We examine a lifetime estimation method for high-density recordable optical disks. It is based on the Eyring acceleration model and statistical analysis. The statistical distribution of life data for the optical disk assumed a lognormal distribution. The standardized life expectancy of an optical disk is defined as the minimum lifetime of 95% survival probability at 25°C / 50%RH with a 95% confidence level. An acceleration test was conducted under stress conditions of temperature and relative humidity. Results have demonstrated that the statistical distribution of lifetime data using the digital error criterion item can be applied to a lognormal distribution. Thereby, we can estimate a standard life expectancy of high-density recordable optical disks as the minimum lifetime of 95% survival probability at a 95% confidence level.
This study examined a lifetime estimation method for optical disks. It is based on the Eyring acceleration model and statistical analysis. The statistical distribution of life data for the optical disk assumed a lognormal distribution. Analysis of statistical techniques based on the ISO standard is proposed as a life expectancy prediction method for CD-R disks. The standardized life expectancy of an optical disk is defined as the minimum lifetime of 95% survival probability at 25/50%RH with a 95% confidence level. An acceleration test was conducted using a high-density optical disk under stress conditions of temperature and relative humidity. Consequently, we confirmed the capability of this method for estimating life expectancy by considering the stresses of temperature and relative humidity, and providing for a confidence level. The statistical distribution function of optical disk lifetime data must be clarified experimentally to apply this technique to lifetime estimation of optical disks in the future.
To cope with the trend of high-speed access, a high-performance optical head with a sliding and rotary-type of lens actuator has been developed. An advantage of this type of lens actuator is that the moving part of the actuator is dynamically well balanced so that the objective lens is not shaken by acceleration or deceleration during seeking. As a result, the stability of the velocity control during seeking has been improved and the waiting time when the operation mode changes from the seek mode to the tracking mode has been reduced. To cope with the trend of high-speed transfer, we have increased driving efficiency and set the frequency of the parasitic resonance sufficiently high. Also, the rotational latency, which is an important factor of the access time, has been shortened. As a result, a data transfer rate of 7.4 Mbits/s and average access time of 48 ms have been attained in a 130-mm rewritable optical disk drive.
A new composite tracking method suitable for a two-beam split-type optical head is suggested. Using twin spot and push-pull tracking method, and with ana auxiliary actuator combined, this method is designed so as to be applied, in particular, to optical disks having continuous grooves. In this method, a read-out spot is controlled by the twin-spot method, and moreover an auxiliary actuator for write spot positioning is driven by a differential signal of two push-pull tracking error signals derived from read-out and write beams. To examine tracking performance of this method, we constructed a two-beam optical head and successfully confirmed that the two spots could be easily positioned on the same track center independent of +/- 100 micrometers objective lens shift.