JP2011215344A - Image forming apparatus, method for controlling image forming apparatus, and control program for image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus which can promptly obtain a favorable image, a method for controlling the image forming apparatus and a control program for the image forming apparatus.SOLUTION: The image forming apparatus has a photoreceptor temperature sensor 143 that detects a temperature of a photoreceptor 31, a storing section that stores a correspondence relationship between the temperature of the photoreceptor 31 and at least one of gradation characteristic correction table and a correction amount of maximum density of an image, a specifying section that specifies at least one of the gradation characteristic correction table and the correction amount of the maximum density of the image corresponding to the temperature of the photoreceptor 31 detected by the photoreceptor temperature sensor 143 based on the correspondence relationship, and a print section 100 that performs image formation based on image forming conditions according to at least one of the gradation characteristic correction table and the correction amount of the maximum density of the image specified by the specifying section.

Description

  The present invention relates to an image forming apparatus, an image forming apparatus control method, and an image forming apparatus control program. More specifically, the present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile that performs image formation by electrophotography, The present invention relates to an image forming apparatus control method and an image forming apparatus control program.

  Electrophotographic image forming apparatuses include a scanner function, a facsimile function, a copying function, a function as a printer, a data communication function, and a server function, an MFP (Multi Function Peripheral), a facsimile apparatus, a copying machine, a printer, and the like. is there. Generally, an image forming apparatus forms an electrostatic latent image on a photosensitive member by exposing a charged photosensitive member, develops the electrostatic latent image to form a toner image, and transfers the toner image from the photosensitive member to a transfer medium. To form an image on a sheet.

  The quality of an image formed by the image forming apparatus greatly depends on the optical characteristics of the photoreceptor. In particular, when the image forming apparatus is continuously operated by continuous paper passing in a low humidity environment where the absolute humidity around the image forming apparatus (ambient environment) is low, the image forming process in the image forming apparatus (image forming) There is a possibility that defects (image defects) such as density fluctuations may occur in the formed image. This is because a change in the latent image contrast potential on the photoconductor occurs due to a change in PIDC (Photo Induced Discharged Characteristic) of the photoconductor. This change in PIDC is presumed to be caused by a change in absolute characteristics of the CGL (Charge Generation Layer) layer on the surface of the photoconductor, thereby changing the sensitivity characteristics of the photoconductor. Unlike image density fluctuations caused by deterioration due to the lifetime of the photoconductor, image density fluctuations caused by changes in the absolute humidity of the CGL layer are transient and recover after a certain amount of time. For this reason, it is difficult to cope with image density fluctuations caused by changes in the absolute humidity of the CGL layer.

  Conventionally, as a countermeasure against the fluctuation of the latent image contrast potential on the photosensitive member, an environment detection unit that detects an environment such as temperature and temperature / humidity in the image forming apparatus, and an arbitrary environment (temperature / humidity) There has been proposed an image forming apparatus including a storage device in which an exposure amount, a characteristic of an exposed portion potential on a photosensitive member, and a latent image (development) contrast potential are stored in advance. The image forming apparatus calculates an appropriate image forming condition according to the environment detected by the environment detecting unit based on the data recorded in the storage device, and corrects the density.

  However, with this technique, density correction can be performed without the need for density detection means when image formation is not being performed, but transients that occur during continuous operation of the image forming apparatus (during continuous image formation). It was not possible to perform density correction according to the density fluctuation. In addition to the above-described environment detection means, as a technique that can prevent transient density fluctuations that occur during continuous image formation, a potential detection means that detects a potential on the photoreceptor (photosensitive drum), and a formed image There has been proposed an image forming apparatus provided with a density detecting means for detecting the density of the toner. This image forming apparatus corrects the density of the output image based on detection information detected by each of the environment detection unit, the potential detection unit, and the density detection unit, and obtains a stable output image.

  As another countermeasure against image density fluctuation, an image forming apparatus including an external reading unit such as a scanner for reading an output image and a communication unit has been proposed. This image forming apparatus reads an image density (gradation pattern) using an external reading unit, and corrects a gradation characteristic table using a communication unit.

  Further, Patent Document 1 below discloses a technique relating to image density correction in a conventional image forming apparatus. The image forming apparatus disclosed in Patent Document 1 performs necessary correction for fluctuations in image density and halftone density due to lowering of the exposure area potential when continuous image output is performed in a low-humidity environment. When this image forming apparatus determines that continuous image output is performed in a low humidity environment using a temperature / humidity sensor or a measurement sheet counter, the image characteristic and halftone density change are corrected by correcting the gradation characteristic table. Is corrected.

JP 2001-281939 A

  However, in the above-described two technologies that can prevent transient density fluctuations during continuous operation, it is necessary to detect the density of the image using density detection means or external reading means, which increases the cost. was there. Further, since it is necessary to form a test pattern for detecting the density of an image, there is a problem that a long downtime occurs in the image forming apparatus and a good image cannot be obtained quickly.

  Further, the image forming apparatus disclosed in Patent Document 1 has a problem that a good image cannot be obtained. In the case of performing single-sided paper passing or double-sided paper passing, the measured number counter of Patent Document 1 counts one sheet as “one sheet”. However, the behavior of the density fluctuation of the image is different because the curve of the photosensitive member temperature rise with respect to the paper count is different between the single-sided paper passing and the double-sided paper passing. In particular, paper that passes through both sides has a longer time in the image forming apparatus than paper that passes through one side. For this reason, it is presumed that the effect of sensitivity reduction appears more conspicuously in the case of double-sided paper passing than in the case of single-sided paper passing. However, in the image forming apparatus disclosed in Patent Document 1, since the same correction is performed at the time of double-sided paper passing as at the time of single-sided paper passing, a good image cannot be obtained.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus, a control method for the image forming apparatus, and a control program for the image forming apparatus that can quickly obtain a good image. That is.

  An image forming apparatus according to one aspect of the present invention is an image forming apparatus that forms an electrostatic latent image by exposing a charged photosensitive member to form an image based on the electrostatic latent image. Based on the above correspondence relationship, temperature detecting means for detecting the temperature, storage means for storing the correspondence relationship between the temperature of the photoconductor and at least one of the gradation characteristic table and the correction amount of the maximum density of the image A specifying means for specifying at least one of a gradation characteristic table corresponding to the temperature of the photosensitive member detected by the temperature detecting means and a maximum density correction amount; a gradation characteristic table specified by the specifying means; An image forming unit configured to form an image according to an image forming condition according to at least one of the correction amounts of the maximum density.

  Preferably, in the image forming apparatus, the gradation characteristic table is a curve indicating a relationship between the toner adhesion amount and the exposure intensity for exposing the photosensitive member.

  Preferably, in the image forming apparatus, the storage unit includes a first correspondence relationship between the temperature of the photosensitive member and the gradation characteristic table when the first gradation reproduction method is used, the temperature of the photosensitive member, and the second temperature. And the second correspondence relationship with the gradation characteristic table when the gradation reproduction method is used.

  Preferably, in the image forming apparatus, the storage unit is a temperature of the photosensitive member, a charging output that is an output of the charging unit for charging the photosensitive member, and a developing unit that is an output of the developing unit for developing the electrostatic latent image. The correspondence relationship with at least one of the outputs is stored.

  Preferably, the image forming apparatus further includes a humidity detection unit that detects humidity, and the storage unit includes at least one of the temperature and humidity of the photosensitive member, the gradation characteristic table, and the maximum density correction amount of the image. The identification means stores at least one of the gradation characteristic table corresponding to the temperature of the photosensitive member detected by the temperature detection means and the humidity detected by the humidity detection means and the maximum density correction amount. Is identified.

