JP2001174249A - Surface shape measuring device and surface shape measuring method - Google Patents

Abstract

[PROBLEMS] To accurately and efficiently measure the amount of unevenness existing on a measured surface of a disk such as a signal recording surface of an optical disk and the amount of tracking servo tracking error caused by the unevenness. Provided are a surface shape measuring device and a surface shape measuring method that can be performed and that can easily grasp the surface shape from the measured unevenness amount and the following error amount. A rotation unit for rotating an optical disk, a speed calculation unit for detecting a vertical speed generated by unevenness existing on an optical disk signal recording surface, detected speed data, and a signal recording surface of the rotating optical disk A tracking error that calculates a tracking error amount that cannot follow the unevenness of the signal recording surface expected to occur in the focus servo system based on a gain characteristic of the focus servo system that causes the objective lens to follow a target position in a direction perpendicular to the target lens. Quantity calculation unit 7
And 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface shape measuring apparatus and a surface shape measuring method for measuring, for example, irregularities present on a surface to be measured of a disk such as an optical disk and various characteristic values caused by the irregularities. .

[0002]

2. Description of the Related Art As shown in FIG. 9, an optical disk 1, which is a disk-shaped recording medium, has a signal recording surface 4 on one surface of an optically transparent plastic optical disk substrate 3. A signal recording area 2 is provided in a predetermined area. The signal recording area 2 in the signal recording surface 4
For example, as shown in FIG. 10 (a), a continuous groove-shaped groove 5 and a land 6 adjacent thereto are formed on one signal recording surface 4 of a disk substrate 3 at a predetermined track pitch P (1) for each track. 10 .mu.m), and a row of pits 8 is provided on the signal recording surface 4 in a spiral pattern at a predetermined track pitch for each track as shown in FIG. 10B. Things are also known. For example, in a phase-change type or magneto-optical type optical disk capable of recording information, a phase-change film or a magnetic film, a light reflection layer, And protective film layer (both not shown)
Are formed in order, and one of the groove 5 and the land 6 on the signal recording surface 4 is used as a recording area, and the other is used as a tracking light reflection area. In a read-only optical disk, a light reflection layer and a protective film layer (both not shown) are sequentially formed on a signal recording surface 4 provided with a row of pits 8 shown in FIG. 10B. Many use the rows of pits 8 on the signal recording surface 4 as recording areas and tracking diffraction gratings.

In the optical disk having the above structure, an objective lens (not shown) mounted on an optical pickup is rotated from the non-signal surface 7 of the optical disk substrate 3 opposite to the signal recording surface 4 while rotating the optical disk. Irradiate the laser light collected in step (1). In an optical disk capable of recording information, information is optically written on, for example, a recording layer on the land 6 by the irradiation light, or optically written information on the recording layer is read by reflected light.
Further, tracking is performed by detecting, for example, reflected light from the groove 5 so that a laser beam for recording or reproduction is always irradiated on a predetermined track. In a read-only optical disk, the light irradiated from the non-signal surface 7 by the optical pickup is reflected and reflected from the surface 4 provided with the row of pits 8.
Reading and tracking of information are performed by detecting the diffracted light.

On the other hand, in a high-density optical disk which has been developed in recent years, as shown in FIG. 11, a light reflection layer comprising a light reflection layer and a phase change film or a magnetic film is formed on a signal recording surface 4 provided with a groove 5. It is known that a transparent layer 11 having a constant thickness of about 4 and 0.1 mm is formed in this order. Similarly, a read-only optical disk is known in which a light reflection surface 4 formed of a light reflection layer and a transparent layer 11 having a constant thickness of about 0.1 mm are formed in this order. In the case of an optical disk formed as described above, an optical pickup (not shown) is arranged on the transparent layer 11 side formed on the surface 4 of the optical disk substrate 3 while rotating the optical disk, and a laser beam is irradiated. I do.

[0005]

The optical disk substrate 3 is generally formed by injection molding plastic. It is known that the optical disc substrate 3 manufactured by this method is warped due to changes in the environment such as thermal strain during molding, temperature and humidity. further,
The distortion of the mold during molding causes undulation on the disk surface. When the optical disk substrate 3 is rotated in a state where the optical disk substrate 3 has unevenness such as warpage or undulation, the surface of the optical disk substrate 3 is vertically shaken, and the focal position of the signal reading lens deviates from the signal recording surface of the disk (defocus). The signal recording surface is inclined (skewed) from the focal plane of the signal reading lens. At this time, the spot condensed by the optical pickup is affected by aberration. The magnitude of this aberration depends on the numerical aperture (NA) of the pickup lens.
The aberration due to defocus is proportional to the square of NA, and the aberration due to skew is proportional to the cube of the numerical aperture (NA). That is, the larger the numerical aperture (NA), the smaller the allowable defocus and skew.
On the other hand, the smaller the thickness from the disk surface to the signal recording surface 4, the smaller the aberration due to defocus and skew. For this reason, with the recent increase in the density of optical disks, the numerical aperture (NA) has been increased and the thickness of the disks has been reduced. For example, in the case of a high-density optical disc as shown in FIG.
Some have a disk structure on which a thin transparent layer 11 of about 1 mm is placed. As described above, an optically thin disk is being developed in order to reduce the influence of aberration caused by an increase in the numerical aperture (NA). Recently, short wavelength (λ ≦ 430 nm) and high numerical aperture (NA ≧ NA)
0.76) has been proposed.

