This paper models the velocity and trajectory of an arbitrary point belonging to the upper link relative to the lower link when the flat surfaces of optical workpieces are being fabricated by the free-lapping method.
Woo Dang Dong, E´ . S. Putilin, and Ya. V. Rudin, "Modelling the velocity and trajectory of the relative motion of a zone of a workpiece during surface lapping," J. Opt. Technol. 70, 573-575 (2003)