JPH03165324A - Focusing servo device - Google Patents

Abstract

PURPOSE:To speed up the reacquisition of a focusing servo and to obtain a desired search waveform by limiting the variation range of the search signal and generating a digital signal corresponding to the signal. CONSTITUTION:The staircase wave voltage (V) generated by a focusing search signal generating circuit 11 is supplied to a focusing servo driver 7. A focusing point detecting circuit 5 when detecting a focus error signal reaching a range where the focusing servo is effective a time (t) later switches a switch 8 and supplies a switching signal to a digital pattern generator 10 to perform focusing servo operation. Then a generator 10 limits the amplitude value of the voltage V which is generated the time (t) later, sets the center value to the voltage at the time (t), and equalizes the variation rate of the voltage V to a value which is the time (t) precedent. Consequently, the period of the voltage V after the time (t) is made short to speed up the reacquisition.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a focus servo device, and particularly to a focus servo device suitable for use in an optical disc reading device such as a CD player.

[Prior Art J] An optical pick amplifier for a CD (compact disc) player focuses a laser beam on a spiral track provided on a compact disc and reads out a digital signal by detecting the reflected light. Since the convergence spot of this laser beam needs to be 1.6 μm or less, a reading error occurs even if there is a slight error in the distance between the optical pink-up objective lens and the compact disk. Therefore, the CD player is provided with a focus servo device that moves the objective lens of the optical pickup up and down in accordance with the fine irregularities of the compact disc. The details will be explained with reference to FIG.

In the figure, 1 is a compact disc, and an optical pickup 2 is provided close to the recording surface (lower surface) of the compact disc. Inside the optical pickup 2, there is a laser diode that emits a laser beam, a heel splitter that splits this laser beam into a main laser and a sub laser, an optical system such as a lens that converges the divided laser beam, and a main beam that is reflected by a compact disk. A light receiving section and the like for detecting the laser and sub-laser are provided (not shown).

Here, details of the light receiving section of the main laser and the focus error signal generation circuit 3 will be explained with reference to FIG. 4(A).

In the figure, 2a, 2b, 2c, and 2d are photodetectors,
Detection signals A, B, and CSD according to the detected light amount, respectively
is output and supplied to the focus error signal generation circuit 3. Inside the focus error signal generation circuit 3, the detection signals A and C are added by an adder 31 and supplied to the positive input terminal of a differential amplifier 33. Furthermore, the detection signals B and D are added by an adder 32 and supplied to the negative input terminal of a differential amplifier 33. As a result, from the differential amplifier 33, S, -(A+C)-(I3+D)...
- A signal S1 (1) is output. Here, if the distance between the compact disc 1 and the objective lens of the optical pickup 2 is appropriate, a spot of the main laser is formed as shown by XI in the figure. That is, the main laser spot becomes circular, and each photodetector 2a to 2d
The same amount of laser light is supplied to From this, since each detection signal A to D has the same magnitude, it can be seen that the signal SI becomes "0" according to equation (1).

In addition, if the distance between the compact disc 1 and the objective lens of the optical pickup 2 is not appropriate, that is, if there is an error (disk displacement) with respect to the appropriate distance, the main laser spot may be Detector 2
an ellipse (or photodetector 2) elongated in directions a and 2c
b, an ellipse that is longer in the 2d direction). This is due to the fact that a cylindrical lens (not shown) is provided in the path of the main laser. When the spot is formed as indicated by X in the figure, the light receiving areas of the light receiving elements 2a and 2C become wider, and the light receiving areas of the light receiving elements 2b and 2d become narrower. As a result, the detection signals A and C become large and the detection signals B and D become small, so it is clear from equation (1) that s + > 0.

In this way, the shape of the main laser spot is determined by the disk displacement, and the value of the signal S is determined. That is, the signal Sl becomes a signal indicating displacement (shift of focus). Hereinafter, the signal S1 will be referred to as a focus error signal. Further, the relationship between the disk displacement and the focus error signal Sl is shown in FIG. 4(b). According to the figure, the disk displacement is P.

When , the focus error signal S1 becomes maximum,
When the disk displacement is P, the focus error signal S1 is minimum.

