Coupling types - Quasi-Kinematic Couplings

The next level of repeatability below the pure kinematic coupling is the quasi-kinematic coupling, which consists of line contact situations such as a cylinder on a flat or a ball in a cone. By reducing a surface contact to a line, over constraint is reduced from three degrees of freedom to two degrees. Since line contacts only weakly overconstrain an interface, more deterministic relationships can be formed to provide improved repeatability. In industrial settings, line contacts do not appear as often as surface contacts, but the optics industry has made use of line contacts for aligning lenses in cylindrical capsules in v-grooves. Recent work by Prof. Culpepper (Culpepper, 2000) has developed a framework for designing and implementing quasi-kinematic couplings for high load, industrial environments, specifically in the assembly of an automobile engine. More detailed information about quasi-kinematic couplings can be found in Prof. Culpepper's Ph.D. thesis.

Since quasi-kinematic couplings reduce the amount of surface interaction area, less useful area is available for the distribution of stress. Therefore, quasi-kinematic couplings can no longer support the highest loads with the best stiffness, but can provide improved precision with reasonable stiffness. Culpepper's design combines quasi-kinematic couplings using revolved line contacts with predetermined and predictable plastic and elastic deflections to optimize load capacity and stiffness, without sacrificing repeatability.