JPH0555933B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to servo cane control of a focal position control loop or a tracking control loop in an apparatus for recording, reproducing, or reproducing an information recording medium (hereinafter referred to as a disk) using a light beam. It is related to the device.

BACKGROUND ART FIG. 3 shows an example of a focal position control loop including a servo gain control device used in a conventional video disc player or recordable optical disc file device.

The photodetectors 1 and 2 are for detecting the amount of deviation between the focal position of the objective lens and a desired focal point position, and usually PIN photodiodes or the like are used. The reflected light from the disk surface is detected by a photodetector 1,
2 is converted into current, and further preamplifier 3,
4, current-voltage conversion is performed. Each signal converted into a voltage is converted into a differential signal by a differential amplifier 5. This differential signal indicates the deviation from the focused point.

On the other hand, each signal converted into a voltage is made into a sum signal by the summing amplifier 6. This sum signal indicates the total amount of light irradiated to the photodetectors 1 and 2, and is input as a denominator signal to the divider 7. A differential signal is input as the numerator signal to the divider 7, and is normalized by the sum signal. For example, when the reflectance of the disk increases, the denominator increases and the differential signal decreases. On the other hand, when the reflectance of the disk becomes low, the denominator becomes small and the differential signal becomes large. In this way, the divider 7 makes the detection sensitivity for the amount of deviation from the focused point, which occurs due to fluctuations in the reflectance of the disk or large changes in the detected power during recording and reproduction, substantially constant.

The output signal of the divider 7 is subjected to phase lead compensation by a phase compensation circuit 8 in order to improve the stability of the control loop. The lead-compensated signal passes through a switch 11, is converted into a current by a drive amplifier 12, and is applied to a coil 13 that drives the objective lens. In this way, the objective lens is driven in accordance with the amount of deviation from the focal point, and is controlled so that the focal point position is always on the reflective surface in response to surface wobbling of the disk reflective surface.
In order to pull in this control loop, a pull-in start signal is generated in the pull-in start circuit 10 in response to the pull-in start command signal 14, and the current is amplified by the drive amplifier 12 through the switch 11 to drive the objective lens drive coil 13. When the retraction detection circuit 9 detects that the focal position of the objective lens has entered the vicinity of the operating point of the control loop, the switch 11 is switched and a closed loop is established.

FIG. 4 shows the open-loop frequency characteristics of the control loop, where represents the gain characteristics and represents the phase characteristics. In general, it shows the characteristics of a secondary system with a primary resonance point fo as shown by the solid line.
Furthermore, in the case of an actuator such as a linear motor, the characteristics shown in the dashed line are shown.

For example, if the gain intersection point when reproducing a disk with average reflectivity is B, then in this case, the phase margin at fc becomes θc [deg] due to the phase lead compensation circuit.

Now, in the case where there is no servo gain control device using the divider mentioned above, for example, if you try to play back a disc whose reflectance is considerably lower than the average level, the gain intersection will be point A, and the phase margin at f _C1 will be Q _C1 [deg]. In addition, when playing back a disc whose reflectance is considerably higher than the average level, the gain intersection will be at point C, and the phase margin at f _C2 will be θ _C2 [deg], and in both cases, the phase margin will be quite small. Therefore, the stability of the control loop may be impaired.

As described above, if there is no servo gain control device, the gain intersection will vary greatly, leading to a decrease in loop stability.

Considering this situation, it is possible to sufficiently increase the amount of phase advance in the phase compensation circuit, but this will result in a decrease in gain at low frequencies and a decrease in gain margin at the secondary resonance point. Since the components are emphasized, many problems arise such as increased power consumption and saturation of the coil drive stage.

So far, it has been stated that a servo gain control device is necessary to deal with fluctuations in the disk reflective surface during playback, but in the case of recordable disks, information is often recorded by changes in reflectance. Since playback is being performed, gain adjustment is required not only during playback but also during recording.

As described above, the detection sensitivity in which the reflectance of the disk reflective surface is a large factor often differs greatly between when reproducing a recording agent track, when reproducing an unrecorded track, and when recording. For example, if the variation in reflectance in each state is very small, it is sufficient to simply switch the gain according to each state, as proposed in Japanese Patent Laid-Open No. 58-94138. However, if there is a large variation in reflectance in each state, the above-mentioned means cannot absorb the variation, and a servo gain control device is required.

