JPH03130930A - Automatic focus adjuster for optical pickup - Google Patents

Abstract

PURPOSE:To smoothly determine the optimum adjusting position of an objective lens by cutting off to a frequency lower than the resonance frequency of an actuator and executing driver control when a focus servo loop is closed. CONSTITUTION:At the time of focusing, since the vibration of an objective lens 3 is remained while being affected by the frequency property of an actuator 4 and the focus servo loop of an optical pickup is hardly closed, a driver control circuit 16 is provided. The circuit 16 is operated to decrease the peak of the resonance frequency existent in the frequency property of the actuator 4 at the time of focus-in and composed of an LPF and a driver amplifier. The cut-off frequency of the LPF is set at a value lower than the resonance frequency of the actuator 4 and the excess vibration is reduced for the objective lens 3 to be vertically driven by a focus coil. Then, focusing operation can be started smoothly and speedily.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an information recording/reproducing apparatus for recording or reproducing information on an optical disc recording medium such as a CD (compact disc) or a VD (video disc), and particularly relates to an information recording/reproducing apparatus for recording or reproducing information on an optical disc recording medium such as a CD (compact disc) or a VD (video disc). The present invention relates to a device that automatically adjusts the gain of a focus servo loop of an optical pickup at the time of starting.

[Conventional technology]

For example, a CD player has a built-in focus servo device that focuses a reading light beam emitted from an optical pickup onto the information recording surface of the CD to form an appropriate light spot. In order for this focus servo device to function accurately, the focus servo loop gain of the optical pickup needs to be adjusted correctly.

Conventionally, the gain adjustment of the focus servo loop of an optical pickup has been manually performed at the time of shipment from the factory. However, manual adjustment is complicated.

Further, even if the optimum gain is set at the time of adjustment, the adjusted gain is not always optimum for all CDs used, and some CDs may deviate from the optimum gain. This is due to the fact that the pit shape, reflectance, degree of warping, etc. differ depending on the individual CDs used.

Therefore, recently developed digital servo devices are equipped with an automatic focus adjustment circuit that automatically adjusts the gain of the focus servo loop of the optical pickup according to the CD that is set before starting the CD playback operation (PLAY). It is being Note that the digital servo device includes not only focus control but also tracking control and spindle servo control.

As shown in FIG. 4, the automatic focus adjustment circuit adjusts the objective lens to CD by applying a focus drive signal C1 as shown to the actuator of the optical pickup.
The operation of approaching (up) and separating (down) from the information recording surface of The gain of the focus servo loop of the optical pickup is determined by sampling the signal EF, determining its maximum value, comparing it with a reference value, and bringing the deviation close to zero. In the automatic adjustment procedure, as shown in FIG. 4, the spindle motor is started to rotate the CD during a period Tt, and the CD is vibrated with a large adjustment amplitude A1 at a frequency f2 (for example, 50 Hz) during a period T. During vibration with this adjustment amplitude A+, automatic adjustment is performed as described above while taking the difference in focus error signal E a predetermined number of times, and then when focus-in is achieved, focus servo is performed. Therefore, period T can be said to be a startup period, T can be said to be an automatic adjustment period, and T3 can be said to be a focus servo period.

[Problem to be solved by the invention]

However, the problem with the conventional focus automatic adjustment circuit is that the automatic adjustment period T
The point is that the vibration of the objective lens is not smoothly attenuated and quickly converged to the in-focus position at the time of transition from to the focus servo period T3, that is, at the time of focus-in. This is because the actuator has a frequency characteristic as shown in Fig. 3(a), and the drive frequency during automatic adjustment by the automatic focus adjustment circuit (period T2) is, for example, 50Hz, but when the focus is in, the focus servo Even if the loop is closed, the actuator's resonant frequency f. This is because free vibration occurs due to the influence of , making it difficult to smoothly shift to focus-in.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an automatic focus adjustment device that can rapidly and smoothly transition from automatic adjustment to closing operation of a servo loop of an optical pickup during automatic focus adjustment.

[Means to solve the problem]

In order to solve the above problems, the present invention drives the actuator of the optical pickup at a predetermined frequency and a predetermined amplitude in order to adjust the servo loop gain of the objective lens of the optical pickup to a focused position with respect to the information recording surface. In an automatic focus control device for an optical pickup, the automatic focus control device outputs a focus drive signal to output a focus drive signal, and then closes a focus servo loop when the objective lens is located near the in-focus position, at least at the time when the focus servo loop closes. The actuator is configured to include a driver control circuit that outputs a drive signal whose cutoff frequency is set to a frequency lower than the resonance frequency of the actuator and whose high frequency components are attenuated.

