JPH06274903A - Optical head controlling device - Google Patents

Abstract

PURPOSE:To obtain an optical head controlling device being excellent in a highly accuracy, stability and reliability by improving the delay of response in the digital servo control of an optical head and an error accompanied by a separated value control. CONSTITUTION:In this device, sampling data sampled at every constant period are inputted to a prediction unit 40 from a data register 39 and a prediction value of a next period is estimated and a digital servo control is performed by correcting predict-ed value to a limiting value when the predicted value exceeds the limiting value set in a limiting value generating part 45. Furthermore, the limiting values are made so as to be changed by sampling data at every previous period via the register 39. Thus, the optical head controlling device being excellent in a highly accuracy and reliability is obtained by improving the delay of the response in the digital servo control and the error accompanied by the separated value control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to control of an optical head of an optical disk device, and more particularly to an optical head control device for performing servo control of the optical head by a digital signal.

[0002]

2. Description of the Related Art An optical disc has a high recording density and is capable of large-capacity recording. However, the track pitch is 1-2 μm
Since the rotating disk is displaced due to surface wobbling and eccentricity, it is necessary to control the positioning of the light spot on the target track with high accuracy. For example, a method is used in which the light is incident on an objective lens integrated with an actuator via, for example, to narrow down a minute light spot on the optical disc. The position control of the light spot is performed by detecting the focus and radial positions of the light spot with a photodetector and servo-controlling the objective lens actuator based on the detected values.

The structure and control of this optical head controller will be described below with reference to FIGS. 4 to 9.

In FIG. 4, 1 is an optical disk, 2 is a spindle motor for rotating the optical disk, and 3 is an optical head.

The optical head 3 is composed of a mechanism section and an optical section, and the mechanism section has an objective lens 4 for condensing light on the recording surface of the optical disc and a direction perpendicular to the surface of the optical disc 1 (hereinafter referred to as the objective lens 4). , An objective lens actuator 6 that is integrally formed with an actuator 5 that drives in a focus direction) and a disk radial direction (hereinafter, referred to as a tracking direction).

The optical section is composed of various prisms including the semiconductor laser 7 and a sensor.
The light from is converted into parallel light by the collimator lens 8, and then is transmitted through the deflecting beam splitter 9 to the objective lens 4
To form a minute spot on the optical disk 1.
The reflected light from the optical disk returns to the objective lens 4 again, and the deflected beam splitter 9 changes the optical path thereof by 90 degrees. This light is separated by the deflecting beam splitter 10 into S-polarized light and P-polarized light. The S-polarized light is optically detected by the sensor 12 divided into a plurality of light receiving surfaces in order to detect the positional deviation of the light spot in the focus direction via the astigmatism lens 11. The P-polarized light is detected by the sensor 14 via the lens 13 for detecting the positional deviation of the light spot in the tracking direction.

Signals from the sensors 12 and 14 are processed by a focus servo control unit 15 and a tracking servo control unit 16 and become a focus direction position control signal 17 and a tracking direction position control signal 18 to drive the objective lens actuator 6. , The position control of the objective lens is performed.

On the other hand, the signals from the sensors 12 and 14 are also used for the detection of information signals, and these signals enter the information signal detection section 19 and, after being detected, are composed of a modulation / demodulation circuit and an error correction circuit. Signal processing such as modulation / demodulation and data error correction is performed by the processing circuit 20, and the signal is sent to the host device such as a personal computer through the interface control unit 21.

In the figure, reference numeral 22 denotes a controller which controls the sequence of these blocks and also controls the access / laser control unit 23 and the spindle motor control unit 24.

Next, the focus servo control unit 15 and the tracking servo control unit 16 for controlling the objective lens actuator 6 will be described.

The control of the optical head has heretofore been performed by servo control using analog signals, but recently, with the speeding up of digital arithmetic processing processors, low-priced ones have become available, and servo control has become possible. Digital servo control, which converts part of the loop into a digital signal for processing, is beginning to be adopted.

The digital servo control is not only susceptible to the influence of circuit noise and offset in the servo loop, but also various control parameters of the servo can be freely set and changed, and the circuit can be downsized, resulting in reliability. It is a control method that has features such as high performance and is expected to expand its application range in the future. Here, the control of the optical head by this digital servo will be described.

In controlling the optical head 3, focus,
The tracking servos are basically controlled by individual servo control loops. Here, the focus servo control unit 15 of the objective lens actuator 6 will be described with reference to FIG.

