III. The 2nd Generation Rotational Mechanism

"Whenever there is some part that requires motion, a little bit of tolerance between the moving parts are an indispensable consequence. When designing cryogenic devices where the overall thermal conductivity is a critical factor, any compromise due to this non-zero tolerance often drives the devices to its limit of losing its desired efficiency. A clever cryogenic device should not settle between its functionality and thermal efficiency. We have to find an optimal balance."

The rotational mechanism of the zeroth generation coldfinger houses a worm gear mating with a custom made gear driving the docking station. Since it was designed by physicists without any engineering background, the end result was unacceptable. Its problems, to name a few,...

1. The teeth of the custom gear is not mating with the worm shaft properly. In other words, the thread of worm shaft is usually at an angle of 20 degrees whereas the direction of the custom gear teeth was in parallel with its axial direction. 
2. Between the custom gear and coldfinger is a total of about 20 copper ball bearings! If you don't understand why this is absurd, bear with me for the moment.
3. The worm shaft is not properly fixed to the coldfinger that upon an application of torque the joint gets disengaged and the whole rotational mechanism becomes inoperable.
4. To house the unnecessarily large gear and awkwardly positioned internal electrodes, almost 70% inside of coldfinger is hollowed out! The net effect of this? A huge decrease in the overall thermal conductance not to mention the structural instability.

Now the above picture is the improved geometry of the rotational mechanism. Notice that instead of having only copper balls, cylindrical bearings are also used. There are a total of ten cylindrical bearings and six of them are not shown since they are embedded on the other side of the coldfinger.

This is just another picture showing how the ball bearings above engages with the axle and axle cover. Basically the axle cover clamps onto the end of axle while it grazes on the ball bearings. From this angle, once can see how the four side electrodes engages with two concentric circular electrodes (for details regarding the electrodes, look at my other post). I have more pictures of these, but since I'm a little concerned about revealing too much details of my device without a proper publication work, I will make the rotational mechanism discussion short! For anyone who are interested in the details though, drop me an email or comments.

No comments: