JPS61219817A - Apparatus for measuring shape of disc - Google Patents

Abstract

PURPOSE:To correct the signal of a displacement converter, by the recording of an error memory means for measuring the difference or sum of the positive and negative outputs of the displacement converter of the disc and recording the same along with the angle of rotation of the disc of an angle converter. CONSTITUTION:An angle converter 8 measures the angle of rotation of a disc 1 and an error memory means 9 measures the deflection from the reference surface of the disc 1 to store the same along with the angle of rotation of the disc 1 measured by the converter 8. A differencial amplifier 10 takes the difference between the output signals of the converter 5 and the means 9. Because a vertical degree error is corrected by taking the positive and negative of the disc, the shape of the disc is easily measured with high accuracy without using a reference disc.

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) The disc has 佽) A device that forms a groove and detects it with a stylus.

(b) A device that forms a groove and detects this as a change in capacitance.

(c) A groove is formed and detected by an optical displacement transducer.

(d) A magnetic recording medium is coated on the surface and the direction of magnetization is detected using a magnetic head.

etc.

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

Optical Disc> As a device for extracting information stored on a disc, there is, for example, an optical video disc developed by Philly-Bus in the Netherlands. This uses light to detect and reproduce a frequency-modulated signal from a medium on which it is recorded as unevenness. The disc that is the recording medium for this optical video disc has a diameter of approximately 3
It is a 0 cm disc, and on its surface, grooves containing information called bits are arranged concentrically or spirally. This pit has a width of 0.5 pm, a length of 2 to 15 pm, and a depth of 0.5 pm.
15 pm (1 (e-distance is 21 Jm).

In order to detect the shape of this bit with good resolution, the position of the focal point of the optical detector must be set at Q-1urn in the width direction of the bit.
H must be maintained within 0.5 pm in the depth direction. Therefore, the detection uses a focus servo mechanism to automatically focus and track accurately! A servo mechanism is provided for this purpose.

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

<Necessity of Disk Shape Measuring Device> However, the actual disk differs from the 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 reading and writing rad as it rotates (hereinafter referred to as wobbling).

(b) The geometric center of the track (bit string 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 but has an inclination (hereinafter referred to as "anti-shi").

It has morphological errors such as.

For this reason, the focal position of the optical detector on the surface of the rotating disk varies irregularly three-dimensionally within a range of several 1100 pixels. Therefore.

If the deviation of the disk from the datum becomes large, the track and focus servo mechanism will be unable to follow it.
A disk shape measuring device is used to check that the morphological error falls below a certain defined tolerance.

(Prior Art) FIG. 2 is a block diagram showing the principle of a disk shape measuring device. In the figure, 1 is a disc, 2 is a turntable on which the disc 1 is placed, and 3 is a turntable 2.
4 is a shaft that rotates 0; 4 is a shaft that drives the turntable 2; 5 is a presser that moves in the radial direction of the disk 1 in the direction of the arrow G2 and fixes the disk 1 on the turntable 2; 7
is a moving means for linearly moving the displacement transducer 5.

In the apparatus configured in this way, the disk l 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 of the entire surface of the disk 1, and the disk l is rotated by the turntable 2. It is designed to measure runout and eccentricity of 1 in.

(Problems to be Solved by the Invention) However, with the apparatus shown in FIG. 2, the shape of the disk 1 could not be accurately measured for the following reasons.

In Figure 2, arrow B is the rotation axis of disk l, arrow C
is the vertical axis formed by the disk surface, and the angle θ is the vertical axis error. r is the distance between the rotation center of the disk 10 and the displacement transducer 5. For example, θ=0.01'.

If r=150 mm, a runout error of 52 pm will occur.

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.

Furthermore, an error between the center of the shape of the turntable and the center of rotation gives an error in the measurement of eccentricity.

The present invention solves the above-mentioned problems, and it is possible to measure the damage of the disc with a vertical axis error without comparing it with a reference disc with a flat rotating surface, and even with the eccentricity of the turntable. The purpose of the present invention is to realize a disk shape measuring device that can measure the shape without comparing it with a standard disk without eccentricity.

(Means for Solving the Problems) The present invention achieves the above object by providing a turntable that rotates with a disk placed thereon, and a turntable that rotates with a disk mounted thereon, and a turntable that prevents the disk from running out from a reference surface or from the radial direction of tracks formed on the disk. A displacement transducer that measures displacement, and an angle transducer that measures the rotation angle of the disk.

and an error storage means for measuring the difference or difference between the outputs of the displacement converter between the positive and negative sides of the disk and recording it together with the rotation angle of the disk of the angle converter; It is designed to correct the signal of the converter.

