JPH0714179A - Focus controller for optical disk device - Google Patents

Abstract

PURPOSE:To evade a failure in focus drawing at the time of focus control by controlling a position of a lens according to an output of an adder. CONSTITUTION:By a focus controller of an optical disk device, the position of the lens 4 converting a light beam 3 is controlled so as to focus the light beam 3 on an optical disk 2. This device is provided with a voltage generation means 70 generating an offset signal for moving the lens 4 to the position where the light beam 3 is focussed on the optical disk 2 only when the light quantity of a reflected light or a transmitted light from the optical disk 2 is smaller than a prescribed value when the optical disk 2 is irradiated with the light beam 3, and the adder 60 adding the offset signal to a focus error signal. Then, the device is constituted so that the position of the lens 4 is controlled according to the output on the adder 60. In such a manner, since the lens 4 is controlled to be at the position where the light beam 3 is focussed on the optical disk 2, the failure in the focus drawing is evaded at the time of focus control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus control device for an optical disk device.

[0002]

2. Description of the Related Art In an optical disk apparatus, it is necessary to keep a light beam in a good focused state on a recording surface of an optical disk when recording / reproducing information. Therefore, focus (or focusing) servo is performed.

FIG. 16 shows a conventional optical disk device,
It is an example of a focus control device. The optical pickup 1 irradiates the recording surface 2A of the optical disc 2 with a light beam 3 as focused light through a lens 4 to record / reproduce information. Further, the optical pickup 1 sends a signal obtained from an optical system (not shown) inside the optical pickup 1 to the error signal generating circuit 5 based on the light reflected from the optical disc 2, and the error signal generating circuit 5 follows the focusing position of the light beam 3 accordingly. 3A and optical disc 2
The focus error signal FES indicating the amount of vertical deviation from the recording surface 2A of the optical disk 2 and the track (not shown) and the light beam 3 engraved on the recording surface 2A of the optical disk 2
Of the tracking error signal TES indicating the amount of deviation in the radial direction of
And so on.

The focus error signal FES is applied to the focus actuator 9 in the optical pickup 1 via the phase compensation circuit 6, the switch 7 and the driver 8,
The focus actuator 9 drives the lens 4 in a direction perpendicular to the recording surface 2A of the optical disc 2 to change the focusing position 3A of the light beam 3. Focus search circuit 10
Drives the focus actuator 9 for the focus search described later. The controller 11 observes the focus error signal FES and manages and controls the entire focus control device.

Next, the relationship between the amount of deviation between the recording surface 2A of the optical disc 2 and the focusing position 3A of the light beam 3 and the focus error signal FES will be described. FIG. 17 shows the focus error signal F generated by the optical system inside the optical pickup 1 and the error signal generating circuit 5 with the displacement amount Δx between the recording surface 2A of the optical disc 2 and the focusing position 3A of the light beam 3 as the horizontal axis.
It is the graph which showed the amplitude of ES on the vertical axis.

The origin of FIG. 17 is the recording surface 2A and the focusing position 3A.
Are the just focus points that coincide with each other, the left side is the area FAR where the focusing position 3A is far from the recording surface 2A, and the right side is the near area NEAR. From this figure, the focus error signal FES indicates that the recording surface 2A of the optical disc 2 is
It can be seen that the signal has a polarity and a magnitude depending on the distance between the light beam 3 and the focus position 3A of the light beam 3.

Therefore, in the focus control device of FIG. 16, the focus error signal FES output from the error signal generation circuit 5 has the polarity as shown in FIG. 17, and when a positive signal is applied to the phase compensation circuit 6. If the lens 4 is driven via the focus actuator 9 in the direction away from the optical disc 2, the focusing position 3A can be controlled so as to always be in the vicinity of the recording surface 2A of the optical disc 2.

However, as described above, the significant focus error signal FES is obtained at a few tens of microns in both the far and near directions with respect to the just focus point.
In the out-of-focus state beyond this range, the focus error signal FES becomes almost 0 regardless of the focusing position 3A of the light beam 3. Therefore, the focusing position 3A and the recording surface 2
The positional relationship with A becomes unclear, and focus control cannot be executed. In other words, when the focus servo is operated, the focus position 3A of the light beam 3 needs to be within several tens of microns from the just focus point.

However, the focus position 3A of the light beam 3 rarely falls within this range when the focus servo is started. Therefore, in general, before starting the focus servo, a significant focus error signal FES
A focus search is performed to find a range in which is obtained.

In FIG. 16, the controller 11 switches the switch 7 to the terminal A side, supplies the output of the focus search circuit 10 to the driver 8 and drives the focus actuator 9 to move the position of the lens 4 to the optical disk 2.
It is largely moved in the direction perpendicular to the recording surface 2A. At this time,
If the output of the focus search circuit 10 changes with time, such as a triangular wave or a sine wave, the lens 4 can be moved from far to near or from near to far, so that the focus error signal FES. Changes as shown in FIG.

While the focus error signal FES reaches a positive (or negative) peak to a negative (or positive) peak of the opposite polarity, that is, the significant zero-cross point of the focus error signal FES is just as described in FIG. Since it is the focus point, the controller 11 switches the switch 7 to the terminal B side at or near the zero cross point of the focus error signal FES to start the focus servo. A series of procedures for switching from focus search to focus servo is generally called focus pull-in.

