Disc player using a servo loop with a variable transfer function

Abstract: A disc playing apparatus having a tracking servo loop and a focus servo loop is configured such that a transfer function of at least one of the servo loops (3-­ 7, 10-13) is adjustable. Disc defect detection signals are generated (15,18) in response to a change in a low frequency component (15) and a high frequency component (18) of a read signal output from the pickup (3), and the transfer function of at least one of the tracking servo loop and the focus servo loop is adjusted in response to the disc defect detection signal. According to another feature of the invention, the transfer function of at least one of the tracking servo loop and the focus servo loop is gradually changed each time an erroneous jumping movement of the information reading light spot is detected by information contained in the read signal output by the pickup.

Description: The present invention relates to a disc player for playing a recording disc such as a digital audio disc and a video disc. Disc players are structured such that an optical beam is used to trace a recording track constituted by depressions called pits formed in the recording surface of the disc, and a recording signal is read-out by detecting the light from the recording surface of the disc. For such operations, it is necessary to use a focus servo system for converging the light beam onto the surface of the disc to form a light spot for reading information (information reading point) and a tracking servo system for moving the information reading point so that it follows the recording track accurately. As the focus servo system, systems according to a so-called astigmatic method are known, which systems are arranged such that the light beam is converged, by using a cylindrical lens for example, as a focal line in the horizontal direction at one of two points on the light path of the light beam which are apart from each other, and also converged as a focal line in the vertical direction at the other of the two points, and a light sensor of a quadrant type is disposed at a middle position of the two points, to generate an error signal. As the tracking servo system, systems according to a so-called three-beam method is known, which systems are arranged such that three beams including a main beam for reading information and two sub-beams for detecting tracking errors disposed on both sides of the main beam are prepared and arranged so that a line passing through the centers of the three beams forms a predetermined off-set angle with respect to the direction of the track, and an error signal is generated from a difference between the amount of the two sub-beams reflected by the recording surface of the disc. With this type of tracking servo system, if there is a defect called a splash defect such as a flaw in the aluminium layer evaporated on the recording pits, the defect is read by the sub-beam, and a pulse-like noise will be generated in the tracking error signal. In such an event, the noise in the tracking error signal in turn causes a fault called a track jumping by which the information reading light spot erroneously jumps to another track. In the focus servo systems, if there is a defect called a black spot defect such as a stain on the recording surface of the disc, a noise will be generated in the focus error signal. In such an event, the control operation of the focus servo system is disturbed, and the sub-beams of the tracking servo system are adversely affected by such a disturbance. This also will result in the track jumping fault. As described above, faults of the disc do not occur uniformly, and it has been very difficult to prevent faults such as the track jumping fault caused by a defect of the disc. More specifically, in order to cope with faults caused by defects of the disc it is effective to lower the loop gain of the servo loop so as to reduce the influence of noises. However if a vibration is applied to the player from outside, the relative distance between the disc and the objective lens is varied by the vibration, and this also will cause the track jumping fault. For the track jumping fault caused by external vibrations, it is effective to increase the loop gain of the servo loop, so as to improve the response of the servo loop against the change in the relative position. It then follows that a measure to counter the defects of the disc will deteriorate the stability of the player against vibrations. Thus it has been very difficult to prevent faults caused by defects of the disc and faults caused by external vibrations at the same time. The present invention is based on the recognition of the above-described points. An object of the present invention is to provide a disc player which is capable of preventing faults caused by defects of the disc. Another object of the present invention is to provide a disc player which is capable of preventing faults caused by external vibrations. EP-A-207374 discloses a disc player which discriminates between errors caused by mechanical vibrations and those caused by errors on the recording medium by detecting whether or not acceleration is applied to the main body of the player. FR-A-2536196 discloses an arrangement where the envelope of the information signal is compared to a reference voltage to detect disc errors. EP-A-183435 