JPS61208638A - Focus servo circuit - Google Patents

Abstract

PURPOSE:To execute suitable servo function by fetching an output of a comparison means and applying servo when a focus error signal is equal to the change point level of the 1st comparison means and that of the 2nd comparison means in this order or in crossing state. CONSTITUTION:A point (a) data of an FE signal at the inside of the locking range and a point (b) data of the FE signal at the just focus L0 within the lock range are inputted to a CPU 11 and an output of a port 14 is set to interrupt an interruption switch 20. The first processing is to clear a data of a port B 15, from which its initial data is inputted to a D/A converter 19 and its output is fed to an actuator coil 25 as a step drive signal via an amplifier 23 to displace the objective lens 24. The FE signal outputted from an error amplifier 17 goes to a slightly higher level than the level S0. Thus a point within a lock range detected after an optional point of the lock range is detected, e.g., just focus point is detected surely.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to information devices such as optical disks and magneto-optical disk devices that optically record and reproduce signals, or only reproduce signals, and particularly relates to information devices that optically record and reproduce signals, such as optical disks and magneto-optical disk devices. The present invention relates to an improvement of a focus servo circuit that controls the focus direction.

[Technical background of the invention]

2. Description of the Related Art Optical means for writing information on an optically recordable and reproducible recording medium (hereinafter referred to as a disk) or reading information from a disk on which information has already been recorded utilizes the magneto-optical effect and the diffraction phenomenon of light. The former is applied to magneto-optical disk devices and allows information to be freely written and erased. °
Also. The latter has already been put into practical use as compact disc players and optical disc players. In the above-mentioned writing/reading means or means for reading or writing only, a focus servo is indispensable for constantly irradiating a finely focused light beam onto the disk regardless of surface wobbling of the disk. The focus servo detects the focus error signal (generally less than the focus error signal C or the FE signal) and, based on this, makes the spot of the light beam follow the displacement caused by the -f disk surface vibration.The method for obtaining this signal is as follows. , astigmatism method.

Skewbeam method
, knife method, critical angle method, etc. are known.

FIG. 7 shows an example of the FE signal characteristics obtained by the above-mentioned astigmatism method. In the figure, the vertical axis shows the FE flaw signal level, and the horizontal axis shows the relative distance between the objective lens and the disk. This signal is obtained when the disk moves in the distance direction through the focus range (depth) of the objective lens, and the specific detection means is as follows.

A light beam spot is irradiated onto a photodetector formed by dividing a light-receiving surface into four parts, and a signal is generated as a difference between the sums of the amounts of light between a pair of diagonal light-receiving surfaces. The characteristics of this signal are, for example, when the disk approaches the focal point from a close state within the focal length of the objective lens, it exhibits a free level point S1, and when it approaches the focal point from a far distance, it exhibits a minimum level point S2 (and vice versa). In some cases).

Then, the relative distance Ll from which each of these levels is obtained.

There is a just focus point approximately in the middle of L2, and the signal level at this point is 811! : Approximately the midpoint level of 82. Therefore, when the relative distance between the objective lens and the disk is L1 to L, an FE flaw signal of 8l-8o is applied, and when it is LO-L2, an FE flaw signal of SO to S2 is applied to the actuator means for driving the objective lens. By doing so, it becomes possible to always maintain the focus point LO at just the focus point, and the range between L1 and L2 provides the focus pull-in range.

By the way, in conventional devices, it is difficult to accurately place the disk in the retracting range from the beginning with respect to the optical system, so the objective lens is gradually moved closer to the installed disk from a position away from the disk. Find the focal point by moving it so that it passes through the focal point,
The servo is activated when it is detected that the focus is within the target focus pull-in range.

[Problems with background technology]

However, the focus servo retraction range is extremely narrow, and even if the servo loop is closed immediately when the focus position is detected, the objective lens will already be out of the retraction range by the time the servo is actually applied due to the transmission delay of the 1g circuit. There are times when the servo is turned on in this state, causing the inconvenience of malfunction.

