OPTICAL RECORDING MEDIUM AND RECORDING AND REPRODUCING APPARATUS THEREFOR

Abstract: An optical disk (10) is disclosed which records informa­ tion that can be optically read. The disk has a spiral guide track (14). The disk further includes a single index field (20) and a plurality of sectors (18). The index field includes an index mark (22) that indicates the position at which an optical head is caused to jump for repeated trace of a specific portion of the guide track. Each of the sectors has a sector head (26) and a data field (30) that comes following the sector head. The sector head comprises a sector mark (26) located at the head of the sector and an address field (28). This address field contains a track address, a sector address, and an error detecting and correcting code. The index mark in the index field is detected, and the optical head is made to perform a jumping operation in response to the resulting signal, whereby the jumping operation is rendered certain. When the address fields are being read, if some sector addresses cannot be read due to drop-out or for other cause, the signal produced by detecting the index marks are counted by a counter into which the signal produced by detecting the sector marks is clocked, for preparing the sector addresses.

Description: The present invention relates to an optical recording medium for recording and reading information by the use of a light beam such as a laser beam and, more particularly, to the format of such guide track on an optical recording medium that takes a spiral form. An optical recording medium such as an optical disk is able to record information using a laser beam which is emitted by an optical head and which is focused to a spot of the order of 1µm. The information can be read by a read/write head that is placed in noncontacting relation to the disk. Accordingly, it has attracted interest as a high-density, digital mass storage. A guide track in the form of a groove has been previously formed on an optical disk, and the neighboring turns of this track are spaced apart a distance of the order of microns. A layer to be recorded is pierced or the reflectivity of the layer is changed by the energy of a laser beam having a minute diameter while the guide track is being traced by the thin laser beam, in order to record information. Optical disks for recording digital data have a guide track which is divided into a plurality of sectors in accordance with a certain format, like magnetic disks. Thus, a user can select a desired one of the sectors at will to record and read information. This format is formed at the same time when the guide track is cut by a laser cutting machine on a master disk coated with photoresist. The obtained master disk is subjected to development, and then it is plated with nickel. The plating layer of nickel is peeled off from the body of the master disk to provide a master disk of nickel on which the images that were formed on the photoresist layer by laser cutting have been transferred. This master disk of nickel is then set in a plastic mold, into which a plastic material is injected to form a replica disk that stores information formatted as described above. A recording material is then deposited onto the replica disk to form a recording layer. Subsequently, a protective layer is formed on this recording layer, thus completing an optical disk. One example of this format of the optical disk is disclosed in U.S. Patent 4,535,439 (corresponding to EP-A-081,138) in which the disk is divided into a plurality of sectors equally spaced apart from each other. The sectors are provided with a sector separator of identical structure at their foremost positions. Address parts which store addresses for the turns of the track are formed in the specific portion of the disk, i.e., the region extending radially from the center of rotation of the disk. Those which are cut in the innermost region of the disk are first and second index parts corresponding to the address parts and the sector separators, respectively. The first and second index parts are detected as changes in the quantity of reflected light by specially installed index detecting devices. The first index parts are used to determine the timing at which the light beam jumps back to its starting point after completing one trace of a specific portion of the spiral guide track, for retracing purposes. The second index parts are counted by a counter which delivers an output signal to indicate sector addresses for the sectors on the optical disk. The sector separators and the first and second index parts are shaped into depressions according to signals in the form of a burst. A modulation and demodulation system for an optical data recording and reproducing apparatus is disclosed in EP-A-064,196, in which, in an optical disc (1) having an optical guide track (2) and capable of recording and reproducing optically, the guide track is divided into a plurality of sectors (S₁₋S₁₀) and the recording or reproduction or reading is effected by a data sector. The modulation system for the data field (8) for recording the data is different from that for the identification field (7) containing identification data (76) such as a track address and a sector address in such a way that the identification field (7) is reproduced at high reliability and high demodulation speed while at the same time recording data at high density in the data field. A large archival mass memory system using optical diskettes with annular tracks is disclosed by J.W. Watkins et al in Optical Engineering , Vol. 20, No. pp. 399-403 (1981), Bellingham, U.S.A. The system provides 10¹³ bits storage; variable data ingest rates up to 50 Mbits/sec for sources such as telephone links, computer links and satellite downlinks; Reed-Solomon error detection and correction (EDAC) coding to preserve better than a 10⁻⁹ bit error rate (BER) for up to 10 years of operation without re-recording; real-time optical spot recording of 10⁻⁹ user bits on each diskette; storage and automatic online retrieval of data from 1024 diskettes housed in each storage and retrieval unit, less than 15 second access time to any record in the archive; simultaneous data recording and readout; forward file management for rapid user-oriented access down to byte level; simultaneous access to multiple modular storage and retrieval units; and variable output rates of up to 50 M bits/second direct or interleaved for multiple variable rate users tied to the fibre-optic distribution bus. The format of the above-mentioned optical disks is characterized by the following features. Since the optical head is caused to jump in response to the detection of one first index part, it is hardly affected by drop-out occurring on the optical disk. This ensures that the head is made to jump with certainty. Further, the sector addresses are read at a low error rate. However, special devices are needed to detect the first and second index parts. In addition, it is difficult to correctly adjust the positions of these detecting devices relative to the read/write head. If some sector separators cannot be detected, the corresponding sector addresses will be judged to be absent. Accordingly, it is an object of the present invention to provide an optical recording medium which is so formatted that it permits an optical head to stably jump without requiring the aforementioned index parts or special index-detecting devices on or over the medium such as an optical disk, and which allows the positions of sectors to be sensed with certainty even if addresses are read incorrectly. It is another object of the invention to provide an optical recording and reading apparatus which is used with the optical recording medium as described just above and which assures both stable jumping operation and certain reading of sector addresses. The present invention provides a rotary optical information recording and reproducing medium, comprising: a spiral guide track, said guide track comprising sector portions and index portions, the sector portions and index portions of adjacent turns being radially aligned so as to form sector fields and index field; said index field having an angular width sufficient for track jumping; said sector portions comprising a first identification part, an address recording address field and a data recording data field; and a second identification part suitable for producing track jumping of an optical head, provided angularly adjacent a jumping region of the index field, and consisting of grooved parts; characterized in that a second identification signal part is recorded in the index portion of each turn. When the second identification signal part is detected, a signal for initiating a jumping operation is generated. The jumping operating is performed to trace any arbitrary turn of the spiral track. This signal (hereinafter referred to as "the second identification signal") is also used to start the rotation of the medium. A first identification signal that is produced by detecting each first identification signal part cooperates with the second identification signal to recover errors produced in reading sector addresses held in the address fields. Specifically, when such an error occurs, the signal indicating the corresponding sector address is replaced by a substitute address signal which is formed by counting the first identification signal. This counting is initialized by the second discrimination signal. The present invention also provides an optical information recording and reproducing apparatus adapted for use with a rotary optical information recording and reproducing medium comprising: a spiral guide track, said guide track comprising sector portions and index portions, the sector portions and index portions of adjacent turns being radially aligned so as to form sector fields and an index field; said index field having an angular width sufficient for track jumping; said sector portions comprising a first identification part, an address recording address field and a data recording data field; and a second identification part provided angularly adjacent a jumping region of the index field, the apparatus comprising: an optical head for recording and reproducing information on such a rotary optical information recording and reproducing medium; tracking means for tracking the optical head to said spiral guide track provided on the recording and reproducing medium; recording and reproducing means for recording information in and reproducing information from said plurality of sector portions provided on the guide track; and detection means for detecting said second identification signal part and generating a signal to produce jumping of the optical head in response thereto characterized in that the apparatus is further adapted for use with a rotary optical medium in which a second identification signal part is recorded in the index portion of each turn and further comprises jumping means, responsive to said signal, for producing jumping of the optical head in said jumping region provided adjacent the second identification signal part; and in that the detection means includes means for detecting the second identification signal part, and means for detecting, in each sector successively provided on the guide track, the first identification signal part the address recording address field and the data recording data field, via the optical head. The apparatus combines the function stable and reliable track jumping with the function of recovering errors produced in reading sector addresses. The novel optical recording and reading apparatus as described above yields the following advantages: (1) It is possible to trace repeatedly any arbitrary turn of the spiral guide track without the need to use special detectors. (2) Even if some sector addresses held in address fields are incorrectly read, the signals indicating these sector addresses are replaced by the output from the counter to which the first and second discrimination signals are applied in cooperative relation, thus reducing the rate of sector addresses not detected. (3) The optical reading and recording apparatus that is used with the novel optical recording medium detects the second discrimination portion of the medium and causes an optical head to perform a jumping operation over the jumping region in response to the resulting signal without using special detectors, thereby permitting the head to repeatedly trace any arbitrary turn of the spiral track. If some sector addresses held in address fields are incorrectly read, a substitutive address signal is produced utilizing the first and second discrimination signals to use it in place of the signal indicating the sector addresses, whereby reducing the rate of sectors not detected. This increases the efficiency of utilization of sectors. For identical rate of sectors not detected, the novel optical recording medium can be manufactured with a high yield. While the novel features of the invention are set forth with particularity in the appended claims, the invention, both as to organization and contents, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a plan view of an optical recording medium such as an optical disk according to the present invention, for showing the data format of the track; Fig. 2 is a diagram showing the data format of the track on the medium of Fig. 1; Fig. 3 is a diagram specifically showing one example of address field on the medium shown in Fig. 1; Fig. 4 is a diagram showing examples of index mark and sector mark both of which are formed on the medium shown in Fig. 1; Fig. 5 is a diagram showing the time relation between the index mark and the sector mark; Fig. 6 is a diagram showing the frequency bands occupied by various signals generated in accordance with the data format of the track on the medium shown in Fig. 1; and Fig. 7 is a block diagram of an optical recording and reading apparatus that is used with the optical disk according to the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 1, there is shown an optical disk 10 that is an example of optical recording medium. The disk 10 is provided with a hole 12 at its center, and is rotatable about this hole. A guide track 14 that is shaped into a spiral groove is formed in a region 16 on the disk 10. As an example, the track 14 has a width of 0.7 µm and a depth of one-eighth to one-fifth of the wavelength used. The pitch, i.e., the distance between the successive turns of the track, is 1.6 to 2 µm. The optical disk 10 has a plurality of (32 in the present example) sectors (S₀-S n ) 18 for storing visual or aural information as derived from a television signal and an index field 20 that does not contain such information. The index field 20 is used either as the starting point for the disk 10 or for jumping purposes as described below. Where visual information is recorded on the optical disk, for example, if a user wants to see a still, or motionless, picture for some time, one specific turn of the spiral guide track 14 is required to be traced repeatedly. To perform this operation, the light beam that traces the track 14 must be caused to move out of the track, i.e., to jump once from some location on the track,because the track 14 is spiral, and then the beam must be returned to the starting point of that one revolution of trace. This operation will hereinafter be referred to "jumping". There is an index mark 22, which will be described in detail later, at the head of the index field 20. This mark 22 is followed by a jumping region 24 (G1 in Fig. 2). The light beam is caused to jump when the beam is moving across this jumping region 24. The sectors 18 have the same format. Specifically, the front portion of each sector 18 has a sector mark (SM) 26, which is followed by an address field (one of A₀-A n ) 28. Following the address field 28 comes a data field (one of D₀-D n ) 30 for storing visual or aural information. Each sector mark 26 indicates the beginning of the sector. If the sector address cannot be read in the succeeding address field, this sector mark is used to recover the sector address. Each address field 28 contains a track address and a sector address which are read through the use of the light beam to accurately sense the position of the light beam. As described previously, the index mark (IDM) 22 in the index field 20 is used to generate a trigger signal which causes the light beam to return to its starting point after the beam traces one turn of the spiral guide track 14 on the disk 10. This trigger signal is detected by an optical head that reads or writes on the optical disk. The output signal from this head drives an actuator to quite slightly move a focusing lens incorporated in the optical head radially of the disk so that the light beam from the light head may move out of the track within the jumping region 24 and return to the previous turn of the track. After completing the jumping operation, the address field A₀ in the sector S₀ that lies next to the jumping region 24 will be read. If this address field A₀ should not be read, then the address field A₁ in the following sector S₁ would be read. If the field A₁ should not be read, the address field A₂ in the further next