Optical disk drive

Abstract: An optical disk according to the present invention has thereon an uninterrupted preformed groove adjoining a track. The address information of the track and sectors is prerecorded by variations in the preformed groove in a radial direction of the optical disk. An optical disk drive converts a detection signal, that is generated when the spot of a light beam crosses the track, into a binary signal in accordance with the comparison between the detection signal and two different slice levels, whereby a correct track crossing number is obtained. Another optical disk has thereon index marks that are prerecorded by partially varying the width of the preformed groove. Another optical disk drive detects the index mark on a specific track line, whereby formatting data with respect to address information is generated. The optical disks and optical disk drives are thus compatible with writing of the address information by means of soft-formatting.

Description: FIELD OF THE INVENTION The present invention relates to an optical disk and to an optical disk drive which records, reproduces and erases information on/from the optical disk by projecting a light beam. BACKGROUND OF THE INVENTION On a conventional optical disk, generally, information (hereinafter referred to as address information) indicating the addresses of tracks and sectors is prerecorded in the forms of bumps and pits at manufacture (the bumps and pits providing the address information, hereinafter referred to as address marks). The allocation of data thus prerecorded on an optical disk is called pre-format or hard-format. Recording, reproduction and erasing of desired information are carried out while optically detecting the address information with an optical head of an optical disk drive and identifying a desired track address and sector address. Regarding the address marks, as illustrated in Fig. 11, marks 2 may be intermittently formed on the track provided between preformed grooves 1 on the optical disk. Also as illustrated in Fig. 12, marks 4 may be formed by partially interrupting grooves 3. A desired location on the optical disk is accessed by access process including track seeking and sector searching operations. In the track seeking operation, the optical head is moved in a radial direction of the optical disk towards a desired location. In the following sector searching operation, the optical head waits for a specified sector to come to a projection position of a light spot on the optical disk by rotation. With the above-mentioned method, since the address information of track and sectors are prerecorded as address marks in the form of bumps and pits, the format is inflexible. Therefore, the user can not freely change the format of the optical disk after manufacturing, and consequently the use of the optical disk is limited. On the contrary, information such as address information is magnetically written on a conventional floppy disk after the floppy disk is manufactured. This method is hereinafter called soft-formatting. In other words, as illustrated in Fig. 13 and Fig. 14, a floppy disk 6 is provided with an index hole 7 for determining the start or reference position of soft-formatting. When the index hole 7 is detected by a photo-interrupter 8 (a detector incorporating a light emitting element and light receiving element) of a floppy disk drive, an index hole detection signal U is sent to an information recording and reproducing circuit 10. According to the detection signal U, the information recording and reproducing circuit 10 determines the start or reference position of soft-formatting. Then, a recording signal V is sent to a magnetic head 11, whereby address information is recorded on the floppy disk 6. This method is employed in the disk drive disclosed in JP-A-58-155549. EP-A-0 326 437 discloses an optical disk drive for reading a disk having a hard format area and a soft format area. When soft-formatting used for the floppy disk 6 is adopted by an optical disk, the following problems are presented. Specifically, the recording density of the optical disk is substantially twenty times to some hundred times that of the floppy disk 6. Therefore, in determining the recording location on the disk, the optical disk requires substantially twenty times to some hundred times the accuracy of that required by the floppy disk. Thus, even when the optical disk is provided with the above-mentioned index hole 7, it is impossible to ensure sufficiently high accuracy in determining the recording location. SUMMARY OF THE INVENTION It would thus be desirable to provide an optical disk drive capable of accurately soft-formatting an optical disk for a wide variety of applications. According to the invention there is provided an optical disk drive comprising: an optical head for illuminating a spot on an optical disk having a plurality of preformed tracks; reproducing means for detecting variations in the intensity of light reflected from the illuminated spot, and for generating therefrom a track crossing signal in a track seeking mode; optical