JP2005178160A - Image forming condition correction method and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To recognize an abnormality in an optical system of an image forming device. <P>SOLUTION: A first density correction procedure 16-1 corrects detected density value characteristics to a gradient by using a prescribed arithmetic formula on the basis of a detected density value to the gradient of a prescribed test patter printed, a second density correction procedure 16-2 reprints a test pattern on the basis of the result of the correction, and normalizes the result of the reprinting by a reference density in percentage of a 100% gradient in reference gamma characteristics, a measured gamma characteristics computation procedure 16-3 obtains an integrated density value from a first gradient to a second gradient by computing the measured gamma characteristics, a both gamma characteristics comparison procedure 16-4 compares both the gamma characteristics with each other and an alarm generation procedure 16-5 generates a warning when a difference of a prescribed amount or larger is recognized between the gamma characteristics. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for correcting image forming conditions when a multi-tone toner image is formed on a photoreceptor, and the toner image is transferred onto a recording medium and output, and an image for executing the correction method. The present invention relates to a forming apparatus.

In recent years, the number of image forming apparatuses having multi-heads such as an ink jet printer and an electrophotographic printer having a plurality of image forming units has been rapidly increasing. In such an image forming apparatus, the relationship between the detected density value and the gradation level of input image data is called a gamma characteristic. Ink jet printer ink discharge amount In electrophotographic printers, the developer is used to bring the gradation versus detected density value characteristic detected using a predetermined test pattern before execution of the printing process closer to a preset reference gamma characteristic. Correction is performed by changing the developing bias voltage to be applied or the exposure amount of the exposure part (see Patent Document 1).
This correction is performed because it is extremely difficult to accurately and uniformly manufacture the exposure amounts of the plurality of ink discharge ports and the plurality of light sources included in the multihead.
Japanese Patent No. 3059451

  However, in the above-described conventional technique, an optical system constituting an exposure unit in an electrophotographic printer (F- in the case of using an LED array as a light source, a lens array, and a laser diode as a light source). If the focus of the [theta] lens is deviated from the photosensitive member, it becomes difficult to correct. Furthermore, there remains a problem to be solved that it is impossible to recognize that the optical system is incomplete.

  The problem to be solved is the focus of the optical system constituting the exposure section (a lens array in the case where an LED array is used as a light source, and an F-θ lens in a case where a laser diode is used as a light source). This is because it is not possible to recognize that there is a deviation from the photoconductor or due to a defect in the optical system.

  In the present invention, after correcting the image forming conditions based on the conventional technique by the first density correction procedure, the measurement gamma characteristic is obtained by the second density correction procedure. This measured gamma characteristic curve is compared with a pre-stored reference gamma characteristic curve. If there is a large difference in shape between the two characteristic curves, the optical system (LED array is used as the light source) constituting the exposure unit. The most important feature is that it is inconvenient due to the lens array used in the above-mentioned lens array and the F-θ lens in the case where a laser diode is used as the light source.

  Inconveniences caused by the optical system constituting the exposure unit (a lens array in the case where an LED array is used as a light source and an F-θ lens in a case where a laser diode is used as a light source) can be easily recognized. In addition, since the optical system is started to be corrected without changing the light emission amount and the development bias, it is possible to execute the correction of the image forming condition accurately and within a short time.

  The first density correction procedure, the second density correction procedure, the measurement gamma characteristic calculation procedure, the gamma characteristic comparison procedure, and the alarm generation procedure are all realized by a computer control procedure.

FIG. 1 is a block diagram of a control system according to the first embodiment.
As shown in the figure, the image forming condition correction method of the first embodiment includes an image forming unit 1 (1C, 1M, 1Y, 1K), a developing bias variable unit 2, and an LED head 3 (3C, 3M, 3Y, 3K). ), The light emission amount variable unit 4, the test pattern storage unit 5, the density sensor 6, the density reading unit 7, the density value storage unit 8, the development bias value calculation unit 9, and the light emission unit light amount value calculation unit 10. A density value normalization calculation unit 11, a measured gamma curve shape characteristic value Sp2 calculation unit 12, a reference gamma curve shape characteristic value Sp1 storage unit 13, a determination unit 14, an alarm display unit 15, and a control unit 16. Executed by a control system comprising:

Before describing the details of these components, an outline of a printing mechanism to which the present invention is applied will be described using a color printer as an example.
FIG. 2 is a cross-sectional view of the main part of the printing mechanism.
As shown in the figure, four image forming units 1K, 1Y, 1M, and 1C are arranged in the printing mechanism unit along the conveyance path from the recording medium insertion side to the discharge side. Here, K, Y, M, and C represent black, yellow, magenta, and cyan colors, respectively (hereinafter the same). The inside includes photosensitive drums 23K, 23Y, 23M, and 23C whose surfaces are uniformly charged by charging rollers 22K, 22Y, 22M, and 22C. An electrostatic latent image based on image data is formed on the surface by the LED heads 3K, 3Y, 3M, and 3C.

