JP4905602B2 - Image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine that combines these functions.

  In an image forming apparatus to which electrophotographic technology is applied, an electrostatic latent image formed on an image carrier is developed by a developing device to form a toner image.

  When the electrostatic latent image has a predetermined density and outputs an image pattern having a uniform density over the entire image, the density of the toner image obtained by developing it is constant. In addition, it is desirable that there is no density difference in the image.

  In order to suppress this variation, a rectangular image pattern having a uniform density called a patch is stored in advance, the electrostatic image is formed on the image carrier, and the density of the toner image obtained by development is determined. Based on this, a technique for changing image forming conditions has been widely used.

  Here, the image forming conditions mean conditions set for each means related to toner image formation such as charging voltage, developing bias, and toner density.

  However, the toner image obtained from the patch as described above is uniform when, for example, a phenomenon called “sweeping” in which a large amount of toner adheres to the rear end portion of the image on the downstream side during development occurs. Since a density image is not obtained, accurate density measurement may be difficult.

  The above sweeping particularly appears in an image forming apparatus in which an alternating current component is superimposed on a developing bias in order to suppress an edge effect and improve developer mobility.

  In order to cope with such a problem, the toner image obtained from the patch is divided into a plurality of areas, the density measurement is performed for each area, the deviation of the density of the toner image is detected, and the image forming condition is determined. The proposal to change is also made (for example, refer patent document 1).

  In the case of a color image forming apparatus, the density of the patch image corresponding to each color needs to be measured more accurately than in the case of a monochrome image forming apparatus, but this measurement may be more severe.

  For example, in a tandem color image forming apparatus, patch images formed and developed on image carriers of each color are sequentially transferred to an intermediate transfer member having a high density color.

  The density of each color patch image arranged on the intermediate transfer member is detected by one sensor (patch sensor) at a predetermined timing.

  Therefore, the patch sensor needs to have a sensitivity wavelength region for detecting the toner image density of all colors, and is obtained as compared with a case where individual patch sensors are provided corresponding to the colors to be detected. The S / N of the detection signal becomes low.

  Furthermore, since the intermediate transfer member is often a high density color, for example, dark green or a dark color close to black, there is a difference in density between the area where no toner is attached and the patch area where the toner is attached. There is also a problem that the dynamic range for detection becomes small.

  Accordingly, the density of the patch image formed and developed on the image carrier of each color is measured by an individual patch sensor before being transferred to the intermediate transfer member, or the patch image of each color transferred to the intermediate transfer member. It is desirable to increase the measurement accuracy by measuring the density of each color with a patch sensor provided for each color.

  However, such technical means cause problems such as an increase in cost and complicated adjustment, and are not necessarily good measures.

JP-A-7-175367

  The present invention has been made in view of the situation as described above, and an object of the present invention is to control image quality deterioration based on a development current profile without optically detecting the density of a patch image. The present invention is to realize an image forming apparatus.

The present invention is achieved by realizing the following invention.
1. An image having a developing device that forms an alternating electric field between an image carrier on which an electrostatic latent image is formed and a developer carrier that holds a developer, and transfers toner to the image carrier to develop the image. In the forming device,
Development current detection means for detecting a development current flowing between the image carrier and the developer carrier;
A plurality of image patterns having different densities are arranged to generate a detection image pattern for detecting development characteristics, the detection image pattern is output as an electrostatic latent image to the image carrier, and the development current detection Obtaining the temporal change of the developing current that flows during the development of the electrostatic latent image from the detection signal of the means,
A numerical value obtained by multiplying the time from the start to the end of the increase or decrease in the development current due to the increase or decrease in the amount of developer attached to the developer carrier by the increase or decrease in the development current By detecting the occurrence of sweeping or white spots that are image defects due to non-uniform density occurring in the sub-scanning direction, and image defect detection means for obtaining a value that quantifies the degree of the defects,
An image forming apparatus comprising:
2. The image forming apparatus according to claim 1, wherein an image pattern having the highest density and an image pattern having an intermediate density are included in the plurality of image patterns having different densities.
3. The image defect detection means generates different image patterns for detection in which a plurality of image patterns are arranged in a predetermined arrangement order or arrangement interval according to the type of defect of an image to be specified. The image forming apparatus according to 1 or 2.
4). The image defect detection means includes
When the interruption time of the image forming operation of the image forming apparatus continues for a predetermined time or more and the image forming operation is possible,
The image forming apparatus according to claim 1, wherein an image defect detection operation is performed to detect the image defect and obtain a value obtained by quantifying the degree of the defect.
5. The image defect detection means includes
When the accumulated operation time of the developing device reaches a preset time,
5. The image forming apparatus according to claim 1, wherein an image defect detection operation for detecting the image defect and obtaining a value obtained by quantifying the degree of the defect is performed.
6). The image defect detection means includes
When the difference between the print rate of the image to be output and the print rate of the image output immediately before is equal to or greater than the preset value,
The image forming apparatus according to claim 1, wherein an image defect detection operation for detecting the image defect and obtaining a value obtained by quantifying the degree of the defect is performed.
7). The image defect detection means includes
When the environmental change exceeds the preset range,
The image forming apparatus according to claim 1, wherein an image defect detection operation is performed to detect the image defect and obtain a value obtained by quantifying the degree of the defect.

