147 research outputs found
Evaluation of servo, geometric and dynamic error sources on five axis high-speed machine tool
Many sources of errors exist in the manufacturing process of complex shapes.
Some approximations occur at each step from the design geometry to the machined
part. The aim of the paper is to present a method to evaluate the effect of
high speed and high dynamic load on volumetric errors at the tool center point.
The interpolator output signals and the machine encoder signals are recorded
and compared to evaluate the contouring errors resulting from each axis
follow-up error. The machine encoder signals are also compared to the actual
tool center point position as recorded with a non-contact measuring instrument
called CapBall to evaluate the total geometric errors. The novelty of the work
lies in the method that is proposed to decompose the geometric errors in two
categories: the quasi-static geometric errors independent from the speed of the
trajectory and the dynamic geometric errors, dependent on the programmed feed
rate and resulting from the machine structure deflection during the
acceleration of its axes. The evolution of the respective contributions for
contouring errors, quasi-static geometric errors and dynamic geomet- ric errors
is experimentally evaluated and a relation between programmed feed rate and
dynamic errors is highlighted.Comment: 13 pages; International Journal of Machine Tools and Manufacture
(2011) pp XX-X
Adaptive Monte Carlo applied to uncertainty estimation in a five axis machine tool link errors identification
Knowledge of a machine tool axis to axis location errors allows compensation
and correcting actions to be taken to enhance its volumetric accuracy. Several
procedures exist, involving either lengthy individual test for each geometric
error or faster single tests to identify all errors at once. This study focuses
on the closed kinematic Cartesian chain method which uses a single setup test
to identify the eight link errors of a five axis machine tool. The
identification is based on volumetric error measurements for different poses
with a non-contact measuring instrument called CapBall, developed in house. In
order to evaluate the uncertainty on each identified error, a multi-output
Monte Carlo approach is implemented. Uncertainty sources in the measurement and
identification chain - such as sensors output, machine drift and frame
transformation uncertainties - can be included in the model and propagated to
the identified errors. The estimated uncertainties are finally compared to
experimental results to assess the method. It shows that the effect of the
drift, a disturbance, must be simulated as a function of time the Monte Carlo
approach. The machine drift is found to be an important uncertainty in sources
for the machine tested
Developments in the understanding and modeling of the agglomeration of suspended crystals in crystallization from solutions
International audienc
BANYAN. IV. Fundamental parameters of low-mass star candidates in nearby young stellar kinematic groups - Isochronal Age determination using Magnetic evolutionary models
Based on high resolution optical spectra obtained with ESPaDOnS at CFHT, we
determine fundamental parameters (\Teff, R, \Lbol, \logg\ and metallicity) for
59 candidate members of nearby young kinematic groups. The candidates were
identified through the BANYAN Bayesian inference method of \citet{2013malo},
which takes into account the position, proper motion, magnitude, color, radial
velocity and parallax (when available) to establish a membership probability.
The derived parameters are compared to Dartmouth Magnetic evolutionary models
and to field stars with the goal to constrain the age of our candidates. We
find that, in general, low-mass stars in our sample are more luminous and have
inflated radii compared to older stars, a trend expected for pre-main sequence
stars. The Dartmouth Magnetic evolutionary models show a good fit to
observations of field K and M stars assuming a magnetic field strength of a few
kG, as typically observed for cool stars. Using the low-mass members of
Pictoris moving group, we have re-examined the age inconsistency problem
between Lithium Depletion age and isochronal age (Hertzspring-Russell diagram).
We find that the inclusion of the magnetic field in evolutionary models
increase the isochronal age estimates for the K5V-M5V stars. Using these models
and field strengths, we derive an average isochronal age between 15 and 28 Myr
and we confirm a clear Lithium Depletion Boundary from which an age of
263~Myr is derived, consistent with previous age estimates based on this
method.Comment: Accepted for publication in Ap
Discovery of the Widest Very Low Mass Binary
We report the discovery of a very low mass binary system (primary mass <0.1
Msol) with a projected separation of ~5100 AU, more than twice that of the
widest previously known system. A spectrum covering the 1-2.5 microns
wavelength interval at R ~1700 is presented for each component. Analysis of the
spectra indicates spectral types of M6.5V and M8V, and the photometric distance
of the system is ~62 pc. Given that previous studies have established that no
more than 1% of very low mass binary systems have orbits larger than 20 AU, the
existence of such a wide system has a bearing on very low mass star formation
and evolution models.Comment: accepted ApJL, 4 page
Discovery of the brightest T dwarf in the northern hemisphere
We report the discovery of a bright (H=12.77) brown dwarf designated SIMP
J013656.5+093347. The discovery was made as part of a near-infrared proper
motion survey, SIMP (Sondage Infrarouge de Mouvement Propre), which uses proper
motion and near-infrared/optical photometry to identify brown dwarf candidates.
A low resolution (lambda/dlambda~40) spectrum of this brown dwarf covering the
0.88-2.35 microns wavelength interval is presented. Analysis of the spectrum
indicates a spectral type of T2.5+/-0.5. A photometric distance of 6.4+/-0.3 pc
is estimated assuming it is a single object. Current observations rule out a
binary of mass ratio ~1 and separation >5 AU. SIMP 0136 is the brightest T
dwarf in the northern hemisphere and is surpassed only by Eps Indi Bab over the
whole sky. It is thus an excellent candidate for detailed studies and should
become a benchmark object for the early-T spectral class.Comment: 4 pages, 3 figures, To be published in November 1, 2006 issue of
ApJL. Following IAU recommendation, the survey acronym (IBIS) was changed to
SIM
WEIRD: Wide-orbit Exoplanet search with InfraRed Direct imaging
We report results from the Wide-orbit Exoplanet search with InfraRed Direct
imaging (WEIRD), a survey designed to search for Jupiter-like companions on
very wide orbits (1000 to 5000 AU) around young stars (120 Myr) that are
known members of moving groups in the solar neighborhood (70 pc). Sharing
the same age, distance, and metallicity as their host while being on large
enough orbits to be studied as "isolated" objects make such companions prime
targets for spectroscopic observations and valuable benchmark objects for
exoplanet atmosphere models. The search strategy is based on deep imaging in
multiple bands across the near-infrared domain. For all 177 objects of our
sample, , , [3.6] and [4.5] images were obtained with
CFHT/MegaCam, GEMINI/GMOS, CFHT/WIRCam, GEMINI/Flamingos-2, and /IRAC.
Using this set of 4 images per target, we searched for sources with red
and colors, typically reaching good completeness
down to 2Mjup companions, while going down to 1Mjup for some targets, at
separations of AU. The search yielded 4 candidate companions with
the expected colors, but they were all rejected through follow-up proper motion
observations. Our results constrain the occurrence of 1-13 Mjup planetary-mass
companions on orbits with a semi-major axis between 1000 and 5000 AU at less
than 0.03, with a 95\% confidence level.Comment: 55 pages, 16 figures, accepted to A
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