JP2962806B2 - Defect inspection method for image receiving paper sheet surface - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a surface of a sheet continuously fed from a web for defects.

[Related Art] Image receiving paper used for heat-sensitive melting transfer, heat-sensitive sublimation transfer, and the like is supplied in a form in which a fixed number of sheets are bundled,
Alternatively, it is supplied as a so-called take-up roll by winding it on a cylindrical core as it is long. Among them, the sheet-shaped image receiving paper is made by cutting the band-shaped image receiving paper fed out from the winding into a fixed length by a sheet cutter. After the cutting, it is automatically sorted into non-defective products and defective products. (For example, refer to JP-A-63-31546) In the conventional apparatus used for the above-described method,
A set of light sources is used to inspect the sheet surface for defects and stains.
A surface inspection unit with a CCD camera is provided.

[Problems to be Solved by the Invention] However, when the above-described surface inspection unit having a set of light sources and a CCD camera is used, a differential signal obtained by differentiating an image signal from the CCD camera is used. Depending on the threshold level setting that is set in advance to determine the presence or absence of a defect by comparing with the threshold value, if the setting value is high, scratches or dirt that should be a defect can not be detected, or conversely, the setting value When the value is low, scratches and stains that do not need to be regarded as defects are detected, and the number of sheets discharged as defective products may increase.

Therefore, the present invention has been made in view of such problems of the conventional technology, and an object of the present invention is to provide a method capable of accurately grasping various disadvantages.

Means for Solving the Problems In order to achieve the above object, a method for inspecting an image receiving sheet surface according to the present invention comprises:
A defect inspection method on a receiving paper sheet surface in which a differentiated signal obtained by differentiating the image signal from the D camera is compared with a preset threshold level, and when the voltage of the differential signal exceeds the threshold level voltage, it is recognized as a defect. In the above, two threshold levels are set to high and low, and the voltage of the differential signal exceeds once the voltage of the higher threshold level to recognize a small and high density defect, and the threshold level of the differential signal is lower. When the voltage exceeds a predetermined number of times continuously, a defect having a large area and a low density is recognized.

In addition, in order to achieve the same object, the inspection method of the sheet surface of the image receiving paper of the present invention is preferably provided with two CCD cameras, one receiving the regular reflection from the image receiving sheet and the other receiving the irregular reflection. is there.

[Operation] In the inspection method of the receiving paper sheet surface configured as described above, the differential signal obtained by differentiating the image signal obtained by one CCD camera is compared with two high and low threshold levels, and the voltage of the differential signal is obtained. When the voltage exceeds the voltage of the higher threshold level, the defect of small and high density is recognized, and when the voltage of the lower threshold level exceeds the set number of times continuously, it is difficult to discriminate at one time. By recognizing low faults, it is possible to efficiently recognize not only clear faults but also faults that are thin and inconspicuous but have wide spread, by setting two high and low threshold voltage levels well. become.

Further, by providing two CCD cameras that receive regular reflection and irregular reflection from the image receiving paper sheet, an image signal can be obtained for each type of defect, and the types of defects that can be recognized are increased.

[Examples] Hereinafter, the present invention will be described based on examples shown in the drawings.

As shown in FIG. 1, irradiation light is emitted from a light source 3 to a sheet surface of an image receiving paper 2 conveyed on a guide roller 1, and a fixed CCD camera 4 receives reflected light and receives an image signal of the sheet surface. Get. As shown in FIG. 2, the CCD camera 4 scans the sheet surface from left to right at regular intervals. Here, a CCD camera having a lens and 1024 elements and having a resolution of 0.1 mm per element was used. The scanning interval was 0.1 mm. FIG. 2 shows a situation where scanning from n to n + 8 is performed. Further, 5 and 6 are examples of the defects, 5 is a high and small defect represented by black spots and scratches, and 6 is a low concentration represented by blisters. It is a rather wide drawback.

