JPH04145350A - Defectiveness inspection device - Google Patents

Abstract

PURPOSE:To prevent an article from being decided as a defective article because of a number of scratches contained within a connection range by arranging so that the changeover of thresholds whose purpose is to detect defectiveness, may be conducted within a predetermined range containing a joint and ordinary defectiveness may not be detected. CONSTITUTION:At a memory means 60, a set of threshold nu1 against an inspection range that does not contain a joint, and other inspection conditions, and a set of a threshold nu2 against an inspection range that contains a joint, and other inspection conditions, are contained. A sensor 64, when it detects a joint 66, outputs joint signals alpha1. alpha2 respectively. A connection range detecting means 68 seeks a connection range that contains the joint 66 on the basis of signals alpha1, alpha2, and delivers out a changeover signal beta showing its range, to a selecting means 70. The means 70, when the signal beta is '1', selects a set opposing the connection range from the memory means 60.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention uses an image signal obtained by scanning the surface of a rolled inspection object such as a steel plate, aluminum plate, copper plate, paper, or plastic film. The present invention relates to a defect inspection device that inspects for the presence or absence of defects.

(Technical Background of the Invention) A defect inspection device is known that optically scans the surface of a steel plate, paper, or the like to detect scratches on the surface or internal defects. Conventionally, the image signal obtained by scanning the inspection object is compared with a preset threshold value, and if the image signal falls outside the range determined by this threshold value, it is determined that there is a defect.

On the other hand, in the case of an inspection object rolled into a roll, there are usually many scratches at the leading and trailing ends of the roll, so these parts are ultimately cut off and discarded without being used as a product. In addition, in production lines for steel plates and the like, when changing rolls, the ends of the rolls before and after the change are welded together and sent to a splicing line. For this reason, there are many scratches near these welded joints, and the parts around these joints are not used as products and are eventually cut out and discarded.

When inspecting such inspection objects, conventional snowmaking systems detect defects using a predetermined threshold as described above, which causes many defects to occur at the edges of the rolls or at the joints (hereinafter simply referred to as joints). This means that the scratches will be judged as defects. For this reason, there is a problem in that a product is judged to be defective due to large scratches or multiple scratches on the part that is to be ultimately discarded.

(Purpose of the Invention) The present invention was made in view of the above circumstances, and even if many scratches occur near the joints of rolls (including the ends of the rolls), the product may be judged to be defective depending on these scratches. The object of the present invention is to provide a defect inspection device that detects defects only in the range that is actually used.

(Structure of the Invention) According to the present invention, the object is to detect defects in the inspection target by comparing an image signal obtained by scanning the inspection target with a predetermined threshold value. A joint range detection means detects a predetermined joint range including the target joint, and a threshold value at which it is difficult to detect defects is set for the joint range, and a normal method for detecting defects is set for other ranges. comprising memory means for separately storing threshold values; and selection means for selecting and reading out threshold values corresponding to the connecting range and other ranges from the memory means; This is achieved by a defect inspection device characterized in that it detects defects using.

Here, the joint sensors are provided at predetermined positions upstream and downstream of the inspection position of the object to be inspected, and the joint range detection means switches to a threshold value corresponding to the joint range based on the output of the upstream joint sensor. The threshold value may be reset to the original value based on the output of the joint sensor on the side.

Alternatively, one joint sensor may be provided only on the upstream side of scanning position 1, and the threshold value may be switched to a threshold value corresponding to the joint range within a certain range after the joint is detected.

(Function) When the seam sensor detects a seam while the inspection object is being fed, the seam range detection means changes the threshold value for defect detection while a predetermined range (joint range) including this seam is in the inspection position. do. For this reason, defects of a size less than a certain level or a depth less than a certain level within the joint range near the seam are not detected as defects. Also, by setting this threshold sufficiently large (or small), it is prohibited to detect defects within this transition range. As a result, most or all of the flaws within the connecting range are not detected as defects, and the product is not determined to be defective based on the flaws within this range.

(Embodiment) FIG. 1 is a block diagram of a first embodiment of the present invention, FIG. 2 is a diagram showing an example of a set of test conditions stored in a memory means,
3 to 5 are explanatory diagrams of signal processing. That is, FIG. 3 is an explanatory diagram of digital differential filtering processing, FIG. 4 is a diagram illustrating an example of a differential filter, and FIG. 5 is an explanatory diagram of density conversion characteristics of an image signal.