  Preferably, in the image forming apparatus, when the humidity detected by the humidity detecting unit is higher than a predetermined value, the specifying unit corresponds to the temperature of the photosensitive member detected by the temperature detecting unit and the humidity detected by the humidity detecting unit. When at least one of the gradation characteristic table and the correction amount of the maximum density is specified at the first time interval and the humidity detected by the humidity detection unit is equal to or lower than a predetermined value, the specification unit At least one of the gradation characteristic table corresponding to the temperature detected by the detection means and the humidity detected by the humidity detection means and the correction amount of the maximum density is a second shorter than the first time interval. Specify by the time interval.

  Preferably, in the image forming apparatus, the specifying unit specifies at least one of the gradation characteristic table corresponding to the temperature of the photoconductor detected by the temperature detecting unit and the maximum density correction amount at a predetermined timing. .

  Preferably, in the image forming apparatus, the specifying unit specifies a gradation characteristic table corresponding to the temperature of the photosensitive member detected by the temperature detecting unit at the first timing, and the photosensitive member detected by the temperature detecting unit. The correction amount of the maximum density corresponding to the temperature is specified at a second timing different from the first timing.

  Preferably, in the image forming apparatus, the specifying unit is at least one of a gradation characteristic table corresponding to a difference between a reference temperature and a temperature of the photosensitive member detected by the temperature detecting unit and a correction amount of the maximum density. Is identified.

  In the image forming apparatus, the reference temperature is preferably a temperature around the image forming apparatus.

  Preferably, the image forming apparatus further includes a table storage unit that stores a gradation characteristic table previously specified by the specifying unit, and the image forming unit includes the gradation characteristic table specified by the specifying unit and the previous time by the specifying unit. When the specified gradation characteristic table is different, the image forming condition is changed.

  Preferably, the image forming apparatus further includes a temperature storage unit that stores the temperature of the photoconductor detected by the temperature detection unit when the specifying unit performs the previous specification. The image forming means includes the temperature of the photoconductor detected by the temperature detecting means when the specifying means performs the current specification, and the temperature of the photoconductor detected by the temperature detecting means when the specifying means performs the previous specification. Are different from each other by a certain value, image formation is performed under the changed image formation conditions.

  An image forming apparatus control method according to another aspect of the present invention is an image forming apparatus control method in which an electrostatic latent image is formed by exposing a charged photoconductor to form an image based on the electrostatic latent image. A temperature detection step for detecting the temperature of the photoconductor, an acquisition step for acquiring a correspondence relationship between the temperature of the photoconductor and at least one of the gradation characteristic table and the correction amount of the maximum density of the image; Based on the correspondence, a specific step for specifying at least one of a gradation characteristic table corresponding to the temperature of the photoconductor detected in the temperature detection step and a correction amount for the maximum density, and a floor specified in the specific step An image forming step of forming an image according to an image forming condition according to at least one of the tone characteristic table and the correction amount of the maximum density.

  A control program for an image forming apparatus according to still another aspect of the present invention forms an electrostatic latent image by exposing a charged photoreceptor and forms an image based on the electrostatic latent image. A temperature detection step for detecting the temperature of the photoconductor, an acquisition step for acquiring a correspondence relationship between the temperature of the photoconductor and at least one of the gradation characteristic table and the correction amount of the maximum density of the image; Based on the correspondence relationship, a specific step for specifying at least one of a gradation characteristic table corresponding to the temperature of the photoconductor detected in the temperature detection step and a correction amount for the maximum density, and a specific step An image forming step for forming an image according to image forming conditions according to at least one of the gradation characteristic table and the maximum density correction amount; To be executed by a computer.

  According to the present invention, it is possible to provide an image forming apparatus capable of quickly obtaining a good image, a control method for the image forming apparatus, and a control program for the image forming apparatus.

1 is a cross-sectional view schematically showing a hardware configuration (overall configuration) of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view schematically illustrating a configuration near a toner image forming unit in the image forming apparatus of FIG. 1. 1 is a block diagram (system configuration diagram) illustrating a configuration of an image forming apparatus 1. FIG. It is a figure which shows the some gradation characteristic table about the gradation reproduction system F1 memorize | stored in the memory | storage part. 5 is a table (gradation characteristic correction table) showing a correspondence relationship between absolute humidity AH1 and temperature difference ΔT (° C.) stored in a storage unit and a plurality of gradation characteristic tables in FIG. It is a figure which shows the some gradation characteristic table about the gradation reproduction system F2 memorize | stored in the memory | storage part. 7 is a table (gradation characteristic correction table) showing a correspondence relationship between absolute humidity AH1 and temperature difference ΔT (° C.) and a plurality of gradation characteristic tables in FIG. 6. It is a table | surface which shows the correspondence (maximum density correction table) of absolute humidity AH1 and temperature difference (DELTA) T (degreeC) which are memorize | stored in the memory | storage part, and the correction amount for correct | amending the maximum density of an image. It is a flowchart which shows the change process of the gradation characteristic table which a control part performs. It is a flowchart which shows the change process of the correction amount of the maximum density of the image which a control part performs. It is sectional drawing which shows typically the hardware constitutions of the image forming apparatus in the 2nd Embodiment of this invention. It is a figure (experimental result) which shows the relationship between the laser intensity level at the time of driving all day in a low humidity environment, and image density. It is a figure (experimental result) which shows the fluctuation amount (difference) of the surface potential of the photosensitive member at the start of printing and the surface potential of the photosensitive member at the end of printing when continuous operation is performed in a low humidity environment. It is the figure which showed the relationship between temperature difference (DELTA) T in a low-humidity environment, and image density at the time of employ | adopting a different laser intensity | strength level. It is a figure which shows the relationship between temperature difference (DELTA) T in each time at the time of single-sided continuous paper passing in a low-humidity environment, and double-sided continuous paper passing, and time passage (rise transition). It is a figure which shows the relationship between the laser intensity level at the time of employ | adopting an error diffusion system, and image density. It is a figure which shows the relationship between the laser intensity level at the time of employ | adopting a screen system, and image density.

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

  [First Embodiment]

  FIG. 1 is a cross-sectional view schematically showing a hardware configuration (overall configuration) of the image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing a configuration in the vicinity of the toner image forming unit in the image forming apparatus of FIG.

  Referring to FIGS. 1 and 2, image forming apparatus 1 is an MFP for monochrome printing, and includes control unit 10, paper feed cassette 50 (paper feed unit), paper discharge tray 51, and print unit 100. With.

  The paper feed cassette 50 is disposed in the lower part of the image forming apparatus 1 so as to be detachable from the housing of the image forming apparatus 1. The paper loaded in the paper feed cassette 50 is fed one by one from the paper feed cassette 50 and sent to the printing unit 100 at the time of printing. The number of paper feed cassettes 50 is not limited to one, and may be larger than that.

  The paper discharge tray 51 is disposed above the housing of the image forming apparatus 1. A sheet on which an image is formed by the printing unit 100 is discharged from the inside of the housing to the discharge tray 51.

  The print unit 100 is disposed inside the housing of the image forming apparatus 1. The printing unit 100 is configured to be able to form a monochrome image on a sheet, and roughly includes a sheet conveying unit 20, a toner image forming unit 30, and a fixing device 40.