  The electrostatic latent image is supplied from the toner cartridges 27K, 27Y, 27M, and 27C by the developing rollers 24K, 24Y, 24M, and 24C, the developing blades 25K, 25Y, 25M, and 25C, the sponge rollers 26K, 26Y, 26M, and 26C, and the like. Color toner is supplied and developed.

  The toner obtained by developing the electrostatic latent image is transferred onto the recording medium conveyed on the conveyance belt 29 in the direction from the image forming unit 1K to the image forming unit 1C by the transfer rollers 28K, 28Y, 28M, and 28C. The conveyor belt 29 is circulated by a driving roller 30 and a driven roller 31.

  Around the transport belt 29, a density sensor 6 for detecting the color density of the test pattern, a cleaning blade 33, and a waste toner tank 34 are arranged. The density sensor 6 is a sensor that irradiates a later-described test pattern formed on the conveyor belt 29 with a predetermined light beam, receives the reflected light, and detects the density value. The cleaning blade 33 is a part that removes a later-described test pattern formed on the conveyor belt 29, and the waste toner tank 34 is a part that stores the removed waste toner.

  When the recording medium at the time of printing is taken out from the paper storage cassette 35 by the hopping roller 36, the recording medium is guided by the guide 37 and reaches the registration roller 38. The oblique feeding of the recording medium is corrected by the registration roller 38 and the opposing pinch roller 39. The recording medium is then guided between the suction roller 40 and the conveyance belt 29 by the registration roller 38. The suction roller 40 charges the recording medium together by being pressed against the driven roller 31, and electrostatically attracts the recording medium onto the transport belt 29.

  The recording medium on which the toner image is transferred by the transfer rollers 28K, 28Y, 28M, and 28C is sent to the heat roller 41 and the pressure roller 42. Here, the toner image is heated and fixed on the recording medium. Here, the temperature of the heat roller 41 is detected by the thermistor 41-1.

The recording medium after fixing is stored in the stacker 44 through the guide 43, and the printing process is completed.
In order to detect the position of the recording medium in the process described above, position sensors 45-1, 45-2, 45-3, and 45-4 are arranged at predetermined positions.
Now, the description of the outline of the printing mechanism is finished, and the control system of the present invention will be described in detail with reference to FIG.

  The image forming unit 1 (1C, 1M, 1Y, 1K) is a part that receives image data and forms an image for each color (C, M, Y, K) in a tandem state on a recording medium. That is, it is a part for forming an output image corresponding to the gradation of the image data for each color, and is a part to be controlled by the present invention.

The developing bias variable unit 2 is a part that adjusts the density of the output image by changing the bias voltage of the developing rollers 24K, 24Y, 24M, and 24C (FIG. 2) based on the control of the control unit 16.
The LED head 3 (3C, 3M, 3Y, 3K) exposes the surface of the uniformly charged photosensitive drums 23K, 23Y, 23M, 23C (FIG. 2) to form an electrostatic latent image based on the image data. Part.

The light emission amount variable unit 4 is a part that varies the light emission amount by increasing or decreasing the exposure voltage applied to the LED head 3 (3C, 3M, 3Y, 3K) based on the control of the control unit 16.
The test pattern storage unit 5 is a memory that stores in advance image data of a test pattern for obtaining a measurement gamma characteristic that represents a detected density with respect to the gradation. Usually, it is stored in a ROM (not shown) in which the control data of the image forming apparatus is stored together with other control data.

Here, an example of the test pattern will be described.
FIG. 3 is an explanatory diagram of a test pattern according to the first embodiment.
(A) is a pattern configuration diagram, (b) is a pattern layout diagram. As shown in (a), the test pattern 6-1 has a gradation of 100%, which is continuously arranged at equal distances in the medium conveyance direction. It is a pattern composed of 80%, 50%, 40%, 25%, and 10% regions.
As shown in (b), the test pattern 6-1 passes through a part of the conveyance belt 29 (FIG. 2) directly below the density sensor 6 (FIG. 2), so that the image forming units (1C, 1M, 1Y) are formed. 1K).

Returning to FIG. 1, the density sensor 6 is a reflection type optical sensor, and measures the reflection intensity of the test pattern printed on the conveyor belt 29 (FIG. 2), and detects the density value with respect to the gradation degree from the reflection intensity. It is a sensor.
The density reading unit 7 stores a density value corresponding to the gradation detected by the density sensor 6 in the density value storage unit 8 or reads a density value stored therein from the density value storage unit 8. It is.

The density value storage unit 8 is a memory that stores density values for the gradation levels detected by the density sensor 6.
The development bias value calculation unit 9 is a part that calculates the value of the development bias based on the density value for the gradation stored in the density value storage unit 8 in accordance with the first density correction procedure 16-1 of the control unit 16. is there.

