JP2016018129A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To discharge deteriorated toner and identify a source of image density change, while reducing toner consumption.SOLUTION: A discharge control section controls a charging section, an exposure section, and a developing section, to form a pattern on a photoreceptor drum, primarily transfers the pattern to an intermediate transfer belt, and forcibly discharges deteriorated toner stored in the developing section. The discharge control section detects density-change period of the pattern, to be used for identifying a source of the density change. A read sensor detects density of the pattern. An identifying section analyzes a result detected by the read sensor, to determine density-change period in the pattern, and identifies a rotating body corresponding to the determined period, from among rotating bodies, such as the photoreceptor drum, the charging section, the developing section, and a primary transfer section, as a source of the density change.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an image forming apparatus such as an electrophotographic system or an electrostatic recording system.

  A periodic density change (density unevenness) may occur in an image output from the image forming apparatus. Since various rotating members are used in the image forming apparatus, the density change occurs at a cycle that matches the rotation cycle of these rotating members. According to Patent Document 1, a pattern image having a uniform density is created by an image forming apparatus, the pattern image is read by a sensor, and the density data is subjected to frequency analysis to obtain a density change cycle. It has been proposed to correct the density change by identifying the part causing the density change by comparing this period with the circumference of each roller part.

JP 2006-106556 A JP 2006-23327 A

  By the way, if images with low toner consumption are continuously formed, the toner staying in the developing unit for a long time deteriorates. Therefore, an invention for forcibly discharging deteriorated toner has been proposed (Patent Document 2). Even in the above-mentioned Patent Document 1, toner is consumed to create a pattern image. Therefore, when the invention described in Patent Document 1 and the invention described in Patent Document 2 are mounted on an image forming apparatus, they are not transferred to paper. The amount of toner consumed increases. SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of reducing both toner consumption and identifying both the discharge of deteriorated toner and the source of the change in image density.

The present invention is, for example,
An image carrier;
Charging means for uniformly charging the image carrier;
An image forming means for forming an electrostatic latent image on the image carrier;
Developing means for developing the electrostatic latent image with a developer to form a toner image;
An intermediate transfer member;
Primary transfer means for transferring the toner image to the intermediate transfer member;
Secondary transfer means for transferring the toner image carried on the intermediate transfer member to a sheet;
Measuring means for measuring a parameter based on the consumption amount of the developer or the rotation amount of the intermediate transfer member;
When the parameter measured by the measuring unit satisfies a predetermined condition, the charging unit, the image forming unit, and the developing unit are controlled to form a pattern image on the image carrier, and the pattern image is formed on the intermediate transfer unit. Control means for forcibly discharging the developer contained in the developing means,
Detecting means for detecting the density of the pattern image transferred to the intermediate transfer member;
Based on the detection result of the detection means, a period of density change in the pattern image is obtained, and a plurality of rotating bodies included in the image carrier, the charging means, the developing means, the primary transfer means, and the secondary transfer means are obtained. An image forming apparatus comprising: a specifying unit that specifies a rotating body corresponding to the cycle as a generation source of the density change.

  According to the present invention, it is possible to detect the periodic density change of an image by using toner that is forcibly discharged and identify the generation source thereof. And the identification of the generation source of the density change of the image can be made compatible.

Sectional view showing an example of an image forming apparatus The figure which shows an example of a control part The figure which shows an example of an operation part The figure which shows an example of a belt image Figure showing an example of a display message Flow chart showing printing operation Explanatory diagram of cycle detection Cycle detection flowchart Flow chart showing the identification of the cause component Flowchart of other print operations The figure which shows an example of another belt image

  As shown in FIG. 1, the image forming apparatus 100 includes a document feeder 120, an image reader 140, and a printer 119. The document feeder 120 supplies the documents one by one from the first page in order, passes the curved path, further conveys the platen glass from the left to the right, and discharges it to the discharge tray. The image reader 140 reads an original, generates an image signal indicating each luminance of RGB, and outputs the image signal to the printer 119.

  The printer 119 receives the image signal output from the image reader 140, performs image processing such as color space conversion and gamma correction, and sends the image signal to the exposure unit 103. In this example, since toners of four colors such as yellow (Y), magenta (M), cyan (C), and black (K) are used, the printer 119 includes four image forming stations. The internal structure of the four image forming stations is basically the same. The photosensitive drum 10 is an example of an image carrier. The toner supply unit 101 supplies a developer (toner) to the developing unit 102. The charging unit 130 is an example of a charging unit that uniformly charges the image bearing member, and charges the surface of the photosensitive drum 10 to a uniform potential using a charging roller. The exposure unit 103 is an example of an image forming unit that forms an electrostatic latent image on the image carrier, and irradiates the photosensitive drum 10 with laser light to form an electrostatic latent image on the photosensitive drum 10. The developing unit 102 is an example of a developing unit that develops the electrostatic latent image with a developer to form a toner image. The developing unit 102 uses a developing sleeve to attach the toner to the electrostatic latent image on the photosensitive drum 10 and develop the toner image. A toner image is formed. The primary transfer unit 105 is an example of a primary transfer unit that transfers a toner image to an intermediate transfer member, and primarily transfers the toner image from the photosensitive drum 10 to the intermediate transfer belt 104 using a primary transfer roller. The intermediate transfer belt 104 is an example of an intermediate transfer member, and conveys a toner image to the secondary transfer unit 106. At this time, the reading sensor 107 may read the toner image. The secondary transfer unit 106 is an example of a secondary transfer unit that transfers a toner image carried on an intermediate transfer member onto a sheet. The secondary transfer unit 106 uses a secondary transfer roller for a sheet fed from a cassette 109 or the like. Secondary transfer of image. The cleaning unit 108 collects toner remaining on the intermediate transfer belt 104 without being transferred to the sheet by the secondary transfer unit 106. The fixing device 170 fixes the toner image into a sheet shape. A discharge roller 118 discharges the sheet to the outside of the image forming apparatus 100.

