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Analysis of the motion mode change of a metamorphic 8R linkage

Research output: Contribution to journalConference paper

A. Müller, K. Zhang, J. S. Dai

Original languageEnglish
Pages (from-to)39-47
Number of pages9
JournalMechanisms and Machine Science
Early online date24 Nov 2015
Publication statusPublished - 2016

King's Authors


By definition, metamorphic mechanisms can change their mobility. This change can be achieved by actively locking certain elements, or can be due to the inherent kinematics of the linkage. In the latter case the mobility is altered when passing through configuration space singularities. In a recent development, these two phenomena are combined. As such it was shown that a single-loop 8R linkage, possessing certain symmetry, turns into an overconstrained 6R linkage by only locking one joint while another joint is then implicitly constrained. This phenomenon has been analyzed by means of a first-order analysis in terms of instantaneous joint screw system. Thereupon the metamorphism was concluded and verified experimentally. An analytic proof was not yet provided. In this paper finite kinematics of the metamorphic 8R linkage is established and its ability to change to a 6R linkage by means of locking only one joint is shown analytically. The presented methodology is general and applicable to arbitrary mechanisms. It does provides a basis for the analysis and eventually the synthesis of novel metamorphic mechanisms.

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