JPH0367631B2 - - Google Patents

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 stems from the fact that each piece of printed matter has a different pattern, and because inspection items for printed matter have been thought to involve subtle differences that require reliance on human vision. 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. It was conducted. However, these methods were not systems that could be called inspection machines in that they relied on human vision for inspection. In addition, attempts have been made to print color patches 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 performed on behalf of the user. However, with this method, if printing defects (oil drips, stains, etc.) occur in the pattern area, they will be overlooked, and the inspection machine cannot be said to perform its function satisfactorily.

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 the "Printed Material Inspection Apparatus" disclosed in Japanese Patent Application Laid-Open No. 59-109832. By using this method, the pattern itself of the printed matter can be automatically inspected in-line, so it is free from the above-mentioned drawbacks and can be expected to have excellent effects as an inspection machine.

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

In order to solve this problem, Japanese Patent Application Laid-Open No. 60-63168
A method of sampling while correcting synchronization is proposed as seen in the publication ``Method for correcting synchronization failure in inspection of running printed matter'', and a method of performing sampling while correcting synchronization deviation is proposed, as seen in Japanese Patent Application Laid-open No. 12344-1983 entitled ``Method for inspecting printed matter''. ”
A method has also been proposed that uses optical blur and an adder circuit to prevent false abnormality detection 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 picture edges due to phase shifts 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 inspected pattern information for each pixel into a digital signal, and converts the pattern information for each pixel stored in advance into a digital signal. A printed matter inspection method in which a difference is made between the obtained difference information and the reference information, the obtained difference information is again made different from the difference information obtained by moving several pixels in the scanning direction of the sensor, and it is determined whether or not the result is within the allowable range. (Japanese Unexamined Patent Publication No. 60-64850 "Inspection Method for Printed Materials"), by masking whether inspection is possible or not on the edges obtained as a result of edge extraction in the scanning direction of the sensor, pattern edges due to phase shift can be removed. This is a printed matter inspection method characterized by preventing the generation of false abnormal signals.

[Detailed Description 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-shaped printing paper 3 fed from a roll-shaped paper roll 2 is printed in four colors (black, indigo, red, and yellow) on the front and back sides in the printing section 1. , a dryer, and a folding machine section (not shown). The printed matter inspection device inspects the printing condition after the front and back sides have been printed in four colors each, so the rotary encoder 5 attached to the printing section measures the sampling timing and transmits the pattern information in a direction perpendicular to the flow direction of the printed matter. of the detection section 4 extending to
Using a line sensor such as a CCD or MOS, the scanning of the line sensor is used as a main scan, and the flow of the printed matter is used as a sub-scan, and the entire image is input pixel by pixel into a processing circuit 6, which determines whether the printed material is 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, rejects, etc. As the processing circuit 6, the present applicant proposed a method for detecting printing defects with high accuracy using the circuit configuration shown in FIG. are doing.

To explain this inspection method, as shown in FIG. 1, the timing control unit 11 performs memory control based on timing pulses TMP generated by the rotary encoder 5 attached to the plate cylinder or impression cylinder of the printing unit. Part 1
3 and the sampling control section 12, and the memory control section 13 takes in the reference signal SSS to the reference memory 17, controls the difference circuit 16, and the cumulative counter according to the signal from the timing control section 12 and the mode switching signal MSS from the CPU 23. 21. The sampling control section 12 supplies a transfer clock and a sampling start signal to the detection section 4, which is composed of a CCD line sensor and the like. The above circuit controls the timing and switching of this processing circuit.

Next, the picture signal for each pixel inputted from the detection unit 4 is converted into a digital signal via the A/D converter 15, and then, prior to inspection, when the picture signal of a normal printed matter is taken in, The picture signal is stored in the reference memory 17 in the reference signal capture mode. After the reference signal is set, the mode shifts to the test mode, and the picture signal is sent to the first difference circuit 16 as the test signal SIS. At this time, the reference signal SSS is read out from the reference memory 17 based on the control signal from the memory control section 13 and transferred to the first difference circuit 16.

The first difference circuit 16 calculates the difference between the reference signal SSS and the test signal SIS for each corresponding pixel,
As a result, a differential test signal DIS is obtained. After this,
The differential test signal CDS is branched into three parts, one of which is
One passes through the delay circuit 19 to the second difference circuit 18;
The other one is transferred directly to the second difference circuit 18. The appropriate amount of delay in the delay circuit 19 is equivalent to several pixels (3 to 5 pixels) to be inspected. The second difference circuit 18 performs a pixel-by-pixel difference calculation between the difference test signal DIS and the difference test signal DIS delayed by several pixels to obtain a secondary difference signal DDS.

