JPH0617877B2 - Print error detection method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for detecting printing errors.

An object of the present invention is to provide a printing error detection method capable of accurately detecting a printing error.

SUMMARY OF THE INVENTION The present invention provides a printing error detection method as set forth in claim 1.

SUMMARY OF THE INVENTION The printing error detection method of the present invention illuminates a paper surface and determines a printing error based on the difference in the amount of reflected light.

According to the printing error detection method of the present invention, a signal on the standard paper surface is used as a reference value, which is preferably stored in a memory, and the quality of the printing surface is determined by comparing the reference value with the signal on the detected paper surface.

The printing error detection method of the present invention uses a plurality of points on the paper surface as measurement points. At that time, a plurality of light receiving elements
A large number of measurement points are obtained by arranging them in a row and time-dividing the continuous quantity of electricity from each light receiving element.

Simple comparison at each measurement point E ₁ −E ₁ ′ = 0 (E ₁ is the signal on the standard paper surface measured at one point,
E ₁ ′ indicates a signal on the detection paper surface), there is a risk that all may be judged to be defective due to slight paper surface irregularities, measurement point errors, positional deviations, and the like. For this reason, E ₁ −E ₁ ′ <± M is set, the level considered to occur in the measurement of the amount of reflected light at the same position is entered in M as a level allowance, and the error is judged when the level is exceeded. To do.

However, when two print surfaces are measured and individual measurement points are compared with each other, an error signal may be output even when an error signal should not be output depending on the position.

Therefore, in the present invention, the points that have become defective points are compared by comparing at the same position as the standard paper surface, and the ratio of the number of defective points to the number of all points or the number of error points in all points) is calculated in advance. When the number of defective points exceeds this ratio (or number), it is determined that the detected paper surface has a printing error.

Also, another determination method can be adopted. That is, the difference between the reference value and the amount of light reflected from the detection paper surface is taken for each measurement point, and if the difference exceeds the level allowance and / or the point allowance, it is regarded as an error point. Then, the print error is determined by one of the following methods.

Judgment method (1) An error occurs if the number of error points exceeds the set value among all points.

Judgment method (2) An error block is a place where error points are continuous, and an error is generated when the next calculated value exceeds the set value.

L + S / P L is the peak value of the error block S is the sum of the levels of the error block P is the error point number of the error block.

This will be described with reference to the example shown in FIG. The vertical axis represents the amount of reflected light on the paper surface, that is, the signal. The axis A shows the level of the white paper surface, and the axis B shows the level of the black paper surface. Also,
(B), (B), (C) ... (G) show the positions of a plurality of measurement points of one light receiving element by the encoder.
Since the same measurement points are taken for each light receiving element, a large number of measurement points will be distributed over the entire printing surface.

If only one light receiving element is described, the signal 100 is a signal on a standard paper surface, the signal 100a is a signal obtained by adding the level allowance M to the signal 100, and the signal 100b is a signal obtained by subtracting the level allowance M from the signal 100. is there. The surface of the detection paper is measured, and the signal 100a and the signal 100b are measured.
If a predetermined number or more of measurement points are entered in between, it is determined that the measurement paper surface is printed well.

Now, even though the detected paper surface is a good print, the amount of reflected light may be different due to a difference in the material of the paper surface, and a printing error may occur. To avoid such determination errors, _'E 1 by adding or subtracting a correction level alpha in _{- (E 1' E 1 ±} α) < compares the ± M, determined by correcting the difference in reflected light quantity You can do this.

For example, when the detection paper surface is dark, the detection paper surface signal 101
(FIG. 1) generally approaches axis B. Signal 1 as it is
When 01 is compared with the signal 100, it is determined that the detected paper surface is a printing error. Therefore, the correction level α is added to the signal 101, and the signal 101 ′ is compared.

Such level allowance is mainly due to paper surface, paper unevenness,
Although it corresponds to the sensor drift, the point allowance described below is mainly to deal with the deviation between the encoder and the printing surface (measurement point on the printing surface).

For one measurement point, the level allowance is the vertical direction allowance (allowance value) in FIG. 1, and the point allowance is the allowance (allowance value) in the horizontal direction (that is, different measurement point) in FIG. ).

If the level allowance and the point allowance are set to have exactly the same length in the figure, the allowable range looks like a square around the measurement point in the figure. This point will be described in detail later. Of course, the level allowance and the point allowance can be set to different lengths. In that case, the two have different lengths in the figure, and they look like a rectangular allowable range. This point will also be described in detail later.

The point allowance will be described in detail with reference to FIGS. FIG. 2E is an explanatory diagram showing in detail an enlarged portion W of FIG. Figures 2A-2D show 2E
It is explanatory drawing for demonstrating intelligibly how to determine the point allowance shown in the figure. As described above, the point allowance is introduced in order to properly detect the printing error even when the measurement point on the printing surface and the encoder are misaligned. To obtain the point allowance, first, the deviation width is set to an appropriate value. The deviation width is appropriately determined depending on, for example, a feed error on the printing paper surface or elongation of the paper surface. Here, as an example, the deviation width is set to twice the distance between the measurement points. Of course, the deviation width may be one measurement point or three or more. For convenience, it is considered that the measurement points deviate.

