JP2000009658A - Measuring method for linearity of tape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a measuring method in which the linearity of a visualized magnetic tape can be measured with high accuracy and at high speed by a method wherein the visualized magnetic tape is illuminated with a light source whose irradiation angle can be adjusted, the magnetic tape is imaged by a camera, an imaged image is image-analyzed and the linearity of a recording pattern is measured. SOLUTION: A magnetic tape 1 which comprises a black-and-white visualized recording pattern 2 is placed on an X-Y stage 10. A CCD camera 11 to which a control device 14 is connected via a CCD driver 13 is installed at the upper part of the X-Y stage 10. In the control device 14, a digital video board 16 which is connected to the CCD driver 13 is contained, an image processing part 17 which is composed of a preprocessing part, an FET, an analytical part, a pasting part and the like is contained, and a GPIP board 18 is contained. The movement position of the X-Y stage 10 is controlled by a controller 19. A plurality of light sources 12 are installed at the obliquely upper part of the X-Y stage 10 so as to be capable of being changed over, and an irradiation angle onto the magnetic tape 1 is changed over and controlled by the control device 14. Since an image which is imaged by the CCD camera 11 is image-processed in this manner, the linearity of the magnetic tape 1 can be measured without the intermediary of man power.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for measuring tape linearity. More specifically, the present invention relates to a method for measuring the linearity accuracy of a recording pattern on a magnetic tape in order to confirm the accuracy of a rotary magnetic head device.

[0002]

2. Description of the Related Art In a helical scan recording system used as a magnetic recording system, a track is being narrowed in order to improve a recording density. In this case, as the track pitch decreases, a highly accurate track linearity measuring device is desired.

In helical scan recording, a recording pattern 2 is inclined by an angle α with respect to a magnetic tape 1 as shown in FIG.
Magnetic tape 1 composed of such an oblique recording pattern 2
In order to maintain reproduction compatibility with other devices, it is important how exactly the inclination angle α is and how accurately the inclination angle α is linear. Therefore, the accuracy of such linearity is strictly defined by format specifications in various formats, and when manufacturing a helical scan recording device, this linearity must be strictly measured to guarantee the linearity.

In a conventional linearity measuring method, a magnetic tape to be measured is set on a stage of a microscope with a stage, and the edge portion of a recorded pattern is observed with a high-power microscope, and when the observation is completed, the stage is moved. In this method, the edge portion of the next pattern is observed, and the interval is measured using the scale of the stage.

[0005]

However, the conventional linearity measuring method has the following problems. (1) The edges of the magnetic recording pattern are very difficult to see, and large errors are likely to occur when observed by human eyes. (2) In order to increase observation accuracy, it is necessary to use an objective lens with a high magnification. However, there is a limit of an optical microscope, so that a very large magnification cannot be used. (3) There is a technical limit in improving the mechanical accuracy of the stage, and a great deal of cost is required to increase the accuracy of the stage. (4) Since all measurements are performed manually, a large amount of time is required for one measurement, resulting in poor work efficiency.

The present invention has been made in consideration of the above points, and has as its object to provide a method for measuring the linearity of a magnetic tape which can measure the linearity with high accuracy and high speed.

[0007]

According to the present invention, a recording pattern of a magnetic tape is visualized, and the visualized magnetic tape is illuminated with light from a light source whose irradiation angle is adjustable. A method for measuring tape linearity, characterized in that the magnetic tape obtained is imaged by a camera, and the linearity of the recording pattern is measured by image analysis of the imaged image.

According to this configuration, by processing the recording pattern captured by the camera, the linearity can be measured without manual operation, and errors due to human eyes and errors due to the precision of the stage are eliminated, thereby achieving high precision. Measurement can be performed, and manual labor can be omitted, and highly accurate measurement can be performed in a short time without skill. In addition, an effective stage for improving the accuracy is not required, and an inexpensive measurement system can be achieved.

In a preferred configuration example, the recording pattern is visualized by applying a colloid solution containing magnetic particles to a magnetic tape, and the irradiation angle is adjusted according to the recording wavelength of the recording pattern and the wavelength of light from a light source to be illuminated. By adjusting, a black and white pattern corresponding to the recording pattern is formed.

According to this configuration, the colloidal particles are concentrated on the change point of the N pole and the S pole on the magnetic tape to form irregularities,
By appropriately selecting the recording wavelength of the recording pattern, the wavelength of the light to be illuminated, and the irradiation angle with respect to the irregularities, the optical path difference between the irregularities of the adjacent colloid particles is adjusted to utilize the light interference. A monochrome pattern corresponding to the recording pattern can be formed.

Further, in the present invention, the recording pattern of the magnetic tape is visualized, the visualized magnetic tape is illuminated with light from a light source whose irradiation angle is adjustable, and the illuminated magnetic tape is imaged by a camera. The input image is input to the image processing device, the image data input to the image processing device is Fourier-transformed, the Fourier-transformed data is filtered, the filtered data is moved on the frequency axis, and the Provided is a tape linearity measuring method, which performs inverse Fourier transform on data, and averages the inverse Fourier transformed data to remove noise.

According to this configuration, the image data captured by the camera and input to the image processing device (control device) is subjected to Fourier transform, and only data near the reference frequency is extracted from the data by the filtering process. 0Hz
The data is moved on the frequency axis so as to have a component of .times..times..times..times..times..times..times..times.

[0013]

(A) First, an illumination method for obtaining an image suitable for image processing will be described. In the present invention, since the image processing is used, it is necessary to visualize the magnetic recording pattern in a form that can be easily used for the image processing. This method uses a colloid developer.

Here, how the colloid developer can visualize the magnetic recording pattern will be described. The colloid developer contains a magnetic substance of very small particles in a colloidal state. When this is applied to a magnetically recorded tape, as shown in FIG. 2, the colloidal particles 3 which are magnetic particles are concentrated at a change point between the N pole and the S pole of the magnetic tape 1. This makes it possible to form fine irregularities on the tape surface according to the magnetic recording pattern. In the present invention, a black-and-white striped pattern suitable for image processing is formed using the fine unevenness. The method will be described below.

First, by recording a single frequency, regular NS inversions are created on a recording tape at the same intervals. Next, a case is considered in which light is irradiated obliquely to a place where fine irregularities are regularly arranged and observed from directly above. For the sake of simplicity, a case where the wavelength of light is constant (such as laser light, here, wavelength λ) will be considered. Here, as shown in FIG. 3, the optical path difference between the optical path A and the optical path B can be expressed as: optical path difference = Lcos θ. Here, L is the recording wavelength, and θ is the light irradiation angle.

Since the above-described optical path difference occurs between the optical path A and the optical path B, if the optical path difference is an integral multiple of the wavelength of light, that is, if the optical path difference is equal to Nλ, the relationship between the light interference When viewed from above, it can be observed very brightly. On the other hand, if the optical path difference between the optical path A and the optical path B is an integral multiple of the wavelength of light + half wavelength, that is, if the optical path difference = (N + 0.5) λ, interference occurs between the optical path A and the optical path B. The leverage looks dark. That is, by appropriately selecting the recording wavelength, the wavelength of the light to be observed, and the angle at which the light is radiated, the region to be observed can be made brighter or darker.

Here, consider the case where the above-described oblique illumination is applied to “solid recording” of a normal time recording device. The normal-time recording apparatus performs "solid recording" in which recording is performed on adjacent recording tracks at two azimuth angles of + side and-side (see FIG. 4). At this time, the apparent recording wavelength from the light irradiation direction differs between the + azimuth side and the −azimuth side. By using this property, it is possible to separate the two azimuth tracks into black and white. The angle of illumination is the solution of the following equation:

[0018]

(Equation 1)

Here, α: azimuth angle, N: 1, 2, 2,
3,..., L: recording wavelength, λ: light source wavelength, β: horizontal irradiation angle, θ: elevation angle. Light may be emitted from the directions of β and θ that satisfy the above equation. N, θ, and β when the recording wavelength L of the carrier frequency in the VHS format is 1.7 μm and the wavelength of green light is 550 nm are obtained as shown in Table 1 below.

[0020]

[Table 1]

When monochromatic light is irradiated under the relationship between the horizontal angle β and the elevation angle θ, the tracks adjacent to each other can be clearly observed as white and black. In practice, light is irradiated with a spread, but good black-and-white contrast can be obtained only by causing interference with light having slightly different wavelengths or slightly deteriorating the contrast.

(B) Next, an image processing illumination device will be described. As described in the illumination method (A), in the present invention, the angle of illumination with respect to the tape to be measured is important, and it is necessary that the angle can be controlled.

FIG. 5 is a configuration diagram of a lighting device according to an embodiment of the present invention. A lens 5 is provided above the magnetic tape 1 to be measured. The lens 5 is held by a support member 6. The support member 6 further includes a first tilt stage 7 and a second tilt stage 7.
The tilt stage 8 is connected and mounted. The first tilt stage 7 is rotatable in a predetermined direction around the observation position where the magnetic tape 1 is placed. Similarly, the second tilt stage 8 is rotatable in a direction perpendicular to the rotation direction of the first tilt stage 7 around the observation position where the magnetic tape 1 is placed.
A light source 9 is provided at the tip of the first tilt stage 7.

Therefore, the light source 9 is
Light can be emitted from any obliquely upward angle.
That is, each of the tilt stages 7 and 8 is a tilt stage that rotates around the center of the observation range as a center of rotation. By rotating these stages, the angle of illumination can be changed with the center of the observation range as the center of rotation. Becomes possible. In addition, since these stages are fixed not on the observation side but on the lens side, even if the observation side moves to observe a wide range, the angle formed with the observation center remains constant. . For this reason, it is possible to keep the irradiation angle under a certain condition, and to always realize a certain black and white.

(C) Next, a method of recognizing a black and white boundary line with high accuracy will be described. FIG. 6 shows the image obtained in the above description taken in by a high-resolution CCD and the digital data is displayed on a personal computer. FIG. 7 shows a graph of pixel numbers and brightness when only one line in FIG. 6 is scanned in the horizontal direction. here,
Consider measuring the linearity of the recorded tape. The linearity refers to how the recorded pattern has an ideal inclination straight line. From a different point of view, the interval between the rising edges in the graph of FIG. It also means that it is. Therefore, it is required to find the rising edge of this graph as accurately as possible, with a finer precision than the resolution of one pixel. Therefore, the following algorithm was devised.

1. Find the average brightness of one line. 2. It searches from the young pixel number and finds a place that straddles the average value of 1. The average value is calculated from the position shifted by the default pixel at the center of 3.2, the position shifted by the default value in the younger one, and the position shifted by the default value in the larger one. Find a point that crosses the value of 3 near 4.2. The area around 5.4 is linearly complemented, and a pixel point corresponding to the average value of 3 is found.

In this method, since the average of the front and rear black and white is used for the threshold instead of the entire average, the influence of the change in the degree of light and darkness in one screen as described in the above-described illumination method is used. The edge point can be obtained with high accuracy without receiving it. Actually, since the average of the black portion and the average of the white portion are required, the second edge is obtained instead of the first edge. The accuracy is high such that there is only an average shift of 0.06 pixels in a scan of 100 lines.

(D) Next, a method for measuring the degree of bending of a recording pattern will be described. As for the graph of FIG. 7, if all edges are obtained and their intervals are measured as described in the above (C), linearity can be obtained therefrom. However, in practice, this calculation takes a long time, and there are problems such as being easily affected by development unevenness, dirt, and dust, and an error is likely to occur, so that accurate measurement cannot be performed.

Therefore, a moire observation method using a Fourier transform is used to measure the degree of bending. This method is performed by the following algorithm as shown in FIG.

1. Fourier transform the input data. 2. Only the data near the known reference frequency is extracted. 3. Data is moved on the frequency axis so that the reference frequency becomes a component of 0 Hz. 4. Inverse Fourier transform. 5. Averaging is performed to remove noise.

The data thus obtained becomes the data of the degree of bending, and the position VS of the pixel and the amount of bent state pixels are indicated. Actually, one pixel = X μm is obtained in advance, and by multiplying this number, the actual bending degree is obtained, and the position VS bending degree (μm) in the tape is indicated.

(E) Next, a sampling method for measuring the degree of bending will be described. The bending degree can be obtained by complementation by the bending degree measuring method (D), but the following points become problems.

1. If the sampled data is not exactly the data of the reference frequency, the data is greatly affected by aliasing and becomes data with a large error. 2. If the sampled data is not composed of 2 ⁿ , it takes a long time to calculate because FFT cannot be used.

Therefore, as shown in FIG. 9, the above problem is solved by the following algorithm. 1. The first edge is obtained by the algorithm of the method (C) for recognizing the black and white boundary line with high accuracy. 2. Similarly, the last edge is obtained by the algorithm (C). 3.1 Edge—The data between the first edge and the second edge + 1 is complemented by a spline. 4. Resample at (2 edges-1 edge) / 2 ⁿ .

By re-acquisition of data by this algorithm, data of the reference frequency can be accurately acquired from edge to edge, so that the influence of aliasing is eliminated and no calculation error occurs. In addition, since the number of data is 2 ⁿ , FFT can be used, and the calculation time can be significantly reduced. As a result, calculation errors and the like are reduced, but conversely, in this method, since only data corresponding to the reference frequency is used accurately, the component of the slope of linearity becomes invisible. Therefore, the inclination is obtained by the following method.

1. Observe the master in advance,
The number of pixels corresponding to the length of the reference frequency is measured. (M pixels) Find the interval between the last edge and the first edge. (X
Pixel) 3. The slope is calculated by the following equation. (X pixel−M pixel) / M
Here pixels * 2 ^n, 2 ⁿ is 2 ⁿ using the sampling. Thus, the inclination for the 2 ⁿ division can be obtained. In order to convert this value from the sampling number to μm, first, it is necessary to find the correspondence between the number of pixels and the length. That is, the length (L) of the master measured in 1 is measured in advance, and 1 pixel = L / M μm can be obtained from M pixels = L. Next, since the X pixels are re-sampled at 2 ⁿ this time, 1 sampling number = X / 2 ⁿ pixels from the X pixel = 2 ⁿ sampling numbers. Collectively, one sampling number = X * L / M / 2 ⁿ μ
Data obtained by the correction formula of m can be converted to μm. Actually, since an error occurs at the time of complementation, the degree of bending is obtained over a plurality of tracks, and an average value between the plurality of tracks is obtained as data of the image.

(F) Next, a method of pasting a plurality of data will be described. The inclination and the degree of bending in one screen can be obtained by the evaluation method up to now, but it is not possible to put all the tracks to be obtained in one image for analysis for the following reasons.

1. It is difficult to select a lens with an appropriate magnification to exactly include the track to be analyzed in one image. 2. If you put too many tracks in one image, CC
Since the number of pixels of D cannot keep up with the track, an input image cannot be obtained with good image quality. 3. When a very large number of tracks are included in one image, the number of pixels forming one black and white is reduced, the length per pixel is increased, and the resolution per pixel is deteriorated. 4. When linearity is obtained by Fourier transform, the number of pixels in one black and white becomes small, so that an analysis error increases.

For this reason, it is not possible to include all tracks in one image. Therefore, one data is obtained from a plurality of images. For that purpose, how many tracks should be included in one image is determined. This is because it is not preferable to include too many tracks as described above. Conversely, having too few tracks is undesirable for the following reasons.

1. To analyze every track,
Many images need to be input, and analysis takes a very long time. 2. The fact that there are only a few tracks in one image means that the number of data on the frequency axis after passing through the bandpass filter after the Fourier transform decreases, and the error after analysis increases.

That is, there is an optimum number of tracks in one image. As a result of the study, it has been found that in the present invention, the optimum number of tracks is a state where there are about 15 to 100 tracks at the time of 1024 samplings. As described above, since the number of tracks in one image is limited, it is necessary to combine analysis data of a plurality of images to obtain an overall analysis result.

Therefore, when combining data obtained from each image (FIG. 10), first consider data obtained from one image. With this data, the degree of bending and inclination from the starting point can be obtained. This data is data obtained with the start point being 0, and is data from the first edge to the last edge.

Next, consider the case where the object to be measured is moved and the next image is analyzed. At this time, the object to be measured is moved so that the last edge analyzed last time moves near the first edge of the current image. When the analysis is performed in the same manner, it is possible to obtain the degree of bending and the inclination starting from the last edge of the previous analysis. The result is similarly data with the starting point set to 0. That is, this data is data with the last point of the data analyzed last time being 0. That is,
Just by setting the first value as the last value of the result of the previous analysis, continuous data is obtained as it is.

At this time, since the movement amount of the object to be measured becomes irrelevant, it may be rough, and may be of such a degree that it can be determined that the last track of the previous analysis is the current first track.
This can be as high as the track width, which is much larger than the required precision (about 0.01 μm) (VHS
(Approximately 60 μm), which is sufficiently rough on a general-purpose stage or the like. That is, unlike the conventional measuring method, an extremely expensive stage is not required, and an inexpensive system can be constructed.

FIG. 11 shows a configuration diagram of this system.
The magnetic tape 1 having the recording pattern 2 formed into a black and white visible pattern as described above is placed on the XY stage 10. A CCD camera 11 is set above the XY stage. The CCD camera 11 is connected to a control device (image processing device) 14 via a CCD driver 13. The control device 14 includes a digital video board 16 connected to the CCD driver 13, an image processing unit 17 composed of program software such as a preprocessing unit, an FFT and an analysis unit, and a pasting unit, and a GPIB board 18. The GPIP board 18 is connected to the controller 19 and the XY stage 10 via a GPIB cable,
The controller 19 controls the movement position of the XY stage 10. It should be noted that the XY stage may be driven by another communication interface type without using the GPIP type.

Above the XY stage 10, a plurality of light sources 12 are switchably provided. These light sources 12
As described in the illumination method (A), the control device 1 controls the irradiation angle with respect to the magnetic tape 1.
Switching control is performed by the control unit 4. Each light source 12 may be configured to be position adjustable. Further, instead of the configuration in which the plurality of light sources 12 are provided so as to be switchable, the illumination device shown in FIG. 5 described above may be used.

[0047]

As described above, according to the present invention, a recording pattern captured by a camera is processed by image processing.
The linearity can be measured without manual operation, and errors due to human eyes and errors due to the accuracy of the stage are eliminated, and high-precision measurement can be performed. The measurement is performed in a short time. In addition, an effective stage for improving accuracy is not required, and an inexpensive measurement system with a simple structure can be achieved.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an inclined recording pattern of a magnetic tape.

FIG. 2 is an explanatory diagram of colloid particles for visualizing a recording pattern.

FIG. 3 is an explanatory diagram of light interference due to an optical path difference on colloid particles.

FIG. 4 is an explanatory diagram of light interference depending on a light irradiation direction.

FIG. 5 is a configuration diagram of a lighting device according to the embodiment of the present invention.

FIG. 6 is a photograph of an input image of a recording pattern.

FIG. 7 is a graph formed by scanning the photograph of FIG. 6;

FIG. 8 is an explanatory diagram of a linearity measurement method using a Fourier transform.

FIG. 9 is an explanatory diagram of a data sampling method.

FIG. 10 is an explanatory diagram of a data bonding method.

FIG. 11 is a configuration diagram of a linearity measurement system according to the present invention.

[Explanation of symbols]

1: magnetic tape, 2: recording pattern, 3: colloid particles, 5: lens 6: support material, 7: first tilt stage, 8: second tilt stage, 9: light source, 10: XY stage, 11: CCD camera , 12: light source, 13: CCD driver, 14: control device, 15: monitor, 16: digital video board, 1
7: image processing unit, 18: GPIB board, 19: controller.

Continued on the front page F term (reference) 2G051 AA73 AB20 AC12 BB01 BC07 CA03 DA07 EA02 EA11 EA12 EA16 EA25 EC03 EC04 EC05 ED11 5B057 CE02 CE06 CG05 DA03 DB02 DC02 5D091 AA03 BB01 BB03 CC09 FF20 FF20 GG02H

Claims (3)

[Claims] 1. A visualization of a recording pattern of a magnetic tape, illuminating the visualized magnetic tape with light from a light source capable of adjusting an irradiation angle, capturing an image of the illuminated magnetic tape with a camera, and obtaining an image of the captured image. A tape linearity measuring method characterized by measuring the linearity of a recording pattern by analysis. 2. A recording pattern is visualized by applying a colloid solution containing magnetic particles to a magnetic tape, and an irradiation angle is adjusted according to a recording wavelength of the recording pattern and a wavelength of light of a light source to be illuminated. 2. The method according to claim 1, wherein a black-and-white pattern corresponding to the recording pattern is formed. 3. A visualization of a recording pattern of a magnetic tape, illuminating the visualized magnetic tape with light from a light source whose irradiation angle is adjustable, capturing an image of the illuminated magnetic tape with a camera, and capturing the captured image as an image. The image data input to the image processing device is subjected to Fourier transform, the Fourier-transformed data is filtered, the filtered data is moved on the frequency axis, and the moved data is inversely Fourier-transformed. A method of measuring tape linearity, which comprises converting and performing an averaging process on the data subjected to the inverse Fourier transform in order to remove noise.