Theory of Machine
Whitworth quick return mechanism is obtained by inversion of

Kinematic chain
Five link mechanism
Slider crank mechanism
Roller cam mechanism

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Theory of Machine
The relation l = (2/3).(j + 2) apply only to kinematic chains in which lower pairs are used. This may be used to kinematic chains in which higher pairs are used, but each higher pair may be taken as equivalent to

One lower pair and two additional links
Any one of these
Two lower pairs and two additional links
Two lower pairs and one additional link

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