Autocollimator Research Articles

Calibration method of the right-angle error of a hollow corner-cube retroreflector based on an independent autocollimator.

Hollow corner-cube retroreflectors (HCCRs) are an essential reflection component of next-generation lunar laser-ranging technology. The verticality among the three reflectors, known as the right-angle error, is a critical parameter that affects the emission performance, and thus, should be correctly measured and calibrated. However, conventional methods measure the three right-angle errors separately, which can induce error superposition during the measurement process. A one-time measurement method was developed for the three right-angle errors of the HCCR using a single autocollimator (AC). The method establishes a mathematical relationship between the right-angle error of the HCCR and the angle offset of the reflected beam, and it considers the observation coordinates of the AC simultaneously to perform the coordinate transformation of the relationship parameters. The corresponding measurement equation was derived to extract the three-plane right-angle error of the HCCR using the measured readings of a single AC. In addition, a HCCR was designed to freely adjust the angle of the two reflective surfaces and used to simulate the different states of the three right-angle errors in practice. The measurement results show that the root-mean-square error of the proposed method in all right-angle error states is smaller than 16 ' ' .

Characterized environmental influences on autocollimator measurement uncertainty using an extended Allan variance

Autocollimators play an important role in the high-precision testing of the slope errors of X-ray and large flat mirrors. However, the time-varying errors caused by environmental changes exhibit different characteristics over time, such as low-frequency drift errors and high-frequency random errors. Time-varying errors can seriously affect the accuracy of the autocollimator (AC) and the read repeatability. They have become important factors limiting the continued improvement of nano-optic-measuring machines and scanning pentaprism system accuracy. Considering the difficulty in quantitatively analyzing the influence of time-varying errors on the measurement uncertainties of the AC, this paper proposes the extended Allan variance to characterize environmental influences on the AC measurement uncertainty based on a point-wise scanning measurement mode. Taking advantage of the extended Allan variance's characteristics, which allow the identification of various errors and provide stability information about the AC measurement, the characteristic curves of the AC measurement uncertainty in a specific environment were obtained. Based on the characteristic curve parameters, the ultimate accuracy of AC in the current environment was obtained by optimizing the measurement strategy. Experimental results show that the measurement uncertainty of the AC can reach 2.3 nrad RMS in the measurement time-domain window.

Autocollimation angle-measurement method with a large range based on spot deformation.

A novel hollow cylindrical cube-corner reflector (HCCCR) for the autocollimator (AC) is proposed. The angle measuring range of AC will be effectively increased by using the parallel propagation characteristics of the reflected light and the incident light in local area of this reflector. And the yaw and pitch angles of HCCCR will be measured through the morphological changes of the reflected beam. The experimental results show that the measuring range of the autocollimation angle measurement method is extended from ±30' to ±30°, and the dynamic measurement distance is 0.2∼5m, the measurement accuracy of pitch angle and yaw angle is better than 69" and 51", respectively.

Roll angle autocollimator measurement method based on a cylindrical cube-corner reflector with a high resolution and large range.

A novel high-resolution and large-range autocollimator measurement system for roll angle is proposed. The system retains the basic internal structure of the traditional autocollimator (AC), which only uses a novel non-standard cylindrical cube-corner reflector (CCCR) instead of the planar reflector. In the article, the mathematical relationship between the structure of this special reflector and the spatial coordinate vector change of the reflected beam is deduced, and the measurement formula of the roll angle autocollimator (RAC) measurement system is established based on this mathematical relationship. The effectiveness of the measurement system and method is verified by experiments. Experimental results show that this method can effectively enhance the range to ±20°, and the whole measurement accuracy is 6.1", the measuring resolution is 1".

Improved performance of a refurbished photoelectric autocollimator

An old photoelectric Hilger & Watts autocollimator (AC) has been modified at INRIM to perform accurate angle measurements on two axes in a range of ±250″. A CMOS camera was placed in the focus of the AC’s optical system and a software implemented in LabVIEW processes on-line the image of the reticle projected on the camera. The data acquisition is triggerable at a selectable frequency up to some hertz to allow synchronization in critical applications. The AC’s sensitivity was determined through a calibration with respect to the national angle standard. The combined standard uncertainty of the AC calibration results to be equal to 0.035″.

Super-resolution surface slope metrology of x-ray mirrors.

