Method and apparatus for writing and reading optical recording medium

Abstract: An apparatus for writing on and reading an overwritable optical disk comprises writing means including a selector (1901) for selecting a conversion method from a plurality of conversion methods (103,1903) for converting write data, and means (104,109,110,112) for writing the converted data, together with an identifier indicating the selected conversion method, to an optical recording medium. Further, the apparatus comprises reproducing means including a detector (1905) for detecting the identifier and a plurality of restoring means (117,1904) for restoring the original data according to the conversion method indicated by the identifier. The conversion method is selected at random at each overwriting operation, so damage to the recording layer is reduced even if the same write data are repeatedly written to the same portion of the optical recording medium.

Description: The present invention relates to a method and apparatus for writing on and reading an optical recording medium. Recently, optical disks, cards and tapes are developed and have been used for recording information optically. Especially, optical disks are given attention as a medium having large capacity and high density. A conventional method for writing an optical disk is explained below referring to the figures. Fig. 13 shows an example of an optical disk using a phase-change type recording film. A substrate 2301, which is made of a glass or plastic material such as PMMA or polycarbonate, is provided with guide grooves 2302 and pits indicating an address or other information. This area with the pit train is called the ID area. The guide grooves are formed in concentric circles or a coil from the inner to outer portions of the substrate. Areas 2307 between the grooves are called lands. The ID areas are located at a predetermined pitch along the guide grooves. The areas between the ID areas are called sectors. A surface of the substrate 2301 is provided with layers of a protective film 2303, a recording film 2304 and a reflection film 2305 formed by sputtering or other methods. Furthermore, a protective sheet is glued onto the layers. A method for writing on and reading the above-mentioned optical recording medium is explained below referring to the figures. Fig. 14 shows a block diagram of a conventional writing and reading apparatus. Fig. 15 shows the write and read operation for an optical disk. In Fig. 15, (a) indicates a write data signal, (b) indicates a laser-driving signal (corresponding to a laser power), (c) indicates a recorded state of the optical disk, and (d) indicates a record format. The reading process for the optical disk is performed as follows. A system controller circuit 101 drives a spindle motor 114 that rotates the optical disk 113. An optical head 112 focuses a laser beam with a weak power (Pr in Fig. 15) to irradiate the optical disk 113, tracking the guide groove 2302 and the pit train 2502 shown in (c) of Fig. 15. The intensity of the beam reflected by the optical disk 113 varies in accordance with the existence of the pit train 2502 and record marks 2501. Detecting the intensity of the reflected beam generates read signal 122, which is processed into binary data by a read signal processor circuit 115 and demodulated by a demodulator circuit 116. Then the signal is processed in an error correction and deinterleaving circuit 117 to obtain read data. The deinterleaving process restores the original data from the interleaved data, which are changed in order. The writing process for the optical disk is performed as follows. A system controller circuit 101 connected to a host computer gives write data 102 to an error correction and interleaving circuit 103, which adds error correcting data, i.e., parity bits to the write data, and performs an interleaving process. The interleaving process makes error correction easy by converting a burst error (long continuous error) due to a defect of the optical disk into a random error (short error). The write data are divided into blocks and the order of the blocks is changed according to a predetermined rule in the interleaving process. Then a modulator circuit 104 modulates the data in accordance with the (1, 7) RLL modulation method, for example. Consequently, a modulated data signal 105 is obtained for writing the data area 604 shown in (d) of Fig. 15. In the synthesizer circuit 109, each data block to be written into each sector is provided with VFO and RESYNC signals from a synchronizing signal generator circuit 108 as well as dummy data from a dummy data generator circuit 107 if necessary, to make the write data signal 118. The VFO and RESYNC are synchronizing signals for generating a clock signal synchronizing with the read signal in a PLL circuit (synchronizing signal generator) in the read signal processor circuit 115. The VFO signal is added to the head of the modulated data, and the RESYNCH signal is added in the modulated data signal at a predetermined interval. The dummy data are added for reducing a deterioration of the recording film