sector S₂ would be read, and so on. The result of the reading is employed so check that the jumping operation has been correctly carried out. This ensures that the spiral guide track is retraced reliably. As already described, each turn of the track on the optical disk 10 is divided into (n +1) sectors. Each sector is selected using the track address and the sector address which together constitute the address field 28, in order that data is written to, or read from, a desired sector. Visual or aural information is stored in the data field 30 of each sector 18. The data format of the track on the optical disk 10 is next described by referring to Fig. 2. In Fig. 2, the same components as those in Fig. 1 are indicated by the same reference numerals as in Fig. 1 and will not be described hereinafter. The period of one revolution of the disk 10 is indicated by numeral 32. Each sector 18 includes a sector header region 34 which consists of the sector mark 26 and the address field 28. The end of each turn of the track is indicated by EOT. Each data field 30 has a gap (G2) 36 at its front end and another gap (G3) 38 at its rear end. No data is recorded in the gaps 36 and 38. These gaps are determined by the factors: (1) variations in the rotational frequency of an electric motor that rotates the disk; (2) the eccentricity of the disk; (3) external vibration or shock; (4) the rise time or fall time of the envelope of the output light emitted by the laser; and (5) the interval between the erasing light beam from an erase head and the writing or reading beam. The factors (1)-(3) described above result in changes in the velocity of the light beam relative to the disk. The factors (4) and (5) give rise to a value T₀ intrinsic to the apparatus. If we assume that the change in the relative velocity of the beam, its normal velocity, and the length of the data fields 30 are equal to ± ΔV, V₀ ,and T D , respectively, then the length of the data fields 30 changes by ± (ΔV/V₀)· T D . Then, we can have the following relationships: T G3 > (ΔV/V₀)·T D + T₀ T G2 > (ΔV/V₀)·T G2 + T₀ ≃ T₀ where T G2 and T G3 are the lengths of the gaps 36 and 38, respectively. Generally, since T D » T G2 , T G3 » T G2 . As an example, the interval in the factor (5) is 5 µsec, and the rise or fall time in the factor (4) is 10 µsec. Then, T₀ = 15 µsec. The variations in the factor (1) are equal to 0.1%. The eccentricity ratio in the factor (2) is 0.4% when the eccentricity is 100 µm and the radius is 25 mm. With respect to the factor (3), it is assumed that if the disk is subjected to a shock of 1 g (gravitational constant), the value is 1%. Then, (ΔV/V₀) = 1.5%. If T D = 2 msec, T G3 > 45 µsec, and T G2 > 15 µsec. Hence, the gaps (G3) 38 are required to be longer than the gaps (G2) 36 by a factor of three or more. The structure of each address field 28 is next described by referring to Fig. 3, where the address field 28 consists of a preamble 40, an address mark (AM) 42, a track address (TA) 44, a sector address (SA) 46, an error detecting and correcting code (ECC) 48, and a postamble 50. The preamble 40 puts the address field 28 into synchronism with the incoming clock pulses when the address field is read, and permits stable reading of the succeeding portions of the address field. The address mark (AM) 42 indicates the beginning of the address portion, which is composed of one track address (TA) 44 given to that turn of the guide track and one sector address (SA) 46 given to that sector. The track address 44 indicates the address number given to that turn of the track, while the sector address 46 indicates the sector number given to that sector. The error detecting and correcting code 48 is used to see if the track address 44 and the sector address 46 were read correctly. If an error occurs, a correction is made. The postamble 50 assures that these portions of the address field are stably and completely read. As well known in the art, the optical disk produces a bit error rate of the order of 10⁻⁴ to 10⁻⁵. The bit error rate of the address field 28 is worse than that (10⁻³ to 10⁻⁴) of the optical disk by a factor of ten or more and, therefore, an error recovery function is necessitated. Since the address field 28 holds a long item of data, i.e., tens of bits, it is not readily affected by a burst error, and it cannot be interleaved. The optical disk produces burst errors ranging from tens of microns to hundreds of microns (corresponding to the range from tens of bits to hundreds of bits) relatively frequently. For these and other reasons, it is difficult to appropriately correct errors. The device according to the present invention produces a substitutive sector address using the sector mark 26 recorded in the front part of the address field 28 of each sector header region 34 and uses the substitutive sector address in place of an address erroneously read from the address field, in order to recover the error. Thus, sector addresses are read quite reliably. The substitutive sector address is delivered from a counter which is initialized, i.e., cleared, by the signal produced by detecting the index mark 22. The signal generated by detecting the sector mark 26 is clocked into this counter. This operation for replacing the sector address is performed using a flip-flop circuit by switching from the output produced upon reading of the address field 28 to the output from the counter, or vice versa. The flip-flop circuit is designed to be set by the signal generated in response to the detection of an incorrect reading of an address and reset by the signal produced in response to the detection of a sector mark. If errors have occurred in reading the address field 28 and the sector mark 26, or if both of them cannot be