In FIG. 1, reference numeral 10 indicates an object to be inspected, such as a steel plate, paper, or plastic film, and this object 10 to be inspected is sent from a supply roll 12 to a take-up roll 14. This take-up roll 14 is driven by a take-up motor 16. The traveling speed (feeding speed) of the test object 10 being wound up by the motor 16 is detected by a speed detector (pulse generator) 18 . While the inspection object 1o is being transported, an image on the surface thereof is read by an image detection means 20 using a flying spot method. This image detection means 20 scans a scanning beam β made of laser light emitted from a laser light source 22 in the width direction of the inspection object 10 using a rotating mirror (polygonal mirror) 26 rotated by a motor 24 (main scanning). On the other hand, the light reflected by the surface of the inspection object 10 is transmitted to a pair of light receivers 30 (30a, 3
0b) and receives the light. That is, the light receiving rod 28 is disposed close to and parallel to the main scanning line 32 of the scanning beam 2, and when the reflected light is received, the light receiving rod 28
The light is totally reflected on the inner surface of the light beam 8 and guided to both ends thereof, and the amount of light received is detected by a light receiver 30 such as a photomultiplier (photomultiplier tube). The image signal output from each light receiver 30 is amplified by a preamplifier and a main amplifier, and is also waveform-shaped to become an analog image signal a l s a 2.

The level of each signal a + and a 2 decreases as it moves away from the scanning position on the main scanning line 32 of the scanning beam ρ, and on the contrary, the level increases as it approaches the scanning position. Therefore, in this embodiment, both signals a1 and a2 are added by an adding means 34, and the influence of the change in the scanning position on the main scanning line 32 is removed, resulting in a signal a3.

The output adjustment means 36 adjusts the gain and offset so that the image signal a3 has a desired amplitude and output level. Data used for signal processing in the output adjustment means 36, that is, test conditions including gain g, offset Or, other data, etc., are input from memory means 6o, which will be described later.

This output-adjusted signal a4 is converted into a digital signal al+ by the A/D conversion means 38. For example, it is converted into a 256-level density signal a5. and bulk memory 4
It is memorized to 0. Here, data such as the number of gradations for A/D conversion are input from memory means 60, which will be described later.

This bulk memory 4o has a storage capacity equal to the product (Nxn) of the number of pixels in the main scanning line and the number of scanning lines in the image display area on the monitor (Nxn). Store digital image signal a5. That is, it has a ring buffer structure in which when the storage area of the bulk memory 40 becomes full, the oldest data is sequentially overwritten.

Here, the inspection width gate signal indicates the inspection width within one main scan in synchronization with the rotation of the rotating mirror 26.

On the other hand, the signal a4 output-adjusted by the output adjustment means 36 is subjected to signal processing in the signal processing means 42. In this case, analog signal processing is performed, but the output a of the A/D conversion means 38 is
, may be digital signal processing in which the signal processing means 42 processes the signals.

This means 42 performs filtering processing using, for example, a differential filter. To explain this differential processing using the digital signal processing method described above, for example, as shown in FIG. Find the products of , and set their sum as the output value y. This operation is performed in rask scanning order from the upper left pixel to the lower right pixel.

As a spatial filter used in this filtering process, a filter having weighting coefficients shown in FIG. 4 can be employed. This uses two filters: a filter △, f for row direction differentiation and a filter △, f for column direction differentiation.
The final output value is the sum of the absolute values of the outputs of each filter, or the larger value of the outputs of both filters.

Here, the action of the differential filter has been explained using an example of digital signal processing, but in the case of analog signal processing, the image signal for each scan may be differentially processed using a known analog differential circuit.

As a result of such filtering processing, periodic fluctuations (low frequency components) included in the signal a3 due to changes in the optical path length of the scanning beam 2, changes in the angle of incidence, changes in the texture of the surface to be inspected, etc. are removed, and the image The contour in both the χ and y directions is emphasized, improving subsequent defect detection accuracy.

The signal processing means 42 may perform density conversion in addition to or in place of this differential processing. The conversion table used for this density conversion has the characteristics shown in FIG. 5, for example. In FIG. 5, the horizontal axis represents the density of the input density signal y, and the vertical axis represents the output density signal Y after density conversion. These density signals y and Y have, for example, 256 gradations. In addition, this table assumes a constant density (for example, an intermediate density of 127) within a certain density width a on both sides of the background density C, and outside of this width a, the maximum (255) and minimum density (○) are converted with a slope b. It is something to do. This density conversion can eliminate noise in the background area and improve defect detection accuracy. Note that the set values a, b, and c used for this density conversion are stored in a memory means 60 to be described later.
Input from

In the signal y that has been subjected to the filtering process using the differential filter as described above, the low frequency components present in the signal a4 are removed, the defective portion is emphasized, and the background noise is erased by the density conversion.

