JPS6120929B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tracking control device for an optical information reading device.

Optical video discs have recesses called pits arranged on the circular disc surface to form concentric or spiral tracks, and the length and spacing of these pits determines the video information. recorded.

Information is read from the video disk by making light incident on a video track consisting of pits on the disk and demodulating the reflected light, which is modulated depending on the presence or absence of pits. Such an information recording disk reading device is provided with a so-called tracking servo device so that the irradiated light always accurately tracks the video track of the disk.

FIG. 1 is a diagram schematically showing an example of a tracking servo device, in which a light beam irradiated from a light source 1 such as a helium neon laser is transmitted through a collimator lens 2,
The light passes through the beam splitter 3 and the λ/4 plate 4, and further through the tangential mirror 5, the tracking mirror 6, and the focus lens 7, and is focused onto the recording surface of the video disk 8. The reflected light passes through the focus lens 7, tracking mirror 6, and tangential mirror 5, and enters the λ/4 plate 4 and beam splitter 3, where the incident light and the reflected light that read the information are effective. separated into

The reflected light separated by the beam splitter 3 is separated into servo light and signal reproduction light by another beam splitter 11. The reproduction light is detected by a light receiving element (not shown), undergoes signal processing, and is reproduced into a video signal. One servo light passes through the cylindrical lens 12 and enters the light-receiving surface of the light-receiving element 9 placed after it.

The light receiving element 9 generates a tracking servo signal that controls the rotation of the tracking mirror 6, and also controls the vertical movement of the focus lens 7 with respect to the disk 8 so that the irradiated light is always focused on the recording surface. It is also configured to generate a focus servo signal for use. For this purpose, the light receiving element 9 is divided into four parts 9a, 9b, 9c and 9d as shown in FIG.
By taking advantage of the property that the position on the optical axis where the light beam passing through this lens 12 converges is different in the plane including the generatrix of , and in the plane perpendicular to it, the four mutually independent light-receiving surfaces of the light-receiving element 9 are The positional relationship between the recording surface and the focus lens 7 is determined by detecting and measuring the shape of the beam of light projected onto the lens 7.
Focus servo is performed by controlling the vertical movement of.

On the other hand, for tracking servo, adjacent elements 9a, 9d, 9b, 9c of this light receiving element 9 are set as a set, and the sum of each output, ie, Va+
Vd and Vb+Vc are input to the comparison amplifier 10 at the next stage, and the difference voltage Ve is used as an error signal for tracking servo. For this purpose, by appropriately setting the relative relationship between the cylindrical lens 12, the light receiving element 9, and the video track, when the center of the luminous flux of the irradiated light is on the video track center line, the
A pit projection 20 as shown in FIG. 3a may occur, and when the center of the light beam moves away from the track center line, a pit projection 20 as shown in FIG. 3b may occur. That is, an error signal corresponding to the distance between the center of the light beam and the track center line is outputted as the output Ve of the comparator amplifier 10. Therefore, the tracking mirror 6 is rotated by a necessary angle using this error signal, so that the light beam is always accurately tracked on the track.

Note that the tangential mirror 5 controls the position of the light beam in the tangential direction of the video track and has the role of a time base collector, and its details will be omitted.

In addition, a radial feed motor (not shown) is provided to sequentially vary the relative position of the video disk and the irradiation light beam in the radial direction of the video disk, and this motor is driven by the low frequency component of the tracking error signal Ve. It will be done. This motor generally moves the video disk in the radial direction for forward playback, reverse playback, etc.

In such a configuration, if there is any defect in the recording track of the video disc, the tracking servo will be disengaged at that portion. Even if the tracking servo operates again immediately after that, it may not be able to pass through the defective portion and the same track may be reproduced many times.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a tracking control device for an optical information reading device that prevents malfunction of the tracking servo in a defective portion of a video track and prevents the reproduction of the preceding and following portions from being repeated over and over again. It is.

The tracking control device in the optical information reading device of the present invention includes means for detecting that the irradiated light beam has left the center line of the video track and generating an error signal corresponding to the separation distance, and a means for generating an error signal corresponding to the separation distance, and a low frequency A low-frequency equalizer circuit that emphasizes components, and a signal level based on the output of the low-frequency equalizer circuit when the level of the signal based on the output of this low-frequency equalizer circuit matches the irradiation light flux and the center line of the track. means for generating a detection signal by detecting a change in the amount by a predetermined amount or more; and means for generating a control signal for a predetermined period of time in response to the generation of the detection signal. Opening the servo loop of the tracking servo means by the signal and driving a radial feed motor that sequentially varies the relative position of the irradiated light beam and the disk in the disk radial direction, and at the same time discharging the stored charge in the low frequency equalizer circuit. It is characterized by

In order to better understand the features and effects of the present invention, the present invention will be described below with reference to the accompanying drawings.