head control means for radially positioning the illuminated spot on a desired track in accordance with the track crossing signal; index mark detection means for optically detecting an index mark and for generating an index mark detection signal based on detection of an index mark; formatting means for generating formatting data comprising address information upon detection of an index mark detection signal; and recording means for recording the formatting data comprising the address information at a given location on a desired track; characterised in that the index mark detection means is adapted to detect a preformed index mark provided on each preformed track of the optical disk, in response to variations in the intensity of light reflected from said illuminated spot detected by said reproducing means. In an optical disk for use with the optical disk drive of the invention, reference positions, that are needed for writing of address information by soft-formatting, are given by the preformed index marks on the optical disk. Therefore, address information is recorded only in desirable portions when necessary, which allows the range of use of the optical disk to be broadened. The aforementioned optical disk drive is capable of soft-formatting by the following steps: (1) detecting an index mark from a desired track line; (2) generating formatting data; and (3) recording address information. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an explanatory view illustrating index marks formed on a preformed groove on a magneto-optical disk and an output signal corresponding to one of the index marks. Fig. 2 is a block diagram illustrating a reproducing circuit for generating a track crossing signal and an index mark detection signal. Fig. 3 is a block diagram illustrating the structure of a section of a magneto-optical disk drive capable of soft-formatting the magneto-optical disk. Fig. 4(a) is an enlarged view illustrating another index mark formed on the preformed groove of the magneto-optical disk, and Fig. 4(b) is a waveform chart of an output signal corresponding to the index mark. Fig. 5(a) is an explanatory view illustrating a part of the pre-formatted magneto-optical disk, and Fig. 5(b) to Fig. 5(e) illustrate a way of soft-formatting the magneto-optical disk. Fig. 6 is a flow chart illustrating the steps of soft-formatting. Fig. 7 is an explanatory view schematically illustrating the structure of a magneto-optical disk having soft format and preformat areas. Fig. 8 illustrates another way of forming index marks in a preformed groove. Fig. 9 illustrates a further way of forming index marks in a preformed groove. Fig. 10 illustrates the main sections of a magneto-optical disk drive. Fig. 11 to Fig. 14 illustrate conventional examples. Fig. 11 is an explanatory view schematically illustrating a preformed groove on an optical disk and address information recorded on a track. Fig. 12 is an enlarged plan view illustrating another type of a preformed groove on an optical disk. Fig. 13 is a schematic plan view illustrating a floppy disk. Fig. 14 is an explanatory view illustrating the structure of a section of a floppy disk drive. Fig. 15(a) is an enlarged plan view illustrating a state where the spot of the light beam crosses the preformed groove diagonally, and Fig. 15(b) is a waveform chart of an output signal corresponding to Fig. 15(a). Fig. 16(a) is an enlarged plan view illustrating a state where the spot of the light beam diagonally crosses a preformed groove that wobbles to a reduced degree, Fig. 16(b) is a waveform chart of an output signal corresponding to Fig. 16(a), and Fig. 16(c) is a waveform chart of a track crossing signal that is generated by converting the output signal into a binary signal. DESCRIPTION OF THE PREFERRED EMBODIMENTS There will now be described, with reference to Figs. 1 to 6 a method in which address information is magneto-optically written in the header portions 33 of a magneto-optical disk 52 in accordance with preformed index marks 53 formed in disk 52 during manufacture (the method hereinafter referred to as soft-formatting). Fig. 1(a) and Fig. 1(b) illustrate the magneto-optical disk 52 suitable for soft-formatting. The magneto-optical disk 52 is provided with a spiral track 31 and a spiral preformed groove 35 (alternatively, a plurality of tracks and preformed grooves may be arranged in the form of concentric rings). To form the index marks 53, for example, preformed groove lines 35a on each side of a track line 31a are partially undulated in the same direction. For instance, one index mark 53 is formed in a certain location of each track line 31a. The length of each index mark 53 along the track line 31a is about 1 µm to 100 µm (in this case, the wavelength of laser light is 800 nm and the numerical aperture (NA) of an objective lens is 0.5). In a magneto-optical disk drive illustrated in Fig. 2 and Fig. 3, a semiconductor laser 54 of an optical head 20 shown in Fig. 3 projects a beam of laser light onto a specified track line 31a (Fig. 1(b)) to detect the index mark 53. A reflected