Please refer to FIG. 2A. In FIG. 2A, the vertical axis indicates the amount of reflected light (voltage), and d to j on the horizontal axis indicate measurement points (time). Reference numeral 100 represents a signal serving as a reference value. How to determine the point allowance at the point g will be described. As described above, since the deviation width is equal to two measurement points, the amount of reflected light (voltage) at the points up to the two adjacent to the point g, that is, the points e to i, is focused. The maximum value of the reflected light amount (voltage) at the points e to i is the value at the point i,
The minimum value is the value at point e. By the way, when the point g is the maximum and is shifted by two measurement points, the reflected light amount (voltage) takes a value between the maximum value and the minimum value. Therefore, at the position of point g, the maximum value X and the minimum value O
If the line segment is connected with a line segment α, the point allowance at the point g is given by the line segment α. Maximum value X is positive point allowance, minimum value O
Is a negative point allowance.

Next, how to obtain the point allowance at the point i will be briefly described with reference to FIG. 2B. Similar to the method described with reference to FIG. 2A, the maximum value and the minimum value of the voltage signal 100 at the points g to k are obtained. And point i
By connecting the maximum value X and the minimum value O at the position of with the line segment β, the point allowance at the point i can be obtained.

Next, with reference to FIG. 2C, the permissible range that can be seen in the above-described square and rectangle will be described. In FIG. 2C, a rectangular allowable range is shown by a dotted line, but the point allowance can be obtained by utilizing this rectangular allowable range. That is, first, assuming the deviation width in both directions centering on the measurement point g, the lateral side is set. Next, a rectangle is drawn so that all the signals 100 corresponding to this horizontal side are included. The vertical side of this rectangle gives the point allowance at point g. Note that the rectangle in FIG. 2C becomes a square depending on how the deviation width is set.

In this way, the point allowance at each measurement point can be determined. FIG. 2D shows the area W in FIG.
Shows the point allowance at each measurement point. The vertical line segment between X and O at each measurement point corresponds to the point allowance.

Finally, the level allowance is adjusted to the point allowance thus obtained. That is, the level allowance is added to the maximum value of the point allowance, and the level allowance is subtracted from the minimum value. In this way, the signal 100a and the signal 100b shown in FIG. 2E can be obtained. The signal 100a and the signal 100b include a point allowance and a level allowance, and 100a is a positive allowance 100b and is a negative allowance.

When the allowance is created in this way, the point allowance becomes 0 at the smooth portion of the signal change (for example, point C in FIG. 2E), the detection accuracy is improved, and the signal change is abrupt and even a normal signal can be obtained only by the level allowance. At a point where it is determined to be defective (for example, point g in FIG. 2E), the point allowance becomes large, and erroneous determination can be reduced.

By the way, only level allowance (Fig. 1) or combination of level allowance and point allowance (Fig. 2)
In either case, if the sampled data exceeds the positive or negative allowance, it is regarded as an error point.
Then, the print error is determined by one of the following methods.

Judgment method (1) An error will occur if the number of error points exceeds the set value among all points.

Judgment method (2) An error block is a place where error points are continuous, and an error is generated when the next calculated value exceeds the set value.

L + S / P L is the peak value of the error block S is the sum of the levels of the error block P is the number of error points of the error block Embodiment Hereinafter, a preferred embodiment for implementing the method of the present invention will be described with reference to FIG. To do.

The sensor unit 1 is a No. 1 that detects the paper surface. 1-No. n indicates the number of the optical sensor, that is, the light receiving element.

The sensor unit 1 is installed at an appropriate place where the printing surface advances.

The sensor unit 1 is designed so that the light of the light emitting element is reflected on the paper surface and the reflected light is converted into an analog electric quantity by an optical sensor (light receiving element).

The output of the sensor unit 1 is amplified by the amplifier 2. The amplifier 2 is preferably a buffer-up that performs impedance conversion in order to prevent noise and the like from entering.

The amplified signal is sent to the multiplexer 79.
The analog signal is time-divided by the multiplexer 79 and sequentially sent to the AD converter 13 via the AD controller 11.

By omitting the multiplexer 79, each light receiving element No.
Various members after the AD controller 11 may be provided in n.

AD controller 11 is a measurement time controller 12
The analog signal is sampled and sent to the AD converter 13 during the measurement pulse of. The measuring time controller 12 is operated by the signal pulse from the starter 3. The starter 3 is attached to the power shaft of the printing machine or the like and generates a signal pulse at the same time when printing is started. Sampling is encoder 4
Is performed in a time division manner by the pulse from. The encoder 4 can be mounted on the power shaft of the printing machine.