  The paper transport unit 20 transports paper along the paper passing path R, and includes a paper feed roller 21, a transport roller 22 (timing roller), and a paper discharge roller 23 (discharge roller). Each of the transport roller 22 and the paper discharge roller 23 transports the paper by rotating the rollers while sandwiching the paper between two opposing rollers, for example. The paper feed roller 21 feeds paper one by one from the paper feed cassette 50. The paper is fed into the housing of the image forming apparatus 1 by the paper feed roller 21. The transport roller 22 transports the paper fed by the paper feed roller 21 to the toner image forming unit 30. The paper discharge roller 23 discharges the paper transported by the transport roller 22 to the paper discharge tray 51. In addition to the above, the paper transport unit 20 may include a roller used for transporting paper.

  The toner image forming unit 30 includes a photoconductor (photosensitive drum) 31, a charger 32 (charging unit), an exposure unit 33 (exposure unit), a developing device 34, a cleaning blade 35, an eraser 36, a transfer unit, and a transfer unit. A roller 37. Each of the charger 32, the exposure unit 33, the developing device 34, the cleaning blade 35, the eraser 36, and the transfer roller 37 is disposed around the cylindrical photosensitive member 31. An exposure unit 33 exists between the charging charger 32 and the developing unit 34. A high voltage power supply unit (not shown) is electrically connected to each of the charging charger 32 and the developing device 34.

  In the toner image forming unit 30, the photoreceptor 31 rotates in the direction indicated by the arrow A1 in FIG. The charging charger 32 supplies electric charge onto the photoconductor 31 and uniformly charges the photoconductor 31. The exposure unit 33 scans the uniformly charged photoconductor 31 with the laser beam LB based on the image data transmitted from the control unit 10 (exposes the photoconductor 31). As a result, a latent image (electrostatic latent image) is formed on the photoreceptor 31. The developing device 34 causes toner to adhere to the photosensitive member 31 on which the latent image is formed by the developing roller 34a that rotates in the direction indicated by the arrow A2 in FIG. As a result, the latent image is developed, and a toner image (developer image) is formed on the photoreceptor 31. Subsequently, a sheet passing between the photosensitive member 31 and the transfer roller 37 is sandwiched between the transfer roller 37 to which a high voltage is applied and the photosensitive member 31. As a result, the toner image is transferred to the paper and an image is formed on the paper. Thereafter, the transfer blade toner on the photoconductor 31 is cleaned by the cleaning blade 35, and the eraser 36 erases the latent image of the unnecessary area formed on the photoconductor 31.

  The fixing device 40 includes a heating roller and a pressure roller. The fixing device 40 passes the paper on which the toner image is formed and fixes the toner image on the paper. The fixing device 40 is conveyed while being sandwiched between a heating roller and a pressure roller, and heats and presses the paper. The sheet that has passed through the fixing device 40 is discharged from the casing of the image forming apparatus 1 to the discharge tray 51 by the discharge roller 23.

  FIG. 3 is a block diagram (system configuration diagram) showing the configuration of the image forming apparatus 1.

  Referring to FIG. 3, control unit 10 of image forming apparatus 1 includes an engine controller 140, MFP controller 146, and storage unit 150. The engine controller 140 executes image formation control by controlling various motors and rollers for image formation. The engine controller 140 also performs a gradation characteristic table and a maximum density correction amount changing process, which will be described later. The MFP controller 146 outputs an image processing instruction to the image processing apparatus 148. The storage unit 150 stores a control program for controlling image forming operations, a program for correcting image density, and the like. As will be described later, the storage unit 150 stores a correspondence relationship between the temperature and humidity of the photosensitive member, and a table (tone characteristic table) indicating the relationship between the image density and the potential of the exposed portion of the photosensitive member. Yes. Further, as will be described later, the storage unit 150 stores a correspondence relationship (maximum density correction table) between the temperature and humidity of the photoreceptor and the correction amount of the maximum density of the image. Each of engine controller 140 and MFP controller 146 includes CPUs 140a and 146a, ROMs 140b and 146b, and RAMs 140c and 146c, respectively, and may be configured by a microcomputer, for example. The engine controller 140 and the MFP controller 146 are connected so as to communicate with each other.

  The engine controller 140 includes a timer 141, a temperature / humidity sensor 142 (an example of humidity detection means) (environment sensor), a photoconductor temperature sensor 143 (an example of temperature detection means) (photoconductor ambient temperature sensor, PC (Photo Conductor). ) Thermistor), development output circuit 144, charging output circuit 145, and sensor 149. The timer 141 measures a predetermined time interval. The temperature / humidity sensor 142 detects the temperature around the image forming apparatus 1 (apparatus ambient temperature) and the relative humidity (humidity environment) around the image forming apparatus 1. The photoreceptor temperature sensor 143 detects the temperature of the atmosphere of the photoreceptor 31 (photoreceptor ambient temperature). The development output circuit 144 controls the potential of the developing roller during development (development potential), and the charging output circuit 145 controls the charging potential (charging potential) of the photosensitive member. The sensor 149 detects the passage of the sheet at the charging point.

  The temperature / humidity sensor 142 may detect the temperature and humidity in the air in an arbitrary temperature / humidity environment in or around the image forming apparatus. For example, the temperature / humidity sensor 142 may detect the temperature and humidity in the image forming apparatus. The photoreceptor temperature sensor 143 may detect the temperature of the photoreceptor, and may detect the temperature of the outer surface of the photoreceptor, for example.

  An operation panel 147 and an image processing device 148 are connected to the MFP controller 146. The operation panel 147 is provided at a position that is visible from the outside, and includes a liquid crystal display unit that is a touch panel, for example. The liquid crystal display unit of the operation panel 147 displays a guidance screen for the user or displays an operation button to accept an instruction by a touch operation from the user. The operation panel is controlled by the MFP controller 146 to display the liquid crystal display unit. When an instruction from the user is received, the operation panel is transmitted to the MFP controller 146. That is, the user can cause the image forming apparatus 1 to perform various operations by performing operations from the operation panel 147. The image processing apparatus 148 controls the amount of laser light LB (exposure amount of the photoconductor 31) that the exposure unit 33 irradiates the photoconductor 31 with.

  The image forming apparatus 1 according to the present exemplary embodiment has a gradation characteristic (gradation characteristic table) and a maximum image density with respect to an image density variation caused by a change in photoreceptor characteristics that occurs when continuous operation is performed in a low humidity environment. By correcting the correction amount, the density fluctuation of the image formed on the sheet is suppressed. Each of the method for changing the gradation characteristic table and the method for changing the correction amount of the maximum density of the image in the image forming apparatus 1 will be described below.

  [How to change the gradation characteristics table]

  The image forming apparatus 1 according to the present embodiment uses the detected temperature and humidity of the photoconductor 31 based on the correspondence between the temperature and humidity of the photoconductor 31 stored in the storage unit 150 and the gradation characteristic table. A corresponding gradation characteristic table is specified. Then, the image forming apparatus 1 forms an image under image forming conditions according to the specified gradation characteristic table. Hereinafter, a method for changing the gradation characteristic table will be described in detail.

  First, the temperature TM1 and the relative humidity H1 around the image forming apparatus 1 are detected using the temperature / humidity sensor 142. Then, the absolute humidity AH1 around the image forming apparatus 1 is calculated based on the temperature TM1 around the image forming apparatus 1 and the relative humidity H1.

  Further, using the photoconductor temperature sensor 143, the photoconductor atmosphere temperature (temperature near the photoconductor 31) TM2 is detected. Then, the difference between the photoconductor ambient temperature TM2 and the temperature TM1 around the image forming apparatus 1 is calculated (obtained), and this difference is set as a temperature difference ΔT (= TM2−TM1).

