JP4543665B2 - Method and apparatus for detecting surface defects - Google Patents

Description

  The present invention provides a glossy material, for example, a magnetic layer surface or backcoat layer surface of a magnetic recording medium such as a magnetic tape, a surface of a rolled material, a polished metal, a surface of a resin with a high light reflectance, a glass surface, etc. The present invention relates to a surface defect detection method and apparatus that can detect surface defects such as defects, deposits, and scratches at the time of very fine coating on the surfaces of various materials.

  Conventional methods for inspecting magnetic recording media, such as magnetic tape, generally record signals on the magnetic tape using a magnetic head and reproduce them, and determine the presence or absence of defects in the magnetic tape from the reproduction level. .

  Such an inspection method has been considered to be the most reliable inspection method because there is a large correlation between the scratches on the magnetic recording medium and the actual damage appearing in the reproduction signal.

  Specifically, this conventional method of inspecting a magnetic recording medium is designed to inspect at high speed and high efficiency by running the magnetic recording medium at high speed and using a multi-channel fixed magnetic head as a signal reproducing head. I was doing.

  In the field of defect inspection of such magnetic recording media, in order to cope with the recent increase in the density of recorded information on magnetic recording media, high resolution capable of detecting even finer and minute defects than before is required. Has been.

  However, in the defect inspection method on the surface of the magnetic recording medium using the multi-channel fixed magnetic head as described above, it is not easy to increase the detection resolution due to the limitations in the manufacturing technology of the magnetic head. The practical limit is about 50 μm in the width direction of the recording medium, and about 20 μm is the limit even if an expert performs an inspection by adjusting the conditions of the apparatus. In addition, the larger the number of channels, the larger the apparatus, which causes an increase in cost.

  Further, as a magnetic recording medium inspection method capable of obtaining a higher inspection resolution than when using the multi-channel fixed magnetic head as described above, an optical magnetic recording as disclosed in Patent Document 1 or Patent Document 2 is used. There is a method for inspecting a surface defect of a medium.

  In the magnetic tape inspection method of Patent Document 1, light irradiated from a red LED (light emitting diode) light source is reflected on the surface of the magnetic tape, and when the light is received and detected by the sensor head, the light receiving axis direction of the sensor head is set to the magnetic tape. By inclining a certain angle with respect to the normal direction of the principal surface, the signal of the defective portion can be detected with high SN.

  The method for inspecting the surface of a magnetic recording medium disclosed in Patent Document 2 is that when the surface of the magnetic layer is irradiated with halogen light and the reflected light is received and detected by a CCD camera, the light projection / reception angle is set to a specific range, and the incident light By deviating the optical axis position from the reflection point, the signal output level is maximized and the system noise is minimized.

  Furthermore, the optical inspection method for a magnetic disk disclosed in Patent Document 3 is such that a light beam is incident from a direction having an inclination angle with respect to a vertical line of the magnetic disk surface, and light scattered above the disk surface is imaged and darkened. In addition to obtaining a field image, the dark field image is received by a line sensor in which light receiving elements are arranged, and the scattered light intensity is measured. The incident light beam is scanned over the inspection area of the disk surface, and the line sensor One or a plurality of elements are detected as a defective portion when a signal having an intensity of a predetermined level or higher is acquired for a predetermined time or more.

  In particular, in the case of a magnetic recording medium device or the like that makes full use of recent high-density recording technology, for example, in the case of a defect such as a defect at the time of applying a magnetic layer, a deposit, a scratch, etc., its height is low, and the entire shape is gentle. For this reason, the influence on the reproduction signal is relatively gradual, but if many defects are concentrated, the error rate increases. When the size is 10 to 20 μm, an increase in error rate is recognized in the reproduction signal. There is a demand for a method and apparatus that can stably and easily detect defects having a size of about 10 to 20 μm.

Japanese Patent Application Laid-Open No. 8-201309 JP-A-8-233560 Japanese Patent Laid-Open No. 10-143801

  However, although the method disclosed in Patent Document 1 has a small amount of light from the LED light source and is capable of detecting a large foreign matter or the like because of the total reflection method, it can stably detect a defect having a size of 10 to 20 μm. It was difficult to detect.

  Further, the surface inspection method of the magnetic recording medium of Patent Document 2 also has a problem that it is difficult to stably detect a defect having a size of 10 to 20 μm because it is a total reflection detection. .

  Furthermore, in the optical disk inspection method disclosed in Patent Document 3, since a dark field image is obtained by forming an image of scattered light from a direct irradiation region by irradiation light, a defect portion is detected for a minute defect. There is a problem that the strong wave value of scattered light from the light source is at a low level and the SN ratio is low.

