JPH10333501A - Image forming device and control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance control accuracy for the density of an image and to maintain excellent image formation by detecting soiling on a drum and a density detecting sensor. SOLUTION: Plural patch images different in the density which are formed on a photoreceptor drum 1 are made to form and transferred to an intermediate transfer drum 5. A density sensor 8 detects the density of a toner image being as a patch being transferred onto the intermediate transfer drum 5. The linear expression of the detected density is calculated and the soiling of the intermediate transfer drum 5 and the sensor 8 is detected on the basis of the inclination and intercept of the linear expression. When the soiling is prescribed one or more, a report is made to urge cleaning.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine and a laser beam printer and a control method therefor.

[0002]

2. Description of the Related Art In a multi-color image forming apparatus using an electrophotographic system, color reproduction equivalent to the color tone of an original image is always required, but delicate conditions such as changes in the environment used and the number of prints are delicate. The image density fluctuates due to the change,
The original correct color tone may not be obtained.

Therefore, a reference toner image (patch) for density detection is formed on a photosensitive drum or a transfer body on a trial basis with toner of each color, and their densities are detected by a density sensor. A device for obtaining a stable image by performing image density control for feeding back to a bias or the like has been devised.

[0004] Further, as a concentration sensor to be used, a bidirectional or highly directional infrared light emitting diode is used as a light emitting side, and a silicon light receiving sensor is used as a light receiving sensor, depending on each application and usage. PIN type photodiodes are often used.

[0005]

However, an image density control system using a density sensor has the following problems.

That is, by repeating the image formation, scattered toner or the like filled in the image forming apparatus adheres to the light emitting surface or the light receiving surface of the density sensor. The light amount is reduced, control with an appropriate sensor light amount is hindered, control accuracy is greatly reduced, and image processing conditions such as a developing bias cannot be optimally controlled.

For example, particularly with respect to the color toner, the developing bias is controlled in a direction to increase the density, so that the toner is generally applied too much more than an appropriate amount, and more scattering occurs at the time of transfer. In addition, there is a problem that a fixing failure occurs at the time of fixing, and in some cases, an intense ground fog is caused by controlling the developing bias too high.

Further, when a patch is formed on an intermediate transfer member or the like, the surface layer of the intermediate transfer member gradually becomes soiled by repeating image formation, and serves as a reference reflection plate. The sensor output of the patch is affected by the dirt, and the reflection density is lower than the regular reflection density. However, in the case of a patch on which toner is sufficiently applied so as not to be affected by the contamination of the surface layer of the intermediate transfer body, the sensor output becomes the same as a normal value.

Therefore, it is difficult to determine whether the decrease in sensor output is due to dirt on the light emitting surface of the sensor or due to dirt on the surface layer of the patch-formed body from only the sensor output. Even after dirt is cleaned, it is difficult to determine whether or not the dirt is to be cleaned.

The present invention has been made in view of such a problem, and it is possible to enhance the accuracy of image density control by detecting a stain on a recording medium such as an intermediate transfer member or a stain on a density detector. It is an object to provide a simple image forming apparatus and a control method thereof.

[0011]

In order to solve such a problem, for example, an image forming apparatus of the present invention has the following arrangement. That is, an image forming apparatus that forms an image on a recording medium, a reference image forming unit that forms a reference image having a preset density on the recording medium, and a reference image formed on the recording medium. Density detecting means for optically detecting the density of the image, calculating means for calculating a characteristic value of a density distribution based on the density of the reference image detected by the density detecting means, and the recording according to the calculated characteristic value. Determining means for determining whether the medium or the density detecting means is dirty;

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the embodiment of the present invention, the difference between the sensor output behavior with respect to the toner density of the patch when the sensor for detecting the density becomes dirty and when the surface layer of the intermediate transfer member as the drum becomes dirty is described. Use to separate them. The difference in the behavior will be described with reference to FIG.

(First stage) When both the sensor and the surface layer of the patch forming body are not contaminated.

The sensor output when a patch is not formed on the surface of the patch-formed body (hereinafter referred to as an initial output value) becomes the initial output of the surface of the patch-formed body. Also rises (line 1).

