JP2012032547A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus having means for density correction to obtain stable print density.SOLUTION: An image forming apparatus that forms a density detection pattern on a conveyance belt to correct density of an image, and forms an image on a medium includes: means for obtaining resistance information of a medium; means for obtaining information on an amount of reverse transcription of the media based on the obtained resistance information; and means for correcting an image forming condition during the image forming on a media based on the obtained information on an amount of reverse transcription of the media.

Description

  The present invention relates to an image forming apparatus such as an electrophotographic printer or copying machine that forms an image by transferring a toner image formed on an image carrier onto a medium.

  In general, an image forming apparatus such as a color electrophotographic printer uses a plurality of image forming units including a photosensitive drum, a charging roller, an exposure head, a developing roller, and the like, and a tandem image forming apparatus uses black (K). , Yellow (Y), magenta (M), and cyan (C) image forming units are arranged in series on the upper surface of the conveyance belt, and are electrostatically adsorbed onto the conveyance belt. Then, a toner image of each set color is sequentially transferred to form a color image.

  In an image forming apparatus having such a configuration, the internal environment such as the ambient temperature and humidity of each part in the printer changes due to changes in various external environments such as the temperature and humidity at the installation location of the apparatus. Therefore, the density correction is performed by detecting the image density periodically or as necessary.

  In a conventional image forming apparatus, in order to perform density correction, a density detection pattern of each set color composed of three types of duty is continuously printed on the conveyance belt, and the density of the image density of each density detection pattern is detected. The light amount of the exposure head and the developing voltage are corrected based on the difference between the detected density and the target value of each duty (see, for example, Patent Document 1).

JP 2004-258281 (paragraphs 0012-0033, FIGS. 1 and 4)

  However, in the above-described conventional technology, since the density detection pattern of each set color is continuously printed on the conveyance belt, the toner of the toner image that has been transferred first is arranged on the downstream side. There is a problem in that density reduction occurs due to a so-called reverse transfer phenomenon that returns to the body drum, an error occurs in density correction, and the printing density in printing on paper becomes unstable.

  SUMMARY An advantage of some aspects of the invention is that it provides a density correction unit that can obtain a stable printing density.

  In order to solve the above-mentioned problem, in an image forming apparatus that forms a density detection pattern on a conveyance belt to perform density correction and forms an image on a medium, means for acquiring resistance information of the medium; Means for acquiring medium reverse transfer amount information of the medium based on the acquired resistance information, and means for correcting image forming conditions when forming an image on the medium based on the acquired medium reverse transfer amount information And.

  As a result, the present invention has the effect of preventing a decrease in density due to the reverse transfer phenomenon caused by the internal environment of the printer and the type of medium, and always obtaining a stable printing density.

