JPH06203390A - Optical disk - Google Patents

Abstract

(57) [Summary] [Purpose] The servo compensation function can be optimized according to the control situation, and a high-bandwidth stable servo control means is realized. [Structure] An optical pickup 4 for scanning a track of an optical disc 1 with an optical spot and outputting a signal generated from the scanning.
A focusing error signal detecting means 18 for detecting an error signal from the signal, a focusing servo high frequency band compensating means 67 of an analog circuit for outputting a first control signal 68 from the error signal, and a second from the error signal.
Focusing servo low frequency band gain increasing means 78 of the digital circuit for outputting the control signal 57, control signal adding means 69 for adding the first and second control signals and outputting a third control signal, and a third Focusing actuator drive means 27 for driving the optical pickup 4 under the control of the control signal (1).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device used as external storage means of a computer.

[0002]

2. Description of the Related Art Generally, an optical disk device is a storage means for writing or reading information on a track by irradiating a laser beam on pits on a spiral track engraved on the optical disk. The laser light emitted from the semiconductor laser is condensed on the track by the action of optical parts such as an objective lens and a prism arranged on the optical path, and forms a light spot with a diameter of about 1 μm. The light spot must be constantly scanning a track having a width as small as 1 to 2 μm.

However, since the optical disc has a warp of the disc surface of about 200 μm and a track eccentricity of about 50 μm, the track moves greatly as the disc rotates. Therefore, in order to collect and follow the light spot on the target track, it is necessary to drive and control the objective lens by using two systems of servo means, a focusing servo and a tracking servo.

That is, the focusing servo means focuses the laser light on the surface of the track of the disk.
The objective lens is driven in the direction normal to the surface of the disc to control the position of the focal point of the light spot, and the tracking servo means moves the objective lens to the radius of the disc so that the light spot scans along the center of the track meandering. Direction control is performed to control the position of the light spot.

Two actuators used to drive the above-mentioned objective lens, a sensor for detecting the position of the light spot and other optical parts, a carriage for mounting them, and a linear drive for driving the carriage in the radial direction of the disk. A mechanism including an actuator is called an optical pickup.

Next, the structure of the optical pickup schematically shown in FIG. 10 will be specifically described. In the figure, reference numeral 1 designates an optical disk in which tracks 2 having a width of 1 to 2 μm are spirally formed in the circumferential direction. A pit is formed on the track 2, and an address signal, a data signal, and the like are recorded therein as changes in reflectance and magnetization polarity. A spindle motor 3 rotates the optical disk 1 chucked on the upper surface at a high speed of several thousand revolutions per minute.

Reference numeral 4 denotes the above-described optical pickup, which includes a semiconductor laser 6 for emitting a laser beam 5, an objective lens 8 for condensing the laser beam 5 to form a light spot 7 on the track 2, and a track 2 A sensor 10 that detects a position signal and a data signal of the light spot 7 from the reflected light 9 of the above, a focusing actuator 11 and a tracking actuator 12 that drive the objective lens 8 as described above, and a carriage that accommodates and moves the above components. 13 and a linear actuator 14 that drives the carriage 13 in the radial direction of the optical disc 1 to move the light spot 7 between the tracks 2.

As shown in FIG. 11, conventionally, both of the above-mentioned servo means are composed of analog circuits by operational amplifiers such as operational amplifiers. FIG. 11 is a schematic configuration diagram in the case where the servo control means of the light spot in the optical disc device is configured by an analog circuit.

In the figure, 15 is a current-voltage converting means, which converts a weak current signal 16 detected by the sensor 10 into a voltage signal 1
Convert to 7. Reference numeral 18 is a focusing error detecting means for receiving the voltage signal 17 and outputting a focusing error signal 19, and 20 is a tracking error detecting means for receiving the voltage signal 17 and generating and outputting a tracking error signal 21.

As will be described later, 22 is a focusing servo compensating means for advancing the phase of the focusing error signal to increase the gain in the low frequency band, and 23 is also a tracking servo compensating means which operates similarly. Both of these compensating means ensure the stability of the servo means and have a frequency characteristic that obtains a desired follow-up characteristic even when disturbance vibration is applied to the optical disk device.

Numerals 24, 25 and 26 are 3 respectively described below.
It is a control signal for one actuator driving means.
27 is a focusing actuator driving means, 28 is a tracking actuator driving means, and 29 is a linear actuator driving means. These focusing actuator drive means 27, tracking actuator drive means 28, linear actuator drive means 29
Receives the control signals 24, 25, 26, respectively, and outputs actuator drive signals 30, 31, 32 to the respective actuators to drive them.

As can be seen from the above description, the focusing servo means is the focusing error detection means 18
And a focusing servo compensating means 22, a focusing actuator driving means 27, and a focusing actuator 11. The tracking servo means is a tracking error detecting means 20, a tracking servo compensating means 23, a tracking actuator driving means 28, and a tracking actuator. 12 and further includes a linear actuator driving means 29 for driving and controlling the linear actuator 14.

Next, FIGS. 12 and 15 show examples in which the control means shown in FIG. 11 is constituted by an operational amplifier.
FIG. 12 shows a configuration example of the focusing servo means, and FIG. 15 shows a configuration example of the tracking servo means.
In FIG. 12, 10 is a four-division light-current conversion element S.
It is a sensor using 1, S2, S3, S4 (hereinafter referred to as a sensor element).