(Second stage) When only the sensor is dirty.

Since this is the same state as when the light emission amount of the sensor has decreased, the initial output value is also low, and the sensor output remains low even when the toner density of the patch increases (line 2). However, the sensor output returns to the normal output after the sensor dirt is removed, so that the sensor output characteristic of line 1 is shown.

(Third stage) When the surface layer of the patch formed body is dirty.

Although the initial output value decreases, the toner covers the surface of the patch-formed body with the increase in the toner density of the patch, so that the surface of the patch-formed body is not affected by dirt. Follow the trajectory (line 3) approaching 1).

(Fourth stage) When both the sensor and the surface layer of the patch forming body are dirty.

Since the initial output value is low and the output after cleaning the sensor window is low, at this stage, it is not possible to discriminate between dirt on the sensor and dirt on the surface layer of the patch formed body. However, since the state becomes the (third stage) after cleaning the sensor dirt, the sensor output for a sufficient toner concentration approaches the line 1, and the sensor output characteristic before and after the sensor cleaning changes from the line 2 to the line 1. Show.

By using the above-mentioned means, it is possible to accurately read the change in the initial output value of the sensor, to send an accurate message to the user, and to prevent the deterioration of the image quality due to the contamination of the sensor. .

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

<First Embodiment> FIG. 2 is a schematic sectional view of a density sensor according to the present embodiment, and FIG. 3 is a sectional view of an image forming apparatus.

In FIG. 3, the photosensitive drum 1 as a latent image carrier rotates in the direction of arrow A, and its surface is uniformly charged by the charging process by the charging device 2, and the laser diode receives yellow as a first color. When a signal according to the image pattern of the component is input, optical information corresponding to the yellow component is irradiated on the photosensitive drum 1 through the optical path L, and an electrostatic latent image is formed. Further, with the rotation of the photosensitive drum 1 in the arrow direction A, the latent image is developed by a yellow developing device 4Y disposed close to the photosensitive drum 1 and is visualized as a toner image.

The visualized toner image on the photosensitive drum 1 is temporarily transferred onto the intermediate transfer member 5 by applying a predetermined bias to the drum-like intermediate transfer member 5 in contact with the photosensitive drum 1 at a predetermined pressure. Is transcribed.

The above steps are carried out for magenta 4M, cyan 4C,
The process is performed in the order of black 4B, and the images are sequentially stacked and transferred onto the intermediate transfer member 5 to form a full-color image on the intermediate transfer member 5. The full-color image is arranged on the transfer paper P sent from the paper feeder 11 at a predetermined timing, at a position facing the intermediate transfer body 5 with the transfer paper P interposed therebetween, and a transfer roller 6 to which a predetermined bias is applied. Are collectively transferred, and are subjected to a fixing process by the fixing device 7, and are discharged outside the device to complete the printing operation.

In this embodiment, the black developing device 4B employed when the frequency of use of black is high is the photosensitive drum 1
Are fixed to the developing device housing 41, and the developing devices for yellow 4Y, magenta 4M, and cyan 4C are used for image formation, and the developing device housing 41 is used for each developing operation.
And the photosensitive drum 1 rotates only when the developing process is performed.
Is controlled so as to be opposed to. The black 4B is always arranged to face the photosensitive drum 1.

On the other hand, the toner remaining on the photosensitive drum 1 after the completion of the transfer onto the intermediate transfer member 5 is scraped off by the cleaning blade 10a, and the next image formation is continued.

In the multicolor image forming apparatus having the above-described configuration, a patch for performing image density control and gradation control is formed on the intermediate transfer member 5, and each control is executed by reading the density of the patch with a density sensor. It is.

The density sensor will be described with reference to FIG.