  FIG. 2 is a block diagram of a control unit that controls the image forming apparatus. A CPU 201 is a control unit that comprehensively controls the entire image forming apparatus 100. The ROM 202 is a storage device that stores control contents (programs, control data, etc.) to be executed by the CPU 201. The RAM 203 is used as a work area, and stores data detected by the reading sensor 107, image data obtained by the image reader 140 reading a document, and the like. The input unit 205 accepts user instructions to the CPU 201. A display unit 206 displays a message from the CPU 201, a user interface, and the like. The motor 200 drives the intermediate transfer belt 104, the photosensitive drum 10, and the developing unit 102. The voltage generation unit 207 generates a charging voltage of the charging unit 130, a developing voltage of the developing unit 102, a primary transfer voltage of the primary transfer unit 105, a secondary transfer voltage of the secondary transfer unit 106, and the like.

  There are various functions realized by the CPU 201 executing the program. The consumption measuring unit 211 analyzes the image data and measures the toner consumption. The rotation amount measurement unit 212 measures the rotation amount of the motor 200 and measures the rotation amount (circulation distance, operating time, etc.) of the intermediate transfer belt 104 based on the measured rotation amount. The discharge control unit 213 controls the pattern generation unit 217, the charging unit 130, the exposure unit 103, the photosensitive drum 10, and the development unit 102 based on the measurement result, and forcibly discharges the toner from the development unit 102. The discharge control unit 213 may include an integration unit 214, a determination unit 215, and the like. The integration unit 214 performs integration processing on parameters relating to the toner consumption amount and the rotation amount of the intermediate transfer belt 104. The determination unit 215 compares the integrated value with the threshold value, and determines whether or not a toner discharge process is necessary and whether or not a periodic density change detection process is executed using the discharged toner. When a parameter such as an integrated value satisfies a predetermined condition, the discharge control unit 213 controls the charging unit 130, the exposure unit 103, the development unit 102, and the like to form a pattern image on the photosensitive drum 10, and transfers the pattern image to the intermediate transfer. Transfer to the belt 104. Accordingly, the discharge control unit 213 functions as a control unit that forcibly discharges the deteriorated toner stored in the developing unit 102. The reading sensor 107 functions as a detection unit that detects the density of the pattern image transferred to the intermediate transfer member. The specifying unit 216 analyzes the reading result of the reading sensor 107 to determine the density change cycle, and specifies which rotator is the source of the density change from the obtained cycle. The pattern generation unit 217 generates pattern data for forming a pattern image for forcibly discharging toner and pattern data for forming a pattern image for detecting a cycle of density change. In particular, in the present embodiment, one pattern data is used for both forced toner discharge and density change detection. The voltage correction unit 218 corrects the voltage generated by the voltage generation unit 207 so that the periodic density change is reduced.

<Operation unit>
FIG. 3 shows an example of the operation unit 301 including the input unit 205 and the display unit 206. The input unit 205 is mounted on the display unit 206 as a touch sensor, and forms a so-called touch panel. The display unit 206 displays soft keys, the input unit 205 detects which soft key is operated, and notifies the CPU 201 of the detected soft key. With the soft keys, paper selection, single / double-sided printing instructions, color mode / monochrome mode instructions, and the like are input. When the user presses the start key 306 to start printing, the CPU 201 starts printing.

<Band image generation determination>
The consumption measuring unit 211 analyzes the image data received from the image reader 140 or the host computer, calculates the image duty (print ratio in one page) for each color, and stores it in the RAM 203. If image formation continues with low image duty, that is, low toner consumption, the toner in the developing unit 102 deteriorates. Accordingly, when the determination unit 215 determines that the image duty is 5% or less, the discharge control unit 213 maintains the image quality by forcibly consuming the toner so that the toner consumption amount per page is 5%. To do. The RAM 203 may store a low duty counter (variable) indicating how long a low duty image is continuously formed. A low duty counter is prepared for each color. Specifically, the integration unit 214 calculates a difference between the toner consumption amount due to image formation and a reference consumption amount (for example, 5%) at the time of image formation. For example, the difference when the Y image duty is 3% is 5-3 = 2. Therefore, the integration unit 214 adds 2 to the Y low duty counter. The difference when the Y image duty is 10% is 5-10 = −5. Therefore, the integration unit 214 subtracts 5 from the low duty counter. The determination unit 215 compares a low duty counter, which is an integrated value, with a threshold value (for example, 100) for each color. When the determination unit 215 detects that the low duty counter has reached the threshold value for any color, the discharge control unit 213 forms an image with 100% duty and forcibly consumes the toner. For other colors, the discharge control unit 213 executes discharge control according to the low duty counter value at that time. As a result, new toner is supplied into the developing unit 102.

