An effective non-destructive inspection is strongly desired for cracks and air-gaps in reinfoced conceretes in recent years. An ordinary inspection for reinforced concrete has often been done with an electromagnetic wave (radar). But, B-mode image of the received signals having been used, the detection of the abnormalities has not been successfully achieved. This is because the reflected wave from the reinforcing bars is quite larger than those from cracks and air-gaps and inspectors have tried to judge the abnormalities only by seeing the B-mode image.
The present paper provides an accurate and a reliable inspection method which detects the abnormalities in reinforced concrete using the signal propagation model that the author previouusly proposed. For applying the signal propagation model, the paper proposes a preprocessing method for the received signal to reduce the influence from reinforcing bars. Experimental results will show that, in addition to a reliable detection of crack, depth of the crack and the thicknesses of various media constituting the reinforced concrete structure are accurately measured.

View full abstract

When a heavy loading test is performed to a reinforced concrete pile, many small cracks are generated as the increasing load. However, effective methods detecting the cracks have not been developed until now, due to the large number of small cracks. The present paper thus proposes an effective non-destructive inspection system using an acceleration pickup. That is, by making use of the stationary waves of the elastic wave generated in the pile, the method detects the cracks with a high precision and a high reliability. In order to make use of the stationary waves much more effectively, the paper introduces a dynamic model of the stationary waves and applies maximum likelihood method.

View full abstract

This paper proposes a method of detecting fault conditions of escalator using several statistical parameters of vibration and sound. We have developed an inspection step which is equipped with an accelerometer and a microphone, and it can easily acquire the sensor data of the running escalator in a short time. The acquired data is parameterized by amplitude of vibration, kurtosis of vibration, cyclic vibration level, kurtosis of sound, and kurtosis of high-pass sound. When at least one statistical parameter exceeds a threshold, the escalator is judged as the fault condition. The system tests were conducted to evaluate the performance for several conditions. The fault thresholds of the statistical parameters were determined based on many escalator data on the normal condition. The test results showed that the statistical parameters exceed the threshold at the most of the fault cases. Therefore, it is possible to perform fault diagnosis using the differences of the statistical parameters between normal and fault conditions.

View full abstract

In this paper, a novel signal processing method for microwave radar is proposed, which enables to estimate the internal cross-section of concrete structures. By using proposed method, enhanced information such as position, surface shape and material (between metal and non-metal) of buried objects can be discriminated. As the objects are buried near the concrete surface, signal observation is difficult because a reflected wave is often interfering with a surface wave in an observed signal. In order to reduce an influence of the interference, nominal surface waveform identified from the observed waveform without buried objects is subtracting from other observed waveforms. As a result, boundary and material of the buried objects are discriminated more precisely. Next, a boundary model fitness whose shape is the normal distribution function with characteristics of the original model fitness is newly introduced to enhance a vertical resolution of reconstructed images for buried objects. In the back projection images calculated by using them, the boundaries of the buried objects are discriminated more clearly. These proposed methods have applied to experimental application to several concrete test specimen, and position and diameter estimation and material discrimination performance have confirmed.

View full abstract

This paper proposes a new method for improving signal-to-clutter ratio (SCR) for frequency modulated continuous wave (FM-CW) radar. Received signals can be categorized into two types due to either a target or clutter. Target surfaces are generally smoother than clutter surfaces, and thus target signals with different carrier frequencies tend to have stronger correlation than that of clutter. The autocorrelation of linearly FM waveforms from the target and the clutter, when the frequency range is chosen to be large enough, are expected to be significantly different. Based on this statistical difference, the target statistical characteristic is estimated from received signals only, and a matched filter is then designed for improving SCR.

View full abstract

A non-intrusive temperature sensing system is proposed. It is developed for temperature measurement of liquid sodium coolant in fast breeder reactor. Liquid sodium is used as coolant due to high heat flux density in the reactor core.
In this paper, the results of our feasibility study by 2-dimensional numerical simulation, small size experimental test done by Japan Atomic Energy Agency Oarai Institute, and theoretical analysis are described.
The basic principle of temperature measurement is resistant thermometry of liquid sodium. The resistivity of liquid sodium is quite lower than that of the stainless steel (SUS304), which is used in the pipe wall. The resistivity temperature coefficient of liquid sodium (0.337%/deg) is higher than that of stainless steel (0.0865%/deg). If we feed electric current perpendicular to the axis of flow pipe, the current penetrates the pipe wall and flow across the liquid. The current concentrates the liquid sodium, only small portion of the current flows along the pipe wall. The electric potential distribution is almost dominated by resistivity of sodium. The potential distribution can be measured along the out side of the pipe wall. The potential difference between two fixed points on the pipe wall indicates the resistivity of sodium. So the sodium temperature can be measured by potential difference. Measurement accuracy of ±5° is obtained in experimental tests. Better estimation data are obtained by theoretical analysis using three dimensional model.

View full abstract

It is effective that we approach the sensing system on the sea near the key institute to detect a dubious ship early. This paper describes the trial method of discrimination ships by sensing underwater sound. And we tested extracting ship's sound from surrounding sound.