  According to the present invention, it is possible to grasp the change in the developing performance of the image forming apparatus more accurately as compared with the conventional technique in which the density of the patch image is optically detected.

  In addition, by storing a plurality of patch images (image patterns) having different densities in advance and changing the arrangement order or arrangement interval of these patch images, an image in which occurrence of an image defect can be detected sharply ( Detection image pattern) can be generated for each detection purpose.

  As a result, it is possible to detect the occurrence of an image defect at an early stage and take necessary countermeasures, and the quality of the copy image output from the image forming apparatus can be prevented from being deteriorated.

1 is a conceptual diagram of an image forming apparatus. 3 is a block diagram illustrating a control relationship of the image forming apparatus G. FIG. It is a conceptual diagram explaining a developing bias. It is a figure which shows the example of an image pattern and the image pattern for a detection. It is a conceptual diagram of the profile of a developing current. It is an example of the profile of the developing current obtained from a defect image. It is a figure explaining quantification of a sweeping value. It is a figure which shows the example of a sweeping defect correction table. It is a figure which shows the example of a lead part white missing defect correction table. 6 is a diagram illustrating an example of a toner density control reference value correction table. FIG. It is a flowchart which shows the flow of an image defect detection process. It is an experimental result which shows the change of a sweeping value. It is a graph which shows the experimental result in case the printing rate is 40%.

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

  FIG. 1 is a conceptual diagram of an image forming apparatus G according to the present invention.

  The image forming apparatus G is a digital color image forming apparatus, which is a multifunction machine having functions of a copying machine, a printer, and a facsimile machine, and an automatic document feeder ADF is provided on the upper part thereof.

  The documents D placed on the document placement table 101 of the automatic document feeder ADF are separated one by one, sent to the document conveyance path, and conveyed by the conveyance drum 102. The document image of the document D being conveyed is read by the document reading unit 1 at the document image reading position RP. The document D that has been read is discharged to the document discharge table 107 by the first conveyance guide G 1 and the document discharge roller 105.

  When reading the document image on the back side of the document D, the document D that has been scanned on the front surface (first surface) is guided to the document reversing roller 106 by the first conveyance guide G1, and the rear end portion of the document D is sandwiched. The document reversing roller 106 that reverses the document is again sent to the document conveyance path via the first conveyance guide G1 and the second conveyance guide G2. The reverse surface (second surface) of the document D sent out in reverse is read in the same manner as the front surface (first surface) and then discharged onto the document discharge table 107.

  The image forming apparatus G includes an original reading unit 1, image writing units 2Y, 2M, 2C, and 2K, image forming units 3Y, 3M, 3C, and 3K, an image transfer unit 4, a fixing unit 5, a reverse discharge unit 6, The sheet feeding unit 7, the sheet feeding unit 8, the operation display unit 9, the control unit C, and the like are included.

  The document reading unit 1 irradiates the document image with the lamp L at the document reading position RP, and guides the reflected light to the light receiving surface of the image sensor CCD by the first mirror unit 11, the second mirror unit 12, and the lens 13.

  The image signal photoelectrically converted by the image pickup device CCD is subjected to processing such as A / D conversion, shading correction, and compression by the image reading control unit 14, and is stored as original image data in the memory M of the control means C. The

  The original image data stored in the memory M is subjected to appropriate image processing according to a user designation or a set condition, and output image data is created.