In the figure, reference numeral 25 is an error detection unit for converting a signal from the objective lens position detection sensor 12 in the optical head 3 to generate an error signal for servo control. The signal converted by the error detector 25 is converted into a 5 to 16-bit digital signal by an A / D converter 26 including a sample holder. This digital signal is processed by the arithmetic processing unit 2
Various operations are performed at 7. Normally, the arithmetic processing unit 27 is performed by software using a digital signal processor (hereinafter referred to as DSP) or a microprocessor.
The signal arithmetically processed by the arithmetic processing unit 27 is again converted into an analog control signal by the D / A converter 28, and the drive signal for focus control of the objective lens actuator 6 by the drive amplifier 29 (position in the focus direction in FIG. 4). The position of the objective lens 4 is controlled by being converted into a control signal 17).

Here, the arithmetic processing unit 27 performs offset adjustment, gain adjustment, filtering processing, and the like. In the offset adjustment, the offset adjustment of the low frequency component of the D / A converted digital error signal is performed, and the focus is adjusted. This is performed for the preprocessing of correcting the error signal and performing the numerical calculation of the digital filter. Gain adjustment is
The loop gain is set for tracking servo control. The filtering process is performed to compensate the mechanical characteristics of the objective lens actuator 6, and is usually a process for stabilizing the servo system by performing calculation processes such as phase lead compensation and phase delay compensation. By the processing by these software, the focus error detection signal is converted into the feedback control signal of the objective lens actuator 6 and becomes the focus direction position control signal 17 for driving the objective lens 4 in the focus direction.

Next, the flow of data conversion by digital servo control will be described with reference to FIG.

In the digital servo control, the error signal 31 is sampled at a constant cycle T. The sampling period T is determined by the control specifications and the characteristics of the control target. Sampling is executed at a constant cycle T, and for example, at the sampling time point kT, the signal A (k) is taken in as data and converted into a digital signal by A / D conversion. This data is the offset processing described above,
The drive signal 30 for the objective lens actuator 6 is set after gain setting and filtering are performed and D / A conversion is performed.
Is sent as. Then, by repeating this, continuous servo control can be performed. Further, it is possible to perform the optimum control by incorporating the correction control for the environmental change and the characteristic change of the optical head 3 as an intermittent process in the repeated sampling control.

[0018]

In such a conventional digital servo control, a predetermined sampling period T
Although data sampling is performed in, the sampled data requires a predetermined time for A / D conversion and filtering. That is, a certain time delay occurs from the time when the data is captured until the drive signal 30 is transmitted.

For example, in FIG. 7, the data A (k) sampled at the sampling time point kT is transmitted as the digitally processed control signal B (k) after Δt time, which is calculated at the next sampling time point (k + 1) T. It is held until the end of processing. However, at the time of the next (k + 1) T + Δt from the time when the time t has elapsed from the time kT, the error signal 32 is at the level 3 at the time when the sampling is already performed.
The value is different from 3, which causes a problem that more precise control cannot be performed.

For such a problem, it is necessary to minimize the time delay and shorten the sampling cycle T as much as possible, but there is a limit to these measures. For example, in an optical disk device for data storage, 1800-3600r
Although the optical disc 1 rotates at pm, a sampling frequency of 20 to 100 kHz is required for the objective lens actuator 6 to follow the surface runout and eccentricity of the optical disc 1 due to this rotation. Recently, a DSP capable of high-speed calculation has been commercialized, and an A / D converter having a short conversion time and the like can be obtained, but there is a limit to the adoption of these in consideration of cost and the like.

As a countermeasure against this, a method of predicting the next sampled data value and using this to perform control can be considered. This is because, as shown in FIG. 8, at the sampling time point kT, the sampling data A (k-1) at the previous (k-1) T time point and the sampling data A (k) at the kT time point.
And the data at the next (k + 1) T time point is predicted by extrapolation or the like, and this predicted value C (k + 1) is used as the next sample data, and the sampling data at the time point kT is sampled data A (k) and sample data C This is a method of setting the intermediate value 34 of (k + 1). According to this, the value of the error can be reduced, and the influence of the time delay can be reduced.

However, in this method, the error signal 35
Is effective when falling from the (k-1) T time point to the kT time point, but is effective when the error signal 35a rises as shown in FIG. And k
Sampling data A (k) and prediction value C (k + 1) based on the sampling data A (k-1) at time T and (k + 1) predicted value C (k + 1) at time T
If the intermediate value 34a of is the predicted value at time (k + 1) T,
There is a problem that a large error occurs between the predicted value 34a and the actual value A (k + 1), and the stability of servo control is impaired.

