Thin Optical Disk Stabilization Technology Using Air Bearing

This technology, which enables the stable, high-speed rotation of disks as thin as paper, makes possible the stacking of large numbers of disks, high-speed data transfer, and high recording capacity.

Stable Rotation of Thin Optical Disks by Means of an Air Stabilizer Plate

When a flat plate is placed in close proximity to a flexible thin optical disk and rotated stably, airflow occurs between the disk and the plate, and the air acts as a bearing. Therefore, thin, flexible disks rotate with greater stability than rigid disks. Ricoh has applied this principle to optical disks.

The overall configuration is shown in Figure 1. To the right is a cartridge in which multiple thin optical disks are stored. As disk thickness is about the same as that of a sheet of paper (0.1mm), the thickness of a cartridge loaded with ten disks can be kept to less than a centimeter. To the left is a structure configured by adding an air stabilizer plate to an ordinary optical disk drive.

Figure 1: Overall configuration of a thin disk drive
Figure 1: Overall configuration of a thin disk drive

The photographs below show an experiment involving placement of a thin optical disk adjacent to an air stabilizer plate and rotating the disk.

Photo 1: Air stabilizer plate
Photo 1: Air stabilizer plate

Photo 2: Rotating disk
Photo 2: Rotating disk

The copper disc in Photo 1 is the air stabilizer plate. The silver item at the center of the plate is the top of the motor that rotates the disk. Photo 2 shows the rotation of a mounted disk. A gap of about 0.1mm occurs between the disk and the stabilizer plate. As a thin disk is flexible, it becomes floppy when rotated without a stabilizer plate. However, when placed in proximity to a plate and rotated as shown in Photo 2, a thin high-speed airflow occurs, and the flexible disk rotates along with the flow. The force of this airflow suppresses vibration above and below the disk. As shown in Photo 2, a disk rotating free of vibration has the appearance of a motionless mirror.

The difference in the state of disk rotation according to whether or not a stabilizer plate is used is readily apparent from the video clips below.

Video 1: Rotation without a stabilizer plate Video 2: Rotation with a stabilizer plate

Benefits of Thin Disks

As CDs and other conventional disks are used without a stabilizer plate, they are made of rigid material to ensure vibration-free rotation. At times disk rotation speed is increased in order to increase the speed of reading information from disks. However, when rotation speed exceeds 10,000 revolutions per minute, the hardness of the disk increases resonance, excessive vibration occurs, and the disk shatters. Consequently, there is an upper limit to optical disk rotation speed, which in turn limits data transfer speed. (Of course, the disks for products such as CDs and DVDs are used at rotation speeds that offer ample margin for safety.)

On the other hand, in the case of thin optical disks stabilized using the force of air, as the force of air dampens vibrations, resonance does not occur even at speeds exceeding 10,000 revolutions per minute. Therefore, these disks can achieve data transfer at higher speeds.

Furthermore, disk stabilization makes possible thinner, flexible disks that can be loaded into cartridges in greater numbers. This makes possible a dramatic increase in disk capacity; the storage in a single cartridge of 10 disks with recording density equivalent to that of blue laser recording would provide capacity of approximately 250 gigabytes, equivalent to two hours of high-definition moving pictures for broadcasting use.

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Photo 3: Thin optical disk   Provided by NHK Science & Technical Research Laboratories
Photo 4: Thin optical disk drive

Practical Application in Broadcast Archiving and Potential for Further Application

This technology has made it possible to rotate disks at speeds exceeding 10,000 revolutions per minute, performance previously considered impossible. Furthermore, the speed of 15,000rpm has been achieved under experimental conditions. This is the speed required to record high-definition moving pictures for broadcasting use starting from the inner radius of the disk in the same signal format as used for Blu-ray disks. This makes it possible to record on the entire disk surface in exactly the same picture quality as that of VTR (HD-D5), the highest image quality used by broadcast stations. As conventional Blu-ray disks are rigid disks, maximum disk speed is limited to about 10,000revolutions per minute; this means that high-definition moving pictures for broadcasting use can be recorded only on the outer radius of the disk.

In addition, we have enhanced applicability to high-speed rotation by applying the ZPET-FF feed forward control that Japan Broadcasting Corporation Science & Technical Research Laboratories is currently developing to reduce error in the tracking direction.
About 15 minutes of high-definition moving pictures for broadcasting use can be recorded on a single thin optical disk. One thin optical disk cartridge will make it possible to record two hours of programming, higher capacity than that of a tape for broadcasting use.

One currently envisioned application is the archiving of broadcast station video content and television programs. For instance, NHK uses an entire building as a videotape storage warehouse. It currently stores approximately one million tapes at this facility, and the number of archived tapes increases by about 40,000 each year. Tapes for broadcasting use are larger than home VHS tapes and require a large storage space. Also, long-term storage of tapes is inconvenient; for example, it is necessary to occasionally feed (and rewind) the tapes for ventilation purposes.

Figure 2: Target performance for thin optical disks
Provided by NHK Science & Technical Research Laboratories
Figure 2: Target performance for thin optical disks

The use of this thin optical disk cartridge is expected to provide great savings of storage space and eliminate the labor entailed in the tape feeding required for routine maintenance during storage. Also, conversion to smaller, lighter disk cartridges will make it possible to save oil resources required to store an equivalent amount of footage using the current tapes.

Another expected application for thin optical disks is the storage of data currently stored using data tapes. Although signal formats for broadcasting and computers varied until ten years ago, today both are digital. A similar situation exists with respect to needs for high data transfer speed, high data capacity, and long-term storage reliability: if a storage medium suitable for broadcasting applications can be produced, application to ordinary data storage (backup tape media) will also be possible.

Ricoh has jointly developed this technology with the NHK Science & Technical Research Laboratories, a world leader in the development of broadcasting standards and electric devices.


Data Archiving Requirements

In the case of TV program archiving, not only must disks function more than ten years after storage begins, playback equipment must also operate. For that purpose, stable supply of maintenance parts is necessary. The key feature of these thin optical disks is that they can deliver the high speed and high capacity required for broadcasting applications even as they share the same optical pickups and signal processing microchips as those used in consumer Blu-ray disk players. As this playback equipment does not use special components, it is a simple matter to guarantee playback capability into the future. Ricoh considers this the greatest advantage of thin disks as a data archiving medium.

This advanced technology is highly regarded and it was awarded the Excellent Research Announcement Prize for 2008 of The Institute of Image Information and Television Engineers.

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