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1

Odometry Error Correction for a 4-Wheel Omnidirectional Mobile Platform

Blume H., Heimann B., Abelbeck F.

Machine Dynamics Problems

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2006

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Vol. 30, No. 1

5-20

EN

This paper deals with a dead reckoning error correction algorithm for a 4-wheel omnidirectional mobile platform. The platform is powered by 4 identical driven and actively steered wheels, which sums up to 8 actuation DOFs. The platform itself is described as unicycle kinematic by 3 DOFs in the horizontal plane containing speed in x- and y direction, and angular velocity around the vertical axis. For estimating the robot's speed the redundancy is solved by an extended Kalman filter, based on a kinematic model of the robot. Dead reckoning based on the estimated robot speed is subject to different systematic and random errors. Over time small errors sum up to large discrepancies between estimated and real robot position, which - especially in office environments with narrow passages in halls and doors - is a big limitation for position estimation based on dead reckoning. Still, dead reckoning offers high resolution position estimation in the close-up range and by data fusion with a landmark-based low resolution position estimation system qualifies for high accuracy path control. In this paper a dead reckoning error correction algorithm is presented, which splits the speed error into one part originating from straight line movement and a second part originating from rotation around the vertical axis. The parameters of the error correction algorithm are estimated by a recursive least squares algorithm. During operation the robot continuously verifies the set of parameters, to account for a drift of parameters due to wear and varying payload of the robot. A significant improvement against simple dead reckoning can be shown.

2

Dynamics and Control of Robots with Parallel Kinematic Structures

Heimann B., Abdellatif H.

Machine Dynamics Problems

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2005

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Vol. 29, No. 4

59-68

EN

It is often, that the dynamics of parallel robots are mostly restricted to simple models to keep real-time capabilities in control systems. The here presented approach for modelling the dynamics takes especially into consideration real-time and parameter identification aspects. This formulation is automatically obtained by an algorithm, that utilizes Jourdain's principle of virtual power using operational space presentation. It leads to a formulation of the dynamic equations of minimal order. The use of linear estimators is based on a formulation of the dynamic equations, which is linear with respect to a dynamic parameter vector of minimal dimension. The principal design methodology for such machines with parallel kinematic structure is exemplarily discussed by consideration of two different machines: the robot "PaLiDA" and a hydraulic test stand "MSI" with 6 degree-of-freedom each. The experimental application of the identified model to model-based feedforward control of the innovative hexapod PaLiDA, which has been developed by the Institute of Production Engineering and Machine Tools of the University of Hannover, proves the capability and efficiency of the presented algorithms.

3

Grinding Chatter in Experiment and Simulation

Schütte O., Heimann B.

Machine Dynamics Problems

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2004

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Vol. 28, No. 2

41-43

EN

Although high precision grinding systems are highly sophisticated machine tools, manufactures still have to deal with the problem of chatter vibrations, especially in the case of cylindrical grinding between centers. Chatter limits the surface quality of the ground workpieces and hinders the automation of the grinding process. Therefore, basic research was done by the authors and an extended grinding model was developed that is able to simulate chatter vibrations like they appear in experiment (Schütte, 2004; Tönshoff et al., 2004; Schütte and Heimann, 2001). This article gives a short overview of the model presented in work by Schütte (2004). Especially, results of the wheel wear simulation are shown.

4

On Chater Vibrations in Cylindrical Grinding

Schütte O., Heimann B.

Machine Dynamics Problems

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2001

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Vol. 25, No. 3/4

135-137

XX

[Extended abstract] The problem of chatter vibrations still has a high relevance for the handling of high precision finishing systems in manugacturing. This article shortly summarizes papers of the authors that deal with the modeling of chatter in the process of external cylindrical plunge grinding...

5

Contact Models of External Cylindrical Grinding

Schütte O., Heimann B.

Machine Dynamics Problems

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1998

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Vol. 20

245-262

EN

In this paper the goals and first steps of a project dealing with chatter compensation in cylindrical grinding are shown. On the one hand the terms of engagement of cylindrical plunge grinding are described and sources for machine tool chatter are listed. On the other hand the available literature on the subject of grinding is discussed and different approaches to process modelling and contact relations are outlined.