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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Theory of Machine
The displacement of the reciprocating roller follower, when it has contact with the straight flanks of the tangent cam, is given by (where r₁ = Minimum radius of the cam, r₂ = Radius of the roller follower, and θ = Angle turned by the cam from the beginning of the follower displacement)

(r₁ + r₂) [(1 - cosθ)/cosθ]
(r₁ + r₂) (1 + cosθ)
(r₁ - r₂) (1 - cosθ)
(r₁ - r₂) [(1 - cosθ)/cosθ]

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