In addition, although the above-mentioned conventional means normally moves the objective lens from a position far away from the disk in a direction approaching the disk, that is, in the %X direction, the FE scratch signal as shown in FIG. Since it has a focus point Ct-, there is a drawback that these points are detected.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a focus servo circuit that reliably captures the true just focus point and performs accurate servo functions.

[Summary of the invention]

In order to achieve the above object, the focus servo circuit according to the present invention, as shown in Fig. 1M1, drives an optical system A having an objective lens in the near and far directions X and Y relative to, for example, a disc-shaped recording medium A2. The circuit includes an actuator A3 that drives at least the objective lens of the optical system A1 in the distance direction, and an error that detects a focus error signal SGI based on the reflected beam from the recording medium A2. A signal detecting means A4, a switching means A5 for intermittent output of the detecting means A4, a drive circuit means A6 which amplifies the power of the focus error signal SG11F passed through the switching means A5 and supplies it to the actuator A3, and a switching means A5. When in the off state, a signal 502t of a predetermined step level is generated and introduced into the drive circuit means A6 to direct the objective lens to the recording medium A.
A step drive signal generating means A7 that moves the objective lens closer to the disk so that it is at a position less than the focal length of the disk (initial setting), moves it away from the disk in steps from that position, and guides the objective lens into the focus pull-in range; A focus error signal SGl generated under the control of A7 is supplied to each one end, and first and second change point levels Vi corresponding to at least two point positions in the distance variable range of the objective lens are supplied to each other end.
, v2 are set, and one of these signal levels 1
For example, v2 is set to a signal level corresponding to an arbitrary position within the focus pull-in range.
．． A9, these comparison means As, and the output SGa of A9
, SG4, and in each of these outputs, the signal SGI from the error signal detection means A4 is at the signal level Vi, v
When a signal indicating a state equal to or crossing these in the order of 2 is presented, the switching means A
A servo start control means AIO is provided which closes a servo loop consisting of optical system Al→focus error signal detection means A4→drive circuit means A6→actuator A3→optical system A1.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to illustrated embodiments.

FIG. 2 is a configuration diagram showing a first embodiment of a focus servo circuit according to the present invention. FIG. 3 is a flowchart showing the operation of the micro combinator used in the above circuit.

Note that the seventh focus error signal characteristic diagram is also referred to.

In the present invention, the servo is started after confirming that the objective lens has entered the focus pull-in range.For this purpose, the detection of the change point of the FE flaw signal is carried out by a microcomputer (JJ lower CPU). ) 11. In the principle block diagram shown in FIG. 1, this CPU Ull functions as step drive signal generating means Ay, first and second comparing means A8°Ae, and servo start control means AIG. The details will be explained below.

In FIG. 2, the CPU II not only controls the logic operation unit 13, the board Al 4, and the board B 15 via the path line 12, but also connects an analog-to-digital converter (hereinafter referred to as an A/D converter) 16 to the path line 12. ing. The A/D converter 16 is supplied with an FE signal VFE from an error amplifier 17, which will be described later, and samples this signal at high speed as digital data at the control timing of the CPU II.

The boat B 15a is connected to a digital-to-analog converter (hereinafter referred to as a D/A converter) 19 via a path line 18,
A digital signal whose value changes in synchronization with the control timing is introduced into the D/A converter 19.

As a result, the D/A converter 19 outputs a step drive signal VS for finely displacing the objective lens step by step, which will be described later.
T is derived. Furthermore, the output of boat A14 is D/
It is designed to control an intermittent switch 20 whose one end is connected to the output end of the A converter 19, and the other end of this switch 20 is connected to the output end of the A converter 19. Converter 16 and error amplifier 17
connected to the input/output path.