The defect detection means 44 compares this signal a6 with a predetermined threshold value (or range) υ, and when a6 falls outside the range determined by this threshold value V, it is determined that there is a defect. The signal Z indicating this defect is sent to the address determining means 46, and the address Ad of this defect is determined.

Threshold value (or range) used in this defect detection means 44
υ is set to a level υ1 that detects normal defects in normal inspection conditions that do not include seams, and is set to a level υ1 that detects normal defects for a certain range (joint range) that includes a seam 66 detected by a seam sensor 64, which will be described later. Level defects are switched to level υ2 where they are not detected. These thresholds υ
1. v2 is input from memory means 60.

The address Ad is obtained from the operation control section 48. In other words, the operation control unit 48 sets the feed speed of the inspection object 10 to the command speed (2) inputted from the memory means 60 (described later). The motor 16 is driven so as to match the . Further, the motor 24 is controlled so that the scanning speed of the laser beam 2 in the main scanning direction matches the command speed vX similarly inputted from the memory means 60.
to drive. The operation control unit 48 counts the speed pulses from the speed detector 18 to determine the Y coordinate in the sub-scanning direction, and also calculates the X coordinate in the main scanning direction from the rotational speed of the motor 24 and the elapsed time based on the inspection width gate signal. These coordinates (X, Y) are output to the address determining means 46 as the coordinates of the scanning position.

When the address Ad of the defect is determined in this manner, the bulk memory 40 transfers the area containing this address Ad, that is, the area containing the defect, to the frame memory 50. This frame memory 5o contains the signal a as well as the coordinates of the defect (X
, Y) may be stored simultaneously. .

The contents of the frame memory 50 are further subjected to signal processing in a signal processing means 52 as necessary. For example, the defective portion is enlarged or reduced to a magnification (xn) inputted from the memory means 6o described later. And this image is CR
It is displayed on a monitor 54 such as T. The address Ad of the defect may be displayed here together with the image of the defect. This image and address Ad can be stored on a video, magneto-optical disk, or
It may also be recorded on a floppy disk, hard disk, memory tape, etc.

On the other hand, when the address determining means 46 determines the defective address Ad, the signal processing means 56 then performs classification processing, for example. This is to classify defects by determining the degree and type of the defect such as the size and spread of the defect determined by the defect detection means 44. This classification result is output to an output means 58 such as a printer or an external process computer connected via a data line. Data used for this classification process is input from memory means 60, which will be described later.

The data used for the above processing, that is, the inspection conditions are supplied from the memory means 60. As shown in FIG. 2, this memory means 6o stores a plurality of sets that are separately combined for each type of inspection object and its inspection state. Among this group are
A set of the threshold value (or range) vl and other inspection conditions (data such as setting values) for an inspection range that does not include a seam (for example, ■ in the figure), and a set of A threshold value υ2 and other test condition sets (for example, ■) are included. For example, for steel plate A, the set (work,
In addition to ■), separate groups are prepared depending on the condition of the surface, such as dry, oily, colored, etc.
,■... are stored in memory. The test conditions other than the memorized threshold value υ include, for example, the gain g used in the output adjustment means 36 and the offset 0. , the number of gradations k used in the A/D conversion means 38, the filters Δ, f used in the signal processing means 42,
These include Δyf, density conversion setting values a, b, c, scanning speeds V W , VB2 , magnification (Xn), classification processing data, and the like.

These setting values are input manually or automatically from the condition input means 62. For example, while viewing the image on the monitor 54 or the results printed on the output means 58, the inspector manually inputs preferred setting values for each inspection condition of the inspection object 10 using a keyboard or the like. Further, some setting values may be automatically determined. For example, the gain g and the offset 0. can be configured to be set automatically.