(Example) The present invention will be described in detail 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. 2 are given the same reference numerals, and their explanations will be omitted.

In the figure, 8 is an angle converter for measuring the rotation angle of the disk 1, 9 is an error storage means for measuring the deflection of the disk l from the reference surface and storing it together with the rotation angle of the disk measured by the angle converter 8; 1 is a differential amplifier that takes the difference between the signals output from the displacement converter 5 and the error storage means 9; 11 is an output terminal of the differential amplifier 10;

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

The error storage means 9 includes an ADC 9a for AD converting the signal from the displacement converter 5, and a memory 9b for recording the output (hereinafter referred to as positive) of the displacement converter 5 at the rotation angle ψ of the disk l according to the rotation angle ψ. , the staticizer 9c transmits the output of the angle converter 8 to the memory 9b, the positive signal stored in the memory 9b, and the positional relationship between the disc l and the turntable 2.
A subtractor 9d that takes the difference between the signal of the output of the displacement converter 5 (hereinafter referred to as "reverse") in the case of 80 degrees shift, and the subtracter 9.
DAC9e converts the signal output from d to T and converts it to DA
It is composed of.

The operating principle of the device configured in this way will be explained. The perpendicularity error of the disk l is θ (deg), and the rotation angle is ψrd.
ag), and if the distance from the center of rotation of the displacement transducer 5 is r, then the errors δ and (ψ) exerted on the measurement of runout are given by the following equation.

"t, @7%P: f5τgo!i The value to convert to snow 5 near is 57.296 (deg / rad
).

Next, the deflection JD (ψ) of the disk 1 is expressed as a Fourier coefficient using an angle based on the initial mounting state.

JD (ψ) = vessel, δn sin n (ψ ten ψn)
(2) Then, the output v1 of the positive displacement converter 5 becomes the following equation.

vl(ψ)=δD(ψ)+δ, (ψ) (3) Next, the disk 1 is rotated 180 degrees and fixed on the turntable 2. The output v2 of the displacement converter 5 at this time is given by the following equation.

v2 (ψ) = δD (ψ + 180°) + δ6 (ψ) (4)
Furthermore, when data is taken from a position rotated by 180 degrees in this installed state, the output v2 is obtained by the following equation.

v2 (9'+ 180°) = δD (ψ+ 360°
) + δ bar ψ + 180°) (5) Therefore, by taking the difference between the positive and negative signals, the error δ, (ψ) due to the verticality error can be found.

vl (ψ) - v2 (ψ ÷ 180°) = δD (ψ) + 6 mouths (ψ) - JD (ψ + 360') - δa C'/"
180°) = 26g(ψ) (6) So,
If T, the difference between the positive and negative signals, is subtracted from the output v1 (in) of the displacement converter 5, the correct deflection of the disk 1 JD (b) is obtained.
can be known.

In this embodiment, a subtracter 9d is used, but even if the positive and negative measurement angles are changed by 1800 using an adder, the correct deflection JD (ψ) can be found as shown in the following equation. .

vl (ψ) + v2 (ψ + 180 pieces = δD (ψ) + δ, (
ψ)+δD(ψ+360°)+δ, (ψ+180'
) = 2 JD (ψ) (7 n again (
In formula 6), the error δt is calculated using only the angle ψ, but the value of the angle ψ+180'' may also be used.

δ, (ψ)-7(vl(%') -v2 (ψ+180
') - (V] (ψ+180') - v2 (ψ) )
(8) Also, in this embodiment, the case of measuring the runout of the disk 1 was shown, but when measuring the eccentricity of the disk 1 using a displacement transducer that measures the displacement in the radial direction of the track formed on the disk It may be.

Further, an automatic changing device may be used to change the disk 1 between the forward and reverse sides, or the operator may do it himself.

(Effects of the Invention) As described above, according to the present invention, since the perpendicularity error is corrected by taking the positive and negative sides of the disc, highly accurate disc shape measurement is possible without using a reference disc. It's easy to do.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional device. 1...disc, 2...turntable, 5...
displacement converter, 7... moving means, 8... angle converter,
9...Error storage device. Agent: Patent Attorney Shinsuke Ozawa8. ,”
",">z, Q', li: two. Figure 1 Figure 2

Claims (1)

[Claims] A turntable on which a disk is placed and rotates, a displacement transducer that measures the deflection of the disk from a reference surface or a radial displacement of a track formed on the disk, and an angle converter that measures the rotation angle of the disk. and error storage means for measuring the difference or sum of the outputs of the displacement converter for positive and negative directions of the disk and recording it together with the rotation angle of the disk of the angle converter, and the error storage means records the displacement A disk shape measuring device that corrects the converter signal.