The sum of the warp of the optical disk 2 and the mechanical error of the optical pickup 1 or the focus actuator 9 is estimated to be several hundreds of microns. Therefore, the amplitude of the signal output from the focus search circuit 10 is
The focus actuator 9 (and the lens 4) is set to a level at which the focus actuator 9 (and the lens 4) moves at least by the tolerance. As a result, a significant focus error signal FES is always obtained during the focus search.

[0013]

By the way, in order to shorten the time required for pulling in the focus, the frequency of the output signal from the focus search circuit 10 is increased to increase the focus error signal FES per time.
It is first considered to increase the frequency of passing through the zero-cross point, that is, the pull-in possible point.

However, this case has the following problems.

The range in which the focus can be pulled in is several tens of microns before and after the just focus point. Therefore, compared with the movement of several hundreds of microns during the focus search, it is only a few percent to at most 10 to 20 percent. Therefore, even if the controller 11 switches the switch 7 to the terminal B side at the zero cross point of the focus error signal FES, if the momentum obtained by the movable actuator such as the lens 4 from the focus actuator 9 during the focus search is large, the just focus is achieved. The transient movement of the lens 4 cannot be stopped within a range of several tens of microns before and after the point, resulting in an out-of-focus state.
Therefore, the focus position 3A of the light beam 3 and the optical disc 2
The positional relationship between the recording surface 2A and the recording surface 2A becomes unknown, and focus pull-in fails.

When the amplitude or frequency of the output signal of the focus search circuit 10 increases, focus pull-in tends to fail. Further, since the recording surface 2A swings in a direction perpendicular to the surface due to the rotation of the optical disk 2, so-called surface wobbling, the relative speed between the recording surface 2A and the lens 4 increases, so that focus pull-in is more likely to fail.

[0017]

According to a first aspect of the present invention, there is provided a focus control device for an optical disk device, comprising: a lens for focusing a light beam so as to focus the light beam on the optical disk. In a focus control device of an optical disc device for controlling the position, the optical beam is directed to the optical disc only when the amount of the reflected light from the optical disc or the transmitted light of the optical disc obtained when the optical beam is irradiated to the optical disc is smaller than a predetermined value. A voltage generator that generates an offset signal for moving the lens to a focus position and an adder that adds the offset signal to the focus error signal are provided, and the lens position is controlled according to the output of the adder. It is characterized by doing.

In order to solve the above-mentioned problems, a focus control device for an optical disk device according to a second aspect of the present invention is the focus control device for an optical disk device according to the first aspect of the present invention, wherein the voltage generating means is a focus device. Discriminating means for discriminating whether the error signal is larger than the first reference voltage or smaller than the second reference voltage, and the reflected light or the reflected light from the optical disc or the transmitted light of the optical disc is smaller than a predetermined value. A voltage generation source that generates a voltage according to the difference between the amount of transmitted light and a predetermined value, and a polarity switching unit that non-inverts or inverts the polarity of the voltage from the voltage generation source according to the determination result and outputs it as an offset signal. It is characterized by being composed of.

In order to solve the above-mentioned problems, a focus control device for an optical disk device according to a third aspect of the present invention is the focus control device for an optical disk device according to the first aspect of the invention, wherein the voltage generating means is a focus device. A discriminating means for discriminating whether the error signal intersects the third reference value from the minus side to the plus side or from the plus side to the minus side, and the light amount of the reflected light from the optical disc or the transmitted light of the optical disc is a predetermined value. Voltage source that generates a voltage according to the difference between the amount of reflected or transmitted light and a predetermined value, and the polarity of the voltage from the voltage source is non-inverted or inverted depending on the determination result. It is characterized in that it is composed of polarity switching means for outputting the offset signal as an offset signal.

[0020]

According to the structure of claim 1, an offset signal for moving the lens to a position where the light beam is focused on the optical disk is output from the voltage generating means. Therefore, during focus control, failure in focus pull-in does not occur. Moreover, since there are no adjustment points, a highly reliable focus control device can be easily realized. Further, the offset signal is output only when the amount of reflected light from the optical disc or the transmitted light of the optical disc is smaller than a predetermined value, and therefore is not output when the light beam is focused on the optical disc. That is, when the light beam is focused on the optical disk, the original focus error signal is output from the adder. Therefore, highly accurate focus control can be realized.

According to the structure of claim 2 or 3, in addition to the operation of claim 1, the voltage generating means of the focus control device can be realized with a simple structure.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention provides a significant focus error signal FES.
The focus is on the manner in which the reflected light amount signal TOTAL changes from the vicinity of the just focus point at which is obtained to the out-of-focus state. FIG. 1 shows a general example of the relationship between the focus error signal FES and the reflected light amount signal TOTAL. In a region near the just focus point where a significant focus error signal FES is obtained, a track on the optical disc recording surface or an optical disc is recorded. Although there is some variation due to the influence of the optical system inside the pickup, etc., the level of the reflected light amount signal TOTAL is generally high. In this region, the focus error signal FES is a signal that clearly indicates the deviation from the just focus point, including the direction thereof, so that the servo means such as the focus actuator can be correctly driven toward the just focus point direction. On the other hand, in the out-focus state, the focus error signal FES becomes almost 0, and the direction of deviation from the just focus point cannot be indicated, as already described.

