Abstract:
An optical disk is provided with a dedicated track area for recording optical conditions for read and write operations. The apparatus includes different types of demodulating circuits for allowing any type of demodulation to be adopted. After parameters, recorded on the dedicatad track area through phase encoding demodulation, are read out, the demodulating circuit compatible with the modulation type adopted in recording the data is selected for demodulation of the data.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to an optical information recording/reproducing method and an apparatus for carrying out the same. More particularly, the invention is concerned with a recording system which is advantageously suited for ensuring interchangeability (compatibility) among existing recording medium of different types or between the currently used recording media and those of increased record density which will become available for practical application in the not too distant future. 
     In the prior art optical disk storage system, it is known that an index area is provided on a disk for storing therein data for retrieval, data for access designation and those for other purposes, as is disclosed, for example, in Japanese Patent Application Laid-Open No. 25278/1981 (JP-A-56-25278). 
     There are, however, established a variety of specifications for the recording system in respect to the recording light (laser) power, reflection factor of the disk and other parameters, and any given recording system is so designed to conform with one of the specifications. Consequently, a recording/reproducing apparatus designed to operate with the disk having the reflection factor of a certain predetermined value is not in the position to perform the recording/reproducing operation on another disk having a reflection factor which differs from the predetermined one. Further, a system in which a new modulation method developed with the aim to realize the high density recording is adopted is incapable of reproducing information recorded on the disk of the old type. Therefore, the disks which are currently used can no more find utility in the recording/reproducing system of the coming generation. It goes without saying that such absence of interchangeability or compatibility among the recording media provides much inconvenience. Thus, there exists a great demand for realizing the interchangeability of the recording media since otherwise the old type of disk could not be used in the future system which will no doubt adopt a novel modulation method in an effort to increase the recording density. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an optical disk recording/reproducing apparatus which is capable of reading control information recorded on a disk together with data, which information is referenced to when the data is to be read out or reproduced from the disk. 
     Another object of the present invention is to provide an optical disk reading system which is capable of reading the information concerning the optical reading conditions imposed inherently to the recording disk, which information is recorded on the disk at a predetermined region and read out to be processed in a manner different from the reading of the data. 
     Still another object of the present invention is to provide an optical recording/reproducing apparatus which can read/write data from/on a disk by utilizing control parameter information indicative of modulation type after the control parameter information has been derived from a corresponding record on the disk through a simple and reliable optical reading method. 
     It is a further object of the present invention to provide an optical recording/reproducing apparatus which is capable of searching a control track on which information about the types of modulations and others are recorded and which apparatus is further capable of reading the above information with a simple optical reading apparatus for the purpose of making access to data. The information and data are recorded, respectively, through different types of modulations on an optical recording medium. 
     It is a still further object of the present invention to provide an optical recording/reproducing apparatus which can discriminatively identify features characterizing various types of optical disks and perform recording/reproducing operations proper to the various disks, respectively, without involving any significant increase in the quantity of hardware. 
     In view of above and other objects which will become more apparent as the description proceedes, it is taught according to the present invention that a specific region is provided on a disk to be mounted on an optical recording/reproducing apparatus, and identification information, for discriminatively identifying the disk, is previously recorded on the track of the same by a modulation method differing from the modulation employed for recording data on a user data region (such as MFM and 2-to-7 modulation usually requiring a phase locked loop); The optical head of the recording/reproducing apparatus is indexed over the abovementioned specific region (e.g. control track area including a plurality of control information tracks) to read the identification data in precedence to a reading of the data from the user data region. In accordance with the result of the identification reading operation mentioned above, circuits of the optical disk apparatus participating in the data recording/reproducing operation are changed over to the state in which the user data can be recorded or reproduced. The modulation adopted in recording the identification information on the specific region is so selected that demodulation can be accomplished with the aid of a microprogram for the purpose of preventing the amount of requisite hardware from increasing. Further, such an arrangement is proposed which allows the optical head to be indexed or positioned onto the abovementioned specific region without need for recognizing addresses recorded on the disk. After the optical head has been positioned onto the control track, the control data read out from that track is demodulated with a microprogram or with a program of a microprocessor, wherein control data or information such as modulation type, recording power and other parameters obtained through the demodulation are loaded in the optical recording/reproducing apparatus to be utilized in intialization thereof. In this manner, the processing procedures and parameter values such as modulation type, recording power and others can be set in correspondence with the disk of concern, whereby recording/reproducing can be performed on a variety of disks with one and the same optical recording/reproducing apparauts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view showing a general arrangement of an optical recording/reproducing apparatus according to an exemplary embodiment of the present invention; 
     FIG. 2 is a view showing a structure of a control track employment according to an embodiment of the present invention; 
     FIG. 3 is a view showing, by way of example, a format of a sector constituting a part of the control track of FIG. 2. 
     FIGS. 4a to 4e are views for illustrating a control information reading and decoding procedure in accordance with an emobodiment of the present invention. 