This secondary difference signal DDS is sent to the threshold hold circuit 20, where it is determined based on the threshold level based on the threshold setting signal SHC from the CPU 14, and the secondary difference signal DDS is
If it exceeds the threshold level, it is determined that there is a printing abnormality and an abnormality signal IRS is sent to the CPU 14.

On the other hand, the remaining one differential test signal that is branched into three
The value of DIS is totaled for each fixed number of pixels by an accumulation counter, and is sent to the discrimination circuit 22 as an integrated density signal IDS.
will be forwarded to. The determination circuit 22 sends an abnormality signal IRS to the CPU 14 when the range of overall density fluctuation exceeds a preset value.

When the CPU 14 receives an abnormal signal IRS from the threshold circuit 20 or the discrimination circuit 22, it outputs a signal for alarming, marking, rejecting, etc. In this way, 2
Accurate inspection can be expected if abnormalities are determined based on the second-order difference signal DDS and the integrated concentration signal IDS.

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 memory 17
At the same time as writing to the pixel, the reference signal SSS is transferred to the first difference circuit 16, and a difference is made with the reference signal SSS from the reference memory 17 for each pixel. At this time, the reference signal SSS is in a zero state since the picture signal is not stored, and as a result, the differential test signal DIS becomes equal to the reference signal SSS. Therefore, the differential test signal DIS
Since there is a change in density at the edge of the picture, the signal becomes, for example, as shown by the solid line in FIG. 3.

When this differential test signal DIS is delayed by several pixels in the delay circuit 19, it becomes a signal that has a relationship with the original differential test signal DIS as shown by the dashed line as shown in FIG. By calculating the difference between the two in the second difference circuit 18, it is possible to obtain a secondary difference signal DDS that stands out at the edge of the pattern where the density changes as shown in FIG. An edge extraction signal can be obtained by setting an appropriate threshold level SHC at step 20 and extracting a signal exceeding this level. This edge extraction signal corresponds to the abnormality signal IDS at the time of inspection.

The CPU 14 receives the edge extraction signal and writes the edge extraction result for each pixel into the mask memory 30 as, for example, edge 1 and non-edge 0.

After the mask memory 30 is set at the same time as the reference memory 17 in this manner, the picture information taken in by the detection section 4 is inspected as described above, and printing abnormalities are determined for each pixel.
The CPU 14 outputs a discrimination signal of 1 for printing abnormality and 0 for normal printing for each pixel, and in synchronization with this, an edge extraction signal (edge 1, non-edge 0) is read out for each pixel from the mask memory 30. A signal that is inverted to have an edge of 0 and a non-edge of 1 is input to the AND circuit 31 together with the discrimination signal. As a result, the edge part of the pattern is masked, and even if a printing error occurs in the edge part, the AND circuit 3
The output of 1 is always 0 at the edge portion, and a signal of 1 indicating printing abnormality 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 scanning direction of the line sensor of the detection unit 4. Because the inspection means detects abnormalities that occur in printed matter, it is possible to perform highly accurate inspections that are not affected by overall density changes and are less susceptible to synchronization deviations in the printed matter conveyance direction. Of course, it is possible to extract the edges (contours) of a pattern by using the circuit for carrying out the above-mentioned "printed matter inspection method", which makes it possible to simplify the circuit configuration, and also to extract the edges. By using the signal, it is possible to cancel the inspection of edge portions where a false abnormal signal is likely to be generated when a phase shift occurs, and more accurate inspection can be performed.

[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. Figure 3 is a model diagram showing an example of a reference signal at the edge of a pattern;
FIG. 4 is a model diagram showing a second-order difference signal. 4...Detection unit, 5...Rotary encoder, 16
...first differential circuit, 18...second differential circuit, 14
...CPU, 30...mask memory, 31...AND circuit.

Claims (1)

[Claims] 1. Decompose the entire picture of the printed matter into a plurality of pixels and capture the picture signal, set the picture signal of the normal printed matter in the reference memory as the reference signal, and compare the picture signal of the subsequent printed matter with the reference signal and the first difference circuit. A second difference circuit calculates a difference 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 printed matter inspection method that detects the presence or absence of printing failure by comparing this difference calculation value with a reference value,
The picture information to be used as the reference information is set in the reference memory, and the content of the reference memory in the zero state is subjected to a difference calculation in the first difference circuit, and this difference signal is converted into a signal delayed by several pixels. is calculated by a second difference circuit, a tolerance value is set for this difference signal, a pixel corresponding to a signal exceeding the tolerance value is extracted as an edge part of the picture, and a pixel corresponding to the edge part of this picture is extracted. A method for inspecting printed matter, comprising performing mask processing on the printing failure detection signal for each pixel.