<About band images>
FIG. 4A shows an example of the value of the low duty counter. FIG. 4B shows an example of the band image parameters. FIG. 4C shows an example of the band image. FIG. 4D shows an example of the band image parameters. FIG. 4E shows an example of the band image.

  A pattern image used for forced toner discharge will be referred to as a band image. There are two types of band images. One is a normal band image formed only for forced toner discharge. The other is a combined band image used for both forced toner discharge and density unevenness detection. 4B and 4C show an example of a normal band image formed when the low duty counter has the value shown in FIG. Since a band image is formed during a period from when an image is formed on a certain sheet to when an image is formed on the next sheet, the productivity of the image forming apparatus 100 temporarily decreases. Therefore, the length of the belt image in the conveyance direction (sub-scanning direction and rotation direction of the intermediate transfer member) is desired to be as short as possible. The pattern generation unit 217 generates pattern data so that a predetermined amount of toner is forcibly discharged with a density of 100% for all colors in order to shorten the sub-scanning length as much as possible. The pattern generator 217 variably controls the sub-scanning length of the band image in accordance with the low duty counter for each color.

  FIGS. 4D and 4E show an example of a combined band image formed when the low duty counter has the value shown in FIG. FIG. 4F shows an example of a periodic concentration change source and its diameter and circumference. In order to accurately detect the density change cycle, an image length obtained by adding a margin α to twice the maximum circumference among the circumferences of a plurality of rotating bodies is required. The image length is a length in the sub-scanning direction, and may be called a sub-scanning length. Therefore, since the maximum circumference in this example is 125.66 mm, which is the circumference of the photosensitive drum, the sub-scanning length of the band image needs to be at least 251.32 mm. Actually, since the circumferential length varies, the sub-scanning length of the band image is determined to be 300 mm in consideration of the margin α. Therefore, in FIGS. 4D and 4E, the density is adjusted so that a predetermined amount of toner can be forcibly discharged from a 300 mm band image for each color. As described above, the pattern generator 217 may variably control the density of the band image in accordance with the low duty counter of each color.

  The toner total amount is the same whether it is a normal band image or a combined band image. That is, the toner deterioration preventing ability is equal. Further, as can be seen from the above description, the sub-scanning length of the combined band image is often longer than the sub-scanning length of the normal band image. Therefore, the pattern generation unit 217 may always generate a combined band image when it is time to execute forced ejection. However, in order to prevent a decrease in productivity, the pattern generation unit 217 generates a combined image at a rate of once every n times when the forced discharge is performed, and the remaining n-1 timings. Then, a normal band image may be generated.

<Detection flow of periodic concentration change>
FIGS. 5A and 5B are examples of messages displayed on the display unit 206 when a periodic density change is detected. The CPU 201 reads these messages from the ROM 202 and displays them on the display unit 206. FIG. 6 is a flowchart showing the printing process of this embodiment. This flowchart is executed by the CPU 201.

  In step S600, the CPU 201 analyzes the print job data and determines whether there is an image (next image) that has not yet been printed. If there is no next image, the CPU 201 ends the printing operation. If there is a next image, the process proceeds to S601. In step S601, the CPU 201 controls the printer 119 and executes image formation based on the image data. In S602, the CPU 201 (consumption measuring unit 211 and integrating unit 214) analyzes the image data and calculates a low duty counter for each color. In step S603, the CPU 201 (determination unit 215) determines whether a band image is necessary. For example, the CPU 201 determines that a band image is necessary when the low duty counter value of any color is 100 or more. The need for the band image means that, for example, toner must be forcibly discharged. If no band image is required, the process returns to S600. If a band image is necessary, the process proceeds to S604.

  In S604, the CPU 201 (accumulation unit 214) clears (sets to zero) the low duty counter for each color. In step S <b> 605, the CPU 201 adds the density unevenness counter M. The density unevenness counter M is a counter for managing the detection timing of periodic density change. In step S <b> 606, the CPU 201 (determination unit 215) determines whether periodic density change detection (density unevenness detection) is necessary according to the density unevenness counter M. For example, if the density unevenness counter M is greater than or equal to a threshold value (example: 2), the CPU 201 determines that density unevenness detection is necessary. When the threshold is set to 2, density unevenness detection is executed at a rate of once every time toner is forcibly discharged twice. If density unevenness detection is not necessary, the process proceeds to S607. In step S <b> 607, the CPU 201 forms a normal band image on the intermediate transfer belt 104 in order to forcibly discharge the toner. A normal band image is formed according to the series of electrophotographic processes described above. Thereafter, the process returns to S600.

  On the other hand, if density unevenness detection is necessary, the process proceeds to S608. In step S <b> 608, the CPU 201 forms a combined band image on the intermediate transfer belt 104 for forced toner discharge and density unevenness detection. A combined band image is formed according to the series of electrophotographic processes described above. In step S <b> 609, the CPU 201 (specification unit 216) reads the combined band image with the reading sensor 107, analyzes the reading result, and obtains the density change cycle. In step S610, the CPU 201 clears the density unevenness counter M. In step S611, the CPU 201 (determination unit 215) determines whether there is an abnormality in the density change based on the analysis result. If there is no abnormality, the process returns to S600. On the other hand, if an abnormality is found, the process proceeds to S612.

