Eiji Ueda

Development of multirate sampling repetitive learning servo system and its application to a compact camcorder

The authors have developed a new servo system, called the multirate sampling repetitive learning servo system, having the multirate sampling repetitive learning compensator newly developed so as to reduce the learning memory size. It was applied to the speed control of the capstan motor in a camcorder, and the speed fluctuation of the capstan was reduced considerably as a result of the improved sensitivity to disturbances.<<ETX>>

Physical Characteristics and Format of a Two-Inch-Diameter Magneto-Optical Disk System with 3 GB Capacity

Recording at a high density four times that of a current digital versatile disk random access memory (DVD-RAM) has been achieved by applying the domain wall displacement detection (DWDD) technology using a conventional optical head with the same wavelength of 660 nm and numerical aperture (NA) of 0.60 as those the DVD head. It has been confirmed by using an alternating sampled servo, laser annealing of the inter track area and partial response maximum likelihood (PRML) that a recording density of 15 Gbit/inch2 with a track pitch of 540 nm and bit length of 80 nm has sufficient system margins. A newly developed 1-bit-distributed address format has achieved a redundancy of 23%. Furthermore, the edge shift compensation technique has reduced the recording magnetic field. These indicate that a capacity of 3 GB on a two-inch-diameter disk is now available for mobile use. If applied to a digital video camera, one hour or more of moving-picture-experts-group-2 (MPEG2) video contents can be recorded at a bit rate of 6 Mbps.

Ultrasonic CT by Finite and Boundary Element Methods

We propose a new approach to diffraction tomography. We solve the wave equation, which governs the propagation of sound through a medium with spatially varying material parameters, using a combination of the finite element method and boundary element method. A computer simulation shows fine and quantitatively exact reconstruction of the two-dimensional distribution of refractive index and absorption coefficient of the material. This method is applicable not only to ultrasonic CT but also to microwave CT.

New Technology for Compact VTR: Sensorless Capstan Motor

Recent advances in VTR camcorders have been remarkable, and with the appearance of compact and lightweight models the market has grown rapidly. But in order to achieve further expansion of the market for camcorders, it will be necessary to develop models which are even smaller, lighter and more inexpensive. From the standpoint of electromechanical control, this im¬ plies a need to improve and reduce the size of driving motors. Among the motors used in camcorders, cyl¬ inder motors employing sensorless drive meth¬ ods which do not require rotor magnet position sensors have been put into practical use, and are contributing to reduce camcorder sizes and prices [1]. On the other hand, in order to