Akihito Ogawa

Advanced phase change media for blue laser recording of 18 GB capacity for 0.65 numerical aperture and 30 GB capacity for 0.85 numerical aperture

We attempted to improve phase change media to achieve larger capacity for systems with blue lasers using numerical apertures (NA) of both 0.85 and 0.65. It was found that the Bi-added GeTe-rich pseudo-binary composition promised high erase ratio even when we did not use any interface layers on a recording layer. The use of an absorption control layer (ACL) was also attempted to suppress the cross erase (XE). It was found that the ACL was very effective in suppressing the XE. The advanced phase change media that used the above novel technologies showed good analog performance. The advanced media also showed bER of less than 1.0×10-4, promising 18 GB capacity for an NA of 0.65 and 30 GB capacity for an NA of 0.85.

Cogging-Torque Reduction of Transverse-Flux Motor by Skewing Stator Poles

Transverse-flux motors basically have coils wound in the rotational direction and armature cores surrounding them. This configuration allows the motors to be designed for multipole structures with the simple coil geometry independent of the pole number. Therefore, they have an advantage on high-torque generation over most motors having windings wound around teeth and put in slots. However, transverse-flux motors still have a production problem for their multipole rotor due to the assembly of the small and numerous permanent magnets. Thus, we have designed a consequent-pole transverse-flux motor, having a half amount of magnets on the rotor compared with the conventional surface-mounted magnet rotors, and capable of generating almost the same torque under the same size and excitation conditions. However, this motor also has large cogging torque due to the consequent poles, having deformed magnetomotive-force distribution. Thus, we propose a new skewed core structure for reducing the cogging torque, compatible to axially non-uniform structure of this motor. The Finite Element Method analysis result indicates the peak-to-peak value of the cogging torque that can reduce by 82% with this proposed skewed structure.

Combined adaptive controlled PRML signal processing for high-density optical disk

The combined adaptive controlled PRML signal processing was newly developed. The new method is a combination of the adaptive controlled FIR filter and the adaptive controlled Viterbi decoder. The adaptive controlled Viterbi decoder was operated under the condition that the Viterbi decoder is controlled such that the unity gain is kept. We report the simulation results, which are evaluated using signal asymmetry margin and tangential tilt margin to verify the effectiveness of this method expanding the margins. The combined adaptive controlled PRML signal processor is effective for these signal tolerances. Furthermore, the experimental results confirm the simulated effectiveness for expanding the tangential tilt margin. Consequently, a new method of combined adaptive controlled PRML signal processing is effective in reducing the deteriorations of data detection for high-density optical disk.

New write shift compensation method modified for optical disk systems to which partial response maximum likelihood (PRML) detection is applied

A new write shift compensation method is proposed in this paper. The method is suitable for an optical disk system which adopts partial response maximum likelihood (PRML) detection, and it can optimize adaptive controlled writing pulses even under severe inter-symbol interference (ISI) conditions to reduce detection errors. This advantage is attributable to the use of the Euclidean distance as the estimation index of the mark edge shift error. The effect is confirmed by the experimental results for blue laser systems.

Temperature Compensation Servo Algorithm for Holographic Data Storage

Photopolymers are widely used as media for holographic data storage because of their high dynamic range, high photosensitivity and availability. However, the most photopolymers have a large coefficient of linear thermal expansion. Therefore, it is known that the temperature changes cause deterioration of readout image under the Bragg-mismatch conditions. This paper proposes a new servo algorithm which includes both the servo error signals detection method and the automatic compensation procedures with feedback servo for the holographic data storage system. Experimental results for the proposed technique are demonstrated for temperature changes of up to +25 K successfully.

A new method of evaluating signal quality for systems to which partial response and maximum likelihood is applied

The partial response and maximum likelihood (PRML) detection method is promising as a detection scheme for next-generation optical disk systems. For application of the PRML detection, a new value is required in order to evaluate signal quality instead of jitter, which is used in current optical disk systems. For this requirement, we developed a new evaluation method that is based on the principle of the PRML detection. This evaluation value is defined as the occurrence probability of miss-detection in the PRML detection. We evaluated the proposed method using a simulated waveform and an experimental waveform for two systems. Each system consists of a phase change disk with cover layer thickness of 0.6 mm and 0.1 mm, a blue laser with wavelength of 409 nm and 407 nm and an objective lens with numerical aperture of 0.65 and 0.85, respectively. As a result, we confirmed the validity of the proposed method for each system.

Experimental study of 28-GB optical disk using a blue laser

The possibility of an optical disk capacity of 28GB/side is studied. The read-write characteristics of a phase-change optical disk are examined using a thin cover layer, a blue laser diode, high NA objective lens and the PRML method. The wide tilt margins of high-density recording are achieved.

Advanced phase change medium of over 30 GB capacity for blue laser and high-NA objective lens

Advanced phase change medium of over 30GB data capacity has been proposed and the recording characteristics of the medium have been described. The medium has L-H polarity, Bi-substituted GeTe-rich pseudo-binary alloy film as the recording layer, and thin metal absorption control layer. The recording measurement was carried out by using a blue laser light source with the wavelength of 405nm and an objective lens with NA of 0.85. Both CNR and ER have been improved by the use of the Bi-substituted GeTe-rich composition. XE has been reduced by the use of the absorption control layer. The bER measurement demonstrated its capability for over 30GB data capacity.

High-speed and compact depalletizing robot capable of handling packages stacked complicatedly

For a depalletizing robot to be practical, it has to be able to work skillfully in a limited space with a depalletizinging speed equal to or exceeding that of a human. Our new robot has the following advantages. A gantry robot and a telescopic arm mechanism are adopted so that the robot, although space-saving, has a large workspace. Using camera image and depth image, the robot recognizes the various package stacked complicatedly and decides the handling order of the package. The robot generates the most suitable handling path and performs handling control such that stacks do not collapse. The robot achieves fall prevention of the package and stable conveyance by supporting beneath the package with another arm, the conveyor arm. Moreover, in order to accelerate processing of packages, we thought it was important for the robot to be equipped with a wide end effector capable holding multiple packages simultaneously. Therefore we developed a depalletizing simulator and performed the optimal design of the end effector by using a simulator. This, we were able to realize a compact depalletizing robot with a depalletizing speed equal to that of a human.

Phase-change recording media of 20-GB capacity for system with 0.6-mm-thick substrate

We have developed phase change media of 20GB user data capacity for the next generation optical recording system using a blue-violet laser diode with the wavelength of 405nm. An objective lens with the numerical aperture of 0.65 has been used along with mm-thick substrates on which the laser is incident. We have employed the land and groove recording. A transparent film with high thermal conductivity has been adopted at the light incident side of the recording layer in order to improve the carrier to noise ratio and the erase ratio as well as to reduce the cross-erase. Bottom channel bit error rate of less than 1×10-6 has been obtained and its wide tilt margins have successfully demonstrated the strong feasibility for the next generation rewritable system.