Explanatory drawing which shows the side of schematic structure of the printer of Example 1. FIG. Explanatory drawing which shows the density | concentration sensor of Example 1. FIG. FIG. 3 is a block diagram illustrating a configuration of a control system of the printer according to the first embodiment. Explanatory drawing which shows the structural example of the voltage density value conversion coefficient table of Example 1. FIG. The graph which shows the output characteristic of the density | concentration sensor of Example 1 Explanatory drawing which shows the structural example of the density | concentration target value table of Example 1. FIG. Explanatory drawing which shows the structural example of the developing voltage adjustment amount table of Example 1. FIG. Explanatory drawing which shows the structural example of the element drive time adjustment amount table of Example 1. FIG. Explanatory drawing which shows the structural example of the setting reverse transfer amount information table of Example 1. FIG. Explanatory drawing which shows the structural example of the volume resistivity correction coefficient table of Example 1. FIG. FIG. 3 is an explanatory diagram illustrating a configuration example of a reference medium reverse transfer amount information table according to the first embodiment. 6 is a graph showing the relationship between the volume resistivity of the paper and the medium reverse transfer amount in Example 1. FIG. 3 is a flowchart illustrating print job processing of the printer according to the first embodiment. Explanatory drawing which shows the density | concentration detection pattern of Example 1. FIG. Explanatory drawing which shows the printing method of the density | concentration detection pattern when there is no reverse transfer of Example 1. Explanatory drawing which shows the example of a structure of the detection density value table of the 1st time of Example 1. FIG. Explanatory drawing which shows the structural example of the detection density value table of the 2nd time of Example 1. FIG. Explanatory drawing which shows the structural example of the detection density value table when there is no reverse transfer of Example 1. Explanatory drawing which shows the printing method of the density | concentration detection pattern in case there exists reverse transfer of Example 1. FIG. Explanatory drawing which shows the example of a structure of the detection density value table in case there exists reverse transcription of Example 1. Explanatory drawing which shows the structural example of the present condition reverse transfer amount information table of Example 1. FIG. Explanatory drawing which shows the structural example of the reverse transfer amount correction factor table of Example 1. FIG. Explanatory drawing which shows the structural example of the medium reverse transfer amount information table of Example 1. FIG. Explanatory drawing which shows the concrete numerical example of the density | concentration target value table of Example 1. FIG. Explanatory drawing which shows the specific numerical example of a detection density value table when there is no reverse transfer of Example 1. Explanatory drawing which shows the specific numerical example of the detection density value table when there exists reverse transfer of Example 1. Explanatory drawing which shows the concrete numerical example of the developing voltage adjustment amount table of Example 1. FIG. Explanatory drawing which shows the specific numerical example of the element drive time adjustment amount table of Example 1. FIG. Explanatory drawing which shows the concrete numerical example of the present condition reverse transfer amount information table of Example 1. FIG. Explanatory drawing which shows the specific numerical example of the setting reverse transfer amount information table of Example 1. FIG. Explanatory drawing which shows the specific numerical example of the reverse transfer amount correction factor table of Example 1. Explanatory drawing which shows the specific numerical example of the volume resistivity correction coefficient table of Example 1. Explanatory drawing which shows the concrete numerical example of the reference | standard medium reverse transfer amount information table of Example 1. FIG. Explanatory drawing which shows the concrete numerical example of the medium reverse transfer amount information table of Example 1. FIG. Explanatory drawing which shows the effect of Example 1 Explanatory drawing which shows the side of schematic structure of the printer of Example 2. FIG. Explanatory drawing which shows the medium resistance measuring mechanism of Example 2. Explanatory drawing which shows the electrical resistance measurement circuit of the medium resistance measurement mechanism of Example 2. FIG. 3 is a block diagram illustrating a configuration of a printer control system according to the second embodiment. Explanatory drawing which shows the structural example of the resistivity reverse transfer amount conversion coefficient table of Example 2. FIG. Graph showing the relationship between the volume resistivity of the paper of Example 2 and the black medium reverse transfer amount Flowchart illustrating print job processing of the printer according to the second embodiment. Explanatory drawing which shows the structural example of the medium reverse transfer amount information table of Example 2. FIG. Explanatory drawing which shows the specific numerical example of the resistivity reverse transfer amount conversion coefficient table of Example 2. Explanatory drawing which shows the specific numerical example of the medium reverse transfer amount information table of Example 2. FIG. Explanatory drawing which shows the effect of Example 2

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the drawings.

  In FIG. 1, reference numeral 1 denotes an electrophotographic printer as an image forming apparatus, which is configured to be able to print an image based on input print data on a paper P as a printing medium. .

  Reference numeral 2 denotes a paper conveyance path, which is arranged in an approximately S shape in the apparatus housing of the printer 1. A paper feed accommodation cassette 3 for accommodating paper P is arranged at one end, and printing is performed at the other end. A stacker 4 is provided for collecting the sheets P that have been finished.

  A hopping roller 6 is provided at the connecting portion between the paper transport path 2 and the paper feed storage cassette 3 to feed the paper P fed from the paper feed storage cassette 3 by a pickup roller (not shown) to the paper transport path 2 one by one. The sheet P fed by the hopping roller 6 driven by the hopping motor 6a (see FIG. 3) is disposed opposite to the registration roller 7 driven by the registration motor 7a (see FIG. 3) by the sheet transport path 2. After the skew is corrected by the registration roller 7 and the pinch roller 8 (referred to as a state in which the paper P is conveyed obliquely), it is passed over the drive roller 9 and the tension roller 10. The conveyance belt 11 is conveyed between the tension roller 10 and the adsorption roller 12 disposed opposite to the conveyance belt 11, and the adsorption roller Is electrostatically attracted to the upper surface of the pressing has been conveyor belt 11 to conveyor belt 11 by the 2 and the tension roller 10.