  In S612, the CPU 201 (determination unit 215) determines whether or not the abnormality level is large based on the analysis result. For example, the CPU 201 determines whether or not the abnormal level exceeds an allowable value. If the abnormal level exceeds the allowable value, the process proceeds to S613. The allowable value is, for example, an abnormal level that requires replacement of the rotating body that is causing the abnormality. In step S <b> 613, the CPU 201 displays an abnormality message on the display unit 206, and prohibits printing until the replacement of the rotating body causing the abnormality is completed. For example, when the yellow primary transfer roller is abnormal, the display unit 206 displays a message as shown in FIG. If the abnormal level is less than the allowable value, the process proceeds to S614. In step S614, the CPU 201 changes image forming parameters (charging voltage, developing voltage, primary transfer voltage, secondary transfer voltage, etc.) so that periodic density changes are not noticeable. For example, the CPU 201 specifies a density change source based on the density change cycle, and modulates and outputs the voltage applied to the specified source with a frequency corresponding to the cycle. As a result, the periodic concentration change is alleviated. In step S615, the CPU 201 displays a message on the display unit 206. For example, when the yellow primary transfer roller is abnormal, the display unit 206 displays a message as shown in FIG. This allows the user to continue printing, but recognize that replacement of the primary transfer roller for yellow is recommended. Thereafter, the process returns to S600 and continuation of printing is allowed.

<Cause part identification method>
A method for identifying a causal component that causes a periodic density change will be described with reference to FIGS. 7, 8, and 9. A method of density unevenness image analysis will be described. FIG. 7A shows a band image of one color. The band image is a halftone image having a uniform density. By using such a band image, it is possible to specify which of the plurality of rotating bodies is the cause component. Since the density unevenness occurs according to the cycle (peripheral length) of the rotating body, the cause component is specified from the cycle of the density unevenness.

  FIG. 7B shows the reading result of the band image by the reading sensor 107. Here, the reading result is composed of luminance data in the conveyance direction of the intermediate transfer belt 104. The horizontal axis indicates the number of pixels. FIG. 7C shows the sum of squares (absolute values of complex numbers) of the real part and the imaginary part obtained by Fourier transform of the luminance data. The sum corresponds to the wave number. The horizontal axis represents the reciprocal number (frequency) of the number of pixels. By expressing the density of the band image as the intensity for each frequency by Fourier transform, it is possible to determine what period is included in the density unevenness. Thus, after converting the luminance data into the intensity for each frequency, the CPU 201 emphasizes the intensity of the characteristic frequency component. Further, the CPU 201 performs inverse Fourier transform on the emphasized feature. By doing so, it is possible to discriminate even a period of density unevenness that is difficult to discriminate with the original luminance data. FIG. 7D shows the luminance value of the band image obtained by emphasizing the feature of density unevenness by inverse Fourier transform. The CPU 201 performs inverse Fourier transform after multiplying the intensity of the characteristic frequency by 10 in this embodiment. This shows that density unevenness is emphasized.

<Calculation of concentration change cycle>
FIG. 8 is a flowchart showing the cycle calculation process (S609). This flowchart is executed by the CPU 201 (specification unit 216). Here, for convenience of explanation, the band image is a halftone image, and the sub-scanning length is 300 mm. When the sub-scanning length is converted into the number of dots, it is 7086 (dot). Luminance data is managed by a variable called Sample [m]. Here, m = 0 to 7086. In an example of the reading result, as shown in FIG. 7B, the horizontal axis is expressed by a pixel m, and the vertical axis is expressed as a luminance value.

  In step S <b> 801, the CPU 201 performs frequency analysis on the luminance data using fast Fourier transform (FFT). As a result, the luminance data Sample [m] is converted into a complex number representation of a real part re [m] and an imaginary part im [m] and stored in the RAM 203. Thus, the CPU 201 functions as a fast Fourier transform unit.

  In step S802, the CPU 201 calculates the sum of the square of the real part and the square of the imaginary part. Thereby, a frequency spectrum in the frequency domain is obtained. The frequency spectrum is the intensity for each frequency. That is, the horizontal axis represents frequency, and the vertical axis represents intensity for each frequency. In this embodiment, since the horizontal axis represents the frequency of the number of pixels, the unit is 1 / dot which is the reciprocal of the number of pixels. The fast Fourier transform is an example for performing frequency analysis, and other frequency analysis methods capable of equivalent frequency analysis may be employed. The square sum of the real part and the imaginary part is shown in FIG. The CPU 201 selects N square sum peaks in descending order. N is 10 for convenience of explanation. As a result, m1 to m10 are selected and stored in the RAM 203. By emphasizing the characteristics of these 10 frequencies, the wavelength of density unevenness is determined. In this way, the CPU 201 functions as a square sum calculator.

  In step S <b> 803, the CPU 201 performs a filter process for increasing the values of the real part re [m] and the imaginary part im [m] by X times (for example, 10 times) for m <b> 1 to m <b> 10. For example, the CPU 201 performs a calculation of re_2 [m] = re [m] * 10 and im_2 [m] = im [m] * 10, and stores the result in the RAM 203. By doing so, the CPU 201 emphasizes the amplitude at the frequencies m1 to m10, which has a characteristic as a peak value. As described above, the CPU 201 functions as a feature enhancement processing unit or a filter unit.