Further, in Japanese Patent Laid-Open No. 61-162837, an optical pickup is compared by comparing a focusing signal when accessed by a reference optical pickup with a focusing signal when accessed by an optical pickup to be discriminated. The method of determining whether the optical pickup is good or not is performed and whether the error of the optical pickup is within an allowable range, that is, the quality of the optical pickup is determined. With this configuration, if there is a difference in the focusing signal value, it is the characteristic of the optical pickup.
That is, it is caused by the inclination of the laser optical axis, the inclination of the reflected light detection system, the error due to the characteristics of the optical pickup drive system, and the like. Therefore, if the difference between the focusing signal values is a certain reference value or more, it is determined that the optical pickup used for the determination is a defective product, which is a method for sorting the optical pickup into a good product and a defective product. It was

The present invention solves the above problem, and provides an optical head controller which is highly accurate and highly reliable, in which the influence of control delay in digital servo control is reduced to reduce the discretization error. Has an aim.

[0025]

In order to solve the above problems, the present invention provides a digital servo control device for an optical head, which samples the position detection signal of the objective lens at regular intervals to control the position of the objective lens. Then, the sample value of the next cycle is estimated by the sampling value of at least one cycle, and the estimated value or a value converted from the estimated value is fed back as a predicted value to perform the digital servo control operation, and the estimated value Alternatively, the predicted value is provided with a limit value, and the limit value is made variable.

In addition, the limit value is determined from the maximum value of a plurality of sample values sampled in the past or a conversion value from the maximum value, and the limit value is sequentially updated.

[0027]

In the above structure, even if the predicted value estimated from the sampling value of at least one cycle or earlier is greatly deviated from the error signal, the deviation is suppressed by setting the upper and lower limit values to the predicted value. To be done.

Further, by changing the limit value to a limit value that can be estimated from the current operating state based on the immediately preceding data, the deviation between the predicted value and the error signal is minimized.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.
Will be described with reference to.

In this embodiment, focus servo control,
The present invention can be applied to any control such as tracking servo control and optical head access control, but in this embodiment, focus servo control will be described as an example.

The same parts as those described in the conventional example will be described with the same reference numerals. In FIG. 1, 3 is an optical head including an objective lens actuator 6. A position detection signal from the focus position detection sensor 12 in the optical head 3 is sent to the error detection unit 37 and converted into an error signal for focus servo control. This signal is sent to the A / D converter 38 and converted into a digital signal. The digital signal is usually converted into a signal of 5 to 16 bits, and the number of bits is determined by the specifications of the servo and the characteristics of the controlled object. This digital signal is sent to the data register 39
Sent to. The data register 39 is loaded with k
Sampling data at time T and (k-1) one cycle before
The sampling data of some previous cycles such as the time T are held, and these sampling data are transferred to the next predictor 40. In the predictor 40, based on these sampling data, (k +
1) The predicted value at time T is estimated by linear extrapolation or the like, and the predicted value is sent to the next arithmetic processing unit 41 as output data at time kT. The arithmetic processing unit 41 performs processing such as data offset adjustment, gain adjustment, and filtering processing. The offset adjustment of the data is performed for the purpose of adjusting the offset of the low frequency component due to an external factor of the error signal and the convenience of calculation for performing the filtering process. The gain adjustment is to set the gain of the servo system, and is set to a predetermined value so that the objective lens actuator 6 can follow the surface wobbling of the optical disc 1. The filtering process is a phase compensation process for compensating the mechanical characteristics of the objective lens actuator 6, and is intended to improve the frequency characteristics.

The signal digitally processed by the arithmetic processing unit 41 is converted into an analog signal by the D / A converter 42, and the drive amplifier 43 uses the actuator 5 as a position control signal in the focus direction of the objective lens actuator 6.
Sent to. The loop 44 including these control units serves as a focus servo control loop, and feedback control is performed.

On the other hand, the signal converted into a digital signal and taken into the data register 39 is sent to the limit value generating section 45. The limit value generation unit 45 is for storing the maximum value of the error signal so far, and sends the limit value based on this maximum value to the predictor 40 to limit the amplitude of the predicted value.

Next, the limit value processing will be described with reference to FIG. In the figure, 46 is an error signal, and 47 is a final predicted value obtained by sampling and processing the error signal 46 in each cycle.

