JPS63146232A - Servo device for optical disk information recording/ reproducing device - Google Patents

Abstract

PURPOSE:To record information onto an optical disk or to reproduce the information out of the disk with high stability and high accuracy, by using a triangular wave signal generator having the power proportional to the laser beam power and converting a servo error signal into a PWM signal by a triangular wave to drive an actuator. CONSTITUTION:A servo system 10 comprises a triangular wave generator 6 which produces a triangular wave V of a level proportional to the beam power by the control signal VCP of a laser output means 4 and a closed loop including a detecting circuit 5, a comparator 7, a drive circuit 8 and an actuator 9. Then a triangular wave V having a level proportional to the beam power is provided by means of the signal sent from the means 4 and generating the prescribed beam power. The waveform V is compared with an error signal (e) of the servo system by the comparator 7 and therefore the pulse width of the PWM signal MS delivered from the comparator 7 can be set adversely proportional to the laser beam power. Thus the proper open loop gain is obtained in response to the laser power supplied in a recording/reproducing mode or an erasion mode.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a servo device in an optical disk information recording/reproducing device, and in particular, to a servo device for recording, reproducing, or recording information on an optical disk with high precision and stability with a simple circuit configuration. The present invention relates to a servo device in an optical disk information recording/reproducing device useful for erasing information.

[Summary of the invention]

In an optical disk information recording and reproducing device that records, reproduces, or erases information on an optical disk, a triangular wave generator generates a triangular wave proportional to the beam power using a signal from a laser output means, and an error signal is detected by comparing this triangular wave with an error signal. A comparator that performs PWM modulation and a drive circuit that converts the obtained PWM modulation signal into an appropriate drive signal are provided,
record.

A constant drive signal is always supplied from the drive circuit to the actuator even when the drive signal changes during reproduction or erasure, thereby ensuring that information is always recorded, reproduced, or erased appropriately.

[Conventional technology]

Generally, in the case of an optical disc that has a recording and reproducing section, the laser power irradiated during recording is operated to be several times higher than during reproducing.

Therefore, the level of the servo error signal for controlling the optical pickup device obtained from the reflected light of the optical disk also increases in proportion to the laser power. So, for example, a tracking servo loop.

Alternatively, in a focus servo loop or the like, it is necessary to convert the loop gain in order to supply an appropriate servo signal to the actuator.

Conventionally, such a change in the servo loop gain is achieved by using feedback resistors rl, r7 . r3 are arranged in a ladder shape, and this feedback resistance r I +r2 . r3 was switched by switch 51152.53 according to the corresponding laser power during recording, reproduction, and erasing.

[Problem that the invention seeks to solve]

However, as described above, in the conventional example, the feedback resistors r1. Since this is an AGC circuit that uses r21r3 to adjust the gain of the amplifier, it requires a switch S for switching and a control circuit to control this switch, making the circuit configuration complicated. In particular, when an optical disc is driven by the constant angular velocity method (CAV method), the linear velocity changes at the inner and outer peripheries even during recording, so it is necessary to switch the laser beam in about 6 steps just during recording. Eight types of feedback resistors and their control circuits are required to vary the beam power in eight stages corresponding to a total of eight modes: one reproduction stage and one erasure stage. Furthermore, when using optical disks of different sizes, an even larger number of feedback resistors is required.

The present invention has been made in view of such problems, and an object of the present invention is to provide a servo device for an optical disc information recording/reproducing device that records, reproduces, or erases information on an optical disc with high precision and stability with a simple circuit configuration. With the goal.

[Means for solving problems]

As shown in FIG. 1, the servo device in the optical disk information recording and reproducing apparatus of the present invention includes a triangular wave generating circuit SG that generates a triangular wave proportional to the beam power according to a signal from the laser output means APC, and a servo system error signal e. triangular wave V
A comparator CM that PWM-modulates the error signal e by comparing the
P and a drive circuit FA which converts the PWM modulation signal output from the comparator CMP into an appropriate drive signal, and outputs a triangular wave having a level proportional to the beam power of the laser output means APC.

[Effect]

In the servo device in the optical disk information recording and reproducing apparatus of the present invention, a signal for generating a predetermined beam power from the laser output means is used to form a triangular wave with a level proportional to this beam power, and a comparison circuit CMP is used to detect errors in the servo system. Since the pulse width of the PWM signal outputted from the comparator circuit CMP can be made to be inversely proportional to the laser beam power.

In other words, the open loop gain G of the servo circuit is G = -
・Ve ■ (However, vB is the supply voltage of the drive circuit FA),
Appropriate open-loop gain can be provided depending on the laser power supplied during recording, playback, or erasing.

〔Example〕

FIG. 2 is a block diagram showing an embodiment of a servo device in an optical disc information recording/reproducing apparatus according to the present invention.

This device outputs a laser beam 1 with a predetermined beam power by controlling a laser power control voltage using a mode signal during recording, reproduction, or erasing, and transmits this laser beam 1 via an optical system 2 to a recordable optical disc 3. a detection circuit 5 which detects the light reflected through the optical system 2 and outputs an error signal e such as focusing or tracking that is proportional to a predetermined beam power; A triangular wave generator 6 which generates a triangular wave (■) at a level proportional to the beam power by the control signal VCP of the output means 4, a comparator 7 which compares the error signal e and the triangular wave V and PWM-modulates the error signal e, The PWM modulation signal MS output from the device 7 is converted into an appropriate drive signal D.
The main part thereof is constituted by a drive circuit 8 which supplies S to an actuator 9.

Among these main parts, the detection circuit 5. Triangle wave generator6.
Comparator 7. A servo system 10 is formed by a closed loop formed by a drive circuit 8 and an actuator 9, and the actuator 9 is driven by a drive signal DS.
When using focus servo, the objective lens 21 and the optical disk 3 are kept at a predetermined distance so that they are always in focus, and when using tracking servo, the objective lens 21
It is controlled so that a predetermined track is faithfully traced by deflecting the track.

The laser output means 4 includes mode terminals arranged in multiple stages,
For example, in the case of the above-mentioned CAV method, the address is such that the desired mode is selected when the mode signal S is supplied to each terminal of 6-stage recording W, 1-stage reproduction R, 11-stage erasure E, or backup X terminals. Decoder 40, depending on the mode selection signal M of this address decoder 40, for example, six levels of recording mode voltage, one level of reproduction mode voltage,
1-stage erase mode voltage, etc. El, E2. E3.・・・・・・
. . A voltage source 41 that selects and outputs En, an amplifier 42 that adjusts these mode voltages E, , E2 . . . to appropriate gains. Auto power control means 43 for controlling minute fluctuations in beam power due to temperature changes and outputting a laser power control voltage VCP necessary for recording, reproducing, erasing, etc. A light emitting diode 4 outputs a predetermined laser beam during recording, reproduction, erasing, etc. by applying this laser power control voltage VCP.
4. and a light receiving element 45 that photoelectrically converts the transmitted laser beam 25 of the second polarizing beam splitter 24 of the optical system 2 into an electric signal.

These automatic power control means 43,! An automatic power control circuit (Arc) 46 is formed in a closed loop consisting of a photodiode 44 and a light receiving element 45 to keep the beam power of the laser beam 1 constant.

The detection circuit 5 detects the focus or tracking state of the optical system 2. For example, the focus state detection means consists of a semiconductor divided into four light-receiving surfaces A, B, C, and D as shown in the figure. Light receiving element 51. and a differential amplifier 52 that calculates focus information according to the light-receiving pattern of the light-receiving element 51 and outputs a focus error signal e.

Note that, as is well known, the optical system 2 includes an objective lens 21. First polarizing beam splitter 2.21 cylindrical lens 23. It consists of a second polarizing beam splitter 24, and other optical devices such as a tracking error detector, an RF signal detector, etc. are added as necessary.

The triangular wave generator 6 applies the laser power control voltage VCP output from the laser output means 4 from the input end 47 and outputs a triangular wave proportional to the beam power, as shown in FIG. 3, for example. transistor Q
1. A current mirror circuit 61 consisting of Q2. Operational amplifier OP, transistor Q3. A non-inverting amplifier circuit 62 consisting of a resistor R and the like. Transistor Q41 charging capacitor C
It is formed by a transistor Q5 that discharges the charge of the capacitor C. The terminal 6 of this triangular wave generator 6
The comparator 7 to which the triangular wave V outputted from the detector 3 and the servo error signal outputted from the detection means 5 are inputted, outputs a PWM signal that is pulse width modulated with a constant period, as will be described later.

The drive circuit 8 outputs a drive signal DS necessary to drive the actuator 9 with the average DC voltage of the pulses of this PWM signal.

The operation of the servo device of the present invention will be described below with reference to the waveform diagram in FIG.

The same figure (A) shows the clock C that defines the sweep time of the triangular wave V.
The LK waveform, (B), (C), and (D) in the same figure respectively show the triangular wave V waveform, the error signal e waveform, and the PWM modulation signal MS waveform at the time of recording W, replaying, and erasing 8.

When recording information from the outer circumference to the inner circumference of the optical disc 3 using the CAV method, it is necessary to change the irradiation beam power between the inner and outer recording tracks, and the mode terminal w,
, w2. . . . mode signals sl, s2 . ....sn is input.

Therefore, in this case, the mode signal S1 is first input to the mode terminal W1, the address decoder 40 detects this mode and outputs the mode selection signal M1, and the voltage source 4
1 outputs a high recording mode voltage E1 necessary for the optical beam power.

After the recording mode voltage E1 is properly gain-adjusted by the amplifier 42, the automatic power control means 4
3, a constant laser power control voltage VC necessary for recording is temperature-compensated by the A20 circuit.
Form PI.

This laser power control voltage V c p + is simultaneously superimposed with write information WS and applied to the light emitting element 44. Next, by driving the light emitting element 44, the laser beam l modulated by the write information WS is optically A laser spot is transmitted through the system 2 and irradiated onto a recording track near the outer circumference of the optical disk 3. The laser beam reflected from the recording surface of the optical disk 3 is reproduced as an RF signal by a device (not shown), but the - section thereof is reflected by the polarizing beam splitter 22 and enters the light receiving element 51 of the detection circuit 5. , the light receiving element 51 outputs an electrical signal of a light receiving pattern indicating the focus state.

As is well known, the differential amplifier 52 converts the detection signals output from the light-receiving surfaces A, B, C, and D into (A+D), for example.
)-(B+C).

If the light receiving pattern is elliptical and the calculation result is not O, a focus error signal e proportional to the defocus state is output to the comparator 7.

Here, the triangular wave generator 6 receives the power control voltage V of the automatic power control circuit 43 at its input terminal 47.
CPI is input, and this voltage VCPI drives transistor Q3 via the operational amplifier OP of FIG. 3 described above, causing current i to flow.

Transistor Q+ of current mirror circuit 61.

The pair of output currents from Q2 are made equal in phase, and the capacitor C is charged with a current i equal to the above current i.

The electric charge charged in this capacitor C is connected to the base electrode of the switching transistor Q5 (A
) is instantaneously discharged in synchronization with the clock CLK. The output terminal 63 connected to the collector electrode of the transistor Q5 has a power control voltage V CP in the recording mode W.
A triangular wave v1 with a peak value proportional to I is shown in Fig. 4 (
It is output as shown in B).

This triangular wave vl is then input to the comparator 7.

The comparator 7 is at the H level at the sweep start point d1 of the triangular wave v1, but when it compares two inputs, that is, the error signal el and the triangular wave v1, and the two become equal, it switches to the L level and performs PWM modulation.

As the recording track of the optical disc moves toward the inner circumference, a control voltage is applied to reduce the beam power in stages, so the power control voltage Vcp of the automatic power control circuit 43 also changes from VCPI to VCP2.・・・・・・
The triangular wave generator 6 is gradually reduced to Vcp6.
The level of the triangular wave V output from vl also varies from vl to ■2.
. . . The beam power is gradually reduced in proportion to the change in beam power reduction.

At this time, the level of the error signal output from the detection circuit 5 also decreases step by step as shown in e2, for example, so the modulation degree of the PWM signal formed in the comparator 7 is almost constant, and the level of the error signal output from the detection circuit 5 is reduced in stages. The servo signal also becomes constant.

