JP2510411B2 - Focus Servo Device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a focus servo device, and more particularly to a focus servo device in an optical information reading device that optically reads recorded information on a recording disk.

BACKGROUND ART In an optical information reading device for reading recorded information on a digital audio disc, a video disc, etc., a spindle servo device controls a rotational drive of a recording disc (hereinafter simply referred to as a disc) so that the disc can be moved in a radial direction of the disc. The recorded information is read by the provided pickup. Further, in order that the spot light for detecting information by the pickup may be correctly converged on the recording surface of the disc, and further, the spot light may accurately trace a recording track formed in a spiral shape on the recording surface of the disc. A focus servo device and a tracking servo device that are controlled as described above are provided. In the tracking servo device, the higher the loop gain, the higher the trackability of the spot light for information detection (track following ability), and the occurrence of malfunctions such as so-called track skipping does not occur even if external vibration or disk eccentricity exists. Therefore, stable tracking control can be performed.

In an information reading device equipped with such various servo devices, when there is an abnormal portion due to a defect, a scratch, etc. on the recording surface of the disc to be reproduced, when the information reading spot light by the pickup tracks the recording track in the abnormal portion. In addition, the servo system error signal may be disturbed and a malfunction such as a track jump may occur.

Therefore, conventionally, when an abnormal portion on the recording surface is detected, the tracking servo device performs the servo by lowering the loop gain or holding the previous error value, or the abnormal portion obtained by another method. By taking measures such as switching to servo by a tracking error signal that is not related to the above, it is possible to obtain a stable tracking operation without causing a malfunction such as a track jump due to a defect or scratch on the recording surface.

On the other hand, when reading recorded information in an abnormal area due to defects or scratches on the recording surface, so-called dropout due to defects or scratches is detected, and the read information at the time of detection is detected by a dropout compensation circuit (not shown). Since the output is controlled so as not to output, the control for the focus servo device at the abnormal portion of the recording surface is not particularly required.

However, as a result of an experiment conducted by the inventor, since the mechanical crosstalk exists in the structure of the pickup, when the lens moves in the focus direction, the lens also moves in the tracking direction. It was found that when the system is greatly disturbed, the lens is also shaken in the tracking direction and the tracking servo system is affected. That is, for an abnormal state due to a defect, a scratch or the like on the recording surface of the disk, a sufficiently stable tracking operation cannot be obtained unless the tracking servo system as well as the focus servo system is controlled.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and a focus servo device capable of improving the trackability of information detection spot light when there is an abnormal portion such as a defect or a scratch on the disk recording surface. The purpose is to provide.

The focus servo apparatus according to the present invention detects the preceding tracking information by irradiating the recording surface with a pair of preceding and succeeding preceding and following tracking information detecting spot lights when the recording information detecting spot light moves relative to the recording disk. The spot light of the spot light for use on the recording surface is received by the first light receiving means, and the abnormality of the output signal from the first light receiving means is compared with the reference level by the abnormality detecting means to indicate the abnormality of the recording surface. A control signal is generated, and the hold value of the focus error signal held in the hold circuit in the presence of this control signal is output as a focus error signal.

Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

In FIG. 1, three spot lights obtained by converging a laser beam, that is, a recording information detecting spot light 1 and a pair of preceding and succeeding tracking information preceding and succeeding respectively when the spot light 1 moves relative to the disc. The detection spot lights 2 and 3 are applied to the recording track 4 in the positional relationship shown in the figure. That is, when the recording information detecting spot light 1 is on the center line of the track 4, the pair of tracking information detecting spot lights 2 and 3 are located on both side edges of the track 4.
Therefore, when the recording information detection spot light 1 is deviated in the track orthogonal direction (disk radial direction), the light amount difference of the reflected light by the pair of tracking information detection spot lights 2 and 3 corresponds to the deviation direction and the deviation amount. It will be.
The reflected light from the spot lights 1 and 2 and 3 is the photoelectric conversion element 5 and the first and second photoelectric conversion elements built in a pickup (not shown).
The light enters the photoelectric conversion elements 6 and 7 as light receiving means.

In FIG. 2, the reflected light from the tracking information detecting spot lights 2 and 3 incident on the photoelectric conversion elements 6 and 7 is converted into an electric signal by the elements 6 and 7, and the operational amplifier 8 and
A waveform shaping circuit 11 including a capacitor 9 and a resistor 10, an operational amplifier 12, a waveform shaping circuit 15 including a capacitor 13 and a resistor 14 is supplied to a subtractor 21 including an operational amplifier 16 and resistors 17 to 20. By this subtractor 21, the photoelectric conversion element
A signal corresponding to the level difference between the outputs of 6 and 7 is formed and derived as a tracking error signal.

