Robert Brik — Kinematic Coffee Cup Holder

Kinematic couplings are used to very accurately constrain a part with high repeatability. This is accomplished by making contact at six points to eliminate all the degrees of freedom.
As a result, kinematic couplings are utilized as a cost effective method for high reproducibility (on the order of ¼ micron) and reliability.

A kinematic coupling was embodied in a coffee cup holder.
A three groove and three hemisphere kinematic coupling was chosen for the base to provide stability and reliability.
The cup holder was matched with a set of cups that have plates with the same base stand diameter so either the cups themselves or the cups with plates could be placed on the kinematic design.
Each cup was oriented directly above hemisphere so that the force would be projected directly down to avoid tipping so that one, two, or the three cups could be used.
The material properties and dimensions were used to calculate the hertz contact forces and estimate how much deflection would occur in the coupling.

The coffee cup holder consists of three aluminum plates that were cut out using a waterjet.
The top two pieces of metal were riveted together for aesthetic appeal and to create a plate for the cups.
Acorn nuts were attached to a cut bolt and threaded onto to the bottom of the top plate to act as hemispheres for the kinematic coupling.
Finally, conical bits were used to cut the grooves at 120 degree angles to each other.

A laser pointer was attached to the kinematic coupling at the centroid to determine how much deflection occurred when a weight was applied.
With a 2kg weight applied (significantly more than any cup of coffee), a deflection error of .00148 degrees occurred.
The error was reasonable considering the high mass applied and lack of necessary repeatability for the application.
Overall, the strength of the materials allow for a robust design that should function as a presentation piece that can simultaneously demonstrate the fundamentals of kinematic couplings.