Since the depth of focus becomes shallow with the increase in the NA as described above, a more severe value is required for the surface deviation allowed for the optical disk substrate 3, that is, the size of the unevenness on the surface of the optical disk substrate 3. It has become. Therefore, it is necessary to accurately measure the amount of unevenness on the surface of the optical disk substrate 3. In addition, the optical disc substrate 3 is required to have an accuracy such that a tracking error amount that cannot follow irregularities on the surface of the optical disc substrate 3 generated when the focus servo is actually applied falls within a predetermined range. Need to be measured accurately and efficiently. Further, the optical disk substrate 3 can be obtained only from the values of the measured unevenness amount and the following error amount.
It is difficult to grasp the state of the surface shape and the distribution of the unevenness, it is difficult to determine the cause of the occurrence of the unevenness existing on the optical disk substrate 3, and to visually check the state of the surface shape of the optical disk substrate 3, It is necessary to be able to grasp the distribution of unevenness.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made in consideration of the amount of unevenness existing on a measured surface of a disk such as a signal recording surface of an optical disk, and the amount of tracking servo tracking error caused by the unevenness. It is an object of the present invention to provide a surface shape measuring apparatus and a surface shape measuring method which can accurately and efficiently measure the surface shape, and can easily grasp the surface shape from the measured unevenness amount and the following error amount.

[0008]

According to a first aspect of the present invention, there is provided a surface shape measuring apparatus comprising: a rotating means for rotating a disk; Speed detecting means for detecting a vertical speed of the surface to be measured, and the detected speed data, and a servo system for following a predetermined target to a target position in a direction perpendicular to the surface to be measured of the rotating disk body. Tracking error amount calculating means for calculating a tracking error amount that cannot follow the unevenness of the surface to be measured which is expected to occur in the servo system based on the gain characteristic of the servo system.

The disk is a recording medium capable of optically recording and / or reproducing information, the measured surface is a signal recording surface of the recording medium, and the object is the recording medium. An optical pickup that performs at least one of recording information on a signal recording surface of a medium and reproducing information from the signal recording surface, or a lens mounted on the optical pickup, wherein the servo system is an optical pickup or the optical pickup; And a focus servo system for causing a lens mounted on the lens to follow a target position in a direction perpendicular to the signal recording surface.

Preferably, the tracking error amount calculation means has a digital filter having a transfer function approximating the frequency characteristic of the servo system, using the speed data as an input signal, and using the tracking error amount as an output signal. .

[0011] More preferably, the digital filter is constituted by an IIR filter.

A surface shape measuring apparatus according to a second aspect of the present invention comprises:
Rotating means for rotating the disk, speed detecting means for detecting a vertical speed of the measured surface generated by irregularities present on the measured surface of the rotating disk, and speed data based on the detected speed data. A characteristic amount calculating means for calculating at least one of the unevenness amount or various characteristic amounts caused by the unevenness, and a distribution in the disk body of the calculated amount calculated by the characteristic amount calculating means can be grasped three-dimensionally. Display means for displaying on a screen.

Preferably, the display means allocates a calculation amount at each measurement point of the recording medium in correspondence with all pixels in an area of the screen similar in shape to the recording medium; Based on the calculated amount assigned to each pixel, when it is assumed that unevenness having a height corresponding to the calculated amount is present on the measured surface of the recording medium, light is emitted from a predetermined direction with respect to the unevenness. Shade simulation means for expressing on the screen virtual shadows generated by irradiation.

According to the surface shape measuring method of the present invention, a step of rotating a disk body and a step of detecting a vertical velocity of the surface to be measured, which is generated by irregularities existing in the surface to be measured of the rotating disk body. And, based on the detected speed data, and frequency characteristics of a servo system that causes a predetermined target to follow a predetermined position in a direction perpendicular to the surface to be measured of the rotating disk body, is predicted to occur in the servo system. Calculating a tracking error amount that cannot follow the unevenness of the surface to be measured.

According to the present invention, the velocity data obtained by rotating the disk and detecting the vertical velocity of the surface to be measured, which is generated by the unevenness existing in the surface to be measured by the speed detecting means, is measured. The amount corresponds to the amount of unevenness on the surface, and the amount of unevenness can be measured efficiently and accurately. The tracking error calculation means calculates a tracking error amount that cannot follow the unevenness of the measured surface expected to occur in a servo system that causes a predetermined object to follow a predetermined target position from the measured surface of the disk,
It is calculated based on the obtained speed data and the frequency characteristics of the servo system. To calculate the tracking error amount of the servo system based on the speed data and the frequency characteristics of the servo system, for example, the speed data is subjected to a fast Fourier transform, and the obtained speed spectrum data is multiplied by the gain characteristic of the servo system. Although the tracking error amount of the servo system can be calculated by performing the inverse Fourier transform, the present invention has a transfer function that approximates the frequency characteristic of the servo system, and uses the obtained speed data as an input signal to calculate the tracking error amount. The tracking error amount is calculated by a digital filter that uses as an output signal. That is, the obtained velocity data is directly passed through a digital filter having frequency characteristics of a servo system to obtain a tracking error amount. Therefore, it is not necessary to convert the obtained speed data into the frequency domain and return it to the time-series data again, and the processing time is shortened.

The digital filter includes an IIR (Infinite)
It is preferable to use an Impulse Response) filter. I
If an IR filter is used, for example, FIR (finite Im
pulse Response) The order of the digital filter can be reduced as compared with the filter, and a transfer function close to the frequency characteristic of the servo system can be obtained.

