1,721,147 research outputs found
Biologically Inspired Joints for Innovative Articulations Concepts
No full textFinal Report for the European Space Agency, activity AO/1-4532/03/NL/MV – ARIADNA ID: 04/640
Multi-cycles deformation modeling of hot forming tools under creep-fatigue regime
No full textHot forming processes (extrusion, die ca
sting and forging) allow the production
of a wide variety of products, both in terms
of worked material and achievable shapes.
However, critical working conditions are involved for the tools subjected to severe thermo-
mechanical loads, thus requiring an accurate design. Among the different classifications
proposed in literature for hot forming die failures, one focus on separating manufacturing
and in service failures. The latter category is additionally split, as proposed by the authors,
in static failure, damage and deformation/deflec
tion failures. Static failure appears after e
reduced number of extruded billets as a consequence of an overload or of a poor initial die
design. Damage and deflection failures are ind
eed induced by the synergic detrimental
action of creep and fatigue phenomenon. In disc
riminating the relative dominant role of
creep and fatigue in leading to the final die discard, the level of temperature and of the
applied load as well as of the dwell-time are d
ecisive. In extrusion, the latter is the time in
which a constant load acts on the die and represents the time required to extruded each
single billet function of both ram speed and billet length. Fatigue and creep can be seen as
limit cases with zero and infinite
dwell-time. A novel model is proposed for the prediction
of the deformation undergone by hot forming t
ools in the creep-fatigue regime after
multiple cycles. The model is presented as applied to extrusion dies and is based on a
modified version of a simple creep law already
implemented in all the FE codes. The model
is validated against small scale dies used
in physical experiments and then against
industrial extrusion dies
Real-Time Direct Position Analysis of Parallel Spherical Wrists by Using Extra Sensors
No full textThe paper presents an algorithm for the real-time evaluation of the actual end-effector orientation of general parallel spherical wrists. Conceptually, the method relies on evidence that the pose of a rigid body is defined once the location of at least two linearly independent vectors attached to the body is known. The location of these vectors of the wrist end-effector is determined by the solution of the direct position analysis of some properly chosen kinematic chains (legs) of the manipulator In order to accomplish this analysis, extra sensors, which measure suitable non-actuated variables of the chosen legs, need to be placed in addition to the ones normally embedded in the servomotors, i.e., the sensors which measure the actuated variables. From a mathematical point of view, the algorithm is built on the polar decomposition of a matrix and has inherent least square features. Thus, together with measurement redundancy, i.e., more sensors (extra sensors) than the mechanism degrees of freedom, the method also makes it possible to minimize the influence of both round-off and measurement errors on the estimation of the location of the wrist end-effector The method is general but, in order to prove its effectiveness, without loss of generality it has been customized to the solution of the 3(UPS)-S fully parallel wrist architecture (where U, P and S are for universal, prismatic and spherical joint, respectively). Comparison of the proposed method, in both its general and specialized form, with others from the literature is provided
Accurate and Fast Body Pose Estimation by Three Point Position Data
No full textThe paper presents an algorithm for estimating the pose of a rigid body in real-time. The method relies on the measurement of the location of three body points and minimizes the influence of measurement errors on the estimate. The method is applied to the solutions of the direct position analysis of the Stewart platform manipulator of type 6-3 and of the fully parallel spherical wrist. Comparison with other methods shows that the proposed algorithm performs better in terms of estimate accuracy and computation. © 2006 Elsevier Ltd. All rights reserved
Kinematic analysis of partially decoupled fully-parallel manipulators of type 5-5 and 4-5
No full textThis paper presents two fully parallel manipulators of
type 5-5 and 4-5 with special geometry that makes them
partially decoupled. The direct kinematic analysis and
the singularity study of these manipulators are addressed,
which show that the motion of the manipulators can be
easily controlled. Computational considerations are reported,
which demonstrate that the algorithms proposed for the direct
kinematic analysis are very efficient. Moreover, a comparison
with other special geometries illustrates that the proposed
manipulators are valuable solutions and represent a good
compromise between an efficient controllability and a simple
practical feasibility
Extrusion of Magnesium Hollow Profiles for Automotive Applications
No full textThe use and adoption of magne
sium extruded profiles in
structural application is
limited because magnesium extrusion technology is at its first. Once extruded hollow
sections will be available at
a reasonable cost, a tremendous in
crease of market demand is
going to be expected due to the lowest weight of the magnesium alloys in comparison with
aluminum based ones. The press productivity re
present a key factor in this scope and the
die, due to the strong incidence of strain
and temperature in the extrudability, will play a
basic role to achieve the required stem
speed. This paper present a new approach for
designing extrusion dies specifically for
magnesium alloy ZM21 by means of FEM
simulation. The goodness of the new design has
been validated extruding an hollow profile
using an industrial press with data logging
Validazione del codice Qform per l’analisi del processo di estrusione di leghe di alluminio
No full textScopo del presente lavoro è stato qu
ello di validare un codice FEM di nuova
generazione, QForm®, per
giungere all’
implementazione di una user-routine per la
previsione dell'evoluzione micr
ostrutturale durante
processi di deform
azione plastica, in
particolare di estrusione. È stata quindi c
ondotta una campagna preliminare di simulazioni
al fine di validare i modelli di
attrito disponibili nel codice
così come le condizioni di
scambio termico e i parametri che influenzano
la discretizzazione
della maglia e il
processo. I risultati numerici sono stati co
nfrontati con indagini sperimentali di
visioplasticità riportate in letteratura [1] in te
rmini di griglie di deformazione, andamento
corsa-carico sul pistone, temperature d
el profilo estruso e della matrice. La
determinazione del mod
ello ottimale di attrito e dei suoi
fattori caratterizzanti, reso
possibile dal confronto
numerico-sperimentale,
ha permesso in seguito l’implementazione
di una routine per la previs
ione dell'evoluzione micros
trutturale nel
codice Qform
Real-time direct position analysis of parallel spherical wrists by using extra sensor data
No full text- …
