JPH11334187A - Print density controller and control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform printing at a desired density by controlling to decrease print density if the average value of output is higher than a target level otherwise to increase the print density thereby detecting the print density of a density decision mark accurately. SOLUTION: A first density sensor (first sensor) 21 and a second density sensor (second sensor) 22 read out a density decision mark 26 printed on a print sheet (sheet) 25 running in the direction of an arrow A and the white paper part and deliver detection signals proportional to a detected density to a control section 23. The control section 23 receives detection signals proportional to density values detected by the first and second sensors 21, 22 and determines the difference of detection values of the density decision mark 26 and the difference of detection values of the white paper part. A decision is then made whether the difference deviates from a specified range and a command is delivered to an image printing section 24 based on the decision results thus controlling the print density.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a print density control method and apparatus used in an image forming apparatus of an electrophotographic system or the like and used to maintain a print density at an optimum state.

[0002]

2. Description of the Related Art A conventional print density control device used in an image forming apparatus such as an electrophotographic system and used to maintain a print density at an optimum state has been used for printing on printing paper or forming on a photoreceptor. A control means is employed which outputs a detection signal proportional to the density detected by reading the density determination mark with one density sensor, and compares the output density detection signal with a target value to approach the target value.

FIG. 6 is a block diagram showing an example of such a conventional print density control device, and FIG. 7 is a characteristic diagram showing output characteristics of the density sensor of the example of FIG.

In FIG. 6, a density sensor 101 includes a density determination mark 10 printed on a printing paper (paper) 104.
5 and outputs a detection signal proportional to the read density to the control unit 102, and the control unit 102 controls the operation of the print control unit 103 accordingly.

As shown in FIG. 7, when the maximum value of the read density (output value of the density sensor) is V1, the target density V
m, the print density is not adjusted. However, when the output value of the density sensor reaches V2 or V3 due to a change in the printing environment or a change in the characteristics of the image printing unit, the output density approaches the target density Vm. By controlling the print density to be low and, in the case of V3, the print density to be high, control is performed so that printing at a constant density can be performed. In FIG. 7, the output value V0 of the density sensor is the output value of the density sensor of the blank portion.

[0006]

As described above, the conventional print density control device reads the density determination mark with one density sensor, compares the output density detection signal with the target value, and sets the target value as the target value. If the output value fluctuates due to contamination or failure of the density sensor, a signal with a value different from the actual density of the density determination mark is output. May be controlled.

In order to avoid this, the conventional print density control device constantly monitors the output value V0 of the density sensor in a blank portion (a portion where no image is formed in the case of a photoreceptor) and outputs this value. When the value V0 changes, it is determined that dirt or a failure has occurred in the density sensor, and a measure is taken accordingly.

Therefore, when printing paper of different colors or a photoconductor having a different reflectance is used, the output value of the density sensor in a blank area changes, so that printing paper of a different color or a photoconductor having a different reflectance is used. There is a problem that cannot be done.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described drawbacks of the conventional print density control means, and to accurately use a printing paper of a different color or a photoreceptor of a different reflectance without using the same. Another object of the present invention is to provide a print density control unit that can always perform printing at a desired density by enabling the print density of a density determination mark to be detected.

[0010]

According to a first printing density control method of the present invention, the density of a density determination mark printed on printing paper is detected by a plurality of density sensors. The difference between the maximum value and the minimum value of the density detection value of the density determination mark, the difference between the maximum value and the minimum value of the detection value of the blank portion, and the average value of the detection values of the density determination mark are obtained. When the difference between the maximum value and the minimum value of the density or the difference between the maximum value and the minimum value of the detection value of the blank portion exceeds a predetermined value range, it is determined that the density sensor is dirty or defective. When the difference between the maximum value and the minimum value of the density of the density determination mark or the difference between the maximum value and the minimum value of the detection value of the blank portion is within a predetermined value range, the detected value of the density of the density determination mark The average of When the average value is higher than the target value, the print density in the image printing unit is controlled to be low.When the average value is lower than the target value, the print density in the image printing unit is low. This includes controlling to increase the density, and in particular, setting the number of density sensors to two or three.

According to a second printing density control method of the present invention, the density of a density determination mark formed on a photoreceptor is detected by a plurality of density sensors, and the density determination mark detected by the plurality of density sensors is detected. The difference between the maximum value and the minimum value of the density detection value and the difference between the maximum value and the minimum value of the detection value of the blank portion and the average value of the detection values of the density determination mark are obtained, and the maximum value of the density of the density determination mark is calculated. When the difference between the minimum value or the difference between the maximum value and the minimum value of the detection value of the blank portion exceeds a predetermined value range, it is determined that the density sensor is dirty or defective, and the density of the density determination mark is determined. When the difference between the maximum value and the minimum value of the density determination mark or the difference between the maximum value and the minimum value of the detection value of the blank portion is within a predetermined value range, the average value of the density detection values of the density determination mark is set to the target value. Compared to the above When average value is higher than the target value is controlled so that the print density in the image printing unit becomes thin,
When the average value is lower than the target value, this includes controlling to increase the print density in the image printing unit. In particular, the number of density sensors is set to two or three.

According to a first aspect of the present invention, there is provided a print density control apparatus comprising: a plurality of density sensors for detecting the density of a density determination mark printed on printing paper; The difference between the maximum value and the minimum value of the density detection value and the difference between the maximum value and the minimum value of the detection value of the blank portion and the average value of the detection values of the density determination mark are obtained, and the maximum value of the density of the density determination mark is calculated. When the difference between the minimum value or the difference between the maximum value and the minimum value of the detection value of the blank portion exceeds a predetermined value range, it is determined that the density sensor is dirty or defective, and the density determination mark is When the difference between the maximum value and the minimum value of the density or the difference between the maximum value and the minimum value of the detection value of the blank portion is within a predetermined value range, respectively, the average value of the detection values of the density of the density determination mark is targeted. Compare to the value When average value is higher than the target value is controlled so that the print density in the image printing unit becomes thin,
And a control unit for controlling the printing density in the image printing unit to be high when the average value is lower than the target value. In particular, the number of density sensors is two or three. It is.

A second printing density control device according to the present invention comprises a plurality of density sensors for detecting the density of a density determination mark formed on a photoreceptor, and a plurality of density sensors for detecting the density of the density determination mark detected by the plurality of density sensors. The difference between the maximum value and the minimum value of the density detection value and the difference between the maximum value and the minimum value of the detection value of the blank portion and the average value of the detection values of the density determination mark are obtained, and the maximum value of the density of the density determination mark is calculated. When the difference between the minimum value or the difference between the maximum value and the minimum value of the detection value of the blank portion exceeds a predetermined value range, it is determined that the density sensor is dirty or defective, and the density of the density determination mark is determined. When the difference between the maximum value and the minimum value of the density determination mark or the difference between the maximum value and the minimum value of the detection value of the blank portion is within a predetermined value range, the average value of the density detection values of the density determination mark is set to the target value. Compared to the average When the value is higher than the target value, the control unit controls the print density in the image printing unit to decrease, and when the average value is lower than the target value, controls the print density in the image printing unit to increase. In particular, the number of density sensors is two or three.

[0014]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a print density control apparatus according to the present invention. FIG. 2 is a plan view showing an example of a sheet used in the embodiment of FIG. 1 and a density determination mark printed thereon. 1 is a flowchart showing the operation of the embodiment of FIG. 1, FIG. 4 is a characteristic diagram showing general output characteristics of the density sensor in the embodiment of FIG. 1, and FIG. 5 is a difference between output values of the density sensor in the embodiment of FIG. FIG. 10 is a characteristic diagram showing output characteristics when the value exceeds a limit value.

In FIG. 1, a first density sensor (first sensor) 21 and a second density sensor (second sensor)
Reference numeral 22 reads a density determination mark 26 (see FIG. 2) and a blank portion printed on a printing paper (paper) 25 traveling in the direction of arrow A, and outputs a detection signal proportional to the detected density value to the control unit 23. .

The control unit 23 receives signals from the first sensor 21 and the second sensor 22 as described later,
The difference between the detection value of the density determination mark 26 and the difference between the detection values of the blank portion are determined, and it is determined whether each of them exceeds a predetermined value range. From this result, a command is given to the image printing unit 24 to control the print density.

Next, the operation of the print density control device configured as described above will be described with reference to FIGS.

FIG. 4 is a characteristic diagram showing general output characteristics of the density sensor in the embodiment of FIG.

In FIG. 4, the output values (output values) V1a and V2a of the density sensors
The first sensor output and the second sensor output when the second sensor 22 reads the density determination mark 26 are output values when reading values close to the target density value Vm, and the output values V1b and V2b are , The output of the first sensor 21 and the output of the second sensor 22 are both output values when reading a value darker than the target density value Vm. The output values V1c and V2c are the first sensor 21 and the second sensor 22 respectively. Are output values when reading densities lower than the target density value Vm. The output values V1w and V2w are output values when a blank portion of the sheet 25 is read. Difference ΔV33
Is the output value V1a of the first sensor 21 and the second sensor 2
2, and the difference ΔVw34 is the difference between the output value V1w and the output value V2w of the blank portion.