However, focusing on the reflected light amount signal TOTAL, the focus error signal FES becomes 0 from the vicinity of the just focus point to the out-focus state.
It decreases gradually as it approaches asymptotically. Therefore, FIG.
As shown in (b), when the reflected light amount signal TOTAL falls below a certain reference value VT, an amount of the reflected light amount signal TOTAL itself is obtained by an electric circuit, and a signal TDIF for driving the focus actuator toward the just focus point (see FIG. c))
Should be able to be used as. However, when the level of the reflected light amount signal TOTAL is equal to or higher than the reference value VT, the signal TDIF is set to 0.

Of course, it is necessary to switch the polarity of this signal TDIF according to the direction of out-focus, but this is the plus or minus peak of the focus error signal FES from the vicinity of the just focus point to the out-focus state. Alternatively, it can be easily performed by detecting and storing in which direction the zero cross appears, and if the polarity of the signal TDIF is switched according to this, an offset signal VOFF ((d) in the figure) is obtained. When this is added to the focus error signal FES ((a) in the figure), a signal FES '((e) in the figure) having a polarity for always driving the focus actuator toward the just focus point is obtained even in the out-focus state.

On the other hand, when the level of the reflected light amount signal TOTAL is equal to or higher than the reference value VT, that is, the focus error signal FES is clearly obtained in the vicinity of the just focus point, it is not necessary to add the offset signal VOFF, but rather the offset signal VOFF is used. In addition, this may act as a disturbance that causes the focus servo to be performed at a position deviated from the just focus point. Therefore, if a circuit that outputs the difference as the signal TDIF only when the reflected light amount signal TOTAL falls below the reference value VT, the offset signal VOFF drives the focus actuator toward the just focus point in the out-focus state. The signal becomes a signal and becomes 0 in the vicinity of the just focus point so as not to interfere with the focus servo, so that these problems can be solved at once.

The present invention has been made based on the principle and consideration as described above.

A first embodiment of the present invention will be described with reference to FIGS. 3 to 8. FIG. 3 is a block diagram of a focus control device in an optical disk device according to an embodiment of the present invention. The same parts as those described in FIG. 16 as a conventional example are designated by the same reference numerals and the description thereof will be omitted. .

In FIG. 3, the focus error signal FES
Is given to the error direction detection circuit 20 (determination means), and the plus reference voltage + VF1 having the focus error signal FES.
Signal OVER when it becomes more positive than memory circuit 3
0 (discriminating means) and outputs the signal UNDER to the memory circuit 30 when the focus error signal FES becomes less than a certain negative reference voltage -VF2.

The memory circuit 30 uses the error direction detection circuit 20.
The signal + SEL is output by the signal OVER from and the signal -SEL is output by the signal UNDER. In addition,
Signals OVER and UN from these error direction detection circuits 20
It is not possible that the DER is output at the same time because the focus error signal FES never shows a plus or minus voltage at the same time. Therefore, these signals + SEL and -SEL are not output at the same time. .

On the other hand, the light quantity of the light reflected from the optical disk 2 and returned to the optical pickup 1 is supplied to the light quantity signal generation circuit 70 (voltage generation source) as a photocurrent by an optical system or a photodetector (not shown) therein. , Reflected light amount signal TOTA
It is given as L to the light amount difference detection circuit 40 (voltage generation source).

The light amount difference detection circuit 40 uses the reference value V of the light amount signal.
The voltage source 41 indicating T is compared with the reflected light amount signal TOTAL, and when the reflected light amount signal TOTAL is equal to or less than the reference value VT, the difference (reference value VT-reflected light amount signal TOTAL) is output as a signal TDIF and reflected. When the light amount signal TOTAL exceeds the reference value VT, 0 (V) is output as the signal TDIF. It is assumed that the signal TDIF does not become negative according to the above description.

When the signal + SEL is output from the memory circuit 30, the polarity switching circuit 50 (polarity switching means) outputs the signal TDIF as it is as the offset signal VOF.
When it is output as F and the signal -SEL is output,
Offset signal VOF by inverting the polarity of signal TDIF
Output as F. Here, the signal + SEL is also -SEL
If neither is given, the offset signal VOFF of any polarity is not output, but the offset signal VOFF of any polarity may be output, as will be apparent from the operation description below.

The offset signal VOFF from the polarity switching circuit 50 is sent to the adding amplifier 60 (adder) and added with the focus error signal FES. The output signal FES ′ of the summing amplifier 60 passes through the phase compensation circuit 6 and the terminal B side of the switch 7 through the common terminal C to drive the focus actuator 9 and move the lens 4 to change the focus position 3A of the light beam 3. A focus search circuit 10 is connected to the terminal A side of the switch 7.

