A four-body linkage with two cylindrical joints and two sliding or prismatic joints is called a double slider-crank kinematic chain. The link that is constrained by two prismatic joints is called a cross-block by Reuleaux. In model D-9, the crank link is grounded, and the cross-block rotates in an epicycloid motion equivalent to a large circle rotating on its inside circumference on the outside of a smaller circle of diameter equal to the length of the crank link between centers of the two cylindrical joints. Reuleaux called this motion Cardanic circles, and called this mechanism a turning cross-block. A version of this mechanism is used in Oldham’s coupling (Model Z-5) to produce uniform rotation about two parallel shafts.

Francis Moon 2004-07-00