JPH056574Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to an optical pickup that can be installed in a write-once optical disc device, a compact disc player, etc., and in particular, the invention relates to an optical pickup that can be installed in a write-once optical disc device or a compact disc player. death,
The present invention relates to a sample servo device that corrects the irradiation state of a detection beam on the recording surface of an optical disk based on this error signal.

[Background of the invention]

The optical pickups installed in compact disc players, etc. that are currently in practical use,
A continuous servo system is used as a mechanism for correcting the irradiation state of the detection beam on the information recording surface of the optical disk. In this continuous servo system, the focus error of the spot of the detection beam that is irradiated from the objective lens onto the recording surface of the optical disk, and the tracking error signal that indicates the state in which the spot scans the information track are continuously detected. The irradiation state of the objective lens onto the optical disk is continuously corrected by a servo mechanism in accordance with each error signal.

On the other hand, the sample servo method may be standardized for optical pickup in write-once optical disk devices, etc., which are expected to be put into practical use in the future. In this sample servo method, the objective lens is driven for correction based on a focus error signal or a tracking error signal that is sampled at a predetermined cycle.

3 to 5 show conventionally devised sample servo devices for tracking correction.

In the sample servo method, pits as shown in FIG. 5A are formed on the recording surface of the optical disk D. This figure shows the arrangement of information pits P formed on a track, and in the middle of the information pits P are formed pits Pa and Pb for obtaining a tracking error signal. These pits Pa, Pb are provided at intervals of a predetermined period Ts at several hundred to several thousand locations per revolution of the track. The pits Pa and Pb are placed on both sides of the track.

As the detection beam spot S converged by the objective lens 1 (see Fig. 3) scans the track, the reflected beam is detected as a light reception signal from the light receiving member 4 as shown in Fig. 5B. RF signals can be obtained. This RF signal contains an information pit P.
and the light intensity modulation signals (P ₁ and P ₂ ) caused by the pits Pa and Pb. In this case, if the levels of signals P ₁ and P ₂ based on pits Pa and Pb are equal, it means that no tracking error has occurred, and if the modulation level of either signal P ₁ or P ₂ is large, spot S is off track. If the difference between the level of this signal _P1 and the level of _P2 is determined, this becomes the sampled tracking error signal.

FIG. 4A shows a tracking error signal sampled at a period Ts. The conventional sample servo device shown in FIG. 3 is provided with a zero-order hold circuit 3 having a switch member _SW1 made of an active element such as a transistor, and a capacitor C having a small capacity. The switch member SW ₁ is shown in FIG. 4B.
As shown in , it turns ON for a short time at the same timing as the rising or falling edge of the sampled tracking error signal. By turning off the switch member _SW1 , the level of the tracking error signal is held until the next error signal is sampled. As a result, the fourth
A stepwise changing servo signal as shown in Figure C is obtained. Based on this servo signal, the servo mechanism 2 is driven by the drive circuit. This servo mechanism is composed of a coil, a magnet, etc., and the objective lens 1 is driven by this mechanism, and correction is made so that the spot S of the detection beam accurately scans the track.

(Problems to be solved by the invention) Compared to the conventional continuous servo method, the sample servo method described above simplifies the configuration of the optical device in the optical pickup, and also makes it easier to produce masters for optical disks. It has certain advantages.

However, the sample servo device described above has a problem in that the phase of the correction drive operation by the servo mechanism 2 is delayed. This phase delay in the correction drive operation is caused by the provision of the zero-order hold circuit 3, and this phase delay is caused by the transfer function {1-e×p(-S・Ts)}/S. It is sought after.

FIG. 7 conceptually explains the phase delay of the above-mentioned correction drive operation. The solid curve in the figure shows the servo signal Ec obtained by the conventional continuous servo system. The servo signal by the sample servo device is shown by the solid curve (the servo signal
Ec) and has flat parts starting from each point on the curve. These gradual changes are actually high frequency components, and the servo characteristics based on the actual sample servo method are represented by the dashed curve Es connecting the midpoints of the flat parts of the gradual change signal.
This servo curve Es shown by the dashed line is obtained by connecting the midpoints of the flat parts having a length of time Ts, so the curve Es has a time delay of half the servo period Ts (Ts/2) with respect to the servo signal Ec of the continuous servo system, and as a result, the phase of the correction drive operation is delayed.

The straight line α in the diagram of Fig. 6 is the relationship between the phase delay (vertical axis) of the correction drive operation in the conventional sample servo system and the frequency (Hz) of the curve Es showing approximate servo characteristics in Fig. 7. It shows a relationship. As mentioned above, the approximate servo curve Es in the sample servo method has a time delay multiplied by half the sample period Ts (Ts/2) to the servo signal Ec in the continuous servo method. The frequency of s=(1/
Ts) (Hz), that is, when the frequency is the same as the frequency at which the sample signal is obtained, the phase delay of the correction drive operation is 180°, which is half of one cycle. Further, when the frequency is 0, the phase delay is 0°.