  In step S <b> 804, the CPU 201 performs inverse Fourier transform on the filtered real part re_2 [m] and imaginary part im_2 [m], obtains luminance data Sample_2 [m], and stores it in the RAM 203. Here, the result of performing the filter processing that emphasizes the characteristic frequency in both the real part and the imaginary part is subjected to inverse Fourier transform. Therefore, the calculated luminance data Sample_2 [m] is data in which the feature of density unevenness is emphasized as illustrated in FIG. Thus, the CPU 201 functions as an inverse Fourier transform unit.

  In step S <b> 805, the CPU 201 extracts a periodic peak in the luminance data and obtains an interval between two adjacent peaks. This interval is a pitch L (dot) of density unevenness and is stored in the RAM 203. The determined pitch L indicates a peak-to-peak interval as shown in FIG. Thus, the CPU 201 functions as a pitch measurement unit or a cycle measurement unit.

  In step S806, the CPU 201 obtains an average value of each peak as an abnormal level. When this average value exceeds a predetermined value, the change in density is clearly recognizable with the naked eye. Even if the voltage is corrected, the image quality cannot be recovered. In this embodiment, when the abnormal level exceeds 80, the CPU 201 prohibits printing and outputs an exchange message.

<Identification of the cause component>
As shown in FIG. 4F, the image forming apparatus 100 includes a plurality of rotating bodies having different circumferential lengths. There is a correlation between the density change period and the circumference of the rotating body. Therefore, the CPU 201 can identify the cause component by comparing the density change period and the circumference of the rotating body.

  FIG. 9 is a flowchart showing the cause component identifying process. This flowchart is executed by the CPU 201 (specification unit 216). The following S901, S902, and S906 to S908 correspond to S611 in FIG. 6, and S903 to S905 correspond to S612.

  In step S <b> 901, the CPU 201 resets the index data i stored in the RAM 203 to 0. In step S <b> 902, the CPU 201 compares the pitch L stored in the RAM 203 with the circumference. For example, the ROM 202 stores the table shown in FIG. The CPU 201 obtains the circumference [i] by sequentially referring to the table stored in the ROM 202 with the index data i. Further, the CPU 201 determines whether or not the circumference [i] is included between L−1.5 mm and L + 1.5 mm. The reason why the range of ± 1.5 mm is set with respect to the pitch L is to consider manufacturing variations of components. Thus, ± 1.5 mm is determined based on the tolerance of the parts. When the circumference [i] is included in this range, the circumference [i] corresponding to the circumference [i] is the cause component, and the process proceeds to S903. In step S903, the CPU 201 determines whether or not the peak average value (abnormal level) exceeds the correctable level (allowable value). If the abnormal level exceeds the correctable level, the abnormal level is high, and the process proceeds to S905. In step S <b> 905, the CPU 201 identifies the component [i] as an inoperable abnormal component, creates a message, and further prohibits the printer 119 from printing. Thereafter, the process proceeds to S613. On the other hand, if the abnormal level does not exceed the correctable level, the process proceeds to S904. In step S904, the CPU 201 identifies the component [i] as an operable abnormal component, creates a message, and proceeds to step S614.

  If the circumference [i] does not satisfy the condition in S902, the process proceeds to S906. If the index data i does not reach the total number of parts in S906, the CPU 201 proceeds to S907. In step S907, the CPU 201 adds 1 to the index data i and returns to step S902. On the other hand, if the index data i has reached the total number of parts, the process proceeds to S908. In step S908, the CPU 201 determines that the cause component does not exist.

  In the table shown in FIG. 4F, data indicating the circumference of each component is held in the ROM 202 so that the circumference is in ascending order. For example, if the pitch L of density unevenness obtained by frequency analysis is 56.2 mm, the primary transfer roller having a peripheral length of 54.98 mm is identified as the cause component from the table shown in FIG. . As described above, according to the present embodiment, the band image formed for forcibly discharging the deteriorated toner is also used for specifying the period of density unevenness and the cause component, thereby reducing the image quality while suppressing toner consumption. Stabilization and density unevenness cycle and identification of cause components are realized.

<Forcible consumption of toner triggered by the rotation amount of the intermediate transfer member>
In the above-described embodiment, the forced discharge of the deteriorated toner is executed using the toner consumption as a trigger. However, other parameters can be used as trigger parameters. Hereinafter, a case will be described in which the rotation amount of the intermediate transfer belt 104 (circulation distance or cumulative operation time proportional thereto) is employed as the trigger parameter.

<Band image generation determination>
FIG. 10 shows a flowchart. Compared with FIG. 6, S602 to S604, S607, and S608 are replaced with S1000 to S1004, respectively, but the others are common. Therefore, the difference between the two will be mainly described.

  In S1000, the CPU 201 integrates (accumulates) the rotation amount of the intermediate transfer belt 104. The parameters representing the cumulative rotation amount of the intermediate transfer belt 104 include the number of rotations of the intermediate transfer belt 104, the rotation distance, and the operation time. For example, the rotation distance can be calculated by multiplying the operation time by the rotation speed (circumferential speed) of the intermediate transfer belt 104. The CPU 201 can acquire the operation time by measuring from the timing at which the rotation of the motor 200 is started to the timing at which it is ended by a timer or the like.

