JPS61153548A - Inspecting method of printed matter - Google Patents

Abstract

PURPOSE:To improve inspection precision by decomposing the entire surface of the pattern of printed matter into plural picture elements and inputting a pattern signal, extracting picture elements whose print trouble detection signal exceeds a permissible value and edge parts of the pattern, and masking detection signals of corresponding picture elements. CONSTITUTION:A pattern signal of each picture element inputted from a detection part is stored in a reference memory 17 in reference signal fetch mode through an A/D converter 15. At the same time, a reference signal SSS is transferred to a difference circuit 16 to calculate a difference of each picture element from the signal SSS. At this time, the signal SSS is in the zero state and a difference inspection signal DIS becomes equal to the signal SSS. The signal DIS is delayed by several picture elements through a delay circuit 19 and a difference circuit 18 performs difference arithmetic to obtain a secondary difference signal DDS. A threshold circuit 20 extracts a picture element corresponding to the secondary difference signal DDS exceeding the permissible value as an edge part of the pattern and a CPU14 writes the edge extraction result of each picture element in a mask memory 30. Then, inspection as to pattern information inputted to a detection part 4 is carried out to improve the precision of the inspection.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a printed matter inspection method for in-line comparing the condition of a printed matter being printed with a standard state in a printing press to detect abnormalities in the printed matter.

[Technical background of the invention and its problems]

Conventionally, the mainstream method for inspecting printed matter has been offline and relying on human vision. This is one printed item.
This comes from the fact that the dot patterns are different, and the subtle differences in inspection items on printed matter that require reliance on human vision have been thought to be a problem. On the other hand, in response to the desire to evaluate printed matter while it is being printed, attempts have been made to use strobe lighting that is synchronized with the printing speed and to use mirrors that rotate synchronously at high speed to judge printed matter that is being printed as a still image. I was disappointed. However, in that these methods rely on human vision for inspection, they are no longer systems that can be called inspection machines. In addition, attempts have been made to print color batches at the same time as the patterns on the printed matter and inspect the color patches, thereby allowing the inspection of the printed matter to be carried out for them. However, with this method, if printing defects (oil stains, stains, etc.) occur in the pattern area, they will be overlooked, and it could not be said that the function of the inspection machine was fully fulfilled.

On the other hand, a system has recently been proposed in which printed matter is inspected in-line using a line sensor, as seen in Japanese Patent Application No. 57-220515 titled "Print Inspection Apparatus." By using this method, the pattern itself of printed matter can be automatically inspected in-line, so the above-mentioned drawbacks are avoided (excellent effects can be expected as an inspection machine).

However, this system is not without its problems, and because the design of printed matter is input and handled pixel by pixel as image information, the phase shift between the pixels on the printed paper and the input sampling has been highlighted as a major problem.

In order to solve this problem, patent application No. 58-172777
A method of sampling while correcting synchronization errors has been proposed, as seen in the issue of ``Method for correcting synchronization errors in inspection of running printed matter''.

Furthermore, a method has been proposed, such as the ``printed matter inspection method'' of Japanese Patent Application No. 59-134816, which utilizes optical blur and an addition circuit to prevent false detection of abnormalities at edges due to synchronization deviations.

As described above, the phase shift when inputting the pattern information of printed matter is a major problem in in-line inspection of printed matter, and this tendency is particularly noticeable at the edges (contours) of the pattern.

[Purpose of the invention]

The present invention solves the above-mentioned problems, and provides a printed matter inspection method that prevents the generation of false abnormal signals at the edge of a pattern due to a one-phase shift, and enables highly accurate inspection.

[Summary of the invention]

The present invention has been made to achieve the above-mentioned object, and it captures the pattern of a printed matter pixel by pixel, converts the detected pattern information for each pixel into a digital signal, and converts the detected pattern information of each pixel into a digital signal. Print inspection that performs a difference with reference information for each time, then performs a difference again with the difference information obtained by moving several pixels in the scanning direction of the sensor, and determines whether the result is within the allowable range. Method (Patent application No. 58-172778
By masking whether the inspection can be performed or not on the edges obtained as a result of edge extraction in the scanning direction of the sensor, it is possible to prevent the generation of false abnormal signals at the edges of the picture due to phase shift. This is a printed matter inspection method characterized by preventing.