Further, the CPU 11 has a memory means in which program data for executing the flowchart of the third factor and various numerical data for detecting a change point according to the present invention are stored. Among these data, the numerical data are the FE flaw signal and b in FIG. 7 when the focus servo is pulled in by gradually moving the objective lens away from the disk. Level a is determined corresponding to an arbitrary position in the range of O(fl (LX), where the distance A between the objective lens and the disk is The lens is at the rising edge of the FE scratch signal (0<
This is to confirm that ffi<Lx) is passed. Level baLx (1 (It is determined corresponding to any position within the range of L2. In the sg7 diagram, it is determined corresponding to the just focus point Lo. Level b indicates that the objective lens has entered the focus pull-in range. Thus, CPU 1 checks these change points a and b.
The FE flaw signal is sampled from the A/D converter 16 at a predetermined timing, and each time it is output, it is read out from the memory means and the two are compared. One important point here is that you can't simply sample the FE flaw signal at regular intervals, detect both points a and b, and then apply the servo based on the logical product.
The program for detecting point a and the program for detecting point b are independent. That is, when the subroutine for detecting point a ends, the subroutine for detecting point b is executed to ensure that point b is detected. C
PU1l has the above functions.

Next, the connection point between the D/A converter 19 and the intermittent switch 20 is connected to one input end of the power amplifier 23. The other input end of this amplifier 23 is connected to a ground point, and its output end is an objective lens 24t-1 which functions as a condensing lens.
It is connected to an actuator coil 25 for movement in the X and Y directions of the arrows.

With this configuration, the objective lens 24 is moved in the direction of distance from and near the disk according to the output level of the power amplifier 23.

On the other hand, reference numeral 26 is a light source such as a semiconductor laser.

A collimator lens 27 is placed in front of this light source, and the light beam passing through the lens 27 is transmitted through a beam splitter 28 and is incident on a mirror 29. The mirror 29 is set to guide the reflected light to a disk 30 supported by a turntable, and an objective lens 24 is interposed between the mirror 29 and the disk 30. In addition, a condenser lens 3 is provided on the reflective surface side of the beam sgelitter 28.
1 is provided to guide the light beam condensed by the condenser lens 31 to the flat surface of the cylindrical lens 32. The nine light beams passing through this cylindrical lens 32 are irradiated onto a four-split photodetector 33 . In this case, when the objective lens 24 and the disk 30 are separated by the focal length of the lens 24 (just focus state), a perfect circular spot is formed on the light receiving surface of the photodetector 33 as shown by the dashed line. Each divided light-receiving surface receives an equal amount of light. Furthermore, when the distance between the disk 30 and the objective lens 24 deviates from the just focus point, an elliptical spot becomes an elliptical spot having a major axis corresponding to the deviated distance, as shown by a two-dot chain line. The long axis direction of this elliptical spot coincides with the geometric arrangement direction of the pair of light receiving surfaces of the photodetector 33, and the output of the photodetector 33 changes its polarity depending on the direction and distance away from the just focus point. and the level changes.

Furthermore, each divided light-receiving surface of the photodetector 33 is connected to a resistor R.
1 to R4 are connected to the ground, and a signal voltage that spreads depending on the amount of light received is formed at both ends of the resistor R1.
, R2 is a signal from one pair of light-receiving surfaces, and the voltages across resistors R3 and R4 are signals from the other pair of light-receiving surfaces, then the signals from resistors R1 and R2 are applied to adder 3.
The signals from the resistors R3 and R4 are respectively introduced into the adder 35. And each of these adders 34
The .degree. 350 output terminal is connected to the error amplifier 17.

The present invention is constructed as described above, and its operation will now be explained with reference to FIGS. 3 and 7. Note that FE scratch signal detection is performed by moving the objective lens 24 away from the disk 30 (any point within the focal length) and by moving the objective lens 24 away from the disk 30 (any point within the focal length).
There are two methods of approaching 0 from a state far away from it (an arbitrary point in the area outside the focal length), but in this example, the former is adopted (in the latter, if point a' is detected instead of point a), good),.

First, as described above, the 8-point FE flaw signal data inside the retraction range and the 8-point data of the FE signal corresponding to the just focus point Lo Vc within the retraction range are input to the CPU II. Further, the output of the baud Al 4 is set so that the on/off switch 20 is turned off.

Once the initial state of the circuit is set in this way, the program shown in the flowchart shown in FIG. 3 starts. This flowchart consists of two subroutines SR1 and SR2 and a branch BL.