     FIG. 5 is a view showing a portion of a signal waveform produced by an optical head upon reading of the control information in accordance with an embodiment of the present invention. 
     FIG. 6 is a view for illustrating a decoding of data making appearance in succesion to a bit signal &#34;SYNC&#34; recorded in the sector. 
    
    
     DETAILED DESCRIPTION 
     Now, the present invention will be described in detail in conjunction with the exemplary and preferred embodiment by reference to the drawings. 
     FIG. 1 shows a general arrangement of an optical recording/reproducing apparatus according to an embodiment of the present invention. A reference numeral 1 denotes an optical disk driven rotationally by a spindle motor 4. Provided for the purpose of writing on and reading from the optical disk 1 is an optical head 2 which is composed of an objective lens 14, a galvano-mirror 13, a semiconductor laser 19 and a photodetector 15. In order to allow the whole optical head 2 to make access to the optical disk 1 over the whole surface thereof, a voice coil motor (hereinafter referred to as VCM) 3 is provided. The objective lens 14 and the galvano-mirror 13 are controlled so that automatic focussing and tracking operation can be accomplished. However, since such control constitutes no essential part of the subject matter of the present invention, detailed description thereof will be unnecessary. Further, those parts which are not important to the present invention are also omitted from illustration. 
     A position detector 12 serves for detecting that the optical head 2 has attained the permissible innermost position. 
     When the optical disk 1 is set on the spindle motor 4, the latter starts rotation. Upon attainment of the steady rotation state of the motor 4, the seminconductor laser 19 is energized to emit light. 
     The VCM 3 is supplied with a current through a VCM control circuit 26 under the control of a microprocessor 24, whereby the optical head 2 is moved to a position to which the position detector 12 makes a response. Although the position detector 12 is assumed to be located at the permissible innermost position in the illustrated apparatus, it may be disposed on the outermost peripheral position. Further, a pair of such position detectors may be installed at the innermost and the outermost positions, respectively. In any case, the position detector 12 is composed of a light emitting element and a light receiving element (both being omitted from illustration). By providing the optical head 2 with a projection 11 which can be inserted between the light emitting element and the light receiving element of the position detector 12 in such a positional relationship that upon track following operation activated when the optical head 2 has attained the position at which the position detector 12 can respond, the optical head 2 assumes the position just over a control data area 17, it is possible to index the optical head 2 at the position just over the control track area 17 without reading any information from the optical disk 1 as it traverses the disk on the way. It will be readily understood that another position detector can be provided in association with an outer control track 18. 
     Information on the optical disk 1 is detected by the photodetector 15, the output signal of which is processed through a reproduction circuit 20, whereby a data signal 27 is obtained. Data read from a user data area 16 is demodulated by a data demodulation circuit 21 or 22 to be transferred to a control unit 37 by way of an interface circuit 5. On the other hand, the data signal 27 originating in the control track area 17 or 18 is decoded directly by a known microprogram, by hardware, or by a program running on a microprocessor 24. Thus, the information recorded on the control track is fetched by the microprocessor 24. On the basis of this information, the microprocessor 24 effectuates initialization of the optical recording/reproducing system. 
     In FIG. 1, reference numeral 28 denotes a signal for changing over the demodulation circuits 21 and 22 so that the demodulation circuit corresponding to the modulation type detected from the data retrieved from the control track is turned on, and a numeral 40 denotes a power command signal for designating a maximum read power to be supplied to the semiconductor laser 19 upon data reading operation (reproduction mode) and a maximum record power to be supplied to the laser 19 in the data writing operation (recording mode). A numeral 29 denotes collectively other switching/control signals. The control track areas 17 and 18 are provided within the track region with predetermined distances from the center of the optical disk 1, respectively. 
     When data is to be written in the user area 16, the type of modulation for the data is determined on the basis of information supplied to the control unit 37 from the control track area 17 or 18 through the microprocessor 24 and the interface circuit 5. In dependence on the type of modulation determined, modulation-A circuit 38 or modulation-B circuit 39 is energized to generate write data and a write clock signal which are then supplied to a recording pulse generator circuit 33 through the interface circuit 5. On the basis of the input write data, the recording pulse generator circuit 33 produces a pulse signal having a pulse duration corresponding to that of the recording current to be supplied to the laser. To this end, the recording pulse signal 34 is applied to the laser drive circuit 35 for generating the current to drive the semiconductor laser 19. 