Note that the focus error signal FES is negative when the focus position 3A of the light beam 3 is far from the just focus point and positive when the focus error signal FES is close to it, as in FIG. 17 used in the description of the prior art. Focus actuator 9
When the focus error signal FES is positive, the polarity is driven so as to move the focus position 3A of the light beam 3 away from the recording surface 2A of the optical disc 2, and when the focus error signal FES is negative, the focus position 3A is driven closer. .

Subsequently, the error direction detection circuit 20, the storage circuit 30, the light amount difference detection circuit 40, and the polarity switching circuit 5
0 will be described in more detail.

As shown in FIG. 4, the error direction detection circuit 20 is composed of comparators 201 and 202, and voltage sources 203 and 204 for generating positive and negative reference voltages + VF1 and -VF2, respectively. The focus error signal FES is commonly applied to the non-inverting input of the comparator 201 and the inverting input of the comparator 202. The reference voltages + VF1 and -VF2 from the voltage sources 203 and 204 are input to the other inputs of the comparators 201 and 202, respectively, and when the focus error signal FES becomes more positive than the reference voltage + VF1, the signal from the comparator 201 is output. OVER is output, and when the focus error signal FES becomes less than the reference voltage −VF2, the signal UNDER is output from the comparator 202.

Next, a configuration example of the memory circuit 30 is shown in FIG.
The memory circuit 30 includes an R formed by NOR gates 301 and 302.
It is composed of an S flip-flop 31.

When the signal OVER of the logic "H" level is given, the output + Q of the RS flip-flop 31 becomes "H".
And the output −Q becomes “L” level. Conversely, when the signal UNDER is given, the RS flip-flop 3
1 output + Q goes to "L" level, output -Q goes to "H"
It becomes a level and holds its state until the other inputs are given to each other. These outputs + Q and -Q are output as signals + SEL and -SEL, respectively.

As shown in FIG. 6, the light amount difference detection circuit 40 comprises a differential amplifier 401, a diode D1, a resistor R1, and a buffer amplifier 402.

The differential amplifier 401 calculates the voltage value generated by the voltage source 41, that is, the difference between the reference value VT of the light quantity signal and the reflected light quantity signal TOTAL, (reference value VT-reflected light quantity signal T
OTAL) is obtained and output, but since the diode D1 is connected to the output, this voltage appears at both ends of the resistor R1 only when (reference value VT-reflected light amount signal TOTAL)> 0, and (reference value VT-Reflected light amount signal TOTAL)
When ≦ 0, the voltage does not appear and becomes 0. When (reference value VT-reflected light amount signal TOTAL)> 0, the signal T
Considering the error of the forward voltage drop of the diode D1 (about 0.7 V) included in DIF, the reference value VT
It is sufficient to avoid this error by a method such as setting a higher value.

Now, the configuration of the polarity switching circuit 50 is shown in FIG.
Described in. The polarity switching circuit 50 is a non-inverting amplifier 50.
1, an inverting amplifier 502, and switches 503 and 504. Since the switch 503 is turned on when the logic "H" level signal + SEL is input, the signal TDIF is directly output as the offset signal VOFF, and the switch 5 is input when the signal -SEL is input.
Since 04 is turned on, the signal TDIF is output as the offset signal VOFF after the polarity is inverted.
When neither signal + SEL or -SEL is input,
That is, when both are at the logic "L" level, both the switches 503 and 504 are turned off and the offset signal VOFF is not output.

Next, the focus pull-in operation of the focus control apparatus according to this embodiment will be described with reference mainly to FIGS. At the time of focus search prior to focus pull-in, the controller 11 switches the switch 7 to the terminal A side, and the focus search circuit 10
Is supplied to the driver 8 to drive the focus actuator 9 (and the lens 4).

While the focus actuator 9 (and the lens 4) is being driven, each time the focus position 3A of the light beam 3 reaches before and after the just focus point which coincides with the recording surface 2A of the optical disc 2, the focus as shown in FIG. The error signal FES is obtained. At this time, the lens 4 moves to the optical disc 2
The focus error signal FES plus / minus depending on whether it approaches from a far side or moves away from a near side.
The figure shows a case where the focus search is started from a position far from the just focus point, although it differs depending on which of the minus peaks first appears.

Further, the reflected light amount signal TOTAL becomes a high level near the just focus point as shown in FIG.

Focus error signal FES is reference voltage + V
When it is larger than F1 on the plus side, the signal OVER shown in FIG. 7C is output from the error direction detection circuit 20, and when the focus error signal FES is larger on the minus side than the reference voltage −VF2, FIG. The signal UNDER shown in is output from the error direction detection circuit 20. The output signal + SEL of the memory circuit 30 is the signal O as shown in FIG.
Set by VER and reset by signal UNDER. The output signal -SEL of the memory circuit 30 is set by the signal UNDER and reset by the signal OVER, as shown in FIG.

Output signals of memory circuit 30 + SEL, -SE
L is indefinite which is at the logic "H" level at the start of operation. An offset signal VOFF, which will be described later,
The same applies to the signal FES ', but when the first signal OVER (or UNDER) during focus search is input, these are all fixed.

