Optical recording/reproducing method and apparatus

Abstract: An optical disk (1) is provided with a dedicated track area (17; 18) for recording optical conditions for read and write operations. The apparatus includes different types of demodulating circuits (21; 22) for allowing any type of demodulation to be adopted. After parameters recorded on the dedicated 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: The present invention relates to a method for recording/reproducing information as defined in the preamble of claim 1 and to an apparatus and an optical disk for performing said method as defined in the preambles of the claims 4 and 10 respectively. In the art of optically storing information it is common technique to use as a recording medium an optical disk which in addition to an information area destined to receive information data comprises an index area destined to store therein data for retrieval, data for access designation and data for other purposes. An example for the said technique is known from JP-A-56-25278. Further, from EP-A-0 064 196 there is known an optical data recording and reproducing apparatus for an optical disk with an optical guide track having a plurality of data sectors each of which is a recording/reproducing unit. Each of said sectors includes an identification field and a data field. The identification fields and the user data are alternatively stored in the tracks of the user area and the identification fields are read during recording and reproducing periods to identify the user data address. The whole disclosure is directed to realize a recording and reproducing system in which the identification field contains identification data such as the track address and the sector address. Additionally, it shall be provided a clock reproduction system for reproducing the data field in a stable manner against the time variations caused by an eccentricity of the optical disk or variations of rotation. From EP-A-0 126 682 there is known a calibration device for the optical power applied to an optical disk for recording information data. The said calibration device is designed to provide for controlling the power of a light beam which is radiated to a sensitive layer, in order to obtain correct engraving, depending on several physical conditions. The general object is to take into account the influence of the aging of the optical elements, of variations in the parameters of the radiated light and of the limited accuracy of the electronic control. For the said purpose binary test words are recorded on the optical disk using mutually different optical power levels. The said test words consist of bit sequences in the form of digits repeated in a specific order and they are reproduced to deduce a mean value of bit numbers therefrom so as to determine a beam power and other control parameters. Said EP-A-0 126 682 is reflected in the preambles of the main claims. Considering the prior art outlined above and, additionally, considering the fact that there are recording media of different types including those of increased recording density it is an object of the present invention to provide for the possibility to deal with each one of a plurality of different types of recording media by means of only one recording/reproducing apparatus. According to the present invention the said object is achieved by means of a method defined in the claim 1. Advantageous further developments of the said method as well as preferrred embodiments for an optical recording/reproducing apparatus and an optical disk to be used for performing the said method are defined in the subsequent claims. In view of above and other objects which will become more apparent as description proceedes, it is taught according to the present invention that a specific region is provided on a disk mounted on an optical recording/reproducing apparatus, and identification information for identifying discriminatively 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), wherein 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 reading of the data from the user data region. In accordance with the result of 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 address 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 initialization 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 apparatus. 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 the structure of a control track employed according to the teaching of the invention; Fig. 3 is a view showing, by way of example, the format of a sector constituting a part of the control track; Figs. 4a to 4e are views for illustrating control information reading and decoding procedure; Fig. 5 is a view showing a portion of signal waveform produced by an optical head upon reading of the control information; and Fig. 6 is a view for illustrating decoding of data making appearance in succesion to a bit signal "SYNC" recorded in the sector. DESCRIPTION OF THE PREFERRED EMBODIMENTS Now, the invention will be described in detail in conjunction with the exemplary and preferred embodiments by reference to the drawings. Fig. 1 shows a general arrangement of an optical recording/reproducing apparatus according to an embodiment of the invention. A reference numeral 1 denotes an optical disk driven rotationally by a spindle motor 4. Provided for the purpose of writing and reading on and from the optical disk 1 is an optical head 2 which is composed of an objective 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 irrelevant to the 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 semiconductor 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 at which the position detector 12 responds. 