Hereinafter, the operation of the print density control device will be described with reference to the flowchart of FIG.

When the paper 25 is transported in the direction of arrow A, the first sensor 21 reads the density determination mark 26 and sends the output value V1a (or V1b or V1c) to the control unit 23 (step 71). Subsequently, the first sensor 21 reads a blank portion of the sheet 25 immediately below the determination mark 26 and sends an output value V1w to the control unit 23 (Step 72).

Next, the second sensor 22 reads the density determination mark 26 and outputs the output value V2a (or V2b or V2b).
2c) is sent to the control unit 23 (step 73), and a blank portion immediately below the determination mark 26 of the paper 25 is read, and the output value V2w is sent to the control unit 23 (step 74).

The output value V1a (or V1b or V1
c) and V1w and V2a (or V2b or V2b)
2c) and V2w, the control unit 23 outputs the output value V
1a (or V1b or V1c) and V2a (or V1a
2b or V2c) is calculated (step 7).
5) It is determined whether the difference ΔV exceeds a predetermined value (step 76).

As a result, as shown in FIG.
Is larger than the limit value 46 (in the case of an abnormal value), at least one of the first sensor 21 and the second sensor 22 is dirty or a failure has occurred, and therefore, a measure is taken (step 80). The procedure displays the status, stops the printing operation, and cleans or replaces the density sensor.

If the difference .DELTA.V does not exceed the predetermined value, the routine proceeds to step 77, where the difference .DELTA.Vw between the output values V1w and V2w is calculated, and it is determined whether or not the difference .DELTA.Vw exceeds a predetermined value (step 78). .

As a result, as shown in FIG. 5, the difference ΔVw4
If 5 exceeds the limit value 47 (in the case of an abnormal value), the difference Δ
Similarly to V44, at least one of the first sensor 21 and the second sensor 22 is dirty or has a failure.

If the difference ΔVw34 does not exceed the limit value 47, the average value of the output values V1a and V2a is calculated (step 79), and the calculated average value is within a predetermined range with respect to the target density value Vm. (Step 8)
1).

As a result, if the average value is within a predetermined range with respect to the target density value Vm, it is determined that both the first sensor 21 and the second sensor 22 are normal (step 81). The printing process is executed (step 85).

If the average value of the output values V1a and V2a is not within a predetermined range with respect to the target density value Vm, it is determined whether or not the average value is higher than the target density value Vm (step 82). If the average value is higher than the target density value Vm, the control section 23 gives an instruction to the image printing section 24 to reduce the density (step 84).

If the average value is lower than the target density value Vm, the control section 23 gives an instruction to the image printing section 24 to increase the density (step 83).

Thus, using two density sensors,
The difference between the output values from the density determination mark and the blank portion and the average value of the output values from the density determination mark are obtained.
By comparing them with a predetermined value, it is possible to accurately detect the print density of the density determination mark without being affected even when using a printing paper of a different color or a photoconductor having a different reflectance. Therefore, printing with a desired density can be performed.

In the above-described embodiment, two density sensors are provided so as to read a density determination mark printed on printing paper. However, in an image forming apparatus such as an electrophotographic system, the density sensor is formed on a photosensitive member. The density of the density judgment mark
The same control as described above can be performed by reading with the individual density sensors.

It is also possible to use three or more density sensors instead of two density sensors. In this case, the difference between the maximum value and the minimum value of the output values of the plurality of density sensors is used instead of the difference between the output values of the two density sensors.

[0035]

As described above, the printing density control method and apparatus of the present invention use a plurality of density sensors,
By inputting the density judgment mark formed on the printing paper or the photoreceptor and the output value from the blank portion, when the difference between the maximum value and the minimum value is within a predetermined range, the output from the density judgment mark is output. Determines whether the average value is higher than the target density value, and if the average value is higher than the target density value, controls to reduce the density.If the average value is lower than the target density value, Is controlled so that even when using printing papers of different colors or photoreceptors with different reflectances, the printing density of the density determination mark is accurately detected without being affected by the Has the effect that it is possible to perform

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an embodiment of a print density control device according to the present invention.

FIG. 2 is a plan view showing an example of a sheet used in the embodiment of FIG. 1 and a density determination mark printed on the sheet.

FIG. 3 is a flowchart showing an operation of the embodiment of FIG. 1;

4 is a characteristic diagram showing general output characteristics of the density sensor in the embodiment of FIG.

5 is a characteristic diagram showing output characteristics when a difference between output values of a density sensor in the embodiment of FIG. 1 exceeds a limit value.

FIG. 6 is a block diagram illustrating an example of a conventional print density control device.

FIG. 7 is a characteristic diagram showing output characteristics of the density sensor of the example of FIG.