The tracking error amount obtained as described above is displayed on the screen so that the distribution in the disc body can be grasped three-dimensionally. Specifically, the tracking error amount at each measurement point of the disk is assigned in association with all pixels in a region similar to the disk on the screen. Then, based on the tracking error amount assigned to each pixel, when it is assumed that unevenness having a height corresponding to the tracking error amount is present on the measured surface of the disk, from a predetermined direction with respect to the unevenness. Virtual shadows generated by irradiating light are represented on the screen. By observing the virtual shadow on the screen, the distribution state and size of the tracking error amount can be visually grasped.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a surface shape measuring apparatus according to an embodiment of the present invention. In FIG. 1, a surface shape measuring apparatus 1 includes a spindle motor 61 for holding and rotating an optical disk 46 as a disk-shaped recording medium, and a laser light source 40 for outputting a laser beam 41.
And a beam splitter 42, an optical fiber 44, an objective lens 45, an acousto-optic element 49, and a reference mirror 50 that constitute an interference optical system, a photodiode 51, and a light intensity signal 51s detected by the photodiode 51 are input.
A frequency counter 52 for detecting the frequency of the light intensity;
A / D converter 53 for converting an analog signal 52 s detected by frequency counter 52 into a digital signal, and a computer 55 to which signal 53 s is input from A / D converter 53
And a display device 56 connected to the computer 55.

Here, the spindle motor 61 corresponds to a specific example of the rotating means of the present invention.
Constitutes the characteristic amount calculating means and the display means of the present invention. Further, the frequency counter 52 and the computer 55
This constitutes the speed calculation means of the present invention.

The spindle motor 61 is connected to the optical disk 46
Is a predetermined value, for example, 10 m / sec, at the incident position of the laser beam condensed by the objective lens 45.
Rotate so that

The optical disk 46 has, for example, a 0.1 mm light transparent layer on a signal recording surface 47. The signal recording surface 47 of the optical disk 46 is, for example, a light reflecting surface that reflects light on which a metal film is formed by vapor deposition. However,
The optical disk 46 is not limited to the one having a 0.1 mm transparent layer on the light reflection surface, and various other optical disks can be used.

The laser light source 40 outputs a laser beam 41 having a frequency f ₀ to a beam splitter 42. The beam splitter 42 converts a part of the laser beam 41 having the frequency f ₀ output from the laser light source 40 into the laser beam 4.
3 and the remainder is reflected as a laser beam 48 toward a reference mirror 50. Further, the beam splitter 42 reflects the return light of the laser beam 43 incident on the signal recording surface 47 of the optical disc 46 through the objective lens 45 toward the photodiode 51.

The optical fiber 44 includes a beam splitter 42
The laser beam 43 that has passed through is input, and the laser beam 43 is guided to the objective lens 45. The optical fiber 44 guides the return light from the signal recording surface 47 input through the objective lens 45 to the beam splitter 42.

The objective lens 45 focuses the laser beam 43 output from the optical fiber 44 on a signal recording surface 47. Specifically, the objective lens 45 is, for example, a lens having a focal length of about 100 mm, a numerical aperture (NA) of about 0.01, and a light reflecting surface of the optical disc 46 so that the spot diameter becomes a spot of about 100 μm. 47 is irradiated with a laser beam 43 perpendicularly. Further, the objective lens 45 condenses the return light reflected on the light reflection surface 47 of the optical disk 46 onto the optical fiber 44 again. Note that the objective lens 45 is positioned at a desired position in the radial direction of the optical disk 47 indicated by the arrow R by a driving device (not shown). At this time, the optical fiber 44 also moves integrally with the objective lens 45.

The acousto-optic modulator 49 receives the laser beam 48 reflected by the beam splitter 42 and shifts the frequency f of the laser beam 48 having a predetermined frequency f ₀ by a constant frequency Δf. Reference mirror 50
Reflects the laser beam 48 whose frequency f has passed through the acousto-optic modulation element 49 and has been shifted by the frequency Δf, and makes the laser beam 48 input to the acousto-optic modulation element 49 again. The frequency f of the laser beam 48 input to the acousto-optic modulator 49 is further shifted by the frequency Δf.

The photodiode 51 receives the return light from the signal recording surface 47 reflected by the beam splitter 42 and the laser beam 48 reflected by the reference mirror 50 and passing through the acousto-optic device 49 and the beam splitter 42.
The intensity of these lights is detected, and this light intensity signal is output to the frequency counter 52.

Here, the signal recording surface 47 of the optical disk 46
Has a velocity component in the direction perpendicular to the signal recording surface 47, the frequency of the return light reflected by the signal recording surface 47 is shifted by the Doppler effect. Assuming that the frequency of the laser beam 41 output from the laser light source 40 is f0 and the speed of the light is c, the frequency f1 of the return light that has undergone the Doppler shift can be expressed by the following equation (2).

[0028]

(Equation 2)

On the other hand, the frequency f2 of the laser beam 48 reflected by the reference mirror 50 and passed through the acousto-optic device 49 and the beam splitter 42 can be expressed by the following equation (3).

[0030]

(Equation 3)

The return light having undergone the above-described Doppler shift and the laser beam 48 having passed through the beam splitter 42 interfere with each other to cause undulation, and enter the photodiode 51 in a state where the light intensity oscillates with time. The frequency fb of this undulation is expressed by the following equation (4).