A light emitting diode 8a having a light emitting characteristic at a wavelength of 950 nm and a light receiving photodiode 8b having a light receiving characteristic are arranged so as to have a positional relationship parallel to the longitudinal direction of the intermediate transfer member 5 which is a patch forming body. A shielding plate 8 is provided between the light emitting diode 8a and the light receiving photodiode 8b so that the light is not directly irradiated on the light receiving photodiode.
c. Further, between the light emitting diode 8a and the light receiving photodiode 8b and the intermediate transfer member 5, the light emitted from the light emitting diode 8a and the light receiving photo sensor 8b is irradiated in order to prevent the light emitting diode 8a and the light receiving photo sensor 8b from being stained by the toner filled in the image forming apparatus. It is shielded by a colorless and transparent shielding plate 8d that does not affect the transmittance. Note that a colorless and transparent acrylic plate having a thickness of 2 (mm) is used as the shielding plate 8d used in the present embodiment.

Since the density sensor 8 has a peak light receiving sensitivity when the gap with the object to be measured is 2 (mm), it has a gap of 2 (mm) from the surface of the intermediate transfer member. Arranged in position.

After adjusting the amount of light emitted from the light emitting diode 8a, the density sensor 8 adjusts the reference pattern having a predetermined density (the surface of a photosensitive member or a transfer member to which no toner is attached, or the factory shipment) under the amount of emitted light. (A reference medium used at that time), and the gain of the light-receiving photodiode 8b is adjusted based on the amount of light reflected by the reference pattern. The density sensor 8 adjusted in this way is adjusted so that the sensor output by the patch formed on the intermediate transfer member 5 falls within 0 to 5 (V). The color toner has this wavelength. Therefore, in the case of color toner, the sensor output also increases as the toner density increases, and in the case of black toner, the sensor output decreases as the toner density increases.

In this case, an output (hereinafter, referred to as an initial output) according to the color of the surface layer of the intermediate transfer body 5 on which no patch is formed is important.
(Mm), a hydrin rubber having a thickness of 5 (mm), which has been subjected to resistance adjustment with conductive carbon, is adhered to the periphery of a core metal of aluminum (a 6000 series alloy) having a thickness of 3 (mm) via a primer. The surface layer is coated with a predetermined amount of titanium oxide by air spray to adjust the color, and then coated with a toner and a transfer material (paper P) from the intermediate transfer body 5.
For example, in order to enhance the releasability, a coating layer containing urethane rubber and containing a fluorine-type powder is automatically baked. Therefore, in the present embodiment, the initial output value of the intermediate transfer body 5 is set to 2.5 (V) in the above-described density sensor 8 by adjusting the amount of titanium oxide. In handling the sensor output for control, the maximum value of the sensor output is set to 5 (V), and 8b
It (255 level) data. That is, the initial output value is ideally set to 128.

In the present embodiment, the image density control for detecting the density sensor stain and the intermediate transfer member surface layer stain is intended to stably maintain the optimum density, and in order to achieve this, an optimum developing bias is mainly used. (Voltage applied to developing unit)
Is performed. The control system reads the density of the patches formed on the intermediate transfer member 5 while changing the developing bias for each color, and calculates and calculates the developing bias for the target density. In this embodiment,
Assume that the number of patches to be formed in the drawing color is eight, and the patches are formed by eight stages of developing bias. Color toners (yellow, magenta, cyan) are also controlled.
(The color is not limited if it is colored). Accordingly, when the direction in which the density of the patch is increased is taken on the horizontal axis and the output from the sensor is taken on the vertical axis, the graph becomes a straight line or curve rising to the right.

A patch pattern used as a patch is a pattern which performs PWM modulation and has an image signal level of A0.
Each patch was formed using h (the amount of laser emission divided into 8 bits (255 levels) and expressed in hexadecimal notation).

The feature of this embodiment is that the initial output value S0 (corresponding to the amount of received light without a patch), the toner density is sufficiently high, and the color of the underlayer of the surface of the intermediate transfer member 5 affects the patch density. Is provided as a virtual point, and the initial output value S0 and the maximum virtual output value S
A gradient m0 of a linear expression obtained by interpolating a is obtained in advance. The initial output value S1 read at the time of actual image density control and the gradient m1 of a linear expression obtained by linearly interpolating the sensor output S2 of the patch are compared with the gradient to judge sensor dirt and intermediate transfer member surface dirt. . Then, a more correct message is warned to the user based on the determined information.

FIG. 4 shows a flow chart of a sequence up to sensor dirt detection and message warning.

