Sonko Osawa

Geometric calibration of a coordinate measuring machine using a laser tracking system

This paper proposes a calibration method for a coordinate measuring machine (CMM) using a laser tracking system. The laser tracking system can measure three-dimensional coordinates based on the principle of trilateration with high accuracy and is easy to set up. The accuracy of length measurement of a single laser tracking interferometer (laser tracker) is about 0.3 µm over a length of 600 mm. In this study, we first measured 3D coordinates using the laser tracking system. Secondly, 21 geometric errors, namely, parametric errors of the CMM, were estimated by the comparison of the coordinates obtained by the laser tracking system and those obtained by the CMM. As a result, the estimated parametric errors agreed with those estimated by a ball plate measurement, which demonstrates the validity of the proposed calibration system.

Whole-viewing-angle cat's-eye retroreflector as a target of laser trackers

A spherical cats-eye retroreflector made from a glass material having a refractive index of two was developed. The geometrical sphericity of the cats eye and the sphericity examined optically were approximately 100 nm and 500 nm respectively. The discrepancy between these two values is discussed. This optical device is very versatile in terms of applications since it is free from viewing angle restrictions.

Design of laser interferometric measuring device of involute profile

The vibration and noise of gears is one of the serious problems for devices, such as vehicles and wind turbines. The characteristics of the vibration and noise of gears are considerably affected by the tooth flank form deviation of micrometer order. The quality of product gears is controlled using a gear measuring instrument and calibrated with an involute artifact. However, the conventional calibration of the involute artifact cannot achieve a sufficient accuracy. In this report, a direct method of measuring the involute artifact using a laser interferometer is proposed. Fundamental experiments are carried out, in which the effects of the surface condition of the measured object and the effect of the driving of the artifact are investigated. It is confirmed that the proposed method enables the measurement of the detailed form of an involute tooth flank and has the potential of accomplishing a highly precise measurement of an involute artifact.

Traceability strategy for gear-pitch-measuring instruments: development and calibration of a multiball artifact

There is a strong demand to ensure the traceability of gear-measuring instruments (GMIs). We propose a multiball artifact (MBA) for the evaluation of pitch-measuring accuracy. The aim of the MBA is to transfer the minimum uncertainty from a calibrated value at the National Metrology Institute of Japan (NMIJ) to a measured value of GMIs at a shop floor. The MBA is composed of equally spaced high-accuracy balls around an axis. The pitch-measuring accuracy of GMIs is evaluated by measuring the angular pitch deviation of the balls instead of the angular pitch deviation of a gear. We calibrated the angular pitch deviation using a coordinate measuring instrument (CMM) at the NMIJ and adapting a multiple-orientation technique. We proposed a calibration strategy of the angular pitch deviation. The calibration value of the pitch deviation for the MBA at the NMIJ was obtained with a measurement uncertainty (U95) of 0.2 µm. We evaluated the pitch-measuring accuracy of a GMI using the calibrated MBA. Each value of U95 for the cumulative and single pitch deviations for the left and right flanks was less than or equal to 0.5 µm. The small uncertainty was transferred from the NMIJ to the GMI.

Design and Error Analysis of Multiball Artifact Composed of Simple Features to Evaluate Pitch Measurement Accuracy

The strength and vibration/noise of gears are influenced by the pitch deviation of micrometer order and therefore, advanced quality control is needed in gear manufacturing processes using measuring instruments. The accuracy of the pitch measuring instrument is verified using a master gear or artifact, but their accuracy is not sufficiently high. An artifact with higher accuracy for the evaluation and calibration of the pitch measurement is necessary in order to respond to the requirement of gear accuracy. In this research, the multiball artifact, a novel high-precision pitch artifact, is proposed for use in the evaluation of pitch measuring instruments. The multiball artifact is composed of balls, a cylinder, and a plane, where the center cylinder or center ball is surrounded by the balls on the plane. The positions of those elements are decided automatically by the contact among those elements. Balls, cylinders, and planes can be manufactured with accuracy on the order of several tens of nanometers. Therefore, this artifact can realize high accuracy. In addition, this artifact does not need advanced techniques in manufacturing and assembly. This leads to the reduction in manufacturing cost. In this report, the concept and structure of the multiball artifact are proposed, and theoretical analysis on the measurement of the artifact is carried out. Feasible angular pitch is analyzed theoretically. For a cylinder-centered artifact, it is easy to realize the target angular pitch by adjusting the cylinder diameter. Ball-centered types suffer from the limitation of the variation in ball diameter if standard balls are used, but an angular pitch close to the target pitch is possible through the selection of an appropriate combination of balls. The effects of the dimensional deviation of the diameter of the center cylinder, the inclination of the center cylinder, the dimensional deviation of the surrounding ball diameters, the sphericity of balls, and the flatness of the base plane are analyzed. Deviations in the cylinder have a comparatively large effect on angular pitch. On the other hand, the effect of the deviation of the ball or base plane is smaller. The feasible angular pitch is clarified, and it is verified that the concept and structure of the multiball artifact are effective. The effects of deviations in the form and dimension of the composing elements are analyzed, and it is clarified that the accuracy of the cylinder is important. DOI: 10.1115/1.3087535

