Optical disk systems are expected to meet the demands of large memory capacity because their recording density is about ten times higher than that of magnetic disks or tapes. A mass storage library system already implemented for a jukebox system. It used write-once optical disks and had a long access time. Recent advances in optical disk technology have increased the demand for erasable disks. Faster access times for mass storage systems are needed.

We have optimized the beam splitter in a magneto-optic system for improving a signal amplitude and carrier-to-noise ratio. We calculated the optimum conditions using the Jones matrix and taking the optics and media characteristics into account. We obtained a good readout signal.

In near future, many autonomous robots will be used to perform, to help with housework and to take care of the elderly people. However, their power consumption is very high, so it is significant to supply the power to robots efficiently. The three major power supply methods have been used; "wired style", "internal rechargeable battery" and "change style". Each method has some advantages and disadvantages. We focused on "change style" but it requires the high-level control to change battery correctly. If we could solve this problem, the robot's efficiency will become better. In this study, we will show that the electrical current controller using diode-bridge can flow the electrical current only one direction without depending position and the automatic battery charging system can use only putting the battery on it and charge the battery automatically.

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