This operation is performed by a printer controller (actually, a CPU in the printer controller) to be described later, and each time a predetermined number of prints are performed, or by a user's instruction from the operation panel, If the image forming apparatus of the present embodiment is a printer connected to a host computer, it is performed when a predetermined instruction command is received from the host computer.

First, with the transmission of the density control start command from the printer controller, the image forming apparatus main body shifts to the density control sequence of step 100 after the print job is completed. Here, as explained earlier,
Each patch is formed by changing the developing bias on the surface of the intermediate transfer member where the patch is to be formed, and the amount of received light including no patch is determined. Here, the detected amount of received light without a patch becomes the initial value S1. In addition, a slope M1 obtained by linearly interpolating the amount of light received by each patch is obtained.

Next, in step 101, it is detected whether or not the initial output value S1 is equal to or greater than a preset threshold Th1. If it is not less than the threshold value Th, it is not determined that the sensor is dirty or the surface of the intermediate transfer member is dirty, and the process proceeds to step 102 where the density control process is performed normally and the process is continued. Will be performed.

If the initial output value S1 is smaller than the threshold value Th1, it is determined that the sensor is contaminated or the surface of the intermediate transfer member is contaminated, and the density control is stopped at that time (step 10).
4), alert the user by warning a "sensor cleaning" message (step 105). In addition to notifying the message on the panel of the image forming apparatus main body, if the message is connected to the host computer through an interface capable of two-way communication, the fact is notified to the host computer side, and the host computer operates. Printer driver or the like displays a message to that effect on a display screen or the like.

Thereafter, it is detected by a door sensor (not shown) whether or not the user has opened the door for cleaning the sensor (step 106). If the door is not detected after a lapse of a predetermined time or until the next image formation is performed. , The image forming operation is continued by substituting the developing bias obtained in the previous density control (step 10).
7).

If a door open is detected, the density control sequence is repeated (step 10).
8) After confirming the initial output S1, the operation shifts to a normal patch forming operation. At this time, if it is determined that the initial output S1 is equal to or more than the threshold Th1 (step 109), the state has returned to a normal state for the cleaning operation, and the process proceeds to step 102.

If it is determined that the initial output S1 is smaller than the threshold value Th1, the same as in step 100,
Eight patches are respectively formed while increasing the developing bias so that the patch density becomes lower to higher in the order of magenta, cyan, and black. As the patches are sequentially formed, the sensor output value of the patch is determined by the density sensor. 8 may be read, but in order to simplify the processing, the sensor output value (Y8) of the eighth patch having the highest density of yellow as the first color is set as the control target. Of course, other colors and other patches may be used.

In the next step 111, the initial output value at the time of Y8 patch measurement / the gradient m1 of the linear interpolation linear expression of the patch sensor output is calculated as a gradient m0 (initial output value / maximum) prepared in advance in a look-up table. (M1 / m0) is taken with respect to the (virtual output value), and if it is equal to or larger than the threshold Th2, it is determined that the surface of the intermediate transfer member is dirty, and the density control is continued. However, when it is determined that the ratio is smaller than the threshold Th2, it is determined that the sensor is dirty, and “sensor cleaning” is performed.
A message is warned (step 112).

After the message warning, the door sensor detects that the user has opened the door of the main body for cleaning the density sensor, and further detects that the door has been closed and the main body has been set again. Is determined, the sensor is determined to be cleaned, and an optimum developing bias is obtained from data based on the density control (steps 102 and 103). However, when the door open is not detected, the warning of the “sensor dirt” message is continued, the feedback of the developing bias by the density control is not performed, and the image forming operation is performed by using the developing bias obtained by the previous density control. To continue.