  The continuous operation status of the image forming apparatus 1 is determined based on the temperature difference ΔT calculated by the above method. The ambient temperature TM1 around the image forming apparatus 1 is a reference temperature, and is maintained substantially constant regardless of the operation state of the apparatus. On the other hand, the photoreceptor ambient temperature TM2 rises due to continuous operation (printing). Accordingly, it is possible to determine the state of continuous operation based on the magnitude of the temperature difference ΔT between the temperature TM1 and the temperature TM2. That is, if the temperature difference ΔT is large, the degree of continuous operation is large, and if the temperature difference ΔT is small, the degree of continuous operation is small.

  Next, a gradation characteristic table is calculated (specified) based on the absolute humidity AH1 and the temperature difference ΔT.

  FIG. 4 is a diagram illustrating a plurality of gradation characteristic tables for the gradation reproduction method F1 stored in the storage unit. The vertical axis in FIG. 4 indicates the amount of toner adhering (to the paper or the photoconductor), and the horizontal axis in FIG. 4 indicates the laser light intensity level (exposure intensity for exposing the photoconductor).

  Referring to FIG. 4, the gradation reproduction method F1 is, for example, an error diffusion method. The toner adhesion amount corresponds to the image density, and the laser light intensity level corresponds to the potential of the exposed portion of the photoreceptor 31. That is, as the laser light intensity level is larger, the amount of change in potential of the exposed portion of the photoconductor 31 becomes larger. Each of the plurality of gradation characteristic tables is No. 1-No. It is numbered 10. Each of the plurality of gradation characteristic tables is a gamma curve showing the relationship between the toner adhesion amount and the laser light intensity level under different temperature conditions and humidity conditions. Each of the plurality of gradation characteristic tables converges to one point when the toner adhesion amount is maximum and minimum, and is different from each other when the toner adhesion amount is an intermediate value thereof.

For example, no. Under the temperature condition and humidity condition in which the gradation characteristic table of 1 is used, the laser light intensity level is corrected to about 8 when about 0.8 (mg / cm ² ) of toner is adhered to a sheet or the like. No. Under the temperature condition and humidity condition in which the gradation characteristic table of 10 is used, the laser light intensity level is corrected to about 6 when about 0.8 (mg / cm ² ) of toner is attached to a sheet or the like.

  FIG. 5 is a table showing a correspondence relationship between the absolute humidity AH1 and the temperature difference ΔT (° C.) stored in the storage unit and the plurality of gradation characteristic tables in FIG. 4 (an example of a first correspondence relationship). (Tone characteristic correction table).

  Referring to FIG. 5, the range of absolute humidity AH1 is defined along the horizontal direction (row direction) in FIG. 5, and the range of temperature difference ΔT is defined along the vertical direction (column direction) in FIG. ing. Regarding the range of absolute humidity AH1, a range of less than 1.4 corresponds to an LL (low temperature and low humidity) environment, and a range of 1.4 to 4.5 is equivalent to an NL (room temperature and low humidity) environment, and is 8.6 or more. The range less than ˜13.4 corresponds to an NN (room temperature and humidity) environment. The range from 20.6 to less than 25.8 corresponds to an HH (high temperature and high humidity) environment. The number given to the gradation characteristic table shown in FIG. 4 is described at the location where the specific absolute humidity AH1 and the temperature difference ΔT intersect.

  For example, when the absolute humidity AH1 is a value in the range of 1.4 or more and less than 4.5 and the temperature difference ΔT is a value in the range of 12 ° C. or more and less than 15 ° C., No. 1 shown in FIG. 4 gradation characteristic tables are calculated. Further, when the absolute humidity AH1 is a value within the range of 16.1 to less than 20.6 as described above, and the temperature difference ΔT is a value within the range of 12 ° C. or more and less than 15 ° C., FIG. No. 8 gradation characteristic tables are calculated.

  Accordingly, the information of the gradation characteristic table shown in FIGS. 4 and 5 includes the absolute humidity AH1 and the temperature difference ΔT, and the variation amount of the image density that varies due to the variation of the exposed portion potential of the photoconductor 31 that occurs during continuous operation. Shows the relationship. Based on the information of the gradation characteristic table shown in FIGS. 4 and 5, the gradation characteristic table corresponding to the absolute humidity AH1 and the temperature difference ΔT at that time is calculated. Then, image formation is performed under the image formation conditions changed (corrected) according to the calculated gradation characteristic table.

  Incidentally, it is preferable that the storage unit 150 stores the information of the gradation characteristic tables as shown in FIGS. 4 and 5 by the number of gradation reproduction methods. In this case, each of the information of the plurality of gradation characteristic tables is different from each other, and corresponds to each of the plurality of gradation reproduction methods. This is because the behavior of the density fluctuation of the image differs depending on the gradation reproduction method. In this case, the gradation reproduction method is designated by the user from the operation panel 147. Since the image formation (printing) is performed based on the gradation reproduction method designated by the user from the operation panel 147, when the gradation characteristic table is calculated, the gradation characteristic table is calculated for all the gradation reproduction methods. May be performed.

  FIG. 6 is a diagram showing a plurality of gradation characteristic tables for the gradation reproduction method F2 stored in the storage unit. The vertical axis in FIG. 6 represents the toner adhesion amount, and the horizontal axis in FIG. 6 represents the laser light intensity level (exposure intensity for exposing the photosensitive member). FIG. 7 is a table (tone characteristic correction table) showing a correspondence relationship (an example of the second correspondence relationship) between the absolute humidity AH1 and the temperature difference ΔT (° C.) and the plurality of gradation property tables in FIG. .

  With reference to FIGS. 6 and 7, the gradation reproduction method F2 is, for example, a screen method. The shapes of the plurality of gradation characteristic tables in FIG. 6 are different from the shapes of the plurality of gradation characteristic tables in FIG. Further, the number described at the location where the specific absolute humidity AH1 and the temperature difference ΔT intersect in FIG. 7 is different from the number described at the location where the specific absolute humidity AH1 and the temperature difference ΔT intersect in FIG. ing. Other information shown in FIGS. 6 and 7 is the same as the information in the gradation characteristic table shown in FIGS. 4 and 5.

  In addition to the above-described two gradation reproduction methods, information on the gradation characteristic table corresponding to another gradation reproduction method such as a dither method may be stored in the storage unit 150.

  Therefore, when information of a plurality of gradation characteristic tables is stored in the storage unit 150, the gradation characteristic table is calculated based on the information of the gradation characteristic table corresponding to the gradation reproduction method selected by the user ( Specified). Then, image formation is performed under the image formation conditions changed (corrected) according to the calculated gradation characteristic table.

  [How to change the maximum image density correction amount]

  The image forming apparatus 1 according to the present embodiment changes (corrects) the correction amount of the maximum density of the image as well as changing the gradation characteristic table. When the correction amount of the maximum density of the image is changed, for example, the gradation characteristic table shown in FIG. 4 is shifted to the high density side (upper side in FIG. 4) or the low density side (lower side in FIG. 4). The image forming apparatus 1 corresponds to the detected temperature and humidity of the photoconductor 31 based on the correspondence relationship between the temperature and humidity of the photoconductor 31 stored in the storage unit 150 and the correction amount of the maximum density of the image. Specify the correction amount of the maximum density of the image. The image forming apparatus 1 forms an image under image forming conditions according to the correction amount of the maximum density of the specified image. Hereinafter, a method for changing the correction amount of the maximum density of the image will be described in detail.