Each of the four sensor elements independently generates an electric current proportional to the light intensity of the reflected light 9 from the optical disk 1 which is incident. Reference numeral 15 is a current-voltage conversion means (amplifier), which converts the weak current signal 16 output from the sensor 10 into a voltage signal 17. Reference numeral 18 is a focusing error detecting means corresponding to the focusing error detecting means 18 of FIG. 11, and a voltage signal 17 from each sensor of the sensor 10 is provided.
Are added and subtracted to generate a focusing error signal 19. 33 and 34 are adders, and 35 is a subtractor.

Here, the principle of detecting the focusing error signal 19 will be briefly described with reference to FIG. FIG. 13 is a diagram showing changes in the shape of the disc reflected light 9 on the surface of the sensor 10 with respect to the distance between the light spot and the disc surface when the astigmatism method is used as the focusing error detection method. As shown in FIG. 13A, when the light spot 7 is focused on the surface of the track 2, the reflected light 9 on the sensor 10 has a circular shape.

However, as shown in FIG. 13B, when the light spot 7 is focused on a position far from the surface of the optical disc 1, the shape of the reflected light 9 is the sensor element S1 and the sensor element S.
It becomes an ellipse having a major axis in the direction of 3. Also, FIG. 13 (C)
As shown in FIG. 5, when the light spot 7 passes through the surface of the track 2 and is focused too close to it, the shape of the reflected light 9 becomes an ellipse whose major axis is in the direction of the sensor elements S2 and S4.

Therefore, the voltage signal 17 from each of the sensor elements S1 and S3 shown in FIG. 12 and the voltage signal 17 from each of the sensor elements S2 and S4 are added respectively, and the sum signals of both are subtracted. As a result, the change in the amount of light is enlarged, and a focusing error signal indicating whether the light spot 7 shown in FIG. 11 is on the surface of the track 2 or is too close or far can be obtained.

Reference numeral 22 is a focusing servo compensating means, and its constituent element 36 is a phase advancing circuit for advancing the phase of the focusing error signal by about 60 degrees in the band from 500 Hz to 5 kHz. Further, 37 is a low frequency band gain increasing circuit for increasing the gain of the focusing error signal from 50 Hz to 500 Hz. Reference numeral 27 is a focusing actuator driving means for supplying a current according to the control signal 24 to the focusing actuator 11.

In order to allow the light spot 7 to follow the surface of the track 2 without deviation by the focusing servo means having the above-described structure, the focusing servo means has a specific open-loop frequency characteristic. Must meet specifications. FIG. 14 shows an open loop frequency characteristic curve diagram of the focusing servo means of the conventional optical pickup.

In FIG. 14, the upper characteristic curve is a phase characteristic curve and the lower characteristic curve is a gain characteristic curve. F1 shown in the figure is a phase characteristic curve of the focusing actuator 11 shown in FIG. 12, and F2 is a phase advance circuit 3.
6 is a phase characteristic curve of F6, and F3 is a low frequency band gain increasing circuit 3
7 is a phase characteristic curve, F4 is a gain characteristic curve of the focusing actuator 11, F5 is a gain characteristic curve of the phase advance circuit 36, and F6 is a gain characteristic curve of the low frequency band gain increasing circuit 37.

In the gain characteristic curve, the hatched area is called a required gain, which is determined by the rotation frequency of the optical disk 1 and the external vibration applied to the optical disk device. The open loop gain curve must cover this required gain area. Further, in order to secure the stability of the servo means, the phase margin θ at the gain intersection frequency fc at which the open loop gain curve becomes 0 dB needs to be about 50 degrees or more. The fc in the focusing servo means of the conventional optical disk device is about 1 kHz.

In the conventional focusing servo means, the phase advancing circuit 36 and the low frequency band gain increasing circuit 37 are used in order to clear the above specifications. That is, the phase margin θ is secured by superimposing the phase characteristic curve F1 of the focusing actuator 11 and the phase characteristic curve F2 of the phase advance circuit 36. The required gain requirement is cleared by superimposing the gain characteristic curve F4 of the focusing actuator 11 and the gain characteristic curve F6 of the low frequency band gain increasing circuit 37.

Next, the conventional tracking servo means will be described. FIG. 15 is a schematic configuration diagram of the tracking servo means. In FIG. 15, the sensor 10 and the current-voltage conversion means 15 are the same as those of the focusing servo means. Reference numeral 20 denotes a tracking error detecting means, which is each sensor element S1, S2, S3, S of the sensor 10.
4, the voltage signal 17 output from the current-voltage conversion means 15 is added and subtracted to obtain the tracking error signal 21.
Is generated and output. 38 and 39 are adders, which are 4
0 is a subtractor.

Here, the principle of detecting the tracking error signal will be briefly described with reference to FIG. FIG. 16 shows the distance between the center of the light spot 7 and the center of the track 2 when the push-pull method is used as the tracking error detection method, and the disc reflected light 9 on the surface of the sensor 10.
It is a figure which shows the relationship with the shape of. The amount of reflected light 9 on the sensor 10 is determined by the reflected light at the center and the diffracted light on both sides thereof. As shown in FIG. 16A, when the light spot 7 is completely on the track 2, the reflected light amount on the sensor 10 is symmetrical.

However, as shown in FIGS. 16 (b) and 16 (c), when the center of the light spot 7 deviates from the center of the track 2, due to the influence of diffracted light, a diagonal line is drawn to the left or right of the center. Areas with reduced light are created. Therefore,
5, the voltage signals 17 from the sensor elements S1 and S2 and the sensor elements S3 and S4 are detected.
And the voltage signal 17 from each of them are added, and the sum signals of both are subtracted to expand the change of the light amount, and the center of the light spot 7 is located on the track 2 or deviated to the right or left side. It is possible to obtain the tracking error signal 21 that clearly indicates whether or not there is any.