View full abstract

Under-sampling technique for estimating fundamental parameters of sine wave is proposed. Algorithm for finding excess factor, direction of sampling, and final estimates including signal frequency, amplitude, initial phase angle and magnitude of pedestal, is shown in detail. The technique combined with non-uniform sampling and the Prony's method is evaluated by numerical experiments. The technique gives accuracy on each estimate, showing higher precision especially on higher frequency up to extraordinary higher limit. Thus, the technique enables us to utilize slower A/D converters for higher frequency measurement, or to achieve extremely high frequency measurement with using faster A/D converters.

View full abstract

Coded aperture imaging is one of emission CT techniques. It uses a gamma camera equipped with a coded aperture in place of a ordinary parallel collimator, and reconstructs three dimensional distribution of radionuclide from a projected data collected only from one direction. We have developed a small gamma camera using fully semiconductor area detectors with 16 × 16 pixels and M-array coded apertures made of a lead antimony alloy plate with 1mm thickness. This camera was designed for diagnosis of a breast cancer. In this paper, we will show you the reconstruction algorithm, design approach for coded aperture system, and some experimental results using the developed gamma camera.

View full abstract

In this paper, a new design method for a self-repairing control system (SRCS) is developed for accommodation of actuator failures. The proposed SRCS can detect an abrupt actuator failure and switch from the faulty actuator to the healthy one. The repairing control is carried out with only three signals; the plant output, the designed control input and the test signal, and so it needs no a priori information about plants. Therefore, one can construct the simple SRCS whose structure does not depend on the order of the plant.

View full abstract

We present an application of Interconnection and Damping Assignment Passivity-Based Control (IDA-PBC) method to an underactuated manipulator with the third joint unactuated which is subject to second-order nonholonomic constraints. We give a port-Hamiltonian representation of the manipulator system by selecting an appropriate set of generalized coordinates and applying a global input transformation. And we clarify the applicable conditions and design an inertia matrix and a potential energy function of the closed Hamiltonian system. Numerical experiments are given to show the validity of the derived controller.

View full abstract

In the model predictive control (MPC) of hybrid systems, the problem of reducing the online computational complexity for generating a control input is one of the main issues. Thus focusing on how concisely a model of discrete dynamics is expressed, the authors have recently proposed a minimal representation of a finite automaton, which is given as a linear state equation with the smallest number of free binary variables (called here binary input variables). This representation enables us to reduce the computational time for solving the MPC problem of hybrid systems. This paper proposes a more effective modeling method for the MPC problem. The main idea is to derive an initial-mode-dependent model by using the above minimal representation, which expresses only mode trajectories for a given initial mode to save the number of binary input variables. The effectiveness of the proposed method is shown by numerical examples.

View full abstract

Disturbance rejection problem with communication constraints for the first order system is considered. The performance limitation of the control system is shown by describing the trade-off between channel capacity and control performance quantitatively. The optimal control performance can be achieved by the state observation based on the coding of state prediction error and control to cancel the state by the predicted value.

View full abstract

This paper considers optimal tracking control problems. Our primary objective is to derive analytical solutions of fundamental limitations for a class of references in tracking control problem. It is well known that L₂ norm of an error, which is defined by difference between an output and a reference, doesn't go to zero when we consider transient response for non-minimum phase systems. In the existing results, fundamental limitation is derived for each reference signal such as the step reference. In these results, we need consider whether the plant is easy to control or not in each reference. On the other hands, fundamental limitations are derived as functionals of references in this paper. In other words, we derive analytical performance limitation for a class of references. As a result, we can expect to separate contribution of references and that of plants in performance limitations.

View full abstract

This paper proposes a new calibration method of magnetic sensors for measurement of human finger tapping movements. The magnetic sensors consist of two coils; the detection coil and the oscillation coil. A voltage of the detection coil induced by the electromagnetic induction law changes depending on a distance between two coils. Therefore, by modeling relations between the measured voltages and the distances, we can estimate the distance between two fingertips in wearing two coils from the measured voltage.
In this paper, first, the relation between the output voltage and the distance is derived as a set of highly nonlinear equations. Then, using first-order approximations, it is shown that the nonlinear calibration equations can be reduced to a linear one, so that the unknown parameters included in the calibration equation can be estimated with the linear least-squares technique using a data set of measured output voltages and corresponding distances. Experimental results show that the relation between the output voltages and the distances can be identified by using only three calibration points (0.02, 0.03, 0.09 [m]) measured from each subject, and that the estimation accuracy is confirmed by comparing with the results using a camera. Finally, the differences of finger tapping movements among patients with Parkinson's disease, old healthy subjects and young healthy subjects are explored using the magnetic sensors with the proposed calibration method.

View full abstract

In this paper, the gradient-based iterative (GI) algorithm for solving the cross-coupled algebraic Lyapunov equation (CALE) that arises in many control theory such as Nash games is proposed.It should be noted that the convergence and the reduced-order computation are both attained. In order to demonstrate the efficiency of the proposed algorithm, a numerical example is provided.

View full abstract