detected, then the sector address will unable to be detected, although such a situation quite rarely takes place. Each track address 44 stores the same contents, the number of the items of which is equal to the sector number. This creates no problems, because there is no possibility that the address fields 28 of the sectors are all incorrectly read. Two specific examples of each structure of the index mark 22 and the sector mark 26 are next described with reference to Fig. 4. Referring to Fig. 4, there are shown pulses 52 which constitute the index mark 22 and the sector marks 26 and which are yet to be subjected to a modulation. Shown as a first example of the index mark 22 and the sector marks 26 is an RF pulse-gated signal 54. Shown as a second example of them is a signal 56 which has been subjected to phase modulation. Specifically, the signals 54 and 56 are waveforms recorded on the optical disk 10. These waveforms are detected by an optical head and demodulated to regenerate the pulses 52. The RF pulse-gated signal 54 is obtained by gating the higher level. The remaining higher level portions are recorded as marks and the lower level portions are recorded as grooves. The lower level portions are so formed as to permit the minute light beam to be correctly detected when it crosses the track during the examination of the track. The phase-modulated signal 56 has been obtained by subjecting the pulse signal 52 to phase modulation in such a way that the higher and lower level portions of the signal 52 are respectively 0 phase-modulated and π phase-modulated. For example, the phase-modulated signal 56 that provides the second example is passed through a band-pass filter to form a continuous signal of a single frequency. As a result, the index mark 22 and the sector marks 26 are extracted without being materially affected by the signals derived from the data fields. The single frequency of the continuous signal makes it easy to reproduce the signals derived from the data fields using clock pulses if said single frequency is set equal to a submultiple of the frequency of the clock pulses. The time relation between the index mark 22 and the sector marks 26 is now illustrated by referring to Fig. 5. As indicated by the signal 54 or 56 of Fig. 4, these marks 22 and 26 have the same fine structure, and they can be distinguished from each other only by their lengths. The length T₂ of the index mark 22 is made longer than the length T₁ of the sector marks 26, taking into account the efficiency of the format. To facilitate distinguishing between them, T₂ is made twice or thrice as long as T₁, for instance. The width t of the higher level portions (marks) and the lower level portions (spaces) is so selected that drop-outs of several microns encountered often with optical disks can be accommodated. Also, since the pulses 52 can be sufficiently accurately detected even if several marks are missing, drop-outs of tens of microns can be allowed. As an example, typical optical disks frequently have drop-outs of 10 to 100 µm and so the index mark 22 and the sector marks 26 are designed as follows. Suppose that an optical disk has a radius of 25 mm and that it rotates at 1,200 rpm. As described later in connection with Fig. 6, in order to accurately read the marks shown in Fig. 4, the relation t = 5.5/f₁ = 3.14 µsec must be established, provided that the frequency f₁ of the RF-gated signal is 1.75 MHz and that the period of time t is longer than f₁ by a factor of six. The period t corresponds to a drop-out of about 9 µm. Since the maximum drop-out on the optical disk is assumed to be 100 µm, each sector mark 26 should be at least twice as long as that length. Then, let us assume that the number of pulses included in each mark is twelve (T₁ = 75.4 µsec). As the index mark 22 is required to be detected with greater accuracy than the sector marks 26, the number of pulses included in the index mark 22 is set to 36, i.e., three times as many as the pulses included in each sector mark 26 (T₂ = 226.1 µsec). Thus, about three times as many drop-outs can be tolerated for the index mark 22 as those allowed for the sector marks 26. The frequency bands occupied by the signals involved in the data format of the track shown in Fig. 2 are now described with reference to Fig. 6, where the signals produced by reading one address field 28, one data field 30, and the index mark 22 or one sector mark 26 are shown as an address signal 58, a data signal 60, and an index mark signal or a sector mark signal 62, respectively. Indicated by numeral 64 is a signal used for a servo control, such as a tracking error signal or focus error signal. The clock frequency f c for the data signal, the gate frequency or the modulation frequency f₁ of the index mark or the sector mark signal 62, the highest fundamental frequency f₂ of the data signal 60, and the highest fundamental frequency f₃ of the address signal 58 are selected to satisfy the relations: f c = m₁f₁ = m₂f₂ = m₃f₃ where m₁, m₂, and m₃ are integers. For example, for the optical disk which has a radius of 25 mm and rotates at 1,200 rmp, f c = 7 MHz, f₁ = 1.75 MHz (m₁ = 4), f₂ = 1.75 MHz (m₂ = 4), and f₃ = 0.875 MHz (m₃ = 8). In this way, the frequency of the clock pulses for the data field is a submultiple of the frequency of the clock pulses for the address fields, thus facilitating the reading of the data fields in synchronism with the clock pulses. Although the data signal 60 and the address signal 58 are shown to occupy different frequency bands in Fig. 6, it is obvious that both can occupy the same frequency band and can be modulated in the same way. An example of optical recording and reading apparatus for recording or reading data on the optical disk according to