3,776 research outputs found
Harmonic drive gear error: Characterization and compensation for precision pointing and tracking
Imperfections and geometry effects in harmonic drive gear reducers cause a cyclic gear error, which at a systems level, results in high frequency torque fluctuations. To address this problem, gear error testing was performed on a wide variety of sizes and types of harmonic drives. It was found that although all harmonic drives exhibit a significant first harmonic, higher harmonics varied greatly with each unit. From life tests, small changes were found in harmonic content, phase shift, and error magnitude (on the order of .008 deg peak-to-peak maximum) occurred for drives with many millions of degrees of output travel. Temperature variations also influenced gear error. Over a spread of approximately 56 C (100 F), the error varied in magnitude approximately 20 percent but changes in a repeatable and predictable manner. Concentricity and parallelness tests of harmonic drive parts resulted in showing alignment influence gear error amplitude. Tests on dedoidaled harmonic drives showed little effect on gear error; surprisingly, in one case for a small drive, gear error actually improved. Electronic compensation of gear error in harmonic drives was shown to be substantially effective for units that are first harmonic dominant
Pollen Collection From Alsike Clover by High and Low Alfalfa Pollen Collecting Lines and by a Commercial Line of Honey Bees
The collection of alsike clover pollen by high alfalfa pollen collecting (APe) and low alfalfa pollen collecting lines of honeybees and by bees from commercial colonies were compared at Donnelly, Idaho, U.S.A., in an area where alsike clover was flowering. All three lines collected an overwhelmingly high percentage of alsike clover pollen (92-99 %), and there were no significant differences between them. A limited amount of rape pollen was collected every day by all groups, and also a small amount of dandelion pollen on one or two days. Only one (high APC) colony collected pollen from a small nearby field of alfalfa, and only one (low APC) colony collected pollen from scattered patches of Senecio spp
Supersymmetric Laser Arrays
The theoretical framework of supersymmetry (SUSY) aims to relate bosons and
fermions -- two profoundly different species of particles -- and their
interactions. While this space-time symmetry is seen to provide an elegant
solution to many unanswered questions in high-energy physics, its experimental
verification has so far remained elusive. Here, we demonstrate that, notions
from supersymmetry can be strategically utilized in optics in order to address
one of the longstanding challenges in laser science. In this regard, a
supersymmetric laser array is realized, capable of emitting exclusively in its
fundamental transverse mode. Our results not only pave the way towards devising
new schemes for scaling up radiance in integrated lasers, but also on a more
fundamental level, they could shed light on the intriguing synergy between
non-Hermiticity and supersymmetry
A selected history of expectation bias in physics
The beliefs of physicists can bias their results towards their expectations
in a number of ways. We survey a variety of historical cases of expectation
bias in observations, experiments, and calculations.Comment: 6 pages, 2 figure
Significant elastic anisotropy in TiAlN alloys
Strong compositional-dependent elastic properties have been observed
theoretically and experimentally in TiAl N alloys. The elastic
constant, C, changes by more than 50% depending on the Al-content.
Increasing the Al-content weakens the average bond strength in the local
octahedral arrangements resulting in a more compliant material. On the other
hand, it enhances the directional (covalent) nature of the nearest neighbor
bonds that results in greater elastic anisotropy and higher sound velocities.
The strong dependence of the elastic properties on the Al-content offers new
insight into the detailed understanding of the spinodal decomposition and age
hardening in TiAlN alloys.Comment: 3 figures, 3 page
- …