generated at the end of writing when writing on the same sector repeatedly. The dummy data is not required to include any information. The example of the write data signal 118 is shown in (a) of Fig. 15. Corresponding to the write data signal 118, the laser driver circuit 110 generates a laser driving signal 111 to drive a laser in the optical head 112, modulating the intensity of the laser beam. An example of the laser-driving signal 111 is shown in (b) of Fig. 15. When the optical head 112 irradiates the recording film of the optical disk 113 with the focused laser beam having a high intensity (Pp shown in (b) of Fig. 15) for a predetermined period, the temperature of the recording film rises above the melting point and drops rapidly. As a result, the melted spot becomes a recorded mark 2501 (shown in (c) of Fig. 15) having an amorphous state due to rapid cooling. On the contrary, when the recording film is irradiated with the focused laser beam having a middle intensity (Pb shown in (b) of Fig. 15) for a predetermined period, the temperature of the recording film rises to the temperature below the melting point but above the crystallization point. Then the irradiated spot is cooled gradually and assumes a crystalline state. A recorded pattern having crystalline and amorphous spots as mentioned above, which corresponds to the modulated data signal 105, is created in the data area 604 on the guide groove 2302. Thus, writing and reading of information are performed using a difference of reflectivity between the crystalline and amorphous states. As shown in (d) of Fig. 15, there is a gap area 602 between the ID area 601 and the VFO area 603, as well as a buffer area 606 between the dummy data area 605 and the next ID area 601. The gap area 602 generates a time for controlling the laser power, and the buffer area 606 compensates for a difference of recording position due to rotation variability of the spindle motor. When scanning an ID area 601 between sectors 607 of the optical disk, address data are read by the laser irradiating the optical disk with the same weak power as the reading power. The system controller circuit has a configuration shown in Fig. 16. Transmission of write data and read data between a host computer and the write/read apparatus is performed using a write data buffer 2601 and read data buffer 2602 respectively. The read data is given to the read data buffer 2602 as well as an address data detector circuit 2603. An address data detecting signal is transmitted to the write data buffer 2601 and the read data buffer 2602. A motor driver circuit 2604 drives the spindle motor. When writing on the optical disk repeatedly as mentioned above, a quality of the read signal of the written data in a sector may be deteriorated at a certain part. Especially, writing similar data into the same sector repeatedly makes the deterioration serious because that part of the sector undergoes repeated melting and hardening while another part never melts. As a result, the thickness of the recording film changes at the boundary of the two parts, so that the thermal and optical characteristics are deteriorated at the boundary. In this case, it is difficult to record (write) and reproduce (read) data properly. There is a writing method to solve the above-mentioned problem proposed in the Japanese laid-open patent application (Tokukaihei) 2-94113. This method writes data while varying the start point for writing a sector at random within a predetermined range. A method according to the present invention as defined in claim 1 comprises the following steps for recording and reproducing. The writing steps comprise selecting one of two or more different methods for converting write data into converted data, writing an identifier for identifying the method used as the converting method, together with the converted data into an optical recording medium. The reproducing steps comprise reading the converted data and the identifier from the optical recording medium, and selecting one of two or more methods for restoring the original data from the read data in accordance with the identifier. According to this method, the write data signals have different patterns by changing an order of blocks even if the same write data are written into the same part of the optical recording medium repeatedly. As a result, a damage at a specific part of the recording film can be dispersed, and a deterioration of the recording film due to repeated overwriting can be reduced. In the accompanying drawings: Fig. 1 is a block diagram of a writing and reading apparatus according to an embodiment of the present invention; Fig. 2 is a flow chart showing a process for overwriting a sector of the optical disk in the apparatus shown in Fig. 1; Fig. 3 is a flow chart showing a process for reproducing data written in a sector in the apparatus shown in Fig. 1; Fig. 4 shows write data before permutation and the data after permutation in the apparatus shown in Fig. 1; Fig. 5 shows read data before restoring and the data after restoring in the apparatus shown in Fig. 1; Fig. 6 is a block diagram of a