In accordance with the first density correction procedure 16-1 of the control unit 16, the light emitting unit light amount value calculation unit 10 is based on the density value for the gradation stored in the density value storage unit 8, and the LED head 3 (3C, 3M, 3Y, 3K).
In accordance with the second density correction procedure 16-2 of the control unit 16, the density value normalization calculation unit 11 performs the density value for the gradation stored in the density value storage unit 8 (correction result of the first density correction procedure). Is normalized with a reference density rate of 100% gradation in the later-described reference gamma characteristic.

The measurement gamma curve shape characteristic value Sp2 calculation unit 12 obtains a measurement gamma curve using the least square method or the like from the correction result of the second density correction procedure 16-2 according to the measurement gamma characteristic calculation procedure of the control unit 16. It is.
The reference gamma curve shape characteristic value Sp1 storage unit 13 is a memory that stores a reference gamma curve in advance as a reference density ratio of the image data with respect to the gradation of the image data.

The determination unit 14 is a part that compares the shapes of both gamma characteristic curves in accordance with both gamma characteristic comparison procedures 16-4 of the control unit 16 and detects the difference between them. The shape difference detection is performed by storing the integrated density value between the gradation degree 70% and the gradation degree 100% in the measurement gamma curve calculated by the measurement gamma curve shape characteristic value Sp2 calculation unit 12 and the reference gamma curve shape characteristic value Sp1. This is performed by comparing the integrated density value between the gradation degree 70% and the gradation degree 100% in the reference gamma characteristic stored in the unit 13 in advance.
The alarm display unit 15 is a part that generates a warning when a difference of a predetermined amount or more is recognized between the two gamma characteristics according to the alarm generation procedure 16-5 of the control unit 16.

  The control unit 16 is a CPU (central processing unit) that controls the entire apparatus, and in the present invention, in particular, the first density correction procedure 16-1, the second density correction procedure 16-2, and the measured gamma characteristic. This is a part for executing the calculation procedure 16-3, the gamma characteristic comparison procedure 16-4, and the alarm generation procedure 16-5.

  The first density correction procedure 16-1 is a control procedure for correcting the gradation degree / detected density value characteristic using a predetermined arithmetic expression based on the detected density value with respect to the gradation degree of the printed predetermined test pattern.

  That is, the image forming unit 1 prints the test pattern (one example) shown in FIG. 3 on the conveyance belt 29 (FIG. 2), and the density sensor 6 detects the density of the test pattern and develops based on the detected density. The bias value calculation unit 9 calculates the development bias applied to the development roller 24 (FIG. 2) of the image forming unit 1, and the development bias variable unit 2 sets the development bias based on the calculated value. At the same time, the light emitting unit The light quantity value calculation unit 10 calculates the light emission amount of the LED head 3 based on the detected density, and the light emission amount variable unit 4 sets the exposure voltage of the LED head 3 based on the value. This procedure is similar to the image forming condition setting method in the prior art.

  In the second density correction procedure 16-2, the image forming unit 1 again applies the test pattern (one example) shown in FIG. 3 to the conveying belt 29 (see FIG. 3) based on the correction result of the first density correction procedure 16-1. 2) A procedure for reprinting on top and normalizing the reprint result with a reference density rate of 100% gradation in the reference gamma characteristic stored in the reference gamma curve shape characteristic value Sp1 storage unit 13 in advance. is there.

FIG. 4 is an explanatory diagram of the second density correction procedure.
(A) is a figure showing the reference gamma characteristic stored in the reference gamma curve shape characteristic value Sp1 storage unit 13 in advance, and the black circle in (b) shows the test pattern (one example) on the transport belt 29 (FIG. 2). This is the detected density ratio that is printed on and represents the result of printing. The white circle in (b) is normalized by the standard density ratio of 100% gradation in the standard gamma characteristic. It is the value.

  That is, in the second density correction procedure 16-2, the test pattern (one example) shown in FIG. 3 is printed on the conveyor belt 29 (FIG. 2), and the detected density ratio indicated by the black circle in (b) is measured. Further, it is a procedure for obtaining a white circle value of (b) by normalizing with reference to a gradation degree of 100% in the reference gamma characteristic.

  Returning to FIG. 1, the measurement gamma characteristic calculation procedure 16-3 is performed during the period from the first gradation degree to the second gradation degree based on the correction result of the second density correction procedure 16-2 (as an example, 70). % To 100%). That is, an approximate curve (measured gamma curve) is obtained from the set of white circles in FIG. 4B using the least square method or the like, and as an example of the measured gamma curve, a density integral value of 70% to 100% gradation is obtained. This is the procedure to seek.

  Both gamma characteristic comparison procedures 16-4 are the integrated value of the density from the first gradation degree to the second gradation degree calculated based on the result of the measurement gamma characteristic calculation procedure 16-3 and the reference gamma characteristic. It is a procedure to compare with. That is, for the measured gamma curve obtained from the set of white circles in FIG. 4B, the integrated density value from 70% to 100% gradation, and for the reference gamma curve shown in FIG. This is a procedure for comparing the concentration integrated value up to 100%.