  The sheet P electrostatically adsorbed on the conveyance belt 11 includes a plurality of image forming units 13 disposed on the upper surface of the conveyance belt 11 and a transfer roller 14 disposed inside the conveyance belt 11 so as to face the image forming unit 13. The toner image as the developer image is transferred onto the paper P by the electric field generated by the high voltage applied from the transfer voltage generator 14a (see FIG. 3). After being fixed on the paper P by pressure and heat by a fixing device 17 constituted by a pressure roller 16 that pressurizes the paper, it is further transported by the paper transport path 2 and discharged onto the stacker 4.

  Further, conveyance monitoring sensors 18a and 18b for detecting the position of the paper P are respectively arranged before and after the registration roller 7 in the paper conveyance path 2, and the conveyance direction (paper) of the paper P of the driving roller 9 of the conveyance belt 11 is arranged. On the downstream side of the conveyance direction) and upstream of the fixing device 17, a conveyance monitoring sensor 18c for checking the paper P that has failed to be separated from the conveyance belt 11 or detecting the trailing edge of the paper P is provided. A conveyance monitoring sensor 18 d for monitoring jamming in the fixing device 17 and winding of the paper P around the heat roller 15 is disposed on the downstream side of the fixing device 17.

  Note that a sheet guide for guiding the sheet P conveyed through the sheet conveyance path 2 is provided at a portion of the sheet conveyance path 2 excluding the conveyance belt 11.

  A heater 20 such as a halogen lamp that functions as a heat source is built in the heat roller 15 that is rotationally driven by the heater motor 15a (see FIG. 3) of the fixing device 17 described above. A thermistor 21 for monitoring the temperature is disposed, and the pressure roller 16 rotates following the heat roller 15.

  The conveyor belt 11 is an endless belt made of a high-resistance semiconductive plastic film, and is driven by a belt motor 9a (see FIG. 3) while being tensioned rightward in FIG. The drive roller 9 is rotated in the paper conveyance direction (counterclockwise in FIG. 1).

  In the printer 1 of this embodiment, four independent image forming units 13k, 13y, 13m, and 13c are arranged in the order in which the toner images are developed along the paper conveyance direction. Toner cartridges 23 containing toners as set color, that is, K color (black), Y color (yellow), M color (magenta), and C color (cyan) are provided. The image forming unit 13 includes a photosensitive drum 24, a charging roller 25, a developing roller 26, a developing blade 27, a supply roller 28, and a static elimination light source 29 that neutralizes the photosensitive drum 24. When attached to the printer 1, the corresponding charging voltage generator 25a, development voltage generator 26a, supply voltage generator 28a (see FIG. 3) It is gas-connected.

  Further, each image forming unit 13 is provided with a contact / separation mechanism including a cam (not shown), and the photosensitive drum 24 can be brought into contact with the conveyance belt 11 and can be separated by about 2 to 3 mm. The exposure head 31 is disposed above the photosensitive drum 24 so as to be opposed to the exposure head 31.

  A belt cleaning mechanism including a belt cleaning blade 32 and a waste toner tank 33 is provided on the tension roller 10 side of the lower surface of the conveyance belt 11 opposite to the image forming unit 13. The belt cleaning blade 32 is flexible. The toner is formed of a rubber material or plastic material having a surface and is opposed to the tension roller 10 with the conveyor belt 11 interposed therebetween. The toner remaining on the surface of the conveyor belt 11 is scraped off into the waste toner tank 33. Configured to be removed.

  A density sensor 35 that detects the density of a density detection pattern (see FIG. 14) directly printed on the conveyor belt 11 is located at a position facing the conveyor belt 11 on the drive roller 9 side of the lower surface of the conveyor belt 11. Has been placed.