The light amount difference detection circuit 40 is provided with a reflected light amount signal TO.
Only when TAL falls below the reference value VT, the difference between the level of the reflected light amount signal TOTAL and the reference value VT is shown in FIG.
The signal TDIF is output as shown in FIG.

The polarity switching circuit 50 outputs the signal TDI when the logic + H level signal + SEL is output.
The polarity of F is left unchanged, and when the signal -SEL is being output, it is inverted and output as an offset signal VOFF, as shown in FIG. Offset signal V
As described above, OFF is 0 in the vicinity of the just focus point regardless of the states of the signals + SEL and -SEL, and therefore does not affect the focus pull-in in the vicinity of the just focus point or the focus servo. On the other hand, in the out-focus state, the signal is not 0, but has a polarity according to the direction.

Therefore, the original focus error signal FE
The signal FES ′, which is the output obtained by adding the offset signal VOFF to the S (FIG. 11A) by the adding amplifier 60, is the same as the original focus error signal FES near the just focus point, as shown in FIG. Although the same, in the out-focus state, the offset signal VO that drives the focus actuator 9 toward the just focus point
It is almost the same as FF.

Therefore, once the switch 7 is switched to the terminal B side to start the focus servo, even if the out-of-focus state is reached by deviating from the vicinity of the just focus point, the lens 4 (and the light beam 3) are immediately output. Since the focusing position 3A) is returned to the vicinity of the just focus point, the failure in focus pulling does not occur as a result.

A second embodiment of the present invention will be described with reference to FIGS. 9 and 10. For convenience of explanation, members having the same functions as those of the members shown in the drawings of the above-described embodiments are designated by the same reference numerals, and the description thereof will be omitted.

In the focus control device of this embodiment, the memory circuit 30 is different from that of the above embodiment. Memory circuit 30
Is a three-input NOR gate 30 as shown in FIG.
The RS flip-flop 32 is composed of 3, 304.

The changes of the output signals + SEL and -SEL by the signal OVER and the signal UNDER are the same as those in the above-mentioned embodiment, but in this embodiment, the RS flip-flop 32 is used.
The NOR gates 303 and 304 constituting the above are three inputs, and the signals SET and RESET are input from the controller 11 to each of these inputs as shown in FIG.

In the memory circuit 30 of the above embodiment, it is uncertain which of the signals + SEL and -SEL is at the logic "H" level at the start of operation, and when the signal OVER (or UNDER) is first input. This is confirmed. From this point onward, the offset signal VOFF added to the focus error signal FES always has the correct polarity for pulling the lens 4 (and the focus position 3A of the light beam 3) from the out-focus state to the vicinity of the just focus point.

However, in the memory circuit 30 of the present embodiment, if the controller 11 sends out the signal SET (or RESET) at the logic "H" level even for a moment before the focus search, the levels of the signals + SEL and -SEL are set. As a result, the polarity of the offset signal VOFF added to the focus error signal FES can be fixed.

Since the memory circuit 30 has the inputs of the signals SET and RESET, the focus pull-in in the focus control device of FIG. 9 is simplified as compared with the above-described embodiment.

For example, the controller 11 uses the switch 7
Is switched to the terminal A side, and the focus search circuit 10 is controlled to drive the focus actuator 9 to move the lens 4 to a position sufficiently far from the optical disc 2 (out-of-focus state on the far area FAR side). And Here, the signal RESE is sent to the memory circuit 30.
If T is sent out for a moment and the signal -SEL is output as the initial state, the focus actuator 9
(And the lens 4 and the focusing position 3A of the light beam 3) are moved toward the just focus point.
It is output from 0. Therefore, only by switching the switch 7 to the terminal B side, the lens 4 (and the focusing position 3A of the light beam 3) is automatically positioned in the vicinity of the just focus point, and the controller 11 performs other processing. The focus pull-in is completed without performing it. Further, as already mentioned many times, the offset signal VOFF automatically becomes 0 near the just focus point, so the offset signal VOFF has no influence on the focus servo near the just focus point.

In the above embodiment, the offset signal VOFF
The focus search circuit 10 needs to drive the focus actuator 9 at least once to the vicinity of the just focus point in order to determine the polarity of, and therefore a voltage source that generates a time-varying signal such as a sine wave or a triangular wave is required. Met. However, in this embodiment, as is clear from the above-described focus pull-in procedure, the focus search circuit 10 need only include a DC voltage source that drives the focus actuator 9 and moves the lens 4 away from the optical disk 2 sufficiently.

Third Embodiment of the Present Invention FIGS. 11 to 13
Will be described with reference to. For convenience of explanation, members having the same functions as those of the members shown in the drawings of the above-described embodiments are designated by the same reference numerals, and the description thereof will be omitted.

In the focus control device of this embodiment, the error direction detection circuit 20 is different from that of the second embodiment. As shown in FIG. 11, the error direction detection circuit 20 includes a hysteresis comparator 205, a delay line (delay element) 206, a NOT gate 207, and an AND gate 20.
The AND gate 208 outputs the signal + OVER, and the NOR gate 209 outputs the signal −UNDER.