Here, the first gradation value 70% and the second gradation value 100% are determined empirically as optimum values based on many experimental results.
The alarm generation procedure 16-5 is a procedure for generating a warning when a difference of a predetermined amount or more is recognized between the two gamma characteristics based on the both gamma characteristics comparison procedure 16-4.

Next, the operation of the first embodiment will be described using a flowchart.
FIG. 5 is a flowchart of the operation of the first embodiment.
The image forming condition correction method according to the first embodiment will be described in the order of steps S1 to S9 in the figure.

Step S1
3 is stored in the test pattern storage unit 5 (FIG. 1) by the image forming units (1C, 1M, 1Y, 1K) (FIG. 1) based on the control of the control unit 16 (FIG. 1). The image is transferred to the conveyance belt 29.
Step S2
A density value for each gradation in the test pattern is acquired by the density sensor 6 (FIG. 2) disposed on the conveyor belt 29 (FIG. 2) and sent to the density reading unit 7 (FIG. 2). This density value is stored in the density value storage unit 8 (FIG. 1).

Step S3
The control unit 16 (FIG. 1) converts the density value stored in the density storage unit 8 (FIG. 1) via the density reading unit 7 (FIG. 1) to obtain a normal development bias value. Ask. This development bias value is sent to the development bias variable section 2 (FIG. 1), and the development bias of the image forming sections (1C, 1M, 1Y, 1K) is set. At the same time, the light intensity value is obtained by converting the density value (conventionally known). This light amount value is sent to the light emission amount variable unit 4 (FIG. 1), and the normal light emission amount of the image forming units (1C, 1M, 1Y, 1K) is set. When both settings are completed, a bias value change end notification is sent from the developing bias variable unit 2 (FIG. 1) to the control unit 16 (FIG. 1), and the light amount is changed from the light emission amount varying unit 4 (FIG. 1) to the control unit 16 (FIG. 1). Each notification is sent. This step corresponds to the first density correction procedure 16-1.

Step S4
When the control unit 16 (FIG. 1) accepts both the notifications, the image forming units (1C, 1M, 1Y, 1K) (FIG. 1) based on the control of the control unit 16 (FIG. 1) perform the same as in step S1. The test pattern shown in FIG. 3 stored in the test pattern storage unit 5 (FIG. 1) is retransferred to the conveyor belt 29.
Step S5
Similar to step S2, the density sensor 6 (FIG. 2) arranged on the conveyor belt 29 (FIG. 2) acquires the density value for each gradation in the test pattern, and the density reading unit 7 (FIG. 2). Sent to. This density value is stored in the density value storage unit 8 (FIG. 1).

Step S6
The control unit 16 (FIG. 1) divides the density value stored in the density value storage unit 8 (FIG. 1) by the maximum density value to obtain a detected density rate, and this detected density rate is a level in the reference gamma characteristic. Normalize based on 100% furniture. That is, the black circle detection density ratio shown in FIG. 3B is normalized with reference to a gradation degree of 100% in the reference gamma characteristic to obtain the white circle value of FIG. The value of the white circle normalized here is sent to the measured gamma curve shape characteristic value Sp2 calculation unit 12 (FIG. 1). This step corresponds to the second density correction procedure 16-2.

Step S7
The control unit 16 (FIG. 1) obtains an approximate curve (measured gamma curve) from the set of white circles in FIG. 4B using the least square method or the like, and the measured gamma curve has a gradation degree of 70% to 100%. Obtain the integrated value of concentration. The concentration integrated value obtained here is sent to the determination unit 14 (FIG. 1). This step corresponds to the measurement gamma characteristic calculation procedure 16-3.

Step S8
Based on the control of the control unit 16 (FIG. 1), the determination unit 14 (FIG. 1) stores the density integrated value Sp2 of the measured gamma characteristic obtained in step S7 and the reference gamma curve shape characteristic value Sp1 storage unit 13 (FIG. 1). ) Is compared with the integrated density value Sp1 obtained by calculating the integrated density value from 70% to 100% with respect to the reference gamma curve stored in advance. As a result, if | Sp2-Sp1 |> X (predetermined value) is satisfied, the process proceeds to step S9. If not satisfied, the flow ends. This step corresponds to both gamma characteristic comparison procedures 16-4.

Step S9
Based on the control of the control unit 16 (FIG. 1), the alarm display unit 15 (FIG. 1) is an optical system (in the case of using an LED array as a light source, a lens array, and in the case of using a laser diode as a light source). In this case, after displaying that the inconvenience is caused by the F-θ lens) and giving a warning to the user, the flow is ended. If | Sp2-Sp1 |> X is not satisfied in step S8, no inconvenience is found in the optical system, and the flow is terminated. This step corresponds to the alarm generation procedure 16-5.