In the above sequence, the threshold value T of the initial output value
It is necessary to set h1 and a threshold value Th2 of the gradient of the interpolation linear expression in accordance with the sensor output characteristics of the image forming apparatus main body.
In the present embodiment, the threshold value Th1 of the initial output value is set to 60h (the dirt rate of the sensor (the dimming rate (%) by the sensor output at the time of detection with respect to the initial output) is 25%), and the threshold value T of the slope is set.
A verification experiment with an actual machine was performed with h2 being 25 (%).
More specifically, the ideal initial output (linear intercept) is 80
Since the value of h is 75% or more of the measured value (intercept), the normal range is defined as the normal range, and the slope M0 × 理想 or more of the ideal state is defined as the normal range in the slope ratio (“1” in the ideal state). still,
Naturally, the actually measured slope M1 and the ideal state M0
Can be regarded as M1 ≧ C (= 0.25) × M0 (in this case, the threshold value is C × M0 as a whole).

FIG. 7 shows the case where the density control is performed for each of the dirt on the sensor and the dirt on the surface layer of the intermediate transfer member as they are, and the warning of the "sensor cleaning" message described in the above embodiment is given to perform the cleaning. An image evaluation pattern in the case where the control is performed is output, and the effectiveness of the present control is shown based on the image quality.

According to the present embodiment, the image after cleaning the sensor in accordance with the warning of "sensor cleaning" is properly developed and the image quality is sufficient. In some cases, the developing bias was controlled to be relatively high, and toner was scattered, and poor fixing occurred in a low-temperature and low-humidity environment.

In order to realize higher image quality, the thresholds Th1 and Th2 are set to 66h (corresponding to a dirt rate of 20%), 20% or 6Dh (corresponding to a dirt rate of 15%), respectively.
By reducing the value to 5%, the message warning frequency increases, but the "sensor cleaning" message is more reliably displayed, and high image quality can be maintained by finely cleaning the sensor dirt.

Therefore, some of these thresholds are provided in advance, and can be selected in accordance with the usage environment of the user.

The threshold value of the initial output and the threshold value of the gradient of the interpolation linear expression in the present embodiment are not limited to those described above, and these are specific to the image forming apparatus. Needless to say,
The intermediate transfer member on the drum is used, but the present invention is not limited to this, and a belt-shaped intermediate transfer member or a transfer belt may be used.

As shown in the present embodiment, without increasing the normal density control sequence time, the "sensor dirt" is determined from the relationship between the initial sensor output on the patch formed body and the patch sensor output after the patch formation. And "patterned body surface dirt" can be identified and the appropriate message can be given to the user at the appropriate time to remove dirt on the sensor and prevent image quality deterioration due to dirt on the sensor. Was.

<Second Embodiment> FIG. 5 shows the concept of the present embodiment. Eight yellow patches formed at the time of density control are detected by sensor output, and an initial output value and its detection output are detected. The sensor contamination is determined from the relationship with the value. That is, since the patches are formed in accordance with the developing bias during the density control, the density transition is incorporated in the control system of the present embodiment.

First, a method similar to that of the first embodiment is used until an interpolation linear expression is created. In this case, the threshold value for the initial output value and the subsequent processing are the same as in the first embodiment.

Next, the eight patch sensor output values of yellow are read, a linear expression is obtained from the eight patch sensor output values by an approximation method, and judgment is made from the ratio of the gradient between the interpolation linear expression and the approximate linear expression. is there. The slope ratio used here was the same value as in the first embodiment, and the approximate expression was calculated by the least square method.

When the same evaluation as in the first embodiment was performed by the above-described method, the "sensor cleaning" message was warned at an appropriate timing also in the second embodiment, and the process according to the message was performed. It has become possible to always maintain high image quality.

As shown in the present embodiment, it is possible to issue appropriate message warnings at appropriate timing without changing the time of the density control sequence and controlling the change in the sensor output of the patch with respect to the developing bias during density control. It has made it possible to maintain high image quality.

<Third Embodiment> The third embodiment is different from the third embodiment in that
It is characterized in that a value to be controlled is simply performed using a converted density calculated based on a sensor output.

When the patch-formed body is an intermediate transfer body or the like, the sensor output value fluctuates according to the stain on the surface layer. When the sensor output value is converted to density data, the sensor output value is directly converted into density data. Rather than converting the density using a table, the sensor output value was corrected according to the change in the reflection output value of the surface layer of the patch formed body, and a value obtained by converting the corrected sensor output value into density data was used. Incidentally, this sensor output correction method is based on the sensor output S2 on line 2 in FIG.
The method of placing on the line 1 according to the ratio between the initial output values S0 and S1 and the maximum density virtual point Sa was used. Therefore, the required sensor output S2 'is obtained by the following equation.