In the out-focus state, in order to know whether the focus position 3A of the light beam 3 is too close to or far from the recording surface 2A of the optical disc 2 (area NEAR side or area FAR side), the just focus is used in the above embodiment. The polarity of the focus error signal FES that has appeared from near the point to the out-of-focus state is set to the reference voltage + VF.
It was judged by comparing with 1 and -VF2.

However, the direction of the out-of-focus state can be determined also in the zero-cross direction of the focus error signal FES. For example, the focus error signal FES shown in FIG.
In the above, it is assumed that the focusing position 3A of the light beam 3 is at the point A on the area FAR side in the figure in the initial state. Then, if the focus position 3A moves from the point A of the area FAR to the point B of the area NEAR, the focus error signal FES zero-crosses from minus to plus. Conversely, focusing position 3
If A moves from the point B in the area NEAR to the point A in the area FAR, the focus error signal FES crosses zero from plus to minus.

On the basis of the above facts, the error direction detection circuit 20 of this embodiment detects that the focus error signal FES is zero-crossing from minus to plus, and the focus error signal FES passes through the plus peak and becomes the area. The signal OVER is output upon determining that the NEAR out-of-focus state is reached, and when it is detected that the focus error signal FES is zero-crossing from plus to minus, the focus error signal FES is detected.
The signal UNDER is output when it is judged that the out-of-focus state of the area FAR is reached after a negative peak.

The operation will be described with reference to FIG. The same figure (a)
When the focus error signal FES shown in is input,
Output signal FLVL of hysteresis comparator 205
Is the focus error signal FE as shown in FIG.
Does S cross zero from positive to negative?
The logic "H" level or the logic "L" level is obtained depending on whether the zero crossing is performed from the minus side to the plus side.
The signal FLVL 'is the same as the signal FLVL in the delay line 20.
It is obtained by delaying by the time td at 6 and then inverting by the NOT gate 207 ((c) in the same figure). Signal O
VER is the signal FLVL and FLV at the AND gate 208.
It is obtained by calculating the logical product of L '((d) of the same figure). The signal UNDER is obtained by obtaining the inversion of the logical sum of the signals FLVL and FLVL ′ by the NOR gate 209 ((e) in the figure).

When the signals OVER and UNDER are compared with the focus error signal FES, the signal OVER indicates that the focus error signal FES is zero-crossing from minus to plus, and the signal UNDER is the focus error signal FES from plus to minus. It can be seen that it indicates the time when the zero cross was made toward. The hysteresis voltage of the hysteresis comparator 205 ± VH
By this, it is possible to reliably indicate the time when the focus error signal FES zero-crosses from the plus side to the minus side and the time point when the zero-crossing goes from the minus side to the plus side, and at the time of the out-focus state, that is, the malfunction in the focus error signal FES≈0 Can be prevented.

In the error direction detection circuit 20 of the second embodiment, the signal OVER is not output until the focus error signal FES exceeds the reference voltage + VF1 (or -VF2).
(Or UNDER) logic is determined, and the storage circuit 30
The output signals + SEL and -SEL logic and the polarity of the offset signal VOFF are also determined.

On the other hand, in the error direction detection circuit 20 of this embodiment, the logic of the signal OVER (or UNDER) is determined only when the focus error signal FES crosses zero, and the output signals + SEL, -SE of the memory circuit 30 are determined.
The logic of L and the polarity of the offset signal VOFF are also determined.

In any case, the focus pull-in is performed in the area F.
Depending on whether it is started from the AR side or the area NEAR side, the controller 11 outputs the signal SET or R.
If the initial state of the memory circuit 30 is determined by outputting ESET, these signals OVER, UNDER, + SEL, -SEL, and V from the beginning of focus pull-in.
The logic or polarity of OFF can be established.

Therefore, also in the focus control apparatus of this embodiment, focus pull-in is performed as in the above-described embodiment.

Fourth Embodiment of the Present Invention FIGS. 14 and 15
Will be described with reference to. For convenience of explanation, members having the same functions as those of the members shown in the drawings of the above-described embodiments are designated by the same reference numerals, and the description thereof will be omitted.

In the focus control device of this embodiment, as shown in FIG.
As shown in FIG. 4, the error direction detection circuit 20 is different from that of the first to third embodiments. Error direction detection circuit 20
As shown in FIG. 15, a comparator 210, a voltage source 211 for generating a reference voltage VJ, AND gates 212, 2 are provided in the error direction detection circuit 20 (FIG. 11) of the third embodiment.
It has a configuration in which 13 is added.

In this embodiment, the focus error signal FES used to determine the polarity of the offset signal VOFF.
By detecting the zero-crossing point of 1 only in the vicinity of the just focus point, erroneous detection in the out-of-focus state in which the focus error signal FES becomes almost 0 is further reliably prevented. In the out-of-focus state, the reflected light amount signal TOTAL is at a low level, so the reflected light amount signal T
The signal TOTOK obtained by comparing OTAL with the reference voltage VJ by the comparator 210 becomes the logic "L" level. At this time, the AND gates 212 and 213 have the AND gate 208 and the NOR gate 20 at the preceding stage.
The output from 9 is blocked and the signal OVER and the signal UND are blocked.
Does not output ER.