  First, the temperature difference ΔT between the absolute humidity AH1 around the image forming apparatus 1 and the ambient temperature TM2 of the photoconductor and the temperature TM1 around the image forming apparatus 1 is the same as the method for changing the gradation characteristic table described above. And are calculated.

  Next, the correction amount of the maximum density of the image is calculated based on the absolute humidity AH1 and the temperature difference ΔT.

  FIG. 8 shows a correspondence relationship (maximum density correction table) between the absolute humidity AH1 and temperature difference ΔT (° C.) stored in the storage unit and the correction amount for correcting the correction amount of the maximum density of the image. It is a table.

  Referring to FIG. 8, the range of absolute humidity AH1 is defined along the horizontal direction (row direction) in FIG. 8, and the range of temperature difference ΔT is defined along the vertical direction (column direction) in FIG. ing. Regarding the range of absolute humidity AH1, a range of less than 1.4 corresponds to an LL (low temperature and low humidity) environment, and a range of 1.4 to 4.5 is equivalent to an NL (room temperature and low humidity) environment, and is 8.6 or more. The range less than ˜13.4 corresponds to an NN (room temperature and humidity) environment. The range from 20.6 to less than 25.8 corresponds to an HH (high temperature and high humidity) environment. A correction amount for correcting the maximum density of the image is described at a location where the specific absolute humidity AH1 and the temperature difference ΔT intersect. This correction amount is, for example, the correction amount of the charging output (Vc) that is the output of the charging means for charging the photosensitive member. The correction amount may be a correction amount of a development output (Vdc) that is an output of a developing unit for developing the electrostatic latent image. In an image forming apparatus using an electrophotographic process, the maximum density of an image depends on the charge output of the photoconductor and the development output during toner development. Accordingly, the correction amount of the charging output or the development output shown in FIG. 8 corresponds to the correction amount of the maximum density of the image. In FIG. 8, the maximum density correction amount is set to be larger as the humidity is lower and the temperature difference ΔT is larger.

  For example, when the absolute humidity AH1 is a value in the range of 1.4 or more and less than 4.5 and the temperature difference ΔT is a value in the range of 12 ° C. or more and less than 15 ° C., the charge output correction amount is -60. That is, when the reference value of the development output is −400 (V), the charging output is specified as −460 (V). Further, when the absolute humidity AH1 is a value within the range of 16.1 to less than 20.6 as described above, and the temperature difference ΔT is a value within the range of 12 ° C. or more and less than 15 ° C., the charging output The correction amount is specified as -30. That is, when the reference value of the development output is −400 (V), the charging output is specified as −430 (V).

  Therefore, based on the maximum density correction table shown in FIG. 8, the correction amount of the maximum density of the image corresponding to the absolute humidity AH1 and the temperature difference ΔT is calculated (specified). Then, image formation is performed under the image formation conditions changed (corrected) according to the calculated maximum density correction amount of the image.

  [Timing characteristics table and timing for changing the maximum image density correction amount]

  The change (correction) of the above-described gradation characteristic table and the correction amount of the maximum density of the image may be performed at the following timing.

  For example, when the humidity (for example, absolute humidity AH1) detected by the temperature / humidity sensor 142 is higher than a predetermined value, the gradation characteristic table and the maximum density correction amount are changed at the time interval TI1 and detected by the temperature / humidity sensor 142. When the applied humidity (for example, absolute humidity AH1) is equal to or lower than a predetermined value, the gradation characteristic table and the maximum density correction amount may be changed at a time interval TI2 shorter than the time interval TI1. The time interval is measured using a timer 141. The time interval TI2 may be set to 30 seconds, for example. In a low humidity environment, image density fluctuations are more likely to occur than in other environments. Accordingly, in a low-humidity environment, the change timing can be made shorter than usual, and the gradation characteristic table and the maximum density correction amount can be changed a lot to reduce image density fluctuation.

  The gradation characteristic table and the maximum density correction amount of the image may be calculated at a predetermined timing TG1, and image formation may be performed based on the calculated gradation characteristic table and the maximum density correction amount of the image. Further, the previously calculated gradation characteristic table is stored in the storage unit 150, and the previously calculated gradation characteristic table is compared with the currently calculated gradation characteristic table. Conditions may be changed.

  Further, the gradation characteristic table may be calculated at timing TG1, and the correction amount of the maximum density of the image may be calculated at timing TG2 different from timing TG1.

  In particular, since a predetermined time is required when changing the gradation characteristic table, downtime may occur if switching (change) is performed during printing. Since the occurrence of downtime leads to a decrease in productivity, it is preferable that the gradation characteristic table is changed with a minimum frequency. Therefore, since it is experimentally known that the timing at which image density correction is required during continuous operation is about every 1 minute from the experiment, it is preferable that the gradation characteristic table is changed about every 1 minute. On the other hand, it is preferable that the correction amount of the maximum density of the image is changed for each sheet (the first sheet). Thereby, the image density fluctuation can be further reduced.

  Further, the temperature difference ΔTA when the gradation characteristic table and the maximum density correction amount were previously calculated (specified) (or the photosensitive member temperature sensor 143 detects when the gradation characteristic table and the maximum density correction amount were previously calculated). The photoconductor ambient temperature TM2A) is stored in the storage unit 150, and the temperature difference ΔT (or the gradation characteristic table when the gradation characteristic table and the maximum density correction amount are calculated this time) is calculated. Even if the image forming condition is changed when the photosensitive member ambient temperature TM2) detected by the body temperature sensor 143 and the temperature difference ΔTA (or the photosensitive member ambient temperature TM2A) stored in the storage unit 150 are different from each other by a certain value or more. Good.

  Further, when the calculated temperature difference ΔT is in the vicinity of the threshold value in the range of the temperature difference ΔT defined in the table showing the correspondence relationship such as FIG. 5, for each timing at which the gradation characteristic table (gradation characteristic) is calculated. There is a possibility of calculating different gradation characteristic tables (acquiring different gradation characteristics). For example, in the case where the gradation characteristic table is calculated based on the table of FIG. 5 and the detected temperature difference ΔT is around 10.5 ° C., no. 3 is calculated, and No. 3 is obtained at the second timing after the elapse of a predetermined time from the first timing. 2 gradation characteristic tables may be calculated. However, in such a case, it cannot be said that the photosensitive member ambient temperature has increased due to continuous operation, and it is expected that no change in image density has occurred, so there is no need to change the gradation characteristic table. Therefore, overcorrection can be prevented by comparing the temperature difference ΔT when the gradation characteristic table is changed with the previous temperature difference ΔTA. In this case, when the current temperature difference ΔT is 10 ° C. and the difference from the previous temperature difference ΔTA is as large as 1.5 ° C., for example, the gradation characteristics may be corrected.

  [Flowchart showing change process of gradation characteristic table and correction amount of maximum density of image]

  FIG. 9 is a flowchart showing the gradation characteristic table changing process executed by the control unit.

  Referring to FIG. 9, CPU 140a of engine controller 140 determines whether or not a predetermined timing has elapsed (S1). The CPU 140a may determine whether or not a predetermined timing has elapsed depending on whether or not a predetermined time interval has elapsed in the timer 141. In this case, the CPU 140a may change the time interval (timing) to the time interval TI1 or the time interval TI2 according to the calculated value of the absolute humidity AH1. In addition, the CPU 140a determines whether or not the predetermined timing has elapsed, or determines whether or not the predetermined timing has elapsed, and calculates the temperature difference ΔT calculated this time and the gradation characteristic table last time. It may be determined whether or not the difference from the temperature difference ΔTA when the temperature is set is greater than a certain value.

