Papers by Author: Kiyoshi Takamasu

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: Micro plastic structures, typified by photoresists for semiconductor devices or various MEMS devices, photosensitive resins of microstereolithography, and so on, play one of the most important roles in the microdevices manufacturing. In order to process finer plastic structures with higher reliability for more complexly-modulated microdevices in the next generation micromanufacturing field, a nano removal processing method, which can be applied to a corrective machining process with the removal resolution less than 10nm in both lateral and vertical direction, is strongly required. In this study, we propose a novel nano removal processing method for micro plastic structures with photocatalyzed oxidation. Here, we apply photocatalysts micro particles as a specially designed material removal tool tip. Since a light energy is not directly used for processing the material, a material removal resolution does not depend on the diffraction limit. Further, using photocatalysts is free from micro tool wear problem. As the first report, in order to verify the fundamental feasibility of the proposed method, we performed basic experiments using TiO₂ micro particles with the diameter of 500nm for cured photosensitive resin surface. An AFM observation of the processed surface showed that a vertical removal resolution of 8nm was achieved.

Abstract: Large aspheric mirrors with diameter over 300 millimeters with high surface accuracy are wildly used in many areas such as astronomical telescopes. Interferometers are widely used in profile measurement of optical flat and sphere. However, standard reference aspheric surface which is necessary for this method is difficult to make. Scanning defletometry based on ESAD (Extended Shear Angle Difference) is used to measure ultra-precise large near-flat and slight curved optical surface with the accuracy of sub-nanometer. However, it is not possible for it to measure aspheric surface because of the limitation of the measuring range of autocollimators. We proposed a new measuring method to scan the surface of a large aspheric optical surface using autocollimator with rotatable optical devices fixed on linear motion stage. To eliminate the influence of the pitching error of the scanning stage, we use two mirrors reflecting laser comes from autocollimator, which have the same effect with a pentaprism used in ESAD. To enlarge the measuring range of the autocollimator, we use a rotatable mirror to fit the changes of the slope of the mirror surface under measurement. The error analysis of the method is done. Measurement of an optical flat mirror and a sphere mirror with diameter of 50 mm and biggest slope of 6000 arc-second are done. The rotatable optical devices that we designed are proved effective on eliminating the pitching error of the moving stage.

Abstract: To develop a high precision Micro Coordinate Measuring Machine (Micro-CMM), it is important to evaluate an X-Y stage on the Micro-CMM. A precision multi-probe measurement system has been designed and developed for simultaneously measuring the yaw and straightness errors of the X-Y stage. In the system, an autocollimator measures the yaw error of the stage, and two laser interferometers measure the profile of a standard mirror which is fixed on the X-Y stage. The straightness error is reconstructed by the application of simultaneous equation and least-squares methods, and the uncertainty associated with the multi-probe method is simulated. When the interval of the laser interferometers equals 10 mm, the standard deviation of multi-probe method using the high accuracy autocollimator and the laser interferometers is about 10 nm. The simulation results satisfy our purpose for the uncertainty of 50 nm, and practical considerations are discussed.

Abstract: The uncertainty estimation of coordinate and profile measurement is essential for accurate measurement and establishment of traceability. We proposed an uncertainty propagation method to estimate the uncertainty of coordinate and profile measurement. In this article, the multi sensor algorithm with uncertainty estimation method is described for the profile measurement. Additionally, two examples of multi sensor method are introduced. According to the simulation results of assessing uncertainty and the experimental results, the validity of the method was confirmed.

Abstract: Simple and easy uncertainty estimation method is proposed. Provided that specification or simple experimental result is available, possible variance and covariance in error are estimated and Monte-Carlo simulation reflecting constraint caused by the covariance can be performed. Comparison between uncertainties obtained by the proposed method and that by actual measurements on real CMM shows good agreement within 1 m µ over-estimation.

Abstract: This paper presents a scanning squareness measurement method for large ultra-precision components. A rectangular block as the squareness reference is used. The squareness error of the rectangular block is eliminated according to the geometric principle that the sum of four internal angles of a rectangle is 360°. And the straightness error of each line of the rectangular block is eliminated by means of scanning method with two 1D probes. The above two error separation technologies are combined effectively and the data processing method is developed. Additionally, the standard uncertainties including tilt and squareness errors of the rectangular block, temperature drift and random errors of the measured values of the probes are analyzed theoretically. It is confirmed that a combined standard uncertainty of less than 1 arcsec can be obtained for typical values of the parameters.

Abstract: In the semiconductor industry, a device that can measure the surface-profile of photoresist is needed. Since the photoresist surface is very smooth and deformable, the device is required to measure vertical direction with nanometer resolution and not to damage it at the measurement. We developed the apparatus using multi-cantilever and white light interferometer to measure the surface-profile of thin film. But, this system with scanning method suffers from the presence of moving stage and systematic sensor errors. So, in this paper, an error separation approach used coupled distance sensors, together with an autocollimator as an additional angle measuring device, was consulted the potentiality for self-calibration of multi-cantilever. Then, according to this method, we constructed the experimental apparatus and do the measurement on the resist film. The results demonstrated the feasibility that the constructed multi-ball-cantilever AFM system combined with an autocollimator could measure the thin film with high accuracy.

Abstract: A new linear motor based on the Sawyer principle is firstly introduced. Some important features of the linear actuator are discussed for better understanding of its performances and functions with absolute positioning. We investigated the static characteristics of the linear motor such as the relationship between the current and the maximum thrust force (I-F curve), the relationship between the displacement and the thrust force (D-F curve), and the positioning accuracy. The measuring methods for these characteristics are explained in detail. We analyzed the experimental data and evaluated the characteristics. We obtained that the suitable working current is 1A and the maximum thrust force is 15N for the linear motor. The positioning accuracy is ±12µm.

Abstract: For flexible 3D positioning of a complex 3D mechanism, it is needed to measure 3D displacement of the end-effecter of the mechanism in high precision and by non-contact method. It was common to use plural sensors or scales together to measure the 3D displacement. However, it is difficult to calibrate the sensitivities of the plural sensors or scales. A novel 3D displacement measurement is proposed using an optical system in which lens focuses are collected at the center of the sphere, which has been used for the radius measurement of the sphere. Instead of facing in the XY direction that has high sensitivity, new ideas are necessary for the measurement in the Z direction of the optics where focuses are collected at the center of the sphere. The displacement in the XY direction and the one in the Z direction can be measured at the same time by using a ring-shaped laser beam instead of a simple ray.