S2 '= (Sa-S0) × (S2-S1)
÷ (Sa−S1) + S0 Further, as the control target patch in the third embodiment,
In addition to the 90h image data patch pattern, which is a normal density control pattern, the ninth ninth mode, in which only one color is not used for density control,
The first patch is formed at the time of density control, and the patch always has an optical reflection density (made by Macbeth: RD918).
An FFh image pattern indicating 1.0 or more and a developing bias were used.

FIG. 6 is a flowchart showing a processing procedure in the third embodiment.

In the drawing, reference numerals 200 to 214 are substantially the same as 100 to 114 in FIG. The following is the details of the operation.

First, when the initial output value S1 is larger than the threshold value Th1, the density control is continuously performed and no message warning is performed. If the initial output value S1 is lower than the threshold Th1, the density control is stopped and a "sensor cleaning" message is warned. In addition to notifying the message on the panel of the image forming apparatus main body, the message may be displayed on a monitor output by a user via a printer driver. Thereafter, the door sensor detects whether or not the user has opened the door to clean the sensor.If the door is not detected after a predetermined time has elapsed or until the next image formation is performed, the development determined at the previous density control is performed. The image forming operation is continued by substituting the bias.

When the door open is detected, the sequence shifts to the density control sequence again, and after confirming the initial output S1,
The operation shifts to a normal patch forming operation.

At this time, at the time of density control, a ninth patch of color (yellow in this embodiment) for detecting sensor dirt is formed, and the ninth patch density DY9 is corrected based on the sensor output. Calculated from the density conversion table, and the density DY9
Is greater than or equal to a predetermined threshold Th3 (verified in this embodiment as 0.75 (corresponding to a sensor contamination rate of 25%)), it is determined that the sensor is not contaminated, and no "sensor cleaning" message is issued. However, when the patch density DY9 indicates a value smaller than the threshold Th3, it is determined that the sensor is dirty, and a "sensor cleaning" message is warned. Subsequent operations are the same as those described in the first embodiment.

In this method, since the value obtained by correcting the dirt on the surface layer of the patch forming body is used, there is an advantage that the dirt on the sensor itself can be identified from the converted density of the patch. Is effective.

When this control was evaluated in the same manner as in the first embodiment, no problematic image quality deterioration occurred. Further, by setting an appropriate value for the threshold density Th3 according to the image forming apparatus, it is possible to select control accuracy of simpler control.

According to the present embodiment, it is possible to identify the sensor stain from the converted density of the patch without being affected by the stain on the surface layer of the patch-formed body, and to perform the operation of the present embodiment during the density control sequence. Can do it,
This makes it possible to appropriately send a warning message of sensor contamination at an appropriate timing without extending the density control sequence time, thereby maintaining high image quality.

<Description of Apparatus Configuration> The processing described in the first to third embodiments can be realized, for example, by a configuration block diagram of a control system (printer controller) shown in FIG.

In the figure, reference numeral 300 denotes a CP which controls the entire apparatus.
Reference numerals U and 301 denote ROMs storing operation processing procedures (print processing programs and programs corresponding to the flowcharts of FIG. 4 or FIG. 6 described above) of the CPU 300 and threshold information and tables described above. Is CPU
A RAM used as a work area 300 and used to develop image data during print processing.
Reference numeral 303 denotes an interface for communicating with the host computer, reference numeral 304 denotes an operation panel having a display unit for displaying messages and the like, and reference numeral 305 denotes a printer engine having a structure as shown in FIG. The printer engine 305 has a developing bias control unit 306 that controls the developing bias under the control of the CPU 300.

