Ryoshu Furutani

The estimation method of uncertainty of articulated coordinate measuring machine

The articulated coordinate measuring machine (A-CMM) is a measuring machine, the traceability of which should be kept. However, it is difficult to keep the traceability because the calibration of A-CMM is performed by the manufacturers own method. We planed to use a 3D artifact which consists of 9 balls for the calibration and testing of the A-CMM. The kinematical model of A-CMM was described in the D-H notation. In A-CMM measurement, a cone-shaped stylus was used. We measured the artifact in five different locations and orientations. Each ball was measured five times in different postures of A-CMM. Totally, 45 points were measured in each location and orientation of the artifact. After that, five sets of the kinematic parameters were estimated. One set of kinematic parameters was applied to the measured points in five different locations and orientation of the artifact one after the other. Then the root mean squares are calculated in 25 different combinations to estimate the correctness of the kinematical parameters. As a result, the calibration achieved a better result than the specified accuracy of A-CMM.

Basic concept of feature-based metrology

Abstract In coordinate metrology, an associated feature (or the Gaussian associated feature) is calculated from an extracted feature that is determined by a measured data set of a CMM (coordinate measuring machine) on a real feature using the least squares method. This data processing flow, which is called ‘feature-based metrology’ disagrees with the data processing methods in profile metrology and length measurement. In this report, the basic concepts of feature-based metrology are discussed, such as feature modeling, the least squares method and the statistical estimation of the uncertainty of measurement. Theoretical analysis and simulations for feature-based metrology in statistical ways directly imply that the basic concepts and data processing methods in this report are useful in estimating the uncertainty of measurement in coordinate metrology.

Calibration of Articulated Arm Coordinate Measuring Machine Considering Measuring Posture

A three-dimensional coordinate measuring machine (CMM) is widely used for measurement accuracy and wide measurement range. It is necessary to calibrate the parameters which describe the mechanism to use it as CMM. The geometric calibration is to find the parameters related with the straightness, rotational and scale errors and so on. Non-geometric calibration is to find the parameters except geometric parameters. The method to calibrate CMM is that the artifact is measured by the target CMM. However the most studies of the calibration of CMM are focused on the orthogonal CMM. The only some studies are focused on nonorthogonal CMM. This paper describes the calibration method and the result of the articulated arm CMM (ACMM) which is one of nonorthogonal CMM. It has more measuring freedom than orthogonal CMM. However, the measuring error of ACMM is larger than that of the orthogonal CMM. The kinematic parameters of ACMM are calibrated using the center coordinates of the spheres as the artifact. As in this method, a part of measuring volume is calibrated, ACMM is not sufficiently calibrated. Moreover, as it has more freedom of mechanism, the identical coordinates can be measured in a various posture of it. Therefore the deformations of the arms are different in each measurement. In this paper, to calibrate the deformations of the arms in different measuring posture in addition to the kinematic parameters, a new artifact is produced, a calibration method is proposed and the experiment is reported.

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.

Artefact calibration of parallel mechanism, kinematic calibration with a priori knowledge

In the application of parallel mechanisms, it is necessary to calibrate the kinematic parameters and improve the positioning accuracy for accurate task performance. However, there are strong correlations between all the parameters in the kinematic calibration of a parallel mechanism. Therefore, it is difficult to identify all kinematic parameters included in a kinematic model of the parallel mechanism from measuring data. In this study, we proposed to use ap rioriknowledge of the kinematic parameters to eliminate their correlation and to give robustness to the calibration. Ap riori knowledge can be given without extra measurement when the manufacturing process of the mechanism is under quality control. Using ap rioriknowledge, all kinematic parameters of the parallel mechanism are identified in the artefact calibration without divergence. First, an artefact calibration with ap rioriknowledge is formulated. Second, the estimation of ap rioriknowledge under quality control is described. Finally, the robustness and effectiveness of the artefact calibration with ap riori knowledge is demonstrated through simulations.

Development of a new artifact for the calibration of large scale instruments

A manipulator and a parallel robot is used as a Coordinate Measuring Machine (CMM) to be able to measure a large scale measuring volume. However an adequate artifact had not been developed yet. So in this paper, a new artifact to calibrate and certify a large scale CMM is proposed. The principle of this artifact depends on the double ball bar. The design of the artifact, and measuring result are presented. The accuracy of each part of this artifact is estimated in order to make the artifact more accurate.