Next, when the switch 8 is set to the 1 side in FIG. The signal is supplied to the servo driver 7. The focus servo driver 7 drives a focus actuator (not shown) built into the optical pickup 2 so that the distance between the compact disc 1 and the objective lens of the optical pickup 2 is appropriate according to the focus error signal S1. Finely adjust the position of the objective lens of the optical pickup 2.

By the way, according to FIG. 4 (b), when the disk displacement is small, the above-mentioned configuration allows normal focus servo operation, but when the disk displacement is relatively large (
For example, immediately after a compact disc I is set in a CD player, or when the focus servo comes off due to vibration, etc., the focus error signal S,
It can be seen that the focus servo operation cannot be performed normally because the level is too low. Therefore, in the configuration shown in FIG. 3, a focus search signal generation circuit 6 is provided which can drive the focus servo driver 7 without depending on the focus error signal S. Inside, 61 and 62 are constant current sources, one of which is connected to a capacitor 64 via a switch 63. Further, the switch 63 is configured to be switched at every predetermined period.

As a result, the capacitor 64 is repeatedly charged and discharged by the constant current sources 61 and 62, and the capacitor 64
The terminal voltage ■ has a waveform as shown in Fig. 2 (a).

According to the figure, the voltage V is a triangular wave with a period T and an amplitude value v. In FIG. 3, when this terminal voltage V is applied to the focus servo driver 7 via the voltage follower 65 and the switch 8 sequentially, the focus servo driver 7 is activated by the focus actuator built in the optical pickup 2 according to the level of the voltage V. A ducator (not shown) is driven, and the objective lens of the optical pickup 2 is driven up and down.

Reference numeral 5 denotes a focus detection circuit, which constantly monitors the focus error signal S1, and when it determines that the focus error signal S1 has reached a range in which focus servo is possible (near the origin in FIG. 4 (b)), it closes the contact of the switch 8. The contact point is set to the a side, and in other cases, the contact point is set to the b side.

According to the above configuration, in a situation where focus servo is not possible, the switch 8 is set to the b side, and the voltage V (second
The objective lens of the optical pickup is driven up and down according to the method (see figure (a)). Then, in the process of this vertical movement, when the distance deviation reaches the range where the force search is possible,
The contact point of the switch 8 is set to the a side, and the objective lens is driven according to the focus error signal S1. That is,
A focus servo operation is performed by each component 2.3.4.7.

``Invention or problem to be solved'' By the way, according to the configuration shown in Fig. 3, the period and amplitude of the voltage ■ are constant, so if the focus servo is disengaged due to external vibrations, etc., it takes time to re-bow. There was a problem that it took a while. In addition, the voltage V
There was also the problem that the waveform (focus search waveform) varied.

The present invention has been made in view of the above-mentioned circumstances, and provides a focus servo that enables extremely quick re-retraction when the focus servo becomes disconnected, and that also allows the focus search waveform to accurately match the desired waveform. The purpose is to provide equipment.

"Means for Solving Problems" In order to solve the above problems, the present invention includes a position detection means that outputs a detection signal when it detects that the distance between the recording surface of the optical disc and the optical pickup is within a predetermined range; When the detection signal is not output, a search signal that fluctuates at a predetermined first amplitude is output; on the other hand, when the detection signal is output, a search signal that fluctuates at a predetermined first amplitude is output, and when the detection signal is output, the search signal changes to a level near the level of the search signal at the time when the detection signal is output. The search signal generating means includes a search signal generating means for limiting a variation range of the search signal, and a driving device for setting a distance between the recording surface and the optical pickup according to the search signal, and the search signal generating means It is characterized by comprising a digital signal generating means for generating a digital signal corresponding to the signal, and a converter for converting this digital signal into an analog search signal.

``Effect J When the position detection means outputs a detection signal, the maximum and minimum values of the search signal are limited, so if the rate of change of the search signal is kept the same, its period becomes shorter.As a result,
The time it takes to activate a force attack is reduced.

Further, in the present invention, since the digital signal generating means generates the digital signal corresponding to the search signal, an extremely accurate focus search waveform is generated.