The first process N1 of the routine SR1 is to clear the data of the port B15, so that the port B15 inputs its initial data to the D/A converter 19 and sends its output to the step via the amplifier 23. A drive signal is applied to the actuator coil 25 to displace the objective lens 24't to the position indicated by the dotted line in FIG. This displacement position is closer to the disk 30 than the Lo point, and at this time, the light beam that has passed through the single cylindrical lens 32 is irradiated onto the light receiving surface of the west detector 33 in a greatly expanded manner. As a result, the FE multiplied signal outputted from the error amplifier 17 becomes, for example, a So level or a medium/high level as shown in Fig. 7.

Subsequently, the contents of the boat B15 are incremented by 1 bit by executing process N2, and the step drive signal vST is lowered in level by, for example, 1 step, thereby slightly displacing the objective lens 24 in the Y direction.

This situation will be explained using Sections 41(a) and 41(b). By incrementing port B by 1 bit.

Assume that the objective lens moves from a point LfnO to a point Ln at a distance from the disk. The objective lens has a moving distance on the vertical axis,
If time is plotted on the horizontal axis, it will gradually move along the curve shown in Figure 4, for example, and 1=1. ) completes the movement to the point Ln. FIG. 4(a) shows the FE multiplied signal that changes with this movement. As the VFEO value moves from Lm to Ln, it is input into the CPU II as a digital value by the A/D converter 16 multiple times (for example, 40 times) (hereinafter referred to as sample/vh c) *II! 4
Diagram (a)? Words, tha, Vrgz, VFI2.

""" e VFI39, VFI40 cadet values are read. VFICI "' V
)'l1t40 is sequentially compared with VFm at point a N3. The next comparison N3 is to determine whether or not the VFI is smaller than the 8-point data.If the result is YES, the process moves to the next confirmation N4, and if the result is NO, the process moves to subroutine SR2, which will be described later. Confirmation N4 is for determining the number of sampling times, that is, the number of times a YES result is obtained.

In the embodiment, the combing is performed, for example, 40 times.

Take the tiger and add up the number of YES answers, and this total number of times is 4.
If it is not 0 times (NO), the program returns to comparison N3 again. In this way, when it is determined in comparison N3 that VFIC≧a during the 40 samplings within JM, the process moves to subroutine SR2. This determination of VFE≧a indicates that the 8-point level in FIG. 7 has been detected.

If it is not determined that VyE<a is NO even after templating 40 times, it is determined that there is no point a within the range from Lm to Ln, and the process returns to step N2, where the 8-point level is detected again from that position.

Next, subroutine SR2 is a program for detecting the FE signal level corresponding to point b. That is.

When the CPU II obtains a determination result No from the comparison N3 of the previous routine SRI, it moves to execution of the process N5. This process corresponds to process N2 and updates the data of boat B15.
By lowering the level of the step drive signal VgT, which is incremented by one bit, the objective lens 24 is brought closer to the position Lo corresponding to point b in a stepwise manner. Then, an intermediate comparison N6 is performed in which the data is moved a distance corresponding to one bit. This comparison N6 also corresponds to the comparison N3 of routine SRx (F), compares Vvz and 8-point data, and if Vrm>b, I/c moves to sampling number confirmation N7, and if VFE≦b, Move on to brunch BL.

Confirmation N7 is also a program that judges the number of samplings performed 40 times during one step movement, and if a 5-point level is not obtained even after sampling this number of times (YE
In step S), the process returns to process N5. Also.

If the 5-point level is not detected at the stage less than 40 times, return to comparison N6 and repeat the routine until the 5-point level is detected.
The greater the number of samplings in SRz, the higher the detection accuracy, and the lower the number of samplings, the shorter the time required for focus search. Therefore, an appropriate number of samplings is set to balance both factors.

Now, when vFE≦b is determined in the comparison N6, the process moves to the branch BL and its process N8 is executed. This process N8 is to transfer a servo start command to the baud A14, and a signal is thereby derived from the baud A14 to bring the switch 20 into the continuous state. This is as follows: actuator filter 25 → objective lens 24 → disk surface → objective lens 24 → photodetector 33 → adder 34
This means that the servo loop consisting of °35→error amplifier 17→low-pass filter 22→phase compensation circuit 21→switch 20→amplifier 23→actuator coil 25 is turned on. Of course, at this time, the objective lens 24 is at or close to Lo in the Lo-L2 range.

