Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-10-22
2001-01-30
Edun, Muhammad (Department: 2753)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044260, C369S044280, C369S053130
Reexamination Certificate
active
06181652
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the recovery of data from rotating data storage disks such as, typically, compact disks (CDs) used as read-only memories (ROMs) in computer systems. More specifically, the invention concerns how to determine the optimum speed of rotation for reading each CD-ROM or like data storage disk according to the particular eccentricity of that disk.
Although originally developed for consumer audio reproduction in substitution for analog phonograph records, CDs have now found wide-spread commercial acceptance as compact, high-speed, large-capacity ROMs for computers. The only difference of CD-ROMs from audio CDs is that CD-ROMS are driven at speeds several times as high as the standard audio CD speed (1.2-1.4 meters per second).
There have been problems left unsolved in use of CD-ROMs with high-speed CD-ROM drives in computer systems. CD-ROMs are presently being made under the same design specifications and manufacturing standards as low-speed audio CDs. Inevitably, therefore, a substantial percentage of CD-ROMs on the market are not of truly satisfactory quality for use as high-speed computer data storage media. Some have their spindle holes cut eccentrically; others have their multiturn spiral tracks not centered at the geometric center of the disk.
Such eccentric disks, particularly eccentric hole disks, are easy to vibrate when driven at a speed as high as, say, twenty times the standard audio CD speed. The disk vibration can be resolved into horizontal and vertical components, it being understood that the disk is laid horizontally. The horizontal component can overload the tracking servo of the CD-ROM drive whereby the radial position of the beam spot on the disk is maintained in alignment with the spiral data track. The overloading of the tracking servo has resulted in the overheating of the voice-coil actuator for tracking control, in the degradation of its performance and, in the worst case, in the burning of the actuator coil.
The vertical component of disk vibration, on the other hand, can cause the overloading of the beam focusing servo of the CD-ROM drive, again resulting in the overheating of the focusing actuator of voice-coil construction, in the degradation of its performance and, in the worst case, in the burning of the focusing actuator coil. The malfunctioning, not to mention total destruction, of the tracking or the focusing servo must be averted by any means because of ensuing read errors and retries, which is a waste of time running counter to the objective of high speed data recovery for which CD-ROMs are intended.
Disk vibration can give rise to additional inconveniences. A vibrating disk may cause vibration of the complete CD-ROM drive and, in consequence, of the hard disk drive (HDD) in particular which is currently being preferentially built into the computer system along with the CD-ROM drive. The vibration of the HDD is just as undesirable, causing both read and write errors, to the detriment of the reliability of the complete computer system. Even if not so excessive as to cause read and write errors, the vibration of the CD-ROM drive certainly gives a shoddy image of the product to the user or to prospective buyers.
The reader might think that all such troubles and inconveniences would not manifest themselves if only high quality CD-ROMs, altogether free from the physical defects pointed out earlier, were used. CD-ROM drive manufacturers cannot, and should not, expect their products to be used only with such high quality disks, since in the current state of affairs the existence of poor quality CD-ROMs must be more or less taken for granted.
Fujimoto et. al. U.S. patent application Ser. No. 08/890,924, filed Jul. 10, 1997, teaches to check the eccentricity of each CD-ROM loaded into the disk drive and to read the disk at a speed matching its particular eccentricity. The maximum possible reading speed according to this prior related application is assumed to be eight times the standard audio CD speed. More recently, however, CD-ROMs have begun to be read at as high as twenty or even thirty times the standard audio CD speed. The higher the speed of rotation, the more will the disk vibrate if it is eccentric. A more accurate determination of the amount, and “nature”, as will be later explained, of the eccentricity of each disk has proved necessary for reading only high quality disks at such ultrahigh speeds, and other disks at less speeds matching their particular eccentricities.
SUMMARY OF THE INVENTION
The present invention has it as an object to ascertain the amount and nature of the eccentricity of each disk more accurately than heretofore and to drive the disk at a speed suiting the particular eccentricity of the disk.
Another object of the invention is to recover data from disks of varying physical qualities at the highest possible speed suiting each particular disk without causing read errors or retries.
Still another object of the invention is to make utmost use of the preexisting parts and components of CD-ROM drives or like apparatus in order that the inventive concepts may be implemented in such apparatus without any substantial alteration of its construction.
Briefly summarized in one aspect thereof, the present invention concerns, in an apparatus for data recovery from rotating data storage disks having varying degrees of hole eccentricity and track eccentricity, a method of reading each disk at a speed suiting the particular hole eccentricity of that disk. The method comprises making a first measurement of the hole eccentricity and track eccentricity of a disk in rotation at a first disk eccentricity check speed, and a second measurement of the hole eccentricity and track eccentricity of the disk in rotation at a second disk eccentricity check speed which is higher than the first. The subtraction of the first measurement from the second measurement provides the hole eccentricity of the disk, according to which a matching speed of rotation for reading the disk is determined.
Stated in another aspect thereof, the present invention provides an apparatus for carrying the foregoing method of this invention into practice. A rotating disk data recovery apparatus, particularly a CD-ROM drive, of standard design is readily adaptable for implementation of the method.
The invention as summarized above is based upon the fact that there are two types of disk eccentricities, namely, hole eccentricity and track eccentricity. Hole eccentricity is such that the spindle hole is situated off the geometric center of the disk. In track eccentricity the data track is not centered at the geometric center of the disk. Usually, both hole eccentricity and track eccentricity coexist in each disk. It is, however, hole eccentricity that causes vibration of the disk and of the disk drive upon rotation of the disk, with the intensity or amplitude of vibration increasing with disk speed. Track eccentricity, on the other hand, is no inherent cause of disk vibration, and the vibration of a disk having only track eccentricity, if any, does not increase in intensity with disk speed.
Thus the present invention advocates to measure the hole eccentricity and track eccentricity of each disk at two different disk speeds. The subtraction of the eccentricity measurement at the lower disk speed from that at the higher results in the elimination of the track eccentricity, leaving only the hole eccentricity. The hole eccentricity thus detected is solely relied upon in determination of the speed for reading the disk with a minimum of vibration and therefore a minimum of read errors and retries.
The invention is particularly well applicable to optical disk drive as typified by CD-ROM drives, such devices having a transducer for reading data recorded on each optical disk along a multiturn spiral track thereon by irradiating the disk with a beam of light. The hole eccentricity of an optical disk manifests itself during disk rotation as periodic vibration of the disk and, in consequence, periodic departures of the light beam from the track t
Fukinuki Shigeru
Kanenaga Junichi
Katou Noriyuki
Edun Muhammad
Teac Corporation
Woodcock Washburn Kurtz Mackiewicz & Norris LLP
LandOfFree
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