Optical disk recording/reproducing device

Abstract: An optical disk recording/reproducing device in accordance with the present invention has a controller that, during the recording, performs the rotation control of the optical disk in Constant Linear Velocity according to reproduced signals of pre-recorded information that was preliminary recorded on the optical disk, during the reproduction, performs the rotation control according to reproduced signals of recorded information, and when the rotation control based on the reproduced signals of the recorded information is infeasible, switches the rotation control and performs the rotation control based on the reproduced signals of the pre-recorded information during the reproduction also. As a result, a suitable and appropriate CLV control may be executed during the recording and during the reproduction.

Description: The present invention relates to an optical disk recording/reproducing device that records and/or reproduces information while performing a control such that a so-called Write-Once type or Rewritable type optical disk is rotated at Constant Linear Velocity. BACKGROUND OF THE INVENTION In the conventional art, compact disks (herein after referred to as CDs) whereon audio information or other information is recorded in the form of digital signals through minute pits that can be detected optically, are widely used as optical disks. The information recorded on a CD is reproduced by means of a Read-Only optical disk recording/reproducing device. In a CD, a plurality of pieces of information are usually recorded in succession. In addition, absolute addresses that provide information concerning recording/reproducing positions on the disk are preliminarily recorded on the disk in the form of physical alterations. During the reproduction, absolute addresses read from the disk and absolute addresses indicating the recording start position of each piece of information and recorded in a TOC (Table Of Contents) area provided in the inner periphery or other location of the disk, are compared, and the desired pieces of information may be reproduced successively or selectively. An optical disk recording/reproducing device that records and reprcduces audio informaticn of other information on rewritable optical disks developed recently such as magneto-optical disks or Write-Once type optical disks where information can be recorded only once, should preferably adopt the same method of reproduction as the one used in a conventional optical disk recording/reproducing device for CDs only and should be able to be employed compatibly with the different types of optical disks in use. In this case, a so-called constant Linear Velocity (hereinafter referred to CLV) that is employed with CDs may be adopted as the rotation control method for the optical disk during the recording and the reproduction. The CLV method may be implemented by for example controlling the rotational speed of a motor in accordance with the radial position of an optical head. In this case, the rotational speed of the motor is detected by means of a rotary encoder or other member, and the radial position of the optical head is detected by means of a position detecting sensor. However, when the CLV method is implemented in such a manner, a rotation control that is sufficiently accurate cannot be expected as errors occur in, for instance, the detections performed by the rotary encoder and the position detecting sensor. The accuracy of the rotation control may be improved by enforcing the CLV method according to disk position information that was preliminarily recorded on the optical disk such as the absolute addresses described above. In the conventional art, Japanese Publication for Unexamined Patent Application 1989-39632 (Tokukaisho 64-39632) discloses a method for recording absolute addresses. Namely, the disk position information goes through a biphasemark modulation process and the guiding groove of the optical disk is made to deviate inward or outward in a radial direction or the width of the guiding groove is changed, depending on whether the modulated code is "1" or "0". The absolute addresses and the recorded information can be reproduced separately by having their respective frequency bandwidths differ from each other. However, even if the information is recorded while the optical disk is driven to rotate according to the information preliminarily recorded on the optical disk such as absolute addresses, etc., in practice, there is a possibility that the information might be recorded in a condition that is slightly different from the CLV requirements because of CLV control errors happening during the recording. In this case, if the information recorded is audio information, variations might occur in the speed at which music is played during the reproduction. Therefore, during the reproduction, a CLV control that is based on the information to be reproduced should be performed. However, when during the reproduction, reproduction errors occur frequently, or when the optical head moves from a recorded area to an unrecorded area, a rotation control that is based on the reproduced information becomes infeasible. In addition, once the rotation control based on the reproduction information has become infeasible, a significant lapse of time is needed before the rotation control can be executed correctly even after the quality of the reproduced signals has been restored. SUMMARY OF THE INVENTION The present invention provides the optical disk recording/reproducing device defined by claim 1. The sub-claims 2 to 5 