  The photoconductor drum 24 as an image carrier is a cylindrical member formed by coating an organic photoconductor on the outer peripheral surface of a metal pipe, and transports the paper P by a drum motor 24a (see FIG. 3). It is rotationally driven in a direction (referred to as a clockwise direction and a conveyance rotation direction in FIG. 1).

  The charging roller 25 as a charging means is formed by covering a metal rotating shaft with a semiconductive rubber layer, and is driven to rotate while being in contact with the photosensitive drum 24 as the photosensitive drum 24 rotates. It has a function of uniformly charging the surface of the photosensitive drum 24 with a voltage applied from the generator 25a.

  An exposure head 31 as an exposure unit holds an element array formed by arranging a plurality of light emitting elements such as LEDs (Light Emitting Diodes) in a direction orthogonal to the paper conveyance direction, a drive IC that drives the element array, and image data. It consists of a substrate equipped with a register group and a SELFOC lens array that collects the light from the element array. Each light emitting element emits light according to the image data signal based on the print duty of each light emitting element formed based on the image data. The surface of the photosensitive drum 24 is exposed in dot units to form an electrostatic latent image on the surface.

  Further, the exposure head 31 arranged in the image forming units 13k, 13y, 13m, and 13c for each set color sensitizes an electrostatic latent image corresponding to each color in accordance with an image data signal corresponding to each color. It is formed on the surface of the body drum 24.

  A developing roller 26 as a developer carrying member is formed by coating an outer peripheral surface of a metal rotation shaft with an elastic body, and is driven to rotate in a direction opposite to the photosensitive drum 24 (a driven direction of the conveyance rotation direction). The head 31 has a function of forming a toner image by attaching toner to the electrostatic latent image formed on the photosensitive drum 24 by electrostatic force.

  The developing blade 27 as a developer layer regulating member is an L-shaped cross-sectional thin plate formed by bending the tip of an elastic material having elasticity, such as a stainless steel plate, and is provided on the back side of the bent portion on the tip side. The surface of the developing roller 26 is pressed by the surface, the thickness of the toner on the surface of the developing roller 26 is reduced to a predetermined thickness, and an appropriate amount of toner is conveyed to the developing roller 26 to scrape excess toner. It has a function.

  A supply roller 28 as a developer supply means is formed by coating a foamed rubber material on a metal rotation shaft, rotates in the same direction in contact with the development roller 26, and is a voltage applied from a supply voltage generator 28a. Thus, the toner supplied from the toner cartridge 23 is supplied to the developing roller 26.

  Further, the toner on the surface of the developing roller 26 is frictionally charged by being strongly rubbed by the developing roller 26 and the supply roller when a thin layer is formed by the developing blade 27.

  The transfer roller 14 as a developer image transfer means rotates following the conveyance belt 11, and transfers the toner image formed on the surface of the photosensitive drum 24 to the sheet by the electric field generated by the voltage applied from the transfer voltage generator 14 a. It has a function of transferring onto P.

  A density sensor 35 serving as a density detection unit measures the intensity of reflected light of a density detection pattern printed directly on the conveyance belt 11 and detects a print density value of the printer 1. As shown in FIG. 2, it is composed of an infrared LED 36, a specular reflection light receiving phototransistor 37, a diffuse reflection light receiving phototransistor 38, and the like. Both can be detected.

  When color density detection is performed, the light emitted from the infrared LED 36 and diffusely reflected by the density detection pattern on the conveyor belt 11 is received by the diffuse reflected light receiving phototransistor 38 and output from the diffuse reflected light receiving phototransistor 38. Detected by a voltage corresponding to the received light quantity.

  When black density detection is performed, the light reflected from the infrared LED 36 and specularly reflected by the density detection pattern on the conveyor belt 11 is received by the specular reflection light receiving phototransistor 37, and the specular reflection light receiving phototransistor 37 is received. It detects with the voltage according to the received light quantity output from.

  In FIG. 3, reference numeral 40 denotes a host interface unit, which is composed of a connector and a communication chip, and is a part responsible for a physical layer interface with a host computer (for example, a personal computer) (not shown).