64 (64a, 64b) are joint sensors. The seam sensor 64a is provided at a certain distance away from the inspection position of the inspection object 10, that is, upstream of the main scanning line 32, and the seam sensor 64b is provided at a certain distance downstream from the main scanning line 32. There is. These seam sensors 64 may be configured, for example, to determine the seam 66 based on a sudden change in the reflectance of the surface of the inspection object 10, or to detect a pinhole or mark made at the joint opening. can. When this sensor 64 detects a seam 66 of the inspection object 10, it outputs seam deviation codes aI and α2, respectively. Reference numeral 68 denotes a joint range detection means, which determines a predetermined range (joint range) including the joint 66 based on the joint decoding α1 and α2, and sends a switching signal β indicating the range to the selection means 70.

The joint range detection means 68 switches the switching signal β to "1" by, for example, the joint signal α, and
2 returns the switching signal β to 0". Selector E5k
70, when the switching signal β is 1'', the memory means 6
A set corresponding to the connecting range from 0, for example, ■ is selected.

Further, when the switching signal β is "O", one set of machining, ■, ■, . . . corresponding to the type of inspection object and inspection state is manually or automatically selected. The switching means 72 reads out the set of test conditions selected by the selection means 70 from the memory means 60 and sends them to each section.

In the above embodiment, in addition to the threshold values υ1 and υ2 for the transition range and other ranges, different sets of test conditions are also stored in memory in response to changes in the type of test object and the test state. However, in the present invention, the threshold values υ3 and υ2
. . . may be stored in memory.

Further, the joint range detection means 68 can also use the output of the upstream joint sensor 64a and the feed amount determined from the speed detector 18 to determine a predetermined joint range across the joint 66. be.

Furthermore, instead of the sensor, the seam detection means may be one that compares roll length data input in advance with the feed amount determined by the speed detector 18, and detects the seam by calculation.

The above embodiment uses a flying spot method in which the laser beam is reflected on the surface of the inspection target, but the inspection target is irradiated with a rod-shaped light source arranged in the width direction, and the reflected light is sent to the receiver via a rotating mirror. It may be a flying image type reading method, or a type reading a line sensor or an area sensor.

Although the above embodiments have been described as detecting defects appearing on the surface of the object to be inspected, the present invention also includes detecting defects inside by scanning the surface.

For example, internal defects in a steel plate may be detected using a magneto-optical effect. This detects the leakage magnetic field from a defect when the inspection object is magnetized with an alternating magnetic field as a change in the polarization of reflected light.

(Effects of the Invention) As described above, the present invention detects the joint to be inspected using a joint sensor, and within a predetermined range including the joint, that is, within the joint range, the threshold value υ for detecting defects is switched and the Since the defect is not detected, there is no possibility that the product will be determined to be defective due to a large number of defects due to a large number of scratches included in the joint area (Claim (1)).

The sensor for detecting the joint may be provided on the upstream and downstream sides of the scanning position (Claim +21), but the sensor may be provided only on the upstream side to determine the joint range from the relationship with the feed rate of the inspection target. (Claim (3)).

[Brief explanation of drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention, FIG. 2 is a diagram showing an example of a set of test conditions stored in a memory means,
FIG. 3 is an explanatory diagram of spatial filtering processing, FIG. 4 is a diagram illustrating an example of a differential filter, and FIG. 5 is an explanatory diagram of density conversion characteristics of an image signal. DESCRIPTION OF SYMBOLS 10... Inspection object, 20... Image detection means, 60... Memory means, 62... Inspection condition input means, 64... Seam sensor, 66... Seam, 68... Seam range Detection means, 70...Selection means.

Claims (3)

[Claims] (1) In a defect inspection device that detects defects in the inspection target by comparing an image signal obtained by scanning the inspection target with a predetermined threshold value, a predetermined range of joints including the seams of the inspection target is bridging range detection means for detecting the bridging range, and memory means for separately storing a threshold value at which it is difficult to detect defects for the bridging range and a normal threshold value for detecting defects for other ranges; , comprising a selection means for selecting and reading out threshold values corresponding to the connecting range and other ranges from the memory means, and detecting defects using the selected threshold values. Defect inspection equipment. (2) Joint sensors are provided at predetermined positions upstream and downstream of the inspection position of the inspection target, and the joint range detection means sets a threshold value corresponding to the joint range based on the output of the upstream joint sensor. 2. The defect inspection apparatus according to claim 1, wherein the threshold value is returned to the original value based on the output of the joint sensor on the downstream side. (3) The defect inspection apparatus according to claim 1, further comprising a joint sensor provided upstream of the scanning position, and switching to a threshold value corresponding to the joint range within a certain range after the joint is detected.