  Further, the surface defect inspection method disclosed in each of the above patent documents is applicable to fields other than the surface of the magnetic recording medium, for example, a defect inspection of the strip surface in the rolling process, a defect inspection of the plating surface, and a glass product such as a glass substrate. It is used for inspection of surface defects, inspection of polished metal surfaces in machining processes, etc., but in any case, it is difficult to detect because the ratio of scattered light at the defect portion and its background light is small There were many things.

  The present invention has been made in view of the above-described conventional problems, and provides an optical surface defect detection method and apparatus capable of reliably detecting even a minute defect with a high S / N ratio. With the goal.

  The present inventor has conducted extensive research on a method for inspecting the surface of a magnetic tape or the like, and has inspected the camera optical axis tilted at a fixed angle with respect to the normal of the surface of the object to be inspected, and slightly shifted from this area Then, a light source image area where the mirror image of the parallel light exit is located is set, and the scattered light from the surface defect in an area darker than the area, that is, an area where the amount of background light is small is received by the camera. It was found that surface defects can be detected by the S / N ratio.

  That is, the above object can be achieved by the following present invention.

(1) An inspection area by a camera is set on the surface of the inspection object, and a camera optical axis passing through the center of the inspection area has an inclination angle β with respect to the normal of the inspection object surface is 0 <β ≦ 10 ° When the light is incident on the irradiation area including the inspection area, a mirror image of the light emission port is located at a position in the irradiation area and adjacent to the outside of the inspection area. The light exit port is set so as to be positioned, and a set straight line passing through the center of the light exit port and the center of the inspection region is a camera symmetric optical axis of the camera optical axis with respect to the normal line. Is set to 0 <α <25 °, and the scattered light from the inspection region is received by the camera and converted into a light reception signal, which is received from a defect-free portion of the inspection region. When the intensity of the received light signal is greater than a certain value, Detecting a surface defect on the surface of the test object, the light source image area mirror image of the exit port of the light is positioned, when the total length of the adjacent direction from the examination region and is W, the said light source image area A method for detecting a surface defect, wherein a distance D from the center position in the adjacent direction to the inspection region is set to W / 2 <D ≦ 3W / 2 .

(2) the angle of inclination α, 0 <α <How to detect surface defects according to the above wherein the 5 ° and the fact (1).

(3) The inclination angle α is set to any one of 5 ° ≦ α <10 °, 10 ° ≦ α <15 °, or 15 ° ≦ α <25 °. how to detect surface defects.

( 4 ) The light source image area where the mirror image of the light exit port is positioned by the camera has a linear band shape, and the irradiation optical axis is in a plane parallel to the center line in the width direction of the light source image area. And the inspection area has a linear band shape parallel to the linear light source image area, and the camera optical axis has the light exit port with respect to the normal line. (1) to ( 3 ), characterized in that they are inclined at an inclination angle β on the opposite side of the set straight line, and are within a plane including a center line in the width direction in the inspection region of the straight band shape. The surface defect detection method according to any one of the above.

( 5 ) With respect to the first virtual plane parallel to the center line in the width direction of each of the light source image area and the inspection area and perpendicular to the surface of the inspection object, the first virtual plane and the surface of the inspection object In a second vertical virtual plane, the irradiation optical axis of the parallel light is inclined at an inclination angle α with respect to the camera symmetric optical axis, and the camera optical axis is opposite to the irradiation optical axis. ( 4 ) The method for detecting a surface defect according to ( 4 ), wherein the surface defect is set at an inclination angle β with respect to one virtual plane.

( 6 ) When the inspection object is a belt-like material, the light source image region and the inspection region are set to a straight belt shape that traverses the belt-like material in the width direction, and the belt is run in the longitudinal direction. The method for detecting a surface defect according to ( 4 ) or ( 5 ), wherein a defect is detected.

( 7 ) The camera is a CCD line camera, and an incident optical axis plane including a plurality of incident optical axes of the CCD line camera is set to coincide with a plane including a center line in the width direction of the inspection region. to (4) to the detection method of surface defects according to any one of (6).