[Effect]

According to the present invention, the driver control circuit outputs the drive signal to the actuator at least when the focus servo loop of the optical pickup is closed. This drive signal has a cutoff frequency at a frequency lower than the resonant frequency of the actuator, and has a characteristic that the signal level on the high frequency side is attenuated. As a result, the speed amplitude that increases at the resonant frequency point of the actuator is suppressed by the drive signal, and the signal peak at the time of resonance is reduced due to the frequency characteristics of the actuator.

Therefore, the objective lens does not vibrate excessively during focus-in, and the transition to focus-in is performed quickly and smoothly.

〔Example〕

Next, embodiments of the present invention will be described based on the drawings.

FIG. 1 shows an outline of an automatic focus adjustment device for an optical pickup according to the present invention. CD1 is spindle motor 2
is rotated a predetermined number of times.

The optical pickup PU, which is disposed facing the information recording surface of the rotated CDI, records while sequentially tracking the information tracks of the CDI from the inner circumferential side to the outer circumferential side in the radial direction of the CDI by a carriage mechanism (not shown). The information is read optically and the reading light is converted into an electrical signal R.
Convert to F and output. This electric signal RF is sent to an RF amplifier (not shown) and processed in an audio reproduction system.

On the other hand, the optical pickup PU includes, for example, four divided light receiving elements for focus detection, and an electrical signal is output from each divided light receiving element. This electrical signal is given to the focus error detection circuit 5. The focus error detection circuit 5 generates a focus error signal E by calculating a difference signal between the input electrical signals. The generated focus error signal E, is the VCA
(variable voltage control amplifier) to the A/D converter 7. The A/D converter 7 converts the input focus error signal E into corresponding digital data and sends it to the system controller 8.

The system controller 8 controls the automatic focus adjustment according to the present invention according to a preset program.
It executes normal focus servo control and control necessary for the operation of the CD player.

The automatic focus adjustment is performed by the system controller 8 and the automatic focus adjustment circuit 9 according to the procedure shown in FIG. That is, when the spindle motor 2 is started during the period T1 and reaches a predetermined rotation speed, the automatic adjustment period T
2, the system controller 8 samples the peak value of the focus error signal EF, determines the difference between the maximum value of the sampled data and the reference value, and outputs a control signal corresponding to the difference to the automatic focus adjustment circuit 9. . The automatic focus adjustment circuit 9 is the system controller 8
The gain control signal CG is set to V by the control signal from
Output to CA6. The VCA 6 changes the gain using the gain control signal CG. Thereafter, the changeover switch 13 is changed over at a corresponding timing by a changeover signal C5 from the system controller 8. Adjustment amplitude A of focus drive signal CF during this automatic adjustment period T2
I has a large amplitude as shown in FIG. 4, and the focus error signal EF at that time is detected by the focus error detection circuit 5 and applied to the VCA 6. Based on the focus error signal EF, the system controller 8 sequentially samples each amplitude, and determines the deviation between the maximum value of the sampling data and the reference value, and the automatic focus adjustment circuit 9
Output to. The automatic focus adjustment circuit 9 feeds back the deviation to the VCA 6 as a gain control signal CG.

The VCA 6 performs gain control based on the gain control signal CG. Next, the focus error signal E
, passes the zero cross point corresponding to the in-focus position, the system controller 8 outputs a switching control signal C3 to the changeover switch 12, and also outputs the changeover control signal C3 to the changeover switch 12.
3, the changeover switch 13 is turned on by outputting the changeover control signal C3 as a focus-in command.
The changeover switch 12 is set to 0FFL, and an operation stop command is output to the automatic focus adjustment circuit 9.

After that, the focus error signal EF is detected by the focus error detection circuit 5, and the A/D converter 7 detects the focus error signal EF.
After the D conversion, the objective lens 3 is controlled and driven by the PWM circuit ↓0, the changeover switch 13, the driver control circuit 16, and the actuator 4 in a focus servo loop.

Now, during this period, when switching from T2 to T3, that is, when focus is in, vibration of the objective lens 3 remains due to the influence of the frequency characteristics of the actuator 4 shown in FIG. 3(a), and the focus servo loop of the optical pickup is closed. As mentioned earlier, it is difficult. Therefore, in this example,
A driver control circuit 16 is provided. This driver control circuit 16 controls the actuator 4 at the time of focus-in.
The resonant frequency f that exists in the frequency characteristic of . (about 14-18
Hz).

Details of this driver control circuit 16 are shown in FIG.