[0032]

(Equation 4)

The frequency counter 52 receives the light intensity signal 51s from the photodiode 51, measures the swell frequency fb of the light intensity signal 51s, and converts the voltage according to the measured value into a signal 52s as an A / D conversion signal. Output to the device 53.

The A / D converter 53 includes a frequency counter 52
Signal 5 having swell frequency fb input from
2s is set to a predetermined sampling frequency, for example, 100 k
Sampling is performed at Hz, which is converted into a digital signal and output to the computer 55.

FIG. 2 is a configuration diagram showing a configuration inside the computer 55. The computer 55 includes a characteristic amount calculation unit 71 and a display unit 81. Characteristic amount calculation unit 71
Includes a memory 72, a speed calculator 73, a tracking error calculator 74, and an unevenness calculator 75. Display section 81
Includes an assigning unit 82 and a shadow simulating unit 83. Note that the characteristic amount calculation unit 71 is a characteristic amount calculation unit of the present invention, the display unit 72 is a display unit of the present invention, and the speed calculation unit 7
3 is a speed calculating means of the present invention, a tracking error amount calculating section 74 is a tracking error amount calculating means of the present invention, an unevenness calculating section 75 is an unevenness calculating means, and an allocating section 82 is an allocating means of the present invention. Reference numeral 83 corresponds to a specific example of each of the shadow simulation means of the present invention.

The configuration memory 72 of the characteristic quantity calculating section 71 stores the swell frequency f sampled at a predetermined sampling cycle inputted from the A / D converter 53.
b is stored and held.

The speed calculation section 73 calculates the signal recording surface 4 shown in FIG. 1 generated by the unevenness existing in the signal recording surface 47 from the data of the swell frequency fb stored in the memory 72.
7, the velocity data V in the vertical direction is calculated. That is, the velocity V in the direction perpendicular to the signal recording surface 47 of the optical disc 46
Can be expressed by a function related to the undulation frequency fb, the modulation frequency Δf of the acousto-optic modulator 49, and the frequency f0 of the laser beam 41 output from the laser light source 40, as shown in the following equation (5). The speed calculator 73 calculates (5)
The speed V is calculated based on the equation.

[0038]

(Equation 5)

The tracking error amount calculating section 74 includes a speed calculating section 73.
The velocity data V calculated in step (2) and the signal recording surface 47 at a target position perpendicular to the signal recording surface 47 of the optical disk 46.
When an error occurs in the focus servo system based on a gain characteristic of an optical pickup that performs at least one of recording information on the optical disc and reproducing information from the signal recording surface 47 or a focus servo system that follows a focus of an objective lens of the optical pickup. The tracking error amount of the objective lens that cannot follow the expected unevenness existing on the signal recording surface 47 is calculated.

Here, the gain characteristic of the focus servo system will be described. FIG. 3 is a block diagram showing an example of the focus servo system. As shown in FIG. 3, the focus servo system includes a low-frequency compensation circuit 91, a phase lead compensation circuit 92, an actuator driving circuit 93, and an actuator 94. Feedback, the manipulated variable R and the position X
, Ie, the following error E is equal to the low-frequency compensation circuit 91.
Is input to the system.

The actuator 94 drives an objective lens, which is an optical system for focusing a laser beam on the signal recording surface 47 of the optical disk 46, in a direction perpendicular to the signal recording surface 47, and is, for example, a voice coil motor. .

The low band compensation circuit 91 and the phase lead compensation circuit 92 perform phase delay compensation in a low frequency band and phase lead compensation in a high frequency band in order to obtain an open loop gain required for a focus servo system. It is a circuit for performing.

The actuator driving circuit 93 is a circuit for driving the actuator 94 based on the control amount compensated by the low frequency compensation circuit 91 and the phase advance compensation circuit 92.

In the above-described focus servo system, a target position command R ₀ that defines the position of the focal point of the objective lens with respect to the signal recording surface 47 of the optical disk 46 is input.
To this target position command R ₀ , the unevenness amount (surface runout amount) D present on the signal recording surface 47 of the optical disk 46 is added as indicated by an adder 95, and the target position command R ₀ and the unevenness amount D are added. The operation amount R is input to the focus servo system. When the optical disk 46 is rotated, the displacement of the base of the spindle motor 61 causes the optical disk 46 to rotate.
Surface runout occurs, but this surface runout amount will be ignored and described.

The above-described focus servo system is required to have, for example, an open loop gain characteristic as shown in FIG. That is, the focus servo system uses the low-frequency compensation circuit 9.
1. Phase lead compensation circuit 92, actuator drive circuit 9
3 and the gain characteristic of the transfer function G ₀ which combined actuator 94 is designed to meet the minimum required gain as shown in FIG.

The following error calculating section 74 calculates the following error shown in FIG. 3 based on the open loop gain characteristic of the focus servo system and the speed data V calculated by the speed calculating section 73 as shown in FIG. The error amount E is calculated. That is, the tracking error amount calculation unit 74 measures the tracking error amount E while actually rotating the optical disk 46 and performing focus servo of an optical system such as an objective lens on the signal recording surface 47 of the optical disk 46. Instead, the tracking error amount E is calculated using the gain characteristic of the focus servo system as shown in FIG.

More specifically, the tracking error amount calculation section 74 has a transfer function approximating the gain characteristic of the focus servo system as shown in FIG. 4, uses the speed data V as an input signal, and outputs the tracking error amount E. It is composed of a digital filter used as a signal. This digital filter includes, for example,
An IIR (infiniteImpluse Response) having the configuration shown in FIG.
) Use a digital filter.