Reference numeral 23 is a tracking servo compensating means corresponding to the tracking servo compensating means 23 shown in FIG. 11, and its constituent element 41 is a phase advancing circuit for advancing the phase of the tracking error signal by about 60 degrees in the band from 100 Hz to 10 kHz. Is. Reference numeral 42 is a Butterworth type second-order low-pass active filter that attenuates a component of the tracking error signal at 500 Hz or higher. 43 is 300H
It is a phase advancing circuit that advances the phase of z by about 60 degrees. Reference numeral 28 is a drive unit that supplies a current according to the control signal 25 input to the tracking actuator 12 to drive it. Reference numeral 29 is a drive means for supplying a current according to the control signal 26 input to the linear actuator 14 to drive it.

In the conventional tracking servo means, there are two stages: the servo by the linear actuator 14 corresponding to the track shake in the low frequency band and the servo by the tracking actuator 12 corresponding to the track shake in the high frequency band configured as described above. Servo is used.

As described above, the conventional method shown in FIG.
The servo of the optical pickup 4 shown in (1) has been realized by an analog circuit. However, recently, it has become necessary to change the characteristics of the servo compensating means according to the control state and to perform advanced control in which the control algorithm is complicated. With the servo means composed of the conventional analog circuit in which the structure of the servo compensating means is fixed, I can't handle it.

In order to solve the problem, digital control in which control calculation is performed by a digital calculator is currently under study. The control compensating means by digital control can be realized by computing the algorithm described in software by the computing means. Therefore, the characteristic of the control compensation means can be changed only by changing the software online. FIG. 17 is a schematic configuration diagram of a servo unit of an optical pickup using a digital circuit.

In FIG. 17, 4 is an optical pickup and 1
5 is a current-voltage converting means, 18 is a focusing error signal detecting means, 20 is a tracking error signal detecting means,
Reference numerals 27, 28 and 29 denote actuator driving means, which have the same structure as that of the above-mentioned analog servo. Reference numerals 44 and 45 denote A / D converters for converting the analog focusing error signal 19 and the tracking error signal 21 into the digital focusing error signal 46 and the tracking error signal 47, and 54 and 5
5, 56 are digital control signals 51, 52, 5 respectively.
D / for converting 3 into analog control signals 57, 58, 59
It is an A converter.

Reference numeral 48 is a storage means such as a RAM which stores the control calculation in the form of software, and 49 is a central processing means. Then, in response to a command from the central processing means 49, the software is stored in the storage means 48 and is operated at high speed.
Is read in and servo calculation is performed. The calculation results are output from the calculation processing means 50 as digital control signals 51, 52, 53, and the D / A converters 54, 55, respectively.
It is converted into analog control signals 57, 58 and 59 via 56 and is given to each actuator driving means 27, 28 and 29.

The above calculation means executes the control calculation at a constant cycle. Hereinafter, this calculation cycle peculiar to digital control will be described. The calculation cycle is a period of time from when the A / D converter takes in the error signal, then the control calculation is performed, the control signal is output from the D / A converter, and the A / D converter takes in the error signal again. is there.

Here, the focusing actuator 1
It is assumed that the calculation cycle of control of 1 is Tf, the calculation cycle of control of the tracking actuator 12 is Tt, and the calculation cycle of control of the linear actuator 14 is T1. At this time, the calculation cycle based on one count time tc of the internal clock of the calculation processing means 50 is as shown in (Equation 1).

[0034]

[Equation 1]

The arithmetic processing means 50 counts the internal clocks and starts the control calculation when the clock count number corresponding to the cycle of the control calculation is reached. Generally, the D / A converter is held at a constant value between the time when the control signal is once output from the D / A converter and the time when the next control signal is output. Further, the time from the error signal to the calculation of the control signal is the delay time.

Corresponding to the hold operation and the operation delay time, a phase delay phenomenon occurs in the frequency characteristic between the input and output signals of the digital circuit. This impairs the stability of the control means, as described below. Therefore, it is necessary to set the calculation delay time and the hold time as short as possible. Usually, the calculation cycle is short, about several tens of microseconds.

Next, the control calculation by the calculation processing means 50 will be briefly described. In order to obtain the same frequency characteristic as that obtained by the analog control servo compensating means from the digital control, it is achieved by digitally operating the following equation described in software to form the control signal.

[0038]

[Equation 2]

[0039]

[Equation 3]

[0040]

[Equation 4]

[0041]

[Equation 5]

[0042]

[Equation 6]

These control calculations are executed by the calculation processing means 50 (FIG. 17) according to the flow chart shown in FIG. The arithmetic processing of the digital circuit shown in FIG. 17 will be described below with reference to FIG.
A description will be given according to the flow chart shown in FIG. After the control is started, the variables U _f1 , U _t1 , U _l1 , and E in the memory are (step a).
_{All of f1} , E _t1 , E _t2 , V _f1 , W _l1 , W _l2 and calculation start timing parameters nf, nt, nl are initialized to 0.

Next, the operation proceeds to (step b), and if an abnormality is detected there, the execution of the operation is stopped (step c), and if there is no abnormality, the operation proceeds to (step d). On the other hand, in the parameter count block 62, the arithmetic processing means 50
In response to the timing signal generated by the internal counter, the calculation cycle count number and the timing parameters nf, nt, and nl for starting the servo calculation are incremented by one.

In step (d), the clock count number Nf corresponding to the focusing servo operation cycle is compared with the operation start timing parameter nf. If nf is larger than Nf, the focusing servo control is performed according to the flow following (step e). Calculate. That is, the control calculation in that case is executed as follows. First, the analog focusing error signal 19 output from the focusing error detecting means 18 is A / D converted by the A / D converter 44, and a digital focusing error (F
E) The signal 46 is output to the arithmetic processing means 50.

