JPS641866B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting eccentricity of a record in order to align the center of the record with the center of rotation of a turntable.

When playing a record, if the center of the record and the center of rotation of the turntable do not coincide, a wow will occur due to a difference in linear velocity due to the difference in radius, and the playback characteristics will deteriorate.

A turntable is equipped with a spindle to center the record, but according to Japanese Industrial Standards, for example, in the case of a 30cm diameter LP disc, the eccentricity of the record is allowed up to 0.2mm, and the inner diameter of the center hole of the record and spindle outer diameter is 7.24 respectively
~7.33mm and 7.05~7.15mm.
When these errors are cumulatively added, the amount of eccentricity when actually placing a record becomes considerable.
The rotational unevenness caused by eccentricity far exceeds the rotational unevenness of modern high-precision turntables themselves.

A method for correcting the placement position of a record so that the center of the record placed on the turntable coincides with the rotation center of the turntable is known. At this time, the innermost circumferential groove of the record created by cutting the master in the first stage of record manufacturing can be considered to be a perfect circle with virtually no eccentricity. According to the known technique, this groove is traced by means of a swingable arm with a tracing needle at one end;
The amount of eccentricity and its position are detected through the swing angle of this arm. More specifically, a photoelectric device is provided across the other end of the arm, and the photoelectric device produces an output voltage proportional to the swinging displacement of the arm. If there is no eccentricity in the innermost groove and the innermost groove is a perfect circle, this output voltage will be a constant DC voltage, but if there is eccentricity, this output voltage will vary depending on the amount of eccentricity with a period of one revolution of the record. This results in a sinusoidal voltage with a corresponding amplitude.

On the other hand, the innermost circumferential groove, which was a perfect circle when cutting the master record, also becomes deformed during the record manufacturing process, especially during hardening after pressing, and this deformation cannot be ignored. Deformation consists of eccentricity, elliptical deformation, triangular deformation, and polygonal deformation. In this case, eccentricity is no different from eccentricity based on record placement; on the other hand, polygonal According to actual measurements, the absolute amount of the deformation is small, so the explanation will be given here particularly in relation to the elliptical deformation. As is well known, an ellipse has two maximum radii and 2
has a minimum radius of one. In other words, when an elliptical orbit is traced by the arm, the output voltage of the photoelectric device generates a sinusoidal voltage having two cycles for one rotation of the record and a peak value of 1/4 of the difference between the major axis and the minor axis.

When the arm traces the innermost groove of an actual record, the output voltage of the photoelectric device is
It has been observed that the voltage is a combination of a sine wave with one cycle of one revolution of the record and a sine wave with two cycles of one revolution of the record. Since the error to be corrected by the value detected by the method of the present invention is only the eccentric component, the rotation angle position (hereinafter referred to as eccentric position) of the turntable where the eccentric record center exists from this output voltage and the turntable The distance between the center of rotation of the table and the center of the record (hereinafter referred to as eccentricity) must be detected.
If the output voltage is a sine wave voltage whose period is one revolution of the record, its peak value and peak position directly represent the amount and position of eccentricity of the record.
However, a composite voltage consisting of two sine waves having different periods has various waveforms depending on their phase and amplitude relationships, and it is extremely difficult to detect the amount and position of record eccentricity.

One solution is to find the area over one cycle of this output voltage, that is, find the average value of this output voltage, calculate the peak voltage from the relationship between the average value and peak value of the sine wave voltage, and calculate the area of this output voltage. A method has been proposed in which the peak position is determined 1/4 cycle after the 0 intersection.

Although this method provides fairly good results, it is an object of the present invention to provide a method for detecting eccentricity of a record that can detect eccentricity more accurately even when the elliptical deformation is large. There is a particular thing.