are directed to embodiments of the invention. According to the invention, a suitable and appropriate CLV control may be always performed. The preamble of claim 1 relates to the disclosure of EP-A-0 302 680, which describes an optical disk apparatus in which CLV control of the disk rotation is switched between a control based on the reproduced signal when a recorded region of the disk is reproduced and a control based initially on the detected radial position of the optical head and later on pre-recorded rotation-control information consisting of convexo-concave patterns formed on the surface of the disk, when an unrecorded region of the disk is reproduced. EP-A-0 178 657 discloses a disk recording/reproducing apparatus capable of operation in both CLV and CAV modes. Address information identifying the mode adopted for each recorded area of the disk is stored in a TOC area of the disk, whereby the appropriate rotation control is applied to the disk during reproduction. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 to Fig. 6 illustrate an example which is useful for understanding the present invention. Fig. 1(a) is a flow chart illustrating a CLV control procedure during recording. Fig. 1(b) is a flow chart illustrating a CLV control procedure during reproduction. Fig. 2 is a schematic plane view illustrating a magneto-optical disk. Fig. 3 is an enlarged partial plane view illustrating the magneto-optical disk. Fig. 4 is a block diagram illustrating schematically the configuration of the optical disk recording/ reproducing device of the example. Fig. 5 is an explanatory view illustrating the frame format of a signal. Fig. 6 is a block diagram illustrating the circuit 21 of the optical disk recording/reproducing device shown in Fig. 4. Fig. 7 and Fig. 8 illustrate one embodiment of the present invention. Fig. 7(a) is a flow chart illustrating a CLV control procedure during recording. Fig. 7(b) is a flow chart illustrating a CLV control procedure during reproduction. Fig. 8 is a block diagram illustrating schematically the configuration of the optical disk recording/ reproducing device of the embodiment. DETAILED DESCRIPTION An example which is useful for understanding the present invention will first be described with reference to Fig. 1 to Fig. 6. As illustrated in Fig. 2, a magneto-optical disk 1 as a rewritable optical disk, is provided with a TOC (Table Of Contents) area la located in the inner periphery, as well as with an information recording area 1b occupying most of the area outside the TOC area la. Different types of information such as music programs or other data, are recorded in the information recording area 1b while additional information concerning the different pieces of information recorded in the information recording area lb, is recorded in the TOC area 1a. The additional information might consist for example of absolute addresses indicating the recording start position and absolute addresses indicating the recording end position of each information. As illustrated in Fig. 3, a guiding groove 2 of a spiral shape (shown by hatching for reasons of convenience) is preliminarily formed in the TOC area 1a and the information recording area 1b of the magneto-optical disk 1 and spirals out at predetermined intervals in a radial direction. The guiding groove 2 may also be composed of concentric circles. The guiding groove 2 is used for the tracking control during the recording and the reproduction. The guiding groove 2 is made to deviate inward or outward in a radial direction depending of whether the modulated codes obtained after the absolute addresses provided on the disk went through a biphasemark modulation process, are "1" or "0". The above absolute addresses form pre-recorded information to be used as rotation control information. As illustrated in Fig. 4, the optical disk recording/reproducing device of the present example comprises a spindle motor 3, as driving means for supporting and driving the magneto-optical disk 1 to rotate, an optical head 4 that projects a laser beam on the magneto-optical disk 1 during the recording and the reproduction, and a coil 5 that applies a magnetic field on the magneto-optical disk 1 during recording. The present optical disk recording/reproducing device adopts a magnetic modulation method as method for recording information and is capable of overwriting by recording new information over information already recorded. The optical disk recording/reproducing device includes an input terminal 6 where the information to be recorded is entered to. An analog information that is entered through the input terminal 6 is converted into a digital signal in an A/D (analog/digital) converter 7, goes through a prescribed EFM (Eight to Fourteen Modulation) process in a recording signal processing circuit 8, and is fed into a coil driver 10. The signal is recorded as the coil driver 10 drives the coil 5 in response to the signal that was fed thereto, while at the same time a laser beam is projected from the optical head 4 and is irradiated on the magneto-optical disk 1. Fig. 5 shows the frame format of signals used in a CD. An information "a" of one frame is composed of a data field "d" comprising an audio information or other information of 24 bytes and an error correction parity of 8 bytes added thereto, a sub code "c" indicating the number of the piece of music, the time and other information about the audio information, and a synchronizing signal "b" appended to each frame and indicating the leading edge of the frame. Pieces of information "a" of one frame are recorded in succession. Sub codes "c" comprised in the pieces of additional information recorded in the TOC area la further include at least information concerning the recording end position of each information, or information indicating the recording time from the recording start position to the recording end position of each information recorded according to the above frame format. The reproduction system of the optical disk recording/reproducing device will be described hereinbelow. As illustrated in Fig. 4, a signal reproduced by means of the optical head 4 is amplified by a reproduction amplifier 11. The amplified signal is sent to a pre-recorded information detecting circuit 12 and to a reproduced signal processing circuit 16. The pre-recorded information detecting circuit 12 is for example composed of a band-pass filter and a phase locked loop. Clock signals that are synchronized with the reproduced signals of the pre-recorded information (that is, constituted by a biphasemark modulated wave) extracted from the reproduced signals by means of the band-pass filter, are generated by the phase locked loop. The frequency of the clock signals and a first reference frequency supplied by a first oscillator 13 are compared in a first comparator 14 and differential signals are fed into a switching device 15. The present device further comprises a pre-recorded information demodulating section, not shown. When necessary (for instance when accessing, etc.), the biphasemark modulated waves go through a biphasemark demodulation process in the pre-recorded information demodulating section, thereby permitting the absolute addresses to be recognized. Magneto-optical signals extracted from the reproduced signals supplied from the reproduction amplifier 11, i.e. the reproduced signals of the recorded information, go through a process for demodulating the signals that were modulated through an EFM process, and other prescribed processes in the reproduced signal processing circuit 16. After the signals have passed through these reproduction processes, they are output via a D/A (digital/analog) converter 17 and an output terminal 18. The frame synchronizing signals described earlier comprised in each of the frames composing the reproduced signals of the recorded information are detected by means of the reproduced signal processing circuit 16. When a synchronizing signal is detected, a synchronizing signal detection pulse is generated by the reproduced signal processing circuit 16 and sent to a second comparator 20. The frequency of the synchronizing signal detection pulse is compared with a second reference frequency supplied from a second oscillator 19 and the differential signal resulting from this comparison is sent to the switching device 15. When the same reference frequency is employed in the first oscillator 13 and the second oscillator 19, a common oscillator may be used for the first oscillator 13 and the second oscillator 19. Also, when the first and second reference frequencies of the first and second oscillators are such that one frequency equals an integer number of times the other, a single oscillator may be used and the frequency of this oscillator divided appropriately by means of a divider. The signals processed by the reproduced signal processing circuit 16, are sent to a reproduced signal state detecting circuit 21 serving as reproduced signal state detecting means. In the signal state detecting circuit 21, it is determined whether the magneto-optical signals recorded on the magneto-optical disk 1 are reproduced correctly, or whether the optical head 4 is presently reproducing a recorded area or an unrecorded area. That is, the reproduced signal state detecting circuit 21 detects that frame synchronizing signals are successively missing due to anomalies in the synchronization, or that frame synchronizing signals are successively missing because the optical head 4 entered into an unrecorded area. The optical disk recording/reproducing device further comprises control means composed of a controller and other members, not shown. As illustrated in Fig. 1(a), during recording, the control means switches the switching device 15 toward the first comparator 14 and executes the recording operation (S2) while performing the CLV control according to the reproduced signals of the pre-recorded information (S1). The CLV control is performed such that the differential signals released by the first comparator 14 are sent to the spindle motor 3 through the switching device 15 and the frequency of the clock signals released by the pre-recorded information detecting circuit 12 coincides with the first reference frequency of the first oscillator 13. The clock signals are synchronized with the biphasemark modulated waves of the absolute addresses serving as pre-recorded information. As illustrated in Fig. 1(b), during reproduction, the condition of the reproduced signals is detected by means of the reproduced signal state detecting circuit 21 (S11) and the control means determines whether the reproduced signals are in a suitable condition (S12). When the reproduction of a recorded area is performed and when the reproduced signals are in a suitable condition, the control means switches the switching device 15 toward the second comparator 20 and executes the reproduction operation while performing the CLV control according to the reproduced signals of the recorded information (S13). In this case, the CLV control is performed such that, the differential signals released by the second comparator 20 are fed into the spindle motor 3 through the switching device 15 and the frequency of the synchronizing signal detection pulses released from the reproduced signal processing circuit 16 coincides with the second reference frequency of the second oscillator 19. As a result, the amount of information reproduced per unit time during the reproduction is kept constant even when slight variations occur in the linear velocity during recording. As described earlier, during the reproduction, an alternative method is followed when the CLV control based on the reproduced signals of the recorded information is infeasible, that is when the reproduced signal state detecting circuit 21 detects that the optical head 4 entered into an unrecorded area, or that reproduction errors occur frequently and that the condition of the reproduced signals is deteriorated. The alternative method consists in switching to a CLV control executed based on the reproduced signals of the pre-recorded information during reproduction also (S14). Inconveniences such as the infeasibility of a CLV control during the reproduction, are thus eliminated. The configuration and operation of the reproduced signal state detecting circuit 21 will be described more precisely hereinbelow. As illustrated in Fig. 6, the reproduced signal state detecting circuit 21 comprises a counter 22, a comparator 23 and a reference value supply circuit 24. synchronizing signal detection pulses, that are released when frame synchronizing signals are detected in the reproduced signal processing circuit 16, are fed with a predetermined timing into a reset terminal of the counter 22. Meanwhile, synchronizing signal absence pulses that are released when frame synchronizing signals are missing in the reproduced signal processing circuit 16, are fed into a clock terminal of the counter 22 with a predetermined timing. In such a manner, the number of times a synchronizing signal absence pulse is supplied is counted by the counter 22. Provision is made such that the counter 22 is reset when a synchronizing signal detection pulse is fed thereto. The value released by the counter 22 is compared with a reference value supplied by the reference value supply circuit 24 in the comparator 23. When the value released by the counter 22 is greater than the reference value, in other words when frame synchronizing signals are continuously missing in a number exceeding a predetermined number, it is determined that a synchronization anomaly has occurred in the recorded area, or that the optical head 4 has entered into an unrecorded area and that frame synchronizing signals cannot be detected while the CLV control is executed according to the reproduced signals of the recorded information. A CLV control switch signal is subsequently released by the comparator 23 and is fed into the switching device 15. In such a manner, the optical disk recording/reproducing device is designed such that during the reproduction also, the CLV control can be switched from the CLV control based on the reproduced signals of the recorded information to the CLV control based on the reproduced signals of the pre-recorded information. A suitable and appropriate CLV control is thus ensured during the recording as well as during the reproduction. One embodiment of the present invention will now be described with reference to Fig. 7 and Fig. 8. For reasons of convenience, the members having the same functions as in the previous example will be designated by the same references and their description will be omitted. As illustrated in Fig. 8, the optical disk recording/reproducing device of the present embodiment differs from the optical disk recording/reproducing devices of the previous example in that it is not equipped with the reproduced signal state detecting circuit 21. Fig. 8 shows an address decoder 55, a TOC memory 56 and a controller 57 that are always part of the optical disk recording/reproducing device. The address decoder 55 decodes the sequences of data of the absolute addresses that went through the biphasemark demodulation process described earlier. The absolute addresses are recognized in the controller 57 based on the results obtained in the address decoder 55. The address decoder 55 and a TOC memory 56 constitute an address management section. During the recording, the absolute addresses indicating recording start positions and the absolute addresses indicating recording end positions mentioned earlier (hereinafter referred to as recording start/end absolute addresses) are read from the TOC memory 56 by means of a recording/reproduction control section (not shown) comprised in the controller 57. The coil driver 10 drives the coil 5 and the optical head 4 to access the TOC area 1a in response to the instruction of the recording/reproduction control section. This instruction is based on the absolute addresses supplied by the pre-recorded information detecting circuit 12 and the address decoder 55. In such a manner, the recording start/end absolute addresses are recorded in the TOC area 1a after going through a prescribed signal process in the recording signal processing circuit 8. On the other hand, during the reproduction, the recording start/end absolute addresses recorded in the TOC area 1a are stored in the TOC memory 56 of the address management section following the instruction of the recording/reproduction control section. Besides, absolute addresses processed and detected one after another in the pre-recorded information detecting circuit 12, are also fed into the TOC memory 56. The recording start/end absolute addresses and the absolute addresses detected one after another are compared in a comparison section (not shown) included in the controller 57. According to the result of the comparison, the comparison section determines whether the optical head 4 is reproducing a recorded area or an unrecorded area of the information recording area 1b. A recording control operation that follows the flow illustrated in Fig. 7(a) and that is performed by control means composed of the controller 57 and other members will be described hereinbelow. First, a switch control section of the controller 57 (not shown) switches the switching device 15 toward the first comparator 14. Consequently, the CLV control of the spindle motor 3 is executed based on the reproduced signals of the pre-recorded information (S21). When the recording of audio information or other information starts, the corresponding recording start absolute address is stored in the TOC memory 56 (S22). When the recording of the audio information or other information is completed, the corresponding recording end absolute address is also stored in the TOC memory 56 (S23). Then, the recording start/end absolute addresses are recorded as additional information in the TOC area la of the magneto-optical disk 1 as described earlier (S24). On the other hand, during the reproduction of signals, the control means switches the switching device 15 toward the comparator 20 permitting the CLV control of the spindle motor 3 to be performed according to the reproduced signals of the recorded information. A reproduction control operation performed by the control means that follows the flow illustrated in Fig. 7(b) will be described hereinbelow. During the reproduction of signals, first, preceding the reproduction of the signals, the additional information written in the TOC area la is reproduced, and the recording start/end absolute addresses are read through the reproduced signal processing circuit 16 and stored in the TOC memory 56 (S31). Next, the absolute addresses obtained one after another as the pre-recorded information preliminarily recorded on the magneto-optical disk 1 is reproduced, are compared with the recording start/end absolute addresses stored in the TOC memory 56 (S32). Then, it is determined whether the optical head 4 is located over a recorded area or an unrecorded area (S33). For instance, if the absolute addresses reproduced one after another, are greater than the recording start absolute address and smaller than the recording end absolute address, it is assumed that the optical head 4 is located over a recorded area. Accordingly, the switching device 15 stays connected to the second comparator 20 and the CLV control is performed based on the reproduced signals of the recorded information (S34). On the other hand, when the absolute addresses reproduced one after another are smaller than the recording start absolute address, or greater than the recording end absolute address, it is determined that the optical head 4 is positioned over an unrecorded area. The switching device 15 is consequently switched from the second comparator 20 to the first comparator 14. As a result, the CLV control changes from the CLV control executed according to the reproduced signals of the recorded information to the CLV control executed according to the reproduced signals of the pre-recorded information (S35). Accordingly, in the cases where a CLV control executed according to the reproduced signals of the recorded information is infeasible such as for example when the optical head 4 has entered into an unrecorded area, an alternative method that consists in performing the CLV control based on the reproduced signals of the pre-recorded information during the reproduction also, is employed. Inconveniences such as the infeasibility of the CLV control during the reproduction, are thus eliminated. Moreover, in the present embodiment, whether the optical head 4 is positioned over a recorded or unrecorded area, is determined by merely comparing the absolute addresses. There is thus no need to implement an additional detecting means and the configuration of the circuit may be simplified. In the embodiment, the absolute addresses recorded on the magneto-optical disk 1 went through a biphasemark modulation process. However, these are not restrictive examples, and other modulation methods that restrict the frequency bandwidth may be adopted. Also, in the embodiment, the magneto-optical disk was taken as an example of optical disk. However, the present invention may be applied to other Rewritable optical disks such as optical disks of the phase change type, or to Write-Once type optical disks. Further, in the embodiment, the absolute addresses serving as pre-recorded information were recorded on the optical disk by having the guiding groove 2 deviate. The absolute addresses may also be recorded on the optical disk in the form of aligned pits. In this case, the CLV control based on the reproduced signals of the pre-recorded information is carried out by comparing the cycle at which the pits are reproduced, with a predetermined reference frequency. Furthermore, the embodiment described a case where the pre-recorded information is recorded on the optical disk in the form of absolute addresses. However, the pre-recorded information may also be recorded by having the guiding groove 2 snake. In addition, in the embodiment, the unrecorded areas represented areas of the information recording area 1b that were not recorded. However, the present invention may be applied to for example unnecessary areas such as blank spaces or unstable recorded areas of recorded areas.