  The image writing units 2Y, 2M, 2C, and 2K include a laser light source, a polygon mirror, and a plurality of lenses.

  The image writing units 2Y, 2M, 2C, and 2K are photosensitive members that are image carriers of the image forming units 3Y, 3M, 3C, and 3K by scanning with a laser beam that performs scanning exposure corresponding to the output image data. Electrostatic latent images are formed on the surfaces of 31Y, 31M, 31C, and 31K.

  The image forming unit 3Y includes a photoconductor 31Y as an image carrier, a charging unit 32Y, a developing device 33Y, a first transfer roller 34Y, a cleaning unit 35Y, and the like disposed around the photoconductor 31Y.

  The same applies to the image forming units 3M, 3C, and 3K. These configurations are well-known techniques employed in many electrophotographic color image forming apparatuses.

  The electrostatic latent images formed on the photoreceptors 31Y, 31M, 31C, and 31K are developed by the corresponding developing devices 33Y, 33M, 33C, and 33K, and toner images are formed on the photoreceptors.

  Inside the developing device 33Y, a toner concentration detection sensor 310Y that detects a change in the magnetic permeability of the developer is provided.

  The toner density in the developing device 33Y is maintained so as to maintain a preset toner density reference value based on the detection signal of the toner density detection sensor 310Y by executing the toner density control 800 which is a program. The amount of toner replenished from the container 5Y is controlled.

  The toner density control 800 sets the toner replenishment amount so as to maintain the toner density value specified in the toner density reference value correction tables 600 and 700 in which the toner density in the developing unit 3Y is stored in a table format. Control.

  The toner images formed on the photoreceptors 31Y, 31M, 31C, and 31K are sequentially transferred to predetermined positions on the transfer belt 41 by the first transfer rollers 34Y, 34M, 34C, and 34K of the image transfer unit 4.

  The toner image transferred onto the transfer belt 41 of the image transfer unit 4 is a sheet that is a transfer material that is fed from the sheet feeding unit 8 and fed at the timing of sheet feeding by the sheet feeding roller 81. Transferred to P by the second transfer roller 42.

  After the transfer of the toner image onto the paper P, the surface of the transfer belt 41 is cleaned by the cleaning unit 43 and is used for the next image transfer.

  On the other hand, the paper P carrying the toner image is sent to the fixing unit 5 and is heated by pressure by the opposing pressure roller and heating roller, whereby the toner image is fixed on the paper P.

  The paper P that has undergone the fixing process by the fixing unit 5 is conveyed by the paper discharge unit 6 and discharged to the paper discharge tray 10.

  When the paper P is reversed and discharged, the paper guide P is once guided downward by the sorting guide 64, the reverse roller 62 sandwiches the rear end of the paper P, and the paper P is reversed. The paper is guided to the paper discharge roller 61 by the sorting guide 64 and discharged to the paper discharge tray 10.

  When image formation is also performed on the back surface of the paper P, the paper P on which the front surface image has been fixed is conveyed to the re-feeding means 7 below by the sorting guide 64 and is moved back by the re-feed reverse roller 71. After sandwiching the end portion, the paper P is reversed by reverse feeding and sent to the refeed conveyance path 72 to be used for image formation on the back surface.

  The paper P to be used for the image forming process is sent out one by one from the plurality of paper trays 85, 86, 87 of the paper feeding unit 8, and the paper tray to be fed is set by the operation display unit 9. A paper tray storing paper P of a size corresponding to the job that has been selected is selected.

  FIG. 2 is a block diagram illustrating a control relationship of the image forming apparatus G.

  The control means C of the image forming apparatus G is a computer system having a CPU, a memory M, an I / O port, a communication interface, and a circuit for driving and controlling each means.

  Control by the control means C is performed by selecting and executing a plurality of programs stored in the memory M.

  Further, the image forming apparatus G can be connected to other image forming apparatuses or information processing devices, and the control unit C can control other image forming apparatuses or information processing apparatus control units via the communication unit TR. Exchange information with.

  In the drawing, description of blocks that are not directly related to the description of the present invention is omitted.

  FIG. 3 is a conceptual diagram illustrating the development bias.