the present invention is now described by referring to Fig. 7, where the optical disk 10 is rotated by an electric motor 66, which is driven by a driver circuit 68 under the control of a control unit 70. Data is recorded or read on the disk 10 by an optical head 72 that is moved along the face of the disk 10 by a linear motor 74. This motor 74 is driven by a linear motor driver circuit 76 under the control of the control unit 70. The optical head 72 is so controlled by a focus servo circuit 78 that the light beam emitted by the head 72 is focused onto the disk 10. The optical head 72 is also controlled by a tracking servo circuit 80 such that the light beam from the head correctly traces the guide track on the disk 10. During jumping operation, a jumping circuit 82 is operated to cause the optical head 72 to repeatedly trace an identical turn of the track on the disk 10. The focus servo circuit 78, the tracking servo circuit 80, and the jumping circuit 82 are also controlled by the control unit 70. The electrical signal produced by the optical head is supplied via a head amplifier 84 and an equalizer 86 to a demodulator circuit 88, where the signal is demodulated. The demodulated signal is then delivered as an output data 96 after passing through a scrample buffer 90, an error correcting circuit 92, and a data buffer 94. An input data 96 is applied to the data buffer 94, and then it is furnished via the error correcting circuit 92 and the scramble buffer 90 to a modulator circuit 98, where the signal is modulated. The modulated signal is then fed to a laser driver circuit 100 to control the light beam emitted from the optical head 72 during recording. The signal delivered from the equalizer 86 is applied to an index mark/sector mark detecting circuit 102, which produces an index mark signal 104 and a sector mark signal 106. The index mark signal 104 is supplied to a counter 108 as a reset signal, and it is also given to the jumping circuit 82 as a trigger signal. The sector mark signal 106 is applied to the counter 108, where it is counted. The signal delivered from the equalizer 86 is also impressed on an address reading circuit 110, which produces a sector address signal 112 and a track address signal 114. The track address signal 114 is provided to the control unit 70, while the sector address signal 112 is applied to a multiplexer circuit 116 that also receives the output 118 from the counter 108. The multiplexer circuit 116 is so designed that if an address error detecting circuit 120 delivers an error signal 121, the output 118 from the counter 108 is allowed to be applied to a sector control circuit 122, and that if the detecting circuit 120 does not, the selector address signal 112 is permitted to be applied to the sector control circuit 122. The address error detecting circuit 120 is connected to the address reading circuit 110, and acts to sense whether errors have taken place in reading addresses. The sector control circuit 122 applies a read sector gate signal 124 to the demodulator circuit 88 during reading, and it supplies a write sector gate signal 126 to the modulator circuit 98 during recording, for controlling the reading and writing operations. The operation of the optical recording and reading apparatus constructed as described above is now described. The focused thin beam from the optical head 72 is directed to the optical disk 10 that is rotated at a given frequency by the motor 66. The light beam is caused to trace the guide track under the control of the focus servo circuit 78 and the tracking servo circuit 80. Since the guide track is spiral in shape, the optical head 72 moves along track, under this condition, in such a way that the track is always placed just above the head 72 under the control of the linear motor 74 and the linear motor driver circuit 76. Each time the optical disk 10 makes one revolution, the optical head 72 is caused to jump back to its original position by the action of the jumping circuit 82 so that the head 72 may trace the same turn of the track. The index mark 22 recorded on the disk 10 is detected by an index mark/sector mark detecting circuit 102, which produces an index mark signal 104 and a sector mark signal 106. The index mark signal 104 is applied to the jumping circuit 82. While the light beam is moving across the jumping region 24 of the optical disk 10, the focus lens of the head 72 is slightly moved radially by the actuator just when the jumping circuit 82 receives the index mark signal 104, to cause the head to jump back to its original position on the track. The control unit 70 that is formed by a microcomputer receives and reads the track address output 114 from the address reading circuit 110 and the error signal 121 to see if the correct jumping operation has been performed. In particular, each track address 44 on the disk 10 has the same number of items as the number of sectors per turn of the track, the items being equal in contents. The control unit 70 reads those address fields from which no error is detected and confirms their correctness to see if the jumping operation has been correctly done. This attains reliable retrace of the spiral track. Data is recorded on the optical disk in the manner described below. First, the optical head 72 is rapidly conveyed to a designated turn of the guide track by the linear motor 74. Then, the input data 96 is transferred from a system to the data buffer 94, after which an error correction code is added to the data by the error correcting circuit 92. The data is then stored in the scramble buffer 90, which serves to interleave the data recorded on the optical disk 10 for rendering burst errors occurring on the disk random. The sector control circuit 122 detects the