permutation method decision circuit and a permutation circuit of the apparatus shown in Fig. 1; Fig. 7 is a block diagram of a permutation data detector circuit and a restoring circuit of the apparatus shown in Fig. 1; Fig. 8 is a block diagram of a system controller circuit of the apparatus shown in Fig. 1; Fig. 9 is a block diagram of a variation of the writing and reading apparatus shown in Fig. 1; Fig. 10 shows an example of interleaving and deinterleaving operations in the apparatus shown in Fig. 9; Fig. 11 is a block diagram of another variation of the writing and reading apparatus shown in Fig. 1; Fig. 12 shows an example of bit shift and reverse bit shift operations in the apparatus shown in Fig. 11; Fig. 13 is a cross section of an optical disk using a phase-change type recording film in the prior art; Fig. 14 is a block diagram of a writing and reading apparatus in the prior art; Fig. 15 shows write data, modulated laser power, record mark and record format in the prior art; Fig. 16 is a block diagram of a system controller circuit of the apparatus shown in Fig. 14; The writing and reading method and apparatus according to the present invention are further explained in detail using the figures and preferred embodiments. Fig. 1 shows a block diagram of an apparatus for writing on and recording an optical recording disk according to an embodiment of the present invention. Fig. 2 shows a flow chart for overwriting a sector of the optical disk in the apparatus shown in Fig. 1. This embodiment differs from the prior art in the following process. A permutation method decision circuit 1401 decides the permutation method of the write data 102 at random (Step 1503). A permutation circuit 1402 divides the write data into plural groups and changes the order of the groups according to an instruction from the permutation method decision circuit 1401 to obtain converted data 1405 (Step 1504). The permutation circuit 1402 also adds the permutation data as an identifier for restoring original data from the converted data (Step 1505). Fig. 3 is a flow chart showing a process of reproducing a data written in a sector. This process differs from that of the prior art in the following steps. After error correction and deinterleaving (Step 1604), the permutation data detector circuit 1403 detects the permutation data that is the identifier for restoring the original data (Step 1605). A restoring circuit 1404 restores the original data based on the identifier (Step 1606). An example of the permutation and restoring of data is explained below using Fig. 4 and 5. The division and permutation of write data are performed as follows. Dividing positions are determined at random concerning a series of write data shown in (a) of Fig. 4. Then the series of write data is divided, changed in order, and provided with permutation data as an identifier showing the divided position, so as to make a series of data shown in (b) of Fig. 4. For example, if the write data are divided at the 20th byte and changed in order (this means a conversion method), an identifier showing the 20th byte is added to the converted data. It is not required to write the identifier into every sector. The identifier may be written into the directory (directory) area. The conversion method is not required to be changed for each sector, but can be same for plural sectors in a serial writing. Then, the error correction data are added and the interleave process is performed. As shown in (a) of Fig. 5, when reproducing data, after error correction and deinterleaving, the identifier, i.e., permutation data, added to the tail of the converted data, are detected. For example, if the permutation data show the 20th byte, the last 20 bytes of the converted data are divided and added to the head of the data (this means a restoring method), so that the original data are obtained as shown in (b) of Fig. 5. The dividing position is determined at random by the permutation circuit 1402 at every writing of a sector, so a different modulated data signal is used for each writing even if the same data are written into the same sector repeatedly. As a result, the optical disk 113 is written with different write data signals except the VFO and RESYNC areas. Therefore, a probability of forming a record mark 2501 on the guide groove 2303 is substantially uniform in a sector of the optical disk 113. Thus, local damage of the recording film due to repeated overwriting is relieved. Fig. 6 shows an example of the permutation method decision circuit 1401 and the permutation circuit 1402. In this figure, a random number generator 2901 generates random numbers, when being triggered by a permutation-timing signal. If each sector of the optical disk is accessed at random, a usual counter circuit can be used instead of the random number generator to obtain the same effect. An address preset circuit 2902 gives an initial memory address to a memory 2903 for reading the memory 2903. In the above-mentioned example, the initial memory address is an address corresponding to 20th byte from the head of the write data stored in the memory 2903. The memory 2903 stores the write data and outputs the stored data from the given initial memory address to the tail address and the remaining part of the data from the head address in order. Thus, the memory 2903 outputs the converted data. A synthesizer circuit 2904 add an identifier indicating the initial memory address to the data. Fig. 7 shows an example of the permutation data detector circuit 1403 and the restoring circuit 1404. A detector circuit 3001 detects the identifier from the decoded data after error correction and deinterleaving. A hold circuit 3002 holds the identifier and outputs the same to an address preset circuit 3003 until the next identifier is detected. The address preset circuit 3003 gives an initial memory address to a memory 3004. In the example mentioned above, the initial memory address is an address corresponding to 20th byte from the tail of the converted data stored in the memory 3004. The memory 3004 stores the converted data and outputs the stored data from the given initial memory address to the tail address and the remaining part of the data from the head address in order. Thus, the memory 3004 outputs the restored data. Fig. 8 shows the system controller circuit of this embodiment. This circuit differs from that of the prior art in that a permutation timing generator circuit 2801 outputs a permutation timing signal to the permutation method decision circuit 1401 in accordance with the address data and the address data detecting signal from the address data detector circuit 2603. The following explanation is about an example for confirming the effect of this embodiment. The substrate of the optical disk 113 was made of a polycarbonate plate having a diameter of 130 mm. Pits are preformed on the substrate as address-data, and guide grooves for writing are formed in sector areas. Four layers, that is a protective film, a photosensitive film, a protective film and a reflection film were formed on the substrate by sputtering. Then, a protective sheet was glued on the surface of the layers. The protective film was made of ZnS-SiO 2 , the photosensitive film was made of Te-Sb-Ge, and the reflection film was made of Al. This optical disk was rotated at a linear speed of 5 m/s by the spindle motor 113. A laser beam having a wavelength of 680 nm was used for writing, after being focused by an objective lens with a numerical aperture (N. A.) of 0.6. Laser powers for writing and reading were set at Pp = 10 mW, Pb = 4 mW, and Pr = 1 mW. A method of (8-16) pulse width modulation was used for modulating the write data. The shortest mark length was 0.6 micron. According to the above-mentioned condition, the write data were overwritten 100,000 times into the same sector. The error rate of demodulated data was measured for each overwriting with two methods for comparison. The first method used the permutation by dividing the write data and changing the order according to the present invention. The second method didn't use the permutation as the prior art. In both methods, the write data for a sector includes 500 bytes. In the first method using the permutation, the dividing position was selected at random by a step of one byte. The measured result is shown in the following Table. Error rate after 100,000 times overwrite Without permutation 0.011 With permutation 0.000002 As shown in Table 2, the first method with the permutation has smaller error rate than the second method without permutation, so that the number of times of overwriting is enhanced. As mentioned above, according to the writing and reading method of the optical recording medium according to the embodiment of the present invention, the write data signals have different patterns by converting into plural patterns even if the same write data are written into the same sector of the optical recording medium repeatedly. As a result, a damage at a specific part of the recording film can be dispersed, and a deterioration of the recording film due to repeated overwriting can be reduced. The number of divided blocks and other parameter in this embodiment is an example, and should be selected adequately in accordance with the record condition or medium. The method for dividing a series of write data should not be limited to the example mentioned in this embodiment, but may be any method that can convert write data into plural different converted data. For example, as shown in Fig. 9, a different interleaving method can be used by adding another pair of interleaving circuit and deinterleaving circuit to the configuration of Fig. 1. In the configuration shown in Fig. 9, one of two error correction and interleaving circuits 103, 1903 is selected by a first selecting circuit 1902 at random controlled by an interleaving method decision circuit 1901, and an identifier indicating the selected method is added to the converted data in the recording process. In the reproducing process, one of two error correction and deinterleaving circuits 117, 1904 is selected by a second selecting circuit 1905 according to the identifier detected by an interleaving method detector circuit 1906. The interleaving