  A command / image processing unit 41 includes a microprocessor, RAM, and hardware for development into a bitmap, and includes commands and images included in print data transmitted from the host computer and received via the host interface unit 40. This is the part where data is interpreted or expanded into a bitmap.

  Reference numeral 42 denotes a head interface unit, which is composed of a semi-custom LSI, a RAM, and the like. The image data expanded in the bitmap transmitted from the command / image processing unit 41 is matched with the interface of the exposure head 31 of each set color. This is the part to be processed.

  Reference numeral 43 denotes a main control unit of the printer 1. Based on a command from the command / image processing unit 41, each unit in the printer 1 is controlled to execute print job processing in the printer 1 such as print processing and print density correction processing. While controlling the output from each conveyance monitoring sensor 18 and controlling the drive drivers such as the motors 6 a, 7 a, 9 a, 15 a, and 24 a and the high voltage control unit 44, The surface temperature of the heat roller 15 is controlled by increasing / decreasing the power supplied to the heater 20 based on the output, and mainly controls the mechanism of the printing system and the high voltage power source.

  The high voltage control unit 44 is composed of a microprocessor or a custom LSI, and controls the generation of charging voltage, developing voltage, supply voltage, transfer voltage, etc. for each image forming unit 13 based on a command from the main control unit 43. Yes.

  The charging voltage generator 25 a generates and stops the charging voltage applied to the charging roller 25 based on a command from the high voltage controller 44, and the developing voltage generator 26 a generates a developing roller based on a command from the high voltage controller 44. The supply voltage generator 28a generates and stops the supply voltage to be applied to the supply roller 28 based on a command from the high voltage controller 44, and the transfer voltage generator 14a The transfer voltage is applied to the transfer roller 14 on the basis of a command from the high voltage control unit 44.

  Further, the transfer voltage generator 14a is provided with a current or voltage detection circuit so that constant current or low voltage control is possible.

  A storage unit 45 of the printer 1 stores a program executed by the main control unit 43, various data used for the program, processing results by the main control unit 43, and the like.

  47 is resistance information acquisition means, software having a function of reading the type of the paper P and the classification for each type from the medium setting information set in advance by the user, and acquiring the resistance information of the paper P according to them. And functional means formed by the main control unit 43.

  Note that the resistance information in this embodiment is information regarding the electrical resistance of the paper P on which an image is printed, and is specifically the volume resistivity ρ.

  Reference numeral 48 denotes a medium reverse transfer amount calculation means, which has a function of calculating the medium reverse transfer amount of the paper P based on the volume resistivity ρ obtained by the type and classification of the paper P acquired by the resistance information acquisition means 47. It is a functional means formed by the software and the main control unit 43.

  The storage unit 45 of the printer 1 stores a density sensor 35 based on a density detection pattern (see FIG. 14) directly formed on the conveyor belt 11 when the current state of the printer 1 matches a predetermined environment correction execution condition. Based on the detected density of each duty and the target value of each duty in the density target value table (see FIG. 6), the light emitting elements of the exposure head 31 are driven so that the print density of the density detection pattern becomes the target value. The density of the print density of the density detection pattern is corrected by increasing or decreasing the time (referred to as element driving time) and the development voltage applied by the development voltage generator 26a, and the reverse transfer amount correction rate in the current internal environment is obtained in this state. Based on the function of performing environmental correction processing and the resistance information of the paper P to be printed in advance when an image is formed on the paper P, the medium reverse transfer amount of the paper P is calculated and Print density correction processing program having a function of performing density correction processing for each paper for correcting the image formation conditions for each paper by calculating a correction amount of the development voltage and element driving time of each image forming unit 13 during printing, a host (not shown) The voltage or exposure head that receives the print data from the computer and applies the image data included in the print data to each roller of the image forming unit 13 according to the corrected image forming conditions corrected by the density correction processing for each sheet A print job execution program including a print processing program having a function of printing and discharging a color image on the paper P while correcting the element driving time of 31 is stored in advance, and a print job executed by the main control unit 43 Each function unit of the printer 1 of this embodiment is formed by the steps of the execution program.