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 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 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 from 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 numeral 40 denotes a power command signal for designating the 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. It should be mentioned that the disk provided with no control track can not be subject to the processing by the microprocessor. When data is to be written in the user area 16, the type of modulation for that 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. Details of the control track is shown in Fig. 2. As will be seen, one control track is divided into a plurality of sectors in which the identical control informations are recorded, respectively. The division of one track into the plural sectors as mentioned above is for the purpose of preventing an influence of any defect possibly 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 of the order of 0.1 m/m or less. Accordingly, the control information track area including several hundred tracks and having a 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 the phase encoding (PE) which needs no PLL (phase locked loop). As 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 of the 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 for the purpose of explanation, and the invention is never restricted to such format. Figs. 4a to 4e show, by way of example, a recording schema of the control information on the control track. The control information data is so written that the signal waveform shown in Fig. 4a is outputted from the photodetector 15 upon reading of the data. It will be seen that the data is phase-encoded such that dense repetition patterns 31 having a duration of 2 to 4 µm 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, digitazation 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 "PREAMBLE" field to "SYNC". Although the PREAMBLE field is assumed to contain a series of "0s", a same result can be obtained even when the PREAMBLE is constituted by a succesion of "1s". 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: T 2 - ΔT₁ ≦ t ≦ T 2 + ΔT₁ where T: bit length, and ΔT: permissible variation determined under consideration of fluctuations in rotational speed, non-uniformity of disk, errors involved in the processing by electric circuitry and other variables. It is then determined that bits "0s" or "1s" appear 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 "0s", then SYNC is given by bit "1" and vice versa. On the conditions, when a bit makes appearance subsequently with the time span t which meets the following condition: T - ΔT₂ ≦ t ≦ T + ΔT₂ then, that bit is determined to be the SYNC bit. In the following, it is assumed that PREAMBLE bit is logic "0" with SYNC bit being "1" for simplification 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 span defined by T ±ΔT₂. Accordingly, the data bit is "0" (as inverted relative to the preceding bit). In an interval (c), a change occurs in the waveform at a time point T/2 ±ΔT₁ within the time span T ±ΔT₂. Accordingly, the corresponding bit is "0" (same as the preceding bit). In the similar manner, the data of "1" or "0" 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 of the same contents, 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 the majority rule. With this method, influence exerted by a defect can be suppressed more positively. In addition to reading the type of modulation and the power of laser beam for recording, 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, the width of laser beam for writing and the like control information data can be read out and decoded. By setting these data values in the laser drive circuit 35 (Fig. 1) in precedence to the data read operation, data access can be accomplished with a reduced error rate.

Claims: A method for recording/reproducing information on/from an optical disk (1) including (a) a first area (16) comprising a plurality of tracks for recording user information using a first type of modulation and (b) at least one second area (17, 18) comprising a plurality of tracks for recording control information using a secona type of modulation by means of an optical recording/reproducing apparatus including (c) supporting means (4) for rotatably supporting said optical disk (1), (d) an optical head (2) radially movable relative to said optical disk (1) for radiating a laser light beam on said optical disk (1) to read or write information therefrom and thereupon respectively, (e) reproducing means (20) electrically connected to said optical head (2) to reproduce information from said optical disk (1) when irradiated with said laser light beam from said optical head (2), (f) first and second demodulating means (23, 24) electrically connected to said reproducing means (20) for demodulating signals derived from said user information and from said control information respectively when irradiated with said laser light beam from said optical head (2) and (g) laser drive means (35) for controlling the power of said laser light beam from said optical head (2) in response to the demodulation result from said second demodulating means (24), characterised by (h) pre-recording in said second area (17, 18) of said optical disk (1) as said control information data indicative for reading parameters of said optical disk (1), namely for the type of modulation used in said first area (16) and for the maximum admissible reading power for said laser light beam along a plurality of adjacent tracks and within a plurality of subsequent sectors of said adjacent tracks as a series of identical blocks and (i) radially adjusting said optical head (2) relative to said optical disk (1) into a position for irradiating said second area (17, 18) of said optical disk (1) with said laser light beam from said optical head (2) under the control of cooperating position detecting means (11, 12) provided on said optical head (2) and electrically connected to said second demodulating means (24) respectively before activating said optical head (2) to emit said laser light beam. A method according to claim 1, characterised in that the data pre-recorded