Model: L05 Positive Return Cam
A cam is a kinematic pair in which one part is free to slide against the surface of another part. In the L series of models one part is rotated against a straight or curved surface forcing the latter to move in a horizontal or straight-line motion. The action is closed kinematically by using a curve of constant width between two surfaces separated by a constant distance. In model L-1, the former is a curved triangle known today as a Reuleaux Triangle [see model B-2]

In Model L-1, the carved triangle is rotated about one of its vertices. This produces two phases of exact finite time dwell in the motion cycle. In model L-5 the rotor is a five-sided curved polygon of constant width. A screw allows the center of motion of the curved pentagon to be changed. The parallel guides are set to 45¼.

Positive return cams were used in the control of valves in steam engines in the early 19th century. They are still used in modern machines to impose a given motion to a part during a machine cycle.

Cams in general are used extensively in automotive engines. However cam contact is generally maintained with elastic springs instead of parallel guides.

Francis Moon 2003-07-01