We present experimental, analytical, and numerical methods developed for reconstruction (deconvolution) of one-dimensional (1D) surface slope profiles over the spatial frequency range where the raw data are significantly perturbed due to the limited resolution of the measurement instrument. We characterize the spatial resolution properties of a profiler with the instrument's transfer function (ITF). To precisely measure the ITF, we apply a recently developed method utilizing test surfaces with 1D linear chirped height profiles of constant slope amplitude. Based on the results of the ITF calibration, we determine parameters of an analytical model for the ITF that is used in the original reconstruction software. Here, we treat surface slope metrology data obtained with the Optical Surface Measuring System (OSMS), using as a sensor an electronic autocollimator (AC) ELCOMAT-3000. The spatial resolution of the OSMS is limited by the size of the AC light-beam-collimating aperture. For the purposes of this investigation, the OSMS is equipped with a circular aperture with a diameter of 2.5 mm. This is a typical arrangement of most AC-based slope profilers developed for surface slope metrology of state-of-the-art x-ray mirrors. Using the example of surface slope metrology of two state-of-the-art elliptically shaped x-ray focusing mirrors, we demonstrate that the developed data reconstruction procedure allows us to significantly improve the accuracy of surface slope metrology with the OSMS over the spatial wavelength range from ∼1.6 mm to 7 mm. Thus, the amplitude of the quasi-periodic error characteristic of the deterministic polishing process used appears to be higher by a factor of ∼2 than is apparent from the rough metrology data. Underestimation of the surface slope errors in this spatial wavelength range can lead to serious errors in the expected performance of x-ray mirrors in synchrotron beamlines, especially at modern light sources utilizing coherent x rays, where the perturbations can lead to increased speckle-like intensity variation.

Small-sized two-coordinate digital autocollimator

Small-sized two-coordinate digital autocollimator

Note: Autocollimation with ultra-high resolution and stability using telephoto objective together with optical enlargement and beam drift compensation.

An autocollimation (AC) setup with ultra-high resolution and stability for micro-angle measurement is presented. The telephoto objective, which is characterized in long focal length at a compact structure size, and the optical enlargement unit, which can magnify the image displacement to improve its measurement resolution and accuracy, are used to obtain an ultra-high measurement resolution of the AC. The common-path beam drift compensation is used to suppress the drift of measurement results, which is evident in the high-resolution AC, thus to obtain a high measurement stability. Experimental results indicate that an effective resolution of better than 0.0005 arc sec (2.42 nrad) over a measurement range of ±30 arc sec and a 2-h stability of 0.0061 arc sec (29.57 nrad) can be achieved.

A METHOD FOR SELF-CALIBRATION IN SATELLITE WITH HIGH PRECISION OF SPACE LINEAR ARRAY CAMERA

At present, the on-orbit calibration of the geometric parameters of a space surveying camera is usually processed by data from a ground calibration field after capturing the images. The entire process is very complicated and lengthy and cannot monitor and calibrate the geometric parameters in real time. On the basis of a large number of on-orbit calibrations, we found that owing to the influence of many factors, e.g., weather, it is often difficult to capture images of the ground calibration field. Thus, regular calibration using field data cannot be ensured. This article proposes a real time self-calibration method for a space linear array camera on a satellite using the optical auto collimation principle. A collimating light source and small matrix array CCD devices are installed inside the load system of the satellite; these use the same light path as the linear array camera. We can extract the location changes of the cross marks in the matrix array CCD to determine the real-time variations in the focal length and angle parameters of the linear array camera. The on-orbit status of the camera is rapidly obtained using this method. On one hand, the camera’s change regulation can be mastered accurately and the camera’s attitude can be adjusted in a timely manner to ensure optimal photography; in contrast, self-calibration of the camera aboard the satellite can be realized quickly, which improves the efficiency and reliability of photogrammetric processing.

A METHOD FOR SELF-CALIBRATION IN SATELLITE WITH HIGH PRECISION OF SPACE LINEAR ARRAY CAMERA

Abstract. At present, the on-orbit calibration of the geometric parameters of a space surveying camera is usually processed by data from a ground calibration field after capturing the images. The entire process is very complicated and lengthy and cannot monitor and calibrate the geometric parameters in real time. On the basis of a large number of on-orbit calibrations, we found that owing to the influence of many factors, e.g., weather, it is often difficult to capture images of the ground calibration field. Thus, regular calibration using field data cannot be ensured. This article proposes a real time self-calibration method for a space linear array camera on a satellite using the optical auto collimation principle. A collimating light source and small matrix array CCD devices are installed inside the load system of the satellite; these use the same light path as the linear array camera. We can extract the location changes of the cross marks in the matrix array CCD to determine the real-time variations in the focal length and angle parameters of the linear array camera. The on-orbit status of the camera is rapidly obtained using this method. On one hand, the camera’s change regulation can be mastered accurately and the camera’s attitude can be adjusted in a timely manner to ensure optimal photography; in contrast, self-calibration of the camera aboard the satellite can be realized quickly, which improves the efficiency and reliability of photogrammetric processing.

