Hart's Cell

This arrangements of linkages forms the basis of Hart's linkage for a straight line.

Move the points B and C. As you do this notice the lengths FE and FG.

Also notice FE' which is calculated as (AB+BC)/FE. In a sense, this is the "inverse" of FE. Hence, this cell is also called an "inversor".

How does an inversor cell help to generate an exact straight line motion?

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Chris Sangwin, 23 December 2006, Created with GeoGebra