Now, the sampling data A (K) sampled at the time point kT and the sampling data A (k−) sampled at the time point (k-1) T one cycle before
Based on 1), the predicted value C at the (k + 1) T time point after one cycle
Calculate (k + 1). This sampling data A
(K) and sampling data C (k + 1), k
The processed data at time T is the intermediate value D (k) between them, that is, ((A (k) + C (k + 1)) / 2). However, since the intermediate value D (k) exceeds the limit value 48 set by the limit value generation unit 45 from the sample data so far, the predicted value 47 is limited by the level of the limit value 48 and the limit value 48. It becomes E (k), and this is sent to the next arithmetic processing unit 41 as the final predicted value. This allows
It is possible to prevent the data obtained from the prediction calculation from becoming an abnormal value due to a cause such as a calculation rule.

The limit value generator 45, as shown in FIG.
The determination unit 49 includes a maximum value holding unit 50, a conversion unit 51, a data holding unit 52, and the like. The determination unit 49 converts the sampled digital data 53 into data held by the maximum value holding unit 50, that is, a limit value. If it is smaller than this, the digital data 53 is sent to the servo loop 44 via the conversion unit 51. If the sampling data is larger than the limit value held by the maximum value holding unit, the limit value held by the maximum value holding unit is sent to the servo loop 44 via the conversion unit 51. As a result, the control shown in FIG. 2 can be performed.

The maximum value holding unit 50 takes in the maximum value in the data of the data holding unit 52, and this value can be sequentially changed as a limit value. The data holding unit 52 holds some sampling data in the past cycle, and the clock 55 sequentially updates the data group. The clock 55 may use any signal, but if the capacity of the data holding unit 52 is allowed, for example, data for one rotation of the optical disc 1 may be used. This is because the surface wobbling of the optical disc 1 becomes a basic signal component synchronized with the rotation cycle of the optical disc 1.
This is because the focus error signal component also conforms to this.

Although the maximum value of the sample data is used as the limit value in the present embodiment, it may be converted into another value based on this maximum value by the conversion unit 51 shown in FIG.
For example, a value that is α times the maximum value can be set as the limit value. Alternatively, since it is possible that the maximum value is an abnormal value due to external vibrations, in such a case, even if the data holding unit 52 performs processing such as deleting the abnormal value without using the maximum value itself. Good. In addition, the data holding unit 52
It is also possible to use the data obtained by performing the statistical processing of the above data.

As described above, the limit value can be sequentially determined by a method adapted based on the past data, and more accurate predictive control can be performed.

[0040]

As is apparent from the above description of the embodiments, according to the present invention, the influence of the discretization error can be reduced by reducing the influence of the control delay in the digital servo control. The position can be controlled with high accuracy.

Further, since the limit value of the predicted value can be changed according to the environmental conditions and the characteristics of the disk used, more stable control can be performed. With this, high precision, stability,
An optical disc device with excellent reliability can be provided.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing the configuration of a focus servo control unit of an optical head according to an embodiment of the present invention.

FIG. 2 is a signal characteristic diagram of the same prediction value detection.

FIG. 3 is a block circuit diagram of the limit value generation unit.

FIG. 4 is a block circuit diagram showing a configuration of an optical disc device.

FIG. 5 is a block circuit diagram showing the configuration of a focus servo control unit of a conventional optical disc device.

FIG. 6 is a signal characteristic diagram showing a data sampling method in the digital servo control.

FIG. 7 is a signal characteristic diagram of the same prediction value detection.

FIG. 8 is a signal characteristic diagram of the same prediction value detection.

FIG. 9 is a signal characteristic diagram of the same prediction value detection.

[Explanation of symbols]

 1 Optical Disc 3 Optical Head 4 Objective Lens 6 Objective Lens Actuator 39 Data Register 40 Predictor 45 Limit Value Generation Unit 47 Predicted Value 50 Maximum Value Holding Unit 51 Conversion Unit 52 Data Holding Unit

Front page continuation (72) Inventor Koji Muraoka 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A digital servo control device for an optical head, which samples a position detection signal of an objective lens at regular intervals to control the position of the objective lens, wherein a sample of a next period is obtained by a sampling value of at least one period before. A value is estimated, the estimated value or a value converted from the estimated value is fed back as a predicted value to perform a digital servo control operation, a limit value is provided for the estimated value or the predicted value, and the limit value is variable. An optical head control device characterized in that 2. The limit value is determined from the maximum value of a plurality of sample values sampled in the past or a conversion value from the maximum value, and the limit value is updated sequentially. Optical head controller.