NREIP Research

This was a fall internship I did with the Department of the Navy through the Naval Research Enterprise Internship Program (NREIP). I worked with the Corona Surface Warfare Center’s metrology department remotely to research alternatives to their current verification equipment. I had to ensure that all suggestions brought something unique to the table such as price, service, form factor, etc. all the while maintaining a similar level of tolerance to the old specification. I then took all of this information and boiled it down to a concise oral presentation and an accompanying zip file with all of the data sheets, price information and some contact info.

Flow Generators

One of the main technologies I researched were flow generators, devices used to measure anemometers by providing a very precise amount of fluid through a narrow channel. I had found a few companies that provide custom solutions where I compared the range of pressures, fluid velocities, tolerances, and opening diameters to give them some options.

Infrared Generators

Infrared generators run a precise amount of current through a blackbody target to generate a specific amount of heat that could be used to calibrate a pyrometer or infrared gun. With this I had to ensure that a wide range of temperatures could be generated by the devices. It turned out that by using two different generators, one for lower temps and one for higher you could get a much better result.

Table Flatness

For this I needed to come up with ways to measure flatness of laser tables. The 3 main solutions I came up with were as follows:

Use a repeat reading gauge.

A repeat reading gauge is essentially a long, heavy, flat piece of steel with a strategic stress concentration made so it will bend slightly under its own weight if it is placed on even a slightly curved surface. Then a dial indicator is mounted to the gauge and measures the linear displacement of the bar, which can be equated to flatness. This is a very old technique that is simple enough to where plenty of hobbyist machinists can make their own easily. Easy to use, however it is only a very local measurement.

Use an AA granite with a height gauge.

The classic method of taking something more precise than what you have and seeing how the two compare. by setting another smaller piece of more precise granite on top of the other and sliding a height gauge to compare the two you can determine how flat your table is across a straight line. However technically you are measuring parallelism between the two surfaces, the AA granite I found was parallel to a very precise degree, more than what we were trying to measure.

An autocollimator setup.

An autocollimator is by far the coolest of them. An autocollimator is a scope that splits a light source in two directions, one that fires at the user’s eye, and the other that fires directly away from the eye, at a reflective object in question. If that object is not perfectly perpendicular to that beam of light it returns to the eyepiece slightly displaced from the other half of the beam. This can be read using hash marks on the eye piece that correspond to the angle at which it is off. If you know the distance to that object and the vertical displacement of the 2nd beam you can find the angle that the reflective object sits at relative to the autocollimator, and with some simple trig you can get the linear flatness of the table. This is an expensive setup that requires a skilled user, but can be done very quickly for a variety of spots on the table just by sliding a mirror stand around on the table.

Laser Interferometers

By far the coolest and most in depth research was on various commercially available laser interferometers. I contacted 4 different companies’ sales departments to get quotes on their machines and understand each’s capabilities as far as precision, repeatability, measuring area, and more. These devices are marvels of modern technology and comparing all of the advantages and disadvantages when presenting my work was very fun.

NERDY TECHNICAL EXPLINATION, YOU HAVE BEEN WARNED:

A laser interferometer is a device that can very precisely measure small changes in the surface of an object. To explain in more depth, a high-powered laser is hooked up to a stable power source, and as light naturally is an oscillating electric field, following a sine wave. Then, this sinusoidal beam is split and fired at two objects, a known reference and the thing you are trying to measure. The light travels to the objects, then is reflected back to be read by a digital sensor. When the two beams come back to the sensor, they will interfere either constructively or destructively based solely on what phase of the sine wave both beams were on. If both beams traveled the same exact distance, they would interfere perfectly constructively, if one object is one half a wavelength further or closer it will interfere purely destructively. Using these differences in distance over the span of a large digital sensor you can get an INCREDIBLY precise and accurate map of the surface of the object you are trying to measure.