  When it is determined that the predetermined timing has elapsed and / or when it is determined that the difference between the temperature difference ΔT and the temperature difference ΔTA is equal to or greater than a certain value (YES in step S1), the CPU 140a acquires temperature / humidity information (S3). ). The CPU 140a calculates the absolute humidity AH1 and the temperature difference ΔT from the temperature TM1 and the humidity H1 measured by the temperature / humidity sensor 142 and the temperature TM2 measured by the photoconductor temperature sensor 143. Subsequently, the CPU 140a calculates (specifies) the gradation characteristic table corresponding to the absolute humidity AH1 and the temperature difference ΔT based on the information of the gradation characteristic table shown in FIGS. 4 and 5, for example (S5). In step S5, when information of a plurality of gradation characteristic tables is stored in the storage unit 150, the CPU 140a prompts the user to select a gradation reproduction method from the operation panel 147, and the gradation reproduction method selected by the user. The gradation characteristic table may be specified based on the information of the gradation characteristic table corresponding to.

  Next, the CPU 140a compares the previously calculated (specified) gradation characteristic table with the currently calculated gradation characteristic table (S7). If they are different (YES in S7), the CPU 140a notifies the MFP controller 146 of the calculated gradation characteristic table numbers (for example, numbers No. 1 to No. 10 shown in FIG. 4) (S9). The controller 146 notifies (instructs) the gradation characteristic table (gradation characteristics) notified (instructed) from the engine controller 140 to the image processing device 148 (S11). The image processing apparatus 148 changes the gradation characteristic table by adjusting the exposure amount based on the notified gradation characteristic table. Thus, the CPU 140a ends the process.

  If it is determined in step S7 that the previously calculated gradation characteristic table matches the currently calculated gradation characteristic table (NO in S7), the CPU 140a does not need to change the gradation characteristic table. Return to processing.

  FIG. 10 is a flowchart illustrating a process for changing the correction amount of the maximum density of the image executed by the control unit.

  Referring to FIG. 10, CPU 140a of engine controller 140 determines whether there is a next sheet to be printed (S11). When there is a next sheet (YES in S11), the CPU 140a uses the sensor 149 to determine whether or not the rear end of the sheet being processed has passed a predetermined position (for example, a charging point) (S13). When the trailing edge of the sheet passes the predetermined position (YES in S13), the CPU 140a acquires temperature / humidity information (S15). This makes it possible to determine the output of charging and developing after the trailing edge of the paper being processed has passed the charging point. In step S15, the CPU 140a calculates the absolute humidity AH1 and the temperature difference ΔT from the temperature TM1 and humidity H1 measured by the temperature / humidity sensor 142 and the temperature TM2 measured by the photoconductor temperature sensor 143. Subsequently, the CPU 140a calculates (specifies) the correction amount of the maximum density of the image corresponding to the absolute humidity AH1 and the temperature difference ΔT based on, for example, information in the gradation characteristic tables shown in FIGS. 4 and 5 (S17).

  Next, the CPU 140a calculates a charge output value and a development output value based on the calculated maximum density correction amount of the image (S19), and calculates the charge output value and the development output value for each of the charge output circuit and the development output circuit. (S21). Thereby, correction (change) of the correction amount of the maximum density of the image is performed. Next, the CPU 140a returns to Step S11. In step S11, when there is no next sheet to be printed (NO in S11), the CPU 140a ends the process.

  [Second Embodiment]

  The image forming apparatus according to the second embodiment is different from the image forming apparatus according to the first embodiment in that it is a four-cycle MFP capable of color printing. FIG. 11 is a cross-sectional view schematically showing a hardware configuration of the image forming apparatus according to the second embodiment of the present invention.

  Referring to FIG. 11, toner image forming unit 30 further includes an intermediate transfer belt 301, a transfer roller 302 (primary transfer roller), and rollers 301a and 301b. The intermediate transfer belt 301 has an annular shape and is stretched between the rollers 301a and 301b. The intermediate transfer belt 301 rotates in conjunction with the paper transport unit 20. The transfer roller 37 (secondary transfer roller) is disposed so as to face a portion of the intermediate transfer belt 301 that is in contact with one roller 301b. The interval between the transfer roller 37 and the intermediate transfer belt 301 is adjusted by a pressure contact / separation mechanism (not shown). The sheet is conveyed while being sandwiched between the intermediate transfer belt 301 and the transfer roller 37. The transfer roller 302 is disposed at a position facing the photoconductor 31 with the intermediate transfer belt 301 interposed therebetween.

  The developing device of the toner image forming unit 30 includes a developing rack unit 340. The developing rack unit 340 includes four cartridges 341C, 341M, 341Y, and 341K corresponding to the colors C (cyan), M (magenta), Y (yellow), and K (black) (hereinafter collectively referred to as the cartridge 341). May be called). The cartridge 341 includes toner and a developing roller that develops the toner. The developing rack unit 340 is rotatably provided.

  At the time of image formation, the developing rack unit 340 is rotated so that toner of a specific color can be supplied to the photoconductor 31. When a latent image is formed on the photoconductor 31 by the operation of the charging charger 32 and the exposure unit 33, the developing rack unit 340 forms a toner image of a specific color by attaching toner on the photoconductor 31 ( developing). The toner image of a specific color formed on the photoreceptor 31 is primarily transferred to the intermediate transfer belt 301 by the transfer roller 302 to which a high voltage is applied. Thereafter, the transfer blade toner on the photoconductor 31 is cleaned by the cleaning blade 35, and the eraser 36 erases the latent image of the unnecessary area formed on the photoconductor 31.

  The developing rack unit 340 forms a toner image on the photoconductor 31 sequentially for each color of CMYK by the above-described method, and the toner image formed on the photoconductor 31 is transferred to the intermediate transfer belt 301. When the four color toner images are superimposed on the intermediate transfer belt 301, the transfer roller 37 presses the sheet against the intermediate transfer belt 301. As a result, the toner image on the intermediate transfer belt 301 is secondarily transferred to the sheet. The paper on which the toner image is formed is discharged by the paper discharge roller 23 through a fixing process in the fixing device 40.

  The image forming apparatus 1 further includes a rack drive motor 380 for rotating the developing rack unit 340. The control unit 10 controls the rotation of the developing rack unit 340 by controlling the rotation of the rack drive motor 380.

  Since other configurations and operations are the same as those of the image forming apparatus according to the first embodiment, the same members are denoted by the same reference numerals, and description thereof will not be repeated.

  In the image forming apparatus according to this embodiment, the same gradation characteristic table as that of the first embodiment and the correction amount of the maximum density of the image are changed for each color of CMYK.

  [Effect of the embodiment]

  The inventors of the present application have obtained the following knowledge about the density fluctuation of the image and the potential fluctuation of the photoreceptor in a low humidity environment.

  FIG. 12 is a diagram (experimental result) showing the relationship between the laser intensity level and the image density when operated all day (continuously) in a low humidity environment. In FIG. 12, the solid line indicates the relationship at the start of printing (the beginning of the day (morning)), and the broken line indicates the relationship at the end of printing (the end of the day (evening)).

  Referring to FIG. 12, the image density at the end of printing is generally lower than the image density at the start of printing. When the laser intensity level corresponding to the range of the halftone density is in the range of 4.5 to 9.0, the printed image is particularly lowered.