In an actual sample servo device, for example, the frequency s = (1/Ts) to obtain the sample signal is approximately 30kHz.
On the other hand, the servo area used is 0~
The range is around 3kHz. Therefore, the phase delay in the servo area is about 0 to 18 degrees.

If there is an unnecessary phase delay of this degree, the stability of the servo will deteriorate.

The present invention solves the above problems, and provides an optical pickup sample servo device that can stabilize the servo by making the phase delay of the sampled servo signal smaller than before. This is what we provide.

(Specific means for solving the problem) The sample servo device according to the present invention includes an optical member that forms a detection beam spot on the information recording surface of an optical disk, and a light receiver that detects the reflected beam from the information recording surface. A hold circuit that holds the level of the error signal in the detection beam irradiation state sampled at a predetermined period among the light reception signals from the light receiving member until partway through the time to obtain the next error signal, and the level of the error signal. and a servo mechanism that corrects the irradiation state of the detection beam on the information recording surface in accordance with the information recording surface.

In this sample servo device, the level of the sampled error signal is maintained until halfway through the time when the next sampled error signal is obtained. That is, as shown in FIG. 4, in the past, the level of the sample error signal was held for the sampling period Ts, but in the present invention, the level holding time is made shorter than Ts. Therefore, this is equivalent to substantially shortening the time Ts in FIG. 7, and the phase delay of the correction drive operation can be reduced.

(Embodiment of the invention) Hereinafter, an embodiment of the invention will be described with reference to FIGS. 1 and 2.

In FIG. 1, reference numeral D designates an optical disk, which is rotationally driven by a turntable 5. As shown in FIG. The optical pickup is provided with an objective lens 1 facing the optical disk D. A detection beam emitted from a semiconductor laser or the like is focused by the objective lens 1, and a minute beam of the beam is focused on the recording surface of the optical disk D. A spot is formed. As shown in FIG. 5A, information pits P based on, for example, digital signals are formed on the tracks of the recording surface of the optical disc D. Further, pits Pa and Pb for tracking error signals are formed on the track, which are sampled at a predetermined period Ts. The optical pickup is also provided with a tracking servo mechanism 2 consisting of a coil, a magnet, etc., and this tracking servo mechanism 2 corrects and drives the position of the objective lens 1 in a direction that intersects the track of the optical disk D. It's becoming like that.

The optical pickup is provided with a light receiving member (photodiode) 4 for detecting the reflected beam from the recording surface of the optical disk D. The reflected beam is intensity-modulated by a bit formed on the track, and the presence or absence of a pit is detected by the light receiving member 4. As shown in Figure 5B, this detection signal becomes
The RF signal includes a signal for tracking error detection.
Contains P ₁ and P ₂ . The level of this signal P ₁ and
The sample error signal determined by the difference in the level of _P2 is processed by the hold circuit 13 shown in FIG. 2, the objective lens 1 is driven for correction.

The hold circuit 13 includes two switch members constituted by active elements such as transistors.
It consists of SW ₁ , SW ₂ and a small capacitor C.

Next, the operation will be explained.

The beam reflected from the minute spot S of the detection beam formed on the recording surface of the optical disk D is detected by the light receiving member 4. The RF signal shown in FIG. 5B is obtained from the light reception signal of the light receiving member 4.
This RF signal is processed as an information read signal. This RF signal includes tracking error signals _P1 and _P2 . The difference in level between the tracking error signals _P1 and _P2 becomes the sampled tracking error signal. This tracking error signal is sampled at intervals of the period Ts in which the pits Pa and Pb are formed, and this error signal has the waveform shown in FIG. 2A.

The switch member _SW1 in the hold circuit 13 is intermittently turned on at the same timing as the rise or fall of each sampled tracking error signal. Also other switch parts
SW ₂ is turned off at the timing when the switch member SW ₁ is turned on, and then turned on in the middle of the time until the tracking error signal rises or falls. That is, the switch member _SW2 is OFF during the first half (time Ta) of the period Ts in which the tracking error signal is sampled, and is ON during the second half. Switch member SW ₁
ON and switch member SW ₂ is OFF (time
Ta), the level of the tracking error signal sampled immediately before is held. As a result, the tracking servo signal that has passed through the hold circuit 13 has the waveform shown in FIG. 2D. A drive circuit operates based on this tracking servo signal, and the objective lens 1 is driven by the mechanical operation within the tracking servo mechanism 2. Second
The tracking servo signal shown in Figure D is an intermittent pulse, and the frequency of this pulse (the frequency at which the error signal is sampled) is, for example, 30kHz.
Since the servo operation by the tracking servo mechanism 2 actually has operation characteristics as shown by the broken line curve in FIG. 2D.

Here, in the tracking servo signal shown in FIG. 2D, the level retention time Ta of the sampled tracking error signal is longer than the servo signal retention time Ts in the conventional sample servo device shown in FIG. 4C. Becomes shorter. As explained in the background of the invention, the delay in the correction drive operation due to the servo signal is due to the transfer function of the hold circuit 13, and this transfer function is {1-e×p(-S・Ta)}/S It is expressed as

Therefore, the delay in the phase shift of the correction drive operation by the servo signal according to the present invention can be made smaller by (Ta/Ts) than the conventional one shown in FIG. 3 and subsequent figures. That is, in the above embodiment, since the time of Ts in FIG. 7 is substantially Ta, the servo curve Es shown by the broken line is positioned to the left in the diagram by (Ts - Ta)/2. Become. for example
When Ta/Ts is 1/2, the servo curve, which conventionally had a time delay of Ts/2 as shown in FIG. 7, can be made to have a time delay of Ts/4 in the present invention. FIG. 6 is a diagram showing the phase delay of the correction drive operation in the conventional method and the method of the present invention when Ta/Ts is 1/2. The vertical axis represents the phase delay, and the horizontal axis represents the frequency of the curve shown by the broken line in FIG. 2D. As shown by β in this figure, when Ta/Ts is 1/2, the phase delay can be reduced to 1/2 compared to the conventional case (α). In an actual sample servo device, for example, the tracking error sampling frequency s is approximately 30kHz, whereas
The servo range used is approximately 0 to 3kHz. Therefore, in the present invention, the servo phase delay is approximately 0 to 9 degrees, as indicated by β.

Of course, the servo phase delay can be changed by changing the Ta/Ts ratio, and this ratio can be set depending on the error signal sampling cycle and other conditions.

In addition, in the embodiment shown in Fig. 1, the hold circuit is constructed by arranging two switch members, but the switch member is only SW ₁ , and a resistor etc. in parallel with the capacitor C is provided, and this time constant is used as the hold circuit. It is also possible to adopt a configuration in which the holding time Ta of the peak value of the error signal is determined.

Further, the present invention is not limited to tracking servo, but can also be implemented in focus servo.

[Effect of idea]

As described above, according to the present invention, it becomes possible to minimize the phase delay of the correction drive operation in the sampling servo device, and it becomes possible to stabilize the servo.

[Brief explanation of the drawing]

Fig. 1 is a component arrangement diagram showing an embodiment of the sample servo device in an optical pickup according to the present invention; Fig. 2A is a diagram showing a sample error signal obtained from an RF signal in the device of Fig. 1; Fig. 2B and C is a diagram showing the operation timing of switch members SW ₁ and SW ₂ , respectively, and FIG. 2D is a diagram showing servo signals. Figure 3 is a component arrangement diagram of a sample servo device in a conventional optical pickup, and Figure 4A.
is a diagram showing the sample error signal obtained from the RF signal in the device shown in FIG. 3, FIG. 4B is a diagram showing the operation timing of the switch member _SW1 , and FIG. 4C is a diagram showing the servo signal. . Fig. 5A is a plan view showing the information pits recorded on the optical disk and pits for sample error signals; Fig. 5B is a diagram showing the RF signal that detects the pits shown in Fig. 5A; Fig. 6 7 is a diagram comparing the phase delay of the correction drive operation in the conventional example and the embodiment of the present invention.
The figure is a diagram conceptually showing the time delay of the servo curve in the sample servo method. D...Optical disk, P...Information pit, Pa,
Pb... Pit for sample error detection, 1...
Objective lens, 2...Servo mechanism, 4...Light receiving member, 13...Hold circuit, _SW1 , _SW2 ...Switch member.

Claims (1)

[Claims for Utility Model Registration] (1) An optical member that forms a detection beam spot on the information recording surface of an optical disk, a light receiving member that detects the reflected beam from the information recording surface, and a light receiving signal from the light receiving member. Among these, there is a hold circuit that holds the level of the error signal of the detection beam irradiation state sampled at a predetermined period until halfway through the time to obtain the next error signal, and a detection beam that is applied to the information recording surface in accordance with the level of the error signal. An optical pickup sample servo device consisting of a servo mechanism that corrects the irradiation state of the light. (2) The hold circuit includes a zero-order hold circuit that has a switch member that operates at the same time as the error signal is sampled, and another switch member that releases the holding of the signal level in the middle of the time when the next error signal is obtained. A sample servo device for an optical pickup according to claim 1, which comprises: