JPH0229933A - Offset setting system - Google Patents

Abstract

PURPOSE:To execute high accurate offset setting by finding the output amplitude of a tracking sensor when the positive and negative bias offsets of an equal quantity are given and setting the offset when the difference of the output amplitude is within an allowable value. CONSTITUTION:The positive and negative offsets of an equal quantity are given to the outputs of photodetectors (focus sensors) 1 and 2 through an adding amplifier 24, respectively. The output amplitude and the difference of the photodetectors (tracking sensors) 31 and 32 are found in giving the respective bias offsets. When the found difference of the output amplitude is within an allowable value, the offset at this time is set to the outputs of the photodetectors 1 and 2. Thus, the offset which can obtain a focusing point can be set high accurately and automatically. Besides, even when the temperature change or the secular change of the photodetector for focusing is generated, the offset does not become improper, and offset setting whose reliability is high can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an offset setting method, and more specifically, the present invention relates to an offset setting method, and more specifically, a method for directing a laser beam to be controlled in a video disc, compact disc device, etc. onto a track of a rotating disc. This paper proposes an offset setting method that sets an offset to obtain a focused point.

[Conventional technology]

FIG. 5 is a block diagram of the focus servo circuit shown in "Precision Servo in Optical Disk Memory" published on pages 704 to 710 of the magazine "System and Control J V0127.Nα11" published in 1983. Laser light reflected by an optical disc (not shown) is incident on two divided photodetectors 1 and 2 via a converging lens (not shown), respectively.

Each output of the photodetector 1.2 is inputted to preamplifiers 3 and 4 separately, and each output is inputted to a differential amplifier 5 and a summing amplifier 6. Difference signal x of differential amplifier 5
7. The sum signal YF of the addition amplifier 6 is input to the divider 7. The output of the divider 7 is input to a drive amplifier 10 via a phase compensation circuit 8 and a switching section 9, and the output thereof is given to a lens drive coil 11 that drives the focusing lens. Further, a pull-in start command is given to the pull-in detection section 12 and the pull-in waveform generation section 13, and the output of the pull-in detection section 12 is given to the switching section 9. The output of the pull-in waveform generator 13 is manually input to the drive amplifier 10 via the switching unit 9, and the switch 9 selects either the output of the phase compensation circuit 8 or the output of the pull-in waveform generator 13. The structure is as follows. Note that when the laser beam is in focus, the outputs of the photodetectors 1.2 are equal, and when a focus shift occurs, a difference occurs in the re-outputs.

Next, the operation of this focus servo circuit will be explained. Load the optical disc and send the retraction start command to the retraction detection unit 12.
and the retraction waveform generator 13, the switching unit 9 selects the output of the retraction waveform generator 13, applies the selected output to the drive amplifier 10, excites the lens drive coil 11, and moves the focusing lens by a predetermined amount. So-called focus pulling is performed. Thereafter, the pull-in start command disappears, and the switching section 9 switches to select the output of the phase compensation circuit 8.

By the way, the photodetector 1.2 receives the laser beam reflected by the optical disk, and detects the focus shift of the laser beam using the difference signal xF, which is the output of the differential amplifier 5. In addition, a signal corresponding to the total amount of reflected light is detected by the sum signal Y' which is the output of the adding amplifier 6.The divider 7 detects the difference signal X,
is the sum signal Y.

The difference signal X is normalized by dividing by X, thereby preventing the influence of large changes in the detection output or fluctuations in the reflectance of the optical disc during information recording and reproduction. The output of the divider 7 is then compensated for the phase lead by a phase compensation circuit 8 to improve the stability of the servo operation. Focus servo of the laser beam is performed based on xF.

By the way, the offset caused by the assembly error of the optical system such as the photodetector 1, 2, etc., that is, the difference between the focal position indicated by the signal of the photodetector and the actual focused point, is the difference signal XF and sum signal shown in Fig. 6. It can be detected from the change in Y, and the offset is generally adjusted during assembly.

In other words, the focal point is when the sum signal Y of the summing amplifier 6 reaches its peak, and the difference signal x of the differential amplifier 5 at that time
F must be zero. Therefore, if the difference signal XFO value is detected at the timing when the peak of this sum signal YF is detected, the difference from the zero level at that time becomes the offset value.

Therefore, by setting this offset, correcting the difference signal XF using it, and moving the focusing lens in a predetermined direction based on the difference signal XF, it is possible to perform focus servo that does not cause focus deviation of the laser beam. can.

[Problem to be solved by the invention]

As mentioned above, conventional focus servo circuits correct the difference signal by setting an offset value using a variable resistor, etc., and applying it to the output of the photodetector in order to eliminate focus deviations caused by assembly errors in the optical system, etc. It is configured to do this. Therefore, each time the focus servo circuit is assembled, it is necessary to adjust and set the offset value by operating the variable resistor, which causes troublesome adjustment. In addition, there is a risk that the offset value may change due to temperature changes or aging of the optical system.
In that case, there is a problem that the accuracy and stability of the focus servo are impaired.

In view of such problems, the present invention provides a highly accurate offset setting method that does not require an operation to adjust the offset, and does not impair the accuracy and stability of the focus servo due to temperature changes or aging of the optical system. The purpose is to

[Means to solve the problem]

The offset setting method according to the present invention includes means for detecting the output amplitude of a tracking sensor that detects track deviation of coherent light, and an offset setting means for giving an offset, and the offset setting means provides an offset and an equal amount of positive, ° Apply a negative bias offset to each output of the photodetector that detects the defocus of coherent light, calculate the output amplitude of the tracking sensor when each bias offset is applied, and the difference between them, and calculate the determined output. If the difference in amplitude is within a tolerance value, the offset at that time is set to the output of the photodetector.

[Effect]

By means of detecting the output amplitude of the tracking sensor,
Detect the output amplitude of the tracking sensor.

The offset setting means is positive along with the offset.

An equal negative bias offset is given to each output of the photodetector, each output amplitude of the tracking sensor is found when a positive and negative bias offset is given to each of the outputs, and the difference between the two output amplitudes is found. If the difference is within the allowable value, set the offset at that time.

If the difference is outside the allowable value, change the offset sequentially,
Each time, along with the offset, equal positive and negative bias offsets are applied to the output of the photodetector, and the operation is repeated until the difference between the two output amplitudes falls within the tolerance value.

As a result, an appropriate offset is always automatically set.

〔Example〕

The present invention will be described in detail below with reference to drawings showing embodiments thereof.

FIG. 1 is a block diagram of a servo circuit to which an offset setting method according to the present invention is applied.

Each output of a photodetector 1.2, which is a focus sensor that receives laser light reflected from a disk (not shown), is input separately to a low-pass filter 20.21 that removes aliasing noise. The output of the low-pass filter 20 is input to the positive input terminal 5a of the differential amplifier 5 and the positive input terminal 6a on one side of the summing amplifier 6, respectively, and the difference signal X, which is the output of the differential amplifier 5, is an analog/digital signal. It is input to an analog input terminal of a converter (hereinafter referred to as A/D converter) 7. The output of the low-pass filter 21 is input to the negative input terminal 5b of the differential amplifier 5 and the other positive input terminal 6b of the summing amplifier 6, and the sum signal Y, which is the output of the summing amplifier 6, is connected to the A/D. The reference voltage input terminal of the converter 7 is manually inputted.

The output converted to a digital signal by the ^/D converter 7 is input to a logic circuit 22 which is a separation circuit, and the output of the focus center t, which is an output of the logic circuit 22, is sent from a microcomputer with a built-in memory H8l'h. The signal is input to a control unit 25 and a digital/analog converter (hereinafter referred to as a D/A converter) 23. D
The output converted into an analog signal by the /A converter 23 is input to one side positive input terminal 24a of the offset addition amplifier 24. The offset output by the control unit 25 is D/A
The output which is input to the converter 26 and converted into an analog signal is sent to the other input terminal 24 of the offset addition amplifier 24.
input to b. The output of the offset addition amplifier 24 is input to the phase compensation circuit 8, and the output is input to the drive amplifier 10.
The output of the drive amplifier 10 is applied to the focusing drive coil 11.

On the other hand, each output of a photodetector 31.32, which is a tracking sensor that receives laser light reflected by an optical disk, is inputted to a low-pass filter 33.34.

The output of the low-pass filter 33 is connected to the positive input terminal 3 of the differential amplifier 35.
5a and one side positive input terminal 36a of the addition amplifier 36, and is the output of the differential amplifier 35.

is input to the analog input terminal of the A/D converter 37. The output of the low-pass filter 34 is connected to the negative input terminal 35b of the differential amplifier 35 and the other positive input terminal 36 of the summing amplifier 36.
The sum signal Y7, which is the output of the summing amplifier 36, is input to the reference voltage input terminal of the A/D converter 37. The output converted into a digital signal by the ^/D converter 37 is input to a logic circuit 52 which is a separation circuit, and the output of this logic circuit 52 is input to the control section 25 and the D/A converter 53. D/
The output of the A converter 53 is input to the phase compensation circuit 38, and the output thereof is input to the drive amplifier 40. The output of the drive amplifier 40 is given to a tracking drive coil 41. The control unit 25 determines the maximum and minimum values of the output amplitude from the output of the logic circuit 52, which is the output of the tracking sensor, and calculates the difference between them to obtain an appropriate offset of the focus sensor, which will be described later.

Now, when the focusing photodetector 1.2 receives the laser beam reflected by a disk (not shown), its output passes through low-pass filters 20 and 21, respectively, and is applied to the differential amplifier 5 and the summing amplifier 6. The differential amplifier 5 outputs a difference signal XF between the photodetectors 1 and 2, that is, a signal corresponding to the focus shift, and inputs it to the ^/D converter. On the other hand, the summing amplifier 6 outputs the sum signal YF of the photodetector 1.2, that is, a signal corresponding to the total amount of reflected light, and inputs it to the A/D converter 7. The A/D converter 7 normalizes the difference signal XF by dividing the difference signal XF by the sum signal YF. Then, the output of the A/D converter 7 is input to the logic circuit 22 and given to the /^ converter 23 and the control section 25. The output of the D/A converter 23 and the offset output from the D/^ converter 26 are input to the offset addition amplifier 24,
The output of the offset addition amplifier 24 to which the offset has been added is applied to the focus drive coil 11 via the phase compensation circuit 8 and the drive amplifier 1O, and a focus servo is performed to move a focusing lens (not shown) to prevent focus deviation of the laser beam. .

On the other hand, when the tracking photodetectors 31 and 32 receive laser light reflected by an optical disk (not shown), the output causes the differential amplifier 35 to generate a difference signal XT between the outputs of both photodetectors 31 and 32, that is, track deviation. As a corresponding signal, the summing amplifier 36 outputs a sum signal YT of the outputs of both photodetectors 31, 32, that is, a signal corresponding to the total amount of reflected light. These difference signal XT + sum signal YT are input to the A/D converter 37, and the difference signal X is divided by the sum signal yt to normalize the difference signal X7. The output of the ^/D converter 37 is input to the logic circuit 52, and the output thereof is input to the control section 25 and the D/^ converter 53.

The output of the D/A converter 53 is applied to the tracking drive coil 41 via the phase compensation circuit 3B and the drive amplifier 40 to drive a reflection plate (not shown) that changes the optical axis and positions the laser beam on the track. Perform servo.

By the way, the relationship between the output P obtained by converting the output of the A/D converter 7 into analog and the distance Z between the disk and the condensing lens is as shown in FIG.
The relationship with the output Q of the /D converter 37 is as shown in FIG. 2(B). That is, the output P related to focus changes when the distance Z between the optical disc and the condenser lens changes.
It changes symmetrically in the positive and negative directions with respect to 0. on the other hand,
The output Q related to tracking has a maximum peak value at the focal point Z0, and as a focus shift occurs, the resolution decreases and the peak value decreases. The present invention is based on the relationship between the outputs P and Q to determine the point where the peak value of the output Q is maximum and automatically set the offset.

FIG. 3 is a characteristic curve diagram showing the output amplitude of the tracking sensor, with the horizontal axis representing the focus position, that is, the distance 1lIIZ between the disk and the condensing lens, and the vertical axis representing the output amplitude V of the tracking sensor. As is clear from this figure, the output amplitude V decreases as the focus position, that is, the distance between the disk and the condensing lens, increases or decreases with respect to the focal point, that is, its maximum value, and It is symmetrical and sinusoidal.

Next, a control operation for automatically setting an offset to prevent focus deviation will be explained with reference to FIGS. 1, 3, and 4. FIG. 4 is a flowchart showing the control procedure of the control section.

When a disk is loaded, focus retraction is performed to bring the focusing lens closer to the disk. Next, an offset is set. First, the offset value is set to 0 (St), so that the focus position Z becomes Z. Next, the offset value to be shifted by +1tII11 to one side in order to lengthen the focus position, that is, the focus distance, is set as a bias offset (S2). Then, this bias offset is applied to the offset addition amplifier 24, and the difference signal X is corrected, and the focus drive coil 11 is accordingly excited, and the focusing lens (not shown) is moved to bring the focus position to Zll. The output amplitude Vll at that time is read into the memory M1 (S
3). Next, in order to shorten the focus position, that is, the focus distance, an offset value to be shifted by -2 μm to the other side is set as a bias offset (s4).

This bias offset causes the focusing lens to move in the opposite direction, and the focus position Z becomes a focus position Z1□ which is symmetrical with respect to the focus position Z1.

In other words, equal positive and negative bias offsets are applied. And the output amplitude at this time ■1! Memory M2
(S5). Next, move the focus position Z to one side +
The offset value to be shifted by 1 μm is set as a bias offset (S6). As a result, the focus position is set to the initial focus position 2. Return to

Here, the output amplitude V I read into the memories M, , M,
The absolute value of the difference between l and Vlt is compared with the tolerance value ε (S7). If the difference between the output amplitude V and vIz is within the tolerance value ε, the offset given when the focus position is returned to ZI is set (S8) and held. This means that when the re-output amplitudes V l l * V l t are equal, the maximum value of the output amplitude V of the tracking sensor has been obtained, and a focused point of the laser beam has been obtained.

However, in step (S7), if the difference between the output amplitudes vIl and Vlt is large and larger than the tolerance value ε as shown in FIG. 3, the output amplitudes V++ and V+□ are compared in size (S9), Output amplitude vI! is large, in order to shorten the focus distance, the other side, that is, the offset that should make the output amplitude larger, for example, the focus position is -0,
An offset value to be shifted by 1 μm is given (S10).

As a result, the focus position changes from ZI to Z2.

Then, as mentioned above, the offset at which the focus position should be shifted by +1μ is defined as the bias offset (S2
). As a result, as mentioned above, the focus position is Zt+
becomes. The output amplitude VZ+ at that time is read into the memory M. Next, the offset that should shift the focus position by 12 μm is set as a bias offset (S4). As a result, the focus position becomes 222. The output amplitude VZZ at that time is read into the memory Mt. With such a bias offset, equal positive and negative bias offsets are applied based on the focus position Z2 when an offset to set the focus position to 22 is applied. after that,
The offset value for shifting the focus position by +1 μm is set as a bias offset (S6). As a result, the focus position returns to focus position Z2. Here memory M
+, the absolute value of the difference between the output amplitudes ■2I and ■2□ read into Mt is compared in magnitude with the tolerance value ε (S7). If the difference is still greater than the tolerance value ε, the output amplitude v! I and ■2□ are compared in size (S9).

If the output amplitude VZt is large, the offset value is changed again to shift the focus position by -0.1 μm (SIO). As a result, the focus position changes from Zt to Z,
Changes to After that, do the same as above.

A negative equal amount of bias offset is given to each of them, and the output amplitude V31+ vsx when given is stored in the memory M t ,
Mz, and with the focus position returned to Z, the difference between the absolute value of the difference between the output amplitudes V 31 + V 3 t and the allowable value ε is determined. In this case V31 and v,! is the third
As shown in the figure, since the sizes are equal, the difference is within the tolerance value ε, and is set to the offset value that provides the focus position Z3 (S8). In this way, the re-output amplitude V
Since 31 + v3 * was obtained in equal amounts, the maximum value of the output amplitude of the tracking sensor was obtained, and the focused point of the laser beam was obtained.

After the set offset is maintained, focus servo is properly performed as described above in relation to the difference signal χ.

Note that if vII is larger than Vlt in step (S9), an offset is given to shift the focus position by +0.1 μm, and the re-output is performed in the same manner as described above so that the difference in amplitude is within the tolerance value ε. Well, step (S2)~
If the operation of (S9) and (Sll) is repeated and the value is within the tolerance value ε, the offset at that time is set.

In this way, the offset is determined using the characteristic that the output amplitude of the tracking sensor is approximately symmetrical around the maximum value, which is the in-focus point, and the output amplitude changes greatly when it deviates from the in-focus point, so an appropriate offset can be set. This allows the laser beam to be focused with high precision.

Further, since such offset setting is automatically performed after the focus is pulled in, there is no need for the trouble of manually setting the offset.

Further, the offset will not become inappropriate due to temperature changes or aging of the photodetector. Furthermore, the offset will not be incorrect due to differences in the optical characteristics of the disks.

Further, this focus offset setting can be performed not only immediately after focus pull-in, but also at any time such as when data reading performance deteriorates.

Note that although laser light is used in this embodiment, this is just an example and is not limited to laser light.

〔Effect of the invention〕

As described in detail above, according to the present invention, an appropriate offset is given, and equal positive and negative bias offsets are given separately, and the output amplitude of the tracking sensor is determined when each bias offset is given. , the offset is set when the absolute value of the difference between these output amplitudes is within the allowable value, so the offset that provides a focused point can be set automatically and with high precision. Further, even if the temperature of the focusing photodetector changes or changes over time, the offset will not become inappropriate, and an excellent effect can be achieved in that a highly reliable offset can be set at all times.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a servo circuit to which the offset setting method according to the present invention is applied, and FIG. 2 is a waveform diagram showing the relationship between the output of the focus sensor and the output of the tracking sensor.
Figure 3 is a characteristic curve diagram of the output amplitude of the tracking sensor.
Fig. 4 is a flowchart showing the control procedure of the control unit that sets the offset, Fig. 5 is a block diagram of a conventional focus servo circuit, and Fig. 6 is a waveform diagram showing the relationship between the sum signal and difference signal of the circuit. be. 1.2... Photodetector (focus sensor) 5... Differential amplifier 6... Adding amplifier 11... Focus drive coil 22... Logic circuit 24... Offset adding amplifier 25...・Control unit 31.32・
... Photodetector (tracking sensor) 35 ... Differential amplifier 36 ... Addition amplifier 41 ... Tracking drive coil 52 ... Logic circuit M l, M z
...Memory In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. An offset setting method that provides an offset to the output of a photodetector that detects a focus shift of coherent light in order to obtain a focused point of coherent light on a track of a rotating disk, comprising: Means for detecting the output amplitude of a tracking sensor for detecting track deviation of interference light and offset setting means for giving the offset are provided, and the offset setting means sets an equal amount of positive,
Apply a negative bias offset to each of the outputs of the photodetectors, determine the output amplitude of the tracking sensor and the difference thereof when each bias offset is applied, and if the difference between the determined output amplitudes is within a tolerance value, , an offset setting method characterized by setting the offset at that time to the output of a photodetector.