JPH02220233A - Specular surface detector - Google Patents

Abstract

PURPOSE:To obtain a specular surface detector to relatively easily and surely detect an unrecorded area by discriminating the level of a tracking error signal low-band component after opening a tracking servo loop. CONSTITUTION:When an information read spot enters into an unrecorded area, the output of a demodulating circuit 8 is not generated. When such a state is detected by a control circuit 6, it instructs a loop switch 2 to open a tracking servo loop 5. At such a time, an objective lens is returned to the neutral position. With respect to the unrecorded area, the information read spot does not intersect tracks and the level of a tracking error signal A is about zero, and the noise due to flaws or the like of the disk surface is eliminated by an LPF 11 when occurring. An output B of the LPF is subjected to full-wave rectification by an absolute value circuit 12, and an output C is converted to a DC signal D by an LPF 13 and is compared with a reference level VTH by a comparator 14, and the high level is outputted when the output C is lower than the level VTH. Thus, the circuit 6 detects abnormality of read to output the control signal which returns a pickup to the initial position.

Description

TECHNICAL FIELD The present invention relates to a mirror surface detection device for detecting whether an information reading point of a pickup in a disk recording/reproducing device exists in a recording area of a disk or in a non-recording area, that is, a mirror surface portion. .

BACKGROUND ART FIG. 5 shows an example of an optical information recording disc, and from the inner circumferential side to the outer circumferential side of the disk there are a non-recording area (mirror surface) where no information is recorded, a To C (Table
A lead-in area where an index of program information recorded on the disc is recorded, a program recording area where program information is recorded, and a lead-out where a signal indicating the end of the program recording area is recorded. It is a non-recorded area (mirror surface) where no area or information is recorded. The lead-in area, program recording area, and lead-out area form a recording area.

An optical disc player that plays such a disc can forcibly move the information reading spot in the radial direction of the disc to perform track jumps, search for targeted information, perform trick plays, and the like.

By the way, when the pickup is moved in the radial direction of the disk at high speed, when the pickup is moved based on the correspondence between address information such as a time code recorded in the lead-in area and position information of the slider that carries the pickup, If a disturbance is applied to the disc player during performance, the information reading spot may move to the mirror area of the disc. In this case, there are no tracks on the mirror surface and no tracking error signal can be obtained, so the tracking servo and slider servo will no longer function. Therefore, when the information reading spot enters the mirror area, it is necessary to quickly detect the intrusion of the information reading spot into the mirror area in order to promptly perform a backup operation such as returning the pickup to the initial position.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a mirror surface detection device capable of detecting entry of an information reading spot into a mirror surface area of a disk.

In order to achieve the above object, the information reading spot of the pickup is adjusted to suppress the deviation on the recording track based on a tracking error signal representing the amount of deviation in the disk radial direction of the information reading spot of the pickup with respect to the recording track of the information recording disk. a tracking servo loop for biasing the disk in the radial direction; a loop switch for opening the tracking servo loop in response to an opening command; a low-pass filter means for separating low-frequency components from the tracking error signal; The present invention is characterized by comprising level discrimination means for comparing the level of the low frequency component separated by the means with a reference level and generating a level discrimination output based on the comparison result.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a mirror surface detection device according to the present invention, in which a tracking error signal A is supplied from a tracking error generating section 1 to a tracking servo amplifier via a loop switch 2. The tracking error generation unit 1 prepares three beams, for example, a main beam for information detection and sub-beams for tracking error detection arranged on both sides of the main beam, and a line connecting the centers of these beams is aligned in a predetermined direction with respect to the track direction. A device using a so-called three-beam method is known in which a tracking error signal is generated based on the difference in light intensity between two sub-beams that are arranged to have an offset angle and reflected from a recording surface of a disk.

The amplifier 3 amplifies the power of the tracking error signal A and supplies it to the drive coil 4 of the tracking actuator. The drive coil 4 swings the optical unit including the objective lens of the pickup to cause the information reading spot to follow the track. The tracking error generator 1, loop switch 2, amplifier 3, and drive coil 4 constitute a tracking servo loop 5.

Additionally, the tracking error signal is filtered through a low-pass filter (
(hereinafter referred to as LPF) 11, Absolute value circuit 12, LPF
13 and a comparator 14. For example, LPFll has a cutoff frequency of 67
0 [Hzl], and removes high-frequency noise in the tracking error signal caused by scratches on the disk surface and supplies it to the absolute value circuit 12.

The absolute value circuit 12 is constituted by, for example, a full-wave rectifier circuit using an OP amplifier, and obtains a level signal C having only positive amplitude from the tracking error signal. level signal C
For example, LPF1 with a cutoff frequency of 80 [Hz]
3, resulting in a level signal whose level corresponds to the presence of the tracking error signal. This level signal is supplied to a comparison input terminal of a level comparator 14 whose comparison reference input terminal is supplied with voltage vTH.

The comparator 14 sets its output E to a high level when the level signal falls below the voltage VTR. Comparator 1
The output E of 4 is sent to the control circuit 6 as a level discrimination output.
is supplied to

The control circuit 6 issues various control signals such as opening/closing commands for the loop switch 2 based on control information signals such as focus lock signals and synchronization signals supplied from the focus servo device 7, tracking servo loop 5, demodulation circuit 8, etc. Occur.

The focus servo device 7 uses, for example, a cylindrical lens to converge the light beam as a single line in the horizontal direction at one of two points on the optical path of the light beam that are separated from each other. On the other hand, there is known an apparatus based on the so-called astigmatism method, in which a light beam is focused as a single line in the vertical direction, and error signals at the two points are generated.