The output signal of the photoelectric conversion element 6 that receives the reflected light of the preceding spot light 2 of the pair of tracking information detection spot lights 2 and 3 is also supplied to the abnormality detection circuit 22 after passing through the waveform shaping circuit 15. It This abnormality detection circuit 22
When there is an abnormal portion due to a defect, a scratch, etc. on the recording surface of the disc during reproduction of the disc, the signal level of the output signal of the photoelectric conversion element 6 passing through the waveform shaping circuit 15 is compared with the reference level to detect the abnormal state of the disc surface. It is for detecting and generating a control signal indicating the abnormal state.

The abnormality detection circuit 22 includes a capacitor 23 and a resistor 24.
An AC coupling circuit 25, an operational amplifier 26, an amplifier 29 composed of resistors 27 and 28, a time constant circuit 34 composed of a capacitor 30, a diode 31, a charging resistor 32 and a discharging resistor 33, an operational amplifier 35 and a voltage dividing resistor 36, It is composed of a comparator 38 composed of 37.

Reflected light from the recording information detecting spot light 1 (see FIG. 1) passes through a cylindrical lens (not shown) and the photoelectric conversion element 5
Incident on. In the cylindrical lens, the position on the optical axis where the transmitted light flux converges differs between the plane including the generatrix and the plane orthogonal to the generatrix, so that the light beam projected on the light receiving surface of the photoelectric conversion element 5 is different. The shape of the bundle changes depending on the positional relationship between the recording surface of the disk and the convergence point of the laser beam. The photoelectric conversion element 5 is arranged such that the light reception surface is divided into four by two straight lines which are orthogonal to each other so that the change in the shape of the light beam projected on the light reception surface of the photoelectric conversion element 5 can be detected, and the photoelectric conversion elements 5 are independent from each other. It is composed of four light receiving elements.

The addition output of the elements of the photoelectric conversion element 5 which are arranged so as to be located on the diagonal line to each other is added to the operational amplifier 45 via the amplifier 41 including the operational amplifier 39 and the resistor 40, and the amplifier 44 including the operational amplifier 42 and the resistor 43. , Capacitors 46,4
It is supplied to a subtractor 52 including 7 and resistors 48 to 51. The output signal of the subtractor 52 corresponds to the direction and amount of deviation of the convergence point of the laser beam, and is output as a focus error signal. An RF signal which is a recording information read signal can be obtained by adding the output signals of the amplifiers 41 and 42.

The focus error signal is supplied to the hold circuit 53 for constantly holding the signal level via the variable resistor VR. The hold circuit 53 includes, for example, a capacitor 54,
It consists of a changeover switch 59 that switches from the contact a to the contact b in response to the high-level control signal supplied from the resistors 55 to 58 and the abnormality detection circuit 22 described above. The signal level of the focus error signal immediately before being held by the capacitor 54 is output as the focus error signal.

The focus error signal that has passed through the hold circuit 53 is supplied to a phase compensation circuit 60 that performs phase compensation of the signal. The phase compensation circuit 60 is composed of an operational amplifier 61, a capacitor 62 and resistors 63 to 65.

Next, the circuit operation of the focus servo device according to the present invention will be described.

First, in the present embodiment, in the information reading apparatus using the so-called 3-beam type tracking error signal generation method, the reflected light from the preceding spot light 2 of the pair of tracking information detection spot lights 2 and 3 is received. An abnormal portion due to a defect, a scratch or the like on the recording surface of the disk is detected based on only the output of the photoelectric conversion element 6.

That is, the signal level of the output signal of the photoelectric conversion element 6 decreases as shown in FIG. 3 (A) according to the degree of the abnormal state of the disk recording surface. The waveform is shaped by the waveform shaping circuit 15 and then supplied to the abnormality detection circuit 22, whereby the abnormality is detected in the circuit 22 based on the change in the signal level.

In the abnormality detection circuit 22, the capacitor 23 and the resistor 24
The output signal of the photoelectric conversion element 6 AC-coupled by
After the amplification by, the time constant circuit 34 extends the time. The reason for performing the time extension is that when abnormality detection is performed based on the preceding tracking information detection spot light 2, the abnormality detection state does not continue until the subsequent tracking information detection spot light 3 passes through the abnormal portion. Therefore, when abnormality detection is performed based on only the preceding spot light 2, time extension is performed. Specifically, the resistance value R ₃₂ of the charging resistor 32 is set to be extremely smaller than the resistance value R ₃₃ of the discharging resistor 33 (R ₃₃ >> R ₃₂ ), and when charging the capacitor 30, By rapidly charging through the diode 31, the abnormality detection operation is prevented from being delayed, and at the time of discharging, discharging is performed with a time constant determined by the capacitor 30 and the discharge resistor 33, so that time extension is performed. The signal level of the output signal of the time constant circuit 34 is compared with the reference level given by the voltage dividing resistors 36 and 37 in the comparator 38, and the comparison output becomes the abnormality detection output.