According to the invention, this object is achieved as follows. In other words, it detects the tracing position of the arm that traces the grooves of a rotating record placed on a turntable, and determines the rotational angle position of the turntable where the center of the record is located and the distance between the rotational center of the turntable and the center of the record. To detect the turn, at least 2 (2N+1) pieces of the trace position data are sampled at equal intervals while the turntable makes N rotations, and the turn is expanded into a Fourier series based on the sample data obtained. A maximum value constant indicating the distance between the centers and a phase angle constant indicating the rotational angular position in terms having a period corresponding to one rotation of the table are respectively calculated. Each of these constants can then be used to correct the eccentricity of the record.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, a record 1 has a required groove such as a sound groove, a spindle 2 is fitted into a center hole 1a of the record 1, and the record 1 is placed on a turntable 3. An arm 5 swingably supported by a support shaft 4 has a tracing needle (not shown) for tracing grooves on the record 1 at one end, and a shutter plate 8 at the other end. A light emitting element 6a and a photodetector 7a of a photoelectric device are placed with this shutter plate 8 in between. The photodetector 7a outputs a required electrical signal V whose level changes as the amount of received light changes due to the angular displacement of the arm 5. This output is supplied to the control circuit 9.

Another photoelectric device consisting of a light emitting element 6b and a photodetector 7b is arranged near the outer periphery of the turntable 3. In this embodiment, a striped pattern is formed on the outer peripheral surface of the turntable 3, and when the turntable 3 is rotating, the photodetector 7b
Light arrives intermittently, and the photodetector 7b generates a pulse position signal _P1 . This signal is also controlled by the control device 9.
is supplied to The striped pattern of the turntable 3 may be recorded magnetically, and the pulse position signal _P1 may be generated by magnetic means such as a Hall element.

Correction lever 1 for correcting the placement position of record 1
1 is driven by a control motor 10 which is controlled by a control circuit 9 in forward and reverse directions. Correction lever 11
is normally away from the turntable 3, but when driven in the direction of arrow A by normal rotation of the control motor 10, it comes into contact with the circumferential surface of the record 1, and the record 1
radially, possibly together with a slidably mounted auxiliary turntable.

In addition, the drive motor 14 of the turntable 3 and the turntable 3 are located around the turntable 3.
A mechanical brake means 13 is provided to stop the rotation of the drive motor 14 and the mechanical brake means 13 are controlled by a control circuit 9.

The device described above operates as follows.

First, it is assumed that the arm 5 having the tracing needle traces the innermost circumferential groove 16 of the record 1, which is considered to be a substantially perfect circle. In this example, the detection positions of the tracing needle and the photoelectric devices 6b, 7b are in the same radial direction, and the correction lever 11 is
It is assumed that the position is 180 degrees away from the detection position in terms of rotation angle.

When the center of the record 1 and the rotation center of the turntable 3 match, the photoelectric devices 6a and 7a output an electric signal V at a certain level Vo, but if they do not match, the swing of the arm 5 Therefore, the photoelectric devices 6a and 7a generate a sine wave signal having a peak value _V1 with respect to Vo. In that case, for example, the point in time at which the peak level V ₁ occurs is exactly the position of the tracing needle and thus the photoelectric device 6b, 7.
This is the point in time when the maximum eccentric protrusion position of the record 1 has reached the detection position b. From this point on, the photoelectric device 6
When the pulse position signals P ₁ of b and 7b are counted and the number corresponding to 180° rotation of the turntable 3 is counted, the maximum eccentric protrusion position of the record 1 is:
The position of the correction lever 11 is reached. Therefore, so that the rotation of the turntable 3 stops at this position,
The control circuit 9 controls the drive motor 14 and mechanical brake 13 of the turntable 3 in advance while counting the pulses of the photoelectric devices 6b and 7b.

After that, the control circuit 9 controls the control motor 10 of the correction lever 11 to move the correction lever 11 in the direction of the arrow A, and from the contact position of the correction lever 11 and the record 1, the eccentricity is proportional to the peak level V _1. the correction lever 11 in the direction of arrow A. Since the eccentricity of the record 1 has been corrected in this way, the control circuit 9 then controls the control motor 10 in the reverse direction, pulls back the correction lever 11 to the initial position, and simultaneously releases the mechanical brake 13 from the turntable 3. This completes the preparation for playing the record.

The above explanation is based on the assumption that the maximum circumferential groove of the record 1 is a perfect circle. Next, a method for detecting the amount and position of eccentricity when this innermost circumferential groove is deformed into an elliptical shape will be described.