[Details of the invention]

The present invention will be described in detail below with reference to embodiments shown in the drawings. FIG. 1 is a block diagram of an apparatus for implementing the printed matter inspection method according to the present invention, and FIG. 2 is a schematic explanatory diagram showing the apparatus shown in FIG. 1 attached to a rotary printing press.

As shown in Fig. 2, a strip of printing paper (3) fed from a roll of paper (2) is printed at a printing section (11) in four colors (black, indigo, red, yellow) on each side. After the
It is transported to a dryer and a broken section (not shown). The printed matter inspection device inspects the printing condition after the front and back sides have been printed in four colors, so the rotary encoder (5) attached to the printing section adjusts the sampling timing and directs the pattern information in the direction of flow of the printed matter. A line sensor such as a COD-MOS of a detection unit (4) extending in the direction of the image captures the entire image pixel by pixel into the processing circuit (6) with the line sensor scanning as main scanning and the flow of the printed material as sub-scanning. , to determine whether printed materials are normal or abnormal. As a result, if it is determined that the printing condition is abnormal, it becomes possible to take measures such as alarms, markings, and rejects. As the above-mentioned processing circuit (6), the present applicant has filed Japanese Patent Application No. 172788-1988 - "Printed matter inspection method"
proposed a method for accurately detecting printing defects using the circuit configuration shown in FIG.

To explain this inspection method, as shown in FIG. 1, a timing control section 1111
The memory control unit α3 and the sampling control unit (121) are controlled, and the memory control unit (
131 is a timing control section (12+ signal and C
PUc! According to the mode switching signal MSS from 31, the standard memo! The reference signal SSS is taken into the differential circuit (1e, which controls the cumulative counter (2D). The above circuit provides lock and sampling start signals.
The timing and switching of the processing circuitry is controlled.

Next, the picture signal for each pixel input from the detection unit (4) is converted into a digital signal via an A/D converter, and then
Prior to calibration, when the pattern signal of a normal printed matter is captured, the pattern signal is stored in the reference memory (171) in the reference signal capture mode. After the reference signal is set, the mode is shifted to the inspection mode. , the picture signal is the inspection signal SIS
The signal is sent to the first differential circuit as a signal. At this time, the reference signal SSS is read from the reference memory +)-(In based on the control signal from the memory control unit (131) and transferred to the first differential circuit field.

In the first differential circuit, the reference signal SS is set for each corresponding pixel.
A difference calculation is performed between S and the inspection signal SIS.

As a result, a differential test signal DIS is obtained. After this, the differential test signal CDS is branched into six parts, one of which is transferred to the second differential circuit via the delay circuit (11), and the other one is transferred directly to the second differential circuit t18. . The appropriate amount of delay in the delay circuit a9 is equivalent to several pixels (6 to 5 pixels) to be inspected. In the second differential circuit a&, the differential test signal DI
A pixel-by-pixel difference calculation is performed between S and the differential inspection signal DIS delayed by several pixels.

A secondary difference signal DDS is obtained.

This secondary difference signal DDS is sent to the threshold circuit ■, and is determined based on the threshold level based on the threshold setting signal SHC from the CPU (141), and when the secondary difference signal DDS exceeds the threshold level, is a printing error and sends an error signal IR.
3 to the CPU (141).

On the other hand, the value of the remaining three-branched differential test signal DI8 is totaled for each fixed number of pixels by an accumulation counter, and transferred to the discrimination circuit (221) as an integrated signal IDS.The discrimination circuit (2) If the range of overall concentration fluctuation exceeds the preset value, the abnormal signal IR8 is activated.
Send to PU (141).

When the CPU (141) receives the abnormal signal IR8 from the threshold circuit or the discrimination circuit, it outputs a signal for alarming, marking, rejecting, etc. In this way, the secondary difference signal DDS= If an abnormality is determined based on the integrated concentration signal IDS, accurate inspection can be expected.

According to the present invention, the edge portion (contour) of a pattern on a printed matter is extracted using the same circuit configuration as that capable of performing such accurate inspection.

