Abstract: The nondestructive, non-contact, three-dimensional evaluation of optical glass has been important to the manufacturing of high-precision optical components. In order to achieve high-precision nondestructive evaluation of optical heterogeneity, we develop a versatile evaluation system using the parallel phase- shift digital holography, which enables measurements of the optical path differences at a nanometer-scale resolution. The amplitude and phase distributions of the object wave can be reconstructed directly from a single hologram by using the parallel phase-shift digital holography system. The optical heterogeneity of a sample is determined quantitatively based on the distribution of the optical path differences quantitatively.
Abstract: Recently, manufacturing techniques of small-scale products have been improved. As a result, precise measurement is required of small inside diameters, for example, of engine nozzles. However, an in situ measurement and measurement system for small-sized products has yet to be fully established. In this research, a contactless technique to measure small inside diameters is proposed. This new method uses tandem low-coherence interferometry and an optical fiber cut at an angle of 45°. This optical fiber is up to 30 μm in diameter and is used as a probe. Our objective is to measure holes as small as 50-μm inside diameter with an accuracy of 100 nm. In the present paper, we report on the measurement principle, calculate the measurement uncertainty and show that experimental measurements can be obtained of small-size holes up to 300-μm inside diameter with an accuracy of 100 nm.
Abstract: We develop a new method for high-resolution and contactless distance measurement based on self frequency beats of optical frequency combs. We use two optical frequency comb lasers with Rb-stabilized repetition frequencies for doing accurate distance measurement. The repetition frequencies of the optical frequency combs are different, thus parts of the high frequencies such as several gigahertz of self beats are beat-downed to several megahertz without an RF frequency oscillator. The phases of the beat signals of several megahertz frequencies are measured by a lock-in amplifier with a high resolution and high sensitivity. The new method is applied to distance measurement for objects which have rough-surface in the distance range of several-meters.
Abstract: A newly developed practical sphericity measurement system by means of stitching interferometry is described in this paper. Spheres are widely used in industry. In particular, spheres with stem are usually used in metrological applications such as reference sphere for Coordinate Measuring Machines. It is common to calibrate form of spheres with tactile roundness measurement, however a comprehensive form measurement is desired for evolving high precision applications. The developed system consists of commercial base Fizeau type interferometer to capture partial surface areas of sphere and five axes stages to handle sphere with stem. Hence the system is very suitable for measurement of such stemmed spheres. This system yields three dimensional form maps of stitched sphere and peak to valley sphericity. Standard deviation of sphericity value yielded using this system is less than 5 nm in 8 times repetition. Finally, an equatorial profile clipped from stitched sphere shows good agreement with a result of tactile roundness measuring method within 10 nm typically.
Abstract: Recently, developers of machining tools have begun paying more and more attention to multi-joint dual-arm robot, and it is expected the robot will reclaim its place in the field of new automation. Industrial dual-arm robots have therefore gained attention as new tools to control both linear motion and rotational motion accurately. On the other hand, the five-axis control machining center controlling the motion of three translation axes and two rotation axes has put into wide practical use. However, a one problem has been that it may be the difficult to measure the synchronic accuracy of rotation two axes without high accuracy gyro sensor. In the present report, we proposed a novel method to measure the synchronic accuracy of rotation two axes of machine tool table with a ball, which keeps a ball rolling around a circular path on the working plate by dual-arm cooperating control. As a result, we investigated an influence of each axis motion error on a ball- rolling path, and demonstrated this method made it feasible to estimate the synchronic accuracy of rotation two axes of machine tool table.
Abstract: The stereo-camera method is used to measure the positions of robots. In taking the measurements it is important to precisely measure the distance between cameras and the relative posture of the cameras. Therefore, we developed a novel method for measuring a mobile robot's relative position and posture by photographing robots’ pivot turns. A mobile robot system was equipped with a camera and an identification marker that made it possible to measure position and posture with the stereo-camera method when the viewpoint changed freely. One robot photographs the pivot turns of another. As the latter turns, an identification marker on it is used to trace the movement onto an image. The turning robot’s position and posture is determined by the length and angle of the trace. This procedure makes it possible for each of the two robots to obtain their relative position and posture, making the measurement of the stereo-camera method precise. Measuring with a fixed stereo camera is impossible when there are obstacles in the environment and the object being measured moves over a wide range. However, this robot system was able to use the stereo-camera method to expand the measurement range.
Abstract: We propose geometric quality indicators for evaluating the quality of point clouds (sets of scanned points). These indicators represent aspects of quality often considered in practical scanning procedures, such as cloud thickness and cloud density. We defined the indicators mathematically and developed software to compute them, then conducted experiments to evaluate the indicators for point clouds obtained by scanning the same samples with different types of surface scanners and scanning procedures. The results showed that the indicators are capable of highlighting various aspects of point cloud quality.
Abstract: This paper presents a measurement system for 3-D micro structure using an optical fiber probe equipped with a piezo element generating vibration. The optical fiber probe consists of a stylus shaft with a diameter of 3 µm and a glass ball with a diameter of 5 µm attached to the tip. The stylus is set so as to circularly move in a plane. The measurement principle involves the monitoring of the vibrational amplitude of the stylus to prevent adhesion of the stylus tip to the measured surface due to the surface force, and this amplitude is measured optically. In this research, the stylus characteristics are examined. The effects of the relative humidity and the surface roughness on the surface force are then evaluated. As a result, it is shown that the surface force increases remarkably when the relative humidity is greater than 40%, and there is no adhesion of the stylus tip to the measured surface due to the surface force in case of the stylus vibrational amplitude of over 0.5 µm. Also, the adhesion of the stylus tip cannot be observed in the 0.2 - 0.8 µm surface roughness range.
Abstract: A compact optical three-axis surface encoder, which can detect displacements in the XYZ-directions simultaneously by employing a scale grating with a short pitch (0.57 μm) and a single laser beam with a short wavelength (405 nm), is described in this paper. This surface encoder mainly consists of a blue-ray laser diode, a pair of two-dimensional diffractive gratings serving as scale grating and reference grating, respectively, and two quarter photodiodes (QPD) utilized for detecting output optical density. The displacements of the scale grating along X-, Y- and Z-directions are measured by analyzing interference signals caused by the phase shifts and light path difference of diffracted beams from the scale grating and reference grating. Basic measurement principle is illuminated, a compact surface encoder is designed and evaluation experiments are carried out.
Abstract: A three-axis mosaic surface encoder, which can measure the X-directional position and the Y-, Z-directional straightness of the linear stage in a long range, is proposed. The three-axis mosaic surface encoder is composed of multiple scanning probes and a mosaic scale grating. The mosaic scale grating is constructed by placing the multiple two-dimensional reflective-type scale gratings in a line to obtain long measurement range along the in-plane direction of a scale grating. In addition, the optical configuration of the encoder head, which employs multiple scanning probes to be projected on the mosaic scale grating, is proposed so that a long range measurement can be achieved by the mosaic scale gratings. With the proposed encoder head, the measurement information of the X-directional displacement can always be obtained from the probe which is not on the gaps of the mosaic scale grating. The proposed configuration was applied to the three-axis surface encoder, and basic performances of the proposed three-axis mosaic surface encoder are experimentally investigated.