Motion conversion device and rotary displacement device

A motion conversion device comprising a cam mounted for rotation about an axis eccentric to a central axis, said eccentric axis being rotatable about said central axis, the cam having N lobes the outermost points of which are equally spaced around and equidistant from the eccentric axis, N being an odd integer other than 1, means for effecting relative rotation between the central axis and the cam on rotation of the eccentric axis about the central axis or rotation of the cam about its eccentric axis whereby the cam is arranged to rotate about its eccentric axis at an angular velocity of (2/N+1) times the angular velocity of the eccentric axis about the central axis, a pair of cam followers rotatable about an axis substantially coincident with the central axis, the cam followers being in contact with the cam on opposed sides of the central axis and equidistant from the central axis, the cam being formed such that on rotation of the eccentric axis about the central axis at a substantially constant velocity the cam followers undergo 2 N cycles of acceleration from a dwell condition and deceleration to a dwell condition for each revolution of the cam followers.