Takahiro Nakai

DEVELOPMENT OF HDTV DIGITAL TRANSMISSION SYSTEMI THROUGH SATELLITE

A HDTV digital transmission system through satellite has been developed. This system has been designed to utilize QPSK modulation via a 36 MHz bandwidth Ku band transponder. Convolutional code and Reed-Solomon code are applied for the purpose of error protection. The system provides the transmission rate of 40 Mbps for video. A HDTV codec has been fabricated for the system. A transmission experiment has been carried out and gave excellent transmission performance. >

Video buffer models of image division coding

The image division coding is one of the means of coding the image signals with high resolution such as HDTV. Generally the parallel processing scheme is applied to carry out the image division coding by dividing the image in several panels spatially and then employing the coding tools for each panel. However, it is necessary to distinguish the difference in coding performance between parallel and non-parallel processing schemes. This paper deals with the buffer size and buffer delay for coding due to parallel and non-parallel processing schemes. The following conclusion has been deduced through such study. For the same rate control conditions, the J division parallel processing needs the buffer size J times larger than the non-parallel processing, with the buffer delay being the same in both cases.

Digital HDTV transmission system via satellite

This paper describes a study for digital transmission system of HDTV signals through the satellite channel. This system has been designed to utilize QPSK modulation via 36 MHz bandwidth Ku band transponder. Convolutional code of rate 3/4 and (255,239) Reed-Solomon code are applied for the purpose of error protection. The system provides the transmission rate of 40 Mbps for video. In order to achieve such video date rate, we studied adaptive noise reduction filter, adaptive motion compensation and adaptive formation of blocks for DCT. This method provides a good picture quality of HDTV signals at the rate of 40 Mbps. The results of our study prove that the system is feasible. At present, we are assembling the codec which performs source coding and part of channel coding in this system. This codec can effectively confirm the performance of the basic algorithm in MPEG2.

Development of a Lens Driving Maglev Actuator for Laser Beam Off-Axis Cutting and Deep Piercing

In laser beam cutting and laser piercing process, the machining speed and quality are very sensitive to the flow of assist gas and laser beam focusing position. In order not only to improve the cutting speed and the removal capability of the molten material and to save the consumption of the gas flow in laser beam cutting, but also to realize high speed piercing of high aspect-ratio holes, a magnetic-levitated (maglev) lens driving actuator was proposed and fabricated. The actuator can drive the lens to achieve real-time positioning control of the relative radial displacement between the lens axis and the assist gas jet nozzle axis (off-axis control) in radial directions in a range of ±1mm within 1.5 μm of tracking error and bandwidths more than 150Hz, and to achieve real-time positioning control of laser beam focusing point in axial direction in a range of ±5mm within 3 μm of tracking error and bandwidth more than 100Hz.

Precision Control of Magnetic Drive Actuator Used for Laser Cutting with Compensation of Zero Point of Displacement Sensor

This paper describes a precision control method for a magnetic drive actuator used for the laser cutting to realize high speed and high accuracy machining. Firstly, a zero bias current method is applied to drive the electromagnets to achieve a high-precision and long-stroke of the actuator. Secondly, a compensation method of the zero point of the displacement sensors is presented to prevent the generation of the disturbance force produced by the elastic hinges. Finally, the positioning performance of the actuator is evaluated through experiments and the experimental results show that the actuator has a positioning resolution of the order of micrometer, a bandwidth greater than 130Hz, and a positioning stroke of 1mm.

Adaptive Control of Magnetic Drive Actuator for Laser Cutting

This paper describes an adaptive control method for a magnetic drive actuator that used for the laser cutting to realize high speed and high accuracy machining. Firstly, a zero bias current method and a nonlinear compensator are examined and used for the actuator. Secondly, an adative control method is presented. Finally, the coefficient of the gap-current-force is estimated and the effectiveness of the presented control method is verified by experiments. The experimental results show that the coefficient of the gap-current-force reduces exponentially depending on the increase in the length of the air gap. By using the adaptive control, the peak-to-peak vibration amplitude of the lens holder is reduced from 1.95um to 1.55um.

A practical MPEG2 encoder and its techniques to provide high quality images

We have developed a practical MPEG2 encoder which encodes one channel video and two channels audio into single Transport Stream in real time. The encoder is realized in compact size, using a newly developed chip set Furthermore we have studied about composite signal processing and blocking artifacts reduction to provide high quality images. The former method handles composite video well and the latter one helps the decoder reduce blocking artifacts in scene changes and fast pans.

A Study of Scalable Image Coding for Digital Video Disk.

MPEG2をベースにしたディジタルビデオディスクの画像符号化方式として, 良好な早送り再生が可能な階層符号化の検討をシミュレーションにより行った.本稿では提案方式の検討の概要と良好な早送りの実現を可能としたデータ処理手法について述べる.