Next, the arithmetic processing means 50 requires the control signal U _f1 of the focusing actuator before one sampling, the intermediate variable V _f1 thereof, and the focusing error signal thereof, which are necessary for the calculation of (Equation 2) and (Equation 3), respectively. E _f1 is read from the storage means 48. Then, (Equation 2) and (Equation 3) are calculated and the digital control signal 51 is output.

Next, the digital control signal 51 is D / A converted by the D / A converter 54 and applied to the focusing actuator driving means 27 as an analog control signal 57. The analog control signal 57 is held at the same value during the calculation execution cycle. Finally, the values of U _f0 , V _f0 , and E _f0 shown in ( _Equation 2) and ( _Equation 3) are changed to U _f1 ,
It is stored in the storage means 48 as V _f1 and E _{f1 and the} process returns to (step b). (Step f) and (step g) and subsequent steps are the flow of the tracking servo calculation cycle control and the control calculation cycle control of the linear actuator 14, respectively, and each control calculation is performed in the same manner as in the focusing servo.

The frequency characteristic of the servo control means using the digital circuit constructed as described above will be explained based on the open-loop frequency characteristic curve diagram of the focusing servo means of FIG.

In FIG. 19, F7 is a phase characteristic curve of the focusing actuator 11, and F8 is (Equation 2) and (Equation 3).
Is a phase characteristic curve of the filter expressed by, F9 is a gain characteristic curve of the focusing actuator 11, and F11 is a gain characteristic curve of the filters of (Equation 2) and (Equation 3). With these characteristic curves, the gain in the low frequency band and the phase lead characteristic at the gain crossing point can be obtained. However, in the high frequency band of the filter, a phase delay and a decrease in gain appear due to the calculation delay time and the control signal hold between calculation cycles.

F10 is an open loop phase characteristic curve of the focusing servo means, and F12 is an open loop gain characteristic curve. The control band is about 1 kHz, and the phase margin θ is also secured. In this way, within the servo band, the open loop characteristic similar to that of the analog focusing servo of FIG. 14 is obtained,
It can be seen that good control is performed.

In the above example of the digital servo, the case where the analog servo compensating means is replaced with a digital filter is shown for the sake of explanation. Then, (Equation 2) to (Equation 6)
By preparing the optimum filter according to the control state in the storage means in advance and properly using the filter configuration according to the control state, better servo control can be performed. Although not described here, the tracking servo means can be controlled in the same manner as the above description.

[0052]

The above digital control is effective in order to make the servo highly functional. However, in recent years, there has been a growing demand not only for higher functionality of servos but also for higher data transfer rates.
Therefore, it has become necessary to rotate the optical disc 1 at a high speed. Therefore, the following problems have arisen accordingly.

First, when the optical disc 1 is rotated at a high speed, the required gain area is expanded accordingly, and the gain intersection frequency must be moved to a higher frequency. That is, it is necessary to increase the servo band. However, due to the phase delay due to the control calculation delay time and the hold of the control signal during the calculation cycle as described above, the phase margin at the gain crossover frequency becomes insufficient and the servo means becomes unstable. It will be.

Further, for the same reason, it becomes difficult to perform complicated control requiring a long calculation time. These problems can be solved if a high-speed arithmetic processing means is developed. However, at present, even one of the fastest operation means available for the optical disk device requires several tens of nanoseconds for one operation step. In addition, even the most basic (Equation 2) calculation of several tens of steps is required to calculate the control signal. Therefore, several tens of microseconds are calculated from the time when the arithmetic operation means captures the data until the control signal is output. There will be a delay. With such a long calculation delay time, about 3 kHz
In the above high frequency region, the phase delay becomes large, and it is difficult to secure the required servo band.

On the other hand, if the complicated control means is constituted by an analog circuit, it is realized because the circuit scale becomes large, the signal inside the circuit is saturated, and it is difficult to realize the storage element. Very difficult to do.

The present invention has been made in view of the above problems, and has a high function for an optical pickup of an optical disc,
It is also an object of the present invention to provide a high bandwidth servo means for high speed data transfer.

[0057]

In order to achieve the above object, an optical disk device according to the present invention is a device for detecting a signal generated by scanning a track on an optical disk with an optical spot, and an optical disk for the optical spot. An optical pickup including means for moving in the normal direction, a focusing error detecting means for processing a signal generated from scanning by an optical spot and outputting a focusing error signal, and a first control signal for inputting the focusing error signal. And a second arithmetic means comprising a digital circuit for inputting a focusing error signal and outputting a second control signal, a first control signal and a second control means An adding means for adding a signal and outputting a third control signal, and a light spot normal direction moving hand by controlling the third control signal. And a normal direction driving means for driving, characterized in that so as to control the movement of the light spot relative to a substantially normal direction of the optical disc.

Further, in order to achieve the above object, the optical disk device according to the present invention comprises means for detecting a signal generated by scanning a track on the optical disk with an optical spot,
An optical pickup including a means for moving the light spot in a substantially radial direction of the optical disc, a tracking error detecting means for processing a signal generated from scanning by the light spot and outputting a tracking error signal, and a tracking error signal for inputting A first arithmetic means comprising an analog circuit for outputting a first control signal, a second arithmetic means comprising a digital circuit for receiving a tracking error signal and outputting a second control signal, and a first control signal And a second control signal are added to output a third control signal, and a radial drive means for driving the light spot radial direction moving means under the control of the third control signal. It is characterized in that the movement of the light spot in the substantially radial direction is controlled.

