Vasishta Ganguly

Improving the Fabrication Process of Micro-Air-Vehicle Flapping Wings

The aerodynamic performance of flapping micro air vehicles in hover conditions is dependent on many parameters, including the wing design. With the goal of optimizing the wing for hover performance, the initial focus was to reduce the uncertainty in the thrust measurements. This is because lower uncertainty in this metric enables better resolution in comparing the performance of different designs. Aerodynamic performance variability was deemed to be the fault of an imprecise manufacturing technique. Therefore, adjustments were made to the fabrication process until a permissible level of uncertainty was attained for optimization; the goal was less than 5%. This paper chronicles the progression of the wing fabrication process and details how the uncertainty was evaluated. Four fabrication methods and two different wing designs are included in this study: a carbon fiber hand layup technique, carbon fiber cured in a machined mold, and two variations of a machined plastic skeleton reinforced with a carbon fibe...

Analysis of Thrust Production in Small Synthetic Flapping Wings

For flapping micro air vehicles, geometrical parameters such as size, aspect ratio as well as structural topology can affect thrust production in hover mode. Synthetic wings similar in size to that of a humming bird’s were manufactured with the hope of understanding these affects. The experimental method for measuring thrust and the manufacturing process used to make the wings have seen improvement from previous work such that there is less scatter and uncertainty; this allows for smaller variations in thrust to be detected. With confidence in the fabrication and testing procedure, an optimization problem was attempted where three design parameters were chosen as variables and the objective was to maximize thrust. These efforts were coupled with noncontact imaging techniques like digital image correlation and laser doppler velocimetry to help extract the characteristics that are consistent with wings that produce considerable thrust. The results of these tests will help to obtain the relationships between the consciously selected geometric parameters and the thrust produced. It was found that by machining the synthetic wings from acetal resin sheet and pairing that skeleton with a carbon fiber rod less variation was present. This wing construction was found to have a quick production time, making an experimental optimization feasible.

Fabrication and Analysis of Small Flapping Wings

Flapping winged micro air vehicles (MAVs) have been of interest due to their unique flying characteristics. Wing design is an essential aspect of making a robust flapping device. The more popular approach to obtaining an optimized wing is to completely mimic natural species. Rather, our study is only inspired by these biological flyers, suggesting that the optimum design for an active one degree of freedom flapping motion may differ. Error reduction is crucial to the experimental optimization approach, building confidence that variations in thrust are attributed to wing topology. To allow for consistency among replicate wings, the fabrication process must be controlled and accurate along with data acquisition and experimental setup. Digital image correlation and slow motion photography was used to find subtle differences and gain more knowledge of the physics behind flapping. Hovering MAVs serve as the primary application of the optimized wing.

Control of Lay on Cobalt Chromium Alloy Finished Surfaces Using Magnetic Abrasive Finishing and Its Effect on Wettability

Freeform surfaces, including the femoral components of knee prosthetics, present a significant challenge in manufacturing. The finishing process is often performed manually, which leads to surface finish variations. In the case of knee prosthetics, this can be a factor leading to accelerated wear of the polyethylene tibial component. The wear resistance of polyethylene components might be influenced by not only the roughness but also the lay of femoral component surfaces. This study applies magnetic abrasive finishing (MAF) for nanometer-scale finishing of cobalt chromium alloys, which are commonly used in knee prosthetics and other freeform components. Using flat disks as workpieces, this paper shows the dominant parameters for controlling the lay in MAF and demonstrates the feasibility of MAF to alter the lay while controlling the surface roughness. The manually finished disk surfaces (with roughness around 3nm Sa), consisting of random cutting marks, were compared to MAF-produced surfaces (also with roughness around 3nm Sa) with different lays. Tests using deionized water droplets show that the lay influences the wetting properties even if the surface roughness changes by no more than a nanometer. Surfaces with unidirectional cutting marks exhibit the least wettability, and increasing the cross-hatch angle in the MAF-produced surfaces increases the wettability. Surfaces consisting of short, intermittent cutting marks were the most wettable by deionized water. [DOI: 10.1115/1.4026935]

Performance evaluation of a vibration desensitized scanning white light interferometer