  In step S <b> 1001, the CPU 201 determines whether band image control is necessary based on the accumulated rotation amount of the intermediate transfer belt 104. For example, when the circumferential distance of the intermediate transfer belt 104 exceeds a predetermined value (for example, 20000 mm), it is necessary to remove toner, toner external additives, paper dust, and the like attached to the intermediate transfer belt 104. Therefore, a band image as shown in FIGS. 11A and 11B is formed. In this example, a band image having a density of 100% for each color and a sub-scanning length of 150 mm is formed. The CPU 201 separates the secondary transfer unit 106 from the intermediate transfer belt 104 and cleans the intermediate transfer belt 104 by the cleaning unit 108. As a result, the surface of the intermediate transfer belt 104 is maintained in a state suitable for image formation. As described above, if the circumferential distance of the intermediate transfer belt 104 exceeds the predetermined value, the process proceeds to S1002 to form a band image. In step S1002, the CPU 201 clears the accumulated rotation amount of the intermediate transfer belt 104 to zero. The process proceeds to S606 via S605, and the CPU 201 determines whether or not density unevenness detection is necessary. This is for determining whether a normal band image or a combined band image is formed as described above. If density unevenness detection is necessary, the process advances to step S1004, and the CPU 201 forms a combined band image. If density unevenness detection is not necessary, the process advances to step S1003, and the CPU 201 forms a normal band image.

<About band images>
11A and 11B show an example of a normal band image, and FIGS. 11C and 11D show an example of a combined band image. When a band image is formed, productivity is temporarily reduced, so that a shorter band image is better. Therefore, the CPU 201 (pattern generation unit 217) shortens the sub-scanning length by setting the density of the normal band image to the maximum value (100%) for all colors. As a result, a specified amount of toner can be forcibly discharged even if the sub-scanning length is shortened.

  As shown in FIGS. 11C and 11D, the sub-scanning length of the combined band image is set to 300 mm, which is twice the sub-scanning length of the normal band image. This is because the density of the dual-use band image is set to half (50%) so that the period of density change can be easily detected. The 50% density is an example, and other halftone gradations may be used as long as the period of density change can be easily detected. Since the total toner amount of the normal band image and the total toner amount of the combined band image are the same, the cleaning ability of the deteriorated toner of both is equal. The sub-scanning length of the combined band image is longer than the sub-scanning length of the normal band image. Therefore, in order to maintain productivity, the combined image may be formed once every time the normal belt image is formed N times. When the decrease in productivity is not a problem, a combined band image may be formed every time.

  In the above-described embodiment, the combined band image is used to detect the density change period, but the band image may be combined for other purposes. For example, a combined band image may be employed for the purpose of obtaining a correspondence relationship between the exposure amount of the exposure unit 103 and the density of the toner image to stabilize the density. In addition, a combined band image may be employed for the purpose of obtaining a correspondence relationship between the charging voltage, the developing voltage, the primary transfer voltage, and the density of the toner image to stabilize the density. These parameters are obtained by reading the density of the combined band image with the reading sensor 107.

<Summary>
According to the present invention, it is possible to detect the periodic density change of an image by using toner that is forcibly discharged and identify the generation source thereof. And the identification of the generation source of the density change of the image can be made compatible. A consumption amount measuring unit 211 that measures parameters related to the developer consumption amount and a rotation amount measurement unit 212 that measures parameters related to the rotation amount of the intermediate transfer member may be provided. When the parameters acquired by these satisfy the predetermined condition, the discharge control unit 213 causes the printer 119 to form a combined band image. The identification unit 216 analyzes the detection result of the reading sensor 107 to obtain the density change period in the band image, and the period is selected among the photosensitive drum 10, the charging unit 130, the developing unit 102, the primary transfer unit 105, and the secondary transfer unit 106. The corresponding rotating body may be specified as the source of density change.

  The discharge control unit 213 integrates the difference between the toner consumption amount and the reference consumption amount of the developer, and determines an integration unit 214 that obtains an integration value as a parameter, and determines whether the integration value exceeds a predetermined threshold value. And a developer discharge process by forming a pattern image when the integrated value exceeds a predetermined threshold value. When the formation of an image with a low duty (low density) continues, the chargeable amount of toner held inside the developing unit 102 decreases, and the toner is not sufficiently charged. Therefore, for example, the amount of deteriorated toner can be estimated by integrating the difference between the toner consumption estimated from the image data and the reference consumption corresponding to the low duty (low density). When the amount of deteriorated toner exceeds a certain allowable amount, a band image can be formed and forcibly discharged. As a result, the deteriorated toner can be discharged efficiently.

  The discharge control unit 213 includes a determination unit 215 that determines whether or not the rotation amount of the intermediate transfer belt 104 exceeds a predetermined threshold value. When the rotation amount of the intermediate transfer belt 104 exceeds a predetermined threshold value, a pattern is generated. You may perform the discharge process of the developer by image formation. As a result, toner, external additives, paper waste, etc. remaining on the intermediate transfer belt 104 can be efficiently cleaned.

  A pattern generation unit 217 that generates image data that is a base of the band image and supplies the image data to the exposure unit 103 may be further provided. The pattern generation unit 217 generates image data of a combined band image that is the first pattern image when the same pattern image is used in both the toner discharge process and the process for obtaining the density change cycle. The pattern generation unit 217 generates image data of a normal band image that is a second pattern image different from the first pattern image when the toner discharge process is executed but the process of obtaining the density change period is not executed. In this way, it is not always necessary to generate a combined band image, and a normal band image may be used. As a result, the process of obtaining the density change cycle can be omitted, so that a reduction in productivity of the image forming apparatus 100 can be suppressed.