In the IIR digital filter 100 having the configuration shown in FIG. 6, the input signal vn is a data string of the measured velocity V, the output signal xn is a data string of the calculated following error E, and the intermediate variable yn Is a temporary value used for calculation in the IIR digital filter. Note that n is the number of samples. The IIR digital filter 100 includes a multiplier 101 for multiplying the input signal vn by the gain H ₀ , a multiplier 103 for multiplying the intermediate variable yn by the gain a, and an adder for adding the output values of the multiplier 101 and the multiplier 103. 102, a delay unit 104 for delaying the output value of the adder 102 by the sampling time and outputting it as an intermediate variable yn, a multiplier 105 for multiplying the intermediate variable yn by a gain of -1, and an output of the multiplier 105 and the output of the adder 102. And an adder 106 for adding the value. Further, a delay unit 109 for delaying and outputting the output signal xn by the sampling time, a multiplier 108 for multiplying the output value of the delay unit 109 by the gain a, and adding and outputting the output values of the multiplier 108 and the adder 106 Adder 107 which outputs as signal xn
And Note that the gain H ₀ and the gain a are II
These parameters determine the characteristics of the R digital filter 100.

The IIR digital filter 100 is represented by the following equations (6) and (7).

[0050]

(Equation 6)

Gain H of IIR digital filter 100
For example, as shown in FIG. 5, ₀ and the gain a can be determined by performing curve fitting on the gain characteristic diagram of the focus servo system shown in FIG. 4, whereby the focus servo shown in FIG. A digital filter having a transfer function approximating the gain characteristic of the system is obtained. As can be seen from FIG. 5, the IIR digital filter 10
By using 0, the gain characteristic of the focus servo system can be relatively accurately approximated.

The unevenness calculating section 75 calculates the unevenness G at each measurement point on the signal recording surface 47 of the optical disk 46 based on the speed V calculated by the speed calculating section 73. In particular,
The unevenness amount calculation unit 75 is configured by a digital filter that calculates the unevenness amount G by integrating the velocity V. An IIR digital filter can also be used for this digital filter.

The configuration of the display section 81 The allocating section 82 of the display section 81 displays the following error E or the unevenness G calculated for each speed measurement point on the signal recording surface 47 of the optical disk 46 on the optical disk 46 of the display device 56. Are assigned in association with all the pixels in a region similar to the above, and each tracking error amount E or unevenness amount G is stored and held in the memory. That is, the tracking error amount E or the unevenness amount G
Are arranged so as to be similar to the optical disk 46. If there is at least one or more measurement points on the signal recording surface 47 of the optical disk 46 corresponding to one pixel of the screen of the display device 56, the measurement result of the tracking error E or the unevenness G is displayed on the screen of the display 56 without gaps. Can be arranged. Specifically, for example, 128 is set when the tracking error amount E or the unevenness amount G is 0, and 12 when the tracking error amount E or the unevenness amount G is smaller (less than 0).
A value from 0 to 127 is assigned to each pixel according to the tracking error amount E or the unevenness amount G so as to be smaller than 8.
In the case of convex (when larger than 0), values from 129 to 255 are assigned to each pixel so as to be larger than 128.

The shade simulating unit 83 includes the display device 56
On the signal recording surface 47 of the optical disk 46 on the basis of the following error amount E or the unevenness amount G assigned to each pixel of the screen of FIG.
When it is assumed that there is unevenness having a height corresponding to the tracking error amount E or the unevenness amount G, an image having a virtual shadow generated by irradiating the unevenness with light from a predetermined direction is obtained. Expressed on the screen of the display device 56.

The shadow simulating unit 83 is, specifically,
A difference between values assigned to adjacent pixels is calculated. For example, when pixels are arranged vertically and horizontally, a value obtained by subtracting the value assigned to the pixel on the right from the value assigned to the pixel of interest is taken as the difference Δx in the horizontal direction, and assigned to the pixel of interest. The value obtained by subtracting the value of the pixel adjacent to the upper side from the obtained value is defined as a vertical difference Δy.

Next, the difference Δx, calculated for each pixel,
A pixel value of each pixel, that is, a color is determined based on Δy. Specifically, assuming that the light irradiation direction is θ and the virtual light intensity is I ₀ , the pixel value I of each pixel is determined by the following equation (8). By determining the pixel value I in equation (8), it is possible to independently adjust the virtual light intensity and direction.

[0057]

(Equation 7)

For example, in a display device in which 0 is assigned to black and 255 is assigned to white, when the pixel value I is 0, it is assumed to be 128, which is the gray between white and black, and when the pixel value I is positive. To 129 to 255, 0 if negative
Is assigned to 127.

At this time, as shown in FIG. 2, the light irradiation direction θ and the virtual light intensity I
The external signal 83s specifying ₀ to independently enter the shadow simulating unit 83, displays the newly generated image on the basis of the the imaginary intensity I ₀ 0 and irradiation direction of light θ specified by the external signal 83s Configuration.

Next, a description will be given of a method for measuring a surface shape using the surface shape measuring apparatus 1 having the above configuration. First, the optical disk 46 is mounted on the spindle motor 61 and rotated. Further, a laser beam having a frequency f ₀ is output from the laser light source 40 to form a spot of the laser beam at a desired position on the signal recording surface 47 of the optical disk 46.

At this time, the signal recording surface 4 of the optical disk 46
The sampling of the data of the velocity V in the direction perpendicular to the signal recording surface 47 caused by the unevenness of 7 is performed at least while the spot of the laser beam formed on the signal recording surface 47 moves by the spot diameter on the signal recording surface 47. Make it happen once.