specified sector position lying in the turn of the track. When the head 72 begins to trace the specified sector, the write sector gate signal 126 is produced to operate the modulator circuit 98. Then, the signal from the scramble buffer 90 is subjected to digital modulation by the modulator circuit 98. The digitized signal is applied to the laser driver circuit 100 to drive a semiconductor laser incorporated in the optical head 72. Thus, the light beam of a minute diameter is amplitude-modulated to record the data on the disk 10. The data is read out in the manner described below. The read selector gate signal 124 from the sector control circuit 122 is applied to the demodulator circuit 88, which then begins to demodulate the signal that is supplied to it after the waveform is modified by the equalizer 86. The demodulated signal is then held in the scramble buffer 90, from which data is delivered in such a way that the data is de-interleaved. Errors are detected and corrected by the error detecting circuit 92. Then, the data is held in the data buffer 94 which delivers its output as the output data 96 to the system. As thus far described, recording or reading of data is made as a unit of sector, and therefore the detection of the sector addresses is of great importance, requiring high reliability. Further, the number of the sectors not detected must be reduced to a minimum. As well known in the prior art, the bit error rate is of the order of 10⁻⁴ to 10⁻⁵. On the other hand, the error rate occurring in reading the address fields 28 is of the order of 10⁻³ to 10⁻⁴, which is worse than the bit error rate by a factor of ten or more. Hence, an error recovery function is necessitated. Each address field 28 stores short items of information, i.e., tens of bits, so long items of data cannot be interleaved. Optical disks often produce burst errors of the order of tens of microns to hundreds of microns (corresponding to tens of bits to hundreds of bits). For these and other reasons, appropriate error correction cannot be readily made. The device according to the present invention produces a substitutive sector address using the sector mark 26 recorded in the front part of the address field 28 of each sector header region 34 and uses the substitutive sector address in place of an address erroneously read from the address field, in order to recover the error. Thus, sector addresses are read quite reliably. This operation is next described. The substitutive sector address counter 108 has a clock input to which the sector mark signal 106 is applied. The index mark signal 104 is applied to the counter as a load input. The counter begins to count the sector marks 26 after being triggered by the index mark 22. The output 118 from the counter is applied to the multiplexer 116 together with the sector address signal 112 from the address reading circuit 110. One of the two inputs to the multiplexer 116 is allowed to appear at its output by the output signal 121 from the error latch 120 which retains and delivers the error signal 111 indicating the errors when the address fields 28 are incorrectly read. When the output signal 121 from the error latch 120 is switched on, the output 118 from the counter is delivered as sector address data 117 to both the sector control circuit 122 and the control unit 70. When the signal 121 is switched off, the sector address signal 112 is delivered as the sector address data 117 to them. The error latch 120 is set by the read error signal 111 and reset by the sector mark signal 106. Accordingly, a failure to detect a sector takes place in the event both the address field 28 and the sector mark 26 are faulty. Such a case arises much less frequently than the case where only the address field is faulty. As thus far described, the novel apparatus permits reliable retrace of the spiral track and reliable detection of sectors, leaving only a low rate of sectors not detected. Before recording data, the control unit 70 adds the same address data as the addresses (track address and sector address) in the object sector to the user data stored in the data buffer 94. Then, the data is written onto the object sector via the error correcting circuit 92, the scramble buffer 90, and the modulator circuit 98. This writing of data is allowed only when no error is detected in reading the address field in the object sector. That is, during the writing operation, the control unit 70 functions in such a way that if the address field 28 in the object sector is incorrectly read, the read error is not recovered through the use of a substitutive sector address which is produced by the counter 108 using the sector mark 26. When the data is read, if the address field in the object sector is incorrectly read due to deterioration of the optical disk or adhesion of dust to it, the output signal obtained by counting the aforementioned sector mark is used in alternative manner, and then the signal resulting from the data field in the sector having the identical sector address is demodulated. Subsequently, the resulting signal is de-interleaved by the scramble buffer 90, after which the errors are corrected by the error correcting circuit 92. Thereafter, the data is stored in the data buffer 94. The control unit 70 takes the address data from the data buffer 94 and checks to see if it is the correct sector. If it is the correct one, the control unit 70 instructs the data buffer 94 to send out the user data. According to the procedure described above, data is recorded in address fields free of error. If errors occur later about address fields, they are accurately recovered by the use of both sector marks and the address data read from the data fields. Consequenty, data can be read quite reliably.

