Ring Laser Gyroscope (RLG) is a kind of typical inertial device widely used in navigation field. Owing its recent advances, RLG is proposed to be used as angle measuring instrument with highly dynamic performance and loose installation requirement. To prove the reliability of RLG’s angular measuring result, the metrological performance of RLG was analyzed through calibration. A new calibration method was studied to separate RLG’s additional error resource such as bias drift. The special calibrating procedure was designed and the corresponding calibration system was set up. The calibration result shows that the RLG angular measuring system has measuring deviation within ±0.4″ and repeatability within ±0.2″. The study proposes an effective calibration method of RLG’s metrological performance and proves the possibility of RLG’s application in high accuracy in-situ metrology field.
The self-calibration method for angle measurement is introduced, and the optimal arrangement of several equal distance
distribution groups of reading heads was proposed to realize highly effective restraint of the specified Fourier
components of angular measuring deviation in loosely restricted environment. Base on this method, a self-calibration
angle encoder system was developed using micro reading heads, glass scale disc, air bearing, and multi-channel counter.
According the method of examination of the angular measuring standard, the metrological performance of the system
was evaluated using national angle standard of China. The evaluation result revealed that the measuring deviation is
within ±1.5″, the measuring repeatability is less than 1.1″. Referring to the verification scheme of measuring
instrument for plane angle, the system can be used to calibrate the angular measuring instrument with max permissible
error worse than ±4.5″in situ.
At National Institute of Metrology, China (NIM), a portable and real-time self-calibration angle encoder was developed to meet the requirement of angular measurement with high accuracy, high speed, and high adaptability in limited size. In the development, the special arrangement of reading heads, the structure of bearing was designed base on the novel selfcalibration method, and the corresponding signal acquisition and processing system was set up with capability of high speed and multi-channel synchronous data acquisition and processing. The max rotary speed of this angle encoder gets 18 r/min (110°/s) in real-time mode. This angle encoder was compared with NIM’s primary angle standard. The calibration result shows that this angle encoder has angle measuring accuracy better than ±4″.
The angle measurement technology is very important in precision manufacture, optical industry, aerospace, aviation and navigation, etc. Further, the angle encoder, which uses concept ‘subdivision of full circle (2π rad=360°)’ and transforms the angle into number of electronic pulse, is the most common instrument for angle measurement. To improve the accuracy of the angle encoder, a novel self-calibration method was proposed that enables the angle encoder to calibrate itself without angle reference. An angle deviation curve among 0° to 360° was simulated with equal weights Fourier components for the study of the self-calibration method. In addition, a self-calibration algorithm was used in the process of this deviation curve. The simulation result shows the relationship between the arrangement of multi-reading heads and the Fourier components distribution of angle encoder deviation curve. Besides, an actual self-calibration angle encoder was calibrated by polygon angle standard in national institute of metrology, China. The experiment result indicates the actual self-calibration effect on the Fourier components distribution of angle encoder deviation curve. In the end, the comparison, which is between the simulation self-calibration result and the experiment self-calibration result, reflects good consistency and proves the reliability of the self-calibration angle encoder.
At the National Institute of Metrology, China, the national level standard was established for calibrating the level measuring instruments widely used in the field of surveying, construction and engineering. As a key technology in the development, an auto collimation system was set up to compare the level under test with the water level. In the auto collimation system, a charge-coupled device (CCD) camera was set up to acquired the image of a light spot reflected from the water surface and the plane mirror, a composite image processing and analyzing algorithm was designed to find the exact position of the light spot in the image. This target localization algorithm consists of sub-algorithm of background de-noising, dimension transforming, and curve fitting. The experiments prove that this algorithm get resolution of 0.002″, and repeatability of 0.01″.
Gear measuring machine is a specialized device for gear profile, helix or pitch measurement. The classic method for gear measurement and the conventional gear measuring machine are introduced. In this gear measuring machine, the Abbe errors arisen from the angle error of guideways hold a great weight in affection of profile measurement error. For minimize of the Abbe error, a laser measuring system is applied to develop a high accurate gear measuring machine. In this laser measuring system, two cube-corner reflectors are placed close to the tip of probe, a laser beam from laser head is splited along two paths, one is arranged tangent to the base circle of gear for the measurement of profile and pitch, another is arranged parallel to the gear axis for the measurement of helix, both laser measurement performed with a resolution of 0.3nm. This approach not only improves the accuracy of length measurement but minimize the Abbe offset directly. The configuration of this improved measuring machine is illustrated in detail. The measurements are performed automatically, and all the measurement signals from guide rails, rotary table, probe and laser measuring system are obtained synchronously. Software collects all the data for further calculation and evaluation. The first measurements for a gear involute artifact and a helix artifact are carried out, the results are shown and analyzed as well.
In order to calibrate a high precision rotary table, a calibration system was established to measure the position error and repeatability of rotary table. The position error was measured with a polygon, an index table and an autocollimator to separate the angular error of the polygon from the position error of the rotary table, and the position error of rotary table was calculated using least square method. The rotary table was compensated and calibrated with the position error measured. The repeatability of the rotary table established through 10 times full circle rotations was 0.02 arc second. The measurement results indicated that the combination calibration method was suitable for the calibration of a high precision rotary table. It was found through the analysis that the angular measurement uncertainty was 0.08 arc second.
An angle interferometer was set up using concept ‘ratio of two lengths’ and an angle encoder was set up using concept ‘subdivision of full circle (2π rad=360°)’ at the National Institute of Metrology, China (NIM). For the analysis of the systematic errors of each device, two autocollimator calibration systems were separately set up based on the angle interferometer and the angle encoder with a similar measuring uncertainty (around 0.1″). An autocollimator was calibrated using two systems in the same measurement range (±1000″) and the same measurement step (10″). The systematic errors of each system were found through comparison between their original calibration results. The compensation curves were calculated using the analysis results, and two systems’ original calibration results were compensated according to two systems’ compensation curves. The maximum difference between the compensated calibration results of two systems was 0.05″ which is lower than measuring uncertainty of each system.