  As described with reference to FIG. 4E and the like, the pattern generation unit 217 may change the density of the dual-use band image according to the parameter and fix the length of the dual-use band image to a predetermined length. This is to make it possible to accurately detect the period of dynamic change. Also, by determining the density according to the accumulated amount of deteriorated toner, it is possible to efficiently discharge the deteriorated toner and not to discharge the toner that has not deteriorated.

  As described with reference to FIG. 4C and the like, the pattern generation unit 217 fixes the density of the normal band image to a predetermined density and varies the length of the normal band image in the sub-scanning direction according to the parameter. Also good. As a result, the deteriorated toner can be efficiently discharged, and the toner that has not deteriorated can be prevented from being discharged. Further, since the sub-scanning length of the band image can be shortened according to the deteriorated toner accumulation amount, it is possible to reduce the downtime (time during which an image cannot be formed) of the image forming apparatus 100. That is, it becomes easy to suppress a decrease in productivity.

  As described with reference to FIGS. 11A to 11D, the pattern generator 217 fixes the density of the combined band image to the first density and sets the length of the combined band image to the first length. The density of the normal band image is fixed to a second density higher than the first density, and the length of the normal band image in the sub-scanning direction is fixed to a second length shorter than the first length. Also good. Accordingly, it is easy to suppress a decrease in productivity of the image forming apparatus 100 associated with the normal band image while ensuring the detection performance of the density change period in the combined band image. Note that the period of the density change can be detected more reliably by making the length of the combined band image longer than the density change period.

  The combined belt image and the normal belt image may have the same toner consumption. As a result, it is possible to efficiently discharge deteriorated toner and not discharge non-deteriorated toner, regardless of which band image is formed. The execution frequency of the process for obtaining the density change cycle may be less than the execution frequency of the toner discharge process. The processing for obtaining the density change cycle requires a combined band image, which increases downtime. Therefore, by reducing the frequency of processing for obtaining the density change cycle, it is easy to reduce downtime when viewed in total.

  As described with reference to FIG. 4F, the ROM 202 may function as a storage unit that stores a period associated with each of a plurality of rotating bodies. The identifying unit 216 identifies the rotating body that is the source of the density change by comparing the density change period obtained from the detection result of the reading sensor 107 with the period stored in the ROM 202. Can do. Since there is a correlation between the density change period and the circumference of the rotating body, it is possible to identify the cause component from the density change period.

  As described with reference to S614, the voltage correction unit 218 may be further included that corrects the voltage applied to the rotating body specified by the specifying unit 216 to reduce the density change. It is possible to make the density uniform by modulating the voltage so as to cancel the density unevenness according to the density change period. As described with respect to S612 and S613, when the voltage correction value exceeds a predetermined value by the voltage correction unit 218, the CPU 201 outputs a message prompting the replacement of the rotating body specified by the specifying unit 216 to the display unit 206. Also good. As the rotator deteriorates, it becomes difficult to cancel out the density unevenness even if the voltage is adjusted. Therefore, a message may be output to prompt exchange.

  The specifying unit 216 performs Fourier transform on the optical density of the pattern image to separate the real part and the imaginary part, squares the real part and the imaginary part, and calculates a sum, which is larger among the plurality of sums. A predetermined number of sums are selected in order, the selected predetermined number of sums is emphasized by filtering, the emphasized predetermined number of sums is converted into luminance data by inverse Fourier transform, and the distance between the peaks of the two luminance data May be obtained as a cycle of concentration change. By executing such enhancement processing, it becomes easy to specify the cycle efficiently.

  The combined band image may be combined with a pattern image detected in order to keep the density of the toner image constant. That is, the dual-use band image may be used not for the purpose of specifying the density change period but for another purpose. The image forming apparatus 100 often employs control that maintains a constant toner image density. For example, the density of the toner image is maintained at a desired density by adjusting the charging voltage, the developing voltage, the exposure amount, and the like. Even in such a case, the CPU 201 has to form a pattern image and read the pattern image with the reading sensor 107 to adjust the image forming conditions. Therefore. By using the band image for discharging the deteriorated toner together with the pattern image detected for maintaining the density of the toner image constant, toner consumption for maintenance can be reduced.

  10: Photosensitive drum, 101: Toner supply unit, 102: Development unit, 103: Exposure unit, 104: Intermediate transfer belt, 105: Primary transfer unit, 107: Reading sensor, 108: Cleaning unit, 120: Document feeder 140: Image reader, 119: Printer, 106: Secondary transfer unit

Claims (17)