beam from the magneto-optical disk 52 is received by a photodiode 26 shown in Fig. 2. An electric signal A from the photodiode 26 is sent to a reproducing circuit 23. In the reproducing circuit 23, the electric signal A is amplified by an amplifier 27, and an output signal E of the amplifier 27 is input to the positive input terminal of a comparator 28. Meanwhile, according to a comparison voltage Vo input to the negative input terminal of the comparator 28, the output signal E of the amplifier 27 is converted into a binary signal. As illustrated in Fig. 1(c), when a beam of laser light is projected in front of and behind the index mark 53, the level of the output signal E becomes high, while when the beam of laser light is projected onto the index mark 53, it becomes low. Thus, by using the comparison voltage Vo as a slice level, a signal corresponding to the index mark 53, contained in the output signal E, is detected. Meanwhile, during track seeking, the output signal of the comparator 28 is sent as a track crossing signal B to a counter 24 where the track crossing number is counted in the same manner as in the above embodiment. After the laser light beam is directed to the specified track line 31a, the output signal of the comparator 28 is sent as an index mark signal K to an index mark detecting circuit 55. The index mark detecting circuit 55 detects the index mark 53 and then transmits an index mark detection signal L. The index mark detection signal L is sent to a formatting circuit 56, whereby the start or reference position of soft-formatting is detected and formatting data is generated. In accordance with the formatting data, a formatting data signal M is sent to the semiconductor laser 54 and then the soft-formatting of the magneto-optical disk 52 is executed. In Fig. 1, one index mark 53 is formed on each track line 31 by one undulation. However, as illustrated in Fig. 4(a), each index mark 53 may be formed by a plurality of undulations (i.e. by wobbles). Also, in this case, a signal (see Fig. 4(b)) read from the index mark 53 is converted into a binary signal by the comparator 28 and the index mark 53 is detected by the index mark detecting circuit 55. Thus, when the index mark 53 is formed by a series of wobbles, the number of errors in the detection of the index mark 53 is reduced compared to the case using the index marks shown in Fig. 1. Moreover, as shown in Fig. 8, the index marks 53 may be formed by undulating the preformed groove lines 35a on each side of the track line 31a in opposite directions. The index marks 53 may also be formed by groove-width modulation of the preformed groove lines 35a like the address marks 40 shown in Fig. 9. Fig. 5(a) relates to soft-formatting, in which one index mark 53 is formed in a certain location (i.e. the lead) of each track line 31a at the manufacture of the magneto-optical disk 52. When recording information on the magneto-optical disk 52 by means of soft-formatting, firstly the address information of the track 31 and sectors 32 is written thereon. At this time, as described above, if the index mark signal K, that is transmitted by the reproducing circuit 23 in accordance with the reflected beam from the magneto-optical disk 52, includes a signal derived from an index mark 53, the index mark detection signal L is transmitted by the index mark detecting circuit 55 as shown in Fig. 5(c). Consequently, as illustrated in Fig. 5(d), the start positions of soft-formatting are determined in accordance with the respective index mark detection signals L. Then, according to the formatting data signal M the semiconductor laser 54 emits the laser light beam. This allows the address information of the track lines 31a and sectors 32 to be written in the respective header portions 33 as illustrated in Fig. 5(b). Fig. 5 illustrates an example where five sectors 32 constitute one track line 31a. Since the address information is recorded by soft-formatting, the addresses of the track 31 and sectors 32 are identified by reproducing the address information in the header portions 33, and desired information is then recorded on, reproduced or erased from the respective data portions 34. In the above example, one index mark 53 is formed in each track line 31a; however a plurality of index marks 53 may be formed in one track line 31a so as to improve the accuracy of soft-formatting. Fig. 6 is a flow chart of soft-formatting. When soft-formatting of N s th track line 31a to N e th track line 31a is commenced, firstly the start track number N s is substituted for track number N, whereby the start position of soft-formatting is set (S11). Secondly, the N s th track line 31a is found and the index mark 53 on this track line 31a is detected (S12). As the index mark 53 on the N s th track line 31a is detected, soft-formatting of one track line, i.e. the N s th track line 31a is carried out (S13). Then "1" is added to the track number, and it is judged whether the resulting track number is greater than the end track number N e (S14). When the resulting track number is greater than N e , soft-formatting is completed. On the other hand, when it is smaller than N e , the operation is returned to S12 and the same process is carried out. As shown in Fig. 10, the magneto-optical disk drive includes a counter 24 for counting the track crossing number during track seeking, a seek control circuit 25 for controlling track seeking operation in accordance with the numerated data of the counter 24 and other devices. The descriptions of the devices are omitted here. Moreover, the magneto-optical disk 52 is provided with preformed groove lines 35a, each of which has no interruptions in a circular direction. Accordingly, during track seeking, i.e. when the optical head 20 is moved in a radial direction of the magneto-optical disk 52, the spot of the light beam 36 crosses one preformed groove line 35a every time it crosses one track line 31a. Further, since the index marks 53 are formed by, for example, wobbling the preformed groove lines 35a, the level of the track crossing signal B falls and rises only on the preformed groove lines 35a. This achieves an accurate counting of the track crossing number. A magneto-optical signal, that is derived from the address information magneto-optically recorded in the header portion 33 and desired information magneto-optically recorded in the data portion 34, is detected separately from the track crossing signal B that is derived from the index mark 53. Furthermore, when the laser light beam diagonally crosses the index mark 53 (see Fig. 1, 4, 8 or 9) during track seeking, the output signal E of the amplifier 27 is distorted, and which may distort the track crossing signal B. This is due to the distortion of the track crossing signal B that occurs when the spot of the light beam crosses the address mark 40 diagonally. Distortion of the track crossing signal B is restrained by reducing the variation range ΔW of the index mark 53. In this case, however, the S/N ratio of signals derived from the index marks 53 is lowered. Therefore, it is necessary to consider the balance between the variation range ΔW and the S/N ratio when determining the variation range ΔW. The accuracy of track counting can be improved by modifying the arrangement shown in Fig. 2 such that a hysteresis comparator is disposed in parallel to the comparator 28, and an output signal of the hysteresis comparator is input to the counter 24 as the track crossing signal B. Here, the hysteresis comparator is set such that a threshold for inverting the output signal from a low level to a high level is Δy higher than a threshold for inverting the output signal from a high level to a low level. Fig. 16(b) and Fig. 16(c) respectively illustrate the waveforms of the output signal E and track crossing signal B of such a modified arrangement. Here, the variation range ΔW of the address marks 40 is smaller than that shown in Fig. 15, and therefore the output signal E is distorted to a smaller degree. Moreover, the hysteresis level Δy that is set at the above threshold level to convert the output signal E into a binary signal can prevent the track crossing signal B from being distorted. For instance, a distortion Z in the waveform of the output signal E does not affect the track crossing signal B. The following relationship needs to be satisfied: Xt > Δy > Xs where Xt denotes the amplitude of the output signal E, Xs the amount of amplitude distortion of the output signal E, and Δy the hysteresis level. As illustrated in Fig. 7, the recording area on a magneto-optical disk 72 is divided into an inner first area 73 (pre-format area) and an outer second area 74 (soft-format area). Track lines 31a are preformed between adjacent preformed groove lines 35a in the first area 73 and the second area 74. In each sector 32 in the first area 73, address information in the form of an address mark 40 is prerecorded in its header portion 33, while information in the form of an information mark 75 is prerecorded in its data portion 34 (see Fig. 4, 8 or 9). Both of the address mark 40 and the information mark 75 are formed on the magneto-optical disk 72 by wobbling the preformed groove line 35a or by a groove-width modulation at manufacture. Meanwhile, in each sector 32 in the second area 74 one index mark 53 is preformed in a certain location of each track line 31a by undulating or wobbling the preformed groove line 35a or by the groove-width modulation (see Fig. 5(a)). The address information is recorded in the respective header portions 33 in the second area 74 in accordance with detected index marks 53, and then desired information is recorded in, reproduced or erased from the respective data portions 34. With an optical disk drive that is compatible with optical disks of read only type and write once type, and rewritable optical disks including the magneto-optical disk 72, it is necessary to write a description of the disk type, i.e. magneto-optical disk, and recording conditions in the first area 73 on the magneto-optical disk 72. Accordingly, when the optical disk drive reproduces the information from the first area 73, the disk type is identified as