Surface metrology instruments normally require thermal, seismic and acoustic isolation. Shop-floor metrology solutions offer reduced cost and process time. If they operate on the same principles as laboratory devices, an inherent sensitivity to vibration remains. This paper describes a methodology for evaluating ‘environmental tolerance’ and applying it to characterize a recently introduced ‘environmentally tolerant’ scanning white light interferometer (SWLI). Previously published measurements of replicated nickel reference standards on the new instrument and on a stylus profilometer showed good correlation. Surface topography repeatabilities (per ISO 25178-604:2013) were insignificantly different when evaluated on the SWLI instrument in a metrology laboratory and in a manufacturing area. Measurements of reference standards under forced vibration of the entire instrument show maximum ripple error and data dropout in regions of structural resonance. Measurements were performed with large forced horizontal and vertical sample oscillation beneath the objective, exhibiting maximum ripple error near odd integer multiples of half the instrument detector frequency. Error due to data dropout was also investigated.

Characteristics of Cobalt Chromium Alloy Surfaces Finished Using Magnetic Abrasive Finishing

Freeform surfaces, including the femoral components of knee prosthetics, present a significant challenge in manufacturing. The finishing process is often performed manually, leading to high variation in quality. This study proposes using Magnetic Abrasive Finishing (MAF) to finish the cobalt chromium (Co-Cr) alloy femoral components of knee prosthetics and varying the surface pattern to alter surface wettability, which influences the tribological properties of the surfaces. As a first step, flat workpieces of the same material were used in this paper. To obtain an understanding of the relationship between surface pattern and wettability, two sets of finishing conditions were developed to yield two different surface patterns while maintaining roughness values (2–5 nm Ra). One surface consists of long cutting marks exhibiting strong directionality, while the other consists of short, intermittent cutting marks. The surface with strong directionality resulted in an increased contact angle between the workpiece and de-ionized water (from 90.0°±1.5° to 93.8°±2.5°), thus a decrease in wettability. The other surface showed a decreased contact angle (from 98.7°±5.3° to 93.3°±3.7°), thus an increase in wettability. This study experimentally demonstrates the feasibility of MAF to alter surface pattern—and to potentially alter the wettability—while maintaining initial surface roughness at a nanometer scale.Copyright

Periodic error correction in heterodyne interferometry

This paper describes periodic error in differential-path interferometry using a Frequency-Path model of the propagation of light from the source to detector in differential-path interferometers. The model identifies each possible path for each light frequency from the source to detector and predicts the number of interference terms that may be expected at the detector output. The behavior of all possible interference terms with respect to optical path changes may be grouped into one of four categories: Optical Power, AC Interference, AC Reference, and DC Interference. A description of a single pass, Michelson-type heterodyne interferometer is given and the periodic error is calculated for a selected system.

Force Measurement and Analysis for Magnetic Field–Assisted Finishing

Magnetic field–assisted finishing (MAF) is used to polish free-form surfaces. The material removal mechanism can be described as a flexible “magnetic brush” that consists of ferromagnetic particles and abrasives that arrange themselves in the working gap between the magnet and the workpiece. Relative motion between the brush and the workpiece causes microcutting and improves surface finish. In this study, the contributions of the magnetic and polishing force components to the total force were evaluated. The effect of varying the polishing conditions, such as the working gap and the size of the ferromagnetic iron particles, on polishing forces, surface roughness, and material removal rate was also analyzed. It was observed that the polishing forces varied considerably with working gap. Also, the iron particle size was found to have a strong relation to the rate at which the surface roughness improved. Surface roughness values of 2–3 nm were achieved. [DOI: 10.1115/1.4023723]

An Analysis of Polishing Forces in Magnetic Field Assisted Finishing

Magnetic field assisted finishing (MAF) is used to polish free-form surfaces. The material removal mechanism can be described as a flexible “magnetic brush” that consists of ferromagnetic particles and abrasives that arrange themselves in the working gap between the magnet and the work piece. Relative motion between the brush and the work piece causes micro-cutting and improves surface finish. In this study, the contributions of the magnetic and polishing force components to the total force were evaluated. The effect of varying the polishing conditions, such as the working gap and the size of the ferromagnetic iron particles, on polishing forces and surface roughness was also analyzed. It was observed that the polishing forces varied considerably with working gap. Also, the iron particle size was found to have a strong relation to the rate at which the surface roughness decreased. Surface area roughness of 2–3 nm was achieved.Copyright