JP2003130606A - Surface-roughness measuring method of magnetic- recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface-roughness measuring method of a magnetic-recording medium which can measure a surface-roughness on the recording surface of a magnetic- recording medium by the same sensitivity as a magnetic head receives during contact of an actual magnetic-recording medium with a magnetic head. SOLUTION: The surface roughness of a magnetic-recording medium is computable as follows: when a reproduction magnetic head using a magnetoresistance-effect element reproduces a magnetic-recording medium, the peak value level (TA level) of a thermal asperity waveform generated with frictional heat with the magnetic-recording medium is detected. Then the height of a salient is computable from the above TA level by using a predetermined relationship between a TA level and the height of a salient which is on the magnetic-recording medium. According to this method, the height of a salient which is on the magnetic-recording medium can be found easily from a thermal asperity waveform. The height of a salient which is on the magnetic- recording medium can be measured by the same sensitivity as the magnetic head receives during contact of the actual magnetic-recording medium with the magnetic head.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the surface roughness of a magnetic recording medium, and in particular, the surface roughness on the recording surface of the magnetic recording medium is measured with an actual magnetic field. The present invention relates to a method for measuring the surface roughness of a magnetic recording medium that can be measured with the same sensitivity as that received by the magnetic head when the recording medium is in contact with the magnetic head. Conventionally, the presence of protrusions (abnormal protrusions) larger than a certain size on the recording surface of a magnetic recording medium causes reproduction failure. Therefore, the surface roughness of the recording surface is inspected during product inspection. Measurements are being made. Conventional surface roughness measurement methods include a stylus type that makes the stylus contact the surface of the object and obtains the surface roughness from the vertical movement of the stylus, or the surface of the object is measured without contact with an optical probe. Optical measuring methods are known. As a display method of surface roughness, the maximum height (RS
x), ten-point average roughness (Rz) and centerline average roughness (R
There is a). Each of these parameters is a surface roughness parameter defined in JIS (Japanese Industrial Standard).
It is an index of electromagnetic conversion characteristics and running properties of magnetic recording media. In recent years, the recording density of magnetic recording media has been increased, and it is required to measure the surface roughness of the recording surface of the magnetic recording medium with higher accuracy. . Also, since the size of the protrusions present on the recording surface of the magnetic recording medium as abnormal protrusions differs depending on the contact state between the magnetic recording medium and the magnetic head, the actual contact state between the magnetic recording medium and the magnetic head is different. In consideration of this, it is required to measure the surface roughness of the recording surface of the magnetic recording medium. Therefore, in addition to the stylus-type and optical-type measurement methods described above, an interference difference in the contact state between the magnetic recording medium and the magnetic head can be measured with a dummy head made of glass or the like, a laser sensor, etc. Thus, the deformation of the magnetic recording medium in a contact state between the magnetic recording medium and the magnetic head is measured. However, these methods can detect the contact state between the magnetic head and the protrusion existing on the recording surface of the magnetic recording medium, but detect the abnormal protrusion that affects the contact between the magnetic recording medium and the magnetic head. I couldn't. That is, there has been a problem that the surface roughness on the recording surface of the magnetic recording medium cannot be measured with the same sensitivity as the magnetic head receives when the actual magnetic recording medium and the magnetic head are in contact. In view of the above, the present invention can measure the surface roughness on the recording surface of a magnetic recording medium with the same sensitivity as that received by the magnetic head when the magnetic recording medium comes into contact with the magnetic head. An object of the present invention is to provide a method for measuring the surface roughness of a recording medium. The method for measuring the surface roughness of a magnetic recording medium according to the present invention is such that when a reproducing magnetic head using a magnetoresistive effect element reproduces the magnetic recording medium, the magnetic recording medium And detecting the peak value level of the thermal asperity waveform generated by frictional heat, and the peak value level obtained in advance from the peak value level of the thermal asperity waveform and the protrusion existing on the magnetic recording medium The height of the projection is calculated using the relationship with the height of the projection. According to this method, the relationship between the level of the peak value of the thermal asperity waveform and the height of the protrusion existing on the magnetic recording medium is obtained in advance, so that the reproducing magnetic head reproduces the magnetic recording medium. It is possible