is concerned with detecting abnormalities on discs using the radio frequency signal. EP-A-160095 describes an arrangement where modulation of an RF signal due to disc flaws or external vibrations is detected and the gain of the tracking servo circuit appropriately altered. US-A-4722079 discloses a disc apparatus for playing a disc comprising: a pickup means for reading a signal recorded on said disc; a focus servo loop for focusing an irradiation light, which is issued from said pickup means and irradiated on a recording surface of said disc to form an information reading light spot; a tracking servo loop for moving said information reading light spot to follow a recording track of said disc; and a first disc defect detection means for generating a first detection signal from a low frequency component of a read signal output from said pickup means. The present invention is characterised in that the first detection signal is generated when an instantaneous level of the low frequency component of the read signal output from said pickup means has reduced below a first predetermined value; a second disc defect detection means is provided for generating a second detection signal when an instantaneous level of a high frequency component of an error signal of said tracking servo loop has risen above a second predetermined value; and an adjusting means is provided for adjusting a transfer function of at least one of said tracking servo loop and said focus servo loop in response to each of said first and second fault detection signals. According to a feature of the invention, the disc playing apparatus comprises control means for detecting an error or movement tending to cause an erroneous track jumping movement of said information detection light spot by using information contained in the read signal output by said pickup means and changing a transfer function of at least one of said tracking servo loop and said focus servo loop each time said error or movement is detected, wherein said transfer function is gradually changed until the effect of the error or movement has been compensated for. Certain embodiments of the invention will now be described by way of example and with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a first embodiment of the disc player according to the present invention; Figures 2A and 2B are flowcharts showing the operation of the processor in the player system shown in Figure 1; Figure 3 is a block diagram of a second embodiment of the disc player according to the present invention; and Figures 4A and 4B are flowcharts showing the operation of the processor in the player system shown in Figure 3. In Figure 1, the disc is rotated by a spindle motor 2. During the rotation of the disc 1, the signal recorded thereon is read-out by a pickup 3. The pickup 3 incorporates therein a laser diode, an objective lens, a focus actuator, a tracking actuator, and photo detectors, etc. An output signal from the photo detectors in the pickup 3 is supplied to an RF amplifier 4. The RF amplifier 4 is configured to amplify the RF (radio frequency) signal as an information reading signal, and to generate a tracking error signal according to the three-beam method, and a focus error signal according to the astigmatic method. The RF amplifier 4 is also operative to extract a low frequency component of the RF signal and to output the extracted low frequency component. The tracking error signal and the focus error signal output from the RF amplifier 4 are supplied to a signal change-over circuit 7 through variable gain amplifiers 5 and 6 respectively. A change-over control signal a consisting of a square-wave signal of a predetermined frequency output from a timing signal generating circuit 8 is supplied to the signal change-over circuit 7. The signal change-over circuit 7 is configured to output the tracking error signal and the focus error signal alternately in response to this change-over control signal a . The output signal of the signal change-over circuit 7 is supplied to an A/D (analog to digital) converter circuit 10. A sampling pulse signal b synchronized in phase with the change-over control signal a is generated in the timing signal generating circuit 8 and supplied to the A/D converter circuit 10. In the A/D converter circuit 10, the tracking error signal and the focus error signal from the signal change-over circuit 7 are sampled alternately by using this sampling pulse signal b . The output data of the A/D converter circuit 10 is supplied to a digital equalizer 11 consisting of digital filters, etc. A timing pulse signal c synchronized with the sampling pulse signal b is generated in the timing signal generating circuit 8, and supplied to the digital equalizer 11. The digital equalizer 11 is configured to effect a phase compensation of the digitized tracking error signal and focus error signal which are alternately output from the A/D converter circuit 10, in a time-division fashion using the timing pulse signal c . The tracking error signal and the focus error signal treated by the phase compensation process in the digital equalizer 11 are alternately supplied to a PWM (pulse width modulation) circuit 12. The PWM circuit 12 is configured to generate two pulse signals having pulse widths respectively corresponding to the levels of the tracking error signal and the focus error