Therefore, the error direction detection circuit 20 of this embodiment is less likely to erroneously detect the zero cross of the focus error signal FES than the error direction detection circuit 20 of the third embodiment. Therefore, the polarity of the offset signal VOFF can be determined with higher reliability.

In the above embodiment, the focus error signal F
It has been described that ES changes to the positive side or the negative side with the ground potential (0 V) as the reference voltage V _ref (third reference voltage), but the present invention is not limited to this. For example, + 5V
When using the single power source of, the voltage between 0V and + 5V (for example, + 2.5V) is used as the reference voltage _Vref of the focus error signal FES. At this time, the focus error signal FES changes in the range of 0 V to +5 V around the reference voltage V _ref , so the reference voltage + VF1 is set to a positive voltage larger than the reference voltage V _ref and the second reference voltage −E is set as the reference. It may be set to a positive voltage smaller than the voltage V _ref .

A focus control device for an optical disk device according to the invention of claim 1 controls the position of a lens 4 for focusing the light beam 3 so as to focus the light beam 3 on the optical disk 2. In, the light quantity of the reflected light from the optical disk 2 or the transmitted light of the optical disk 2 obtained when the light beam 3 is irradiated to the optical disk 2 (for example, the reflected light quantity signal TOTAL)
Is smaller than the reference value VT, voltage generating means for generating an offset signal VOFF for moving the lens 4 to a position where the light beam 3 is focused on the optical disc 2 and the offset signal VES for the focus error signal FES.
The addition amplifier 60 for adding OFF is provided,
The position of the lens 4 is controlled according to the output of the addition amplifier 60.

According to this, the light beam 3 is directed to the optical disc 2
An offset signal VOFF for moving the lens 4 to a position for focusing on is output from the voltage generating means. Therefore, during focus control, failure in focus pull-in does not occur. Moreover, since there are no adjustment points, a highly reliable focus control device can be easily realized. Further, the offset signal VOFF is output only when the amount of reflected light from the optical disc 2 or transmitted light of the optical disc 2 is smaller than a predetermined value, and therefore is not output when the light beam 3 is focused on the optical disc 2. . That is, when the light beam 3 is focused on the optical disc 2, the original focus error signal FES is output from the addition amplifier 60. Therefore, highly accurate focus control can be realized.

According to a second aspect of the present invention, there is provided a focus control device for an optical disc device, which is the focus control device for an optical disc device according to the first aspect, wherein the voltage generating means has a focus error signal FES larger than a reference voltage + VF1.
The error direction detection circuit 20 and the storage circuit 30 which determine whether the voltage is smaller than the reference voltage −VF2, and the reflected light or the transmitted light only when the light amount of the reflected light from the optical disc 2 or the transmitted light of the optical disc 2 is smaller than the reference value VT. A light amount signal generation circuit 70 and a light amount difference detection circuit 40 that generate a voltage corresponding to the difference between the light amount of light and the reference value VT, and a light amount difference detection circuit 4
The determination result of the polarity of the signal TDIF from 0 (signal + SE
Polarity switching circuit 50 that outputs non-inverted or inverted data as an offset signal VOFF according to L, -SEL).
It consists of

According to this, in addition to the effect of the first aspect, the voltage generating means of the focus control device can be realized with a simple structure.

According to a third aspect of the present invention, there is provided a focus control device for an optical disc device, which is the focus control device for an optical disc device according to the first aspect, wherein the voltage generating means has a focus error signal FES of 0 V (third reference voltage). ) Is crossed from the minus side to the plus side or from the plus side to the minus side, and the error direction detection circuit 20 and the storage circuit 30, and the light amount of the reflected light from the optical disc 2 or the transmitted light of the optical disc 2 are Only when it is smaller than the reference value VT, the light amount signal generation circuit 70, the light amount difference detection circuit 40, and the light amount difference detection circuit 40 that generate a voltage according to the difference between the light amount of the reflected light or the transmitted light and the reference value VT. Signal T
The polarity of DIF is non-inverted or inverted according to the determination result (signal + SEL, -SEL) to offset signal VOFF.
It is composed of a polarity switching circuit 50 for outputting as.

According to this, in addition to the effect of the first aspect, the voltage generating means of the focus control device can be realized with a simple structure.

[0081]

As described above, in the focus control device for an optical disk device according to the first aspect of the present invention, the light amount of the reflected light from the optical disk or the transmitted light of the optical disk when the optical beam is applied to the optical disk is predetermined. Only when it is smaller than the value, there are provided voltage generating means for generating an offset voltage for moving the lens to a position where the light beam is focused on the optical disc, and an adder for adding the offset voltage to the focus error signal. Since the position of the lens is controlled according to the output of the adder, an offset voltage for moving the lens to a position where the light beam is focused on the optical disc is output from the voltage generating means. Therefore, during focus control, failure in focus pull-in does not occur. Moreover, since there are no adjustment points, it is possible to easily realize a highly reliable focus control device. Further, the offset voltage is output only when the amount of reflected light from the optical disc or the transmitted light of the optical disc is smaller than a predetermined value, and therefore is not output when the light beam is focused on the optical disc. That is, when the light beam is focused on the optical disk, the original focus error signal is output from the adder. Therefore, the effect that high-precision focus control can be realized is also obtained.