  Further, the storage unit 45 stores the rotational speed of the photosensitive drum 24 and each roller of each image forming unit 13, ON / OFF of the voltage applied to each roller from each voltage generation unit, setting of the voltage value and its polarity, and exposure. The image forming conditions including the setting of the element driving time of the light emitting element at the print duty set based on the driving voltage of the head 31 and the image data, and the image data of the density detection pattern used for the environmental correction processing are set and stored in advance. In addition, various tables used for the print density correction process of the present embodiment shown below are set and stored in advance.

  The voltage density value conversion coefficient table shown in FIG. 4 stores the coefficients A and B in the first-order approximation expression for converting the detected voltage SD for each print duty of each set color detected by the density sensor 35 into a density value. .

  The coefficients A and B of the voltage density value conversion coefficient table of the present embodiment are experimentally obtained by using a primary approximation formula for each printing duty from the relationship between the detection voltage SD and the density value of the density sensor 35 shown in FIG. It is a thing.

  The density target value table shown in FIG. 6 stores each target value of the detected density value for each print duty of each set color detected from the density detection pattern by the density sensor 35.

  The development voltage adjustment amount table shown in FIG. 7 stores the amount of change in the detected density value for each print duty of each set color per development voltage control unit (in this embodiment, in increments of 1V).

  The element drive time adjustment amount table shown in FIG. 8 stores the amount of change in the detected density value for each print duty of each set color per unit drive time control unit (in this embodiment, in increments of 1%).

  The set reverse transfer amount information table shown in FIG. 9 shows the reverse transfer amount for each print duty of each set color set in advance based on the internal environment (temperature, humidity, etc.) determined as a standard state when the printer 1 is designed. Store.

  The volume resistivity correction coefficient table shown in FIG. 10 corresponds to the type of the paper P and each section for each type in order to correct the influence on the reverse transfer amount when the volume resistivity ρ of the paper P is different. The volume resistivity correction coefficient for each set color is stored. The volume resistivity correction coefficient is uniform regardless of the printing duty.

  The reference medium reverse transfer amount information table shown in FIG. 11 stores the reference medium reverse transfer amount for each print duty of each set color serving as a reference for the recommended paper in association with the type of paper P.

  As shown in FIGS. 10 and 11, the type of the paper P in this embodiment is composed of “high quality paper”, “plain paper”, and “film paper”, and the classification for each type is “no selection”, “low resistance”, “ “High resistance”.

  The volume resistivity correction coefficient and the reference medium reverse transfer amount described above are set based on the relationship between the volume resistivity ρ of the paper P and the reverse transfer amount shown in FIG.

  FIG. 12 shows the relationship between the volume resistivity ρ and the reverse transfer amount of each of the three types of paper P belonging to high-quality paper, plain paper, and film paper. Even if the paper belongs to paper, if the volume resistivity ρ varies depending on the manufacturer or material, the reverse transfer amount also increases or decreases according to the volume resistivity ρ.

  That is, the reverse transfer amount due to the reverse transfer phenomenon changes due to the difference in the volume resistivity ρ caused by the type of the paper P and its classification, and if the correction is performed only by the type of the paper P in the medium setting information, the same type It can be seen that even when the paper P is different, the density change due to the reverse transfer phenomenon occurs when the paper P having a different volume resistivity ρ is used.

  For this reason, in this embodiment, as a substitute index representing the volume resistivity ρ of the paper P preset by the user, the medium setting information preset by the user includes the “quality paper” “normal paper” as the type of the paper P. Setting items for “paper” and “film paper” are provided, and setting items for “no selection”, “low resistance”, and “high resistance” are provided in the category.

  Further, when the category is “not selected”, that is, when the category is not set, the reference medium reverse transfer amount that is the medium reverse transfer amount on the recommended paper for each paper P type is set. If the category of “low resistance” or “high resistance” is set, the volume resistivity correction that represents the rate of change in volume resistivity ρ is used to increase or decrease the amount of media reverse transfer based on the difference in volume resistivity ρ. An appropriate medium reverse transfer amount is set for the medium according to the classification set by correcting with the coefficient.

