A variable controller design for head positioning in a disk file system basing on H_2/H_∞ control theory and co-prime factorization was studied. An H_∞ controller with robust stability was designed for stable following of a magnetic head to an objective track. An H_2 controller was also designed by using a model matching method for high speed track seek. The H_2 controller was assumed to adapt the seek distance. The tow controllers would be switched with each other without deteriorating the system stability since their controllers base on Yula parametorization.

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The difference of the head-tape interface between a window type drum and a non-window type (the head windows were eliminated) drum in a rotating head system was studied. The head tape spacing was observed by using transparent dummy head, and the tape deformation was measured simultaneously by non-contact displacement meter. Furthermore, the tape deformation near the head was simulated numerically. We found that we could realize a low tape tension mechanism for thin tape by using a non-window type drum.

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In order to analyze the causes of the reproduced output variation on VTRs induced by spacing loss and tracking error, we studied a measurering method which utilizes a switching signals between two different frequencies. AS a result, this method has proved useful for obtaining the quantitive assessment of output variation causal factor. Further, the effectiveness of our method was confirmed as a result of a comparison between the 2-frequency switching method and the frequency multiple method. Moreover, the study of off-track correction that takes into account recording blurring demonstrated the validity of this method in analyzing the causes of output fluctuations when recorging on a very narrow track.

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It is important for development of consumer digital VTR system to avoid tape damage for tape loading, and to perform stable head contact and accurate track trace. Therefore we developed new threading and calculated optimum guide timing during tape loading. And we developed the efficient method for numerical simulation of tape transformation. Using this method, we performed stable head contact and accurate track trace.

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We have developed a search playback system for Time Lapse VCR which recorded several input video signals by sequcntially switchiing a plurality of channnels in the field. In this system, writing the reproduced singal to the memory is controlled by track jump signal and search speed is controlled to obtain full screen display, and auto-tracking servo is applied to high stability of the system. And we realized the search reproduction picture of only a desired specific channel without multiple reproduction of each channuel, and retrieved and confirmed the recorded contents easily and at a high speed.

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