It is developed from mechanism shown at
http://www.youtube.com/watch?v=nyALtYMTrAg
Two such mechanisms are arranged separately in AC direction.
Two pink cranks and violet bar create a parallelogram mechanism.
Yellow plate nearly linearly translates and is always parallel to the ground.
Length of pink cranks: a
Length of green bars : 2.5a
Length of blue bars: 2.5a + 2.5a
Distances between stationary bearings AC: 2a.
This arrangement can be applied for any tracing mechanism where the translation of a plate a
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