The green disk carries the driving pin to which is attached a guide, the red block. This guide, working inside of a rectangular yoke, gives a varying speed to the sliding rod, which is slower at the ends than at the center of stroke.
[Virginia Downward & William M. Clark, 1930]

[Editor’s Note: The scotch yoke is a positive return cam. For a constant rotary input the horizontal motion is an exact sinusoidal motion. A similar model can be found in the Cornell Reuleaux Models as D-8. This class of linkages is a double slider mechanism with two prismatic joints and two revolute of joints. FCM]

Francis Moon 2005-00-00