Cam 1 rotates about fixed axis B and has two contours, a and b. Follower 2 oscillates about fixed axis C and carries two rollers, 5 and 6, which roll a long the contours of cam 1: roller 5 along contour b and roller 6 along contour a. Follower 2 is connected by turning pair D to slider 3 which reciprocates along slot d of link 4. Link 4 oscillates about fixed axis A. Positive motion is achieved because the distance between points E and F, lying on the theoretical, or pitch, curves of contours b and a, is constant and equal to the distance between the centres of rollers 5 and 6.
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