X (predetermined value) in step S8 will be described.
FIG. 6 is an explanatory diagram of the predetermined value X.
This is a constant for the absolute value of the difference between Sp1 and Sp2 in each color (C, M, Y, K).

  In the above description, the first density correction procedure 16-1, the second density correction procedure 16-2, the measurement gamma characteristic calculation procedure 16-3, the both gamma characteristics comparison procedure 16-4, and the alarm generation procedure 16-5. Although all have been described as a control procedure executed by the control unit 16 (FIG. 1), the present invention is not limited to this example. That is, the means for executing all or part of the above procedure may be configured by an electronic circuit. Further, this means may be stored in a computer-readable recording medium as a computer program.

  As described above, according to the image forming condition correction method of the first embodiment, the optical system constituting the exposure unit (in the case where the LED array is used as the light source, the lens array, the laser diode is used as the light source) In this case, the inconvenience caused by the F-θ lens) can be easily recognized. Therefore, the correction of the optical system is started without changing the light emission amount and the developing bias, and the correction of the image forming condition is accurately performed. And the effect that it can be executed within a short time is obtained.

FIG. 7 is a block diagram of a control system according to the second embodiment.
As shown in the figure, the image forming condition correction method according to the second embodiment includes an image forming unit 1 (1C, 1M, 1Y, 1K), a developing bias variable unit 2, and an LED head 3 (3C, 3M, 3Y, 3K). ), The light emission amount variable unit 4, the test pattern storage unit 5, the density reading unit 7, the density value storage unit 8, the development bias value calculation unit 9, the light emission unit light amount value calculation unit 10, and the density value normalization Calculation calculation unit 11, determination unit 14, alarm display unit 15, density sensor 17, average density calculation unit 18, measurement gamma curve shape characteristic value D2 calculation unit 19, and reference gamma curve shape characteristic value D1 storage unit 20 and a control system including a control unit 21.

Only differences from the first embodiment will be described. The same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment.
The density sensor 17 is a scanner-type optical sensor that is long in the main scanning direction, measures the reflection intensity of the test pattern printed on the conveyor belt 29 (FIG. 2), and detects the density value with respect to the gradation degree from the reflection intensity. It is a sensor.
The average density calculation unit 18 is a part that calculates an average value of measured values in the main scanning direction obtained from the density sensor 17.

The measurement gamma curve shape characteristic value D2 calculation unit 19 calculates the detected density rate for each gradation degree based on the correction result of the second density correction procedure 16-2 according to the measurement gamma characteristic calculation procedure 16-3 of the control unit 21. This is the part that you want.
The reference gamma curve shape characteristic value D1 storage unit 20 is a memory that stores in advance the reference density ratio of the image data with respect to the gradation of the image data.

The control unit 21 is a CPU (central processing unit) that controls the entire apparatus, and in the present invention, in particular, the first density correction procedure 16-1, the second density correction procedure 16-2, and the measured gamma characteristic. This is a part for executing the calculation procedure 16-3, the gamma characteristic comparison procedure 16-4, the alarm generation procedure 16-5, and the comparison position sweep procedure 21-1.
The comparison position sweeping procedure 21-1 is a procedure of sweeping the position where both gamma characteristics are compared from one end to the other end of the test pattern in the main scanning direction.
All other components are the same as those in the first embodiment, and the description thereof is omitted.

Here, an example of the test pattern of Example 2 will be described.
FIG. 8 is an explanatory diagram of a test pattern according to the second embodiment.
(A) is a pattern configuration diagram, (b) is a pattern layout diagram, and as shown in (a), the test pattern 17-1 has a gradation of 10%, which is continuously arranged equidistantly in the medium conveyance direction. The pattern is composed of 25%, 40%, 50%, 80%, and 100% areas, and 1500 detection areas spread in the main scanning direction.
As shown in FIG. 5B, unlike the test pattern 6-1 (FIG. 3) of the first embodiment, the test pattern 17-1 forms an image so as to pass directly below the density sensor 17 over the entire surface in the main scanning direction. Printed by the copies (1C, 1M, 1Y, 1K).

Next, the operation of the second embodiment will be described using a flowchart.
FIG. 9 is a flowchart of the operation of the second embodiment.
The image forming condition correction method according to the second embodiment will be described in the order of steps from step S11 to step S22 in the figure.

Step S11
8 is stored in the test pattern storage unit 5 (FIG. 7) by the image forming units (1C, 1M, 1Y, 1K) (FIG. 1) based on the control of the control unit 21 (FIG. 7). The image is transferred to the conveyance belt 29.
Step S12
A density value for each gradation in the test pattern is acquired by the density sensor 17 (FIG. 8) disposed on the transport belt 29 (FIG. 8). At this time, the density sensor 17 (FIG. 8) sweeps over 1500 areas in the main scanning direction from end to end of the test pattern based on the control of the control unit 21 (FIG. 7). The 1500 detected density values are sent to the density reading unit 7 (FIG. 7) and stored in the density value storage unit 8 (FIG. 7).