signal using a timing pulse signal d from the timing signal generating circuit 8, synchronized with the timing pulse signal c . These two pulse signals output from the PWM circuit 12 are supplied to the tracking actuator and the focus actuator in the pickup 3 as drive signals, through a tracking actuator driving circuit 13 and a focus actuator driving circuit 14, respectively. The low frequency component of the RF signal output from the RF amplifier 4 is supplied to a black spot defect detection circuit 15. The black spot defect detection circuit 15 comprises, for example, a slicing circuit, and is configured to generate a detection signal S A of a suitable logic level when the level of the low frequency component of the RF signal is equal to or lower than a predetermined detection level V A . The tracking error signal output from the RF amplifier 4 is also supplied to a splash defect detection circuit 18 through an HPF (high pass filter) circuit 16. The splash defect detection circuit 18 comprises, for example, a slicing circuit, and is configured to output a detection signal S B of a suitable logic level when the level of the output signal of the HPF circuit 16 is equal to or higher than a predetermined detection level V B . The detection signals output from the black spot defect detection circuit 15 and the splash defect detection circuit 18 are supplied to a microcomputer 20. The RF signal output from the RF amplifier 4 is supplied to an EFM (eight-to-fourteen modulation) demodulation circuit 21. The EFM demodulation circuit 21 is configured to perform an EFM demodulation process of a pulse signal obtained by slicing the RF signal, to reproduce a PCM data, that is, a digital data including time-division multiplexed audio information of the left and right channels, and a subcode indicating the playing time, etc. The digital audio data including audio information output from the EFM demodulating circuit 21 is supplied to D/A converter circuit (not shown) after being treated by data processing operations such as the de-interleaving and error correction operations, to be converted to an analog audio signal. The subcode output from the EFM demodulating circuit 21 is supplied to the microcomputer 20. Various commands corresponding to key operations in an operation part (not shown) are also supplied to the microcomputer 20. The microcomputer 20 includes a processor operated by programs previously stored in a ROM. By the operation of the processor, various commands and data are supplied though a control-bus interface circuit 22 to the variable gain circuits 5 and 6, the A/D converter circuit 10 and the digital equalizer 11, etc., in response to the detection signals S A and S B , and the subcode. The operation of the processor of the microcomputer 20 in the arrangement described above will be explained with reference to the flowchart of Figures 2A and 2B of the accompanying drawings. When a play command is issued during the execution of a main routine, the processor proceeds to step S1 in which the gain of the variable gain amplifiers 5 and 6, the dynamic range of the A/D converter circuit 10, and the characteristic of the digital equalizer, etc. are set respectively to initial values, and a play operation is started with various servo loops opened. Then, count value data T1 and T2 for detecting the number of the switchings of the gain of the variable gain amplifiers 5 and 6 are set to zero and stored in predetermined addresses of RAM by the processor (step S2). The processor then judges whether or not either of the detection signals S A and S B is output (step S3). If it is detected in step S3 that neither of the detection signals S A and S B is output, the processor in turn judges whether or not all music selections recorded on the disc 1 have been played, by using data of the Q channel in the subcode (step S4). If it is detected in step S4 that all music selections have not been played, the processor then judges whether or not a stop command is issued (step S5). If it is judged that the stop command has been issued, the processor turns various servo loops off, and stops the play operation (step S6). If, conversely, it is judged that the stop command has not been issued, the processor proceeds to step S3 once more. If it is detected in step S4 that playback of all music selections has been completed, the processor proceeds to step S6 immediately. If it is detected in step S3 that either of the detection signals S A and S B is output, the processor then judges whether or not the Q data of the subcode is read-out properly (step S7). If it is judged in step S7 that the Q data is read-out properly, the processor proceeds to step S4. If it is judged in step S7 that the Q data is not read-out properly, the processor then judges whether or not a measure against the track jumping fault is to be taken, by evaluating the highness of the frequency of occurrence of anomalous data in the Q data (step S8). If it is judged in step S8 that the measure against the track jumping fault should not be taken, the processor then proceeds to step S4. If it is judged in step S8 that the measure against the track jumping fault should be taken, the processor then judges whether or not the detection signal SA is output (step S11). If it is detected in step S11 that the detection signal S A is output, the processor lowers