Patent Publication Number: US-2006007802-A1

Title: Optical disk reproducing device

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an optical disk reproducing device and, more specifically, to an optical disk reproducing device reading a value from light reflected from an optical disk.  
      2. Description of the Background Art  
      In an optical disk reproducing device which reads a value from light reflected from an optical disk, an accurate value cannot be measured in measurement of a level of a tracking error signal when there is a scratch on a disk. Various solutions to this problem have been proposed.  
      Japanese Patent Laying-Open No. 61-145736 discloses a tracking jump preventing device which controls an open-loop gain of a tracking servo corresponding to a result of comparisons of a difference between a tracking error signal itself and a tracking error signal subjected to a slew rate limitation and an envelope signal obtained from an output of an optical pickup with respective reference values. With this preventing device, a track jump can be prevented without fault even when there is a scratch on a deposition surface besides a transparent base material of a disk.  
      Japanese Patent Laying-Open No. 63-224035 discloses a reproducing device in which a level of a driving signal to an actuator is suppressed only when an optical disk is in an abnormal condition such that an irradiation position of light to the optical disk is moved onto a track from which information has been already read. With this reproducing device, movement of the irradiation position in a direction opposite to a direction of reading information can be prevented.  
      Japanese Patent Laying-Open No. 09-139037 discloses a track jump preventing circuit which decreases a tracking gain when a scratch signal is output, which scratch signal is a logical sum of a signal of detection of a scratch on a surface of a transparent layer of an optical disk and a signal of detection of a scratch formed on a deposition surface. With this circuit, a track jump can be prevented without fault because not only a scratch on the surface of the transparent layer of the optical disk but also a scratch on the deposition surface are detected.  
      Japanese Patent Laying-Open No. 11-003558 discloses a scratch detecting device which generates a signal corresponding to a result of a comparison between a sum of absolute values of signals each having a phase varying complimentarily in accordance with deviation from a track of an optical disk and a reference value. With this device, an accurate detection of a scratch is enabled with a simple construction and with clear differentiation from tracking error detection.  
      In controlling of an open-loop gain of a tracking servo as disclosed in Japanese Patent Laying-Open No. 61-145736, however, consideration is not given to quality of a resulting signal. When data such as numbers or characters is to be read, required data can be obtained easily even if there is a problem in quality of a resulting signal to a degree (even if a resulting value lacks accuracy). On the other hand, when a signal representing a picture or a sound is to be read, the picture or sound is largely affected by quality of a resulting signal. This means that, it is difficult to obtain a picture or a sound of good quality with the device disclosed in Japanese Patent Laying-Open No. 61-145736. Each of the devices and the like disclosed in Japanese Patent Laying-Open Nos. 63-224035, 9-139037 and 11-003558 also has a similar problem.  
     SUMMARY OF THE INVENTION  
      The present invention is made to solve the above-described problem. An object of the present invention is to provide an optical disk reproducing device which accurately measures a defect signal and has increased accuracy of an automatic adjustment to obtain a picture or a sound of good quality.  
      To attain the aforementioned object, an optical disk reproducing device according to one aspect of the present invention includes an objective lens and light receiving element unit for reading a signal representing a position from an optical disk, a determination circuit for making a determination, according to whether values of at least three signals read by the objective lens and light receiving element unit fall out of a prescribed range or not, as to whether the three signals read by the objective lens and light receiving element unit are defect signals representing existence of a defect or not, a tracking control unit for generating a signal representing an estimated position of the objective lens using a signal read by the objective lens and light receiving element unit immediately before reading of the defect signals when the determination circuit determines that the signals read by the objective lens and light receiving element unit are defect signals, and generating a signal representing the same content as that of a signal read by the objective lens and light receiving element unit when the determination circuit determines that values of the signals are signals other than defect signals, and an actuator for changing a position of the objective lens to the optical disk according to a content of the signal generated by the tracking control unit.  
      That is, when it is determined that the signals representing positions which are read by the objective lens and light receiving element unit are defect signals, the tracking control unit generates, in place of the defect signals, a signal representing an estimated position of the objective lens using a signal read by the objective lens and light receiving element unit immediately before reading of the defect signals, and when it is determined that values of the signals are signals other than defect signals, the tracking control unit generates a signal representing the same content as that of a signal read by the objective lens and light receiving element unit. With this, a signal representing an appropriate position can be output as a signal representing a position of the objective lens and light receiving element unit. As a result, an optical disk reproducing device is provided which accurately measures a defect signal and has increased accuracy of an automatic adjustment to obtain a picture or a sound of good quality.  
