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The optimum selection of a structure for a given application is a capital phase in typological synthesis of parallel robots. To help in this selection, this paper presents a performance evaluation of four translational parallel robots: Delta, 3-UPU, Romdhane-Affi-Fayet, and Tri-pyramid (TP). The problem is set as a multiobjective optimization using genetic algorithm methods, which uses kinematic criteria, that is, global dexterity and compactness, to ensure a prescribed workspace. The results are presented as Pareto fronts, which are used to compare the performances of the aforementioned structures. The obtained results show that the TP robot has the best kinematic performance, whereas the 3-UPU robot is the most compact for a given prescribed workspace.
Serial spherical linkages have been used in the design of a number of robots for minimally invasive surgery, in order to mechanically constrain the surgical instrument with respect to the incision. However, the typical serial spherical mechanism suffers from conflicting design objectives, resulting in an unsuitable compromise between avoiding collision with the patient and producing good kinematic and workspace characteristics. In this paper, we propose a multi-robot system composed of two redundant serial spherical linkages to achieve this purpose. A multi-objective optimization for achieving the aforementioned design goals is presented first for a single redundant robot and then for a multi-robot system. The problem of mounting multiple robots on the operating table as well as the way cooperative actions can be performed is addressed. The sensitivity of each optimal solution (single-robot and multi-robot) to uncertainties in the design parameters is investigated.
The rheological and filtration properties of a Tunisian clay are presented and compared with those of Wyoming bentonite. The study was part of an evauation of Tunisian mining resources in general, and of the bentonitic deposits in particular. Qualitatively, the two clays exhibit the same rheological and filtration behaviour but quantitatively the properties of purified Wyoming bentonite are distinctly better at the same concentration. The difference can be related to the mineralogical structure and the presence of 13% illite in the Tunisian clay. Standard tests show that the rheological behaviour of the purified Tunisian clay is close to that of the raw Wyoming bentonite and conform to the American Petroluem Institute (A.P.I.) standards for medium-depth drilling formulations.
This paper introduces the design and the optimization of a probe holder robot for tele-echography applications. To define its kinematic architecture, an approach based on motion capture of an expert's gestures during ultrasound examinations was proposed. The medical gestures analyzed consisted of ultrasound probe movements and were used to characterize the kinematic specifications of the proposed manipulator. The selected architecture was a Spherical Parallel Mechanism (SPM) with 3 degrees of freedom (DoF) and its optimal synthesis was performed using real-coded Genetic Algorithms (GA). The optimization criteria and constraints were established thanks to the collaboration of medical experts and were successively formulated and solved using mono-objective and multi-objective functions.
The objective of this article is to present the dimensional synthesis of serial and
parallel spherical wrists, an important step in the design process of medical robots. This
step is carried out to obtain optimal dimensions of tool-guidance medical robots. With
this goal, we have first studied the specifications of two robots with different medical
applications: one for tele-echography examination and one for minimally invasive surgery.
Then, we have established that the medical needs expressed by the doctors were very
different but the specifications in robotic terms have a lot of common points (kinematics,
workspace, bulkiness). For both applications studied, robots need a mobility of three
rotations around a fixed point (probe contact point on the patient’s skin or trocar
incision). So, a spherical wrist architecture is adapted to their needs. An important
constraint related to medical applications is that the robot must be compact in order to
not obstruct or collide with its environment (medical personnel or patient). We perform
dimensional synthesis allowing determination of dimensions of the mechanism for serial and
parallel spherical wrists, for a tele-echography robot, and a serial wrist for a minimally
invasive surgery robot. We use multi-criteria optimization methods minimizing a cost
function to obtain both good kinematic performance and compactness for the architecture.
The difficulty/challenge of this design process, depending of the studied applications, is
the choice of efficient criteria describing the performances and the constraints of the
robot. The design variables must faithfully represent the specifications of the robot so
that its performance can respond to the medical requirements. We show, here, the different
methods used for optimizing the chosen kinematic architecture for the particular medical
application. These studies lead to prototypes which are validated after medical
experiments. This process of dimensional synthesis will be applied to other medical
applications with different sets of specified constraints.
The behaviour of clays is not still well understood. Most information
concerning clays has been obtained by techniques which give statistical
information on the structure and chemistry. However papers have reported
results from scanning and high resolution electron microscopy. This work
presents a nanoscopic approach, using electron energy loss spectroscopy
(EELS), of different purified clays. EELS permitted to detect all the
elements found by classical chemistry at a macroscopic level. In particular
it made it possible to determine the Si/Al ratio in kaolinite (Si/Al ~ 1), smectite and illite (Si/Al ~ 2). In all the cases, the K edge
oxygen energy loss near edge structure (ELNES) is often similar to that of
other clays we studied, but a strong heterogeneity has been observed. It was
also possible to highlight an influence of the presence of iron on the
profile of the oxygen peak.
The opto-electronic properties of CuInSe2 and related compounds depend on their defect chemistry in a way that is far from being understood and in which ab initio calculations could help by providing new insights as shown previously. Ab initio calculations of energy and electronic structure of various intrinsic (including defect pairs) and extrinsic (including potential dopants such as Zn) point defects have been performed in the chalcopyrite semiconductors CuInSe2, some of them being computed for the first time by advanced ab initio techniques. The method used is based on the density functional theory within the framework of pseudo-potentials and plane waves basis set. The results are discussed in view of the existing data, models and calculations.
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