The analog signal is converted into a digital signal in the AD converter 13.

The signal from the AD converter 13 is stored as a digital signal in the storage circuit 75 for each measurement point according to an instruction from the memory controller 14.

Hereinafter, one optical sensor (light receiving element) will be described as an example.

The memory circuit 75 largely functions as a standard memory 15 because of its role.
And the detection memory 16 can be divided. There is no functional difference between the standard memory 15 and the detection memory 16. The memory 15 stores the information on the standard paper, and the memory 16
The information of the detected paper surface is stored in.

The operations of the memories 15 and 16 are as follows.

The contents of the memory 16 are compared with the contents of the memory 15 by the level defect and point defect detector 31, and those having a difference of a predetermined defect level or a defect point or more are detected as defect points. That is, information on the first measurement point on the standard paper surface of the memory 15 (hereinafter, E ₁ ) is derived to the level defect and point defect detector 31.
Subsequently, the information (hereinafter, E ₁ ′) of the first measurement point on the detection paper surface in the memory 16 is led to the level defect and point defect detector 31. Then, the level defect and point defect detector 31 determines whether E ₁ ′ is a defect point by determining E ₁ − (E ₁ ′ ± α) <± M.

The correction level α is arbitrarily set by the correction level setter 90. For example, when there is no change in the quality of the standard paper, the level α is set to 0.

The defect level and the defect point M are the level defect setting unit 32.
Is set arbitrarily. It is preferable to be able to set the defect level and defect point separately and independently of each other. In this case, M is a value including both level allowance and point allowance, and as described above, the second and second
It can be set based on the signals 100a and 100b in FIG.

When E ₁ ′ is a defect signal, one pulse is sent from the level defect and point defect detector 31 to the defect rate detector 51. The defect rate detector 51 counts the number of pulses.

Next, the information (E ₂ ) of the second measurement point on the standard paper surface and the information (E ₂ ′) of the second measurement point on the detection paper surface are compared in the same manner to determine whether E ₂ ′ is a defective signal. Be determined.

This operation is performed for all measurement points.

When the comparison is completed for all the measurement points in this way, the defective rate detector 51 stores the number of defective signals. Whether or not printing is defective is determined by the ratio of the number of defective signals to the number of all measurement points. In other words, it is determined by the number of error points in all points.

The defective rate setting unit 42 sets the ratio of the defective signal to the total number of measurement points. For example, the defect rate setting device 4
When 2 is set to 20%, if the total number of measurement points is 10, then 2 points will be the limit of the number of defective signals. Information on these two points is sent from the defect rate setting unit 42 to the defect rate detector 51. The number of defective signals is stored in the defective rate detector 51. The number of defective signals is compared with the information sent from the defective rate setting unit 42, and a signal indicating whether the detected paper surface is a printing error is continuous. It is sent to the defect detector 61.

It is also possible to automatically set the defect level M in the defect level and defect point setting device 32 and the defect ratio in the defect ratio setting device 42.

Further, as shown in FIG. 5, the defect rate setting unit 42 and the defect rate detector 51 are omitted, and instead, an arithmetic unit 50 for calculating the above L + S / P is provided, and the determination method (2) is provided. May be performed.

To support high-speed printing machines, the sampling time at each measurement point must be as short as possible, but if the above-mentioned allowance (allowable value) is stored in memory for all points, Then, the processing of the sample, the comparison and the judgment are speeded up, and the processing speed is improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the principle of the printing error detecting method of the present invention, FIG. 2 is a diagram showing a relationship between a reference value and a level allowance, and FIGS. 2A to 2D are diagrams for explaining point allowance. Explanatory drawing which expanded and showed a part of FIG.
The figure is an enlarged view of the portion W in FIG. 2 and is an explanatory diagram for explaining the point allowance and the level allowance.
FIG. 3 is a diagram showing an error block, FIG. 4 is a block diagram showing an example for implementing the printing error detection method of the present invention, and FIG. 5 is a block diagram showing another example. 1 …… Sensor section 2 …… Amplifier 13 …… AD converter 14 …… Memory controller 15 …… Standard memory 16 …… Detection memory 31 …… Level defect and point defect detector 32 …… Level defect and point defect detector setting 42. Defective rate setter 50. Calculator 51. Defective rate detector 90 .. Correction level setter

Claims (2)

[Claims] 1. First, light is applied to a plurality of measurement points on a standard paper surface, the amount of reflected light at those measurement points is calculated as a reference value, and the difference between the reference value and the amount of reflected light from the detection paper surface is calculated. A printing error detection method characterized in that a printing error is determined by comparing the above with a level allowance mainly corresponding to paper quality or paper unevenness and a point allowance mainly corresponding to deviation of a measurement point. 2. The printing error detecting method according to claim 1, wherein the level allowance and the point allowance are stored in a memory.