Wesley B. Williams

Using quantum dots to tag subsurface damage in lapped and polished glass samples

Grinding, lapping, and polishing are finishing processes used to achieve critical surface parameters in a variety of precision optical and electronic components. As these processes remove material from the surface through mechanical and chemical interactions, they may induce a damaged layer of cracks, voids, and stressed material below the surface. This subsurface damage (SSD) can degrade the performance of a final product by creating optical aberrations due to diffraction, premature failure in oscillating components, and a reduction in the laser induced damage threshold of high energy optics. As these defects lie beneath the surface, they are difficult to detect, and while many methods are available to detect SSD, they can have notable limitations regarding sample size and type, preparation time, or can be destructive in nature. The authors tested a nondestructive method for assessing SSD that consisted of tagging the abrasive slurries used in lapping and polishing with quantum dots (nano-sized fluorescent particles). Subsequent detection of fluorescence on the processed surface is hypothesized to indicate SSD. Quantum dots that were introduced to glass surfaces during the lapping process were retained through subsequent polishing and cleaning processes. The quantum dots were successfully imaged by both wide field and confocal fluorescence microscopy techniques. The detected fluorescence highlighted features that were not observable with optical or interferometric microscopy. Atomic force microscopy and additional confocal microscope analysis indicate that the dots are firmly embedded in the surface but do not appear to travel deep into fractures beneath the surface. Etching of the samples exhibiting fluorescence confirmed that SSD existed. SSD-free samples exposed to quantum dots did not retain the dots in their surfaces, even when polished in the presence of quantum dots.

A magnetic gearbox with an active region torque density of 239Nm/L

In this paper a 1:4.25 ratio ferrite magnet and NdFeB magnet flux-focusing magnetic gearbox with a high pole count is analyzed. A simple parameter sweep analysis is used to show that higher than previously published torque density values are achievable. Experimental results are then presented for the NdFeB design that confirm the calculations and also demonstrate that the proposed magnetic gearbox can operate with a low torque ripple.

A Flux-Focusing Cycloidal Magnetic Gearbox

A magnetic gearbox (MG) offer the ability to operate with low noise and vibration. Its non-contact operation means that no gear lubrication is required and MGs have inherent overload protection [1-4]. A MG also has the potential for high efficiency [5]. Coaxial MGs have been shown to be capable of achieving active region torque densities above 200Nm/L [6]. However, single-stage coaxial MG designs are only able to achieve a high torque density at a low gear ratio [7, 8]. Typically less than 8:1. There are many applications in which a significantly higher gear ratio is desirable, such as in robotic and power generation applications.

Designing the first stage of a series connected multistage coaxial magnetic gearbox for a wind turbine demonstrator

The design of the first stage of a 59:1 multistage magnetic gearbox for a wind turbine demonstrator is presented. The multistage magnetic gearbox (MSMG) is composed of a two stage magnetic gearbox (MG). The first stage of the MSMG has a gear ratio of 6.45. A spoke type MG rotor typology is used with a unique segmented fully laminated rotor structure. Axially segmented magnets and a unique set of radial deflection rotor support rings are utilized.

A low assembly cost coaxial magnetic gearbox

This paper presents the design investigation and experimental testing of a flux-focusing magnetic gearbox with a three piece laminated rotor structure. Each rotor is made of a single lamination stack held together via thin lamination bridges. It is calculated that mechanical bridges reduces the torque density from 156Nm/L to 139Nm/L (a reduction of 11%). The experimentally measured torque density is shown to be only 95Nm/L because the magnets were demagnetized during testing.

An experimental and analytical investigation into the effects of process vibrations on material removal rates during polishing

Experimental testing, using both commercially available polishing machines and a specially built test platform, demonstrates that material removal rates (MRRs) observed during polishing of fused silica are strongly affected by nanometer-scale vibration amplitudes. Specifically, a nanometer level increase in system vibrations can produce MRRs approximately 150% higher than on an inherently smoother running machine. Moreover the higher spatial frequency surface roughness values are little-effected by the spectral content of the polishing machine. Polishing under controlled conditions, using the test platform, shows that for vibration amplitudes, A ≲ 1.6 μm, and over a fairly wide range of vibration frequencies, MRR increases almost linearly with increasing input power. By contrast, for A ≳ 10 μm, MRR exhibits a rapid decay with increasing A. Order of magnitude analyses and physical arguments are presented in order to explain the qualitatively distinct MRR trends observed. In the small-amplitude limit, A ≲ 1...

Development of a remote laboratory architecture for Mission Critical Operations instruction

In order to support the remote training of Mission Critical Operators, a standard interface and interconnection architecture had to be developed. While many others have created schemes for remote operation of equipment, many tend to either be customized to a target hardware, lack the requisite security protocols, or not be scalable. We have created such an architecture, leveraging existing commercial or open source hardware and software, and creating customizations where necessary to integrate the parts into an entire system. The result is an experience that connects students with industrially relevant hardware and software in a manner that approximates an industrial operator involved in remotely troubleshooting or configuring a networked remote resource.

Implementation of a Cartesian robot for remote Mission Critical Operator training

As part of ongoing work to create training for Mission Critical Operators, a new training system was developed offering multiple degrees of freedom (DOF), which was a desirable addition as part of a progression of training systems of increasing complexity. With the addition of multiple DOF, the user may be exposed to a more complex control environment presenting challenging tasks related to full range of motion on multiple axes. The electromechanical training system was developed following a previously developed standard allowing control by two separate controllers; a Micro800 series programmable logic controller (PLC) or a National Instruments myRIO. This gives the user an opportunity to learn two programming languages: ladder logic and LabVIEW. The training system includes 4 DOF and has free range of motion in the X, Y, and Z axis. This allows for multiple applications to be simulated. The overall approach is presented; the final designs are being made available under an open-source license.

Application of novel quasi-electrostatic sensor arrays for time based data collection and processing of supersonic, subsonic, and transonic revolving projectiles

Sensors capable of measuring the quasi-electrostatic field of traveling projectiles have been developed to detect the passage of a bullet in flight. These sensors provide an alternative to existing optical chronograph technologies, which are sensitive to variations in environmental lighting, and magnetic chronographs, which require close proximity to the bullet’s path. In contrast, electric field sensors are insensitive to lighting changes and prior testing has demonstrated the ability to reliably detect bullets at distances of at least three meters. A linear array of these sensors has been used to measure the time of flight between the sensors, which with the known distance between the sensors can be used to calculate the projectile’s velocity. These velocity measurements are compared to established chronograph technology as a measurement validation. By extending this array of sensors along the projected path of the projectile, a profile of the projectile’s position and velocity through flight can be calculated. This expected utility of this data is in refining the calculations that are performed to determine a ballistic solution, particularly in long range engagements, where there has been limited availability of accurate projectile velocity measurements. This robust sensor array that can easily be deployed represents an inexpensive way to experimentally investigate numerous phenomena related to ballistics modeling.

Experimental analysis of fretting related acoustic emission signals

Mating parts often experience repetitive relative motion termed fretting which results in friction, wear, as well as acoustic emission signals. Acoustic emission signals have the potential for monitoring the condition of the surfaces participating in the frictional process. In structural health monitoring studies, where the focus is on quantifying crack growth related acoustic emission signals, the signals generated by other mechanisms give rise to undesirable false positives. A major source of such false positives are fretting related signals. The present paper describes an experimental approach for characterizing the friction related acoustic emission signals. A test fixture is developed to obtain fretting related signals under controlled conditions. The waveforms are analyzed to extract features common to these signals. A comparison of acoustic emission signals related to fretting and crack growth is provided.