JPH0334003B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an apparatus for measuring the shape of a disk-shaped medium (hereinafter referred to as a disk) on which information is recorded.

(Background of the Invention) There are two types of disks: (a) disks with grooves that are detected by a stylus, (b) disks with grooves that are detected as changes in capacitance, (c ) A method in which grooves are formed and the grooves are detected by an optical displacement transducer, and (d) a method in which a magnetic recording medium is coated on the surface and the direction of magnetization is detected by a magnetic head.

In these disks, distortion of the disk surface,
The position from which records are read varies three-dimensionally due to eccentricity between the center of the inner diameter of the disk and the center of the track.

<Optical Disk> As a device for retrieving information stored on a disk, there is, for example, an optical video disk developed by Philips of the Netherlands. This uses light to detect and reproduce a frequency-modulated signal from a medium on which it is recorded as unevenness. The recording medium of this optical video disk is a disc with a diameter of approximately 30 cm. On its surface, grooves containing information called bits are arranged in a concentric or spiral pattern. This bit is 0.5μm wide, 2~15μm long, and 0.15μm deep.
(1/4 wavelength of He-Ne laser), and the distance between adjacent tracks is 2 μm.

In order to detect the shape of this bit with good resolution, it is necessary to keep the focal point of the optical detector within 0.1 μm in the width direction and 0.5 μm in the depth direction of the bit. Therefore, a focus servo mechanism for automatically focusing and a track servo mechanism for accurately following the track are provided for detection.

Furthermore, there is a digital audio disk as a similar playback-only disk. Further, as disks used as storage devices in electronic computers, there are write-once disks and re-recordable disks in which track guide grooves (hereinafter referred to as pre-groups) are formed.

<Need for a disk shape measuring device> However, an actual disk differs from a theoretically accurate geometric standard (hereinafter referred to as a datum) of the disk. That is, (a) the disk surface moves up and down with respect to the read/write head as it rotates (hereinafter referred to as runout).

(b) The geometric center of the track (bit row or pregroup) formed on the disk does not coincide with the center of the outer diameter of the disk (or the inner diameter of the disk if it has an inner hole in the center). (hereinafter referred to as eccentricity).

(c) The disk surface is not completely flat and has an inclination (hereinafter referred to as warpage).

It has morphological errors such as.

For this reason, the focal position of the optical detector on the surface of the rotating disk is three-dimensionally several hundred microns.
It will fluctuate irregularly within a range of m. Therefore, if the deviation of the disk from the datum becomes large, the track and focus servo mechanisms will be unable to follow it, so a disk shape measuring device is used to check that the morphological error is within a certain tolerance. .

(Prior Art) FIG. 4 is a block diagram showing the principle of a disk shape measuring device. In the figure, 1 is a disk, 2 is a turntable on which the disk 1 is placed, 3 is an axis for rotating the turntable 2, 4 is a motor that drives the turntable 2, and 5 is an arrow A indicating the radial direction of the disk 1. a displacement transducer that moves along the reference plane and measures the deflection of the disk 1 from the reference plane;
Reference numeral 6 indicates a presser foot that presses the disk 1 to fix it on the turntable 2, and 7 indicates a moving means that moves the displacement transducer 5 in a linear manner.

In the device configured in this way, the disk 1 is rotated by the turntable 2, and the displacement converter 5 is moved in the direction of arrow A, so that the displacement converter scans the unevenness on the entire surface of the disk 1, and the disk 1 is rotated by the turntable 2. It is designed to measure runout, warpage, etc.

(Problems to be Solved by the Invention) However, with the apparatus shown in FIG. 4, it was not possible to accurately measure the shape of the disk 1 for the following reasons.

In Fig. 4, arrow B is the rotation axis of disk 1, arrow C is the normal to the disk surface, and the deviation angle θ between this rotation axis and the normal is the vertical axis error. r is the rotation center of disk 1. This is the distance from the displacement transducer 5. For example, if θ=0.01°, r=150mm, 52μ
A runout error of m occurs. Even if an attempt is made to reduce θ by mechanically improving the angle between the surface of the turntable 2 on which the disc 1 is placed and the shaft 3, the manufacturing cost will only increase and the vertical axis error will not be improved. Vertical axis errors cause errors in runout measurements.

In addition, the turntable 2 of the disk 1 rotates, so the measured value body (rotation axis B of the disk
The disc surface does not have a constant slope, and as the rotation angle changes, the positional relationship between the main body and the disk surface changes from moment to moment. Therefore, since the shake of the disk 1 is a two-dimensional value, there is a problem in that preparing all the correction values corresponding to the measurement positions would require a huge amount of correction memory.

The present invention solves the above problems, and even if there is a vertical axis error, it is possible to precisely measure the shape of the disk by comparing the deflection of the disk with a standard disk with a flat rotating surface, removing the error component. Another object of the present invention is to provide an apparatus that requires less memory capacity for correcting vertical axis errors.

(Means for Solving the Problems) The present invention, which achieves the above objects, includes a turntable that rotates with a disk placed thereon, and measures the deflection of the disk from a reference surface and measures the radial direction of the turntable. A displacement transducer moves the disc, an angle transducer measures the rotation angle of the disc, and the vertical axis error of the disc is stored in correspondence with the phase angle with respect to the reference position of the turntable, and the vertical axis error is erased. and an error elimination circuit that outputs a signal according to the rotation angle of the disk measured by the angle converter.

The turntable, the reference surface, and the displacement transducer are fixed to the measuring device, and the output signal of the error canceling circuit is proportional to the distance from the center of the displacement conversion record in the radial direction of the disk. The present invention is characterized in that a deflection measurement signal of the displacement transducer is obtained by increasing the vertical axis error of the disk.

<Function> Each component of the present invention has the following function. The error elimination circuit memorizes the vertical axis error of the disk, determined in advance through experiments, in correspondence with the phase angle with respect to the reference position of the turntable, and increases it in accordance with the distance in the disk radial direction in the displacement conversion record. . The error cancellation signal is added to the displacement transducer runout measurement signal to serve to provide a measurement free of vertical axis errors.

(Example) Examples of the present invention will be described below based on the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, parts having the same functions as those in FIG. 4 are given the same reference numerals, and their explanations will be omitted.

In the figure, 8 is an angle converter that measures the rotation angle of the disk 1, and 9 is a statsizer that expresses the signals output from the angle converter 8 in a spatially simultaneous state. For example, an encoder is attached to the angle converter 8. When used, a pulse signal corresponding to the rotation angle is output, so this pulse signal is converted into a sine wave signal corresponding to the rotational motion and stored as a voltage signal corresponding to the rotation angle. 10 is an error canceling circuit that outputs a signal corresponding to the vertical axis error of the disk 1 according to the rotation angle of the disk 1 stored in the statsizer 9; 11 is the output _v1 of the displacement converter 5 and the output of the error canceling circuit 10; Differential amplifier that takes the difference between v ₂ , 1
2 is an output terminal of the differential amplifier 11.

In addition, a circular hole is provided in the center of the disk 1.
It is fixed along a convex portion provided in the center of the turntable 2 for positioning the disk 1.

FIG. 3 is an explanatory diagram of the operation of the apparatus shown in FIG. 1.
The runout error δ〓() due to the vertical axis error θ is given by equation (1).

δ〓()=rθ／ρsin(+〓) (1) Here, the rotation angle of the disk 1 [deg], r is the distance from the displacement converter 5 to the center of rotation, and ρ is the angle for converting degrees into radians. The numerical value is 57.296 [deg/
rad] and 〓 are phase angles determined by the difference between the angle formed by the starting position of the angle converter 8 and the inclination angle of the vertical axis.

Next, the deflection δ _D () of the disk 1 is expressed by a Fourier coefficient using an angle based on the initial mounting state.

δ _D ()= _∞ 〓 ⁿ⁼¹ δ _o sin n (+ _o ) (2) Then, the output v ₁ of the displacement converter 5 is a signal as shown in FIG. 3a and is given by the following equation.

v ₁ ()=δ _D ()+δ〓() (3) Therefore, the error cancellation circuit 10 outputs a signal as shown in FIG. 3b, which is given by the following equation.

v ₂ ()=δ〓()=Rθ／ρsin(+〓) (4) When the difference between the signals of equations (3) and (4) is taken by the differential amplifier 11, as shown in Figure 3c, Disc you should look for 1
The deflection δ _D () can be obtained.

Incidentally, the verticality error θ which is essential for the error cancellation circuit 10
and its direction on the turntable are measured using a reference disk having a rotating surface with good flatness as a reference.

FIG. 2 is a configuration diagram showing another embodiment of the present invention. In the figure, the output of the error canceling circuit 10 is connected to a focus position adjustment device built into the displacement converter 5.

Since a signal corresponding to the vertical axis error δ〓( ) is introduced into the focal position adjustment device, the output of the displacement transducer 5 is freed from the influence of the vertical axis error.

Note that the present invention is not limited to the above-described embodiment, and the displacement transducer 5 may be moved by an amount corresponding to the vertical axis error δ〓() using the output of the error canceling circuit 10.

Also, when scanning the entire surface of disk 1,
Find the vertical axis error δ _* 〓() at a certain distance R, and then calculate the vertical axis error δ _* 〓 in proportion to the distance r of the displacement transducer 5.
A signal corresponding to ()·(r/R) is output from the error erasing circuit 10.

(Effects of the Invention) As explained above, the present invention has the following effects.

Since the influence of the vertical axis error is stored in the error cancellation circuit by comparison with the reference disk, highly accurate disk runout measurement is possible.

The error cancellation circuit stores only the angular component of the vertical axis error, and the radial information uses the distance from the center of the disk radial direction of the displacement transducer, so when storing data two-dimensionally, Comparatively, it requires less storage capacity.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figures are block diagrams showing other embodiments of the present invention, FIG. 3 is an explanatory diagram of the present invention, and FIG. 4 is a block diagram of a conventional device. 1...disc, 2...turntable, 5...
...Displacement converter, 7...Moving means, 8...Angle converter, 10...Error elimination circuit.

Claims (1)

[Claims] 1. A turntable that rotates with a disk placed thereon, a displacement transducer that measures the deflection of the disk from a reference plane and moves in the radial direction of the turntable, and measures the rotation angle of the disk. an angle converter that stores the vertical axis error of the disk (referring to the declination angle between the rotational axis of the turntable and the normal line of the disk) in correspondence with the phase angle of the turntable with respect to the reference position; an error eliminating circuit that outputs a signal for eliminating the vertical axis error according to the rotation angle of the disk measured by the angle converter; the disk shape measuring device comprising: the turntable, the reference surface, and the displacement converter; is fixed with respect to the measuring device, and increases the output signal of the error cancellation circuit in proportion to the distance from the center of the displacement transducer in the disk radial direction to eliminate vertical axis errors of the disk. A disk shape measuring device characterized by obtaining a runout measurement signal of a displacement transducer.