When the abnormality detection circuit 22 detects an abnormality on the disk recording surface, in the hold circuit 53, the changeover switch 59 switches from the contact a to the contact b in response to the abnormality detection output from the abnormality detection circuit 22, so that the capacitor The signal level of the focus error signal immediately before the abnormality detection that was held in 54 is output as the focus error signal. And
In a focus actuator (not shown), control is performed in accordance with this error signal so that the spot lights 1, 2 and 3 are correctly converged on the disk recording surface.

As described above, when the disc is reproduced, the focus error signal is always held even in the focus servo system, and when there is an abnormal portion such as a defect or a scratch on the recording surface of the disc, it is held in the hold circuit immediately before detecting the abnormality. By outputting a constant value as a focus error signal and controlling the focus servo system as well, the spot information 1 for recording information detection is swung in the tracking direction due to the disturbance of the focus servo system due to the abnormality of the disk recording surface, and the tracking servo system It is possible to prevent the disorder from occurring. Therefore, as compared with the case where the control is performed only in the tracking servo system as in the related art, the trackability of the pickup information detection point (recording information detection spot light 1) with respect to the abnormal portion of the disk recording surface can be improved. is there.

In the above embodiment, the abnormality of the disk recording surface is detected based on the preceding tracking information detecting spot light 2, but it is based on the tracking error signal generated by the subtracter 21 (second drawing). You may also do it.

Furthermore, it is also possible to detect an abnormality on the disk recording surface based on the RF signal obtained by adding the output signals of the amplifiers 41 and 42. That is, as shown in FIG. 4 (A), the signal level of the RF signal decreases in accordance with the degree of the abnormal state of the disk recording surface. Therefore, in the circuit shown in FIG. RF is detected by detecting the envelope of (A) by the envelope detection circuit 72.
The change amount (AC component) of the signal level is taken out, and the output signal (B) of the envelope detection circuit 72 is further converted into a waveform shaping circuit.
By shaping the waveform at 73 and supplying the output (C) to the abnormality detection circuit 22, it is possible to detect the abnormality on the disk recording surface.

In the above embodiment, the hold circuit 53 shown in FIG.
The hold value of the focus error signal immediately before the abnormality is detected is output as the focus error signal during the abnormality detection period by the circuit configuration of FIG. 6, but the circuit configuration shown in FIG. can get.

EFFECTS OF THE INVENTION As described above, according to the focus servo apparatus of the present invention, the first tracking information detecting spot light emitted to the recording surface of the disc prior to the recording information detecting spot passes through the recording surface. The abnormal state of the recording surface is detected based on the output of the light receiving element, the focus error signal is constantly held in the hold circuit to generate the hold value, and when the abnormal state is detected on the recording surface, the hold value immediately before is detected. By outputting as a focus error signal and controlling the focus servo system as well, the recording information detection spot light is swung in the tracking direction due to the disturbance of the focus servo system due to the abnormality of the disk recording surface, and the disturbance of the tracking servo system is prevented. Since it is prevented from occurring, it is limited only in the tracking servo system as in the past. As compared with the case where the control is performed, it is possible to improve the tracker clearance of the information detection point of the pickup with respect to the abnormality of the disk recording surface.

[Brief description of drawings]

FIG. 1 is a diagram showing a positional relationship of three spot lights with respect to a recording track, FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG. 3 is a focus error signal (in the vicinity of an abnormal portion of a disc recording surface). A) and a waveform diagram showing the output signal (B) after the waveform shaping, FIG. 4 is a waveform diagram showing the reproduction RF signal (A), its envelope detection output (B) and its waveform shaping output (C), FIG. 5 is a circuit diagram for performing the waveform treatment shown in FIG. 4, and FIG. 6 is a circuit diagram showing a modified example of the hold circuit in FIG. Description of main part code 1 …… Spot light for recording information detection 2,3 …… Spot light for tracking information detection 4 …… Recording track 5,6,7 …… Photoelectric conversion element 22 …… Abnormality detection circuit 53 …… Hold circuit 60 ... Phase compensation circuit

Claims (2)

(57) [Claims] 1. A focus servo device for controlling a spot light for detecting recorded information so as to correctly focus the spot light for detecting recorded information on a recording surface of a recording disk according to a focus error signal,
Irradiation means for irradiating the recording surface with a pair of preceding and succeeding tracking information detecting spot lights respectively when the recording information detecting spot light moves relative to the recording disk, and the preceding and succeeding tracking information detection. By comparing the level of the output signal from the first light receiving means with the first and second light receiving means for respectively receiving the spot light of the spot light for use which has passed through the recording surface, the abnormal state of the recording surface can be determined. An abnormality detecting means for generating a control signal, and a hold circuit for constantly holding the signal level of the focus error signal to generate a hold value and outputting the hold value as a focus error signal in the presence of the control signal. A focus servo device characterized by being provided. 2. The focus servo apparatus according to claim 1, wherein the abnormality detecting means holds the control signal for a certain period of time after the abnormal state of the recording surface ends.