in said at least one second area (17, 18) are modulated to be demodulated with the aid of a microprogram or a program of a microprocessor. A method according to claim 2, characterised in that said data are phase-encoded parameter data including a low frequency component having a half-period of 20 to 40 micro seconds and a high frequency component having a period of 180 to 400 nano seconds and that said parameter information is recorded on one information track in more than three sectors, inclusive thereof, said information tracks being provided in a number greater than one hundred. An optical recording/reproducing apparatus for performing the method according to one of the claims 1 to 3, comprising supporting means (4) for rotatably supporting an optical disk (1) including a first area (16) comprising a plurality of tracks for recording user information using a first type of modulation and at least one second area (17, 18) comprising a plurality of tracks for recording control information using a second type of modulation, an optical head (2) radially movable relative to said optical disk (1) for radiating a laser light beam on said optical disk (1) to read or write information therefrom and thereupon respectively, reproducing means (20) electrically connected to said optical head (2) to reproduce information from said optical disK (1) when irradiated with said laser light beam from said optical head (2), first and second demodulating means (23, 24) electrically connected to said reproducing means (20) for demodulating signals derived from said user information and from said control information respectively when irradiated with said laser light beam from said optical head (2) and laser drive means (35) for controlling the power of said laser light beam from said optical head (2) in response to the demodulation result from said second demodulating means (24), characterised by - cooperating position detecting means (11, 12) provided on said optical head (2) and electrically connected to said second demodulating means (24) respectively for radially adjusting said optical head (2) relative to said optical disk (1) into a position for irradiating said second area (17, 18) of said optical disk (1) with said laser light beam from said optical head (2) before activating said optical head (2) to emit said laser light beam. An apparatus according to claim 4, characterised in that said second demodulation means includes means for detecting the level of a signal obtained through said optical head (2) with successive timing pulses by means of a program. An apparatus according to claim 4 or 5, characterised in that said first demodulation means ((23) include first means (21) for demodulating an MFM-modulated signal and second means (22) for demodulating a 2-to-7 modulated signal and that said second demodulating means (24) includes switch means (28) for selecting either one of said first and second means (21, 22) for demodulating on the basis of information concerning the type of modulation included in the control information stored in said second area (17, 18). An apparatus according to one of the claims 4 to 6, characterised in that said laser drive means (35) includes means for setting a current to be supplied to said optical head (2) on the basis of information contained in the control information as to the value of the recording power of the laser beam. An apparatus according to one of the claims 4 to 7, characterised in that detecting means include a projection (11) mounted on said optical head (2) and an optical sensor (12) installed for producing a signal indicating an interruption of the optical path of said laser light beam by said projection (11) when said optical head (2) has attained a position in which said laser light beam irradiates a track on said optical disk (1) having control parameter information recorded thereon. An apparatus according to one of the claims 4 to 8, characterised in that means (3, 26)are provided for setting said optical head (2) to a predetermined position on said optical disk (1) and that the first demodulating means (23) are connected to said second demodulating means (24) for selecting one of the plurality of means (21, 22) in said first demodulating means (23) on the basis of the control information from said optical disk (1). An optical disk for performing the method according to one of the claims 1 to 3 by means of an apparatus according to one of the claims 4 to 9, including a first area (16) comprising a plurality of tracks for recording user information using a first type of modulation and at least one second area (17, 18) comprising a plurality of tracks for recording control information using a second type of modulation, characterised in that said second area(s) (17, 18) have pre-recorded data therein which are indicative for the type of modulation used in said first area (16) and for the maximum admissible reading power for a reading laser light beam along a plurality of adjacent tracks and within a plurality of subsequent sectors of said adjacent tracks as a series of identical blocks. An optical disk according to claim 10, characterised in that said second area(s) (17, 18) is(are) separated from said first area (16) and is(are) positioned on the inner and/or outer side thereof. An optical disk according to claim 10 or 11, characterised in that the control information pre-recorded in said second area(s) (17, 18) includes data indicating a sector size of tracks in said first area (16). An optical disk according to one of the claims 10 to 12, characerised in that the control information pre-recorded in said second area(s) (17, 18) includes data indicating an erase power for said laser light beam to be used to erase information from said first area (16).

Inventors: ARAI SHINICHI, TAKASAGO MASAHIRO, ARAI, SHINICHI, TAKASAGO, MASAHIRO
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1987
Main classification: G11B7
IPC codes: G11B7, G11B20