Cam 1 rotates about fixed axis A. Follower 2 reciprocates in fixed guides B-B and carries two rollers, 3 and 4, which roll along the working curve of cam 1, composed of two different portions a and b. The contour of cam 1 is designed so that follower 2 has reciprocating motion at constant velocity when cam 1 rotates at constant angular velocity. Positive motion is achieved because the theoretical curve of the cam is designed so that there is a constant distance, equal to the distance between the centres of rollers 3 and 4, between two points of this curve lying on a straight line which passes through these centres for any position of the cam.
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