  FIG. 13 is a diagram (experimental results) showing the amount of variation (difference) between the surface potential of the photosensitive member at the start of printing and the surface potential of the photosensitive member at the end of printing when continuous operation is performed in a low humidity environment. . FIG. 13 shows the fluctuation amount of the surface potential of the photosensitive member for each laser intensity level.

  Referring to FIG. 13, when the laser intensity level is in the range of 8 to 11, the amount of fluctuation of the surface potential of the photoreceptor is large. This laser intensity level range corresponds to the range from the halftone density to the maximum density. When comparing FIG. 12 and FIG. 13, there is a correlation between the change in the surface potential of the photoconductor from the halftone to the maximum density due to the change in sensitivity of the photoconductor and the decrease in the image density (image density change). I understand that. Although it is estimated that there are “development characteristic change” and “photoconductor characteristic change” as the cause of the halftone density decrease in FIG. 12, the result of FIG. It can be seen that this is due to characteristic changes.

  FIG. 14 is a diagram showing the relationship between the temperature difference ΔT in a low humidity environment and the image density when different laser intensity levels are employed. FIG. 14 shows the relationship when three laser intensity levels of 4, 8, and 12 are employed. The temperature difference ΔT is a difference between the photoconductor ambient temperature TM2 and the temperature TM1 around the image forming apparatus 1, and the temperature TM1 around the image forming apparatus is estimated to be a substantially constant value regardless of the operation state of the apparatus. The Therefore, if the temperature difference ΔT is large, it is possible to determine that the photosensitive member ambient temperature TM2 is increased and the continuous operation is performed.

  Referring to FIG. 14, at each laser intensity level (at each gradation), the image density varies with changes in temperature difference ΔT, and there is a correlation between temperature difference ΔT and image density variation. I understand that. In particular, in the case of a halftone having a laser intensity level of 8, the correlation between the temperature difference ΔT and the image density fluctuation is large. Therefore, it can be seen that the image density decreases as the photosensitive member ambient temperature TM2 increases.

  Subsequently, the inventors of the present application examined the fluctuation of the temperature difference ΔT in each of the single-sided paper passing and the double-sided paper passing. FIG. 15 is a diagram illustrating the relationship between the temperature difference ΔT and the passage of time (increase in transition) at the time of single-sided continuous paper passage and double-sided continuous paper passage in a low humidity environment.

  Referring to FIG. 15, the temperature difference ΔT is saturated at about 8 ° C. during one-sided continuous sheet passing, whereas the temperature difference ΔT is increased to about 21 ° C. during two-sided sheet passing. Therefore, it can be seen that the temperature difference ΔT fluctuates more greatly during double-sided continuous paper feeding. Regarding this result, since the photoreceptor temperature fluctuates depending on the temperature of the paper (recording medium), it is presumed that there is a difference in the variation amount of the temperature difference ΔT between when single-sided and double-sided. In other words, in the case of double-sided paper passing, the paper passes through the fixing unit and is heated and then passed again from the re-feeding port to the surface of the photosensitive member. It is speculated that. Therefore, even if the number of sheets to be passed (count number) is the same, it can be seen that there is a difference in the temperature difference ΔT between when single-sided paper is passed and when double-sided paper is passed.

  Furthermore, the inventors of the present application have investigated the difference in the amount of variation in the density of the image formed on the paper when different gradation reproduction methods (image reproduction methods) are employed. FIG. 16 is a diagram showing the relationship between the laser intensity level and the image density when the error diffusion method is employed. FIG. 17 is a diagram showing the relationship between the laser intensity level and the image density when the screen method is employed. 16 and 17, HS indicates the relationship at the start of printing (morning) when the image forming apparatus is used in a high temperature and high humidity environment, and HE indicates the case where the image forming apparatus is used in a high temperature and high humidity environment. The relationship at the end of printing (evening) is shown. LS indicates the relationship at the start of printing (morning) when the image forming apparatus is used in a low temperature and low humidity environment, and LE indicates the relationship at the end of printing (evening) when the image forming apparatus is used in a low temperature and low humidity environment. Show.

  Referring to FIG. 16, when the image forming apparatus is used in a high temperature and high humidity environment, the image density hardly fluctuates between the start of printing (HS) and the end of printing (HE). On the other hand, when the image forming apparatus is used in a low-temperature and low-humidity environment, the image density varies greatly between the start of printing (LS) and the end of printing (LE). The image density is particularly remarkable at halftone density.

  Referring to FIG. 17, even when the screen method is adopted, the image density is large at the start of printing (LS) and at the end of printing (LE) in the low-temperature and low-humidity environment as in the case of employing the error diffusion method. It has fluctuated. However, in both the high temperature and high humidity environment and the low temperature and low humidity environment, the variation amount of the image density when the screen method is adopted is different from the variation amount of the image density when the error diffusion method is adopted. Therefore, it can be seen that when the gradation characteristics are corrected, the correction is preferably performed according to each gradation reproduction method.

  From the above results, the following knowledge was obtained. i) A decrease in density occurs due to a change in sensitivity of the photoreceptor during continuous operation in a low humidity environment. ii) Continuous operation can be estimated from the temperature difference ΔT. iii) It is preferable to correct the gradation characteristics according to the gradation reproduction method.

  Based on the above knowledge, according to the image forming apparatus and the control method of the image forming apparatus (control mounted in the model) in the present embodiment, the potential detecting means and the density detecting means of the photosensitive drum are not used ( (Even an image forming apparatus that does not have an image stabilization mechanism) By correcting (changing) the correction amount of the maximum density of the image and the gradation characteristic table, the potential of the exposed portion by continuous operation in a low humidity environment Variations in image density and halftone density due to the decrease can be corrected. As a result, a good image can be obtained quickly. Further, unlike the technique for correcting the density by switching the maximum light amount of the exposure unit, an expensive exposure unit device is not required. As an alternative to correcting the maximum light amount of the exposure unit, the cost can be reduced by correcting the potential (maximum density) for charging and developing (an inexpensive image forming apparatus can be provided).

  Further, by correcting not only the maximum density correction amount but also the gradation characteristics, it is possible to reduce the fluctuation of the latent image contrast potential due to the change in PIDC of the exposure unit.

  Furthermore, a more accurate gradation characteristic table can be calculated by using information of different gradation characteristic tables depending on the gradation reproduction method to be employed.

  [Others]

  In the above-described embodiment, the case where the image forming condition is controlled based on the temperature difference ΔT and the absolute humidity AH1 has been described. However, in the present invention, the image forming condition is controlled based on at least the temperature of the photoconductor. Just do it. The storage unit 150 only needs to store the correspondence between the temperature of the photoconductor and the gradation characteristic table.

  In the above-described embodiment, the case where the ambient temperature TM1 of the image forming apparatus 1 is set as a reference temperature has been described. Instead of this, photosensitivity when the power supply of the image forming apparatus 1 is turned on at the start of use is shown. The body temperature or the like may be the reference temperature. Further, the gradation characteristic table may be changed based on the relative humidity without calculating the absolute humidity.

  The photoconductor 31 described in the above embodiment is preferably a photoconductor whose light attenuation characteristic changes. An example of such a photoreceptor is one using a CGL layer.

  In the above-described embodiment, the case where the ambient temperature TM1 and the relative humidity H1 of the image forming apparatus 1 are measured by the temperature and humidity sensor has been described. However, the temperature and humidity of the image forming apparatus 1 are measured by different configurations. Also good.

