Albinas Kasparaitis

A vibration source in comparator

Oscillations of the comparator, which is used for the dynamic calibration of long optical line scales, are analyzed in the paper. The accuracy of determination of the position of optical lines on the scale depends on the velocity of the carriage, which transports the microscope with a CCD camera in relation to the line scale. Oscillations influence the velocity equability, its value, and at the same time the error compo measuring. The base part of the comparator is acted upon by external excitations which come through the foundation and supports, also due to natural frequencies of the comparator set. It is shown in the work that vibration surroundings acting on the comparator have a random character and correspond to the criteria of the normal (Gauss) distribution. It is proved experimentally that preaching amplitudes of measured components of vertical and horizontal oscillations influence the stability of the carriage movement which causes the error of measuring.

Line Scale Calibration in Non-Ideal Measurement Situation

The precision line scale calibration in dynamical mode of operation is considered. A new interferometer-controlled comparator with moving microscope has been developed and optimised in order to reduce both the measurement uncertainty and calibration process duration. Modal analysis performed and measurements conducted of the spatial vibrations of comparator structure revealed that dynamically-induced errors can noticeably contribute to the measurement uncertainty budget. They can be prominently reduced, in particular, by proper improvement and optimisation of the carriage structure and elimination of the dry friction in the carriage drive.

Software based control techniques for precision line scale calibration

A precision line scale calibration method in a dynamic regime enables to gain the calibration throughput and simplify the comparatorpsila s structure and control. However, the errors featured by geometrical deviations, static and dynamic loads as well as temperature induced deformations should be considered and incorporated into uncertainty budget. These errors contain random and systematic components and can be minimized by increasing the accuracy of system design and implementing numerical error compensation methods. The paper discusses advances of precision line scale calibration system design gained by implementing new measurement and software based control techniques.

Dynamic Errors of CMM Probes

Here are proposed methods to evaluate the accuracy of measuring heads (MH) of coordinate measuring machines (CMM). Kinematic touch-trigger, piezoresonant touch-trigger and scanning 3D probes are investigated as the most often being used for the 3D measurements. The dominating errors of kinematic touch-trigger probes are expressed by the polygonal (triangular) characteristics of their kinematics and by random dispersion of the contact forces. These features characterize the piezoresonant touch-trigger probes as well but instability of resonance of the system components are also presented here. Dominating error’s characteristics of the scanning probes consist of the instability of pushing the probe stylus out of the measured surface by dynamical forces. Some mathematical models, space error’s approximation and results of experimental investigation of the measuring heads are presented. It may be used for the improvement of CMM and other measuring equipment.

Research of Influence of Vibrations on Calibration Quality of Line Scale Gauge

The essence of the considered problem is to improve line scale gauge calibration quality by studying vibrations that are induced during the calibration process. To assess the influence of vibrations it is necessary to solve a lot of scientific and technical tasks. Serious difficulties were confronted during the mathematical analysis - development of analytical model and determination of its coefficients. An in-depth analysis of line scale measurement means had to be performed to this aim, because only experimental measurements enabled to estimate the majority of coefficients.

Analysis of Dynamic Method of Line Scales Detection

The main causes of uncertainty in measurement regarding long-stroke line scales are line detection errors and external factors, especially temperature effects. The number of calibration errors of this sort increases with the extension of calibration time. Therefore, a dynamic method of line scale detection for modern long-stroke line scale comparators is used [1, 2, 3]. The article discusses the dynamic method of line scale detection by means of an optical microscope equipped with a photosensitive cell matrix and a line scale detection algorithm. Advantages of the dynamic method of scale calibration in terms of rate, accuracy and throughput are presented. The method’s error (detection parameters) correlations with detection rate, number of nominal lines, measuring rate, exposition delay are analyzed and mathematical models are described. The optimal values of these parameters are estimated. We are particularly interested in the improvement of the dynamic calibration program algorithm and minimization of uncertainty in measurement. The method was implemented and tested on the long-stroke line scale comparator, which has been developed and realized by JSC Precizika Metrology [3, 4, 5] in cooperation with VGTU and KUT.

Precision Measurement of the Carriage Vibrations at the Different Speeds

Dependence of a comparator reading dynamic error on vibro activity of a carriage is analyzed in the paper. There is shown how change reading errors at action only carriage drive vibrations and at artificially provoked carriage vibrations at different frequencies. Results achieved enable to evaluate the influence of vibration components on reading errors.

Dynamic Mode of Line Scale Calibration

The need for high-resolution and high-speed detection of line scale graduations is a result of increasing throughput requirements of precision scale calibration systems. These new demanding requirements can be met by exploiting the advantages of the dynamic mode of calibration. The state-of-the-art platform-based approach to improving calibration systems performance will allow both functional extension to already deployed systems and the design of new ones, capable of adapting to different application patterns and user profiles. An interferometer-controlled comparator setup has been designed to measure the performance of the dynamic calibration process. A novel 3D finite element model has been developed in order to both investigate thermo-mechanical processes in the comparator structure and evaluate possible temperature influence on geometrical dimensions of the line scale. A series of measurements has been conducted at PTB and MIKES length calibration laboratories in order to evaluate the capabilities of the dynamic calibration of graduated line scales.

Dynamic Research on Precision Angle Measurement Comparator

The aim of the research was to determine the mechanical stability of angle measurement comparator’s system. For that purpose, vibrations were measured at the significant points of the system and dynamic characteristics of the system were established.

Length Metrology and Calibration Systems

Accurate length measurement plays a vital role in meeting the needs of industry and commerce for traceability to common national and international standards, especially in view of the common market and world trade. Such measurement needs arise across a wide applications base, from large-scale engineering projects such as dam construction, aerospace and shipbuilding, through automotive engineering and components manufacture, to precision engineering and nanotechnology (DTI/NMDS, 2002b).