Claims: An optical disk recording/reproducing device which controls the rotation of an optical disk (1) at a constant linear velocity, the device comprising: driving means (3) for rotating an optical disk; determining means (12,55-57) for determining, during a reproduction operation, whether a recorded region or an unrecorded region of the disk is being reproduced; and control means (15) for controlling the rotation of the disk by the driving means according to a first signal when a recorded region of the disk is determined as being reproduced and according to a second signal when an unrecorded region of the disk is determined as being reproduced, wherein said first signal is derived (16, 19, 20) from the reproduced signal and said second signal is derived (12, 13, 14) from pre-recorded rotation-control information formed on the disk; characterized in that: said determining means (12,55-57) is arranged to compare, during said reproduction operation, absolute addresses sequentially reproduced from the disk as said pre-recorded rotation-control information, with a recording start position absolute address and a recording end position absolute address, the latter two absolute addresses being previously recorded in a predetermined management information area of the disk and serving to define said recorded region, and to determine that said recorded region is being reproduced when said sequentially-reproduced absolute addresses fall within the range defined by said two absolute addresses and that said unrecorded region is being reproduced when said sequentially-reproduced absolute addresses fall outside the range defined by said two absolute addresses. An optical disk recording/reproducing device according to claim 1, comprising: an address management section where, at the beginning of a recording operation, at least one said recording start position absolute address which is obtained from said pre-recorded information, is stored, and at the end of said recording operation, at least one said recording end position absolute address which is obtained from said pre-recorded information, is stored; a recording/reproduction control section which, during recording, records said absolute addresses stored in said address management section in said predetermined area (la) of the disk, and which, during reproduction, reads from said predetermined area of the disk said absolute addresses recorded therein and stores those absolute addresses in said address management section; and a comparison section which compares absolute addresses which are reproduced one after another as reproduction position information with said absolute addresses stored in said address management section, determines that a recorded region is being reproduced when said absolute addresses which are reproduced one after another are greater than said recording start position absolute address and smaller than said recording end position absolute address, and determines that an unrecorded region is being reproduced when said absolute addresses which are reproduced one after another are smaller than said recording start position absolute address or greater than said recording end position absolute address. An optical disk recording/reproducing device according to claim 2, comprising: a pre-recorded information demodulation section (12) where said pre-recorded information, formed on the optical disk by means of a modulation method which restricts frequency bandwidth, is subjected to a demodulation process; wherein said address management section comprises: an address decoder (55) which decodes absolute addresses indicating recording/reproduction position information on the disk, and a TOC memory (56) where said recording start position absolute address and said recording end position absolute address are stored. An optical disk recording/reproducing device according to any preceding claim, wherein: said optical disk (1) comprises an information recording area (1b) where various types of information are recorded, and a TOC area (la), constituting said predetermined management information area, where additional information indicating the recording start position and the recording end position and other information concerning said various types of information, is recorded; a guiding groove (2) is formed in said information recording area (1b) and said TOC area (la) with a predetermined pitch in a radial direction of the disk and is employed for tracking control during recording/reproduction; and said pre-recorded information is formed on the disk by said guiding groove (2) deviating inward or outward in said radial direction of the disk depending on whether the binary code of absolute addresses serving as recording/reproduction position information and which were subjected to a modulation process restricting frequency bandwidth, is "1" or "0". An optical disk recording/reproducing device according to claim 4, comprising: a pre-recorded information detecting circuit (12) composed of a band-pass filter and a phase-locked loop, and where a clock signal which is in synchronization with reproduced signals of said pre-recorded information extracted from reproduced signals by means of said band-pass filter, is generated by said phase-locked loop; a first oscillator (13) which supplies a first reference frequency; a first comparator (14) which compares the frequency of said clock signal and said first reference frequency; a reproduced signal processing circuit (16) which performs a predetermined demodulation process on the reproduced signals of the recorded information, and which generates a synchronizing signal detection pulse when a frame synchronizing signal included in each of the frames composing the reproduced signals of said recorded information, is detected; a second oscillator (19) which supplies a second reference frequency; a second comparator (20) which compares the frequency of said synchronizing signal detection pulse and said second reference frequency; and a switching device (15) which is controlled by said control means such that: during recording said switching device is switched to said first comparator (14) thereby permitting the rotation control at constant linear velocity to be performed so that the frequency of said clock signal and the frequency of said first reference frequency coincide, during reproduction said switching device is switched to said second comparator (20) thereby permitting the rotation control at constant linear velocity to be performed so that the frequency of said synchronizing signal detection pulse and the frequency of said second reference frequency coincide, and when the control of said driving means (3) based on the reproduced signals of said recorded information is infeasible, said switching device is switched to said first comparator (14) and the rotation control at constant linear velocity is performed according to the reproduced signals of said pre-recorded information during reproduction.

Inventors: DEGUCHI TOSHIHISA, FUJI HIROSHI, MAEDA SHIGEMI, TERASHIMA SHIGEO, DEGUCHI, TOSHIHISA, FUJI, HIROSHI, MAEDA, SHIGEMI, TERASHIMA, SHIGEO
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1990
Main classification: G11B19
IPC codes: G11B27, H04N5, G11B19, G11B7