Step S13
Based on the control of the control unit 21 (FIG. 7), the average density calculation unit 18 (FIG. 7) calculates and develops an average value of 1500 density values stored in the density value storage unit 8 (FIG. 7). This is sent to the bias value calculation unit 9 (FIG. 7) and the light emission unit light amount value calculation unit 10 (FIG. 7). The development bias value calculation unit 9 (FIG. 7) converts the average density value (conventionally known) to obtain a normal development bias value. This development bias value is sent to the development bias variable section 2 (FIG. 7), and the development bias of the image forming sections (1C, 1M, 1Y, 1K) (FIG. 1) is set. At the same time, the light emitting unit light amount value calculating unit 10 (FIG. 7) also converts the average density value (conventionally known) to obtain the light amount value. This light amount value is sent to the light emission amount variable unit 4 (FIG. 7), and the normal light emission amount of the image forming units (1C, 1M, 1Y, 1K) is set. When both the settings are completed, a bias value change completion notification is sent from the developing bias variable unit 2 (FIG. 7) to the control unit 21 (FIG. 7), and the light amount is changed from the light emission amount varying unit 4 (FIG. 7) to the control unit 21 (FIG. 7). Each notification is sent. This step corresponds to the first density correction procedure 16-1.

Step S14
When the control unit 26 (FIG. 7) accepts both notifications, the image forming units (1C, 1M, 1Y, 1K) (FIG. 1) based on the control of the control unit 26 (FIG. 7) (FIG. 1) similarly to step S11. The test pattern shown in FIG. 8 stored in the test pattern storage unit 5 (FIG. 7) is retransferred to the conveyor belt 29.
Step S15
Similar to step S12, the density sensor 17 (FIG. 8) disposed on the conveyor belt 29 (FIG. 8) acquires the density value for each gradation in the test pattern, and the density reading unit 7 (FIG. 7). Sent to. At this time, the density sensor 17 (FIG. 8) is swept over 1500 areas in the main scanning direction from end to end of the test pattern based on the control of the control unit 21 (FIG. 7), and N = 1 to 1500. A characteristic group of gradation degree vs. detected density is obtained. The 1500 gradation groups versus detected density characteristic groups are sent to the density reading unit 7 (FIG. 7) and stored in the density value storage unit 8 (FIG. 7).

Step S16
The control unit 21 (FIG. 7) calculates the detected density ratio by dividing the density value of the characteristic group stored in the density value storage unit 8 (FIG. 7) by the maximum density value. The detected density rate is normalized with reference to a gradation degree of 100% in the reference gamma characteristic. That is, the detected density ratio of the black circle shown in FIG. 3B is normalized with reference to a gradation degree of 100% in the reference gamma characteristic, and the white circle value (a characteristic group of 1500 in this case) is obtained. . The 1500 characteristic group values normalized here are sent to the measured gamma curve shape characteristic value D2 calculation unit 19 (FIG. 7). This step corresponds to the second density correction procedure 16-2.

Step S17
N = 1 is set as an initial value to count the sweep position in the comparison position sweep procedure 21-1.
Step S18
The control unit 21 (FIG. 7) obtains an approximate curve (measured gamma curve) from the set of white circles shown in FIG. 4B in the Nth detection region in the main scanning direction using the least square method or the like. Only the detected density rate with a gradation of 70% is extracted from the measurement gamma curve and sent to the determination unit 14 (FIG. 7). This step corresponds to the measurement gamma characteristic calculation procedure 16-3.

Step S19
Based on the control of the control unit 21 (FIG. 7), the determination unit 14 (FIG. 7) stores the detected density rate D2 of the measured gamma characteristic with a gradation of 70% and the reference gamma curve shape characteristic value D1 obtained in step S18. The reference density ratio D1 having a gradation degree of 70% for the reference gamma curve stored in advance in the section 20 (FIG. 7) is compared. As a result, if | D2-D1 |> Y (predetermined value) is satisfied, the process proceeds to step S21. If not satisfied, the process proceeds to step S20. This step corresponds to both gamma characteristic comparison procedures 16-4.

Step S20
While N = 1500 is not reached, N = N + 1 is set and the process returns to step S18. When N = 1500, the flow ends. This step corresponds to the comparison position sweep procedure 21-1.
Step S21
Based on the control of the control unit 21 (FIG. 7), the alarm display unit 15 (FIG. 7) is an optical system (in the case of using an LED array as a light source, a lens array, and in the case of using a laser diode as a light source). In this case, after displaying that the inconvenience is caused by the F-θ lens) and giving a warning to the user, the flow is ended. If | D2-D1 |> Y is not satisfied in step S19, no inconvenience is found in the optical system, and the flow is terminated. This step corresponds to the alarm generation procedure 16-5.