( 8 ) A support device that supports the inspection object so that at least a part of the surface thereof passes through the inspection position at a fixed position in the thickness direction or stops at the inspection position, and an inspection area is provided on the surface at the inspection position. A received light signal having an intensity proportional to the incident light intensity is set and the camera optical axis is inclined with respect to the normal on the surface so that the inclination angle β is 0 <β ≦ 10 °. And a light source in which a mirror image of the light emission port is located in a position adjacent to the outside of the inspection region in the irradiation region. An inclination angle α formed by a straight line that forms an image area and passes through the center of the light exit port and the center of the inspection area, and the camera symmetric optical axis of the camera optical axis with respect to the normal line is 0 ° < The inspection light irradiation device set to α <25 ° and the camera Ri intensity of the received light signal from the LA is Na a, a determination unit that outputs a defect detection signal is greater than a predetermined value than the intensity of the received signal due to incident light from the defect-free portion in the examination region, wherein The camera has a distance D from the center position in the direction of the light source image area to the inspection area, where W is the total length of the light source image area in the direction toward the center of the light source image area when viewed from the inspection area. , W / 2 <surface defect detection apparatus you characterized in that it is set to be D ≦ 3W / 2.

(9) the angle of inclination alpha in the inspection light irradiation device, 0 <a surface defect detection apparatus according to (8) that it has the alpha <5 °.

(1 0 ) The inclination angle α in the inspection light irradiation apparatus is set to any one of 5 ° ≦ α <10 °, 10 ° ≦ α <15 °, or 15 ° ≦ α <25 °. surface defect detection apparatus according to (8) and.

(1 1 ) The inspection light irradiation apparatus is set so that the light source image region has a linear band shape and the irradiation optical axis of the light is in a plane parallel to the center line in the width direction of the light source image region. In the camera, the inspection area has a linear band shape parallel to the light source image area having the linear band shape, and the optical axis of the camera has an exit of the light with respect to the normal line. ( 8 ) to (1 0 ) characterized in that they are inclined at an inclination angle β on the opposite side of the set straight line, and are within a plane including the center line in the width direction in the inspection region of the straight band shape. The surface defect detection device according to any one of the above.

(1 2 ) The inspection light irradiation apparatus uses the first virtual plane with respect to a first virtual plane that is parallel to the center line in the width direction of each of the light source image area and the inspection area and perpendicular to the surface of the inspection object. In the second virtual plane perpendicular to the plane and the surface of the inspection object, the set straight line passing through the light exit port is inclined at an inclination angle α, and the camera has the camera optical axis, The surface defect detection device according to (1 1 ), wherein the surface defect detection device is provided at an inclination angle β on the opposite side to the set straight line.

(1 3 ) The inspection object is a strip-shaped material, and the support device is configured to travel the strip-shaped material in the longitudinal direction, and the inspection light irradiation device and the camera include the light source image region and the inspection region. The surface defect detection device according to (1 1 ) or (1 2 ), wherein the surface defect detection device is set so as to have a linear strip shape that traverses the strip in the width direction.

(1 4 ) The camera is a CCD line camera, and an incident optical axis plane including a plurality of incident optical axes of the CCD line camera is set to coincide with a plane including a center line in the width direction of the inspection area. the constitution (1 1) to the surface defect detection apparatus according to any one of (1 3).

  As described above, when the irradiation optical axis of light that is inspection light, the inspection region of the camera, and the camera optical axis thereof are set, a light reception signal based on scattered light from the defect portion can be obtained with a high SN ratio.

  Since the present invention is configured as described above, it has an excellent effect that surface defects such as magnetic tape can be detected with high SNR.

  An inspection region by a camera is set on the surface of the inspection object, and the camera optical axis passing through the center of the inspection region is set such that the inclination angle β with respect to the normal of the surface of the inspection object is 0 <β ≦ 10 °. When the light is incident on the irradiation area including the inspection area, the mirror image of the light emission port is positioned in the irradiation area and adjacent to the outside of the inspection area. And an inclination angle formed by a setting straight line passing through the center of the light exit port and the center of the inspection region with the camera symmetric optical axis of the camera optical axis with respect to the normal line. α is set to 0 <α <5 °, and the scattered light from the inspection region is received by the camera and converted into a light reception signal. This light reception signal is the intensity of the light reception signal from the defect-free portion of the inspection region. When the surface defect of the inspection object is larger than a certain value To achieve the above object by detecting Te.

  Embodiment 1 of the present invention will be described below in detail with reference to the drawings. In the first embodiment, the inspection object is a magnetic recording medium.