In FIG. 2, the solid line indicates an example of the electrical signal V output from the photoelectric devices 6a, 7a. The respective level of this electrical signal V corresponds to the respective swing angle of the arm 5. This electrical signal V is considered to be the sum of a sine wave signal shown by a dotted line and a sine wave signal shown by a chain line.

The sine wave signal shown by the dotted line is a signal that would be generated if only the eccentricity of the record 1 existed and the innermost groove was a perfect circle. If the record 1, and therefore the innermost groove, is eccentric, the electrical signals output from the photoelectric devices 6a and 7a can be approximated by a sine wave, as long as the amount of eccentricity is sufficiently small with respect to the diameter of the innermost groove. Since it seems intuitively obvious, the mathematical explanation is omitted for the sake of brevity.

On the other hand, when the record 1 is not eccentric and the innermost circumferential groove is elliptical, the signals that would be output from the photoelectric devices 6a and 7a are shown by chain lines. In this case, the output signals of the photoelectric devices 6a and 7a can be approximated by a sine wave that vibrates twice during one rotation of the turntable.
This seems obvious since there are two minimum radii and two maximum radii during one rotation of the elliptical orbit, and the two are smoothly connected.
Therefore, a mathematical explanation will be omitted here as well.

Therefore, the amount by which the innermost circumferential groove of the record, including eccentricity and elliptical deformation, deviates from the ideal circle, that is, the output electric signals of the photoelectric devices 6a and 7a, can be expressed as follows.

Δx=a sinθ+αsin2 (θ−−π/4) …(1) In this case, a is the peak value of eccentricity, α is 1/4 of the difference between the major axis and minor axis of the ellipse, and θ is the difference between the reference point and the point of interest. The angle between them represents the angle between the eccentric direction and the major diameter direction of the ellipse.

In the first equation, the curve shown as a solid line in FIG. 2 shows the relationship between Δx and θ with =0. As is clear from Figure 2, the peak of Δx is
Neither the maximum eccentric amount nor the maximum eccentric position correctly represents the eccentric state of record 1.

Here, in the known technology, the area of one period of the surface surrounded by the solid line and the θ axis (time axis) is calculated,
That is, the electric signal shown by the solid line is considered to be a voltage, and its average voltage is measured, and 1.57 times the electric voltage is taken as the peak value, and the point π/2 ahead from the 0 intersection of the signal is determined as the peak position.

According to this method, in the case shown in FIG. 2, the amount and position of eccentricity can be detected completely correctly. However, in the case shown in Fig. 3, that is, when the direction of eccentricity and the direction of the major axis of the ellipse do not match (a deviation of π/12 in Fig. 3), the 0 intersection of the electric signal shown by the solid line is shown by the dotted line. It does not coincide with the zero intersection of the curve. Generally, the direction of the eccentricity and the direction of the major axis of the ellipse do not match, and the angle between them is unknown.
In the known technology, it is not possible to obtain the curve shown by the dotted line, and therefore it is not possible to accurately detect the amount and position of eccentricity.

According to the present invention, the component corresponding to the curve shown by the dotted line is extracted by Fourier series expansion, so that the amount and position of eccentricity can be detected correctly in any case.

According to the method of the present invention, the output electrical signals of the photoelectric devices 6a, 7a are sampled at appropriate time intervals in synchronization with detection of the rotation angle position of the turntable in the control circuit 9, and are AD converted. The AD-converted digital data is collected over a period corresponding to one revolution of the turntable and is subjected to calculations.

On the other hand, according to the formula of the Fourier series, the output signal f(θ) of the photoelectric devices 6a, 7a having a certain period is expressed by the following equation. (θ is the rotation angle from the sample starting position) f (θ) = a ₀ + C ₁ cos (θ + ψ ₁ ) + C ₂ cos (2θ + ψ ₂ )
+C ₃ cos (3θ+ψ ₃ ) +… =a ₀ +a ₁ cosθ+a ₂ cos2θ+a ₃ cos3θ+…+b ₁ sinθ+
b ₂ sin2θ＋b ₃ sin3θ＋…(2) where C _k =√ ² _k + ² _k , tanψ _k = −b _k /a _k , k=1
, 2, 3...(3) Here, a _k and b _k in the above equation can be found from the following equation.