High-performance laser tracker using an articulating mirror for the calibration of coordinate measuring machine

A high-performance laser tracker that is used for the calibration of a coordinate measuring machine (CMM) is introduced. A specially designed hemispherical-shape articulating mirror is used in the tracking mechanism, which enables reduction of the measurement uncertainties so that they are not more than 0.3 ?m. The uncertainty analysis of the laser tracker is also described.

Gear checker analysis and evaluation using a virtual gear checker

The vibration of gears is one of the serious problems for machines. The characteristics of vibration of gears are considerably affected by the tooth flank form deviation of micrometer order; therefore, strict quality control of the tooth flank form is required. However, because the gear checker (a gear-measuring machine) is structurally complex, it is difficult to analyze how the error factors of the gear checkers affect the measurement result. In this research, a virtual gear checker (VGC) is proposed, that is, a computer program that considers the structures, motions and possible error factors of the real gear checkers, such as motion error. The VGC can be used to simulate the gear measurement, and the effects of the error factors on the measurement result can be analyzed. It is possible to evaluate the uncertainty of tooth flank measurement much more easily and quickly with a VGC than with a real gear checker. A VGC can be used to analyze not only the gear measurement but also arbitrary-shaped objects such as a ball artefact, and the theoretical measurement result is output from the VGC. In this paper, we describe the development of a VGC, and the effect of error factors and the uncertainties of gear measurement are analyzed.

Two highly accurate methods for pitch calibration

Among profiles, helix and tooth thickness pitch is one of the most important parameters of an involute gear measurement evaluation. In principle, coordinate measuring machines (CMM) and CNC-controlled gear measuring machines as a variant of a CMM are suited for these kinds of gear measurements. Now the Japan National Institute of Advanced Industrial Science and Technology (NMIJ/AIST) and the German national metrology institute the Physikalisch-Technische Bundesanstalt (PTB) have each developed independently highly accurate pitch calibration methods applicable to CMM or gear measuring machines. Both calibration methods are based on the so-called closure technique which allows the separation of the systematic errors of the measurement device and the errors of the gear. For the verification of both calibration methods, NMIJ/AIST and PTB performed measurements on a specially designed pitch artifact. The comparison of the results shows that both methods can be used for highly accurate calibrations of pitch standards.

Development of a ball step-gauge and an interferometric stepper used for ball-plate calibration

We propose a new design artifact for the calibration of ball-plates, which are used to assess the performance of coordinate-measuring machines (CMMs) and to calibrate those. Though transferring a length standard is necessary for ball-plate calibration, gauge-blocks are usually used for it. We think that the gauge-blocks are not appropriate gauges for transferring the length standard because of their shape. Therefore, we develop a new artifact, which we call a ball step-gauge. The ball step-gauge consists of a steel bar having the shape of an H and seven ceramic balls. It is rigid and lightweight. In addition, it can be calibrated precisely using special equipment with a laser interferometer; thus it can be used as a transfer length standard in the ball-plates calibration; furthermore, we discuss the uncertainties in measurements using the new interferometric equipment we developed.

3-D shape measurement by self-referenced pattern projection method

Abstract A shape measurement system using time sequential space encoding with multi-gray scale patterns has been developed [1] , [2] , [3] . However, some objects that have colored surfaces and unevenness of reflectivity could not be measured using these methods. Therefore the reference projection images are added to the system. By the reference projection method, the colored objects could be measured by comparing observed space encoding images with the reference images. However the number of projections increased. In this paper, the self-referenced pattern projection method is proposed. This method reduces the number of projections and it is able to measure objects under an illuminated environment and to measure colored objects. Using this system, the measuring space is encoded into n ! sub-spaces with n projections. If there is a commercial projector to encode space with high pixel-resolution and brightness in the near future. it would greatly benefit this method to be able to divide the measuring space into the most sub-spaces when it has the least pattern projections.