JPH0679862A - Method for inspecting quality of printing paper surface and apparatus therefor - Google Patents

Abstract

PURPOSE:To enable the size-minimization and simplification of an inspection apparatus as well as the time-shortening of inspection to be achieved. CONSTITUTION:The method is characterized as detecting the density every picture element of accepted paper surface 101, manufacturing an acceptable histogram comprising the number of picture elements every density gradation on the basis of data of the density 102, detecting density every picture element of the paper surface to be inspected 103, manufacturing a histogram to be inspected comprising the picture element every density gradation on the basis of data of the density 104, detecting difference by comparing the histogram to be inspected with the acceptable histogram 105, and judging the quality of the paper surface to be inspected on the basis of the differentials.

Description

Detailed Description of the Invention

[0001]

This invention relates to a printing process,
The present invention relates to a printing paper surface quality inspection method and apparatus for automatically determining the quality of a printing paper surface and eliminating defective products.

[0002]

2. Description of the Related Art Conventionally, a quality inspection of a printing paper surface has been conducted visually. However, such a method has a problem that it is difficult to secure workers because it requires skill for inspection work, and it is difficult to perform 100% inspection. On the other hand, in order to deal with such a problem, an inspection method and an apparatus that do not depend on the skill of an operator have been developed. This method and apparatus apply recent digital image processing technology, and determine the quality by associating pixels at the same position on the inspected paper surface and the accepted paper surface and comparing their densities. .

[0003]

However, in such a method and apparatus, it is necessary to accurately correspond fine pixel positions on the surface to be inspected and the surface to be passed, and at the same time as a very large number of pixels. It was necessary to perform the comparison operation of. Therefore, there is a problem that the apparatus becomes large and complicated, and the inspection takes a long time.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a printing paper surface quality inspection method and device, which can reduce the size and simplification of the device and shorten the inspection time.

[0005]

A printed paper surface quality inspection method according to the present invention detects a density for each pixel on a passing paper surface,
A pass histogram consisting of the number of pixels for each density gradation is created based on this density data, the density is detected for each pixel on the paper surface to be inspected, and the number of pixels for each density gradation is calculated based on this density data. Create an inspected histogram,
The inspection histogram and the acceptance histogram are compared to detect these differences, and the quality of the inspection paper surface is determined based on the differences.

The printing paper surface quality inspection apparatus according to the present invention is
A density detecting means for detecting the density for each pixel on the passable paper or the inspected paper, and a pass histogram or an inspected histogram consisting of the number of pixels for each density gradation based on the density data on the passable paper or the inspected paper. Histogram creating means, a histogram storage means for storing the pass histogram, a histogram comparing means for detecting the difference between the inspected histogram and the pass histogram, and based on the difference, the inspected paper surface And a quality judgment means for judging the quality.

The above-mentioned pixel is set to a desired size according to the inspection request. The density gradation is also set to a desired number of steps according to the inspection request.

[0008]

The function of the printed paper surface quality inspection method according to the present invention is as follows. The density is detected for each pixel on the acceptable paper surface or the inspected paper surface to obtain density data for each pixel on the acceptable paper surface or the inspected paper surface. At this time, information on the position of the pixel is unnecessary. The pass histogram based on these data and the inspected histogram are compared to detect the difference, and the quality of the inspected paper surface is determined based on the size of the difference.

The operation of the printed paper surface quality inspection apparatus according to the present invention is as follows. The density detecting means detects the density for each pixel on the passable paper or the paper to be inspected. As a result, density data for each pixel on the passable sheet or the sheet to be inspected can be obtained. At this time, information on the position of the pixel is unnecessary. Based on this data, the histogram creating means creates a pass histogram or an inspected histogram consisting of the number of pixels for each density gradation. The histogram comparing means compares the pass histogram stored in the histogram storing means with the inspected histogram and detects the difference. The quality judging means judges the quality of the paper surface to be inspected based on the magnitude of the difference.

[0010]

1 is a flow chart of a printing paper surface quality inspection method according to the present invention, FIG. 2 is a functional block diagram of a printing paper surface quality inspection device according to the present invention, and FIG. 3 is an example of a printing paper surface quality inspection device according to the present invention. It is a functional block diagram which shows an Example. The details will be described below with reference to FIGS. 1 to 3.

The printing paper surface quality inspection apparatus 10 is provided with the passing paper surface 1
2 or density detection means 16 for detecting the density for each pixel on the inspected paper surface 14, and a pass histogram or inspected histogram consisting of the number of pixels for each density gradation based on the above density data for the accepted paper surface 12 or the inspected paper surface 14. Based on the difference, a histogram creating unit 18 for creating the pass histogram, a histogram storage unit 20 for storing the pass histogram, a histogram comparing unit 22 for comparing the inspected histogram with the pass histogram and detecting a difference therebetween. The quality judgment means 24 for judging the quality of the paper 14 to be inspected is provided.