When performing this integral operation by substituting actual numerical values, since a finite number of θ and f(θ) are read by the samples mentioned above, the number of sample data 2n is appropriately selected, and then Approximate calculation is performed using the formula.

For example, when performing data sampling by dividing one revolution of the turntable into 160 equal parts, 2n = 160 for one revolution.
becomes. Therefore, by substituting sample data measured corresponding to each rotation angle into f(mπ/n) in the fifth equation, C _k and ψ _k shown in the third equation can be obtained. The period of the eccentric signal of the turntable is the same as the period of one rotation of the turntable,
Here, since data was collected over one revolution of the turntable, the term of the Fourier series to be extracted is a term corresponding to the fundamental wave, and therefore is a term with k=1. C ₁ obtained in this way represents the maximum amount of eccentricity, and ψ ₁ represents the angle from the measurement start point to the maximum eccentric position. When calculating over N rotations, if _C N and ψ N are found in the same way with k = N (extracting the Nth harmonic term) and 2n = 160N, these _{C N and} ψ _N are respectively It represents the maximum eccentricity amount and the angle from the measurement start point to the maximum eccentricity position.

On the other hand, the output signal f(θ) has a fluctuation component with a period half that of the eccentric component due to elliptical deformation of the record,
Depending on its deformed shape, it has various fluctuation components with even shorter periods. Here, assuming that the deformation of the record is only elliptical deformation, which generally has the largest specific gravity, the number of rotations N of the turntable required for measurement, and the minimum required number of sample data s taken at equal intervals during this time. The relationship is s=2(2N+1).

However, actual records are deformed into various shapes other than ellipses, albeit slightly, and the output signal f
(θ) includes various high-order fluctuation components based on these deformations. In such a case, it is preferable to obtain more sample data in order to more accurately calculate the eccentricity of the record and its position.

According to the present invention, it is possible to easily and accurately detect the eccentricity of a record using a small-scale microcomputer. It is also clear that similar detection can be performed using FFT (Fast Fourier Transform) algorithms, if the computing power of the microcomputer permits. The calculation for determining C ₁ and ψ ₁ using the above method is extremely simple, and the memory capacity used for the calculation is small. In that case, data collection is
Since the detection only needs to be performed over one rotation of the record, the time required is shorter than that of conventional detection methods.

The eccentricity correcting means is not limited to that shown in this embodiment, and various means can be used. For example, by arranging two correction levers facing in two orthogonal directions and making corrections using the two levers, the pressed record will not shift laterally and accurate corrections can be made. Furthermore, if the correction means is provided on the main turntable itself, corrections can be made without stopping the turntable.

[Brief explanation of drawings]

FIG. 1 is a simplified block diagram illustrating an embodiment of the invention, and FIGS. 2 and 3 are diagrams illustrating the operation of the method according to the invention. 1...record, 3...turntable, 5...
...Arm, 6a, 7a, 6b, 7b...Photoelectric device, 9...Control circuit, 11...Correction lever, 14
...Drive motor.

Claims (1)

[Claims] 1. Detects the tracing position of an arm that traces the groove of a rotating record placed on a turntable, and determines the rotation angle position of the turntable where the center of the record is located, and the rotation center of the turntable. In the record eccentricity detection method for detecting the distance between the centers of records, while the turntable makes N rotations, at least 2 (2N+1) pieces of the trace position data are sampled at equal intervals, and based on the obtained sample data. , a record characterized in that a maximum value constant indicating the distance between the centers and a phase angle constant indicating the rotational angular position are respectively calculated in terms having a period corresponding to one rotation of the turntable when expanded in a Fourier series. Eccentricity detection method. 2. Claim 1, wherein the sample data is obtained by tracing the innermost groove of the record.
The method described in section. 3. The method according to claim 1, wherein reading of the sample data is performed in synchronization with reading of the rotational angular position of the turntable. 4. The method according to claim 1, wherein the sample data is sampled over one revolution of the record, and a maximum value constant and a phase angle constant of a term corresponding to a fundamental wave of a Fourier series are calculated.