the gain of the variable gain amplifier 6 by a predetermined amount, so as to reduce the possibility of occurrence of the track jumping fault by the black spot defect (step S21). With this operation, the characteristic of the digital equalizer may be also changed, so that the level only of the high frequency component of the error signal is reduced. Then the processor adds a value 1 to the count value T1 (step S22), and judges whether or not the detection signal S A is output (step S23). If it is detected in step S23 that the detection signal S A is output, the processor judges whether or not the Q data is read-out properly (step S24). If it is judged in step S24 that the Q data is read-out properly, the processor turns back the gain of the variable gain amplifier, which has been changed by the predetermined amount in step S21, by the same amount of change for one processing cycle (step S25). If it is detected that the Q data is not read-out properly, the processor proceeds to step S21 once more. If it is detected in step S23 that the detection signal S A is not output, the processor immediately proceeds to step S25. After executing the operation of step S25, the processor subtracts the value 1 from the count value 1 (step S26), and judges whether or not T1 is equal to zero (step S27). If it is detected in step S27 that T1 is not equal to zero, the processor proceeds to step S23, and conversely if it is detected that T1 is equal to zero, the processor proceeds to step S3 once more. If it is detected in step S11 that the detection signal S A is not output, it follows that the detection signal S B is output. Then the processor lowers the gain of the variable gain amplifier 5 by a predetermined amount, so that the possibility of occurrence of the track jumping fault by the splash defect is reduced (step S31). With this operation, the characteristic of the digital equalizer 11 may also be varied so that the level only of the high frequency component of the error signal is reduced. Then, the processor adds a value 1 to the count value T2 (step S32), and judges whether or not the detection signal S B is output (step S33). If it is detected in step S33 that the detection signal S B is output, the processor then judges whether or not the Q data is read-out properly (step S34). If it is judged that the Q data is read-out properly, the processor turns back the gain of the variable gain amplifier 5, which has been changed by the predetermined amount at step S31, by the same amount for one processing cycle (step S35). If it is judged that the Q data is not read-out properly, the processor proceeds to step S31 once more. Furthermore, if it is judged in step S33 that the detection signal S B is not output, the processor immediately proceeds to step S35. After the execution of the step S35, the processor subtracts the value 1 from the count value T2 (step S36), and judges whether the count value T2 is equal to zero (step S37). If it is detected in step S37 that T2 is not equal to zero, the processor proceeds to step S33, and if T2 is judged to be equal to zero, the processor proceeds to step S3 once more. By the steps S3, S7, S8 and S11 in the above procedure, the kind of disc defect is determined, and an appropriate measure is taken in accordance with the kind of disc defect having been determined. This point will be further explained. Specifically, when the information reading light spot of the pickup traces a portion of the disc where a black spot defect exists, the amount of the light reflected by the disc 1 is reduced, so that the level of the low frequency component of the RF signal is reduced accordingly. In this state, the detection signal S A is output from the black spot defect detection circuit 15. As a result, the loop gain of the focus servo loop, for example, is gradually reduced by the operations of steps S21 through S24 until the Q data is read-out properly. In this state, if noises are generated in the focus error signal by the black spot defect, adverse effects of the noises on the beams provided for the tracking servo control operation are maintained small since the influence of the noises on the focus servo control is small under this condition. Thus, the track jumping fault by the black spot defect is prevented. Subsequently, when the information reading light spot of the pickup reaches an area without defects, the loop gain of the focus servo loop is increased to the former value by the operations of steps S25 through S27. When the information reading light spot of the pickup 3 traces a portion of the disc 1 where a splash defect exists, pulse-like noises will be generated in the tracking error signal, and the detection signal S B is output from the splash defect detection circuit 18. As a result, the loop gain of the tracking servo loop for example is gradually reduced by the operations of the steps S31 through S34 until the Q data is read-out properly. In this state, if the pulse-like noises are generated in the tracking error signal by the splash defect, their influences on the tracking servo control operation are maintained small. Thus, the track jumping fault by the splash defect is prevented. Subsequently, when the information reading light spot of the pickup reaches the area without defects, the loop gain of the tracking servo loop is increased to the former value by the operations