  As shown in FIG. 1, the surface defect detection device 10 according to the first embodiment includes a support device 14 that supports the inspection unit 12 </ b> A of the magnetic tape 12 that is a magnetic recording medium in a plane shape, and the support device 14. A first virtual plane 16 (see FIG. 2) that includes a normal line 16A (see FIG. 2) with the surface of the magnetic tape 12 supported in the shape of a straight plane and crosses the magnetic tape 12 in the width direction. The camera optical axis 21 passing through the widthwise center line 22B (see FIG. 4) of the strip-shaped inspection region 22A set on the intersection with the surface of the magnetic tape 12 has an inclination angle β with respect to the first virtual plane 16. Irradiate light 18 to the irradiation area 30 including the CCD line camera 22 and the belt-shaped inspection area 22A arranged so as to satisfy 0 <β ≦ 10 °, and within the irradiation area 30 from the belt-shaped inspection area 22A. As seen, one outer side in the width direction (Fig. A strip-like light source image region (region where a mirror image of the light exit port 18B, which is the exit port of the light 18) is formed, which crosses the magnetic tape 12 in the width direction at a position adjacent to the left side). A defect signal is output when the intensity of the received light signal from the inspection light irradiation device 20 and the CCD line camera 22 is larger than the intensity of the received light signal by the incident light from the defect-free portion in the strip-shaped inspection area 22A. And a determination device 24.

  The inclination angle β is an angle in the second imaginary plane 17 that includes the normal 16A and is perpendicular to the first imaginary plane 16 and the surface of the inspection unit 12A.

  The camera symmetric optical axis 23 of the camera optical axis 21 with the first virtual plane 16 as a symmetric plane is within the second virtual plane 17 with respect to the first virtual plane 16 and the camera optical axis 21. The angle β is inclined to the opposite side. An irradiation optical axis 19 of the light 18 is set so as to connect a virtual position 22M for observing a mirror image of the CCD line camera 22 with the surface of the inspection unit 12A as a symmetry plane, and a light exit port 18B. Further, the light exit port 18B of the inspection light irradiation device 20 is set so that a setting straight line 19B passing through the center thereof and the center line 22B in the width direction of the strip-shaped inspection region 22A intersects the camera symmetric optical axis 23 at an inclination angle α. Has been.

  As shown in FIG. 3, the support device 14 includes a pair of cylindrical guide members 26A and 26B arranged in parallel. In the range where the magnetic tape 12 is wound around the cylindrical guide members 26A and 26B. The magnetic tape 12, which is wound around the cylindrical guide members 26A and 26B by blowing compressed air therefrom, is formed in a non-contact state with the surface of the guide member. 12 is made to run while maintaining a straight plane shape. The portion of the magnetic tape 12 that is maintained in the shape of a right plane is the detection unit 12A.

  The support device 14 may be any device as long as it can run while maintaining the magnetic tape 12 in a plane shape, and is not limited to a device that does not contact the magnetic tape.

  The setting straight line 19B passing through the center of the light exit port 18B and the center in the width direction of the strip-shaped inspection region 22A is aligned with the camera-symmetric optical axis 23A including the camera-symmetric optical axis 23 and the center line in the width direction of the strip-shaped inspection region 22A. On the other hand, the CCD line camera 22 is disposed on the opposite side of the camera optical axis 21 with an inclination angle α. The inclination angle α is set in the range of 0 <α <25 ° as described later.

  The irradiation optical axis 19 and the camera optical axis 21 are both continuous in the width direction of the magnetic tape 12, and as shown in FIG. 4, the irradiation optical axis plane 19A and the camera optical axis plane 21A are thereby formed. It is formed. The camera optical axis surface 21A is inclined at an inclination angle β with respect to the virtual plane 16, and the irradiation optical axis surface 19A is formed through the center line 18C in the width direction of the light source image region 18A.

  As shown in FIG. 5, the light 18 and the camera optical axis 21 are set to be perpendicular to and overlap with the magnetic tape 12 when viewed from the traveling direction of the magnetic tape 12.

  As shown in FIG. 1, the inspection light irradiation device 20 includes a halogen lamp 28 </ b> A and an optical fiber bundle 28 </ b> B for guiding the light, and is supported by the support device 14 in a plane shape. By irradiating the surface of the tape 12, as described above, the irradiation region 30 including the band-like light source image region 18A that traverses the magnetic tape 12 in the width direction is formed. The irradiation area 30 is composed of the light source image area 18A as a central portion and a light source image outer area 18D (see FIG. 4, which will be described later in detail) outside the light source image but not irradiated with the light source image. Yes.

  Here, the distance D of the strip-shaped inspection region 22A with respect to the center line 18C in the width direction of the strip-shaped light source image region 18A is W / 2 when the width of the light source image region 18A is W as shown in FIG. <D ≦ 3W / 2. In the case of D ≦ W / 2, strong irradiation light may be incident as disturbance light. If D> 3W / 2, the band-shaped inspection region 22A is located away from the light source image region 18A in the light source image outer region 18D, so that the irradiation light is weak, and therefore the scattered light obtained from this region is weak. . Note that since the irradiation light gradually weakens away from the light source image region 18A, the outer peripheral edge of the light source image outer region 18D, that is, the outer peripheral edge of the irradiation region 30, is unclear.