That is, the open loop gain G of the servo system 10 is given by the above formula, and if VB is kept constant, the amplitudes of the servo error signal e and the triangular wave v change in proportion to the laser power control voltage VCP, so the gain of the servo system is G has a constant value regardless of the laser power control voltage VCP, that is, regardless of the beam power.

That is, even if the beam power of the PWM modulation wave S waveform is changed by the laser output means 4, the modulation pulse width does not change as shown in FIG.

This pulse 72 train is supplied to the actuator 9 via the drive circuit 8, and the drive output is represented by the average DC voltage shown by the broken line in FIG.

On the other hand, when the recorded information is reproduced R9 or erased E, almost the same operation as in the above-mentioned recording W is performed as shown in FIG. 4(C) or (D). That is, during playback, the beam power is 176 at the time of recording W.
Therefore, the mode signal S is changed and the triangular wave generator 6 inputs a power control voltage VCP of about 1/6 of the recording W or a little higher, and is synchronized with the same clock CLK. lever voltage vcp
It outputs triangular wave 7 in the same figure (C) which is proportional to .

The comparator 7 compares the level of the triangular wave (1) with the error signal (e) proportional to the beam power shown in FIG.

That is, from the above equation, the open servo loop gain G during playback
is G = k-ve = K-vs = ・−・−・−v
, v2 = k - V a = constant.

Then, the PWM modulated wave is similarly supplied from the drive circuit 8 to the actuator 9, and the seven actuators are driven with the average DC voltage shown by the broken line in FIG.

Therefore, the actuator 9 is operated with a constant loop gain during reproduction R as well as during recording W. Note that during erasing E, a higher beam power is required than during recording, but the operating wave in this case becomes as shown in FIG. 4(D), and similarly, the open servo loop gain does not change.

In addition, in order to cope with sudden changes in beam power such as random access to the optical disk 3 and transition from recording W to reproduction R1 erasing E mode, this device has a constant loop gain in the servo system circuit. can be given.

In this embodiment, the focus servo system has been described, but it goes without saying that the servo gain can be adjusted in a similar manner for the tracking servo system. 41, and the mode voltage E le E 2 *・
... may be used to form the triangular wave V.

〔Effect of the invention〕

As explained above, according to the servo device in the optical disk information recording and reproducing apparatus of the present invention, a triangular wave signal generator proportional to the laser beam power is provided, and the output triangular wave converts the servo error signal into a PWM signal to drive the actuator. Because it is driven, a constant loop gain can always be given to the servo system with a simple circuit configuration, and the effect is that information can be recorded to or reproduced from an optical disc with high precision and stability. play.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the principle of a servo device in an optical disc information recording/reproducing device according to the present invention, FIG. 2 is a block diagram showing an embodiment of the device, FIG. 3 is a triangular wave generation circuit, and FIG. 4 (A) ,(B). (C) and CD) are waveform diagrams explaining each part signal, respectively.
FIG. 5 is a block diagram showing a conventional servo device. In the figure, l is a laser beam, 2 is an optical system, 3 is an optical disk, and 4
is a laser output means, 5 is a detection circuit, 6 is a triangular wave generator,
7 is a comparator, 8 is a drive circuit, 43 is an auto power control means, 44 is a light emitting element, e is an error signal, ■
indicates a triangular wave, MS indicates a PWM modulation signal, and DS indicates a drive signal. ■ Δ(Bututsutsumotofri) "bl, 7th recognition 1 Figure 1 Day rice cake pickled @ se page late row Figure 5

Claims (1)

[Claims] a laser output means configured to output a laser beam with a predetermined beam power; a detection circuit configured to detect reflected light from the optical disk and output a servo error signal; and a signal from the laser output means that is proportional to the beam power. a triangular wave generator that generates a triangular wave signal of a level; a comparator that compares the error signal with the triangular wave and PWM-modulates the error signal; and converts the PWM modulation signal output from the comparator into an appropriate drive signal. and an actuator driven by the drive signal, the optical disc information recording and reproducing device comprising: a drive circuit that drives the drive signal; and an actuator driven by the drive signal, and a predetermined servo error signal is supplied to the actuator even when the beam power changes. servo device.