The density detecting means 16 is a paper surface detecting sensor 3
2. The image sensor 34 and the multiplexer 36. The paper surface detection sensor 32 detects the end surface of the paper surface optically or mechanically. The image sensor 34 is a photoelectric conversion element such as a silicon photodiode. When the paper surface detection sensor 32 detects the paper surface, the image sensor 34 detects the density of each pixel. Although not shown, the paper surface is illuminated with light such as a fluorescent lamp, and the reflected light causes the image sensor 34 to detect the density. The data of these densities are sequentially output to the histogram creating means 18 by the multiplexer 36.

The histogram creating means 18 comprises an A / D converter 38 and a decoder 40. A /
The D converter 38 converts the analog signal output from the multiplexer 36 into a digital signal having the number of bits (two bits in this embodiment) corresponding to the density gradation. That is, the A / D converter 38 outputs the density of each pixel as one of four kinds of density gradation. Decoder 40
Outputs a pulse signal to a separate signal line for each density gradation. As a result, the decoder 40 outputs the number of pixels for each density gradation, and a pass histogram or an inspected histogram is created.

The histogram storage means 20 comprises memories 42a, 42b, 42c and 42d whose number corresponds to the density gradation, and the histogram comparison means 22 includes counters 44a, 44b, 44c and 44d whose number corresponds to the density gradation.
It consists of The counters 44a ...
2 and the inspected paper surface 14 have different functions. In the case of the pass page 12, the pulse signal output from the decoder 40 is added from the state of “0”. Then, when the detection of the density of the passable paper surface 12 is completed, the added value is output to the memories 42a. As a result, the pass histogram is stored in the memory 42a.
... will be remembered. In the case of the sheet 14 to be inspected, after the number of pixels for each gradation in the acceptance histogram is output from the memories 42a ... To the counters 44a ... As an initial value, the pulse signal output from the decoder 40 is subtracted. That is, the number of pixels for each gradation is 12 for the acceptable sheet and 1 for the inspected sheet.
If they match with each other, the value of the counters 44a ... After inspection becomes "0".

The quality judgment means 24 is composed of a comparator 46a, 46b, 46c, 46d and memories 48a, 48b, 48c, 48d of the number corresponding to the density gradation and one AND.
And a circuit 50. The memory 48a ...
An allowable value is input from a digital switch or the like (not shown). The comparators 46a ...
The counter 44 compares the absolute value of a ... With the allowable value.
"0" is output to the AND circuit 50 when the absolute value of a ... Exceeds the above allowable value, and "1" otherwise. A
The ND circuit 50 receives "0" when even one "0" is input.
Is output and is determined to be defective.

In practice, a plurality of printing paper surface quality inspection devices 10 are provided according to the size of the paper surface. in this case,
The outputs of the plurality of AND circuits 50 are connected so as to be input to one AND circuit (not shown). The control circuit 30 controls each functional block.

Next, the operation of the printing paper surface quality inspection device 10 will be described. In order to simplify the explanation, it is assumed that the density gradation is 4 steps and the number of pixels on the paper is 4 × 4 = 16. FIG. 4 shows an example of a passable paper surface 12, and FIG. 5 shows an example of an inspected paper surface 14. The density gradation is set to level 4, level 3, level 2, and level 1 from dark to light. The number of pixels 52 on the acceptable sheet 12 is 5 for level 4, 5 for level 3, 4 for level 2, and 2 for level 1. Since the paper surface 14 to be inspected has stains at the center, 7 levels 4, 4 levels 3 and 4 levels 2
There are two, level one. Further, "1" is stored as an allowable value in the memories 48a .... Hereinafter, a detailed description will be given with reference to FIGS. 3 to 5.

A passable surface 12 is prepared. Counter 44a
Is cleared and the initial value is set to "0". When the passing paper surface 12 is detected by the paper surface detecting sensor 32, the passing paper surface 1
For 2 the image sensor 34 detects the density of each pixel 52 (step 101). This density data is output to the A / D converter 38 by the multiplexer 36. The A / D converter 38 converts the analog signal output from the multiplexer 36 into a 2-bit digital signal corresponding to the density gradation. That is, the A / D converter 38 changes the density of each pixel 52 from level 4 to level 1.
Is output as any one of the four types of density gradations up to. The decoder 40 outputs a pulse signal to the counters 44a ... Which correspond to the input density gradation. That is, if it is level 4, go to the counter 44a, and if it is level 3, go to the counter 44b.
, ..., If level 1, pulse signals are output to the counter 44d. The counters 44a ... Add one by one each time a pulse signal is input from the state of "0". In this way, when the end of the density detection of the passable paper surface 12 is detected by the paper surface detection sensor 32, the added value is output to the memories 42a. As a result, the pass histogram is stored in the memories 42a .... The values of the memories 42a ... Are “5”, “5”, “4”, and “2” in that order (step 1
02).

