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11.
Robotic belt grinding has emerged as a finishing process in recent years for machining components with high surface finish and flexibility.The surface machining consistency, however,is difficult to be guaranteed in such a process.To overcome this problem, a method of hybrid force-position control combined with PI/PD control is proposed to be applied in robotic abrasive belt grinding of complex geometries.Voltage signals are firstly obtained and transformed to force information with signal conditioning methods.Secondly, zero drift and gravity compensation algorithms are presented to calibrate the F/T transducer which is installed on the robot end-effector.Next, a force control strategy combining hybrid force-position control with PI/PD control is introduced to be employed in robotic abrasive belt grinding operations where the force control law is applied to the Z direction of the tool frame and the positon control law is used in the X direction of the tool frame.Then, the accuracy of the F/T transducer and the robotic force control system is analyzed to ensure the stability and reliability of force control in the robotic grinding process.Finally, two typical cases on robotic belt grinding of a test workpiece and an aero-engine blade are conducted to validate the practicality and effectiveness of the force control technology proposed. 相似文献
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K.G. McClements 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(4):1443-1452
Detailed in situ studies of magnetic reconnection and particle acceleration, which play a crucial role in the release and redistribution of energy in solar flares, can be performed in tokamak plasmas under conditions resembling those of the flaring solar corona. Recent measurements and modelling of fast particle production during reconnection events in the Mega-Amp Spherical Tokamak (MAST) are described. Specifically, observations in this device of electron acceleration during edge localised modes, and of both ion and electron acceleration during merging-compression plasma start-up, are presented, and possible implications of these studies for particle acceleration in flares are discussed. The results from MAST lend weight to the conjecture that large numbers of ions are accelerated to sub-MeV energies in flares. 相似文献
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Jürgen Blum 《Space Science Reviews》2000,92(1-2):265-278
For a better understanding of the processes which lead to the formation of planetesimals in the early solar nebula, we performed
an extensive series of laboratory experiments. We find that the capture velocities in collisions between spherical grains
are more than one order of magnitude higher than predicted by Chokshi et al (1993). In contrast, irregular grains have no
capture threshold and can be better described by a sticking probability which is typically a few 10%, even for velocities
exceeding 10 m/s. However, adhesion forces between spherical, micron-sized particles match the theoretical predictions very
well, although contact areas and deformations are of the order of inter-atomic distances only. Aggregation experiments in
rarefied turbulent gases reveal the fractal nature of dust aggregates. Mass distribution functions are bell-shaped. Similar
behaviour can be found in aggregation experiments with sedimenting particles. Experiments on collision-induced aggregate compaction
and fragmentation match the numerical simulations by Dominik and Tielens (1997) very well if revised experimental values of
the break-up energy (from our impact experiments) and the rolling-friction force (from our AFM measurements on particle chains)
are used.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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Colangeli L. Mennella V. Brucato J.R. Palumbo P. Rotundi A. 《Space Science Reviews》1999,90(1-2):341-354
One of the main objectives of modern astrophysics is the characterisation of properties and evolution of materials present
in space. Production, processing and analysis of cosmic dust analogues in the laboratory represents a powerful tool to interpret
astronomical observations and to contribute to the solution of puzzling problems which are so far unsolved. In the present
paper we summarize recent results obtained in our laboratory on carbon-based and silicate materials able to simulate various
types of cosmic grains. The laboratory data are applied to discuss the nature of spectral features observed in the interstellar
medium and in comets.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
16.
针对传统电工实验室存在的问题,在分析虚拟仪器的优点基础上,提出了将虚拟信号发生器及频谱分析仪引入实验教学的意义,论述了虚拟仪器在高校电工实验室的可行性和有效性。 相似文献
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Mikhail E. Gushchin Sergey V. KorobkovAlexander V. Kostrov Mikhail V. StarodubtsevAskold V. Strikovsky 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Modulation of whistler waves in a plasma with time-dependant magnetic field perturbations was investigated experimentally. The experiments were performed on large “Krot” device, which was specially designed to study space plasma physics phenomena. It is shown that magnetic field variations on the wave propagation path can lead to splitting of initially continuous whistler wave into the sequence of bursts, whose repetition rate corresponds to magnetic field perturbation period. The frequency inside each burst is changing from its front edge to the back edge. Relative shift of the wave frequency can be as large as the relative magnetic disturbance. Distortion of whistler wave frequency spectrum after its passing through magnetically disturbed areas can be used as a diagnostics for low-frequency magnetic field variations. The applicability of our laboratory results to space plasma is discussed. 相似文献
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Spencer David B. Hogge Charles B. Campbell W. Spencer Sorge Marlon E. Mcwaters S. Rex 《Space Debris》2000,2(3):137-160
Congressional language in the 1998 US Senate Armed Services Committee authorization bill directed ... the Secretary of the (United States) Air Force to undertake a design study of a system that could catalog and track debris down to one centimeter in size out to 1000kilometer in altitude. The US Air Force Research Laboratory, in conjunction with other US National Laboratories and the National Aeronautics and Space Administration (NASA) conducted a study that examined what technical systems and operations would be required to perform such a mission. This paper outlines the study process, details the findings, draws conclusions, and makes recommendations as to what would be needed to develop an optically based system capable of cataloging and tracking small debris in low Earth orbit. 相似文献
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Robert A. Beaudet 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
NASA Planetary Protection Policy requires that Category IV missions such as those going to the surface of Mars include detailed assessment and documentation of the bioburden on the spacecraft at launch. In the prior missions to Mars, the approaches used to estimate the bioburden could easily be conservative without penalizing the project because spacecraft elements such as the descent and landing stages had relatively small surface areas and volumes. With the advent of a large spacecraft such as Mars Science Laboratory (MSL), it became necessary for a modified—still conservative but more pragmatic—statistical treatment be used to obtain the standard deviations and the bioburden densities at about the 99.9% confidence limits. This article describes both the Gaussian and Poisson statistics that were implemented to analyze the bioburden data from the MSL spacecraft prior to launch. The standard deviations were weighted by the areas sampled with each swab or wipe. Some typical cases are given and discussed. 相似文献