  As shown in FIG. 3A, the developing bias is applied between a developing sleeve 37 (also referred to as a developing roller) that is a developer carrying member of the developing means 33 and a developing drum that is a base of the image carrier 31. It is a generally known voltage.

  The polarity direction and magnitude of the applied voltage are determined by the type of image carrier and developer used, the process speed, and the like.

  In the image forming apparatus G of this embodiment, the process speed is 220 mm / s, the photoconductor 31 as an image carrier has an organic semiconductor layer in which a phthalocyanine pigment is dispersed in polycarbonate, and development is performed by a two-component development system. A high-resistance carrier and a toner having a particle size of about 6.5 μm are used.

  In this embodiment, the developing bias voltage (Vd) is applied so that the potential of the photoconductor 31 is higher than that of the developing sleeve 37.

  As shown in FIG. 3B, the applied voltage is a DC component and an AC component superimposed. For example, a 500 V DC voltage (V1) is alternated with a peak-to-peak voltage of 1 kV and a cycle of 2 kHz. Superimpose AC voltage.

  When the developing bias voltage as described above is applied to the developing sleeve 37 and the image carrier 31 by the developing bias power source 300, an alternating electric field 38 is formed between the developing sleeve 37 and the image carrier 31.

  When the photosensitive member 31 is uniformly charged and an electrostatic latent image is not formed, the toner held on the developing sleeve 37 does not move to the photosensitive member 31, so that the development in a substantially insulated state is performed. Almost no direct current flows between the sleeve 37 and the photoconductor 31.

  However, at the time of development, since the movement of the charge occurs due to the movement of the charged toner, a current including a direct current flows between the developing sleeve 37 and the photoconductor 31. This current flowing during development is referred to as development current.

  In the present invention, a plurality of image patterns having different densities are stored in advance, a detection image pattern for detecting development characteristics is generated from these image patterns, and this is used as an electrostatic latent image on an image carrier. A time change of the developing current flowing when the electrostatic latent image is developed, that is, a profile of the developing current is stored.

  The development current is an output current of the development bias power supply 300 at the time of development, and the measurement changes in proportion to, for example, the voltage across the resistor arranged in the circuit through which the development current flows or the development current. This is performed by the development current detecting means 301 that measures the development current by measuring the current or voltage of the circuit.

  FIG. 4 is a diagram illustrating an example of an image pattern and a detection image pattern.

  FIG. 4A is an image pattern stored in a predetermined area of the memory M in advance, and shows three rectangular image patterns having different densities. These image patterns are provided for each color, and the number is not limited to three per color.

  An image pattern indicated by (3) in the figure is an image for outputting an image with the highest density, and (1) and (2) are images for outputting an image with an intermediate density. However, the concentrations of (1) and (2) are different.

  The size of the image pattern in this example is a 10 × 20 mm rectangle, but an appropriate size depends on the specifications of the image forming apparatus, for example, the process speed, and is determined at the time of design.

  (4) and (5) in FIG. 4 (b) are examples of detection image patterns generated by arranging the image patterns (1) to (3) in FIG. 4 (a). In the figure, the arrow indicates the traveling direction of the photoconductor 31 as an image carrier.

  The detection image pattern (4) is obtained by arranging the image patterns (1), (2), and (3) at a predetermined interval in descending order of density.

  In addition, the detection image pattern (5) is arranged so that the image patterns (1) and (3) are in contact with each other without any interval.

  The detection image pattern is an image pattern formed to measure a development current and obtain a development current profile that is a change over time, and a detection image pattern generation unit that is a program stored in the memory M It is generated by executing 100.

  In this way, the detection image pattern is created by selecting a plurality of image patterns having different densities stored in advance and setting the arrangement order and arrangement interval of the selected image patterns.

  FIG. 5 is a diagram showing an example of the profile of the development current.

  Since the toner of an amount corresponding to the density of the detection image pattern formed as a latent image is transferred to the photoconductors 31Y, 31M, 31C, and 31K that are image carriers, a developing current having a profile shown in the drawing flows.

  FIG. 6 is an example of a development current profile obtained from a defect image.

  FIG. 6A is a development current profile when an image having a defect called “sweeping” in which a large amount of toner adheres to the rear end portion of the developed toner image is formed.