of the steps S35 through S37. As described in the foregoing, the first embodiment of the disc player according to the present invention is so configured that the first fault detection signal is generated when the instantaneous level of the low frequency component of the reading signal output from the pickup has dropped below the first predetermined level, and the second fault detection signal is generated when the instantaneous level of the high frequency component of the error signal of the tracking servo loop has risen above the second predetermined level. In response to each of the first and second defect detection signals, the transfer function of at least one of the tracking servo loop and focus servo loop is adjusted. Therefore, it is possible to prevent easily the faults caused by different kinds of disc defects, such as the black spot defect and the splash defect, which will cause effects on portions of the player different from each other. The second embodiment of the disc player according to the present invention will be described hereinafter. The structure of the second embodiment of the disc player according to the present invention is illustrated in Figure 3. Besides the circuit elements already shown in Figure 1, the disc player includes a shock detection circuit 19 which receives the tracking error signal output from the RF amplifier 4 through an LPF (low pass filter) 17. Like the splash defect detection circuit 18, the shock detection circuit 19 comprises a slicing circuit, and is constructed to produce a detection signal S C of a suitable logic level when the output level of the LPF circuit 17 is equal to or higher than a predetermined level Vc. The output signal of the shock detection circuit 19 is supplied to the microcomputer 20. Since the other circuit elements in this embodiment are the same as the embodiment shown in Figure 1, the explanation thereof will not be repeated. Then the operation of the disc player shown in Figure 3 will be explained with reference to the flowcharts of Figures 4A and 4B. As shown in the flowchart of Figure 4A the processor proceeds to step S1, when a play command is issued during the execution of the main routine, in which step the gain of the variable gain amplifiers 5 and 6, the dynamic range of the A/D converter circuit 10, and the characteristic of the digital equalizer, etc. are set respectively to initial values, and a play operation is started with various servo loops opened. Then, count value data T1, T2 and T3 for detecting the number of switchings of the gain of the variable gain amplifiers 5 and 6 are set to zero and stored in predetermined addresses of the RAM by the processor (step S2′). The processor then judges whether or not any of the detection signals S A , S B , and S C is output (step S3′). The following steps S4 through S8 are the same as those already explained with reference to Figure 2A, and the explanation thereof will not be repeated. When it is determined in step S8 that a measure against the track jumping fault should be taken, the processor proceeds to steps S11′ and S12 shown in Figure 4B. In these steps, a check is made successively to determine whether or not the detection signal S A is output and whether or not the detection signal S B is output. If it is judged in step S11′ that the detection signal S A is output, the processor proceeds to step S21. Since the operation of the steps S21 through S27 are the same as those in the previous embodiment, the explanation thereof will not be repeated in this description. If it is judged in step S12 that the detection signal S B is output, the processor proceeds to step S31. Since the operation of the steps S31 through S37 are the same as those in the previous embodiment, the explanation thereof will not be repeated. If it is determined in step S12 that the detection signal S B is not output, then the processor judges that the detection signal S C is output, and proceeds to step S41. In step S41, the processor increases the gain of the variable gain amplifiers 5 and 6 by predetermined values, so that the track jumping fault will not be caused easily by external shocks or vibrations. Instead of the operation described above, it is also possible to change the characteristic of the digital equalizer 11 so that only the low frequency component of the error signal is emphasized. Then, the processor adds a value 1 to the count value T3 (step S42), and judges whether or not the detection signal S C is output (step S43). If it is judged in step S43 that the detection signal S C is output, the processor judges whether or not the Q data is read-out properly (step S44). If it is judged that the Q data is read-out properly, the processor turns back the gains of the variable gain amplifiers 5 and 6 which have been changed by the predetermined values in step S41, by the same amounts for one processing cycle (step S45). If it is determined that the Q data is not read-out properly, the processor proceeds to step S41 once more. Further, if it is determined in step S43 that the detection signal S C is not output, the processor immediately proceeds to step S45. After the execution of the step S45, the processor subtracts the value 1 from the count value T3 (step S46), and judges whether or not the count value T3 is equal to zero (step S47). If it is determined in step S47 that the count