReferencesLink to record
Permanent link

Direct link