  In the above-described embodiment, the case where both the gradation characteristic table and the correction amount of the maximum density of the image are specified has been described. However, in the present invention, the gradation characteristic table corresponding to the detected temperature of the photoconductor. In addition, at least one of the correction amount of the maximum density and the maximum density correction amount may be specified, and image formation may be performed according to the image forming condition according to at least one of the specified gradation characteristic table and the correction amount of the maximum density.

  In the above-described embodiment, the timing for specifying the gradation characteristic table and the maximum density correction amount of the image has been described. However, the gradation characteristic table and the maximum density correction amount of the image are set at a predetermined (arbitrary) timing. It only has to be specified.

  The processing in the above embodiment may be performed by software or by using a hardware circuit.

  A program for executing the processing in the above-described embodiment can be provided, or the program can be recorded on a recording medium such as a CD-ROM, a flexible disk, a hard disk, a ROM, a RAM, or a memory card and provided to the user. It may be. The program may be downloaded to the apparatus via a communication line such as the Internet. The processing described in the text in the above flowchart is executed by the CPU according to the program.

  The above-described embodiment is to be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Control part 20 Paper conveyance part 21 Paper feed roller 22 Conveyance roller 23 Paper discharge roller 30 Toner image formation part 31 Photoconductor 32 Charging charger 33 Exposure part 34 Developer 34a Development roller 35 Cleaning blade 36 Eraser 37,302 Transfer roller 40 Fixing device 50 Paper feed cassette 51 Paper discharge tray 100 Print unit 140 Engine controller 140a, 146a CPU
140b, 146b ROM
140c, 146c RAM
141 Timer 142 Temperature / humidity sensor 143 Photoconductor temperature sensor 144 Development output circuit 145 Charging output circuit 146 MFP controller 147 Operation panel 148 Image processing device 149 Sensor 150 Storage unit 301 Intermediate transfer belt 301a, 301b Roller 340 Development rack unit 341, 341C, 341M, 341Y, 341K Cartridge 380 Rack drive motor LB Laser light R Paper path

Claims (14)

An image forming apparatus that forms an electrostatic latent image by exposing a charged photoreceptor and forms an image based on the electrostatic latent image,
Temperature detecting means for detecting the temperature of the photoreceptor;
Storage means for storing a correspondence relationship between the temperature of the photosensitive member and at least one of the gradation characteristic table and the correction amount of the maximum density of the image;
A specifying unit that specifies at least one of a gradation characteristic table corresponding to the temperature of the photoconductor detected by the temperature detection unit and a correction amount of the maximum density based on the correspondence relationship;
An image forming apparatus comprising: an image forming unit configured to form an image according to an image forming condition according to at least one of the gradation characteristic table specified by the specifying unit and the maximum density correction amount.   The image forming apparatus according to claim 1, wherein the gradation characteristic table is a curve indicating a relationship between a toner adhesion amount and an exposure intensity for exposing the photosensitive member.   The storage means includes a first correspondence relationship between the temperature of the photosensitive member and a gradation characteristic table when the first gradation reproducing method is used, the temperature of the photosensitive member, and a second gradation reproducing method. The image forming apparatus according to claim 1, wherein a second correspondence relationship with a gradation characteristic table in the case of using is stored.   The storage means is at least one of a temperature of the photosensitive member, a charging output that is an output of the charging means for charging the photosensitive member, and a developing output that is an output of the developing means for developing the electrostatic latent image. The image forming apparatus according to claim 1, which stores a correspondence relationship between the image forming apparatus and the image forming apparatus. It further comprises a humidity detection means for detecting humidity,
The storage means stores a correspondence relationship between the temperature and humidity of the photosensitive member and at least one of a gradation characteristic table and a correction amount of the maximum density of the image,
The specifying means specifies at least one of a temperature characteristic of the photosensitive member detected by the temperature detecting means and a gradation characteristic table corresponding to the humidity detected by the humidity detecting means and a maximum density correction amount; The image forming apparatus according to claim 1. When the humidity detected by the humidity detecting means is higher than a predetermined value, the specifying means is a gradation characteristic corresponding to the temperature of the photoreceptor detected by the temperature detecting means and the humidity detected by the humidity detecting means. Specify at least one of the correction amount of the table and the maximum density at the first time interval,
When the humidity detected by the humidity detecting means is equal to or lower than a predetermined value, the specifying means is a gradation corresponding to the temperature of the photoreceptor detected by the temperature detecting means and the humidity detected by the humidity detecting means. The image forming apparatus according to claim 5, wherein at least one of the characteristic table and the maximum density correction amount is specified at a second time interval shorter than the first time interval.   The specifying unit specifies at least one of a gradation characteristic table corresponding to the temperature of the photosensitive member detected by the temperature detecting unit and a correction amount of the maximum density at a predetermined timing. The image forming apparatus according to any one of the above.   The specifying unit specifies a gradation characteristic table corresponding to the temperature of the photosensitive member detected by the temperature detecting unit at a first timing, and a maximum corresponding to the temperature of the photosensitive member detected by the temperature detecting unit. The image forming apparatus according to claim 7, wherein the density correction amount is specified at a second timing different from the first timing.   The specifying unit specifies at least one of a gradation characteristic table corresponding to a difference between a reference temperature and a temperature of the photosensitive member detected by the temperature detecting unit and a maximum density correction amount. The image forming apparatus according to any one of 1 to 8.   The image forming apparatus according to claim 9, wherein the reference temperature is a temperature around the image forming apparatus. Table storage means for storing a gradation characteristic table specified last time by the specifying means;
11. The image forming unit according to claim 1, wherein the image forming unit changes an image forming condition when the gradation characteristic table specified by the specifying unit is different from the gradation characteristic table specified last time by the specifying unit. The image forming apparatus according to any one of the above. A temperature storage means for storing the temperature of the photoconductor detected by the temperature detection means when the specifying means performed the previous specification;
The image forming unit detects the temperature of the photosensitive member detected by the temperature detecting unit when the specifying unit performs the current specification, and the temperature detecting unit detects the temperature when the specifying unit performs the previous specification. The image forming apparatus according to claim 1, wherein the image forming is performed under the changed image forming condition when the temperature of the photoconductor is different from a predetermined value or more. A method of controlling an image forming apparatus that forms an electrostatic latent image by exposing a charged photoreceptor and forms an image based on the electrostatic latent image,
A temperature detecting step for detecting the temperature of the photoreceptor;
An acquisition step of acquiring a correspondence relationship between the temperature of the photosensitive member and at least one of the correction amount of the gradation characteristic table and the maximum density of the image;
A specifying step of specifying at least one of a gradation characteristic table corresponding to the temperature of the photoconductor detected in the temperature detection step and a correction amount of the maximum density based on the correspondence relationship;
And an image forming step for forming an image according to an image forming condition according to at least one of the gradation characteristic table specified in the specifying step and the correction amount of the maximum density. A control program for an image forming apparatus that forms an electrostatic latent image by exposing a charged photoreceptor and forms an image based on the electrostatic latent image,
A temperature detecting step for detecting the temperature of the photoreceptor;
An acquisition step of acquiring a correspondence relationship between the temperature of the photosensitive member and at least one of the correction amount of the gradation characteristic table and the maximum density of the image;
A specifying step of specifying at least one of a gradation characteristic table corresponding to the temperature of the photoconductor detected in the temperature detection step and a correction amount of the maximum density based on the correspondence relationship;
Control of an image forming apparatus that causes a computer to execute an image forming step for forming an image according to an image forming condition according to at least one of the gradation characteristic table specified in the specifying step and the correction amount of the maximum density program.

Images