value T3 is not equal to zero, the processor proceeds to step S43. If it is determined that T3 is equal to zero, the processor proceeds to step S3 once more. In the above-described operation, the kind of the disc's defect is determined by the operations of steps S11′ and S12, and an appropriate measure is taken depending on the kind of disc defect. When vibrations are applied to the disc player from outside, the relative position between the disc 1 and the objective lens in the pickup 3 is changed by the vibrations, which in turn will generate a level change in the tracking error signal. As a result of this level change in the tracking error signal, the detection signal S C is generated when the instantaneous level of the low frequency component of the tracking error signal has exceeded the predetermined level Vc. In this event, the operations in steps S41 through S44 are executed, so that the loop gains of the tracking servo loop and the focus servo loop, for example, are gradually increased until the Q data is read-out properly. Thus, the responsiveness of the disc player against the change in the relative position caused by external vibrations is improved, so that the generation of track jumping faults is prevented. When the external vibrations disappear subsequently, the loop gains of the tracking servo loop and the focus servo loop are turned back through the operations of steps S45 through S47. As specifically described above, in the second embodiment of the disc player according to the present invention, the transfer function of at least one of the tracking servo loop and the focus servo loop is gradually changed each time an erroneous jumping movement of the information reading light spot towards another track is detected by the information contained in the output read-out signal of the pickup. Therefore, when the measure is taken for preventing the fault caused by the disc's defects, the loop gain of each servo loop will not be reduced excessively to render the disc player susceptible to external vibrations causing faults. Similarly, when the measure is taken to prevent the fault caused by external vibrations, the loop gain of each servo loop will not be increased excessively to render the disc player susceptible to the disc's defects causing faults. In this way, the faults caused by the disc's defects and the faults caused by external vibrations are easily prevented according to the present invention.

Claims: A disc apparatus for playing a disc (1) comprising: a pickup means (3) for reading a signal recorded on said disc (1); a focus servo loop for focusing an irradiation light, which is issued from said pickup means (3) and irradiated on a recording surface of said disc (1) to form an information reading light spot; a tracking servo loop for moving said information reading light spot to follow a recording track of said disc; and a first disc defect detection means (15) for generating a first detection signal (5A) from a low frequency component of a read signal output from said pickup means (3), characterised in that the first detection signal (5A) is generated when an instantaneous level of the low frequency component of the read signal output from said pickup means (3) has reduced below a first predetermined value (V A ); a second disc defect detection means (18) is provided for generating a second detection signal (5B) when an instantaneous level of a high frequency component of an error signal of said tracking servo loop has risen above a second predetermined value (V B ); and an adjusting means (5, 6) is provided for adjusting a transfer function of at least one of said tracking servo loop and said focus servo loop in response to each of said first and second fault detection signals (5A, 5B). A disc playing apparatus as claimed in claim 1 comprising control means (5,6) for detecting an error or movement tending to cause an erroneous track jumping movement of said information detection light spot by using information contained in the read signal output by said pickup means (3) and changing a transfer function of at least one of said tracking servo loop and said focus servo loop each time said error or movement is detected, wherein said transfer function is gradually changed until the effect of the error or movement has been compensated for. A disc playing apparatus as claimed in claim 2 wherein said control means (5,6) increases a loop gain of said at least one of said servo loops if said error or movement is caused by external vibrations. A disc playing apparatus as claimed in claim 2 or 3, wherein said control means (5,6) reduces a loop gain of said at least one of said servo loops if said error or movement is caused by defects of said disc. A disc playing apparatus as claimed in any of claims 2 to 4, wherein said transfer function is returned to its initial value when the cause of the error or movement is no longer present.

Inventors: FUKUDA TATSUYA C O PIONEER TOK, ISHII HIDEHIRO C O PIONEER TOK, MIURA CHIHARU C O PIONEER TOKO, TAKEYA NORIYOSHI C O PIONEER T, FUKUDA, TATSUYA C/O PIONEER TOKOROZAWA PLANT, ISHII, HIDEHIRO C/O PIONEER TOKOROZAWA PLANT, MIURA, CHIHARU C/O PIONEER TOKOROZAWA PLANT, TAKEYA, NORIYOSHI C/O PIONEER TOKOROZAWA PLANT
Applicants: PIONEER ELECTRONIC CORP, PIONEER ELECTRONIC CORPORATION
Application year: 1989
Main classification: G11B7
IPC codes: G11B7