As described above, the focus control device of the optical disk device according to the second aspect of the present invention is the focus control device of the optical disk device according to the first aspect, wherein the voltage generating means has the focus error signal of the first reference voltage. Greater than or
Only when the light amount of the reflected light from the optical disc or the transmitted light of the optical disc is smaller than a predetermined value, the difference between the reflected light or the transmitted light amount and the predetermined value is determined. The voltage generating source for generating a corresponding voltage and the polarity switching means for non-inverting or inverting the polarity of the voltage from the voltage generating source and outputting it as an offset voltage according to the determination result. In addition to the effect, the voltage generating means of the focus control device can be realized with a simple configuration.

As described above, the focus control device of the optical disk device according to the third aspect of the present invention is the focus control device of the optical disk device of the first aspect, wherein the voltage generating means uses the third reference error as the focus error signal. Only when the light amount of the reflected light from the optical disc or the transmitted light of the optical disc is smaller than a predetermined value, a discriminating means for discriminating whether the value crosses from the minus side to the plus side or from the plus side to the minus side. A voltage generation source that generates a voltage according to the difference between the amount of reflected light or transmitted light and a predetermined value, and the polarity of the voltage from the voltage generation source is non-inverted or inverted according to the determination result and output as an offset voltage. Since it is composed of the polarity switching means, in addition to the effect of claim 1, there is an effect that the voltage generating means of the focus control device can be realized with a simple structure. .

[Brief description of drawings]

FIG. 1 is a waveform diagram showing a relationship between a focus error signal and a reflected light amount signal.

FIG. 2 is a waveform diagram showing the principle of the focus control device according to the present invention.

FIG. 3 is a configuration diagram showing a first embodiment of a focus control device according to the present invention.

4 is a configuration diagram showing an error direction detection circuit in the focus control device of FIG.

5 is a configuration diagram showing a storage circuit in the focus control device of FIG. 3. FIG.

6 is a configuration diagram showing a light amount difference detection circuit in the focus control device of FIG.

7 is a configuration diagram showing a polarity switching circuit in the focus control device of FIG.

FIG. 8 is a waveform diagram showing an operation of the focus control device of FIG.

FIG. 9 is a configuration diagram showing a second embodiment of the focus control device according to the present invention.

10 is a configuration diagram showing a storage circuit in the focus control device of FIG. 9. FIG.

FIG. 11 shows a third embodiment of the focus control device according to the present invention, and is a configuration diagram of an error direction detection circuit.

12 is a waveform diagram showing an operation of a focus control device using the error direction detection circuit of FIG.

13 is a waveform diagram showing an operation of a focus control device using the error direction detection circuit of FIG.

FIG. 14 is a configuration diagram showing a fourth embodiment of the focus control device according to the present invention.

15 is a configuration diagram showing an error direction detection circuit in the focus control device of FIG.

FIG. 16 is a configuration diagram of a conventional focus control device.

17 is a waveform diagram showing a focus error signal in the focus control device of FIG.

FIG. 18 is a waveform diagram showing a focus error signal during focus search in the focus control device of FIG. 16.

[Explanation of symbols]

 2 optical disk 3 light beam 4 lens 5 error signal generation circuit 10 focus search circuit 11 controller 20 error direction detection circuit (determination means) 30 storage circuit (determination means) 40 light amount difference detection circuit (voltage generation source) 50 polarity switching circuit (polarity) Switching means) 60 Addition amplifier (adder) 70 Light intensity signal generation circuit (voltage generation source)

Claims (3)

[Claims] 1. A reflected light from an optical disc obtained when a light beam is irradiated onto the optical disc in a focus control device of an optical disc device for controlling the position of a lens that focuses the light beam so that the light beam is focused on the optical disc. Further, only when the amount of light transmitted through the optical disc is smaller than a predetermined value, there is provided a voltage generating means for generating an offset signal for moving the lens to a position for focusing the light beam on the optical disc, and an offset signal for the focus error signal. A focus control device for an optical disk device, comprising: an adder for adding and controlling the position of a lens according to the output of the adder. 2. The voltage generating means includes a determining means for determining whether the focus error signal is larger than a first reference voltage or smaller than a second reference voltage, and a light quantity of reflected light from the optical disk or transmitted light of the optical disk. Is smaller than a predetermined value, a voltage generation source that generates a voltage corresponding to the difference between the amount of reflected light or transmitted light and a predetermined value, and the polarity of the voltage from the voltage generation source is determined according to the determination result. 2. The focus control device for an optical disk device according to claim 1, wherein the focus control device is composed of polarity switching means for inverting or inverting and outputting as an offset signal. 3. The voltage generating means determines whether the focus error signal intersects the third reference voltage from the negative side to the positive side or from the positive side to the negative side, and from the optical disk. The voltage generation source that generates a voltage according to the difference between the reflected light or transmitted light amount and the predetermined value only when the reflected light or the transmitted light amount of the optical disc is smaller than the predetermined value. 2. The focus control device for an optical disk device according to claim 1, further comprising polarity switching means for non-inverting or inverting the polarity of the voltage and outputting the offset signal as an offset signal.