Theory of Machine
Open pairs are those which have

Point or line contact between the two elements when in motion
Elements of pairs not held together mechanically
Surface contact between the two elements when in motion
Two elements that permit relative motion

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Theory of Machine
In a cam drive with uniform velocity follower, the sharp corners of the displacement diagram are rounded off at the beginning and at the end of each stroke. This is done

Because of loose contact of follower with cam surface
In order to have acceleration in beginning and retardation at the end of stroke within the finite limits
Because of difficulty in manufacturing cam profile
Because the uniform velocity motion is a partial parabolic motion

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