  Further, FIG. 6B may appear prominently as a defect image when the detection image pattern shown in FIG. 4 (5) is output. To the rear end of the preceding low-density image pattern. This is a defect referred to as “lead part white spot”.

  The present invention changes the image forming conditions based on the information obtained by quantifying the type and degree of defect of the image from the development current profile obtained from the image having such a defect. This is intended to prevent enlargement and suppress the occurrence of defective images.

  FIG. 7 is a diagram for explaining the quantification of “sweeping”, which is one of the defects.

  In the present invention, the degree of sweeping is indicated by the numerical value obtained by multiplying the time TH from the beginning to the end of the increase in the development current increased by the increase in the toner adhesion amount in the figure and the increase amount IH in the development current. It is a sweeping value that is a value.

  As already described, the development current profile can also be obtained from the voltage across the resistor through which the development current in the bias power source flows, or from a current or voltage profile that changes in proportion to the development current in the circuit. In the present embodiment, image defects are quantified based on the voltage value change VH sent from the development current detection unit 301.

  That is, the sweep value F1 indicating the degree of sweep defect shown in FIG. 7 is expressed by F1 = TH × VH. For example, when TH = 10 ms and VH = 500 mV, the value of F1 obtained as a product of these values 5000 is a value indicating the degree of defects.

  Similarly, the lead white spot defect F2 is also quantified.

  Thus, the control means C first outputs a detection image pattern for detecting a target defect, and obtains and quantifies a development current profile that flows when this pattern is developed.

  Next, based on the quantified defects such as the sweeping value or the lead white blank value, a table stored in advance in the memory M related to the correction of the target defect, for example, the sweeping defect correction table 400. The image forming conditions of the image forming units 3Y, 3M, 3C, and 3K are changed with reference to the lead white missing defect correction table 500.

  FIG. 8 is a diagram illustrating an example of the sweeping defect correction table 400. FIG. 9 is a diagram showing an example of the lead white spot defect correction table 500.

  The correction performed with reference to the correction tables shown in FIGS. 8 and 9 changes the condition of the developing bias. However, the toner density control standard is based on the quantified sweeping defect and lead white defect. Correction that changes the value is also effective.

  FIG. 10 is a diagram illustrating an example of the toner density reference value correction tables 600 and 700 referred to in the correction.

  FIG. 10A is a density standard value correction table 600 referred to based on the sweeping value, and FIG. 10B is a density standard value correction table 700 referred to based on the lead white blank value.

  As described above, a detection image pattern is generated from a plurality of image patterns having different densities, and a defect in the image is detected and detected from the profile of the development current that flows when the detection image pattern is developed. The image forming conditions can be changed to prevent the defect.

  It is desirable that the confirmation of the degree of the image defect and the response to it be performed in a timely manner when there is a possibility that the image defect may occur.

  FIG. 11 is a flowchart showing the flow of the image defect detection processing 900.

  When the power of the image forming apparatus G is turned on and the image forming operation is enabled (step S1: Y), whether or not the time when the power is off has continued longer than a preset time (TT1). Is determined (step S2).

  If the time during which the power is off has continued longer than TT1 (step S2: Y), the development characteristic detection process in steps S6 to S9 is executed, and if necessary, the image forming conditions Make changes.

  If the time during which the power source is in the off state is shorter than TT1, or if the on state continues (step S2: N), the cumulative operation time of the developing device is less than the preset time (TT2). It is determined whether or not the length is longer (step S3).

  If the accumulated operation time of the developing device 33 is longer than a preset time (TT2) (step S3: Y), the development characteristic detection process in steps S6 to S9 is executed, and the operation is performed as necessary. Change the image conditions.

  If the accumulated operation time of the developing device 33 is shorter than the preset time (TT2) (step S3: N), the difference between the printing rate of the image to be output and the printing rate of the image output immediately before However, if it is equal to or greater than the preset value (PP1), the development characteristic detection process in steps S6 to S9 is executed, and the image forming conditions are changed as necessary.

  If the difference between the printing rate of the image to be output and the printing rate of the image output immediately before is smaller than a preset value (PP1), the environmental condition is confirmed (step S5).

  The environmental conditions referred to here are the temperature and humidity around the image forming apparatus G or the temperature and humidity inside the image forming apparatus G, and are measured by the corresponding temperature sensor TS and humidity sensor HS, respectively. .