The demodulation circuit 8 demodulates the read RF signal from the pickup and outputs a video signal, synchronization signal, audio signal, etc.

Next, the operation of the apparatus will be explained with reference to FIG.

The control circuit 6 monitors the output of the video signal and synchronization signal of the demodulation circuit 8. If the information reading spot crosses the lead-in area or lead-out area and enters the non-recording area for some reason, no video information exists and no output from the demodulation circuit 8 is generated. As a result, when the control circuit 6 detects an abnormality, it issues an open command to the loop switch 2 to open the tracking servo loop in order to confirm the cause. When the tracking servo stops, the objective lens returns to its neutral position.

Normally, there is some misalignment between the rotational axis of the disk and the center of the disk, and because the tracks are formed in a spiral, when the tracking servo is turned off, in the recording area formed by the tracks, the tracks intersect with the information reading point. do. Therefore, a frequency component is generated in the tracking error signal in the recording area. On the other hand, when the information reading spot is in a non-recording area with no track, the information reading spot and the track do not intersect, and the level of the tracking error signal becomes approximately zero. This is shown in FIG. 2(A). However, noise as shown in Figure 2 (A) may occur due to scratches on the disk surface, etc., and this noise can be removed by the LPF.
1 as shown in FIG. 2(B). Furthermore, in order to determine the amplitude of the tracking error signal, the output of the LPFII is full-wave rectified by the absolute value circuit 12 to obtain an output as shown in FIG. 2(C). This is smoothed by the LPF 13 as shown in FIG. 2 (D) to become a DC signal, and the comparator 14
Compare with reference level vT,4. This reference level vTo
is set in advance in accordance with the level of the tracking error signal when the information reading spot is in the non-recorded area. The comparator 14 outputs a high level as shown in FIG. 2(E) when the output level of the LPF 13 falls below the reference level vT8.

When the control circuit 6 detects that the output of the comparator 14 is at a high level, it detects an abnormality in the output of the demodulation circuit 8 and that the information reading point does not intersect with the track, and detects that the information reading point is in a non-recorded area. Know what to do. Based on this result, the control circuit 6 supplies a control signal to, for example, a slider servo device (not shown) to return the pickup to its initial position.

In this embodiment, the control circuit 6 does not determine that there is an information reading spot in the non-recorded area based only on the output abnormality of the demodulation circuit 8, but instead detects the non-recorded area based on no change in the tracking error signal by using the tracking servo as an oven. Therefore, even if a track carrying no information signal is formed near the innermost or outermost circumference of the disk, this portion will not be erroneously determined to be a non-recording area.

In this way, it is possible to open the tracking servo loop and detect, based on the level discrimination output of the comparator 14, that the information reading spot is in the non-recording area.

Another example of the configuration of the detection unit 10 is shown in FIG. In the apparatus shown in FIG. 3, parts corresponding to those shown in FIG. 1 are denoted by the same reference numerals, and a description of those parts will be omitted.

In Fig. 3, the tracking error signal A is LPFI
After the noise component is removed by I, peak holder 1
5. The peak holder 15 detects the positive or negative peak level of the tracking error signal A at regular intervals and holds it. This holding level is supplied to the window comparator 16, and it is determined whether the holding level is within a predetermined range determined in correspondence to the tracking error signal level in the non-recorded area. If within the predetermined range, the comparator 16 supplies a high level to the control circuit 6. Therefore, it performs the same function as the detection section 10 shown in FIG.

Note that the loop switch 2 can be configured as a selection switch 2a as shown in FIG. 4, and the tracking error signal A passed through this selection switch can be supplied to the detection unit 10.In such a case, the opening command There is an advantage that the detection unit 10 can be operated depending on the situation.

As described in detail, the specular surface detection device of the present invention has the following features:
It is preferable that the level of the low frequency component of the tracking error signal is discriminated after the tracking servo loop is opened, so that a non-recorded area where no track exists can be detected relatively easily and reliably.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a signal waveform diagram for explaining the operation of the embodiment, and FIG. 3 is a block diagram showing the detection unit 10 shown in FIG. FIG. 4 is a block diagram showing an example of the configuration of , and FIG. 5 is a block diagram showing another embodiment.
The figure is a diagram for explaining a recording area of an information recording disc. Explanation of symbols of main parts 1... Tracking error signal generation section 2.2a
...Loop switch 5 ...Tracking servo loop 6 ...
・Control circuit 10...Detection section Fig. 1 Applicant: Pioneer Corporation

Claims (3)

[Claims] (1) The information reading spot is adjusted to suppress the deviation between the information reading spot and the recording track based on a tracking error signal representing the amount of deviation of the information reading spot of the pickup in the disk radial direction with respect to the recording track of the information recording disk. a tracking servo loop for biasing the disk in the radial direction; a loop switch for opening the tracking servo loop in response to an opening command; a low-pass filter means for separating a low-frequency component from the tracking error signal; 1. A specular surface detection device comprising: level discrimination means for comparing the level of the separated low frequency component with a reference level and generating a level discrimination output based on the comparison result. (2) The level discrimination means compares a rectifying means for rectifying the output of the low-pass filter means, a smoothing filter for smoothing the output of the rectifying means, and an output level of the smoothing filter and a reference level, and compares the output level of the smoothing filter with a reference level. 2. The specular surface detection device according to claim 1, further comprising a comparator that generates the level discrimination output based on the result. (3) The level discrimination means includes a peak value detection means for detecting and holding the peak value of the output of the low-pass filter means, and the level discrimination means when the output level of the peak value detection means is within a predetermined range. 2. The specular surface detection device according to claim 1, further comprising a window comparator that generates an output.