Y (predetermined value) in step S19 will be described.
FIG. 6 is an explanatory diagram of the predetermined value Y.
This is a constant for the absolute value of the difference between D1 and D2 in each color (C, M, Y, K).

  In the above description, the first density correction procedure 16-1, the second density correction procedure 16-2, the measurement gamma characteristic calculation procedure 16-3, the both gamma characteristics comparison procedure 16-4, the alarm generation procedure 16-5, Although all the comparison position sweep procedures 21-1 have been described as control procedures executed by the control unit 16 (FIG. 7), the present invention is not limited to this example. That is, the means for executing all or part of the above procedure may be configured by an electronic circuit. Further, this means may be stored in a computer-readable recording medium as a computer program.

  In the above description, the test pattern shown in FIG. 8 is used for both the test pattern transferred in step S11 and the test pattern transferred in step S14. However, the present invention is not limited to this example. Absent. That is, in step S11, the test pattern shown in FIG. 3 may be used, and in step S14, the test pattern shown in FIG. 8 may be used.

  As described above, according to the image forming condition correction method of the second embodiment, by using a test pattern that covers the entire main scanning direction, the optical system (LED array is used as a light source) in the entire main scanning direction. In the case of using a lens array or a laser diode as a light source, the inconvenience caused by the F-θ lens can be easily recognized. The correction of the optical system is started, and the effect that the image forming condition correction can be executed accurately and within a short time is obtained.

  In the above description, the description is limited to the printer only. However, the present invention can also be applied to a copying machine that records a multi-tone image by exposing light source light to a photosensitive material and transfers the image to a recording medium. It is.

FIG. 2 is a block diagram of a control system according to the first embodiment. It is a principal part cross-sectional view of a printing mechanism part. FIG. 3 is an explanatory diagram of a test pattern of Example 1. It is explanatory drawing of the 2nd density correction procedure. 3 is a flowchart of the operation of the first embodiment. It is explanatory drawing of the predetermined value X. FIG. It is a block diagram of the control system of Example 2. FIG. 6 is an explanatory diagram of a test pattern of Example 2. 10 is a flowchart of the operation of the second embodiment. It is explanatory drawing of the predetermined value Y. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image formation part 2 Development bias variable part 3 LED head 4 Light emission amount variable part 5 Test pattern memory | storage part 6 Density sensor 7 Density reading part 8 Density value memory | storage part 9 Development bias value calculation part 10 Light emission part light quantity value calculation part 11 Density value Normalization calculation unit 12 Measurement gamma curve shape characteristic value Sp2 calculation unit 13 Reference gamma curve shape characteristic value Sp1 storage unit 14 Judgment unit 15 Alarm display unit

Claims (16)

