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In Mechanisms and Machines Theory we were introduced to Assur groups and structural analysis where a mechanism is subdivised into elementary Assur groups of different classes. But what is really the practical use of it?

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Things have to be assembled. Assur group gives you a catalog of possible ways to make a rigid assembly out of joints. Each joint in this case represents a connection that will be assembled later, or locked down in case of foldable structures meant for reuse.

Being 0 degrees of freedom means that analysis of these is straight forward. Recognizing them will also make kinematic and dynamic analysis easier since you can replace them with a single rigid body.

Since assur groups can be predicted in a organized manner nothing stops you from generating a very big catalogue of these. Allowing you to systematically search for new solutions for the task at hand.

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  • $\begingroup$ As far as I know, they can only be applied on planar mechanisms, is there a similar approach for spatial mechanisms? $\endgroup$
    – Abdeljalil
    Commented Feb 1, 2019 at 22:06
  • $\begingroup$ @Abdeljalil Well yes, but there are some cases that dont reflect the theory. So its only 90% accurate, if you refrain from using spherical joints its almost completely accurate. Anyway nearly everything you see around you is designed with planar mechanism in mind $\endgroup$
    – joojaa
    Commented Feb 1, 2019 at 22:11
  • $\begingroup$ Thank you for the clarification, can you recommend resources or books for further reading? The subject is barely mentioned on the web. $\endgroup$
    – Abdeljalil
    Commented Feb 1, 2019 at 22:18

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