FIG. 4 is a schematic block diagram showing an embodiment of the present invention. The respective outputs of the four-division light-receiving elements shown in FIGS. As described above, the output of the comparison amplifier 10 is the error signal Ve corresponding to the distance between the irradiation light beam and the center line of the video track, and the signal Ve is applied to the low-frequency equalizer circuit 13 in the next stage.
The signal components at or near 30Hz are emphasized. The reason is that the video disk is 30r.
This is because the error signal Ve component has a low frequency component of 30Hz or its vicinity because it rotates at a rotational speed of ps and the center of the track and the center of rotation of the disk do not coincide and there is eccentricity. be.

The output signal of the low frequency equalizer circuit 13 is further input to the drive amplifier 14, and the tracking mirror 6
This is the drive signal for the drive coil L. Further, the output signal of the drive amplifier 14 has high frequency components and noise components removed by an LPF (low-pass filter) 15, and becomes an input A of a window comparator 16 at the next stage. The upper and lower reference levels V _RH and V _RL of the window comparator 16 are input as reference voltages,
It is configured to generate a high level output B both when the comparison input A exceeds the upper limit level _VRH and when it falls below the lower limit level _VRL , and a well-known window comparator circuit can be used.

A monostable multi 17 is provided which generates a high level control signal C for a predetermined period (T) in response to the timing of generation of this high level output B, and this control signal C controls the tracking servo loop. It is opened and the radial feed motor is forcibly driven to pass through the defective part. Further, by discharging the charge in the capacitor constituting the low frequency equalizer circuit 13, further effects can be expected as described later.

FIG. 5 is a diagram showing operation waveforms of various parts for explaining the operation of the circuit block of FIG. 4, and in both figures, equivalent signals are indicated by the same symbols. Under normal servo operating conditions, the output A of the low-pass filter 15 changes the rotational speed of the disk as shown in Figure 5A.
If nr.ps, a sinusoidal signal of nHz (30Hz as an example) is obtained due to the disk eccentricity mentioned above, and its DC component is at a substantially constant level.

If the tracking servo comes off due to some defect in the track near time _t1 , the LPF
As shown in the figure, the output A rises or falls (dotted line), and its level changes rapidly. Therefore, the reference voltage level V _R of the window comparator 16
If _H and V _RL are set up or down by a predetermined value with respect to the normal DC level, servo deviation can be detected. Therefore, the detection signal B becomes high level only when it exceeds the reference level V _RH or falls below V _RL . In response to the timing of generation of this high level detection signal B, the monostable multi 17 operates and a high level control signal C is generated for a certain period T.

With this control signal C, the tracking servo loop is opened as described above, and the feed motor is further driven at a constant speed, so that the defective portion on the track can be quickly removed.

Further, the level of the error signal Ve is high just before the servo is disconnected, and therefore the capacitor constituting the low frequency equalizer circuit 13 is charged to correspond to the level. Based on this charge, abnormal voltage continues to be applied to the tracking mirror's drive coil L for a long time, which may cause a delay in the servo's recovery or cause the irradiated light to swing excessively, causing the focus servo to come off. It causes. Therefore, it is necessary to limit the deflection angle of the tracking mirror by some means (for example, mechanical means). In order to eliminate this drawback, the capacitor of the low frequency equalizer circuit is discharged by the control signal C.

As detailed above, according to the present invention, even if there is any defect on the video track, the tracking error signal at that time is used to detect the servo disturbance caused by the defect, and the servo loop is immediately opened. Since the radial feed motor is driven, the defective track portion can be skipped and the regeneration operation can be performed stably again.
Further, since the capacitor of the low frequency equalizer can be discharged to prevent abnormal voltage from being applied to the tracking mirror drive coil, abnormal vibration of the tracking mirror can be eliminated and the servo operation can be restored smoothly and quickly.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram schematically showing an example of a servo system of an optical information reading device, Fig. 2 is a diagram showing a tracking servo signal generation circuit, and Fig. 3 explains the operation of Fig. 2. 4 are circuit block diagrams showing one embodiment of the present invention, and FIG. 5 is an operational waveform diagram of each part of FIG. 4. Explanation of symbols of main parts, 6...Tracking mirror, 8...Video disk, 13...Low frequency equalizer, 16...Window comparator, 17...
...monostable multi.

Claims (1)

[Claims] 1 Tracking servo means for tracking the irradiation light beam on a recording track on the information recording surface of the recording medium; and variable means for sequentially varying the relative position of the irradiation light beam and the recording medium in the radial direction of the recording medium. A tracking control device for an optical information reading device that reads information using light that has passed through the recording surface of the irradiation light beam, the tracking control device detecting that the irradiation light beam has left the center line of the track; means for generating an error signal corresponding to the separation distance; a low-frequency equalizer circuit that emphasizes low-frequency components of the error signal; and a signal level based on the output of the low-frequency equalizer circuit that is at the center of the irradiation light flux and the track. means for generating a detection signal by detecting that the level of the signal based on the output of the low-frequency equalizer circuit has changed by more than a predetermined amount when the lines match, and a means for generating a detection signal in response to the generation of the detection signal. means for generating a control signal for a predetermined period of time, and the control signal opens the servo loop of the tracking servo means and drives the variable means, and at the same time, the control signal opens the servo loop of the tracking servo means and drives the variable means. A tracking control device in an optical information reading device characterized by causing discharge.