A first density correction procedure for correcting the gradation degree / detected density value characteristic using a predetermined calculation formula based on the detected density value with respect to the gradation degree of the printed predetermined test pattern;
Based on the correction result of the first density correction procedure, the predetermined test pattern is reprinted, and the reprint result is stored in advance as a reference gamma characteristic stored as a reference density ratio with respect to the gradation of the printed image data. A second density correction procedure for normalizing with a reference density rate of 100% gradation;
A measurement gamma characteristic obtained by curving the correction result of the second density correction procedure is calculated, and a density integrated value from the first gradation degree to the second gradation degree in the measurement gamma characteristic is obtained. Measurement gamma characteristic calculation procedure,
A gamma characteristic comparison procedure for comparing the result of the measurement gamma characteristic calculation procedure with a density integrated value between the first gradation and the second gradation calculated based on the reference gamma characteristic;
An image forming condition correction method, wherein correction is performed according to an alarm generation procedure for generating a warning when a difference of a predetermined amount or more is recognized between the two gamma characteristics based on the both gamma characteristics comparison procedure. The image forming condition correction method according to claim 1, wherein the predetermined test pattern is:
An image forming condition correcting method, wherein the image forming condition correction method is a pattern composed of a plurality of areas having different gradation levels arranged continuously in the medium conveyance direction. In the image forming condition correction method according to claim 1,
The image forming condition correcting method according to claim 1, wherein the integrated density value from the first gradation to the second gradation is an integrated density from 70% to 100%. A first density correction unit that corrects the gradation level versus the detected density value characteristic using a predetermined calculation formula based on the detected density value for the gradation level of the printed predetermined test pattern;
Based on the correction result of the first density correction unit, the predetermined test pattern is reprinted, and the reprint result is stored in advance as a reference gamma characteristic stored as a reference density ratio with respect to the gradation of the printed image data. Second density correction means for normalizing with a reference density rate of 100% gradation;
A measurement gamma characteristic obtained by curving the correction result of the second density correction means is calculated, and a density integral value from the first gradation degree to the second gradation degree in the measurement gamma characteristic is obtained. A measurement gamma characteristic calculating means;
Both gamma characteristic comparisons for comparing the result obtained by the measurement gamma characteristic calculating means with the integrated density value from the first gradation to the second gradation calculated based on the reference gamma characteristic Means,
An image forming apparatus comprising: an alarm generating means for generating a warning when a difference of a predetermined amount or more is recognized between the two gamma characteristics based on the both gamma characteristics comparing means. The image forming apparatus according to claim 4,
Any one of the first density correction means, the second density correction means, the measurement gamma characteristic calculation means, the gamma characteristic comparison means, and the alarm generation means is a computer-readable computer. An image forming apparatus which is a recording medium for storing a program. The image forming apparatus according to claim 4,
The predetermined test pattern is:
An image forming apparatus, wherein the image forming apparatus is a pattern composed of a plurality of areas having different gradation levels arranged continuously in the medium conveyance direction. The image forming apparatus according to claim 4,
2. An image forming apparatus according to claim 1, wherein the integrated density value from the first gradation to the second gradation is an integrated density from 70% to 100%. A first density correction procedure for correcting the gradation degree / detected density value characteristic using a predetermined calculation formula based on the detected density value with respect to the gradation degree of the printed predetermined test pattern;
Based on the correction result of the first density correction procedure, the predetermined test pattern is reprinted, and the reprint result is stored in advance as a reference gamma characteristic stored as a reference density ratio with respect to the gradation of the printed image data. A second density correction procedure for normalizing with a reference density rate of 100% gradation;
A measurement gamma characteristic obtained by curving the correction result of the second density correction procedure is calculated, and a detected density ratio at a predetermined position and a predetermined gradation on the test pattern in the measurement gamma characteristic is calculated. A measurement gamma characteristic calculation procedure to be obtained;
A gamma characteristic comparison procedure for comparing the result of the measurement gamma characteristic calculation procedure with the density rate at the predetermined gradation based on the reference gamma characteristic;
A comparative position sweeping procedure for sweeping the predetermined position from one end to the other end in the main scanning direction of the test pattern;
An image forming condition correction method, wherein correction is performed according to an alarm generation procedure for generating a warning when a difference of a predetermined amount or more is recognized between the two gamma characteristics based on the both gamma characteristics comparison procedure. In the image forming condition correction method according to claim 8,
The predetermined test pattern is:
An image forming condition correction method, wherein the pattern includes a plurality of areas with different gradation levels arranged continuously in the medium conveyance direction, and the width in the main sweep direction covers the entire area of the main sweep width. In the image forming condition correction method according to claim 8,
The image forming condition correction method according to claim 1, wherein the predetermined gradation is 70%. In the image forming condition correction method according to claim 8 or 9,
The image forming condition correcting method according to claim 1, wherein the detected density of the test pattern in the first density correcting procedure is an average value of detected densities at individual positions over the entire main sweep width. A first density correction unit that corrects the gradation level versus the detected density value characteristic using a predetermined calculation formula based on the detected density value for the gradation level of the printed predetermined test pattern;
Based on the correction result of the first density correction unit, the predetermined test pattern is reprinted, and the reprint result is stored in advance as a reference gamma characteristic stored as a reference density ratio with respect to the gradation of the printed image data. Second density correction means for normalizing with a reference density rate of 100% gradation;
A measurement gamma characteristic obtained by curving the correction result of the second density correction means is calculated, and a detected density ratio at a predetermined position and a predetermined gradation on the test pattern in the measurement gamma characteristic is calculated. A measurement gamma characteristic calculating means to be obtained;
Both gamma characteristic comparison means for comparing the result obtained by the measurement gamma characteristic calculation means with the density rate at the predetermined gradation based on the reference gamma characteristic;
Comparison position sweeping means for sweeping the predetermined position from one end to the other end in the main scanning direction of the test pattern;
An image forming apparatus comprising: an alarm generating means for generating a warning when a difference of a predetermined amount or more is recognized between the two gamma characteristics based on the both gamma characteristics comparing means. The image forming apparatus according to claim 12, wherein
Any of the first density correction means, the second density correction means, the measurement gamma characteristic calculation means, the gamma characteristic comparison means, the comparison position sweep means, and the means alarm generation means Is a recording medium that stores a computer-readable computer program. The image forming apparatus according to claim 12, wherein
The predetermined test pattern is:
An image forming apparatus having a pattern composed of a plurality of areas with different gradation levels arranged continuously in a medium conveying direction, the width of the main sweep direction extending over the entire main sweep width. The image forming apparatus according to claim 12, wherein
The image forming apparatus according to claim 1, wherein the predetermined gradation is 70%. In the image forming condition correction method according to claim 12 or 14,
The image forming apparatus according to claim 1, wherein the detected density of the test pattern in the first density correction procedure is an average value of detected densities at individual positions over the entire main sweep width.

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