平田 慎之介

Microdroplet dispensation is required in current systems and industrial equipment. However, dispensing microdroplets from high-viscosity liquids using dropon-demand inkjet technologies is difficult. Therefore, a needle-type dispenser comprising a thin needle and glass capillary containing the liquid to be dispensed has been developed for microdroplet dispensation. When the needle passes through the capillary, a droplet of the liquid adheres to the needle tip. A microdroplet can be transcribed by bringing the needle-tip droplet into contact with the target surface. The needle-type dispenser can dispense sub-pico-liter droplets with viscosities of several hundred pascalseconds at a throughput of a droplet per 1 s. When a microdroplet is dispensed, a gap between the needle tip and target surface may be formed. Droplet volumes depend on the dispensing gap, and unstable if the gap fluctuates. Thus, a contact-detection method for the needle-tip droplet and target surface is proposed where the needle is vibrated by a piezoelectric actuator using a leaf spring. The needle-vibration characteristics depend on conditions between the needletip droplet and target surface. Contact of the needletip droplet with the target surface can be detected by the needle-vibration characteristics. The dispensing gap can thus be kept constant to dispense precise droplet volumes. In this study, the needle-vibration characteristics of the fabricated mechanism were evaluated experimentally for needle diameters of 500 and 100 µm. The needle-vibration displacements decreased depending on the dispensing gap for liquids with viscosities of 0.1 to 100 Pa•s.

To realize a quantitative diagnosis method of liver fibrosis, we have been developing a modeling method for the probability density function of the echo amplitude. In our previous model, the approximation accuracy is insufficient in regions with hypoechoic tissue such as a nodule or a blood vessel. In this study, we examined a multi-Rayleigh model with three Rayleigh distributions, corresponding to the distribution of the echo amplitude from hypoechoic, normal, and fibrous tissue. We showed quantitatively that the proposed model can model the amplitude distribution of liver fibrosis echo data with hypoechoic tissue adequately using Kullback–Leibler (KL) divergence, which is an index of the difference between two probability distributions. We also found that fibrous indices can be estimated stably using the proposed model even if hypoechoic tissue is included in the region of interest. We conclude that the multi-Rayleigh model with three components can be used to evaluate the progress of liver fibrosis quantitatively.

Pulse compression using maximum-length sequence (M-sequence) can improve the signal-to-noise ratio (SNR) of the reflected echo and distance resolution in the pulse–echo method. In the case of a moving object, however, the echo is modulated due to the Doppler effect. The Doppler-shifted M-sequence-modulated signal cannot be correlated with the reference signal, which corresponds to the transmitted M-sequence-modulated signal. Therefore, Doppler velocity estimation before the correlation and cross correlation of the received signal with Doppler-shifted reference signals has been proposed. In this paper, the proposed Doppler velocity estimation based on spectral characteristics of cyclic M-sequence-modulated signals is described. Then, the Doppler velocity estimation is evaluated based on computer simulations. The Doppler velocity can be estimated from the Fourier-transformed spectral density of cycles of the M-sequence-modulated signal with high resolution even in noisy environments. According to the evaluation, furthermore, the cycle number and the number of carrier waves in 1 digit of the M-sequence-modulated signal should be decreased to improve the resolution and accuracy when the length of the transmitted signal is determined.

The acoustic measurement of vital information such as breathing and heartbeat in the standing position whilst the subject is wearing clothes is a difficult problem. In this paper, we present the basic experimental results to measure small movement of an object behind cloth. We measured acoustic characteristics of various types of cloth to obtain the transmission loss through cloth. To observe the relationship between measurement error and target speed under a low signal-to-noise ratio (SNR), we tried to measure the movement of an object behind cloth. The target was placed apart from the cloth to separate the target reflection from the cloth reflection. We found that a small movement of less than 6 mm/s could be observed using the M-sequence, moving target indicator (MTI) filter, and tracking phase difference, when the SNR was less than 0 dB. We also present the results of theoretical error analysis in the MTI filter and phase tracking for high-accuracy measurement. Characteristics of the systematic error were clarified.