In the above configuration, when the CPU 300 receives a predetermined instruction command from the host computer, or counts the number of switches and the number of recordings on the operation panel, the number reaches the predetermined number. In such a case, the processing shown in FIG. 4 or FIG. 6 is performed. A message prompting cleaning is displayed on the operation panel, or, if connected to the host computer via a bidirectional communication interface, a notification to that effect is sent to the printer driver or the like running on the host computer. Then, it is displayed on the display screen. In the latter case (when notifying and displaying to the host computer), it is necessary to include a program for accepting the transmission of an instruction command and a program for displaying a message. It can also be applied to the case where it is realized by performing

In the above embodiment, the printer device has been described as an example. However, the present invention may be applied to a copying machine or the like.

In the above embodiment, when the initial value S1 is less than the threshold value, a message prompting "sensor cleaning" is displayed, and it is determined whether or not cleaning has been performed by detecting ON / OFF by the door sensor. Thereafter, when the density control is performed again and the ratio of the initial value S1 and the inclination does not fall within the normal range, ON / OFF of the door sensor is determined again and a message prompting sensor cleaning is output.

However, as can be easily understood from the above embodiment, the initial value S1 is caused by the stain on the surface layer of the intermediate transfer member and the stain on the density sensor, and the ratio of the inclination is caused by the stain on the density sensor. For example, if the initial value S1 is out of the allowable range and the inclination ratio is, for example, "1" or a value close thereto, it can be determined that the initial value S1 is mainly due to the contamination of the intermediate transfer member. Conversely, if the inclination ratio is extremely outside the allowable range, it may be determined that the density sensor is contaminated, and in the middle, it can be estimated that both are contaminated. Therefore, it is possible to first determine which of these three states it is in, and to notify the result of the determination.

In the above embodiment, the patches of each density are formed by keeping the emission intensity of the laser beam constant and controlling the developing bias appropriately. However, the present invention is not limited to this, and any method may be used. In particular, when the light receiving range of the density sensor has an appropriate two-dimensional spread, the density is reproduced by applying the dither method or the error diffusion method, and the value of the image data for driving the laser light itself is used. It is also possible by controlling.

Further, in the above-described embodiment, the example in which the patch is transferred onto the intermediate transfer member and the patch is measured has been described. However, in the case of an apparatus having no intermediate transfer member, the patch may be provided on the photosensitive drum. Further, as for the stain on the recording medium, one of the stains on the density detecting means may be measured.

As described above, according to the present embodiment,
During the density control sequence, the sensor dirt or patch dirt surface dirt is appropriately identified from the value of the initial sensor output value of the patch dirt surface and the sensor output of the patch formed thereon, or Since the sensor dirt can be appropriately determined from the converted density of the patch after the dirt has been corrected, it is possible to send an appropriate message to the user at an appropriate timing without extending the density control sequence time. It has become possible to prevent image quality deterioration such as scattering and fixing failure.

[0080]

As described above, according to the present invention, by detecting dirt on a recording medium such as a drum or dirt on a density detecting means, the precision of image density control is increased and good image formation is maintained. It becomes possible to do.

[0081]

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a sensor output with respect to a toner density, which is a feature of an embodiment.

FIG. 2 is a schematic sectional view of a density sensor according to the embodiment.

FIG. 3 is a sectional structural view of a printer engine unit according to the embodiment.

FIG. 4 is a flowchart showing control processing contents according to the first embodiment.

FIG. 5 is a diagram illustrating a relationship between a sensor peripheral force and an approximate expression according to a second embodiment.

FIG. 6 is a flowchart illustrating control processing contents according to a third embodiment.

FIG. 7 is a diagram showing correspondence of verification results in the embodiment.

FIG. 8 is a block diagram of a controller according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging device 3 Exposure device 4 Developing device 5 Intermediate transfer body 6 Transfer roller 7 Fixing device 8 Density sensor 10 Cleaning device 11 Paper feed device

Claims (20)