Further, in order to achieve the above object, the optical disk device according to the present invention comprises means for detecting a signal generated by scanning a track on the optical disk with an optical spot,
An optical pickup including a light spot normal moving means and a light moving means for moving the light spot in a substantially normal direction and a substantially radial direction of the disk, and a signal generated from scanning by the light spot is processed and focused. Focusing error detecting means and tracking error detecting means for outputting an error signal and a tracking error signal, respectively, a first arithmetic means comprising an analog circuit for receiving the focusing error signal and outputting a first control signal, and a focusing error signal. Second arithmetic means for inputting and outputting a second control signal, and addition means for adding a first control signal and a second control signal and outputting a third control signal. A normal direction driving means for driving the light spot normal direction moving means under the control of the third control signal, Third arithmetic means composed of an analog circuit for inputting a tracking error signal and outputting a fourth control signal, and fourth arithmetic means composed of a digital circuit for inputting a tracking error signal and outputting a fifth control signal. And an adding means for adding the fourth control signal and the fifth control signal to output a sixth control signal, and a radial drive for driving the light spot radial direction moving means under the control of the sixth control signal. The second and the fourth arithmetic means include the same digital circuit, and control the movement of the light spot in the substantially normal direction and the substantially radial direction of the optical disk.

Furthermore, in the optical disk device according to the present invention, in order to achieve the above object, the first and third arithmetic means advance the phase of each input signal at the frequency at which each open loop gain becomes zero. It is characterized by including the phase advancing means.

Further, in order to achieve the above object, the optical disk device according to the present invention is characterized in that the second and fourth arithmetic means include a gain increasing means for increasing the gain of the input signal.

Further, in order to achieve the above-mentioned object, the optical disk according to the present invention is such that the second and fourth arithmetic means comprise gain increasing means for increasing the gain of the input signal, and the gain increasing degree of the gain increasing means is variable. Is characterized in that.

[0063]

According to the present invention, the control calculation is performed as described above, and the control calculation that requires high-speed processing is performed by the analog circuit, and the control calculation that is complicated but requires low-speed processing is performed by the digital circuit. In this way, by operating in an analog circuit at a frequency higher than the gain intersection, stability of the control means is ensured by eliminating the phase delay in the operation delay time, and by operating in a digital circuit in the low frequency band. Higher control functionality can be realized.

[0064]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. (Embodiment 1) First, in the first embodiment, the servo band is 3
An example of the focusing servo means that optimizes the open loop gain according to the control state in the high frequency band of kHz and the low frequency band will be described.

FIG. 1 is a schematic block diagram of the focusing servo means 100 of the optical disk device according to the first embodiment of the present invention. In FIG. 1, 1 is an optical disk, 3 is a spindle motor, 4 is an optical pickup, 8 is an objective lens, and 1
0 is a sensor, 11 is a focusing actuator, 1
Reference numeral 5 is a current-voltage converting means, 18 is a focusing error detecting means, and 27 is a focusing actuator driving means, which have the same configurations as those of the conventional analog control means.

Reference numeral 44 denotes A / A for converting the analog focusing error signal 19 into a digital error signal 46.
A D converter, 54 is a D / A converter that converts the digital control signal 51 into an analog control signal 57. Fifty
Is a high-speed arithmetic processing means for performing a servo operation, 49 is a central processing means for designating the arithmetic processing, and 48 is a storage means for storing the control operation in the form of software.

The software is read by the central processing means 49 from the storage means 48 into the high-speed arithmetic processing means 50, and the servo operation is performed there. The calculation result is output as a digital control signal 51, and the D / A converter 5
4 is converted into an analog control signal 57. These hardware configurations are the same as those of the conventional digital control means already described above.

67 is a focusing error detecting means 18
Focusing servo high frequency band compensating means for advancing the focusing error signal 19 from and outputting the control signal 68. 69 is the aforementioned analog control signal 57
And a control signal 68 and outputs a control signal 70. The control signal 70 is output to the focusing actuator driving means 27 to control the focusing actuator 11.

The operation of the focusing servo means 100 of the optical pickup 4 of the optical disc device having the above-described structure will be described below with reference to FIGS. 2, 3 and 4.
The details will be described. FIG. 2 is a frequency characteristic curve diagram of the focusing servo high frequency band compensating means 67 using an analog circuit. The vertical axis represents phase and gain, and the horizontal axis represents frequency.
The curve H1 is the phase characteristic of the compensating means, and the curve H2 is the gain characteristic.

The focusing servo high frequency band compensating means 67 acts so as to advance the phase of the input focusing error signal 19 by about 60 degrees at 3 kHz which is the gain intersection frequency of the open loop characteristic of the focusing servo means. Further, since the focusing servo high frequency band compensating means 67 is composed of an analog circuit, a phase delay due to a calculation delay time or a control signal hold does not occur,
It can be seen that excellent phase characteristics without phase delay in the high frequency band are exhibited.

Next, the focusing servo low frequency band gain increasing means 78 composed of a digital circuit will be described. The focusing servo low frequency band gain increasing means 78 has its configuration changed according to the control state, and operates so as to always take an optimal configuration.

For example, in a normal servo state in which signals are read and written on the optical disc 1, a sufficient open loop gain is required so as not to cause a focus shift even if a vibration is applied to the focusing servo means 100 from the outside of the optical disc device. is there. Therefore, the focusing servo low frequency band gain increasing means 78 is configured to increase the gain in the aforementioned vibration frequency band of 1 to 500 Hz by several tens of decibels in the normal servo state.