同轴米散射激光雷达自准直系统设计

同轴米散射激光雷达自准直系统设计

Weak Signal Detection Method in a Stronger Noise Background

When we use the laser auto collimation theodolite to measure the azimuth error angle of air target, the strong noise background reduces the spot imaging quality and seriously influences the measuring angle ability of the theodolite. In order to solve the problem, a photoelectric detection system used to detect the weak signal is designed based the correlation detection principle and the principle of correlation detection technology is introduced. We use Simulink software presenting a simulation to the detection system and do a feasibility analysis. Finally, it’s proved that the photoelectric detection system could suppress the strong noise background, improve the SNR greatly and detect the weak signal effectively.

激光跟踪仪测角误差补偿

As the angle measurement accuracy for a laser tracker affects the instrument measurement accuracy directly,a discrete calibration method for the angle measurement errors of a metal circular grating in the laser tracker was proposed based on an autocollimator combined with a multi-mirror polyhedron.The error compensation method based on harmonic analysis was studied.Then,a compensation model was built up on the basis of the harmonic wave components whose amplitudes are large and phases remain essentially constant,by which the no convergence from least square method was overcome.Futhermore,the calibration uncertainty of angle measurement errors was analyzed.The analysis results show that the horizontal angle measurement accuracy is reduced from 1.60″to0.90″,and the vertical angle from 4.89″to 0.91″after compensation.The accuracy is improved by44%and 81% respectively,and has been from an arc second scale to a sub-arc second scale.The results indicate that the proposed method effectively compensates angle measurement errors forharmonic and vertical axis systems of the laser tracker,and also provides a reference for other error compensation of angle measuring systems.

The Indexing Precision Testing Techniques of Power Tool Rest Cutter Head

The indexing precision of power tool rest cutter head is the prima choice to judge the performance of the tool rest and the test of it is the premise of the tool rest quality. Considering the lack of an effective indexing precision detection method of power tool rest cutter head, the testing methods of the indexing precision of power tool rest cutter head are discussed and an indexing precision testing system based on photoelectric auto collimator is set up. The testing results can show the indexing error of every tool. The studied system of the indexing precision of power tool rest cutter head is suitable for various indexing device to realize dynamic indexing accuracy testing and the system has a high reliability and testing accuracy.

Investigations into the accuracy of angle calibration

Abstract Technical possibilities to create equipment for the calibration of flat angles are discussed in the article. The angular standard measure, the radian, has not been realised as a standard unit until now. Nevertheless, the unit of angular measure in degrees is used as the geometric measure of length in geodesy, machine engineering and other branches of industry – by multiangular prisms – polygons with an autocollimator, rotary tables, circular scales, etc. It should be noted that these angle measures are calibrated against the upper level measures (etalons) only at the several intervals depending on the number of sides (angles) of the polygon or the other standard measure. The methods of calibration of constant angle value in full circle are used as well. At the same time geodetic instruments, rotary tables of metal cutting tools and instruments, rotary encoders have a great number of discrete values. These values between the calibrated points remain unknown during calibration. The information rece...

高精度无导轨位移平台误差分析

The motion accuracy of a platform based on two compensated flexible four-bar linkages was researched and three error sources,namely,batten size error,the sphere center distance error of ratio lever and the assembling angle between the inner and external battens were analyzed.A semi-beam model was established to analyze the deformation of the batten and the relationship between working displacement and coupled displacement.The expressions of the platform straightness error and the limiting coupled displacement error which was concerned with the platform displacement and the batten sizes were derived.Finally,an autocollimator and a high precise measuring head were used in the measurements of the platform straightness and the coupled displacement.The experimental results show that the straightness error is smaller than 1.5″and the coupled displacement error is less than 13.7 μ m when the stroke of the displacement platform is no longer than 5mm.It is proved that the platform works with high motion accuracy and the experimental result is consistent with the analysis results.