  The determination device 24 is incident on the CCD line camera 22 from the CCD line camera 22 at a position corresponding to the resolution in the tape width direction at a predetermined interval in the longitudinal direction of the magnetic tape 12, that is, a predetermined line scanning cycle. When a luminance signal is received corresponding to the light energy to be received, and the luminance signal is compared with the level (low level) of the luminance signal in the defect-free portion in the strip inspection region 22A, there is a difference of a certain value or more. When a defect signal is output.

  More specifically, the integrated value obtained by accumulating incident light energy is output as a luminance signal from the CCD line camera 22, and in the determination device 24, the luminance signal is preset by the comparator 24A. The defect signal is output when the input luminance signal is larger than the comparison value as compared with the luminance signal (comparison value) obtained by adding a predetermined value to the low-level luminance.

  When the surface defect detection apparatus 10 as described above detects a defect on the surface of the magnetic tape 12, the strip-shaped inspection area 22 </ b> A is set adjacent to the outside of the light source image area 18 </ b> A by the light 18. The luminance signal obtained by the CCD line camera 22 is almost at the black level in the portion having no defect on the surface 12, and the degree of increase in luminance due to the flatness of the magnetic tape 12 and the optical system is small.

  More specifically, as shown in FIG. 4, the band-shaped inspection region 22A is included in the light source image outer region 18D adjacent to the outside of the light source image region 18A by the light 18, and as described above, the camera Since the light exit port 18B is on the setting straight line 19B of the inclination angle α with respect to the camera symmetric optical axis 23 of the optical axis 21, the regular reflection light of the light 18 on the light source image area 18A enters the CCD line camera 22. There is nothing.

  On the other hand, if there is any defect on the surface of the magnetic tape 12, the irradiation light is scattered in the strip inspection region 22 </ b> A, and a part of the scattered light enters the CCD line camera 22.

  As described above, since the brightness of the magnetic tape 12 in the light source image outer region 18D is almost close to the black level, the scattered light from the defective portion has a high brightness with respect to this black level, and as a result, the SNR of the detection signal is greatly increased. To be improved. On the other hand, when the band-like light source image area and the inspection area are matched with each other as before, the brightness of the defect-free part is high and the brightness of the defective part falls, and a certain brightness difference is obtained, but the defect detection Therefore, the high SNR as in the present invention cannot be obtained.

  Here, the relationship between the setting of the inclination angle α and the type of defect on the surface of the magnetic tape 12 will be described.

  As shown in FIG. 6, when the concave portion 32 such as a pressing rod is on the surface of the magnetic tape 12, the amount of scattered light from the concave portion 32 is small, the SN ratio level is considerably small, and the amount of scattered light is specifically large. The angle is close to the normal 16 </ b> A of the surface of the magnetic tape 12 or the first imaginary plane 16. Therefore, in order to increase the level of the SN ratio, the inclination angle α is set to 5 ° or less and as close to 0 ° as possible.

  When the inclination angle α is close to 0, the irradiation optical axis 19 of the light 18 and the camera symmetric optical axis 23 are parallel and close to each other, so that erroneous detection occurs when the magnetic tape 12 flutters during its travel. Therefore, in order to maintain the flatness of the magnetic tape 12 at the time of inspection, the running tension, speed fluctuation, tape guide shape, and the like may be adjusted.

  Further, as shown in FIG. 7, when the surface of the magnetic tape 12 is high in the height of defects, deposits, etc. during application and has a large convex portion 34, the comparison from the side surface 34A of the convex portion 34 is made. A large amount of scattered light can be obtained. Reference numerals γ and γ ′ in FIG. 7 indicate the angles of incident light and scattered light with respect to the normal of the side surface 34A when the light 18 is reflected by the side surface 34A and enters the CCD line camera 22.

  Therefore, as described above, in order to obtain a high S / N ratio, it is preferable to make the inclination angle α as close to 0 ° as possible. However, there is a risk that the inspection area may enter the regular reflection area due to flapping of the magnetic tape or the like. Therefore, it is preferable to set the inclination angle α in a slightly large range of 5 ° or more in consideration of the stability of inspection.

  Furthermore, from the case where priority is given to the stability of inspection to the case where high S / N ratio is prioritized, it is divided into three stages, 15 ° ≦ α <25 °, 10 ° ≦ α <15 °, 5 ° ≦ α <10 °. It is good to select and set any one of the three ranges.