In this way, the present invention makes it possible to apply servo after confirming that the objective lens is within the focus pull-in range.

Next, a second embodiment of the present invention will be described with reference to FIG.

In this embodiment, the one point detection routine SR1 in the a and b point detection 7a-charts is simplified so that the servo is applied more quickly, and FIG. 5 shows a flowchart for this purpose. It should be noted that this chart is also a program for moving the objective lens 24 away from the disk 30 from a state close to it, as in the previous embodiment. There are two differences from the previous embodiment. One is that the distance traveled at one time was equivalent to 1 bit in the previous embodiment, but it is moved by multiple bits (for example, 3 bits). (referred to as steps). The second is that in the previous implementation, the register that stores the A/D converted VFK (
The difference is that, whereas there was only one register (or memory), there are now as many registers (or memories) as there are sampling times.

In FIG. 5, when the data of boat B15 is cleared in step drive signal generation processing N9.

A step drive signal is generated from the D/A converter 19 to set the objective lens 24 to the initial position LR. next.

The CPU II moves the objective lens 24 from this initial position LR to Y.
Data for moving a predetermined step amount in the direction is transferred to the boat B15. This operation is executed by the step drive signal 1 step variable processing NIG, and as the movement corresponds to one step, the magnitude determination between the VFII and the 8-point level is first performed using the next comparison program Nil. Judgment result is VFl
If l > a, vrg21-..."" t vF]C stored in different registers (or memories) one after another
A comparison will be made between n-Z e vFBTl and the 8-point level. In this embodiment, the change level per one step of the step drive signal is larger than in the previous embodiment, so depending on the selection of point a, 1 For example, VFB1 at the initial stage
≧a may be detected. The reason why it is okay to make the sampling interval coarser in this way is that the characteristics of the FEC signal are gentle in the region within the focal length, so even if the sampling interval is widened, it will not go beyond that region. .

When the 8-point level is detected as described above, the 5-point level is detected by sampling at minute step intervals based on the subroutine SR2 as in the previous embodiment, and the process moves to branch BL to start servo. As described above, this embodiment has the advantage that the processing time required for subroutine SRI' is shortened. In the HE2 embodiment, routine SR1' moves 3 bits (1-step routine SR2 moves 1 bit at a time, but this is not limiting. Routine SR2 may also move multiple bits at a time. In the example, routines SR1 and SRz both move one bit at a time, but the moving width may be determined as in the second embodiment.

In each of the first and second embodiments, point b does not need to coincide with the just focus point, and may be set at any change point in the pull-in range. And especially when setting in the range of L1 to Lo (accurately).

(slightly lower), the 8-point level and the 5-point level may be the same value. This is because the present invention does not simply start the servo based on the logical product of the detection of the five point levels, but the routines that detect each point may be executed independently of each other. This is because it has been established.

Next, wJ applied to the critical angle method or the Naifetsu method
A third embodiment will be explained. The critical angle method and the Naifetsu method themselves are well-known methods, and detailed explanations thereof will be omitted. The feature of these methods is that the FE multiplied signal changes as shown in FIG. 6. Therefore, when moving the lens in the Y direction from a position close to the disk, the first... As in the second embodiment, level a and level b may be detected.

Next, a method of moving the objective lens 24 in the X direction from an arbitrary point in the out-of-focal-length region, for example, the LR' position, will be described. In this case, first, as a detection point outside the retraction range,
For example, select the approximate average value point C between S3 and So. Next, if point b corresponding to the just focus position LO is selected as the detection point within the pull-in range, the FE signal characteristic has a minimum point level Sa k that decreases by So in the area outside the focal length, as described above. Therefore, the SSO level is changed from 83 to the maximum point S2 within the pull-in range. Let d be a change point exhibiting a level equivalent to this So level. In other words, this third embodiment attempts to detect c, d, and b in this order. Note that the detection point d is
Any level in the range S2 to S3 may be used. Rounding that detects three points like this.

