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I've seen the term "kinematic" used qualitatively to describe machines several times in books and on YouTube. I think I understand what kinematics is as a study, but I'm not sure what people mean when they say a structure or machine "is kinematic".

Here are two examples:

  1. Multiple times I've seen people describe a tool with three feet as being kinematic. As in "This height gauge has three points of contact with the surface plate which makes it kinematic."

  2. In "Precision Machine Design" there's a paragraph on machine structure where the author says "If the design is not kinematic, bearings can become overloaded by the forced geometric compliance between the structure to which the bearing rails or races are mounted and the smaller structure of the platten or spindle."

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  • $\begingroup$ I think what they are tried to say this it has the ability to move. According to the Merrriam Webster dictionary that is not a "registered" use of the work. However, being a Greek native speaker I have to say that the -atic ending of the word in greek has the meaning of "being related to" or "able to". TL;DR I think they are using it incorrectly. $\endgroup$ – NMech Sep 23 '20 at 18:28
  • $\begingroup$ NMech, consider to place your comment as an answer. A wiki result of a search for kinematic presented almost exactly your comment. $\endgroup$ – fred_dot_u Sep 23 '20 at 18:35
  • $\begingroup$ I don't think they're trying to say it's able to move because in my first example the number of feet doesn't impact its ability of the gauge to move and in the second example it makes no sense for a machine tool to "not be able to move". I think the word must have an industry specific meaning that's different from common usage. $\endgroup$ – Despontene Sep 23 '20 at 18:54
  • $\begingroup$ kinematics surfaces are used sometimes to refer to a 3 point support table to be used without ambiguity as a reference surface. I think the context defines the meaning of the word, kinematic. $\endgroup$ – kamran Sep 23 '20 at 21:18
  • $\begingroup$ I don't know why the term 'kineamtic' is used and I don't think it's quite correct, but it appears in both examples the machines are neither over nor under-constrained. $\endgroup$ – mart Sep 24 '20 at 6:23
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I think it might be shorthand for a kinematically constrained design.

It is the "This height gauge has three points of contact with the surface plate which makes it kinematic." which makes me suggest this interpretation.

I also found a link where they seems to equate a "kinetic mount" to a mount that is "is fully constrained, but not over-constrained": https://practicalprecision.com/kinematic-constraint/.

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  • $\begingroup$ This use - and slight shorthand - is very common indeed in opto-mechanics. When adjusting something like a laser mirror, you want it to be exactly constrained (you also want to avoid crosstalk between adjustments, which is aided by a kinematic design $\endgroup$ – Chris H Sep 24 '20 at 9:50
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See https://en.m.wikipedia.org/wiki/Kinematic_coupling

A kinematic coupling is constrained in (only) 6 degrees of freedom.

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