[Claims] 1. An image forming apparatus for forming an image on a recording medium, comprising: a reference image forming means for forming a reference image having a preset density on the recording medium; Density detecting means for optically detecting the density of the reference image, calculating means for calculating a characteristic value of a density distribution based on the density of the reference image detected by the density detecting means, A determination unit for determining whether the recording medium or the density detection unit is dirty. 2. The calculation means calculates a linear function based on the density of the reference image including the density detected before forming the reference image, and the determination means calculates an intercept and a slope of the linear function calculated by the calculation means. 2. The image forming apparatus according to claim 1, wherein a stain on the recording medium or the density detecting unit is determined based on an allowable intercept threshold and an inclination. 3. The determining means determines that the intercept of the calculated linear function is not within the permissible threshold intercept, that it is a dirt on the recording medium, and determines that the slope of the linear function is not within the permissible gradient. 3. The image forming apparatus according to claim 2, wherein it is determined that the density detecting unit is dirty. 4. The image forming apparatus according to claim 1, wherein the reference image forming unit forms reference images having different densities by controlling a bias voltage of a developing device. 5. The notification that the image forming apparatus is connected to a host computer via a two-way communication interface, and notifies the host computer via the two-way communication interface to display the determination result on a display screen of the host computer. The image forming apparatus according to claim 1, further comprising a unit. 6. The reference image forming means, the density detecting means,
The image forming apparatus according to claim 1, wherein the calculation unit and the determination unit are energized at a predetermined timing. 7. The image forming apparatus according to claim 1, wherein the image forming apparatus forms an image in a plurality of colors. 8. The image forming apparatus according to claim 1, wherein the image forming apparatus is based on an electrophotographic system, and the recording medium is an image carrier that carries a toner image. 9. The image forming apparatus according to claim 1, wherein the determination unit distinguishes between the stain on the recording medium and the stain on the density detection unit. 10. A method for controlling an image forming apparatus for forming an image on a recording medium, comprising: a reference image forming step of forming a reference image having a preset density on the recording medium; A density detection step of detecting the density of the reference image formed on the reference image by a predetermined optical sensor; and a calculation step of calculating a characteristic value of a density distribution based on the density of the reference image detected in the density detection step. A determining step of determining whether the recording medium or the optical sensor is dirty according to the characteristic value obtained. 11. An image forming apparatus for forming an image on a recording medium, comprising: a reference image forming means for forming a reference image having a preset density on the recording medium; An image forming apparatus, comprising: a density detecting unit for optically detecting the density of a reference image obtained by the reference; and a determining unit for independently determining a stain on the recording medium and a stain on the density detecting unit. 12. The image forming apparatus is connected to a host computer via a two-way communication interface, and notifies the host computer via the two-way communication interface to display the determination result on a display screen of the host computer. The image forming apparatus according to claim 11, further comprising a unit. 13. The image forming apparatus according to claim 11, wherein said image forming apparatus forms an image in a plurality of colors. 14. The image forming apparatus according to claim 11, wherein the image forming apparatus conforms to an electrophotographic system, and the recording medium is an image carrier that carries a toner image. 15. A method for controlling an image forming apparatus for forming an image on a recording medium, comprising: a reference image forming step of forming a reference image having a preset density on the recording medium; A density detection step of detecting the density of the reference image formed on the optical sensor by an optical sensor; and a determination step of independently determining the dirt on the recording medium and the dirt on the optical sensor. A method for controlling a forming apparatus. 16. An image forming apparatus for forming an image on a recording medium, comprising: a reference image forming means for forming a reference image having a preset density on the recording medium; Density detection means for optically detecting the density of the reference image obtained, and determination means for determining the stain on the density detection means after creating correction data for correcting the stain on the recording medium. Image forming device. 17. The notification that the image forming apparatus is connected to a host computer via a bidirectional communication interface, and that the determination result is displayed on a display screen of the host computer by notifying the host computer via the bidirectional communication interface. 17. The image forming apparatus according to claim 16, further comprising a unit. 18. The image forming apparatus according to claim 16, wherein said image forming apparatus forms an image in a plurality of colors. 19. The image forming apparatus according to claim 16, wherein the image forming apparatus conforms to an electrophotographic system, and the recording medium is an image carrier that carries a toner image. 20. A method for controlling an image forming apparatus for forming an image on a recording medium, comprising: a reference image forming step of forming a reference image having a preset density on the recording medium; A density detection step of detecting the density of the reference image formed on the recording medium by an optical sensor; and a determination step of determining the dirt on the optical sensor after creating correction data for correcting dirt on the recording medium. A method for controlling an image forming apparatus, comprising: