To obtain the accurate evaluation of minimum zone sphericity, this paper investigates a method in Cartesian coordinates using cuckoo search (CS) algorithm. In this method, an appropriate space is set as the search zone according to the solution obtained which is based on least square criteria. The aim of search is to find the best candidate position infinitely approximating the ideal reference center of minimum zone sphere. In order to improve the search efficiency, two essential parameters in CS, namely the control coefficient α of step size and the probability pa of discovering an invasive cuckoo's egg are set to 0.618 (value of golden ratio) and 0.05 (common value of statistical significance), respectively. The updating of the candidate points is carried out by Levy flights and biased/selective random walk mechanisms. Levy flights mechanism can ensure the real global optimum is not missed, biased/selective random walk mechanism guarantee the diversity of search direction and adaptability of search step size. During the updating, the new solution can be kept when it is better than the old one. In each search iteration, the position which corresponds to the smallest sphericity is regarded as the present optimum solution. When the iteration terminal condition is satisfied, the optimum position and corresponding sphericity are output as evaluation results. The validness of the proposed CS algorithm was tested by an application example, the results indicate that the proposed method has the advantage of excellent convergence and high efficiency, which is suitable for the hith-precision evaluation of minimum zone sphericity efficiently.
In order to solve boundary effect for non-closed circular profile with conventional Gaussian filter, two modified Gaussian filters based on odd and even functions are put forward. By extending original profile data on the boundary effect area, the sampling information on the boundary effect area of non-closed circular profile can be used fully, and then open-loop Gaussian filter is used for filtering. The validity of two designed filters was tested by numerical simulation and experiment. The results demonstrate that the modified Gaussian filter based on even function is more effective to reduce boundary effect than that based on odd function.
With the fast development of the advanced equipment manufacturing toward precision and ultra-precision trend, especially with the continuously improving of the aviation engine’s performance, the problem of high displacement resolution for the large-load two-dimension adjusting and positioning worktable used for the aeroengine assembling become evident. A method was proposed which is based on the invariable restoring force, and the adjusting and positioning physical model was established. The experiment results indicate that under the occasion of a load with 508 kilogram, the worktable has got a displacement resolution of 0.3μm after using the improved method compared to 1.4μm of the traditional method. The improved method could meet the requirements of aviation engine assembling worktable.
Static and dynamic calibration methods of sensor system used in ultra-precision form measuring instrument are investigated. The nonlinear error of sensor system are corrected through static calibration, and the nonlinear characteristic of sensor system is obtained with a piezo nanopositioning stage, then the nonlinear characteristic is stored in a computer in the form of error correction function, while the sensor system works, according to the established error correction function, corrected value of nonlinear error that correspond to the measured point is to be taken out automatically, and the actual measurement data could be compensated by real-time, namely, the dynamic compensation model for nonlinear error could be established. Especially, if the position of measurement data point is not the same as that pre-stored in computer, corrected value could be obtained using linear interpolation. Dynamic calibration of sensor system is performed using the elliptical standards, and in this case the calibration status of sensor system is consistent with its normal measurement status.
PTB and the HIT Institute UOI (Center of Ultra-precision Optoelectronic Instrument) have developed special error
separation procedures for improving the measurement uncertainty of cylinder calibrations. Three glass cylinders, which
were custom-made by HIT, were selected to compare the performance and characteristics of the measurement
procedures. Both procedures effectively eliminate guidance errors of the measurement machines and lead to sufficiently
low measurement uncertainties.
All solid-state flash-lamp pumped passive-active mode-locked Nd3+:YAG laser is designed and experimentally studded.
Saturation absorber Cr4+:YAG with initial transparency 25 and 47% are used as a passive Q-switcher and acousto-optical
fused quartz modulator as an active mode-locker. Efficient length of the laser cavity with fixed mirror positions (1.45 m
spaced) is droved by changes of 100% flat mirror for concave mirrors with different focus lengths. Changeable output mirrors
with transparencies of 15 and 50% are used. Driving of the cavity parameters, laser and acousto-optical modulator power
supply voltages let us to control output pulse train and single pulse parameters. As it goes from the analyses of oscillograms
fixed with pyroelectric detector (τ=0.5 ns) and 1 GHz oscilloscope, over 95% of pulse output energy has been mode-locked.
Average duration of the pulse train envelope of 5 to 50 single pulses at FWHM has been droved within 50 to 600 ns. When
this single pulse duration is controlled but did not exceed 2 ns.
Mastering of the middle IR range is attractive for many applications, such as lidar gas analyzers, optoelectronic
countermeasures for suppression of IR detecting, optical communication systems, and scientific and medical instrument.
However, until now this has been held back by the lack of commercial coherent radiation sources with necessary energy
parameters and efficiency. AgGa1-xInxSe2 and Hg1-xCdxGa2S4 are well-known middle IR crystal families introduced in
recent years. The main advantage of them is that their physical properties including refractive indices and birefringence
can be engineered by varying the contents of Ga, In, Cd and Hg. Consequently, the phase matching range can be
extended and the 90° non-critical phase matching in three-wave interaction can be realized within a certain wavelength
band. In consideration of influence of composition ratio, acceptable composition ratio and group velocity mismatch of
ultra-short pulses on nonlinear properties of AgGa1-xInxSe2 and Hg1-xCdxGa2S4 are investigated for the first time. The
corresponding phase-matching diagrams and spectral dependence of the acceptable composition ratio on wavelengths for
second harmonic generation and optical parametric oscillation pumped by the popular Nd3+:YAG (1.06 &mgr;m) and
Ho3+:ILF (2.08 &mgr;m) lasers are estimated and demonstrated with accounting of available Sellmeier coefficients. Group
velocity matching for second harmonic, optical parametric generation under the pump of the two lasers in AgGa1-xInxSe2
and Hg1-xCdxGa2S4 are carried out as well. All relative results are compared and analyzed within a number of sampling
values or continuum of composition ratios. In addition, the utilities of AgGa1-xInxSe2 and Hg1-xCdxGa2S4 for second
harmonic generation are also discussed finally.
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