That is, when setting the reference signal SSS, the reference memo 'J - (17
At the same time as writing to 1, the reference signal SSS is transferred to the first difference circuit 061, and a difference is made for each pixel with the reference signal SSS from the reference memo IJ-(171. At this time, the reference signal SSS is the picture signal. Since it is before storage, it is in a zero state, and as a result, the differential inspection signal DIS becomes equal to the reference signal SSS.Therefore, since there is a change in density at the edge of the pattern, the differential inspection signal DIS is, for example, as shown in FIG. The signal will be as shown by the solid line.

When this differential test signal DIS is delayed by several pixels in the delay circuit a9, the original differential test signal D is returned as shown in FIG.
The signal has a relationship with the IS as shown by the dashed line. When the difference between the two is calculated by the second difference circuit (181), it is possible to obtain a secondary difference signal DDS that stands out at the edge portion of the pattern where the density is changing as shown in FIG. An edge extraction signal can be obtained by setting an appropriate threshold level SHC and extracting a signal exceeding this level.This edge extraction signal is used as an abnormal signal I during inspection.
This corresponds to ts.

CPUa receives the edge extraction signal and prints mask memo I.
7- (3fl), the result of edge extraction for each pixel, for example, edge 1. Write as non-edge 0.

After the mask memory (7) is set at the same time as the reference memory output in this way, the image information taken in by the detection unit (4) is inspected as described above to determine whether there is a printing abnormality for each pixel. The CPU04+ outputs a discrimination signal of 1 for printing abnormality and 0 for normal printing, for each pixel.
On the other hand, in synchronization with this, an edge extraction signal (edge 1, non-edge 0) is read out for each pixel from the mask memory (30), and the signal is further inverted to make edge 0 and non-edge 1, and is sent to the AND circuit 31 together with the discrimination signal. ). As a result, the edge portion of the pattern is masked, and even if a printing error occurs in the edge portion, the output of the AND circuit (31) will always be 0 at the edge portion, and the output will be 1 indicating a printing error.
The n signal is not output.

〔Effect of the invention〕

As detailed above, according to the present invention, the comparison with the reference signal is always performed only in the running direction of the line sensor of the detection unit (4). Since the proposed inspection means detects abnormalities that occur in printed matter, it is not affected by overall density changes and is not affected by synchronization deviations in the printed matter transport direction (
Not only is it possible to perform high-precision inspections such as It becomes possible to simplify the configuration, and using this edge extraction signal, it becomes possible to cancel the inspection of the edge part where there is a high possibility of generating a false abnormal signal when a one-phase shift occurs. This allows for highly accurate inspection.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is a block diagram showing the circuit configuration of an inspection device according to the present invention, and FIG. 2 is an explanatory diagram when the present invention is applied to a rotary printing press. FIG. 3 is a model diagram showing an example of a reference signal at the edge portion of a picture, and FIG. 4 is a model diagram showing a secondary difference signal. (4)...Detection unit 15)...Rotary encoder housing e...First differential circuit decoy...Second differential circuit (14I...CPU gloss...Mask memory (31)...・AND circuit

Claims (1)

[Claims] 1) Decompose the entire image of the printed matter into a plurality of pixels and capture the image signal, set the image signal of the normal printed matter in the reference memory as the reference signal, and calculate the pattern signal of the subsequent printed matter by the first difference between the reference signal and the reference signal. A difference calculation is performed in the circuit, and a difference is calculated between the signal obtained by this difference calculation and a signal obtained by delaying the signal obtained by this difference calculation by several pixels in a second difference circuit, and a reference value is calculated for this difference calculation value. In a printed matter inspection method for detecting the presence or absence of a printing failure by comparing with the reference information, the picture information to be the reference information is set in the reference memory, and a difference is calculated between the content of the reference memory in the zero state and the first difference circuit. A second difference circuit calculates a difference between this difference signal and a signal delayed by several pixels from this difference signal, sets a tolerance value for this difference signal, and selects a pixel corresponding to a signal exceeding the tolerance value. 1. A method for inspecting a printed matter, comprising: extracting the image as an edge portion of a pattern, and performing mask processing on the printing failure detection signal for pixels corresponding to the edge portion of the pattern.