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Archive of Mechanical Engineering

The Journal of Committee on Machine Building of Polish Academy of Sciences

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Modal Measurements and Model Corrections of A Large Stroke Compliant Mechanism

Pomiary Modalne i Korekcje Modelu Mechanizmu Podatnego O Długim Suwie

W. Wijma
  • Faculty of Engineering Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
/ S.E. Boer
  • Faculty of Engineering Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
/ R.G.K.M. Aarts
  • Corresponding author
  • Faculty of Engineering Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
  • Email:
/ D.M. Brouwer
  • Faculty of Engineering Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
/ W.B.J. Hakvoort
  • Faculty of Engineering Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
  • DEMCON Advanced Mechatronics, Enschede, The Netherlands
Published Online: 2014-08-15 | DOI: https://doi.org/10.2478/meceng-2014-0020

Abstract

In modelling flexure based mechanisms, generally flexures are modelled perfectly aligned and nominal values are assumed for the dimensions. To test the validity of these assumptions for a two Degrees Of Freedom (DOF) large stroke compliant mechanism, eigenfrequency and mode shape measurements are compared to results obtained with a flexible multibody model. The mechanism consists of eleven cross flexures and seven interconnecting bodies. From the measurements 30% lower eigenfrequencies are observed than those obtained with the model. With a simplified model, it is demonstrated that these differences can be attributed to wrongly assumed leaf spring thickness and misalignment of the leaf springs in the cross flexures. These manufacturing tolerances thus significantly affect the behaviour of the two DOF mechanism, even though it was designed using the exact constraint design principle. This design principle avoids overconstraints to limit internal stresses due to manufacturing tolerances, yet this paper shows clearly that manufacturing imperfections can still result in significantly different dynamic behaviour.

Streszczenie

W modelowaniu mechanizmów opartych na ugięciach na ogół zakłada się, Że ugięcia sĄ doskonale wyrównane liniowo i przyjmuje nominalne wartości wymiarów. By sprawdzić zasadność tych załoŻeń dla podatnego mechanizmu o długim suwie i dwu stopniach swobody porównano wyniki pomiarów wartości własnych i kształtu modów z wynikami otrzymanymi na podstawie spręŻystego modelu wielu ciał. W mechanizmie występuje jedenaście poprzecznych elementów giętych i siedem wzajemnie powiĄzanych ciał. Wartości własne wyznaczone pomiarowo były o 30% mniejsze od obliczonych na podstawie modelu. MoŻna wykazać, Że w uproszczonym modelu róŻnice te naleŻy przypisać wadliwie przyjętej grubości spręŻyny płytkowej i złemu wyrównaniu spręŻyn w poprzecznych elementach spręŻystych. Jak stĄd wynika, tolerancje wykonania silnie wpływajĄ na zachowanie mechanizmu o dwu stopniach swobody, mimo Że był on zaprojektowany przy zachowaniu zasady ścisłych więzów. TakĄ zasadę projektowania stosuje się, by zapobiec tworzeniu więzów nadmiarowych i ograniczyć napręŻenia wewnętrzne powstałe w wyniku niedokładności wykonania. Niemniej, w artykule pokazano wyraźnie, Że niedokładności wykonania mogĄ wciĄŻ powodować istotne zmiany we właściwościach dynamicznych mechanizmu.

Key words:: non-linear compliant mechanism; flexible multibody model; modal identification; manufacturing tolerances; exact constraint design

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About the article

Published Online: 2014-08-15


Citation Information: Archive of Mechanical Engineering, ISSN (Online) 2300-1895, DOI: https://doi.org/10.2478/meceng-2014-0020. Export Citation

© 2014 W. Wijma et. al.. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License. (CC BY-NC-ND 3.0)

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