A microsurface measurement system that is composed of the microrobot with the indenter and a vision based navigation system is proposed for investigating hardness and stiffness of such microparts. Here the tiny robot with the electromagnetic legs and the piezo elements incorporates with an electromagnetic driven microforce generator. This force generator can provide small forces up to 17 mN with 50 µN resolutions and push down the microindenter to the surface. The displacement of the indenter head can be also measured by the Linear Valuable Differential Transformer (LVDT) on machine. Thus, this mechanism can generate the small force and monitor the depth behaviour of the indenter during whole dwell time. Since the overall size of this mechanism is small enough to implement on the piezo-driven microrobot, the tiny robot with the microindenter is capable tomove precisely step by step with 1 µm per step so that the microindenter could be penetrated anywhere on the sample surface. With the help of an image processing technique, the vision based coordination system with the local close-up view and the overall global view has been developed to identify the locations of small robot and the indenter precisely within ±3 µm accuracy over the working range. In the experimental results, several results that the indentation load-depth characteristics of the unhealthy human tooth are measured automatically at the specified point are discussed.

Micro-droplet dispensation is required in current systems or industrial equipments. However, drop-ondemand inkjet technologies are difficult to use in dispensing micro droplets from high-viscosity liquids. Therefore, the needle-type dispenser using a thin needle and a glass capillary has been developed for microdroplet dispensation. When the needle passes through the capillary with a sample liquid, a droplet of the liquid adheres to the needle tip. The micro droplet can be transcribed to the target surface by bringing the needle-tip droplet into contact with the target surface. The needle-type dispenser can dispense sub-pico-liter amounts of droplets from liquids of several hundred Pa?s. When a micro droplet is dispensed, a gap is formed between the needle tip and the target surface. Amounts of droplets are unstable, as the dispensing gaps fluctuate. Therefore, a contact-detection method of the needle-tip droplet and the target surface is proposed. The needle is vibrated by a piezoelectric actuator through a leaf spring in the proposed method. The needle-vibration characteristic is made variable by the differences in conditions between the needle-tip droplet and the target surface. Therefore, contact of the needle-tip droplet with the target surface can be detected by needle-vibration characteristics. Then, the dispensing gap can be kept constant by contact detection for dispensing accurate amounts of droplets.

In order to investigate micro hardness and stiffness in a special chamber, the development of a small-force generator mechanism and a piezodriven microrobot is described in this paper. This small-force generator is simply composed of a Voice Coil Actuator (VCA) and the tandem leaf spring mechanism. The small force can be controlled by an electrical current, which is supplied to the coil and positioned precisely at the balance point with the parallel leaf spring with no mechanical friction. The full bridge strain gauges on both sides of the double leaf spring can detect a small force that is applied to the sample with a microindenter. This handmade small device can produce and verify small forces up to 17 mN with good linearity and a 50 µN resolution. The displacement of the indenter head can be also measured by the Linear Valuable Differential Transformer (LVDT) on the machine for monitoring the depth behavior of the indenter during the whole dwell time. The small force generator with the indenter can be implemented on the piezodriven microrobot to check the microscopic hardness and stiffness. This microrobot can move around the measurement area precisely step by step with 1 µm steps on a metal plate, so that the sample can be scanned with microscopic resolution in situ, such as in an SEM chamber. In the experiment results, the basic performance of microelasticity investigations with a certified hardness block was successfully checked and the indentation load-depth characteristics were precisely acquired on the path of the microrobot.

Observation and manipulation technology under scanning electron microscopes (SEM) is required in medicine, biology and mechatronics. A miniature hemispherical tilt stage has been proposed for improvement of microscopic observation and manipulation. The stage can be rotated in arbitrary direction under the SEM. The stage is composed of a hemisphere and three drive units. Furthermore, the drive unit is composed of a drive ball and two piezoelectric actuators. The drive ball is moved by two piezoelectric actuators, which are orthogonally arranged, in a plane. The ball moving plane of each hold ball is same as the tangent plane between the hemisphere and each hold ball. The hemisphere on three hold balls is tilted and rotated in arbitrary direction by stick-slip motion of each hold ball. The tilted or rotated direction of the stage can be controlled by the movable directions of each hold ball. In this paper, design and fabrication of the miniature hemispherical tilt stage is described. Then, the tilted directions and linearity of the stage are evaluated by a laser autocollimator in the micro-tilt experiments.