  Regarding β, noise due to ambient light from the surroundings of the inspection environment tends to gather when β = 0 °, and when β> 10 °, the degree of surface defects viewed from an oblique direction increases, so that the defects are observed small. Since sensitivity is lowered, 0 <β ≦ 10 ° is appropriate.

  In addition, although the said Example 1 is related with the apparatus which detects the surface defect of the magnetic tape 12, this invention is not limited to this, The surface of a glass substrate, a plating surface, a polished metal surface, etc. This can be applied when detecting defects on the surface of a material having a high reflectance.

  In the example of the above embodiment, the light 18 is used. However, this light only needs to have an irradiation area outside a certain area on the irradiation optical axis. Either a bundle or a diverging ray bundle may be used.

  The surface defect detection apparatus 10 forms a band-like light source image area 18A on the surface of the magnetic tape 12 that is the inspection object, and the CCD line camera 22 has a band-like inspection area 22A. The present invention is not limited to this, and the light source image area and the inspection area may be spot-like. In this case, the inclination angles α and β are set based on the normal line of the surface to be inspected. The offset amount D between the light source image spot and the inspection spot is also set in the range of W / 2 <D ≦ 3W / 2. Here, the width W of the light source image spot is the outer diameter in the center direction of the light source image spot as viewed from the inspection spot.

  The inspection light irradiating device 20 may be of various types such as a halogen lamp, an LED, a sodium lamp, and a laser diode as the light source type, but a halogen lamp is particularly preferable because of its large absolute light quantity and easy light control. Are better.

  Furthermore, the strip-shaped inspection area 22A is set so as to cross the surface of the magnetic tape 12 at a right angle to the feeding direction, but the present invention is not limited to this, and this is the width direction of the tape. The inclination may be within ± 40 degrees, preferably within ± 20 degrees.

  In Example 2, a 1/2 inch wide video magnetic tape (including a coating type magnetic layer and a backcoat layer) was used as a measurement object, and a halogen lamp was used as a light source type of the inspection light irradiation apparatus.

  The CCD line camera has a lens for a commercially available Leica size single-lens reflex camera, the CCD array has a number of pixels in the tape width direction of 1024, and the magnetic tape has a feed speed of V = 5 m / sec. Thus, the resolution in the tape width direction was set to 12 μm, and the size in the tape running direction was set to 128 μm.

  FIG. 8A shows the detection result on the magnetic layer side. Corresponding to this, FIG. 8B shows the conventional surface result detection in which the same defect is matched with the band-like light source image region and the inspection region. The result measured by the apparatus is shown. 8A and 8B show the cases where the defect type is a deposit.

  As can be seen from these figures, in FIG. 8B, the luminance signal has fallen significantly at the defective portion indicated by the symbol Xb. It is difficult to discriminate whether or not.

  On the other hand, in the second embodiment of the present invention, as indicated by the symbol Xa in FIG. 8A, the luminance signal rises greatly in the defective portion, and no confusing signal is seen in other portions. Therefore, it can be seen that surface defects can be detected with a high SNR.

  Next, the result obtained by experiment about the relationship between the said inclination-angle (alpha) and (beta) and the SN ratio (SNR) about each when a defect is a convex part and a recessed part is shown.

  Table 1 and FIG. 9 are measured on the magnetic layer side of the same magnetic tape as described above, and show the relationship between the inclination angles α, β and the SNR when the convex portion is formed by the deposit as a defect. ing.

  The value of SNR was obtained as follows. SNR = a / b, where a is the luminance signal intensity from the defect and b is the low level luminance signal intensity. However, when a is smaller than b as shown in FIG. 8B, SNR = − (1−a / b). Further, as illustrated in FIG. 2, α is a positive value when the setting straight line 19B is inclined in the direction away from the normal 16 with respect to the camera symmetric optical axis 23, and the case where it is inclined in the opposite direction. Expressed as a negative value. This minus notation is only for indicating the direction, and the absolute value is the inclination α of the present invention.

  In Table 1, ◯ indicates a range where the obtained SNR is a preferable range, X indicates a range where the set tilt angle is out of a usable range, and Δ indicates a usable range. In addition, no mark also indicates out of use range.

  From Table 1 and FIG. 9, when the defect is a convex part such as an adherent, the inclination angle β is in the range of 0 <β ≦ 10 °, and the inclination angle α is most preferably 5 ° ≦ α <10 °, It can be seen that good SNR can be obtained in the order of 10 ° ≦ α <15 ° and 15 ° ≦ α <25 °.

  For data with β of 15 ° and 20 °, the SNR value itself may be good, but for the reasons described above, the 15 ° and 20 ° columns are meant to be outside the range that can be used in the present invention. Is marked with an X.