Further, it is necessary to limit the open loop gain during the initial focus pull-in operation of the focusing servo and during power saving for reducing the power consumption of the optical disk device. Therefore, the filter constant of the focusing servo low frequency band gain increasing means 78 is changed to supply the necessary and sufficient gain.

Therefore, the control operation of the focusing servo low frequency band gain increasing means 78 is performed by the following (Equation 7). At this time, the optimum values of the filter constants α _f1 and β _f1 of (Equation 7) are read from the storage means 48 according to the above control state, and the control operation is performed to obtain the desired frequency characteristic.

[0075]

[Equation 7]

In order to facilitate the understanding of the control calculation, an example of the flow of the control calculation performed by the calculation processing means 50 will be described with reference to the flowchart of FIG. The control flow is carried out substantially in accordance with the focusing control loop by the digital control means shown in the above-mentioned conventional example (FIGS. 17 and 18), but the flow chart shown in FIG. 3 shows the conventional focusing shown in FIG. The calculation processing 64 for the servo includes "setting of optimum filter constants according to control state" which is not explicitly shown. As a result, it is possible to achieve the high control function required in the present invention. Further, in the case of the present embodiment, the calculation of the high frequency band compensation which requires a short calculation period does not have to be performed, so that the calculation period can be extended to several hundred microseconds or more.

FIG. 4 is a frequency characteristic curve diagram of the focusing servo low frequency band gain increasing means 78 composed of a digital circuit. In this case, the operation cycle is several hundred microseconds, which is larger than that of the conventional digital control means.

In the characteristic curve of FIG. 4, the vertical axis represents phase and gain, and the horizontal axis represents frequency, as in FIG. The characteristic curves H3 and H4 show the phase characteristic and the gain characteristic in the normal servo state, respectively. Characteristic curves H5 and H6 respectively show the phase characteristic and the gain characteristic at the time of power saving. Characteristic curves H7 and H8 respectively show the phase characteristic and the gain characteristic when the focus is pulled in.
It can be seen from those characteristic curves that the gain compensation corresponding to the control state is performed in the required band. In each phase characteristic, a large phase delay of 1 kHz or more is generated by the control signal hold between the calculation delay time and the calculation cycle as described in the conventional example.

Next, the graph shown in FIG. 5 is a frequency characteristic curve diagram of the control signal 70 output by the focusing error signal 19 which is the combined characteristic of the two analog and digital control compensating means according to the first embodiment. is there. Characteristic curves H9 and H10 respectively show the phase characteristic and the gain characteristic in the normal servo state. Characteristic curves H11 and H12 respectively show the phase characteristic and the gain characteristic at the time of power saving.

Characteristic curves H13 and H14 respectively show the phase characteristic and the gain characteristic when the focus is pulled in. From these characteristic curves, it is understood that it is possible to obtain the gain increase at the low frequency and the phase advance at the gain crossover frequency according to the control state required for the control compensating means.

That is, the combined characteristics shown in FIG. 5 are the frequency characteristics of the focusing servo high frequency band compensating means 67 as shown in FIG. 2 and the frequency characteristics of the focusing servo low frequency band gain increasing means 78 as shown in FIG. And is added. Therefore, of the two compensating means, the frequency characteristic with the larger gain dominates the combined characteristic. Therefore, as described above, the phase delay due to the calculation delay time in the high frequency band generated in the focusing servo low frequency band gain increasing means 78 as seen in FIG. Is achieved.

Finally, the graph shown in FIG. 6 is an open loop frequency characteristic curve diagram of the focusing servo means.
Characteristic curves H15 and H16 respectively show the phase characteristic and the gain characteristic in the normal servo state. Characteristic curves H17 and H1
Reference numeral 8 shows a phase characteristic and a gain characteristic at the time of power saving. Characteristic curves H19 and H20 respectively show the phase characteristic and the gain characteristic when the focus is pulled in. clearly,
As described above, it is understood that the gain in the low frequency band is appropriately selected corresponding to each control state controlled by the digital means, and the phase margin θ is always sufficiently secured.

As described above, according to this embodiment,
By providing a focusing servo high frequency band compensating means 67 composed of an analog circuit, a focusing servo low frequency band gain increasing means 78 composed of a digital circuit, and an adding means for adding the control signals output by these, the conventional With this configuration, it is possible to achieve both a wide servo band and high-performance compensation, which was difficult with the configuration, and an excellent control effect can be obtained.

(Second Embodiment) The second embodiment of the present invention will be described in detail below with reference to FIGS. 7 and 8. FIG. 7 is a schematic configuration diagram of the tracking servo means of the optical disk device according to the second embodiment of the present invention.

In FIG. 7, 1 is an optical disk, 3 is a spindle motor, 4 is an optical pickup, 8 is an objective lens,
10 is a sensor, 12 is a tracking actuator, 1
Reference numeral 5 is a current-voltage converting means, 20 is a tracking error signal detecting means, and 28 is a tracking actuator driving means, which are similar to those of the conventional analog control means.

Reference numeral 45 is an A / D for converting the analog tracking error signal 21 into a digital error signal 47.
Converters 55 and 56 are D / A converters that convert the digital control signals 52 and 53 into analog control signals 58 and 59, respectively. As mentioned above, 50 is a high-speed arithmetic processing means for performing a servo operation, 49 is a central processing means for designating the arithmetic processing, and 48 is a storage means for storing the control operation in the form of software.

