Chromatic Aberration confocal error characterization

This research explores the impact of probe angle variation on the accuracy of surface measurements using a chromatic confocal probe. These specialized optical instruments operate based on confocal microscopy principles to achieve high precision non-contact metrology. However, angle of incidence errors can significantly affect measurement reliability. To characterize such errors, an experimental setup using two separate 4 axis precision stage machine equipped with a confocal probe and tilt stage is used. By varying probe orientation relative to the tilt angle the surface angle error can be characterized.

By measuring how the tilt angle impacts accuracy, this study shows that probe orientation is critical for reliable measurements. Carefully controlling the  probe’s angle is key to precisely measuring curved surfaces with confocal probes. Overall, these findings can help improve measurement precision on  curved surfaces.


Free Form Lens Thickness Measurement with Optical Probes

Lens thickness measurement is a continued challenge. Probe errors for angle of incidence on the front and back side of the surface are characterized and compensated. Measurement scheme for


Precision Machine motion error characterization and compensation

Machine error mapping and compensation for 5 axis diamond turning machines. Axis straightness, squareness, wobble and twist measured. Scale error for linear and rotational axes characterized. Compensation scheme for all compounding errors in work.


Nanometer level targeted surface correction for fine optics and lens molds

Nanometer level surface roughness is a critical characteristic of fine optics. There are only a few processes that readily produce this level of surface roughness, but most suffer from poor surface form control or leave surface artifacts unfit for precision optics. EEM is a capable process for
controlling surface roughness. Form control is the challenge that remains. This work is principally focused on precise measurement and targeted material removal only in problem surface areas or in residual high points on lens and lens mold surfaces.


Micro-Indenting for roll to roll lens feature array

A Study of the Incidence and Reduction of Geometric Form Errors in Metal Microlens Array Molds Manufactured for AR/VR Applications Using a Scalable Indenting Process.

Simulation and tooling developed for multi-step over indenting in multiple metal roll molds. These molds were rolled over a film to reproduce the lens array on the film. This film was tested to with a light box to measure intensity.


Balloon Experimental Twin Telescope for Infrared Inteferometry

The NASA BETTII is designed to study the infrared emissions from star formation and active galactic nuclei with a double-Fourier Michelson interferometer located on a balloon at an altitude of 37 km. The BETTII external optics include a pair of identical beam-reducing, four-mirror telescopes, each with a 522 mm aperture off-axis segment of a parabolic surface. These telescopes were designed, built and assembled at the NC State University Precision Engineering Consortium and are composed entirely of thin-walled aluminum components. The mounting structure is designed to be lightweight and stiff to reduce thermal equilibration time in the rarified air at the edge of space and to maintain robust alignment of the optical elements. The mounts also prevent deformation of the large optical elements via custom-build kinematic Kelvin couplings and fixed-load clamps.

The Role of Built-Up Edge (BUE) in Diamond Tool Wear When Machining Steel

Despite its potential in many applications, diamond turned steel has long been considered improbable due to the inability to attain acceptable surface finish. These difficulties lie in the rapid changes of the tool geometry due to wear and workpiece adherence. Experiments were conducted to investigate the effect of tool wear and workpiece adherence on the tool geometry and the subsequent bulk temperatures of the diamond tool, machining forces and chips produced. The results conclude that workpiece pickup dominates changes in effective tool geometry by nearly two magnitudes in size compared with tool wear.

Diamond Turning of Plastic Optics

Single point diamond turning is a common method to create plastic optics. The optics industry claims that tool wear is a major problem. The objective of this research is to optimize machining parameters (such as feed, depth of cut, cutting speed and rake angle) to produce optical surface quality (RMS Surface finish < 10 nm) while minimizing tool wear for Poly (methyl methacrylate) (PMMA) and Polycarbonate (PC). A wide range of experiments were performed on the two materials by varying machining parameters and measuring worn tools using the Electron Beam Induced Deposition (EBID) technique in the Scanning Electron Microscope (SEM). For the experimental conditions used, PMMA was found to have better surface finish than PC when machined with a diamond tool. Polycarbonate was found to wear the tool more than PMMA under similar cutting conditions. It was also found that Polycarbonate is more sensitive to chip management and chip geometry than PMMA. Built up edge on the tool and chip management were identified as the important reasons for poor surface finish on PC. Tribo-electric charging was found to be a major mode of tool wear when machining PC. Holes in the diamond tool were observed on the diamond tool when large depths of cut were used. Detailed effects of all machining parameters for the two materials were reported.