     Detail of the control track is shown in FIG. 2. As will be seen, one control track is divided into a plurailty of sectors in which the identical control information are recorded, respectively. The division of one track into a plurality of sectors, as mentioned above, is for the purpose of preventing the influence of any defect which may be present on the optical disk 1. It is preferred that several hundred or more control data tracks be provided so that the optical head can be positioned on a control information track without resorting to the use of address for the control track. Usually, the degree of precision at which the optical head 2 can be positioned is on the order of 0.1 m/m or less. Accordingly, the control information track area including several hundred tracks and having width of 0.3 to 1.0 m/m can assure that the optical head makes access to one of the control tracks without fail. Further, the bit density of control information data recorded on the control track should be selected so low that the data can be decoded (demodulated) by the microprocessor without exerting any adverse influence to the servo control, as described hereinafter. The encoding of the data to be recorded on the control track may be realized by a simple encoding technique such as phase encoding (PE) which needs no PLL (phase locked loop). 
     An example of the format for one sector of the control information track is illustrated in FIG. 3. The sector format includes fields such as those labelled GAP indicating a start of the sector, PREAMBLE for phase matching or the like purpose, SYNC indicative of the timing at which the data reading is to be started, TRACK/SECTOR ADDRESS containing addresses, DATA in which data is recorded, CRC used for error detection and others. It should be understood that the format shown in FIG. 3 is only exemplary and the present invention is not restricted to such a format. 
     FIGS. 4a to 4e show, by way of example, a recording scheme of the control information on the control track. The control information data is so written that the signal waveform shown in FIG. 4a is an output of the photodetector 15 upon a reading of the data. It will be seen that the data is phase-encoded such that dense repetition patterns 31 having duration of 2 to 4 μs are alternately combined with blank portions 32 containing no data. With such short length or duration of the dense repetition pattern, it is aimed to suppress the influence to the servo-control system to a minimum. In order to allow the read-out signal to be decoded with a microprogram running on the microprocessor, digitization of the signal is required. To this end, a low-frequency signal component such as shown in FIG. 4b is extracted from the waveform shown in FIG. 4a and shaped into a pulse signal shown in FIG. 4c with reference to a slice level 30. The pulse signal (FIG. 4c) is then read by the microprocessor in the form shown in FIG. 4e under the timing pulse of short duration shown in FIG. 4d. 
     A decoding method of the sector information will be described by paying attention to the transition from &#34;PREAMBLE&#34; field to &#34;SYNC&#34;. Although the PREAMBLE field is assumed to contain a series of &#34;0s&#34;, a same result can be obtained even when the PREAMBLE is constituted by a succesion of &#34;1s&#34;. 
     In the decoding, the time interval t between a point of change in the fetched data and the succeeding change point is measured. When the measured time t satisfies the following condition: ##EQU1## where T: bit length, and 
     ΔT: permissible variation determined in consideration of fluctuation in rotation speed, nonuniformity of disk, errors involved in the processing by electric circuitry and other variables. 
     It is then determined that bits &#34;0s&#34; or &#34;1s&#34; make appearance in succession. In this conjunction, it should however be mentioned that allocation of the bit value to PREAMBLE and SYNC is previously determined. For example, when PREAMBLE is represented by a succession of &#34;0s&#34;, the SYNC is given by bit &#34;1&#34; and vice versa. 
     On the conditions, when a bit makes appearance subsequently with the time span t which meets the following condition: 
     
         T-ΔT.sub.2 ±t±T+ΔT.sub.2 
    
     then, that bit is determined to be the SYNC bit. In the following, it is assumed that the PREAMBLE bit is logic &#34;0&#34; with SYNC bit being &#34;1&#34; for simplication of description. 
     FIG. 6 is a diagram showing the waveform as read out. In an interval (a), the timing SYNC bit is detected, whereupon the reading and decoding of data are started. In a succeeding interval (b), no change occurs in the waveform within a time space defined by T±ΔT 2 . Accordingly, the data bit is &#34;0&#34; (as inverted relative to the preceding bit). In an interval (c), a change occurs in the waveform at a time point T/2±ΔT 1  within the time span T±ΔT 2 . Accordingly, the corresponding bit is &#34;0&#34; (same as the preceding bit). In the similar manner, the data of &#34;1&#34; or &#34;0&#34; is successively decoded. 
     FIG. 5 shows comparatively durations of the low frequency portion and the high frequency portion in the waveform illustrated in FIG. 4a. More specifically, the duration (f) is selected to be 20 to 40 micro seconds with the duration (g) being 180 to 400 nano seconds, which is suited for the reading and decoding with the microprogram in the microprocessor. 
     Since a great number of control tracks are provided and each of them include a plurality of sectors having the same content, it is conceivable with a view to enhancing reliability of the data, to perform the reading/decoding on the plural sectors (e.g. three sectors), wherein the valid data is determined in accordance with an algorithm such as the majority rule. With this method, influence exerted by a defect can be more positively suppressed. 
     In addition to reading the type of modulation and the power of laser beam for recording, control information such as the laser light wavelength for recording, the size of sector, the rotational number of disk, maximum permissible read power, erase power suited for erasure of data, and the width of laser beam for writing can be read out and decoded. By setting these data values in the laser drive circuit 35 (FIG. 1) in precedence to a data read operation, data access can be accomplished with a reduced error rate.