Subsequently, the paper surface 14 to be inspected is prepared. The values stored in the memories 42a ... Are output as initial values to the counters 44a. That is, the initial value of the counters 44a ... Is set to the number of pixels for each gradation in the acceptance histogram. When the paper surface 14 to be inspected is detected by the paper surface detection sensor 32, the image sensor 34 is moved to the paper surface 14 to be inspected.
The density of each pixel 52 is detected (step 10).
3). Thereafter, the same processing as in the case of the pass page 12 is performed, and the decoder 40 outputs a pulse signal to the counters 44a ... Corresponding to the inputted density gradation. Counter 44a ...
Is subtracted from the initial value state by "1" each time a pulse signal is input. In this way, when the completion of the density detection of the paper surface 14 to be inspected is detected by the paper surface detection sensor 32, the values of the counters 44a ... After the inspection are sequentially “−2”,
They are "2", "0", and "0" (step 104). These absolute values and the allowable value "1" of the memories 48a ... Are compared by the comparators 46a ... (Step 105). In this example, since the absolute values of the counters 44a and 44b exceed the permissible value "1", the comparators 46a and 46b.
Outputs "0" from the AND circuit 50 outputs "0".
Becomes That is, the quality of the paper surface 14 to be inspected is determined to be defective (step 106).

Further, it is not necessary that the positions of the pixels 52 on the passable paper surface 12 and the inspected paper surface 14 correspond exactly. This is because the histograms match even if the positions of the pixels 52 on the passable paper surface 12 and the inspected paper surface 14 are shifted by, for example, one pixel. Therefore, a mechanism for accurate position detection and positioning can be eliminated. Further, the comparison calculation is performed only by the number of comparators 46a ... Which correspond to the density gradation, and it is not necessary to perform the comparison calculation as many times as the number of pixels as in the conventional device. It should be noted that the quality of a large number of sheets to be inspected is judged using one acceptable sheet. That is,
The pass histogram once created is compared with a large number of inspected histograms. If the resolution of the image sensor 34 is, for example, a (mm ² ), the size of the pixel 52 is a by averaging N densities of that resolution.
It is set to × N (mm ² ).

[0021]

According to the printing paper surface quality inspection method and apparatus according to the present invention, a pass histogram and an inspected histogram composed of the number of pixels for each density gradation are created, and the inspected objects are compared by comparing these histograms. The quality of the paper can be judged. Therefore, it is not necessary to associate the pixel positions of the paper surface to be inspected with the paper surface to be passed, or to perform the comparison calculation the same number of times as the number of pixels, thereby achieving downsizing and simplification of the device and shortening of the inspection time. be able to.

[Brief description of drawings]

FIG. 1 is a flowchart of a printed paper surface quality inspection method according to the present invention.

FIG. 2 is a functional block diagram of a printing paper surface quality inspection device according to the present invention.

FIG. 3 is a functional block diagram showing an embodiment of a printed paper surface quality inspection apparatus according to the present invention.

FIG. 4 is an explanatory diagram showing an example of a passing page.

FIG. 5 is an explanatory diagram showing an example of a sheet to be inspected.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Printing paper surface quality inspection device 12 ... Passed paper surface 14 ... Inspected paper surface 16 ... Density detecting means 18 ... Histogram creating means 20 ... Histogram storing means 22 ... Histogram comparing means 24 ... Quality judging means

Claims (2)

[Claims] 1. A density is detected for each pixel on a passable paper, a pass histogram consisting of the number of pixels for each density gradation is created based on the data of the density, and the density is detected for each pixel on the inspected paper. An inspected histogram consisting of the number of pixels for each density gradation is created based on the density data, the inspected histogram is compared with the pass histogram, and these differences are detected, and the inspected object is based on the difference. A printed paper quality inspection method for determining the quality of a paper surface. 2. A density detecting means for detecting a density for each pixel on a passable paper surface or an inspected paper surface, and a pass histogram composed of the number of pixels for each density gradation based on the density data on the passable paper surface or the inspected paper surface, or Histogram creating means for creating an inspected histogram, histogram storage means for storing the pass histogram, histogram comparing means for comparing the inspected histogram with the pass histogram and detecting a difference therebetween, based on the difference A printing paper surface quality inspection device, comprising: a quality judgment means for judging the quality of the paper surface to be inspected.