The software is read from the storage means 48 into the high-speed arithmetic processing means 50 in accordance with a command from the central processing means 49, and servo calculation is performed there. The calculation result is output as digital control signals 52 and 53, and analog control signals 58 and 5 are output by the D / A converters 55 and 56.
Converted to 9. These hardware configurations are similar to those of the conventional digital control means already described above.

Reference numeral 71 is a tracking servo high frequency band compensating means, which outputs a control signal 72 obtained by advancing the phase of the tracking error signal 21 by about 60 degrees at the gain intersection frequency. Reference numeral 73 is a control signal adding means, which controls the above-mentioned control signal 5
A control signal 74 obtained by adding 8 and the control signal 72 is output. The control signal 74 controls the drive means 28 of the tracking actuator. The control signal 59 also controls the driving means 29 of the linear actuator.

Regarding the tracking servo high frequency band compensating means 71 constituted by the analog circuit of this embodiment,
This is exactly the same as the focusing servo control means of the first embodiment. On the other hand, the control calculation performed by the digital circuit of this embodiment is slightly different from that of the first embodiment for the focusing servo means, because the tracking servo means controls two actuators.

The control operation performed by the digital circuit according to this embodiment will be described below. FIG. 8 is a flowchart of the control calculation performed by the calculation processing means 50 of FIG. A block 75 surrounded by a dotted line on the left side executes a filter calculation for compensating the low frequency band of the tracking actuator, and a block 77 surrounded by a dotted line on the right side processes a filter operation for compensating the linear actuator.
Also in the control calculation according to the present embodiment, as in the case of the first embodiment, "setting of the optimum filter constant according to the control state" is performed, and the high-performance control according to the present invention can be achieved. Besides, the effect of the tracking control according to the present embodiment is achieved similarly to the case of the above-described first embodiment.

(Embodiment 3) Hereinafter, a third embodiment of the present invention will be described in detail with reference to FIG. FIG. 9 is a schematic configuration diagram of focusing and tracking servo means of an optical disk device according to a third embodiment of the present invention. This embodiment exemplifies the configuration of the control means in the case where the same hardware performs the control calculation by the digital circuit for the focusing servo means and the tracking servo means described in the first and second embodiments. .

Therefore, each component is the same as that shown in FIGS. 1 and 7, as can be seen from the fact that the reference numerals are the same, and the details of the control are given in the first embodiment and the first embodiment. Since it is the same as that described in the second embodiment, the description thereof will be omitted. As can be seen from FIG. 9, the control means of the optical disk device according to this embodiment has two analog control systems, but only one digital control means. In other words, the control means according to the present embodiment shares the expensive digital arithmetic processing means for the two servo controls, that is, the focusing servo control and the tracking servo control, so that the control means of the optical disk device can be constructed at a lower cost. It has the feature that it can.

[0093]

As described above, according to the present invention, the error signal from the optical pickup is processed by the analog circuit.
Control signal is generated, the error signal is processed by a digital circuit to generate a second control signal, the first control signal and the second control signal are added, and a third control signal is output. By controlling the drive of the optical pickup thereby, it is possible to provide a servo control means capable of performing high-bandwidth and high-performance servo control even when the optical disc rotates at a high speed. . Therefore, the optical disc according to the present invention can improve the tracking precision of the light spot on the track, and can realize an excellent optical disc device in which recording and reproduction of a data signal are excellent.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of focusing servo means of an optical disk device according to a first embodiment of the present invention.

FIG. 2 is a frequency characteristic curve diagram of focusing servo high frequency band compensating means by an analog circuit which constitutes the optical disk device according to the first embodiment of the present invention.

FIG. 3 is a flow chart of control calculation performed by a calculation processing unit that constitutes the optical disc device according to the first embodiment of the present invention.

FIG. 4 is a frequency characteristic curve diagram of a focusing servo low frequency band gain increasing means composed of a digital circuit which constitutes the optical disk device according to the first embodiment of the present invention.

FIG. 5 is a frequency characteristic curve diagram of the combined characteristic of the focusing servo control compensating means constituting the optical disk device according to the first embodiment of the present invention.

FIG. 6 is an open-loop frequency characteristic curve diagram of focusing servo means constituting the optical disk device according to the first embodiment of the present invention.

FIG. 7 is a schematic configuration diagram of a tracking servo unit of an optical disc device according to a second embodiment of the present invention.

FIG. 8 is a flow chart of control calculation performed by the calculation processing means shown in FIG. 7 of the optical disc device according to the second embodiment of the present invention.

FIG. 9 is a schematic configuration diagram of focusing servo means and tracking servo means of an optical disk device according to a third embodiment of the present invention.

FIG. 10 is a schematic configuration diagram of an optical pickup that constitutes an optical disc device.

FIG. 11 is a schematic configuration diagram in the case where the servo control means of the light spot in the conventional optical disc device is configured by an analog circuit.

FIG. 12 is a schematic configuration diagram in which the control means shown in FIG. 11 in the conventional optical disc device is configured by an operational amplifier.

13A is an explanatory view of a principle of detecting a focusing error signal by the astigmatism method when the light spot in the optical disk device is focused on the track surface. FIG. (C) is an explanatory view of the focusing error signal detection principle by the astigmatism method when the optical spot in the optical disk device is close to the track surface.

FIG. 14 is an open-loop frequency characteristic curve diagram of focusing servo means by an analog circuit of an optical pickup constituting a conventional optical disc device.

FIG. 15 is a schematic configuration diagram of tracking servo means by an analog circuit of an optical pickup that constitutes a conventional optical disc device.