to calculate the height of the protrusions present on the magnetic recording medium from the thermal asperity waveform generated in FIG. Therefore, the width of the protrusion existing on the magnetic recording medium can be easily obtained from the thermal asperity waveform. Further, the height of the protrusions existing on the magnetic recording medium can be measured with the same sensitivity as the magnetic head receives when the actual magnetic recording medium is in contact with the magnetic head. The method for measuring the surface roughness of a magnetic recording medium according to the present invention is generated by frictional heat with the magnetic recording medium when the reproducing magnetic head using the magnetoresistive element reproduces the magnetic recording medium. The generation time of the thermal asperity waveform is detected, and from the generation time of the thermal asperity waveform, the relationship between the generation time obtained in advance and the width of the protrusion existing on the magnetic recording medium is used. The width is calculated. According to this method, the relationship between the generation time of the thermal asperity waveform and the width of the protrusion existing on the magnetic recording medium is obtained in advance, so that it is generated when the reproducing magnetic head reproduces the magnetic recording medium. From the thermal asperity waveform, the width of the protrusion existing on the magnetic recording medium can be calculated. Therefore, the width of the protrusion existing on the magnetic recording medium can be easily obtained from the thermal asperity waveform. In addition, the width of the protrusions present on the magnetic recording medium can be measured with the same sensitivity as the magnetic head receives when the actual magnetic recording medium and the magnetic head come into contact with each other. The apparatus for measuring the surface roughness of a magnetic recording medium according to the present invention is generated by frictional heat with the magnetic recording medium when the reproducing magnetic head using the magnetoresistive effect element reproduces the magnetic recording medium. A thermal asperity waveform detection unit for detecting a peak value level and an occurrence time of the thermal asperity waveform; and a peak value level obtained in advance from the peak value level of the thermal asperity waveform and the magnetic recording medium A projection height calculation unit for calculating the height of the projection using the relationship with the height of the existing projection, and the generation time and the magnetic recording medium obtained in advance from the generation time of the thermal asperity waveform A projection width calculation unit that calculates the width of the projection by utilizing the relationship with the width of the projection existing above, and a medium position information calculation unit. The features. According to this apparatus, the level and occurrence time of the peak value of the thermal asperity waveform are detected by the thermal asperity waveform detection unit, and the peak value of the thermal asperity waveform previously obtained by the projection height calculation unit is detected. The height of the protrusion can be calculated using the relationship between the level of the protrusion and the height of the protrusion existing on the magnetic recording medium. In addition, the protrusion width calculation unit can calculate the protrusion width by using the relationship between the generation time of the thermal asperity waveform obtained in advance and the protrusion width existing on the magnetic recording medium. Further, the position of the protrusion is calculated by the medium position information calculation unit from the position of the magnetic head. Therefore, the height of the protrusion existing on the magnetic recording medium can be easily obtained from the thermal asperity waveform.
Further, the height and width of the protrusions existing on the magnetic recording medium can be measured with the same sensitivity as the magnetic head receives when the actual magnetic recording medium and the magnetic head come into contact with each other. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. In this embodiment described below, a case where a magnetic tape is used as a magnetic recording medium will be described. First, the apparatus for measuring the surface roughness of the magnetic recording medium of the present invention (hereinafter simply referred to as "surface roughness measuring apparatus") will be described. FIG. 1 is a block diagram showing the configuration of the surface roughness measuring apparatus of the present invention. FIG. 2 is a schematic perspective view showing protrusions present on the recording surface of the magnetic tape,
FIG. 3 is a graph showing a thermal asperity waveform detected by the thermal asperity waveform detection unit of the surface roughness measuring apparatus of FIG. As shown in FIG. 1, a surface roughness measuring device 1
Is composed of a thermal asperity waveform detection unit 2, a projection height calculation unit 3, a projection width calculation unit 4, and a medium position information calculation unit 5. When the reproducing magnetic head H reproduces the magnetic tape, From the thermal asperity waveform generated by the frictional heat, the height h and the width d of the projection P existing on the recording surface S of the magnetic tape MT as shown in FIG. 2 are calculated. The reproducing magnetic head H is assumed to use a magnetoresistive effect element. Also, the "protrusion width" here
Is the traveling direction of the magnetic tape MT (the direction of arrow A in the figure).
