Papers by Author: Yusaku Fujii

Abstract: At present, a method for evaluating dynamic characteristics of force sensors against small and short-duration impact forces has been developed. In this method, a small mass collides with a force sensor and the impact force is measured with high accuracy as the inertial force of the mass. A pneumatic linear bearing is used in order to realize linear motion with sufficiently small friction acting on the mass, i.e., the moving part of the bearing. Using this method, the dynamic characteristics of the force sensor are evaluated in detail: small and various-duration impact forces with maximum values of approximately 0.4-6.0 N and full width at half maximum (FWHM) of approximately 0.6-2.8 ms are applied to the force sensor and the impact responses of the force sensor are evaluated.

Abstract: Bamboo shinai is a practice sword for kendo which is the Japanese traditional fencing. The effectiveness of the shock absorption of the bamboo shinai has been shown in our previous study. Although shinai is usually made of bamboo, it is also made of carbon fiber reinforced plastic (CFRP). The impact response of bamboo shinai and CFRP shinai is compared. As a result, the difference of peak value of impact force between bamboo shinai and CFRP shinai against similar initial velocity is small. Impact response measurement of each shinai has been carried out using the Levitation Mass Method (LMM) which has been proposed by us. In this method, a mass, which is levitated with a pneumatic linear bearing and hence affected by negligible friction, is made to collide with a shinai under test. Because bamboo is natual product, resource of suitable bamboos for shinai is limited. On the other hand, carbon-fiber-reinforced-plastic (CFRP) can be designed to be suitable for a shinai, which has a fixed shock absorption characteristic for an application to the structure of robot arms. Therefore, if the shock absorption characteristic of CFRP shinai is the same as that of bamboo shinai, CFRP shinai is more suitable for the structure of robot arms.

Abstract: The purpose of this research is to reduce the measurement time of the first-order mass moment estimation method proposed by us previously. In the previous method, the loads at the three points of the board are measured one by one using one piece of an expensive scale (model: GX-30KR, resolution: 0.1 g, price: 2,542 USD). The relative standard uncertainly of measurement using a rigid body is estimated to be 1.7% and the measurement time is approximately 10 minutes. In this research, three pieces of inexpensive scales (model: HD-660, resolution: 100 g, price: 17 USD) are used to reduce the measurement time. The relative standard uncertainly of measurement is estimated to be 1.9% and the measurement time is approximately 1 minute. In previous measurement, when changing the position of the scale, the position of the frame has been deviated slightly. However, in this method, this kind of error does not occur, since measurements of three points are simultaneously conducted.

Abstract: The resultant force acting on the moving part of the ceramic aerostatic linear bearing is measured highly accurately as the inertial force of the moving part of the bearing by means of the levitation mass method (LMM). The measurement results of the ceramic aerostatic linear bearing and metal aerostatic linear bearing of different mass are compared. The regression equation of the ceramic aerostatic linear bearing and metal aerostatic linear bearing are calculated. The ceramic linear bearing and metal linear bearing have extremely small frictional force.

Abstract: Copper beryllium (CuBe)is materials that are widely used for mechanical applications. In this paper,the use of copper beryllium for cantilever spring of a vibration sensor will beinformed. Cantilever spring plays important role in a vibration sensor, becauseit transfers vibration energy of the measured system into the sensor.Therefore, it is important to know the dynamic characteristics of thecantilever spring. An optical method, called Levitation Mass Method (LMM), isproposed to measure the dynamic characteristic of the cantilever. In themethod, the force of cantilever spring is measured as the inertial force workedon a mass. A pneumatic linear bearing is used to realize a linear motion withsufficiently small friction acting on the mass, i.e., the moving part of thelinear bearing. The inertial force acting on the mass is calculated from thevelocity of the mass, and the velocity is determined highly accurately by meansof measuring the Doppler shift frequency of the laser light beam reflecting onthe mass using an optical interferometer. It is shown that the proposed methodshows the dynamic characteristic of the vibration sensor well.

Abstract: The requirements for evaluating the mechanical characteristics of materials have increased in the various industrial, research and the applications such as materials testing. Therefore, the authors have proposed a method for measuring force acting a material using pendulum [1]. In the Material tester, the mechanical characteristics of material against small force are measured by means of the pendulum mechanism based on the levitation mass method (LMM) [2,3,4].In the LMM, the Doppler shift frequency is measured for measuring the inertial force. The Doppler shift frequency of a laser beam reflected from the mass is accurately measured by using optical interferometer. The velocity, position, acceleration and inertia force of the mass are calculated from the measured time-varying Doppler shift frequency. Thus, the accurate measure of frequency makes that of force.

Abstract: A method of inexpensive material tester based on the levitation mass method is improved. The tester is composed of an interferometer with Zeeman type two frequency He-Ne laser and a small pendulum as a substitute for a pneumatic linear bearing. As an example of a material tester using the pendulum, which evaluates the mechanical response of general objects against impact forces, is developed. The characteristics of the restoring force are measured under the free-swing condition. To demonstrate the performance of the developed instrument, the viscoelasticity of a gel block under an impact load is evaluated.

Abstract: Using a semiconductor laser as a lightsource of a laser Doppler velocimeter (LDV) is desirable to reduce the size and the cost of velocity measurement equipment. However, typical inexpensive semiconductor lasers suffer from the problem of instability in lasing wavelength. In this paper, LDVs with small wavelength sensitivity are reviewed. The wavelength sensitivity can be reduced by using arrayed waveguide gratings (AWGs), Mach-Zehnder interferometers (MZIs) or cascaded MZIs. These structures can be formed by planar lightwave circuit (PLC) technology. The principles and the possibility for realizing wavelength-insensitive operation are discussed.

Abstract: Difficulty in inventory management on space station has been known since 1980’s but still is a new problem. We propose the expanded application of IC tags for the International Space Station inventory management. Use of multiple RFID tags can monitor package use status. Where electromagnetic interference or poor radio propagation is a problem, we may apply ultrasound tags.

Abstract: This paper reviews the present status and future prospects of the levitation mass method (LMM), which is a precision mechanical measurement method. The LMM has been proposed and improved by the author for 10 years. The force generated by the actuator is measured as the inertial force of the mass levitated with sufficiently small friction using an aerostatic linear bearing and connected to the moving part of the actuator. During the measurement, the Doppler shift frequency of the laser beam reflected by the mass is measured with a high accuracy with the help of an optical interferometer. Subsequently, the velocity, position, acceleration, and inertial force of the mass are calculated using based on this frequency. Simultaneously, the current and voltage supplied to the actuator are measured.