Development of a Surrogate System to Study the Dry Turning of Plutonium

To reduce time and costs associated with disposing of cutting fluids used to machine radioactive materials like plutonium, dry machining is being investigated at Los Alamos National Laboratory (LANL). However, such soft radioactive materials present machinability issues when a cutting fluid is not used. The main issue is chip seizure. This occurs when chip material adheres to the rake face of the tool and smears the machined surface, leading to poor surface finish. To safely study this phenomenon, soft, pure 1199 aluminum was chosen as a suitable surrogate material. By conducting machining experiments on 1199 aluminum, feeds, speeds, depths and tool parameters were optimized to reduce the effects of chip seizure and optimize surface roughness. High positive rake angled tools, larger feed rates and depths of cut, and moderate cutting speeds produce the best machined surfaces.

Focused Ion Beam Milling of Microscale Features

This research investigates the fabrication of microscale features in glassy carbon that will be used as a die to stamp features into a mold for injection molding of plastic lenses. The concept is to FIB mill a die with multiple features (4-9) and then stamp those features at a high repetition rate (>100/second) to create a mold for a large lens array. The features are nominally spherical with radii on the order of 15.8 µm that would, with the parameters given above, create a mold with 3×106 lenses in an hour.

The FIB characteristics such as material removal rate, angle of incidence sensitivity, and beam shape were measured. It was estimated that a single lens feature could be milled in a matter of minutes. A simulation tool was developed to assist in planning the FIB milling process. Glassy carbon dies with 4 and 9 features were FIB milled. The FIB process parameters were investigated to improve the form of the die. 1100 Aluminum was indented with the glassy carbon die and arrays of indents were successfully fabricated.

Modeling of the Microindentation Process

This report addresses the design of multi-indenter die and development of indentation strategies to create the negative features of a microlens array on a mold. Initially, correlation of quasi-static nanoindentation results of FEA models to the experimental results is obtained to gain confidence in the models. A material parameter study is performed using commercial finite element analysis software AbaqusTM to understand the effects of different material properties on the spring back amount, pile-up and the maximum force required. Al 1100 is selected as the mold material based on this study. Glassy carbon is used as the die material. Possible drawbacks in the design of the multi-indenter die and the different indentation strategies are discussed.

High Spatial Resolution Infrared Mass Spectrometry Imaging

High spatial resolution in mass spectrometry imaging (MSI) is crucial to understanding the    biology dictated by molecular distributions in complex tissue systems. Here, we present MSI using infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) at 50 µm resolution. An adjustable iris, beam expander, and aspherical focusing lens were used to reduce tissue ablation diameters for MSI at high resolution. The laser beam caustic was modeled using laser ablation paper to calculate relevant laser beam characteristics. The minimum laser spot diameter on the tissue was determined using tissue staining and microscopy. Finally, the newly constructed optical system was used to image hen ovarian tissue with and without oversampling, detailing tissue features at 50 µm resolution.

Mass Spectrometry Imaging Software

A major update to the mass spectrometry imaging (MSI) software MSiReader is presented, offering a multitude of newly added features critical to MSI analyses. MSiReader is a free, open-source, and vendor-neutral software written in MATLAB and is capable of analyzing most common MSI data formats. A standalone version of the software which does not require a MATLAB license is also distributed. Newly incorporated data analysis features expand the utility of MSiReader beyond simple visualization of molecular distributions. A quantification tool allows researchers to calculate absolute concentrations exclusively through MSiReader software, significantly reducing analysis time. An image overlay feature for visualizing complementary imaging modalities, an ionization polarity filter, and a quality assurance feature to calculate and display mass measurement accuracy (MMA) have also been added. Most importantly, as new features have been added performance has not degraded, in fact it has been dramatically improved.


Characterization of Single Abrasive Grit with Force and Visualization Techniques

The goal of this project was to study the tool wear, geometry and forces based on operating parameters in a grinding process experienced by a single abrasive grits. Individual abrasive grits on a coated abrasive are generally within a given size range but can have a range of cutting geometries. Grit geometries can also change as grits wear and fracture. Experiments were performed to determine an effective experimental procedure for testing and visualizing a single triangular shaped alumina grinding grit remove material. Two different geometries of the individual grits were tested in the two different orientations. Cutting forces were measured using a three axis load cell and simultaneous high speed video was recorded at 6006 frames per second.

Design of a Microfluidic Device to Extract Dyes from Fibers for Forensic Analysis

Analysis of fiber evidence from a crime scene is an important aspect of criminal investigation. Fibers are identified and compared by morphology and the molecular makeup of the coloring dyes. Separation of dye from fiber is a tedious process involving aggressive and hazardous solvents that can take a skilled lab technician up to 30 minutes per sample. It is also destructive. The objective of this research was to design and build a microfluidic system to automate the extraction process using a minimal amount of a sample.