Four-bar linkage synthesis with second-order precision points

The case of four pair-wise infinitely close positions of a plane mechanism link is shown to admit to a particularly simple determination of the centre curve, hitherto apparently not noticed. The construction is adapted to the problem of synthesizing a four-bar function-generator with two second-order precision points, keeping convenience on the drafting machine in view. An analytical expression of the procedure is also included. © 1975.