Therefore, the diameter of the spot is, for example,
The rotation speed of the optical disk 46 is set to about 100 μm, the linear velocity at the position where the spot of the laser beam is formed is, for example, 10 m / sec, and the A / D for sampling the swell frequency fb. The sampling frequency of converter 53 is, for example, 100 kHz.
And As a result, a single sampling can be performed on the area where the spot is irradiated on the signal recording surface 47.

However, if a single sampling is performed for the area where the spot is irradiated on the signal recording surface 47, for example, if a pulse-like noise occurs, it is determined whether the noise is due to dust or scratches on the disk, or the like. It is not possible to determine whether the noise is due to electrical noise in the measuring device.
Therefore, it is necessary to reduce the sampling interval of the A / D converter 53. For example, when the measurement is performed at a sampling frequency of 2 MHz, the area irradiated with the spot can be sampled at twenty points, and the above problem can be avoided.

If there are irregularities on the signal recording surface 47 of the optical disk 46, the velocity has a velocity V in a direction perpendicular to the signal recording surface 47, and the return light reflected by the signal recording surface 47 has its frequency f shifted by the Doppler effect. the frequency f ₁ in.

On the other hand, the laser beam 48 split by the beam splitter 42 is reflected by the reference mirror 50 and reciprocates on the same path.
It received the f2 shift of twice the frequency f ₂ in. The return light frequency f ₁ that is reflected in the return light frequency f ₂ by the signal recording surface 47 is incident on the photodiode 51, the interference to cause waviness detection light intensity in time of the photodiode 51 Vibrate. This swell frequency fb is measured by the frequency counter 52, and the swell frequency fb is A / A
It is sampled by the D converter 53.

The undulation frequency fb sampled by the A / D converter 53 is stored and held in the memory 72 of the characteristic quantity calculating section 71. Next, the speed calculation unit 73 calculates the speed V based on the swell frequency fb stored and held in the memory 72 according to the above-described equation (2). As a result, the speed in the vertical direction of the signal recording surface 47 generated by the unevenness existing on the signal recording surface 47 of the rotating optical disk 46 is detected.

The tracking error amount calculating section 74 includes a speed calculating section 73
Are sequentially input, and the IIR digital filter 100 defined by the above equations (6) and (7) calculates the following error E.

At this time, the IIR digital filter 10
0 indicates a relatively small amount of calculation. That is, the IIR digital filter 100 has a calculation amount proportional to the number n of samples. On the other hand, for example, to calculate the following error E,
If the calculation is performed using the fast Fourier transform (FFT) and the inverse fast Fourier transform without using the IR digital filter 100, the calculation amount increases on the order of nlog (n), so that high-speed processing cannot be performed. In particular, when the number n of samples increases, and in order to calculate using the fast Fourier transform (FFT) and the inverse fast Fourier transform, it is necessary to adjust the measurement point to a power of two. There is no limit on the number of points.

Therefore, the tracking error amount calculating section 74 can calculate the tracking error amount E at a very high speed.
The tracking error amount E calculated by the tracking error amount calculation unit 74 is sequentially input to the display unit 81.

Similarly, the data of the speed V calculated by the speed calculation unit 73 are sequentially input to the unevenness amount calculation unit 75. The unevenness amount calculation unit 75 calculates the unevenness amount G of the unevenness existing on the signal recording surface 47 of the optical disk 46 from the input data of the speed V, and the calculated unevenness amount G is sequentially input to the display unit 81. .

In the allocating section 82 of the display section 81, the input following error E or unevenness G is allocated in association with all pixels in a region similar to the optical disk 46 on the screen of the display device 56, It is stored and held in the memory.

In the shadow simulating unit 83, the signal recording surface 47 of the tracking error E or the unevenness G is stored based on the tracking error E or the unevenness G stored in the allocating unit 82.
When it is assumed that there is a three-dimensional image of the distribution in the space, that is, when it is assumed that the signal recording surface 47 of the optical disk 46 has a projection / depression having a height corresponding to the tracking error amount E or the projection / depression amount G, The display device 5 displays an image having a virtual shadow generated by irradiating light from a predetermined direction.
6 is displayed on the screen. At this time, the user can perform an operation of changing the light irradiation direction θ and the virtual light intensity I ₀ using an external input device such as a keyboard or a mouse of the computer 55.

Here, FIG. 7 shows a shadow simulating section 83.
FIG. 7 is a diagram showing an example of an image showing the distribution of the unevenness amount G in the signal recording surface 47 of the optical disk 46, which is generated in FIG.
The image shown in FIG. 7 simulates a shadow formed by irradiating light onto the unevenness of the signal recording surface 47 from a virtual direction. The direction indicated by the arrow in FIG. 7 is the light irradiation direction θ. Further, in the image shown in FIG. 7, the portion where the color becomes pale (white) is the side surface region of the unevenness toward the light irradiation direction, and the portion where the color becomes dark (black) is the direction where the light is irradiated. On the other hand, it is a side surface area of the unevenness with the back turned, and an intermediate color (gray) part is an area with little unevenness. Therefore, the shading becomes darker in a portion where the amount of unevenness is large, and it is possible to easily grasp the surface shape state such as the unevenness distribution and the unevenness state from the color difference of the image. Further, the light irradiation direction θ and the virtual light intensity I ₀
Can be appropriately changed to observe the distribution of unevenness, the state of unevenness, and the like in all regions of the signal recording surface 47.

