Coupling Types - Planar Kinematic Couplings

The planar or directional kinematic coupling, an extension of the quasi kinematic coupling, can be a combination of all three types of contact. For example, a planar coupling consists of a large surface contact area at the interface along with specially designed line or point contacts to constrain the free degrees of freedom. A directional coupling could be any type of coupling, which has precision alignment designed to repeatably constrain specific directions, while relying on surface features, tolerances, etc. in noncritical directions.

One of the more useful implementations of this form of coupling is the three pin coupling. The three pin coupling uses a large surface area with three pins projecting normal to its surface. The large surface area constrains three degrees of freedom, while a line contact on each pin constrains the remaining three degrees. To ensure adequate contact on all three pins, preload is applied to one pin in a direction determined by geometry and loading conditions. Additional preload is appled by more heavily torquing securing bolts normal to the interface. This preload is applied to ensure contact between the two surfaces and to provide increased stiffness of the interface. More information on the three pin coupling can be found in the theses of Patrick Willoughby or John Hart.

Due to the mixed nature of these couplings, repeatability, load capacity, and stiffness are all a function of the individual design. Overall, planar kinematic couplings can provide high stiffness and load capacity with moderate repeatability.


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