magneto-optical disk 72. This allows the optical disk drive to set recording conditions with respect to the second area 74, and therefore desired information can be recorded in, reproduced or erased from the second area 74 after the magneto-optical disk 72 is soft-formatted. In the case of using the magneto-optical disk 72 as a recording medium for use with a computer system, system files such as OS (operating system) need to be recorded in the first area 73 by means of pre-formatting. Particularly, in the case of a word processor, information which does not need to be erased or rewritten, such as dictionary file is recorded in the first area 73, while information which needs to be erased or rewritten such as user file is recorded in the second area 74. The use of the magneto-optical disk 72 is thus broadened by dividing the disk 72 into the first area 73 and the second area 74. The optical disk drive in this embodiment also employs a counter 24 for counting the track crossing number during track seeking and a seek control circuit 25. Each preformed groove line 35a in the first area 73 and the second area 74 has no interruptions in a circular direction. Further, the address marks 40 (in the header portions 33) and information marks 75 (in the data portions 34) in the first area 73, and index marks 53 in the second area 74 are formed by wobbling the preformed groove lines 35a or by other types of modulation. Furthermore, since the level of the track crossing signal B only falls and rises on the preformed groove lines 35a, the track crossing number is accurately counted in the first area 73 and the second area 74. The recording area is divided into the first area 73 and second area 74; however, it may be divided into a greater number of areas. In the aforesaid embodiments, magneto-optical disks are used; however the present invention is also applicable to other types of rewritable optical disks such as optical disks of phase transition type and of write-once type.

Claims: An optical disk drive comprising: an optical head (20) for illuminating a spot (36) on an optical disk (22; 52; 72) having a plurality of preformed tracks (31a); reproducing means (26, 23) for detecting variations in the intensity of light reflected from the illuminated spot (36), and for generating therefrom a track crossing signal in a track seeking mode; optical head control means (21, 24, 25) for radially positioning the illuminated spot on a desired track (31a) in accordance with the track crossing signal; index mark detection means (55) for optically detecting an index mark (53) and for generating an index mark detection signal based on detection of an index mark (53); formatting means (56) for generating formatting data comprising address information upon detection of an index mark detection signal; and recording means (54) for recording the formatting data comprising the address information at a given location on a desired track (31a); characterised in that the index mark detection means (55) is adapted to detect a preformed index mark (53) provided on each preformed track (31a) of the optical disk (22; 52; 72), in response to variations in the intensity of light reflected from said illuminated spot (36) detected by said reproducing means (26,23). An optical disk drive as claimed in claim 1 wherein the index mark detection means (55) is adapted to detect a preformed index mark (53) in the form of a radial variation in a tracking groove (35) of the disk (52;72). An optical disk drive as claimed in claim 1 or claim 2 wherein the optical head control means (21, 24, 25) comprises: counting means (24) for counting the number of track crossings; driving means (21) for moving the optical head (20) in a radial direction of the optical disk (22; 52;72); comparator means (25) for comparing numerated data of the counting means with a desired value; and driving signal generating means (25) for supplying a driving signal to the driving means (21) until the numerated data coincides with the desired value. An optical disk drive as claimed in any one of claims 1 to 3 wherein the recording means (54) is a magnetic head for applying a magnetic field to the optical disk during magneto-optical recording. An optical disk drive as claimed in any one of claims 1 to 4 further comprising: hysteresis comparator means for generating a binary signal by comparing the track crossing signal with first and second threshold levels, the second threshold level being higher than the first threshold level; and counting means (24) for receiving the binary signals from the hysteresis comparator means and for counting the number of track crossings; wherein, for transitions of the binary signal from high to low, the detection signal is compared with the first threshold level, whilst, for transition of the binary signal from low to high the detection signal is compared with the second threshold level.

Inventors: FUJI HIROSHI, MATOBA HIROTSUGU, FUJI, HIROSHI, MATOBA, HIROTSUGU
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1991
Main classification: G11B7
IPC codes: G11B7, G11B11, G11B27