This four-body linkage has two parallel cylindrical joints and two sliding or prismatic joints. The link that is constrained by two sliding joints is called a cross-block. In Model D-11, the cross-block link is grounded and the crank link exhibits oscillating vertical motion while at the same time rotating. Reuleaux called this a swinging double slider-crank or swinging double slider. One application was for a draftpersons “trammel” used to draw elliptical curves, also called an ellipsograph, that is shown in Model D-12.

Francis Moon 2004-07-00