  Next, in Table 2 and FIG. 10, the inclination angles α, β, and SNR are shown in the case of a concave portion (a minute one having a size of about 10 μm) where the defects on the backcoat side surface of the magnetic tape are the same as those described above. The relationship is shown.

  In Table 2, ◯, x, and no marks indicate the same ranges as in Table 1. From Table 2, it can be seen that in the region of 0 <β ≦ 10 °, good detection results can be obtained when the inclination angle α is smaller than 5 ° and as close as possible to 0 °. More specifically, 0 <β ≦ 5 ° and α is preferably 4 ° or less, more preferably 0 <β ≦ 5 ° and α is 3 ° or less. In the range of 5 <β ≦ 10 °, the effect of the present invention can be obtained if α is 3 ° or less.

  In addition, since the size of the concave defect on the back coat side surface of the magnetic tape used is very fine, the amount of scattered light from the defective portion is small, and the SNR value obtained is low, but the magnetic tape running system (Specifically, the traveling speed is set low and the flatness of the inspection unit 12A is increased) so that the SNR can be improved and detected.

1 is a perspective view including a partial block diagram illustrating a surface defect detection apparatus according to Embodiment 1 of the present invention. FIG. The schematic diagram which shows the relationship between the irradiation optical axis (surface) of the parallel light in the same surface defect detection apparatus, and the camera optical axis (surface) of a CCD line camera The perspective view which shows the support apparatus for supporting a magnetic tape in the same surface defect detection apparatus Schematic diagram showing an enlarged relationship between the irradiation area, inspection area, light source image area, and non-light source image area on the magnetic tape surface with light. Schematic view of the relationship between the parallel light irradiation optical axis and the camera optical axis as seen from the tape feed direction Schematic diagram showing the relationship between parallel light and scattered light when the defect on the surface of the magnetic tape is a recess. Schematic diagram showing the relationship between parallel light and scattered light when the defects on the surface of the magnetic tape are convex. The diagram which shows the waveform of the detection signal at the time of detecting the deposit | attachment defect on the magnetic tape surface with the surface defect detection apparatus concerning Example 2 compared with a prior art example. The diagram which shows the relationship between inclination-angle (beta) and (alpha) and the SNR of a detected value in case the defect part of the magnetic tape surface is a convex part Diagram similar to FIG. 9 when the defect on the surface of the magnetic tape is a recess

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Surface defect detection apparatus 12 ... Magnetic tape 12A ... Inspection part 14 ... Supporting device 16 ... 1st virtual plane 16A ... Normal 18 ... Light 18A ... Light source image area 18B ... Light emission port 18C ... Center line 18D in the width direction ... Light source image outer region 19 ... Irradiation optical axis 19A ... Irradiation optical axis surface 19B ... Setting straight line 20 ... Inspection light irradiation device 21 ... Camera optical axis 21A ... Camera optical axis surface 22 ... CCD line camera 22A ... Strip inspection region 22B ... Width direction Center line 22M ... Virtual position 23 ... Optical axis symmetrical to camera 24 ... Determination device 30 ... Concave portion 32 ... Convex portion 32A ... Side surface

Claims (14)

