A control system design for head positioning in a rigid disk system has been studied in this paper. The use of multiple controllers is proposed to cope with variable operating modes. An H_∞ controller with robust stability in the track following mode of a recording head and an H₂ controller were designed by using a model-matching method for high-speed track seeking. The H₂ controller is adapted each seek distance. Finally, a control system was constructed with both controllers. Closed-loop stability is maintained due to the structure of Yula parameterization⁸⁾ even when the controllers are switched according to the operating mode.

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To obtain stable reproduced output on a VTR, it is necessary to analyze the causes of output fluctuation in spacing or off-tracking and study them quantitatively. We have developed a method for such quantitative measurement in which two frequency-time division signals are recorded and the ratios between the reproduced output at each wavelength and the peak output are plotted in 2-D. Using this method, we conducted an experiment and the results confirmed its validity in measuring off-track and spacing fluctuation. In addition, it was confirmed that the time division method is superior to the frequency multiple method on using two-frequency signals. Furthermore, it was demonstrated that fluctuations can be measured even in ultra-narrow-track recording by carrying out off-track correction that takes into account the recording/reproduction crosstalk.

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To record as much information as possible on a very small area, it is necessary to reduce the thickness of magnetic tape and smooth its surface. However, the smoothed tape surface can increase the friction between the tape and the fixed drum, and cause instability in running the tape. We have devised an ultrasonic vibration drum (USV drum) designed to reduce the contact area between the tape and the drum by generating infinitesimal ultrasonic vibration on the drum's surface. We performed recording/reproduction tests using the USV drum in the actual transport of a VHS video tape recorder. As a result of the experiment, we decreased the friction coefficient to less than one third, and we achieved stable tape running and excellent recording/reproduction characteristics.

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To design a low-tape-tension mechanism, the differences in the head-tape interface between a window-type drum and a non-window-type drum (without the head windows) in a rotating head system were investigated. The head-tape spacing was observed using a transparent dummy head instead of the actual magnetic one, and tape deformation was measured using a non-contact displacement meter. In addition, tape deformation near the head was simulated numerically. We found that tape was deformed at the drum gap, and tape tension at the head-tape contact was lower in the non-window-type drum than in the window type. We concluded that a low-tape-tension mechanism useful for thin tapes can be constructed using a non-window-type drum.

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The lubricity, durability and anti-corrosive properties of metal evaporated tape (ME tape) for digital VCRs were investigated. To improve reliability of the ME tape, Diamond-Like Carbon (DLC) film and lubricant were applied as protective layers on a Co-O magnetic layer. This newly developed ME tape has on output +5.0 dB higher than conventional Hi-8 ME tape for a recording density of 100 kBPI. Its still frame life was over 10 hours. The key development of this DLC film is the application of high Vickers hardness and uniform morphology as a protective layer and partially fluorinated alkyl carboxylic acid as a lubricant layer on the film. Even if the surface roughness of the ME tape is low, excellent running durability, still frame life and corrosion resistance are obtained from the combination of effects from the DLC protective layer and the lubricant layer. This ME tape plays a major role in determining consumer-use digital VCR specifications and will help advance the next generation of high density recording technology.

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An image retrieval system providing effective access to desired data in an image database has been studied. Since images are more ambiguous than language, image retrieval that uses only a keyword as a retrieval key is not enough. In this paper, we propose an image retriaval method that uses a rough sketch as the retrieval key. An image in a database system is divided into segments and is described by color, position, size, shape, and geographical relation of each area. These structural features are represented by attributed relational graphs. Similarity is measured by graph matching between stored graphs and a graph derived from a rough sketch.

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[in Japanese]

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[in Japanese]

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