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971.
972.
Uncertainty analysis and allocation of joint tolerances in robot manipulators based on interval analysis 总被引:1,自引:0,他引:1
Many uncertain factors influence the accuracy and repeatability of robots. These factors include manufacturing and assembly tolerances and deviations in actuators and controllers. The effects of these uncertain factors must be carefully analyzed to obtain a clear insight into the manipulator performance. In order to ensure the position and orientation accuracy of a robot end effector as well as to reduce the manufacturing cost of the robot, it is necessary to quantify the influence of the uncertain factors and optimally allocate the tolerances. This involves a study of the direct and inverse kinematics of robot end effectors in the presence of uncertain factors. This paper focuses on the optimal allocation of joint tolerances with consideration of the positional and directional errors of the robot end effector and the manufacturing cost. The interval analysis is used for predicting errors in the performance of robot manipulators. The Stanford manipulator is considered for illustration. The unknown joint variables are modeled as interval parameters due to the inherent uncertainty. The cost-tolerance model is assumed to be of an exponential form during optimization. The effects of the upper bounds on the minimum cost and relative deviations of the directional and positional errors of the end effector are also studied. 相似文献
973.
Deterioration of concrete or reinforcing steel through excessive contaminant concentration is often the result of repeated
wetting and drying cycles. At each cycle, the absorption of water carries new contaminants into the unsaturated concrete.
Nuclear Magnetic Resonance (NMR) is used with large concrete samples to observe the shape of the wetting profile during a
simple one-dimensional wetting process. The absorption of water by dry concrete is modelled by a nonlinear diffusion equation
with the unsaturated hydraulic diffusivity being a strongly nonlinear function of the moisture content. Exponential and power
functions are used for the hydraulic diffusivity and corresponding solutions of the diffusion equation adequately predict
the shape of the experimental wetting profile.
The shape parameters, describing the wetting profile, vary little between different blends and are relatively insensitive
to subsequent re-wetting experiments allowing universal parameters to be suggested for these concretes.
Résumé La détérioration du béton ou du béton armé à travers la concentration excessive de contaminant est souvent le résultat de cycles humides et secs répétés. A chaque cycle, l'absorption de l'eau amène de nouveaux contaminants à l'intérieur du béton non saturé en eau. Pour observer le profil du processus d'humidification, on peut utiliser la Résonance Magnétique Nucléaire (RMN) sur de grands échantillons de béton dans le cadre d'une simple étude unidimensionnelle de ce profil. Il est démontré que l'absorption d'eau par du béton sec peut être précisément modélisée par une équation de diffusion non linéaire où la diffusivité hydraulique non saturée est fonction hautement non linéaire de l'humidité du contenant. Des fonctions exponentielles et puissances peuvent définir la diffusivité hydraulique. Les solutions résultant de l'équation modélisant cette diffusion permettent de prédire avec précision la forme du profil de l'humidification expérimentale. Les paramètres de forme qui décrivent le profil de l'humidification varient peu entre les différents mélanges de béton et sont relativement insensibles à des expériences de réhumidification ultérieures. Cela permet de suggérer que ces bétons suivent des paramètres d'humidification universels.相似文献
974.
R. Meyer Hilde Hardtdegen R. Carius D. Grützmacher M. Stollenwerk P. Balk A. Kux B. Meyer 《Journal of Electronic Materials》1992,21(3):293-298
This paper presents a study of the structural and optical properties of strained GaInAs/ InP multiple quantum well (MQW) structures
fabricated by LP-MOVPE. The composition of the Ga
x
In1−x
As films ranged fromx = 0.17 tox = 1.0 and was determined by sputtered neutral mass spectrometry (SNMS) on thick layers. The structures of the MQW samples
with well widths from 1.5 to 5 nm were investigated by high resolution x-ray diffraction (HR-XRD). Simulations of the diffraction
patterns showed that transition layers of approximately 2 monolayer (ML) thickness with high lattice mismatch exist at the
interfaces. Photoluminescence (PL) measurements indicate well widths of a multiple of a monolayer with local variations of
one monolayer. The PL peak energies vary smoothly with the Ga concentration. These results were confirmed by optical absorption
measurements. 相似文献
975.
Microwave transistor amplifier combinations that have controlled frequency response over a specified bandwidth were designed. Theoretical analysis of such an amplifier with an arbitrary number of sections is presented. The response of the amplifier is controlled by tapering the frequency selectivity or Q of each section of the amplifier. To verify the theory, a three-section amplifier with maximally flat time delay response was designed, constructed, and evaluated. Existing traveling-wave amplifiers were modeled as lossy transmission lines. Although the amplifiers were relatively broadband, a prescribed frequency response was not achieved, and each transistor did not receive an equal portion of the signal power. Resistive elements were required for impedance matching at the input and output. The design seeks to improve on previous techniques by trading bandwidth for controlled gain. By making the transmission line that connects the amplifier sections nonuniform, the frequency response was controlled over the design bandwidth. The designs can easily be implemented using familiar components 相似文献
976.
S. R. Syrtsov V. N. Shut D. A. Il'yushchenko E. L. Gavrilenko 《Journal of Engineering Physics and Thermophysics》2002,75(5):1229-1233
The influence of the parameters of posistor elements and the conditions of their heat exchange on the electrical and dynamic characteristics of a posistor block have been investigated. Good agreement between calculation results and experimental data has been established. 相似文献
977.
978.
Platelet aggregation is known to be inhibited by ethanol, and this has been suggested to be one of the attenuating effects
of ethanol in cardiovascular disease. Recent studies have implicated an inhibition of phospholipase A2 induced arachidonic acid release, since the production of prostanoids that are formed from arachidonic acid and are involved
in the aggregation process has been shown to be diminished by ethanol. Phospholipase A2 is found in platelets in both a cytosolic form, from where it may translocate to the plasma membrane to release arachidonic
acid, and in a secretory form which is released extracellularly upon activition. In the present study, the effect of ethanol
on the secretion of phospholipase A2 and on its activity was determined. It was found that ethanol inhibited trast, the activity of the cytosolic form of phospholipase
A2 was inhibited by ethanol. 相似文献
979.
Rumpel D. Krost G. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1992,80(5):758-764
Applying expert systems (ESs) to power system operation means embedding them in an existing environment which consists of computational facilities (SCADA, EMS) on one side, and the operating staff on the other side. An interface between process data and ES data is required to achieve this goal. For an unambiguous and clear information exchange with and good acceptance by the operators, an approximate natural language dialogue of the ES is desirable. Several approaches to these problems are described 相似文献
980.
D Pang 《Canadian Metallurgical Quarterly》1995,6(2):243-257
The embryogenesis, closure technique, and preoperative preparation of open myelomeningocele are described in this article. Both early and late complications of myelomeningocele closure are discussed with respect to predisposing factors, diagnosis, treatment, and prevention. These complications include worsened neurological level, wound dehiscence, wound infection, cerebrospinal fluid leak, postoperative ileus, symptomatic Chiari malformation, shunt infection, necrotizing enterocolitis, and problems related to kyphectomy. 相似文献