[Example J Next, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a focus servo device according to an embodiment of the present invention. In the drawings, parts corresponding to those in FIG. 3 are designated by the same reference numerals, and their explanations will be omitted.

In the figure, reference numeral 11 denotes a focus search signal generation circuit, which includes a digital vacuum generator 10,
D/A converter (digital/analog converter)
9 is provided. Moreover, at the same time as the switch 8 is switched to the a side, the switching signal S! is sent from the focused point detection circuit 5!
is supplied to the digital pattern generator 10.

The digital pattern generator 10 receives a switching signal S,
Before the voltage V is supplied, the voltage V shown in FIG.
A digital signal corresponding to a triangular wave having the same period T1 amplitude value vp is generated. When this digital signal is supplied to the D/A converter 9, it is converted into an analog signal (voltage V) and supplied to the focus servo driver 7.

Furthermore, after the switching signal S is supplied, the digital pattern generator IO changes the amplitude value of the voltage V to Δ
V (where Δv<V p ), and its center value is set to the level of voltage V at the time when switching signal S is supplied. Also, the rate of change of voltage v (l
dV/dt l ) is the switching signal S.

remains constant before and after the supply of

In the above configuration, when the switch 8 is set to the b side and the focus search signal generation circuit II is operated, the focus search signal generation circuit 11 as shown in FIG.
time t. A voltage V shown in the period -tl is generated, and this voltage V is supplied to the focus servo driver 7. During this period (times t0 to 1.), the waveform of the voltage V in FIG. 2(B) is the same as that in FIG. Change.

Next, after a certain time, when the in-focus point detection circuit 5 detects that the focus error signal S1 has reached the focus servo possible range (near the origin in FIG. 4(b)),
The contact of the switch 8 is set to the 1 side, and a switching signal S2 is supplied to the digital pattern generator 10. By setting the switch 8 to the a side, focus servo operation is performed by each component 2.3.4.7.

On the other hand, the digital pattern generator 10 generates the time [
, the subsequent amplitude value of voltage V is limited to ΔV, and its center value is set to V (however, center value Vl is the level of voltage V at time L1).

Moreover, as mentioned above, the rate of change of voltage V ((dV/dti
) is kept the same as the value before time L1.

As a result, the period T of the voltage V after time j+ is V T,=T脣 (1), which is shorter than the period T after time t1. Therefore, when the focus servo is out of alignment, the time required for re-retraction can be extremely shortened.

Further, in this embodiment, since the waveform of the voltage V can be set by the digital pattern generator IO, the waveform of the voltage V can be made to accurately match a desired waveform.

"Effects of the Invention" As explained above, according to the servo device of the present invention, when the focus servo is disengaged, it is possible to re-retract the focus servo extremely quickly, and the focus search waveform can be changed to the desired waveform. can be matched accurately.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the configuration of an embodiment of the present invention, Figures 2 (a) and (b) are waveform diagrams of the output voltage V of the focus error generation circuit 6.11, and Figure 3 is a diagram of the conventional focus servo. A block diagram of the device, FIG. 1(A) is a circuit diagram of the main part of FIG. 3, and FIG. 1(B) is a characteristic diagram of the output signal. l...Optical disc, 2...Optical pickup, 3...Focus error signal generation circuit (
position detection means), 5... focused point detection circuit (position detection means), 6... focus servo driver (drive device), 7... system controller (gain adjustment means), 9 ......D/A converter (converter), 10...Digital pattern generator (digital signal generation means), 11...Focus search signal generation circuit (search signal generation means) .

Claims (1)

[Scope of Claims] Position detection means that outputs a detection signal when it detects that the distance between the recording surface of the optical disc and the optical pickup is within a predetermined range, and a predetermined first amplitude when the detection signal is not output. search signal generating means for outputting a search signal that fluctuates at a time when the detection signal is output, and for limiting a variation range of the search signal to around the level of the search signal at the time when the detection signal is output; , a driving device configured to set a distance between the recording surface and the optical pickup according to the search signal, and
A focus servo device characterized in that the search signal generating means comprises a digital signal generating means for generating a digital signal corresponding to the search signal, and a converter for converting the digital signal into an analog search signal.