[Explanation of symbols]

 Reference Signs List 21 first density sensor (first sensor) 22 second density sensor (second sensor) 23 control unit 24 image printing unit 25 printing paper (paper) 26 density determination mark 33/44 difference ΔV 34/45 difference ΔVw 46/47 Limit value 71 to 85 Step 101 Density sensor 102 Control unit 103 Image printing unit 104 Printing paper (paper) 105 Density determination mark

Claims (12)

[Claims] 1. A plurality of density sensors for detecting the density of a density determination mark printed on printing paper, and a maximum value and a minimum value of density detection values of the density determination mark detected by the plurality of density sensors. And the difference between the maximum value and the minimum value of the detection value of the blank portion and the average value of the detection values of the density determination mark, and the difference between the maximum value and the minimum value of the density of the density determination mark or the detection of the blank portion When the difference between the maximum value and the minimum value exceeds a predetermined value range, it is determined that the density sensor is dirty or defective, and the difference between the maximum value and the minimum value of the density of the density determination mark or the difference is determined. When the difference between the maximum value and the minimum value of the detection value of the blank portion is within a predetermined value range, an average value of the density detection values of the density determination mark is compared with a target value, and the average value is set to the target value. When higher than the value Controlling the print density in the image printing unit to decrease, and controlling the print density in the image printing unit to increase when the average value is lower than the target value. Control method. 2. The print density control method according to claim 1, wherein the number of density sensors is two. 3. The print density control method according to claim 1, wherein the number of density sensors is three. 4. A density detection mark formed on a photoreceptor is detected by a plurality of density sensors, and a maximum value and a minimum value of density detection values of the density detection mark detected by the plurality of density sensors are detected. And the difference between the maximum value and the minimum value of the detection value of the blank portion and the average value of the detection values of the density determination mark, and the difference between the maximum value and the minimum value of the density of the density determination mark or the detection of the blank portion When the difference between the maximum value and the minimum value exceeds a predetermined value range, it is determined that the density sensor is dirty or defective, and the difference between the maximum value and the minimum value of the density of the density determination mark or the difference is determined. When the difference between the maximum value and the minimum value of the detection value of the blank portion is within a predetermined value range, an average value of the density detection values of the density determination mark is compared with a target value, and the average value is set to the target value. If higher than the value Controlling the print density in the image printing section to be low, and controlling the print density in the image printing section to be high when the average value is lower than the target value. Method. 5. The print density control method according to claim 4, wherein the number of density sensors is two. 6. The print density control method according to claim 4, wherein the number of density sensors is three. 7. A plurality of density sensors for detecting the density of a density determination mark printed on printing paper, and a maximum value and a minimum value of density detection values of the density determination mark detected by the plurality of density sensors. And the difference between the maximum value and the minimum value of the detection value of the blank portion and the average value of the detection values of the density determination mark, and the difference between the maximum value and the minimum value of the density of the density determination mark or the detection of the blank portion When the difference between the maximum value and the minimum value exceeds a predetermined value range, it is determined that the density sensor has become dirty or defective, and the difference between the maximum value and the minimum value of the density of the density determination mark or When the difference between the maximum value and the minimum value of the detection value of the blank portion is within a predetermined value range, respectively, the average value of the density detection values of the density determination mark is compared with a target value, and the average value is set to the target value. When it is higher than the target value A control unit configured to control the print density in the image printing unit to be low, and to control the print density in the image printing unit to be high when the average value is lower than the target value. Concentration control device. 8. The print density control device according to claim 7, wherein the number of density sensors is two. 9. The print density control device according to claim 8, wherein the number of density sensors is three. 10. A plurality of density sensors for detecting the density of a density determination mark formed on a photoconductor, and a maximum value and a minimum value of density detection values of the density determination mark detected by the plurality of density sensors. And the difference between the maximum value and the minimum value of the detection value of the blank portion and the average value of the detection values of the density determination mark, and the difference between the maximum value and the minimum value of the density of the density determination mark or the detection of the blank portion When the difference between the maximum value and the minimum value exceeds a predetermined value range, it is determined that the density sensor has become dirty or defective, and the difference between the maximum value and the minimum value of the density of the density determination mark or When the difference between the maximum value and the minimum value of the detection value of the blank portion is within a predetermined value range, respectively, the average value of the density detection values of the density determination mark is compared with a target value, and the average value is set to the target value. When it is higher than the target value A control unit configured to control the print density in the image printing unit to be low, and to control the print density in the image printing unit to be high when the average value is lower than the target value. Concentration control device. 11. The print density control device according to claim 10, wherein the number of density sensors is two. 12. The print density control device according to claim 10, wherein the number of density sensors is three.