The CCD camera 4 receives the light emitted from the light source 3 and reflected on the sheet surface, thereby extracting an image signal GS reflecting the brightness of the paper surface. Then, as shown in FIG. 3, this image signal GS becomes a differential signal BS in a differentiating circuit 7, and this differential signal BS is input to two judging units 8, 9 and set in the judging units 8, 9, respectively. Is compared to the threshold level. One judging section 8 sets the threshold level to a high level 1 and sets a condition so that if the differential signal BS exceeds the level 1 once, it is judged that there is a defect. Further, the other determination unit 9 sets a condition such that the threshold level is set to the low level 2, and if the differential signal BS continuously exceeds the level 2 three times, it is determined that there is a defect.

4 (a) and 4 (b) show the voltage values of the differentiated signal BS obtained at each stage from scanning n to n + 8. I and II are lines for indicating corresponding portions, and correspond to the left ends of the defects 5 and 6 shown in FIG. 2, respectively. In this graph, since the conditions are set as described above, the fault 5 is recognized as having a fault because the voltage of the differential signal exceeds the level 1 (L1) at n + 4. . Regarding the defect 6, since the voltage of the differential signal exceeds the level 2 (L2) for five times from n + 2 to n + 6, and the number of times the difference signal exceeds the set number of times is three or more, it is recognized that there is a defect. .

Depending on the type of defect, there is little reflected light due to regular reflection from the sheet surface and it cannot be recognized as a defect, but there is more reflected light due to irregular reflection, which can be recognized as a defect. There is also the opposite disadvantage. Therefore, in another embodiment shown in FIG. 5, a CCD camera 11 which receives light reflected from a light source 10 and is regularly reflected on a sheet surface, and a sheet CCD cameras 13 that receive light reflected irregularly on the surface are separately provided. As described above, two determination units are provided for the image signals obtained from the CCD cameras 11 and 13, respectively.

[Effects of the Invention] The present invention is configured as described above, and has the following effects.

By properly setting two high and low threshold voltage levels, it is possible to recognize a small, high-density defect, and also to recognize a large, low-density defect in which the differentiated signal has no significant difference compared to noise. It is possible to appropriately check for defects on the sheet surface for determining whether the paper is good or bad.

In addition, CC that receives regular reflection and irregular reflection from the receiving paper sheet
By providing two D cameras separately, image signals can be obtained for each type of defect, and many types of defects can be appropriately recognized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an inspection portion for inspecting a sheet surface of an image receiving paper, FIG. 2 is a diagram showing a state in which a CCD camera scans a sheet surface, and FIG. 3 is a diagram for processing an image reception signal obtained by the CCD camera. Block diagram for FIG. 4 (a), (b)
Is a waveform diagram showing the voltage value of the differential signal at each stage of scanning, and FIG. 5 is a configuration diagram of an inspection part when two CCD cameras are provided. DESCRIPTION OF SYMBOLS 1 ... Guide roller 2 ... Receiving paper 3, 10, 12 ... Light source 4, 11, 13 ... CCD camera 5, 6 ... Defect 7 ... Differentiator circuit 8, 9 ... Judgment part

Claims (2)

(57) [Claims] 1. A CCD for scanning an image receiving paper sheet surface
A differential signal obtained by differentiating an image signal from a camera is compared with a preset threshold level, and when a voltage of the differential signal exceeds a voltage of the threshold level, a defect inspection method on a receiving paper sheet surface is recognized as a defect. ,
By setting two threshold levels, high and low, the voltage of the differential signal exceeds the voltage of the higher threshold level once to recognize a small and high-density defect, and the voltage of the threshold level of the lower differential signal voltage A defect having a large area and a low density when the number of times exceeds a predetermined number of times continuously. 2. The method according to claim 1, wherein two CCD cameras are provided, one for receiving regular reflection from the receiving paper sheet and the other for receiving irregular reflection.