Development of a Sensitive Probe for Coordinate Measuring Machines

Requirement for precision measurement becomes extremely advanced as industrial needs advances. CMM (Coordinate Measuring Machine) is one of the most adequate measuring machines to meet the requirement. As the precision of CMM becomes higher, it is important to improve the sensitivity of probe. We developed a contact type probe which consisted of a QPD (quadratic photo diode), a ball lens, and a laser diode to detect the displacement of stylus. The probe system has a resolution of 31nm.

Identification of Fluids by the Color of Surface Plasmon Polaritons

When optical waves make the free electrons on a metal surface resonate, optical energy propagates along the surface as density waves of the free electrons. The longitudinal waves and electrical fields of the electrons are called surface plasmon polaritons (SPPs), which are widely applied in high sensitivity sensors because the excitation of SPPs sensitively depends on the refractive index of the surrounding dielectric sample. Here, we report the identification of fluids by using the color dispersion of SPPs. Silver film on a prism surface is illuminated with white light to excite SPPs. A color component in the white light is thereby selectively coupled with SPPs due to the color dispersion that depends on the refractive index of the fluid on the film. Thus, theoretically, when the refractive index is changed, the color of SPPs changes as well. Our application uses a medium consisting of fluid samples to be identified. The proposed identification method can be applied to fluid analysis for label-free visualization of or as a simple analysis method, since the refractive indices or concentrations of the sample fluids directly affect the color of the SPPs, and this color can be visually identified. We theoretically confirmed that the color of SPPs excited with white light illumination can help to differentiate between water and ethanol. Experimentally, SPPs belonging to the frequency region of the color green were detected when the sample was water, and the color changed to red when ethanol was used instead. In the future, we plan to develop simple, small, sensitive, and low-cost sensors that can determine the concentration and refractive index of fluids on the basis of the color of the SPPs.

Evaluation of Straightness of Two-Axes Stage

Two-axes stages (XY stage) are used for precise machining and precise positioning. The XY stage should have the resolution of nanometer in the nanotechonology. In order to determine that the XY stage has enough small resolution, it is necessary to evaluate the positioning accuracy. The shape of stage axes affects measurement result. Therefore, it is necessary to know the shape of the axes. This paper describes the method how to evaluate the straightness of the stage to measure the behavior of the stage. The behavior of the stage is measured by laser interferometer, which measures the displacement. The reflection mirrors are set up on the stage, which reflects the laser. The result of measurement by the laser interferometer includes both of the shape of the reflection mirrors and the shape of the axes. In the case of nanometer positioning, the shape of the reflection mirrors affects measurement result, as the profile error of reflection mirrors are as small as motion error. We theoretically and experimentally inspect whether both errors can be separated from the displacement. In this simulation, the shape of axes and the shape of the reflection mirrors are generated randomly. The shape of axes and the shape of reflection mirrors are estimated by non-linear least-squares method. The estimated shape of axes and shape of reflection mirrors are compared with the ideal shape of them. After simulation, similar method is applied to the actual stage and laser interferometer. The result of simulation and measurement are shown.

Self-Calibration of XY-Stage with Parallel Mechanism

It is important to calibrate the straightness and the squareness of the XY-stage for precision manufacturing and measurement. Normally it is calibrated using much higher precise and accurate measuring instruments and/or artifacts. The high precision and accurate instruments and artifacts are expensive. So, in this paper, Self-calibration method is applied to XY-stage. This method does not require any much high precision and accurate instruments and artifacts. The normal XY-stage moves to the location at the unique coordinates. In this case, it is difficult to apply self-calibration method. Therefore, XY-stage is expanded to XYθ-stage with parallel mechanism. As this stage moves to the location at a lot of coordinates, self-calibration method is applied. This method is confirmed in simulation and experiment. In simulation, the extension lengths of mechanism are estimated from known kinematic parameters and the target coordinates. After that, estimated kinematic parameters are calculated by least-squares method from the extension lengths and the target coordinates. Finally, the positioning coordinates are calculated from the estimated kinematic parameters and the extension lengths. It is proved that the calibration method is effective by comparing the target coordinates and the positioning coordinates. In experiment, the experimental process is similar to the simulation without the estimation of extension lengths. The results of simulation and experiment are shown in this paper.