method decision circuit 1901 includes a random number generator circuit or a counter circuit in the same way as the permutation method decision circuit shown in Fig. 1. Fig. 10 shows an example of interleaving and deinterleaving operations. In Fig. 10, (a) shows write data before interleaving, (b) shows the data after interleaving and provided with an identifier indicating the interleaving method, (c) shows read data before deinterleaving, and (d) shows data after deinterleaving in accordance with the detected identifier. In this case, the same process as the interleaving can perform division and permutation of the write data, so that the configuration of the writing and reading apparatus can be simplified. The method for converting a series of write data into one of two or more different series of converted data may be the following method. Fig. 11 shows a configuration for generating a series of converted data from a series of write data by a scrambling method, which comprises a bit shift process of the write data. In the recording process, a bit shift method decision circuit 2101 decides a shift bit number at random, and a bit shift circuit 2102 performs the bit shift process by a unit of one or more bits according to the decided shift bit number to obtain converted data 1405. An identifier indicating the shift bit number is added to the converted data. These steps correspond to the converting method. In the reproducing process, a bit shift identifier detector circuit 2103 detects the identifier, and a reverse bit shift circuit 2104 performs the reverse bit shift process by a unit of one or more bits according to the detected identifier. These steps correspond to the restoring method. The bit shift method decision circuit 2101 includes a random number generator circuit or a counter circuit in the same way as the permutation method decision circuit shown in Fig. 1. Fig. 12 shows an example of the bit shift and reverse bit shift operations. In Fig. 12, (a) shows write data before bit shift, (b) shows the data after bit shift and provided with an identifier indicating the bit shift method, (c) shows read data before reverse bit shift, and (d) shows data after reverse bit shift in accordance with the detected identifier. In this case, a large memory for permutation is not required, so that the configuration of the writing and reading apparatus can be simplified. By changing the start point for writing a sector with a modulated data signal at random, the RESYNC area included in the data area can also be written in a different position, so the number of times of overwriting is further enhanced.

Claims: A method for writing data on and reading data from a rewritable optical recording medium, comprising the steps of: selecting a conversion method from a plurality of conversion methods for converting write data into converted data, the selectable conversion methods resulting in different recording patterns for same write data in a same area, so as to reduce detoriation of the medium due to repeated overwriting; writing the converted data and an identifier indicating the selected conversion method into an optical recording medium; reading the converted data and the identifier written in an optical recording medium; selecting a restoring method from a plurality of restoring methods according to the read identifier; and restoring an original data from read data by using the selected restoring method. The method according to claim 1, wherein the step of selecting a conversion method is performed at every overwriting step. The method according to claim 1, wherein the plurality of conversion methods are interleaving methods. The method according to claim 1, wherein the plurality of conversion methods are scrambling methods. The method according to claim 1, wherein a start point for writing the converted data in a sector on an optical recording medium is changed. An apparatus for writing data on and reading data from a rewritable optical recording medium, comprising: a first switching portion selecting a conversion method from a plurality of conversion methods, the selectable conversion methods resulting in different recording patterns for same write data in a same area, so as to reduce detoriation of the medium due to repeated overwriting; a converter portion converting write data into converted data according to the selected conversion method; a writing portion the converted data and an identifier indicating the selected conversion method into an optical recording medium; a reproducing portion reproducing the converted data and the identifier written in an optical recording medium; a detector portion detecting the identifier; a second switching portion selecting a restoring method from a plurality of restoring methods based on the detected identifier; and a restoring portion restoring an original data from the converted data according to the selected restoring method.

Inventors: NARUMI KENJI, NISHIUCHI KENICHI, NARUMI, KENJI, NISHIUCHI, KENICHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1997
Main classification: G11B7
IPC codes: G11B7, G11B27, G11B20, H03M13