Claims: A rotary optical information recording and reproducing medium, comprising: a spiral guide track, said guide track comprising sector portions (18) and index portions (20), the sector portions and index portions of adjacent turns being radially aligned so as to form sector fields and index field; said index field having an angular width sufficient for track jumping; said sector portions comprising a first identification part (26), an address recording address field (28) and a data recording data field (30); and a second identification part (22) suitable for producing track jumping of an optical head, provided angularly adjacent a jumping region (24) of the index field, and consisting of grooved parts; characterized in that second identification signal part (22) is recorded in the index portion (20) of each turn. The optical recording medium of claim 1 wherein said address field (28) consists at least of a track address (44), sector address (46), and an error control code (48). The optical recording medium of claim 1 wherein said first (26) and second (22) identification signal parts are constituted of mutually different bit length. The optical recording medium of claim 1, wherein each of said first (26) and second (22) identification parts are constituted of several repeated combinations of a mark part gated by a high frequency signal (f1) and a groove formed space part. The optical recording medium of claim 4, wherein the frequency (f1) of said high frequency signal is the same as or higher than the highest fundamental frequency (f2) of the data field. The optical recording medium of claim 4, wherein said second identification signal length (T2) is longer than that (T1) of the first identification signal. The optical recording medium of claim 1 wherein each of said first (26) and second (22) identification parts are constituted of several repeated combinations of mark and space parts which are high frequency phase-modulated with a predetermined phase difference (π). The optical recording medium of claim 7 wherein the frequency (f1) of said high frequency signal is the same as or more than the highest fundamental frequency (f2) of the data field. The optical recording medium of claim 7, wherein said second identification signal length (T2) is longer than that (T1) of said first identification signal. An optical information recording and reproducing apparatus adapted for use with a rotary optical information recording and reproducing medium comprising: a spiral guide track, said guide track comprising sector portions (18) and index portions (20), the sector portions and index portions of adjacent turns being radially aligned so as to form sector fields and an index field; said index field having an angular width sufficient for track jumping; said sector portions comprising a first identification part (26), an address recording address field (28) and a data recording data field (30); and a second identification part (22) provided angularly adjacent a jumping region (24) of the index field, the apparatus comprising: an optical head (72) for recording and reproducing information on such a rotary optical information recording and reproducing medium (10); tracking means (70,74,76,80) for tracking the optical head to said spiral guide track provided on the recording and reproducing medium; recording and reproducing means (72,84,94,98,100) for recording information in and reproducing information from said plurality of sector portions (18) provided on the guide track; and detection means (72,84,86,102,110) for detecting said second identification signal part (22) and generating a signal (104) to produce jumping of the optical head in response thereto characterized in that the apparatus is further adapted for use with a rotary optical medium in which a second identification signal part (22) is recorded in the index portion (20) of each turn and further comprises jumping means (82,80), responsive to said signal (104), for producing jumping of the optical head in said jumping region (24) provided adjacent the second identification signal part (22); and in that the detection means (72,84,86,102,110) includes means (72,84,86,102) for detecting the second identification signal part (22), and means (72,84,86,110) for detecting, in each sector (18) successively provided on the guide track, the first identification signal part (26) the address recording address field and the data recording data field (30), via the optical head (72). An optical information recording and reproducing apparatus according to claim 10, further comprising a counter (108), coupled to the detection means and initialised by the first signal, for counting the second signal. An optical information recording and reproducing apparatus according to claim 11, further comprising reproduced error detection means (120), coupled to the detection means and to the counter means, for detecting errors reproduced in the address field. An optical information recording and reproducing apparatus according to claim 12, further comprising gate means (116), coupled to the detection means, the counter means and the reproduced error detection means, for selectively outputting the sector address (SA) (112) detected by the detector means or the output (118) of the counter; and wherein the gate means outputs, in response to a reproduced error output (121) from the reproduced error detection means, the output (118) of the counter in substitution for the detected sector address. An optical recording and reading apparatus according to claim 13, including means (70) for substituting the counter output for the sector address of the address field from which errors are detected during reproducing operation, and not substituting the counter output for the sector address during recording operation. An optical recording and reproducing apparatus according to claim 13 or 14, including means (70) for employing the track addresses in address fields within one turn of tracks from which no errors are detected as correct track addresses. An optical recording and reproducing apparatus according to any of claims 13 to 15, including means (70) for recording both the track address of the sector on which user data are desired to be recorded, and said user data to which the address data of the sector address are added on said data field. An optical recording and reading apparatus according to any of claims 13 to 16, including means (70) for sending said user data out only when the address data added to the user data is reproduced and confirmation of desired sector is made.

Inventors: MATSUO, TAMOTSU, SATOH, ISAO
Applicants: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1984
Main classification: G11B7
IPC codes: G11B7, G11B27, G11B20