Further, a servo gain control device is similarly effective in a tracking control loop for accurately following a desired track.

Problems to be Solved by the Invention However, the conventional configuration as shown above has the following problems.

As shown in Fig. 3, in order to keep the varying detection sensitivity, or in other words, the detection gain, approximately constant, the gain of the amplifier is controlled by the magnitude of the sum signal of each output of the photodetector. In the configuration shown, the detection gain is not controlled in a closed loop, but is controlled in an open loop. Therefore, the structure is weak against disturbances caused by temperature changes and the like, and is easily influenced by disturbances.
This is not limited to this example; it is clear that open-loop control is more vulnerable to disturbances than closed-loop control. Another problem is that it is necessary to take into account variations in the elements used in the divider.

In view of the above problems, the present invention aims to provide a servo gain control device that can keep the detection gain substantially constant.

Means for Solving the Problems In order to solve the above problems, the servo gain control device of the present invention time-divides two signals from the photodetector into one signal, and further averages them. The substantially averaged signal is compared with a reference level, and the detection gain is controlled in a closed loop according to the difference.

Effects With the above configuration, the present invention can control the detection gain, which was conventionally controlled in an open loop, in a closed loop, so that it can operate stably against disturbances caused by temperature changes, etc. It is something that can be done.

Further, since the gain control of multiple input signals can be performed using one gain control device, there is a great effect in simplifying the circuit.

Embodiment FIG. 1 shows an embodiment of the servo gain control device of the present invention. In FIG. 1, blocks designated by the same reference numerals as in FIG. 2 have the same functions as in FIG.

Embodiments of the present invention will be described below with reference to FIG. An analog switch 15 provided after the preamplifiers 3 and 4 switches the two input signals in a time-division manner using a switch switching clock signal 20 having a frequency sufficiently higher than the control band. The output signal of the preamplifier, which is synthesized into one signal by time division, is inputted as a numerator signal to the divider 7. The following signal is input to the denominator signal of the divider 7. That is, the output of the divider 7 is filtered through a low-pass filter 17 having a cutoff at a frequency sufficiently lower than the control band.
Let it pass. Passing the two-divided signal through the low-pass filter 17 corresponds to substantially averaging the two signals. The substantially averaged signal is compared with a reference level, and a signal corresponding to the difference is input to the denominator of the divider 7.

For example, when the substantially averaged signal is higher than the reference level, the denominator of the divider 7 becomes larger, and the divider 7 works to reduce the output. On the other hand, when the substantially averaged signal is smaller than the reference level, the denominator of the divider 7 becomes smaller, and the divider 7 works to increase the output. In this way, it can be seen that the detection gain is controlled in a closed loop compared to the conventional servo gain control device.

The output signal of the divider 7 is inverted by an inverting amplifier 18 with a gain of 1. The inverted signal and the output signal of the divider 7 are time-divisionally switched by an analog switch 16 using a switch switching clock signal 20 to form a single signal. The time-divisionally switched signal is input to an integrator or a high-order low-pass filter, and is used as a focus position error signal. That is, the focus position error signal, which was conventionally obtained by a differential amplifier, is transmitted to the analog switch 16 and the inverting amplifier 18 without using a differential amplifier.
and is obtained by the low-pass filter 19.

As described above, the feature of this configuration is not only closed-loop gain control but also the ability to obtain a focal position error signal without using a differential amplifier. According to this device, it is possible to reduce the offset that occurs in the differential amplifier. That is, if the divider 7 is used to multiply the amplification factor corresponding to the amplification factor of the conventional differential amplifier, the offset will occur in the inverting amplifier 18.
Only. Since this inverting amplifier 18 has a gain of 1, the offset of the inverting amplifier 18 can be smaller than that of a conventional differential amplifier having an amplifier several times larger.

The configuration after the phase compensation circuit is completely the same as the conventional one.

Now, in the apparatus shown in FIG. 1, the divider 7 is used for gain control, but any divider 7 may be used as long as the gain can be varied.

Further, although this configuration example is applied within the focal position control loop, it goes without saying that it can also be applied within the tracking control loop.

FIG. 2 shows a block diagram when applied within a tracking control loop. Compared to the one shown in FIG. 1, the one shown in FIG. 2 has a jumping pulse generation circuit instead of the pull-in activation and detection circuit. There are no other changes in the other configurations.

As described above, since the detection signals from the photodetector are sampled and the detection gain is controlled in a closed loop using the approximate average value of those signals,
Becomes more resistant to disturbances caused by temperature, etc.
Furthermore, there is no need to consider variations in the elements used in the divider, and stable control can be achieved.

Although FIGS. 1 and 2 show simple block diagrams, it goes without saying that configurations other than the present embodiment may be modified to achieve the above object.

Further, the present invention is effective not only for focal position control and tracking control, but also for a light beam position control system that controls the position of a beam using a photodetector divided into two or more parts.

Effects of the Invention As described above, according to the present invention, fluctuations in detection gain can be suppressed in a closed loop, making it resistant to external disturbances and allowing stable control, which has great practical effects. It is something.

Another advantage is that no large offset occurs because no differential amplifier is used.

Furthermore, since it can be achieved with a simple circuit, the cost does not increase significantly and it can be widely used in video disks and optical disk file devices.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of a servo gain control device using the present invention in a focus position control loop.
Fig. 2 is a block diagram of a servo gain control device according to an embodiment using the present invention in a tracking control loop, Fig. 3 is a block diagram showing a conventional servo gain control device, and Fig. 4 is a focus position control loop thereof. FIG. 2 is a characteristic diagram showing an example of open-loop characteristics of FIG. 1, 2... photodetector, 3, 4... preamplifier,
7... Divider, 8... Phase compensation circuit, 9... Pull-in detection circuit, 10... Pull-in starting circuit, 11...
Switch, 12... Drive amplifier, 13... Lens drive coil, 15, 16... Switch, 17, 1
9...Low pass filter, 18...Inverting amplifier,
20...Switch switching clock signal.

Claims (1)

[Scope of Claims] 1. A light beam source, an optical means for guiding the light beam from the light source to a desired reflective surface, an objective lens for focusing the light beam on the reflective surface, and the objective lens. a first photodetector divided into at least two parts for detecting the amount of deviation of the objective lens from the focal point position; a first amplifier for amplifying two output signals from said first photodetector; and a first amplifier for amplifying two output signals from said first photodetector; a first switch that switches the output signal to a single signal, a second variable-gain amplifier that amplifies the output of the first switch to a desired level, and a desired amplifier that allows the output signal of the second amplifier to pass through. a low-pass filter having a cut-off frequency of , substantially averaging the output signal of the second amplifier by passing it through the low-pass filter, and comparing the substantially averaged signal with a desired level; The gain of the second amplifier is increased to a desired magnification when the gain is smaller than the reference level, and the gain of the second amplifier is decreased to the desired magnification when the gain is larger than the reference level, and , an inverting amplifier that inverts and amplifies the output signal of the second amplifier;
A second switch which switches the output signal of the amplifier and the output signal of the inverting amplifier into one signal by using the clock signal used for switching the first switch.
a low-pass filter or a high-order low-pass filter that attenuates high frequency components of the output signal of the second switch; and a low-pass filter or a high-order low-pass filter that attenuates the high-frequency components of the output signal of the second switch, and compensates for the output signal of the low-pass filter to compensate for the delay in the mechanical system of the drive means. A servo gain control device comprising: a phase compensation circuit that performs the phase compensation; and a drive amplifier that transmits the phase-compensated signal to the drive means. 2. A tracking drive means configured to cause the light beam to follow a desired track on the reflective surface, and a second tracking drive means configured to detect the amount of deviation from the desired position.
a photodetector divided into at least two parts, and an optical means for guiding the reflected light flux from the reflecting surface to the second photodetector, the output signal from the first photodetector is divided into at least two parts. 2. The servo gain control device according to claim 1, wherein the output signal is an output signal from a photodetector, and the drive means is a tracking drive means.