An inspection region by a camera is set on the surface of the inspection object, and the camera optical axis passing through the center of the inspection region is set such that the inclination angle β with respect to the normal of the surface of the inspection object is 0 <β ≦ 10 °. When the light is incident on the irradiation area including the inspection area, a mirror image of the light emission port is positioned at a position in the irradiation area and adjacent to the outside of the inspection area. And a setting straight line passing through the center of the light exit port and the center of the inspection region is inclined with respect to the normal line with the camera symmetric optical axis. The angle α is set to 0 <α <25 °, and the scattered light from the inspection region is received by the camera and converted into a light reception signal. This light reception signal is a signal received from a defect-free portion in the inspection region. If the surface is larger than the strength by a certain value or more, Detected as, the surface of the test object, the light source image area mirror image of the exit port of the light is positioned, when the total length of the adjacent direction from the examination region and is W, the neighboring direction of the light source image area A method for detecting a surface defect, wherein a distance D from a center position to the inspection region is set to W / 2 <D ≦ 3W / 2 . In claim 1, the inclination angle α, 0 <α <5 ° and then detection method of surface defects, characterized in that the. The surface defect according to claim 1, wherein the inclination angle α is set to any one of 5 ° ≦ α <10 °, 10 ° ≦ α <15 °, or 15 ° ≦ α <25 °. How to detect. In any one of claims 1 to 3, the light, with the light source image area located a mirror image of the exit of the light becomes linear band shape by the camera, the illumination optical axis, the width direction of the light source image area The inspection area is set to be in a plane parallel to the center line, and the inspection area has a linear band shape parallel to the linear light source image area, and the camera optical axis is relative to the normal line. The surface is inclined so as to be opposite to the set straight line passing through the light emission port at an inclination angle β, and is set to be in a plane including a center line in the width direction in the inspection area of the straight belt shape. Defect detection method. 5. The first virtual plane and the inspection object with respect to a first virtual plane parallel to the center line in the width direction of each of the light source image area and the inspection area and perpendicular to the surface of the inspection object according to claim 4 . In a second virtual plane perpendicular to the surface, the irradiation optical axis of the light is inclined at an inclination angle α with respect to the camera symmetric optical axis, and the camera optical axis is opposite to the irradiation optical axis. A method for detecting a surface defect, characterized in that the surface defect is set at an inclination angle β with respect to the first virtual plane. In Claim 4 or 5 , when the inspection object is a strip-shaped material, the light source image region and the inspection region are set in a straight strip shape that crosses the strip-shaped material in the width direction, and the strip-shaped material is set in the longitudinal direction. A method for detecting a surface defect, wherein the surface defect is detected while running. 7. The CCD line camera according to claim 4 , wherein an incident optical axis surface including a plurality of incident optical axes of the CCD line camera coincides with a plane including a center line in the width direction of the inspection region. A method for detecting surface defects, characterized in that A support device that supports the inspection object so that at least a part of the surface thereof passes through the inspection position at a fixed position in the thickness direction or stops at the inspection position, and an inspection region is set on the surface at the inspection position; In addition, the camera optical axis is arranged to be inclined with respect to the normal on the surface so that the inclination angle β is 0 <β ≦ 10 °, and a light reception signal having an intensity proportional to the incident light intensity is output. A light source image region in which a mirror image of the light emission port is located at a position adjacent to the outside of the inspection region in the irradiation region, while irradiating light to the camera and the irradiation region including the inspection region. The inclination angle α formed by the straight line passing through the center of the light exit port and the center of the inspection region and the camera symmetric optical axis with respect to the normal line of the camera optical axis is 0 ° <α <25. From the inspection light irradiation device set to ° and the camera A determination unit intensity of the received light signal to output a defect detection signal is greater than a predetermined value than the intensity of the received signal due to incident light from the defect-free portion in the examination region, Ri na have the camera, When the total length of the light source image area in the direction from the inspection area toward the center of the light source image area is W, a distance D from the center position of the light source image area in the direction to the inspection area is W / 2 <surface defect detection apparatus you characterized in that it is set to be D ≦ 3W / 2. In claim 8, the inclination angle alpha in said inspection light irradiation device, 0 <α <5 ° and surface defect detecting apparatus, characterized in that the. The inclination angle α in the inspection light irradiation apparatus according to claim 8 is set to any of 5 ° ≦ α <10 °, 10 ° ≦ α <15 °, or 15 ° ≦ α <25 °. surface defect detecting apparatus according to claim. In any one of claims 8 to 1 0, wherein the inspection light irradiation device, the with the light source image area is the linear band shape, the irradiation optical axis of the light, and parallel to the width direction center line of the light source image area The camera is set to be in a plane, and the camera has a linear band shape parallel to the linear band-shaped light source image area, and the camera optical axis is set to the normal line. The light beam is inclined at an inclination angle β on the opposite side of the set straight line passing through the light exit and is set to be within a plane including a center line in the width direction in the inspection region of the straight belt shape. Surface defect detection device. According to claim 1 1, wherein the inspection light irradiation device, the light source image region and the inspection region parallel to the respective width-direction center line, and, with respect to the inspection object surface perpendicular to the first virtual plane, the first In the second virtual plane perpendicular to the surface of the object to be inspected and the set straight line passing through the light exit opening is inclined at an inclination angle α, and the camera has the optical axis of the camera Is provided at an inclination angle β on the opposite side to the set straight line. According to claim 1 1 or 1 2, wherein a test object is strip material, wherein the support device is configured to run the belt-shaped member in the longitudinal direction, the inspection light irradiation device and the camera, the light source image The surface defect detection apparatus, wherein the region and the inspection region are set to have a straight strip shape that crosses the strip in the width direction. 14. The camera according to claim 11, wherein the camera is a CCD line camera, and an incident optical axis plane including a plurality of incident optical axes of the CCD line camera is a plane including a center line in the width direction of the inspection region. A surface defect detection device characterized by being set to coincide.

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