Vytautas Giniotis

Optical method for the calibration of raster scales

High quality techniques for the calibration of linear and circular raster scales used in photoelectric transducers and the information-measuring systems of a range of machines and scientific instruments is of particular importance, enabling them to give a more accurate performance. The most significant methods of measurement in this area are discussed in this paper, and a new approach to their calibration is presented. Most methods used for optical measurement scales apply a standard measure of angle or length and use photoelectric devices for the readout. A new half circle method for the calibration of circular scale is described. A novel idea for the measurement of linear and circular raster scales is described, given by the determination of a bias from a straight line and from a circle, respectively. This idea is implemented by applying a Moire fringe conjunction technique and the modification of Moire fringe parameters resulting, expressed by discrete functions, is discussed.

Calibration of precision polygon/autocollimator measurement system

Measuring system of polygon/autocollimator is considered the most accurate widely available means of angle measurement, therefore its accuracy researches are of high importance. In this paper we describe the experiments of both autocollimators and polygon calibration implementing the equipment of average accuracy. The calibration data analysis given allows determining the errors of equipment without implementation of high accuracy reference means of measurement. The results of calibration of both autocollimators and precision polygon are also given in the paper.

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...

Mechatronic means for machine accuracy improvement

The paper deals with the mechatronic means for the accuracy improvement of metal cutting machines, co-ordinate measuring machines, robots, etc. The mechatronic correction means of raster scales, encoders errors and final 3-D position correction of a cutting instrument or touch probe are presented. The technical solutions are given with the application of active materials for smart probes and piezoactuators. A case of calculations for piezoactive raster plates is described together with volumetric control diagrams and the examples of practical implementation.

Creation of a multi-reference-angle comparator

Many geodetic and industrial instruments utilize precise angle determination. Metrological calibration and testing of such devices is very complicated, due to the large number of angular position values generated, and often cannot be accomplished using classical means of angle determination. Therefore a special comparator (test rig) capable of calibration geodetic and other angle-measuring instruments and implementing multiple references for angle determination has been created. Several modernized optical devices were used on the test rig, together with the implementation of a special calibration method. In this paper the construction of the rig, modernization of the optical devices, calibration, and some results of measurements are presented.

Accuracy and performance analysis of digital levels

Optical-electronic leveling devices using a staff with bar codes are discussed. The reading of the staff is taken along its longitudinal axis; the distance to the staff and its vertical position are determined by the readings of a translational transducer connected to the optical system during its focusing on the bars of the staff. The height is determined according to coded signals of the image of the bars transferred into an array of photoelectric cells in the instrument and processed by a microprocessor to the height values. Three main types of image processing are used in various types of digital levels: a correlation method, a geometric method, and a phase method. The correlation functions of measuring and reference codes in the electronic level are calculated in this paper, showing possible errors of height determination. The information obtained during the measurement shows the relationship between the information entropy received from different values of readings from the staff. A new digital level design is proposed, simplifying the design of the instrument and the staff as well. The principal correlation and error determination equations are given, and diagrams of the new design are included.

Analysis of accuracy of measurement by Doppler laser meters

We discuss the accuracy analysis of laser meters based on the Doppler effect and used in the measurement of automobile velocity. Usually, the systematic errors are assessed during calibration and are eliminated by instrumental means. Nevertheless, it is impossible to eliminate random errors. Their analysis is also important for such measurements, and this has been less extensively analyzed in scientific papers. A probabilistic method is used for error analysis assuming that only random errors are present. The accuracy of measurement by Doppler meters depends mostly on parameters of two kinds—laser source stabilization, measuring laser emission frequencies, and the errors in determining the emission speed in the atmosphere. Such analysis shows a value of the random error occurring during the measurement of automobile speed that also can be applied for assessment of other kinds of measurements of moving objects.

The correlation analysis of the angle measurements

Abstract The test bench for testing and calibrating the measuring geodetic instruments for flat angle measurements has been created at Vilnius Gediminas Technical University, Institute of Geodesy. This test rig incorporates multiple‐angular position determination principles ‐ photoelectric angular encoder, polygon‐autocollimator and circular‐scale‐microscope. Such a diversity of implemented methods allows cross‐calibration and testing each principle using the other one. Similarly, there may be multiple methods of testing and cross‐calibration used. The covariation and correlation analysis of the measurement data are received and analysed.

Basic construction of the flat angle calibration test bench for geodetic instruments

In our days precise geodetic instruments are very widely used in geodesy, building structures, surveying, machine engineering etc. Many of those instruments are based on precise measurement of the directions differences (ie measurement of angles). Such instruments are: theodolites, digital theodolites, total stations etc. Testing and calibration of these instruments is quite complicated task, although it is evidently needed. In this paper we present the creation and preliminary research of accuracy of the test bench designed to perform the testing and calibration of such geodetic instruments.

ANALYSIS OF MEASUREMENT SYSTEM AS THE MECHATRONICS SYSTEM

The paper deals with the mechatronic arrangement for angle measuring system application. The objects to be measured are the circular raster scales, rotary encoders and coded scales. The task of the measuring system is to determine the bias of angle measuring standard as the circular scale and to use the results for the error correction and accuracy improvement of metal cutting machines, coordinate measuring machines, robots, etc. The technical solutions are given with the application of active materials for smart piezoactuators implemented into the several positions of angular measuring equipment. Mechatronic measuring system is analysed as complex integrated system and some of its elements can be used as separate units. All these functional elements are described and commented in the paper with the diagrams and graphs of errors and examples of microdisplacement devices using the mechatronic elements.