  If the measurement result of the environmental condition, for example, the temperature is equal to or higher than a predetermined value TH1 or the humidity is equal to or higher than HH1 (step S5: Y), the development characteristic detection process in steps S6 to S9 is executed. Change the imaging conditions as necessary.

  If the temperature is lower than the preset value TH1 or the humidity is lower than the preset value HH1 (step S5: N), the routine is executed without executing the development characteristic detection process of steps S6 to S9. Exit.

  Note that the determination of the environmental condition as to whether or not to execute the development characteristic detection process in steps S6 to S9 is not limited to the determination as to whether or not the predetermined set value or more is as described above.

  That is, for example, it can be determined whether or not the measured value is within a set range, or whether or not the magnitude of the environmental change within a predetermined time is equal to or less than the set value.

  FIG. 12 is an experimental result showing a change in sweep value. FIG. 13 is a graph showing experimental results when the printing rate is 40%.

  Here, the conventional control which is the object of comparison with the present invention is a generally known control that changes the developing bias based on humidity detection.

  As apparent from FIGS. 12 and 13, the present invention prevents an increase in sweep value, that is, suppresses image defects called sweeping in which a large amount of toner adheres to the trailing edge of the image. I understand that.

  As described above, the present invention generates an image pattern capable of more sensitively detecting a decrease in image quality as a change in developing current by changing the arrangement order or arrangement interval of a plurality of image patterns having different densities. It is.

  Then, the image defects are quantified from the obtained development current profile, and the image forming conditions are changed based on the quantified value.

  As a result, it becomes possible to more accurately grasp the change in the developing performance of the developing device in the image forming apparatus compared to the conventional technique obtained from the change in the optical density of the patch image, thereby preventing the occurrence of image defects. Will be able to.

3Y, 3M, 3C, 3K Image forming means 31Y, 31M, 31C, 31K Photosensitive member (image carrier)
33Y, 31M, 31C, 31K Developing device 300 Developing bias power supply 301 Developing current detection means C Control means G Image forming apparatus

Claims (7)

An image having a developing device that forms an alternating electric field between an image carrier on which an electrostatic latent image is formed and a developer carrier that holds a developer, and transfers toner to the image carrier to develop the image. In the forming device,
Development current detection means for detecting a development current flowing between the image carrier and the developer carrier;
A plurality of image patterns having different densities are arranged to generate a detection image pattern for detecting development characteristics, the detection image pattern is output as an electrostatic latent image to the image carrier, and the development current detection Obtaining the temporal change of the developing current that flows during the development of the electrostatic latent image from the detection signal of the means,
A value obtained by multiplying the time from the start to the end of the increase or decrease in the development current due to the increase or decrease in the amount of developer attached to the developer carrying member by the increase or decrease in the development current. By detecting the occurrence of sweeping or white spots that are image defects due to non-uniform density occurring in the sub-scanning direction, and image defect detection means for obtaining a value that quantifies the degree of the defects,
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein an image pattern having the highest density and an image pattern having an intermediate density are included in the plurality of image patterns having different densities.   The image defect detection means generates different image patterns for detection in which a plurality of image patterns are arranged in a predetermined arrangement order or arrangement interval according to the type of defect of an image to be specified. The image forming apparatus according to 1 or 2. The image defect detection means includes
When the interruption time of the image forming operation of the image forming apparatus continues for a predetermined time or more and the image forming operation is possible,
The image forming apparatus according to claim 1, wherein an image defect detection operation is performed to detect the image defect and obtain a value obtained by quantifying the degree of the defect. The image defect detection means includes
When the accumulated operation time of the developing device reaches a preset time,
5. The image forming apparatus according to claim 1, wherein an image defect detection operation for detecting the image defect and obtaining a value obtained by quantifying the degree of the defect is performed. The image defect detection means includes
When the difference between the print rate of the image to be output and the print rate of the image output immediately before is equal to or greater than the preset value,
The image forming apparatus according to claim 1, wherein an image defect detection operation for detecting the image defect and obtaining a value obtained by quantifying the degree of the defect is performed. The image defect detection means includes
When the environmental change exceeds the preset range,
The image forming apparatus according to claim 1, wherein an image defect detection operation is performed to detect the image defect and obtain a value obtained by quantifying the degree of the defect.

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