      An optical disk reproducing device according to another aspect of the present invention includes a reader for reading a signal representing a position from an optical disk, a determination circuit for making a determination as to whether the signal read by the reader is a defect signal representing existence of a defect or not, a tracking control unit for generating a signal representing a position of the reader when the determination circuit determines that the signal read by the reader is the defect signal, and generating a signal representing the same content as that of the signal read by the reader when the determination circuit determines that a value of the signal is a signal other than the defect signal, and an actuator for changing a position of the reader to the optical disk according to a content of the signal generated by the tracking control unit.  
      With this, a signal representing an appropriate position can be output as a signal representing a position of the reader. As a result, an optical disk reproducing device is provided which accurately measures a defect signal and has increased accuracy of an automatic adjustment to obtain a picture or a sound of good quality.  
      In addition, the tracking control unit preferably includes a control unit for generating a signal representing an estimated position of the reader using a read signal which is read by the reader before reading of the defect signal.  
      That is, a signal representing a position of the reader becomes more accurate.  
      In addition, the read signal is preferably a signal read by the reader immediately before reading of the defect signal.  
      Furthermore, the determination circuit preferably includes a circuit for making a determination, according to whether values of a plurality of signals read by the reader fall out of a prescribed range or not, as to whether all of the plurality of signals are defect signals or not.  
      Furthermore, a number of the plurality of signals is preferably at least three.  
      The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a control block diagram of an optical record reproducing device according to an embodiment of the present invention.  
       FIG. 2  shows a construction of an RF amplifier unit according to the embodiment of the present invention.  
       FIG. 3  is a flow chart of a controlling procedure of tracking control processing according to the embodiment of the present invention.  
       FIG. 4  shows relations of a tracking error signal, an RF signal and a scratch detection signal according to the embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       FIG. 1  shows a construction of a main portion of an optical record reproducing device according to an embodiment of the present invention. The optical record reproducing device according to this embodiment is a device for recording data onto a DVD (Digital Versatile Disk) and reproducing recorded data. Referring to  FIG. 1 , the optical record reproducing device includes an optical pickup device including a spindle motor  2  for rotating an optical disk  1 , an objective lens  10  for collecting a beam emitted from a light source which is not shown on optical disk  1 , and an actuator  11  for controlling and driving objective lens  10  in a focus direction and a tracking direction, a light receiving element unit for receiving a beam reflected from a recording surface of optical disk  1 , an RF amplifier unit  30 , a first A/D (Analog-to-Digital) converter  40 , a second A/D converter  41 , a third A/D converter  42 , a fourth A/D converter  43 , a fifth A/D converter  44 , and a sixth A/D converter  45 .  
      The light receiving element unit is formed with a photodetector  20  which is split in four in a cross shape and a photodetector  21  which is split in two. Objective lens  10  and photodetector  20  form a device for reading a signal representing a position (in this embodiment, presence or absence of a tracking error) from optical disk  1 .  
      Photodetector  20  is split in two in a radial direction of optical disk  1  and split in two in a tangential direction to form four regions A-D. When a light beam reflected from optical disk  1  is collected and enters, four regions A, B, C, and D respectively output an electric signal a, an electric signal b, an electric signal c, and an electric signal d corresponding to an amount of reflected light input.  
      Photodetector  21  is split in two in a radial direction of optical disk  1  to form a region E and a region F. When a light beam reflected from optical disk  1  is collected and enters, two regions E and F respectively output an electric signal e and an electric signal f corresponding to an amount of reflected light input.  
      RF amplifier unit  30  is formed with a plurality of differential amplifiers having respective electric signals a-f as input voltages. Differential amplification for each of electric signals a-f is performed in RF amplifier unit  30 , and the result is output.  
      First to sixth A/D converters  40 - 45  are arranged in parallel corresponding to output signals of RF amplifier unit  30 . First to sixth A/D converters  40 - 45  convert electric signals a-f input via RF amplifier unit  30  into digital signals and output the results.  
      The optical record reproducing device further includes an operation circuit  50  for performing operation processing of output signals for electric signals a-f, that is, electric signals a-f converted into digital forms to generate a focus error signal and a tracking error signal, a CPU (Central Processing Unit)  60 , a focus control unit  70 , a tracking control unit  71 , a first D/A (Digital-to-Analog) converter  80 , a second D/A converter  81 , a first driver  90 , and a second driver  91 .  