On the other hand, FIG. 8 shows a display device 56 according to the amount of unevenness at a position corresponding to the signal recording surface 47 of the optical disk 46.
FIG. 6 is a diagram showing a monochrome image in which the shading of pixels on the screen is determined. In the image shown in FIG. 8, it is easy for human eyes to mistakenly recognize the shadow as if it were a shadow formed by illuminating the unevenness, and the surface shape of the signal recording surface 47 and the tracking error E It is difficult to easily grasp the state of distribution.

As described above, according to the present embodiment, the tracking error amount calculation unit 74 has a transfer function approximating the gain characteristic of the focus servo system, and uses the speed data V as an input signal.
By using the IIR digital filter 100 that outputs the tracking error E as an output signal, the tracking error E of the objective lens that cannot follow the unevenness existing on the signal recording surface 47 expected to occur in the focus servo system can be reduced at a high speed. Can be calculated. As a result, the characteristic amount caused by the unevenness of the signal recording surface 47 of the optical disk 46 can be efficiently measured, and the surface shape measuring device 1 can be made practical.

According to the present embodiment, the optical disk 4
By generating an image that simulates a shadow formed when light hits the unevenness existing on the signal recording surface 47 of No. 6, the surface shape of the signal recording surface 47 of the optical disk 46 can be easily recognized.

The present invention is not limited to the above embodiment. In the above-described embodiment, the case of the optical disk 46 as the disk of the present invention has been described, and the case of the signal recording surface 47 as the surface to be measured has been described. In addition, it is possible to measure the surface shape of a stamper for forming a signal recording surface of an optical disk, which may cause surface deflection of the signal recording surface of the optical disk. In addition, it is possible to measure the surface shape of a disk such as a magnetic disk instead of an optical disk. When the surface to be measured is not a light reflecting surface that reflects light, reliable observation can be performed by coating this surface with a metal film.

In the above-described embodiment, the description has been given of the case where the characteristic amount calculated by the characteristic amount calculating section 71 is the unevenness amount existing on the signal recording surface 47 and the tracking servo tracking error amount. It is also possible to calculate the acceleration applied to the objective lens whose position is controlled by the control. In this case, the speed calculation unit 73
By differentiating the velocity V calculated in the above, the acceleration applied to the objective lens can be calculated.

[0079]

According to the present invention, the amount of unevenness existing on the surface to be measured of a disk such as the signal recording surface of an optical disk and the amount of tracking servo tracking error caused by the unevenness can be accurately and efficiently measured. be able to. According to the present invention,
It becomes easy to grasp the surface shape from the measured unevenness amount and the following error amount.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a surface shape measuring apparatus according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing a configuration inside a computer 55.

FIG. 3 is a block diagram illustrating an example of a focus servo system.

FIG. 4 is a diagram showing an open loop gain characteristic of a focus servo system.

FIG. 5 shows the open loop gain characteristics of the focus servo system as I.
FIG. 4 is a diagram illustrating a state where an IR digital filter is fitted.

FIG. 6 is a diagram showing a configuration of an IIR digital filter.

FIG. 7 is a diagram showing an example of an image generated by the shadow simulation unit 83 and showing the distribution of the unevenness amount G in the signal recording surface 47 of the optical disc 46.

FIG. 8 is a diagram showing a monochrome image in which the density of pixels on the screen of the display device 56 is determined according to the amount of unevenness at a corresponding position on the signal recording surface 47 of the optical disk 46.

FIG. 9 is a diagram showing a configuration of an optical disc.

FIG. 10 is a diagram showing a structural example of a signal recording surface of an optical disc.

FIG. 11 is a perspective view showing a layer structure of an optical disc.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Surface shape measuring device, 46 ... Optical disk, 47 ... Signal recording surface, 51 ... Photodiode, 52 ... Frequency counter, 53 ... A / D converter, 55 ... Computer, 56 ...
Display device, 61: spindle motor, 71: characteristic amount calculation unit, 72: memory, 73: speed calculation unit, 74: tracking error amount calculation unit, 75: unevenness amount calculation unit, 81: display unit, 82 ...
Assignment unit, 83: shadow simulation unit.

Continued on the front page (72) Inventor Tsuyoshi Yamazaki 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Kiyoshi Inno 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo Sonny shares In-house F term (reference) 2F065 AA01 AA49 BB03 CC03 DD03 DD06 FF31 GG04 HH04 HH13 JJ18 KK01 LL02 LL57 MM04 MM16 MM26 PP13 PP21 QQ21 RR05 SS12 UU05 UU06 2F069 AA54 AA57 AA15 BB17 GG17 GG17 DD07 GG17 DD07 JJ17 MM04 MM11 MM23 NN12 PP02 QQ05 5D121 AA02 CB08 DD13 GG02 HH07 HH08 HH15 HH18

Claims (22)

[Claims] 1. A rotating means for rotating a disk, a speed detecting means for detecting a vertical speed of the surface to be measured, which is generated by irregularities existing in the surface to be measured of the rotating disk, and the detecting The velocity data estimated to be generated in the servo system based on the velocity data obtained and the gain characteristic of the servo system that causes a predetermined object to follow a target position in a direction perpendicular to the measured surface of the rotating disk. A tracking error amount calculating unit configured to calculate a tracking error amount that cannot follow the unevenness of the measurement surface. 2. The disc body is a recording medium capable of optically recording and / or reproducing information optically, the measured surface is a signal recording surface of the recording medium, and the object is: An optical pickup that performs at least one of recording information on a signal recording surface of the recording medium and reproducing information from the signal recording surface or a lens mounted on the optical pickup; andthe servo system includes an optical pickup or the optical pickup. The surface shape measurement device according to claim 1, wherein the surface shape measurement device is a focus servo system that causes a lens mounted on an optical pickup to follow a target position in a direction perpendicular to the signal recording surface. 3. The tracking error amount calculating means has a digital filter having a transfer function approximating the servo system, using the speed data as an input signal, and using the tracking error amount as an output signal. Surface shape measuring device. 4. The surface shape measuring apparatus according to claim 3, wherein said digital filter is constituted by an IIR filter. 5. The surface shape measuring apparatus according to claim 1, further comprising display means for displaying a distribution of the calculated following error amount in the disk body on a screen so that the distribution can be grasped three-dimensionally. 6. The speed detecting means includes: a laser light source for irradiating a laser beam; a laser beam from the laser light source to a measured surface of the disk body; An interference optical system that interferes with the reflected light; a light receiving unit that receives light obtained from the interference optical system; a light intensity frequency detected by the light receiving unit is detected; and the measured surface is determined based on the detected frequency. 2. A surface shape measuring apparatus according to claim 1, further comprising a speed calculating means for calculating a vertical speed of the surface to be measured, which is generated by unevenness existing in the inside. 7. The surface shape measuring apparatus according to claim 1, further comprising an unevenness amount calculating means for calculating an unevenness amount of the measured surface based on the detected speed data. 8. A surface shape measuring apparatus according to claim 7, wherein said unevenness amount calculating means has a digital filter for calculating the unevenness amount by integrating the detected velocity data. 9. The surface shape measuring apparatus according to claim 1, wherein the surface to be measured is a light reflecting surface that reflects light. 10. The surface shape measuring apparatus according to claim 1, wherein the surface to be measured is coated with a light reflecting film for reflecting light in order to measure the tracking error amount. 11. A step of rotating a disk, a step of detecting a vertical speed of the surface to be measured, which is generated by unevenness existing in the surface of the disk to be rotated, and the detected speed data. And, based on the frequency characteristics of a servo system that causes a predetermined target to follow a target position in the direction perpendicular to the measured surface of the rotating disk body, based on the measured surface of the measured surface expected to occur in the servo system. Calculating a tracking error amount that cannot follow the unevenness. 12. The step of calculating the following error amount comprises:
12. The surface shape measuring method according to claim 11, wherein the method is performed using a digital filter having a transfer function approximating the servo system, wherein the speed data is an input signal and the tracking error is an output signal. 13. The surface shape measuring method according to claim 12, wherein an IIR filter is used as said digital filter. 14. The surface shape measuring method according to claim 11, wherein the measurement is performed by forming a reflective film on a surface to be measured of the disk body where the tracking error amount is to be measured. 15. A rotating means for rotating a disk, speed detecting means for detecting a vertical speed of the measured surface caused by irregularities present on the measured surface of the rotating disk, and detecting the detected speed. A characteristic amount calculating means for calculating at least one of the unevenness amount or various characteristic amounts caused by the unevenness based on the velocity data; and a three-dimensional distribution of the calculated amount calculated by the characteristic amount calculating means in the disk. A surface shape measuring device having a display means for displaying on a screen so that it can be grasped. 16. The assigning means for assigning a calculation amount at each measurement point of the disc to all pixels in a region similar to the disc on the screen, and allocating to each of the pixels Based on the assigned amount,
When it is assumed that unevenness having a height corresponding to the calculated amount is present on the surface to be measured of the disk, a virtual shadow generated by irradiating the unevenness with light from a predetermined direction is displayed on the screen. 16. The surface shape measuring apparatus according to claim 15, further comprising: a shade simulation unit represented above. 17. The shade simulating means calculates a pixel value of one pixel based on a difference between a calculation amount assigned to one pixel and a calculation amount assigned to a pixel adjacent to the one pixel. 17. The surface shape measuring device according to claim 16, wherein the determination is performed. 18. The shadow simulating means calculates a calculation amount assigned to one pixel and a calculation amount assigned to a pixel which is adjacent to one of the one pixel in the vertical and horizontal directions of the screen. Are defined as Δx and Δy, respectively.
The irradiation direction of the light is θ, and the virtual intensity of the light is I
The surface shape measuring apparatus according to claim 17, wherein when ₀ is set, the pixel value I of the one pixel is determined by the following equation (1). I = I ₀ · (cos θ · Δx + sin θ · Δy) (1) 19. The surface shape measuring apparatus according to claim 18, wherein the virtual intensity I ₀ of the light and the irradiation direction θ of the light can be arbitrarily set by inputting an external signal. 20. The calculation amount is based on the detected speed data and a gain characteristic of a servo system that causes a predetermined object to follow a target position in a direction perpendicular to a measured surface of the rotating disk body. The surface shape measuring apparatus according to claim 15, wherein the calculated tracking error amount is such that the calculated tracking error amount cannot follow the unevenness of the measured surface expected to occur in the servo system. 21. The recording medium according to claim 15, wherein the disk is a recording medium capable of optically recording and / or reproducing information, and the measured surface is a signal recording surface of the recording medium. Surface shape measuring device. 22. The surface shape measuring apparatus according to claim 15, wherein the disk is a stamper for forming a signal recording surface of a recording medium capable of optically recording and / or reproducing information.