As shown in FIG. 2, the driver control circuit 16 has a PW in response to switching of the changeover switch 12 or 13 from 0N10FF by the changeover control signal C3 during focus-in.
A pulse signal from the M circuit 10 or a pulse signal from the PWM circuit (pulse generating circuit with frequency f2) 15 is input.

The driver control circuit 16 is composed of a driver amplifier DR connected to a capacitor C for a low-pass filter, input resistors R, R, R2345, and a feedback resistor R6 for gain setting, and a low-pass filter LPF is connected to the input side. has been done.

The low-pass filter LPF is composed of a resistor RSR2, a capacitor C1, and a switch SW that is turned on at least at focus-in (preferably, immediately before focus-in). The cutoff frequency f of this low-pass filter LPF is lower than the resonance frequency f of the actuator 4 (approximately fo/
2=7 to 9Hz). In this case, the cutoff frequency f is expressed as The attenuation amount is set to a gain G that is, for example, 3 [db] lower than the gain G during normal focus servo expressed as R6/R4. This gain G2 is expressed as.

Next, the operation will be explained.

During the automatic adjustment period T2, the changeover switch 12 is ON.
, selector switch 13 is OFF, selector switch SW is also OFF
It is F. Therefore, the pulse signal from the PWM circuit 15 is amplified by the driver amplifier DR and given to the focus coil 14 as the focus drive signal C1. At this time, the objective lens 3 is vibrated as shown in FIG. 4, and the focus gain is adjusted.

Next, at focus-in time (or just before focus-in), the changeover switch SW is turned on to turn on the low-pass filter LPF, and the changeover switch 13 is turned on to close the servo loop of the optical pickup, and then , the changeover switch 12 is turned off and the PWM circuit t
5 is disconnected from the driver circuit 16. At this time, the system controller 8 operates the PWM circuit ■5. It is preferable to control the oscillation to stop the oscillation.

At this time of focus-in, the resonance frequency f in the characteristics of the actuator 4 is
The peak component near o is suppressed, and the focus coil 14
will operate with the characteristics shown by the solid line in FIG. 3(C). Therefore, the focus coil 14 with this characteristic
The objective lens 3, which is driven vertically by the lens, has little excessive vibration due to resonance, and can smoothly and rapidly shift to focus-in operation.

In the above explanation, the most preferable timing is to turn on the low-pass filter LPF at the time of focus-in (or slightly before that), but the low-pass filter LPF is turned on in advance at a point even earlier than the time of focus-in. There is no practical problem even if the

Furthermore, although the above explanation uses a CD player as an example,
LvD players also require focus adjustment, and the present invention can be applied to automatic focus adjustment in that case.

〔Effect of the invention〕

As described above, according to the present invention, when the focus servo clones from the automatic focus adjustment of the objective lens, the resonance characteristics of the actuator are reduced by the actuator control circuit, so unnecessary excessive vibration can be suppressed rapidly. Moreover, it becomes possible to smoothly determine the optimal adjustment position of the objective lens.

[Brief explanation of the drawing]

Fig. 1 is a schematic block diagram showing an embodiment of the present invention. Fig. 2 is a detailed circuit diagram showing an embodiment of the invention. Fig. 3 is an operational characteristic diagram of the actuator and driver control fill path. Fig. 4 is a focus automatic It is an explanatory diagram of adjustment. 1...CD 2...Spindle motor 3...Objective lens 4...Actuator 5...Focus error detection circuit 6...VCA 7...A/D converter 8...System controller 9 ... Focus automatic adjustment circuit 10 ... PWM circuit 11 ... Actuator control circuit ■2 ... Changeover switch 13 ... Changeover switch 14 ... Focus coil 15 ... PWM circuit A1 ... Adjustment Amplitude CG... Gain control signal C1... Focus drive signal C3... Switching control signal DR... Driver amplifier E,... Focus error signal LPF... Low pass filter PU... Optical pickup SF. ...Focus servo signal SW...selector switch

Claims (1)

[Claims] In order to automatically adjust the servo loop gain for controlling the objective lens of the optical pickup to a focused position, a focus drive signal that drives the actuator of the optical pickup at a predetermined frequency and a predetermined amplitude is provided. In the apparatus for automatically controlling the focus of an optical pickup so as to close a focus servo loop when the objective lens is located near the in-focus position, the actuator 1. An automatic focus adjustment device for an optical pickup, comprising: a driver control circuit that outputs a drive signal in which a cutoff frequency is set to a frequency lower than a resonance frequency and high frequency components are attenuated.