An image carrier;
Charging means for uniformly charging the image carrier;
An image forming means for forming an electrostatic latent image on the image carrier;
Developing means for developing the electrostatic latent image with a developer to form a toner image;
An intermediate transfer member;
Primary transfer means for transferring the toner image to the intermediate transfer member;
Secondary transfer means for transferring the toner image carried on the intermediate transfer member to a sheet;
Measuring means for measuring a parameter based on the consumption amount of the developer or the rotation amount of the intermediate transfer member;
When the parameter measured by the measuring unit satisfies a predetermined condition, the charging unit, the image forming unit, and the developing unit are controlled to form a pattern image on the image carrier, and the pattern image is formed on the intermediate transfer unit. Control means for forcibly discharging the developer contained in the developing means,
Detecting means for detecting the density of the pattern image transferred to the intermediate transfer member;
Based on the detection result of the detection means, a period of density change in the pattern image is obtained, and a plurality of rotating bodies included in the image carrier, the charging means, the developing means, the primary transfer means, and the secondary transfer means are obtained. An image forming apparatus comprising: a specifying unit that specifies a rotating body corresponding to the cycle as a generation source of the density change. The parameter is a parameter based on consumption of the developer,
The control means includes
Integrating means for integrating the difference between the consumption amount of the developer and the reference consumption amount of the developer, and obtaining an integrated value as the parameter;
The image forming apparatus according to claim 1, wherein when the integrated value exceeds a predetermined threshold, the developer discharging process is performed by forming the pattern. The parameter is a parameter based on the amount of rotation of the intermediate transfer member,
The control means includes
2. The image forming apparatus according to claim 1, wherein when the amount of rotation of the intermediate transfer member exceeds a predetermined threshold, the developer discharging process by the formation of the pattern is executed. Further comprising generating means for generating image data to be the basis of the pattern image and supplying the image data to the image forming means;
The generating means generates the first pattern image when the developer discharging process and the process for obtaining the density change period are used in common, and executes the developer discharging process. 4. The image forming apparatus according to claim 1, wherein a second pattern image different from the first pattern image is generated when a process for obtaining a change cycle is not executed. 5.   The generating means generates image data such that the density of the first pattern image is varied according to the parameter, and the length of the first pattern image in the rotation direction of the intermediate transfer member is a predetermined length. The image forming apparatus according to claim 4.   The generating means generates image data so that the density of the second pattern image becomes a predetermined density, and varies the length of the second pattern image in the rotation direction of the intermediate transfer member according to the parameter. The image forming apparatus according to claim 4, wherein:   The generating means generates image data so that the density of the first pattern image becomes the first density, and the length of the first pattern image in the rotation direction of the intermediate transfer member becomes the first length. The density of the second pattern image becomes a second density higher than the first density, and the length of the second pattern image in the rotation direction becomes a second length shorter than the first length. The image forming apparatus according to claim 4, wherein the image data is generated as described above.   8. The image formation according to claim 4, wherein the generation unit generates image data such that a length of the first pattern image is longer than a cycle of the density change. 9. apparatus.   9. The apparatus according to claim 4, wherein the generation unit generates image data so that consumption amounts of the developer are equal between the first pattern image and the second pattern image. Image forming apparatus.   The image forming apparatus according to claim 1, wherein an execution frequency of the process for obtaining the density change period is less than an execution frequency of the developer discharge process. Storage means for storing a period associated with each of the plurality of rotating bodies;
The specifying unit compares the period of the density change obtained from the detection result of the detection unit with the period stored in the storage unit, so that the rotating body that is the source of the density change The image forming apparatus according to claim 1, wherein the image forming apparatus is specified.   The image forming apparatus according to claim 1, further comprising a voltage correcting unit that corrects a voltage applied to the rotating body specified by the specifying unit to reduce the density change. apparatus.   13. The apparatus according to claim 12, further comprising: an output unit that outputs a message that prompts replacement of the rotating body specified by the specifying unit when the voltage correction value exceeds a predetermined value by the voltage correcting unit. Image forming apparatus. The specifying means is:
The optical density of the pattern image is Fourier-transformed to separate a real part and an imaginary part, and the real part and the imaginary part are squared to obtain a sum. A sum is selected, the selected predetermined number of sums is enhanced by filtering, the emphasized predetermined number of sums is converted into luminance data by inverse Fourier transform, and the distance between the peaks of the two luminance data is expressed as the density The image forming apparatus according to claim 1, wherein the image forming apparatus is obtained as a period of change.   The image forming apparatus according to claim 1, wherein the pattern image is also used as a pattern image that is detected in order to maintain a constant density of the toner image. An image carrier;
Charging means for uniformly charging the image carrier;
An image forming means for forming an electrostatic latent image on the image carrier;
Developing means for developing the electrostatic latent image with a developer to form a toner image;
An intermediate transfer member;
Primary transfer means for transferring the toner image to the intermediate transfer member;
Secondary transfer means for transferring the toner image carried on the intermediate transfer member to a sheet;
A developer stored in the developing unit by controlling the charging unit, the image forming unit, and the developing unit to form a pattern image on the image carrier and transferring the pattern to the intermediate transfer member. Control means for forcibly discharging,
Detecting means for detecting the density of the pattern transferred to the intermediate transfer member;
Based on the detection result of the detection means, the period of density change in the pattern is obtained, and the image carrier, the charging means, the developing means, the primary transfer means, and the secondary transfer means are among a plurality of rotating bodies. Specifying means for specifying a rotating body corresponding to the cycle as a source of the concentration change,
2. The image forming apparatus according to claim 1, wherein the pattern image is used both as a pattern image for detecting the density change period and a pattern image detected to maintain a constant density of the toner image.   Image formation characterized in that a toner image formed on an intermediate transfer body for forcibly discharging deteriorated toner accumulated in a developing unit is also used as a toner image for detecting a period of density change of the image apparatus.