In this embodiment, even after detecting the C point and the 4-point level, the CPU 1 repeatedly executes the same routine as the routine for detecting the 4-point level.

As described above, the present invention attempts to reliably detect the pull-in range by detecting the level at an arbitrary point outside the pull-in range.

Note that the present invention is also applicable to FE signal detection methods such as the eccentric auxiliary beam method.

〔Effect of the invention〕

As explained above, according to the present invention, in an information device such as an optical disk or a magnetic disk device, when performing focus servo of the optical system with respect to the disk, a focus error at an arbitrary point outside the pull-in range as well as at an arbitrary point outside the same range is achieved. Since the signal level is detected, it is possible to reliably detect, for example, the just focus point in the pull-in range, which is detected after any point in the pull-in range is detected. Since the servo is applied when this just focus point is detected, the servo is reliably applied within the pull-in range.

That is, point C in FIG. 7 has the same vFE level as the just focus point, so in the conventional method of detecting only points, point C is detected with the intention of detecting one point.
Here, I made the mistake of closing the focus servo loop.

In the present invention, unless level a is detected, it is not possible to detect point b, so when moving the lens from LR in the Y direction, point C is ignored and detected as level b. There is no longer a possibility that an IGB will occur.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing an example of the principle configuration of the present invention, FIG. 2 is a block diagram showing a first embodiment of the focus servo circuit according to the present invention, and FIG. 8113 is a flowchart showing the operation of the same embodiment. FIG. 4 is an explanatory diagram for explaining the present invention in detail. FIG. 5 is a flowchart according to a second embodiment of the present invention, FIG. 6 is a characteristic diagram showing an example of focus error signal characteristics related to the present invention, and FIG. 7 is a characteristic diagram showing another focus error signal characteristic. . 1l-CPU, 12-...pass line. 13-...Arithmetic unit, 14...Boat A. Engineering 5...Boat B. 16.-Analog-to-digital converter. 17...Error amplifier, 18...Pass line. 19...Digital-to-analog converter. 20... Intermittent switch, 21... Phase compensation circuit. 22...Low pass filter. 23...Amplifier, 24...Objective lens, 2
5- Actuator fill. 26... Light [, 27... Collimator lens 28...
・Beam - Nupritsuta, 29...Mirror, 30...Disc. 31... Condenser lens, 32... Cylindrical lens. 33...Photodetector, 34.35...Adder. Figure 1 Figure 3 Figure 4 (Kuyo≧ri et al. 11 force (b) Figure 85 Figure 6 FE I1-1 Y
^'a7 figure

Claims (2)

[Claims] (1) A focus servo circuit that controls an objective lens for condensing a light beam to be in just focus with respect to a recording medium on which information can be recorded or reproduced, the objective lens being held movably in the focus direction. an actuator; an error signal detection means for receiving the beam reflected by the recording medium and detecting a focus error signal according to a distance between the recording medium and the objective lens; a switching means for intermittent output of the detection means; drive circuit means for power amplifying the focus error signal that has passed through the switching means and supplying it to the actuator; when the switching means is in an OFF state, generating a signal whose level changes at predetermined interval timing; step drive signal generation means, which is introduced into the drive circuit means and causes the objective lens to approach the just focus point stepwise from the defocus position; and a focus error signal detected under the control of the step drive signal; a first comparing means for comparing a change point level corresponding to at least one change point of the error signal; and a focus servo pull-in of the focus error signal detected under the control of the drive signal of the step and the same error signal. a second comparison means that compares the change point level corresponding to an arbitrary change point within the range; and a second comparison means that takes in the outputs of these comparison means, and that the focus error signal is the change point level of the first comparison means and the second comparison means. 1. A focus servo circuit comprising: servo start control means for causing the switching means to be in a continuous state and applying servo when the change point levels are equal or crossed in order. (2) The focus servo circuit according to claim 1, wherein the second change point is set at a just focus point.