The width of Details of each part will be described below. A thermal asperity waveform detector 2 detects a thermal asperity waveform from a reproduction signal read from a reproducing magnetic head H using a magnetoresistive element,
The peak value level (TA level) and generation time (TA generation time) of the thermal asperity waveform are obtained. An example of the thermal asperity waveform detected by the thermal asperity waveform detector 2 is shown in FIG. In FIG. 3, a portion surrounded by a broken line is a thermal asperity waveform. Thermal asperity is a phenomenon that occurs due to frictional heat between the reproducing magnetic head and the protrusion when the reproducing magnetic head comes into contact with the protrusion on the magnetic recording medium. Hereinafter, thermal asperity will be described. The reproducing magnetic head utilizes the fact that the electric resistance value of the magnetoresistive element changes due to the influence of an external magnetic field from the magnetic recording medium due to the magnetoresistive effect of the magnetoresistive element that is a ferromagnetic material. The signal recorded on the magnetic recording medium is read out. Specifically, a signal is read by flowing a sense current that is a constant current during reproduction and taking out a change in the electric resistance value of the magnetoresistive element as a change in voltage. When this reproducing magnetic head comes into contact with the projection P existing on the recording surface S of the magnetic tape MT as shown in FIG. 2, frictional heat is generated between the reproducing magnetic head and the magnetic tape MT, The frictional heat causes a local and rapid temperature rise in the magnetoresistive element of the reproducing magnetic head. At this time, as the temperature of the magnetoresistive element increases, the resistance value of the magnetoresistive element changes instantaneously and the voltage output from the reproducing magnetic head changes. This phenomenon is called thermal asperity phenomenon. The protrusion height calculation unit 3 pays attention to the peak value of the thermal asperity waveform detected by the thermal asperity waveform detection unit 2, and calculates the peak value and magnetic value of the thermal asperity waveform obtained in advance through experiments and calculations. The height of the protrusion on the magnetic tape is calculated using the relationship with the height of the protrusion existing on the tape. Details will be described later in the method for measuring the surface roughness of a magnetic recording medium. The protrusion width calculation unit 4 pays attention to the generation time of the thermal asperity waveform detected in the thermal asperity waveform 2, and generates the thermal asperity waveform generation time and the magnetic tape previously obtained through experiments and calculations. The width of the protrusion on the magnetic tape is calculated using the relationship with the width of the existing protrusion. Details will be described later in the method for measuring the surface roughness of a magnetic recording medium. The medium position information calculation unit 5 calculates the position information (Xp, Yp) of the projection P existing on the recording surface S of the magnetic tape MT from the position of the reproducing magnetic head H. Here, the position in the running direction of the magnetic tape MT is X, and the position in the width direction of the magnetic tape MT is Y (see FIG. 2). Next, a method for measuring the surface roughness of the magnetic recording medium, which is performed using the surface roughness measuring apparatus 1 described above, will be described. FIG. 4 is a graph showing the relationship between the level of the peak value of the thermal asperity waveform and the height of the protrusion.
These are graphs showing the relationship between the generation time of the thermal asperity waveform and the width of the protrusion. When measuring the surface roughness of the magnetic tape MT shown in FIG. 2 using the surface roughness measuring device 1, first, the thermal asperity waveform detector 2 detects the thermal asperity waveform (see FIG. 3). The level of the peak value of the thermal asperity waveform and the generation time of the thermal asperity waveform are obtained. And projection height calculation part 3
, The height h of the protrusion P present on the recording surface S of the magnetic tape MT is calculated from the level of the peak value of the thermal asperity waveform detected by the thermal asperity waveform detector 2. Further, the projection width calculation unit 4 calculates the width d of the projection P existing on the recording surface S of the magnetic tape MT from the generation time of the thermal asperity waveform detected by the thermal asperity waveform detection unit 2. Further, in the medium position information calculation unit 5, the position information (Xp, Y) of the protrusion P
p) is calculated. Hereinafter, a method for measuring the height h of the projection P in the projection height calculation unit 3 will be described. FIG. 4 shows the peak value level (TA level) of the thermal asperity waveform and the protrusion P present on the recording surface S of the magnetic tape MT.
It is a graph which shows the relationship with height (projection height) h. As shown in FIG. 4, it can be seen that the TA level and the projection height h have a correlation, and the projection height h increases as the TA level increases. Therefore, the projection height calculation unit 3 calculates the projection height h from the peak value level (TA level) of the thermal asperity waveform detected by the thermal asperity waveform detection unit 2 using the graph of FIG. be able to. Next, a method for detecting the width d of the protrusion P in the protrusion width calculation unit 4 will be described. FIG. 5 is a graph showing the relationship between the generation time (TA generation time) of the thermal asperity waveform and the width (protrusion width) d of the protrusion P existing on the recording surface S of the magnetic tape MT. As shown in FIG. 5, there is a correlation between the TA occurrence time and the protrusion width d.
It can be seen that the protrusion width d increases as the generation time increases. Therefore, the projection width d can be calculated from the generation time (TA generation time) of the thermal asperity waveform detected by the thermal asperity waveform detection unit 2 using the graph of FIG. It should be noted that the graph showing the relationship between the peak value level of the thermal asperity waveform and the height of the protrusion in FIG. 4 and the graph showing the relationship between the generation time of the thermal asperity waveform and the width of the protrusion in FIG. It shall be obtained by experiments and calculations. Here, a thermal asperity waveform generated as a result of reproducing a magnetic recording medium having various protrusions is measured, and the protrusion height h and protrusion width d are measured for each protrusion by a three-dimensional measuring optical interference surface roughness meter or the like. Measure and plot these data to create a graph. As described above, according to the method for measuring the surface roughness of the magnetic recording medium of the present invention, the magnetic tape is obtained from the thermal asperity waveform generated by frictional heat generated when the reproducing magnetic head H and the magnetic tape MT are in contact. MT recording surface S
The protrusion height h and the protrusion width d of the protrusion P existing above can be easily obtained. In addition, since the effect of the protrusions on the reproducing magnetic head is measured, by setting an upper limit value as a product standard for the peak value level of the thermal asperity waveform and the generation time of the thermal asperity waveform,
Product performance evaluation can be performed appropriately, and product defects can be prevented. In the present embodiment, the case where a magnetic tape is used as the magnetic recording medium has been described. The thermal asperity waveform varies greatly depending on the relative speed between the reproducing magnetic head and the magnetic recording medium, the shape of the reproducing magnetic head, the magnitude of the sense current, etc.
It differs depending on the type of magnetic recording medium. Therefore, if the shape of the reproducing magnetic head is the same as that of the reproducing magnetic head used during actual reproduction, and the other various conditions are the same as those during reproduction, the contact state between the actual medium and the reproducing magnetic head can be accurately determined. Can be reproduced. According to the method for measuring the surface roughness of the magnetic tape of the present invention, the relationship between the level of the peak value of the thermal asperity waveform and the height of the protrusion existing on the magnetic recording medium is obtained in advance. Thus, the height of the protrusions present on the magnetic recording medium can be calculated from the thermal asperity waveform generated when the reproducing magnetic head reproduces the magnetic recording medium. Therefore, the width of the protrusion existing on the magnetic recording medium can be easily obtained from the thermal asperity waveform. Further, the height of the protrusions existing on the magnetic recording medium can be measured with the same sensitivity as the magnetic head receives when the actual magnetic recording medium is in contact with the magnetic head.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the configuration of a surface roughness measuring apparatus according to the present invention. FIG. 2 is a schematic perspective view showing protrusions existing on a recording surface of a magnetic tape. 3 is a graph showing a thermal asperity waveform detected by a thermal asperity waveform detection unit of the surface roughness measuring apparatus of FIG. 1. FIG. FIG. 4 is a graph showing the relationship between the peak value level of a thermal asperity waveform and the height of a protrusion. FIG. 5 is a graph showing the relationship between the generation time of a thermal asperity waveform and the width of a protrusion. [Explanation of Symbols] 1 Surface Roughness Measuring Device 2 Thermal Asperity Waveform Detection Unit 3 Projection Height Calculation Unit 4 Projection Width Calculation Unit 5 Medium Position Information Calculation Unit H Reproducing Magnetic Head MT Magnetic Tape S Recording Surface P Projection h Projection Height d Protrusion width

Claims (1)

1. A peak level of a thermal asperity waveform generated by frictional heat with a magnetic recording medium when a reproducing magnetic head using a magnetoresistive effect element reproduces the magnetic recording medium. From the peak value level of the thermal asperity waveform, utilizing the relationship between the peak value level obtained in advance and the height of the protrusions present on the magnetic recording medium,
A method for measuring the surface roughness of a magnetic recording medium, wherein the height of the protrusion is calculated.