FIG. 16A is an explanatory diagram of the principle of detection of a tracking error signal by the push-pull method when the optical spot in the optical disc device is located at the center of the track. (B) shows the optical spot in the optical disc device on the left side of the track. (C) is an explanation of the tracking error signal detection principle by the push-pull method when the optical spot in the optical disk device is off the right side of the track. Figure

FIG. 17 is a schematic configuration diagram of a servo unit of an optical pickup using a digital circuit in a conventional optical disc device.

FIG. 18 is a flow chart of control calculation performed by a calculation processing unit of a servo unit of the optical pickup shown in FIG. 17 using a digital circuit in a conventional optical disc device.

FIG. 19 is an open-loop frequency characteristic curve diagram of focusing servo means by a digital circuit of an optical pickup that constitutes a conventional optical disc device.

[Explanation of symbols]

 1 Optical Disc 2 Track 3 Spindle Motor 4 Optical Pickup 5 Laser Light 6 Semiconductor Laser 7 Optical Spot 8 Objective Lens 9 Reflected Light 10 Sensor 11 Focusing Actuator 12 Tracking Actuator 13 Carriage 14 Linear Actuator 15 Current-Voltage Converter 16 Signal 17 Voltage Signal 18 Focusing Error detecting means 19 Focusing error signal 20 Tracking error detecting means 21 Tracking error signal 22 Focusing servo compensating means 23 Tracking servo compensating means 24 Control signal 25 Control signal 26 Control signal 27 Focusing actuator driving means 28 Tracking actuator driving means 29 Linear actuator driving means 30 Actuator drive signal 31 Actuator Motor drive signal 32 Actuator drive signal 33 Adder 34 Adder 35 Subtractor 36 Phase advance circuit 37 Low frequency band gain increase circuit 38 Adder 39 Adder 40 Subtractor 41 Phase advance circuit 42 Butterworth type secondary low-pass active filter 43 phase advance circuit 44 A / D converter 45 A / D converter 46 focusing error signal 47 tracking error signal 48 storage means 49 central processing means 50 arithmetic processing means 51 digital control signal 52 digital control signal 53 digital control signal 54 D / A converter 55 D / A converter 56 D / A converter 57 Analog control signal 58 Analog control signal 59 Analog control signal 62 Calculation start timing parameter count block 67 Focusing servo high frequency band compensating means 68 Control signal 69 the control signal addition unit 70 the control signal 71 the tracking servo high frequency band compensation means 72 control signals 73 control signal adding means 74 control signals 78 focusing servo low-frequency band gain increase unit 100 focusing servo means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shingo Sakata 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] 1. A signal detecting means for scanning a track on an optical disk by an optical spot to detect a signal generated by the scanning of the optical spot, and an optical spot normal line for moving the optical spot in a substantially normal direction of the optical disk. An optical pickup including direction moving means, a focusing error detecting means for processing the signal and outputting a focusing error signal, and an analog circuit for receiving the focusing error signal and outputting a first control signal A second arithmetic means for inputting the focusing error signal and outputting a second control signal; and a first control signal and a second control signal for addition. 3rd
And a normal direction driving means for driving the light spot normal direction moving means under the control of the third control signal, and the movement of the light spot in the substantially normal direction of the optical disc. An optical disk device for controlling the optical disk. 2. A signal detecting means for scanning a track on an optical disk by a light spot to detect a signal generated by the scanning of the light spot, and a radial movement of the light spot for moving the light spot in a substantially radial direction of the optical disk. An optical pickup including a means, a tracking error detecting means for processing the signal and outputting a tracking error signal, and an analog circuit for inputting the tracking error signal and outputting a fourth control signal. A fourth arithmetic means, which comprises an arithmetic means and a digital circuit, which inputs the tracking error signal and outputs a fifth control signal; and a fourth arithmetic means for adding the fourth control signal and the fifth control signal. 6
And a radial driving means for driving the optical spot radial direction moving means under the control of the sixth control signal, and controls the movement of the optical spot in the substantially radial direction of the optical disc. An optical disk device characterized by the above. 3. A signal detecting means for scanning a track on an optical disk by a light spot to detect a signal generated by the scanning of the light spot, and the light spot is moved in a substantially normal direction and a substantially radial direction of the disk, respectively. An optical pickup including a light spot normal direction moving means and a light spot radial direction moving means, a focusing error detecting means and a tracking error detecting means for processing the signal and outputting a focusing error signal and a tracking error signal, respectively. A first arithmetic means comprising an analog circuit for inputting the focusing error signal and outputting a first control signal; and a digital circuit for inputting the focusing error signal and outputting a second control signal 2 calculating means, and adding the first control signal and the second control signal. Third calculated
And a normal direction driving means for driving the light spot normal direction moving means under the control of the third control signal, and an analog circuit for inputting the tracking error signal. A third arithmetic means for outputting a fourth control signal; and a fourth arithmetic means comprising a digital circuit for inputting the tracking error signal and outputting a fifth control signal; and the fourth control signal. Sixth by adding with the fifth control signal
And a radial driving means for driving the light spot radial direction moving means under the control of the sixth control signal, wherein the second and fourth computing means are the same digital signal. An optical disk device comprising a circuit and controlling the movement of a light spot in a substantially normal direction and a substantially radial direction of the optical disk. 4. The first or third arithmetic means includes a phase advancing means for advancing the phase of each input signal at a frequency at which each open loop gain becomes zero. 3. The optical disk device described in 3. 5. The optical disk device according to claim 3, wherein said second or fourth arithmetic means comprises gain increasing means for increasing the gain of the input signal. 6. The method according to claim 3, wherein the second or fourth arithmetic means comprises gain increasing means for increasing the gain of the input signal, and the gain increasing degree of the gain increasing means is variable. Optical disk device.