      Operation circuit  50  includes three adder circuits and a differential circuit (not shown). Two of the adder circuits respectively calculate a sum signal (a+c) of electric signals from region A and region C and a sum signal (b+d) of electric signals from region B and region D, which respective two regions of four regions of photodetector  20  are diagonal to each other. The sum signal (a+c) and sum signal (b+d) of electric signals resulting from adding operations are output to a remaining adder circuit and the differential circuit. The adder circuit obtains a total value (a+c)+(b+d) of the sum signal (a+c) and sum signal (b+d) and provides the result as an RF signal to CPU  60 . The differential circuit obtains a differential (a+c)−(b+d) between the sum signal (a+c) and sum signal (b+d) and provides the result as a focus error signal to focus control unit  70 .  
      Operation circuit  50  further includes a differential circuit which is not shown. The differential circuit obtains a differential (e−f) between electric signal e and electric signal f from regions E and F of photodetector  21  and provides the result as an tracking error signal to tracking control unit  71 .  
      As described above, in this embodiment, an error signal is generated based on a three-beam method. Techniques such as a push-pull method and an astigmatism method are known as other techniques to generate an error signal. The present invention can be applied to these techniques. It is to be noted that, in the astigmatism method, a tracking error signal can be obtained with a signal (a+c)−(b+d) obtained by the operation of electric signals a-d of photodetector  20  split in four, similarly as for the focus error signal.  
      Focus control unit  70  and tracking control unit  71  generate a focus drive signal and a tracking drive signal based on error signals obtained.  
      Generated focus drive signal and tracking drive signal are respectively converted into analog signals with first D/A converter  80  and second D/A converter  81  and input to first driver  90  and second driver  91 .  
      First driver  90  drives actuator  11  in a focus direction based on the focus drive signal so as to bring a light spot into a focus. Second driver  91  drives actuator  11  in a tracking direction based on the tracking drive signal so as to place the light spot on a center of a track of the optical disk.  
      As described above, in this embodiment, a dynamic range of the A/D converter can be made narrower with a construction in which the electric signal detected with the photodetector is directly input to the A/D converter. When an output amplitude of the electric signal is beyond the dynamic range, however, a waveform saturation of the electric signal occurs and accuracy of a servo control is degraded.  
      Therefore, with adjustments of an offset and a gain for the electric signal, the waveform saturation of the electric signal which may occur in the A/D converter having a narrow dynamic range can be avoided to enable a stable servo control. In this embodiment, RF amplifier unit  30  further includes an offset adjustment function and a gain adjustment function to implement a stable servo control.  
       FIG. 2  shows a construction of RF amplifier unit  30  shown in  FIG. 1 . RF amplifier unit  30  includes a plurality of differential amplifiers arranged for respective electric signals a-f. Since each of the differential amplifiers has the same construction, a differential amplifier  51  arranged corresponding to electric signal a is representatively shown in  FIG. 2 .  
      Referring to  FIG. 2 , differential amplifier  51  is an inverting amplifier, and electric signal a is input to an inverting input terminal. An output terminal of differential amplifier  51  is coupled to an input terminal of second A/D converter  41 . A variable resistor  52  is coupled as a feedback resistance between the inverting input terminal and the output terminal. A variable resistor  54  is coupled between a non-inverting input terminal and a ground potential.  
      An output voltage of differential amplifier  51  can be offset by adjusting a resistance value of variable resistor  54  connected to the non-inverting input terminal of differential amplifier  51 . Therefore, variable resistor  54  functions as an offset adjustment unit.  
      Furthermore, a gain of differential amplifier  51  can be increased or decreased by adjusting a resistance value of variable resistor  52 . Therefore, variable resistor  52  functions as a gain adjustment unit.  
      The variable resistor as the offset adjustment unit and the variable resistor as the gain adjustment unit are similarly arranged for each of the differential amplifiers which are not shown.  
      The resistance value of variable resistor  54  is adjusted corresponding to a control signal from CPU  60  shown in  FIG. 1 .  
      Referring back to  FIG. 1 , CPU  60  receives output signals of first to sixth A/D converters  40 - 45  to measure a direct current (DC) level of each output signal. An obtained DC level is compared with a reference voltage (corresponding to a median of the dynamic range of the A/D converter) to calculate a differential therebetween. CPU  60  sends a control signal to variable resistor  54  of RF amplifier unit  30  or the like so as to make the differential “zero”, that is, to match the DC level of the output signal with the reference voltage.  
      Variable resistor  54  adjusts the resistance value according to a corresponding control signal. With this, an output voltage of differential amplifier  51  (that is, each of input signals of first to sixth A/D converters  40 - 45 ) is offset and the DC level is set to the median of the dynamic range.  
      The resistance value of variable resistor  52  is adjusted corresponding to a control signal from CPU  60 . CPU  60  receives output signals of first to sixth A/D converters  40 - 45  to measure a potential difference (output amplitude) between maximum and minimum values of each output signal. CPU  60  further makes a determination as to whether an obtained potential difference falls within the dynamic range of the A/D converter or not. When the potential difference does not fall within the dynamic range, CPU  60  sends a control signal to variable resistor  52  of RF amplifier unit  30  or the like so as to make the potential difference fall within the dynamic range.  
      Variable resistor  52  or the like adjusts the resistance value according to a corresponding control signal. With this, a gain of differential amplifier  51  or the like is adjusted and an output voltage (that is, each of input signals of first to sixth A/D converters  40 - 45 ) is adjusted so as to make the output amplitude fall within the dynamic range.  
      CPU  60  is also a circuit to detect existence of a scratch on optical disk  1  using an output of operation circuit  50 . When the existence of a scratch is detected, CPU  60  outputs a signal representing the existence to focus control unit  70  and tracking control unit  71 . An algorithm for detecting the scratch will be described below in detail.  
      Referring to  FIG. 3 , a program executed in the optical record reproducing device has a control structure as described below regarding a tracking control.  
      In step  100  (hereafter, “step” is abbreviated as “S”), photodetector  20  and photodetector  21  start reading and conversion of light reflected from optical disk  1 . RF amplifier unit  30  amplifies signals converted by photodetector  20  and photodetector  21 . First to sixth A/D converters  40 - 45  convert the signals converted by RF amplifier unit  30  into digital signals. First to sixth A/D converters  40 - 45  output the digital signals to operation circuit  50 .  
      In S 102 , CPU  60  sets a detection flag FL and a time parameter TT to “ ”. In S 104 , operation circuit  50  outputs to CPU  60  a total sum of the digital signals output from first to sixth A/D converters  40 - 45 .  
      In S 106 , CPU  60  makes a determination as to whether or not a value output from operation circuit  50  is below a threshold value (this value can be determined arbitrarily by a designer of the optical record reproducing device according to this embodiment). When it is determined that the value is below the threshold value (YES in S 106 ), processing is moved to S 108 . Otherwise (NO in S 106 ), the processing is moved to S 110 . In S 108 , CPU  60  sets detection flag FL to “1”. In S 110 , CPU  60  sets detection flag FL and time parameter TT to “0”. In S 112 , CPU  60  adds “1” to time parameter TT.  
      In S 114 , CPU  60  makes a determination as to whether or not a value of time parameter TT is at least three times a cycle of the RF signal. When it is determined that the value is at least three times the cycle of the RF signal (YES in S 114 ), the processing is moved to S 116 . Otherwise (NO in S 114 ), the processing is moved to S 118 .  
      In S 116 , each of focus control unit  70  and tracking control unit  71  ignores the signal output from CPU  60  for one signal. In place of the signal output from CPU  60 , each of focus control unit  70  and tracking control unit  71  assumes that a signal which is read by photodetector  20  immediately before reading of a defect signal (a signal representing a position of photodetector  20 ) is input again, and generates a signal representing the same content as that of the signal. Focus control unit  70  and tracking control unit  71  output generated signals to first D/A converter  80  and second D/A converter  81 , respectively.  
      In S 118 , each of focus control unit  70  and tracking control unit  71  generates a signal having the same content as that of a signal output from operation circuit  50  (a signal representing a position of photodetector  20 ). Focus control unit  70  and tracking control unit  71  output generated signals to first D/A converter  80  and second D/A converter  81 , respectively.  
      In S 120 , first D/A converter  80  and second D/A converter  81  change a position of objective lens  10  to optical disk  1  corresponding to contents of the signals generated by focus control unit  70  and tracking control unit  71 .  
      Referring to  FIG. 4 , an operation of the optical record reproducing device based on the structure and flow chart as described above will be described.  FIG. 4  shows relations of the tracking error signal, the RF signal and a scratch detection signal according to the embodiment of the present invention.  
      Concurrently with starting of optical disk reproduction, photodetector  20  and photodetector  21  start conversion of light reflected from optical disk  1  (S 100 ). When the conversion of reflected light is started, CPU  60  sets detection flag FL and time parameter TT to “0” (S 102 ). When the flag and parameter are set, operation circuit  50  outputs to CPU  60  a total sum of the digital signals output from first to sixth A/D converters  40 - 45  (S 104 ). When the total sum is output, CPU  60  makes a determination as to whether or not the value output from operation circuit  50  is below the threshold value (S 106 ). Initially, the value output from operation circuit  50  is not below the threshold value (NO in S 106 ), and therefore CPU  60  sets detection flag FL and time parameter TT to “0” (S 110 ). When the flag and parameter are set, each of focus control unit  70  and tracking control unit  71  generates the signal having the same content as that of the signal output from operation circuit  50 . Focus control unit  70  and tracking control unit  71  output generated signals to first D/A converter  80  and second D/A converter  81 , respectively (S 118 ). When the signals are output, first D/A converter  80  and second D/A converter  81  change a position of objective lens  10  to optical disk  1  corresponding to contents of the signals generated by focus control unit  70  and tracking control unit  71  (S 120 ). Thereafter, the processing of S 104 -S 120  is repeated until a time T( 5 ).  
      At time T( 5 ), CPU  60  again makes a determination as to whether or not the value output from operation circuit  50  is below the threshold value (S 106 ). After time T( 5 ), the output value substantially decreases. Therefore, the value output from operation circuit  50  becomes lower than the threshold value (YES in S 106 ), and thus CPU  60  sets detection flag FL to “1” (S 108 ). CPU  60  adds “1” to time parameter TT (S 112 ). When a value of the flag is set, CPU  60  makes a determination as to whether or not a value of time parameter TT is at least three times the cycle of the RF signal (S 114 ). With the processing of S 106 -S 114 , based on whether values of a plurality (at least three in this embodiment) of signals read by photodetector  20  fall out of a prescribed range or not, CPU  60  makes a determination as to whether or not all of the plurality of signals read by photodetector  20  are defect signals representing existence of a defect (in this embodiment, a defect regarding detection of a tracking error). Since it is not initially determined that the value is at least three times the cycle of the RF signal (NO in S 114 ), the processing of S 118 -S 112  is repeated. According to  FIG. 4 , however, the value output from operation circuit  50  is below the threshold value until a time T( 8 ). As a result of the value output from operation circuit  50  being below the threshold value, it is finally determined that the value of time parameter TT is at least three times the cycle of the RF signal (YES in S 114 ), and therefore each of focus control unit  70  and tracking control unit  71  ignores the signal output from CPU  60  for one signal (S 116 ). After the signal being ignored for one signal, the processing of S 1120 -S 114  is again repeated. With the processing of S 116 -S 118 , when CPU  60  determines that the signals read by photodetector  20  are defect signals, tracking control unit  71  generates a signal representing a position of photodetector  20 , and when CPU  60  determines that values of the signals read by photodetector  20  are signals other than defect signals, tracking control unit  71  generates a signal representing the same content as that of a signal read by photodetector  20 .  
      As described above, when a level of the tracking error signal is measured, the optical record reproducing device according to this embodiment makes a determination as to whether there is a scratch on an optical disk or not from a waveform of a signal read from the optical disk. When there is no scratch on the optical disk, an obtained signal is regarded as a normal signal and the processing is continued. When there is a scratch on the optical disk, a tracking control is performed similarly as in a situation in which a scratch is absent. When there is a scratch on the optical disk, a signal obtained with detecting the scratch is a false signal. When the false signal is reproduced as a sound or a picture, a dropout in the sound or a disturbance in the picture occurs. In the optical record reproducing device according to this embodiment, when a signal of a place of a scratch is detected, the signal will not be processed. When a signal of a place of a scratch is detected, the optical record reproducing device according to this embodiment keeps a previous level of a control. Since the control as such is performed, the tracking error signal is accurately measured and accuracy of an automatic adjustment can be increased. Therefore, a picture or a sound of good quality can be obtained by reproducing picture or sound data with the optical record reproducing device according to this embodiment. As a result, an optical record reproducing device can be provided which accurately measures the defect signal and has increased accuracy of the automatic adjustment to obtain a picture or a sound of good quality.  
      It is to be noted that, in S 106 , CPU  60  may make a determination as to whether or not a rate of change of a value output from operation circuit  50  is larger than a certain value, in place of the determination as to whether the value is below the threshold value or not. In this situation, the determination as to whether or not the rate of change of the value output from operation circuit  50  is larger than the certain value is made based on whether a value resulting from removal of a high frequency component of the value output from operation circuit  50  beforehand with a low-pass filter is larger than the certain value or not.  
      In addition, in S 114 , CPU  60  may make a determination as to whether or not a value of time parameter TT is at least 14 times the cycle of the RF signal. Presence or absence of a scratch on the optical disk can be detected if the value of time parameter TT is less than 14 times the cycle of the RF signal provided that the value is sufficiently larger than the cycle of the RF signal. When the value of time parameter TT is at least 14 times the cycle of the RF signal, however, presence or absence of a scratch on the optical disk can be detected with higher accuracy.  
      Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.