  The volume resistivity ρ varies depending on the thickness of the paper P and the roughness of the paper fiber. Generally, the thicker the volume resistivity ρ is, and the coarser the volume resistivity ρ, the higher the volume resistivity ρ. In consideration of easiness, the classification may be “no selection”, “thin paper”, “thick paper”, or “no selection”, “smooth paper”, “rough paper”.

  Note that the table values in the volume resistivity correction table (FIG. 10) and the reference medium reverse transfer amount table (FIG. 11) of this embodiment are experimentally based on the medium reverse transfer amount due to the actual reverse transfer phenomenon on each paper P. It is the one that was sought and set.

  A print job process performed by the printer 1 having the above-described configuration will be described in accordance with steps indicated by S using the flowchart shown in FIG.

  As shown in FIG. 14, the density detection pattern used in the print density correction process of the present embodiment has a printing duty of 30% along the paper transport direction at the center of the transport belt 11 in the direction orthogonal to the paper transport direction. , 70%, and 100% directly printed in the order of 100%.

  When power is turned on to the printer 1, the main control unit 43 of the printer 1 starts executing the print job process by the print job execution program stored in the storage unit 45.

  Step S1: The main control unit 43 waits for the current state to match a predetermined environment correction execution condition. If the current state matches the predetermined environment correction execution condition, the main control unit 43 performs the environment correction process. It is determined that execution is necessary, and the process proceeds to step S4. If the current state does not match the predetermined environment correction execution condition, it is determined that the execution of the environment correction process is unnecessary, and the process proceeds to step S2.

  The predetermined environment correction execution condition in this step is based on changes in the internal environment based on changes in the external environment, such as when the power is turned on, when a predetermined number of prints are completed, or when the external environment where the printer 1 is installed is changed. When a change in the state of each part such as a change in toner charge amount or a change in resistance value of the transport belt 11 or the transfer roller 14 is assumed, the environment correction process is set in advance.

  On the other hand, when the user inputs medium setting information such as the type and size of paper P to be printed and image data to be printed from an external host computer, the host computer transmits these to the printer 1 as print data.

  Step S2: The main control unit 43 waits for a print command from the command / image processing unit 41 that has received the print data via the host interface unit 40, and when the print command is received, The execution of printing is determined and the process proceeds to step S13. If no print command is received, the process proceeds to step S3.

  Step S3: The main control unit 43 waits for the printer 1 to be powered off. If the power is on, the main control unit 43 returns to step S1 and continues the standby in steps S1 to S3. When the power is turned off, the print job process of this embodiment is terminated.

  Step S4: The main control unit 43, which has determined that the environment correction process needs to be executed, uses the environment correction processing function of the print density correction processing program to reduce the variation in the mounting angle, position, temperature, etc. of the density sensor 35. The light emission current of the outer LED 36 is adjusted (referred to as calibration).

  That is, the main control unit 43 causes the infrared LED 36 of the density sensor 35 to emit light to irradiate the reference reflector (conveyor belt 11 in the case of black, and a reflector provided in advance for other colors), thereby performing specular reflection. The emission current is adjusted so that the detection voltage from the phototransistor 37 for light reception and the phototransistor 38 for diffuse reflected light reception is within the set voltage range set for calibration, and the adjusted emission current is It is stored in the storage unit 45 as a light emission current for density value detection.

  Step S5: After having calibrated the density sensor 35, the main control unit 43 obtains the detected density value for each print duty of each set color for the first time in order to set the print density in the current internal environment as the density target value. To do.

  That is, as shown in FIG. 15A, the main control unit 43 contacts the photosensitive drum 24 of the image forming unit 13k that forms a black toner image with the upper surface of the transport belt 11 by a contact / separation mechanism (not shown). In addition, the voltage applied to the rollers of the image forming units 13y, 13m, and 13c arranged on the downstream side in the paper conveyance direction is turned off, and the photosensitive drums 24 are separated from the conveyance belt 11. While driving the conveyor belt 11, the image data of the density detection pattern read from the storage unit 45 is transmitted from the command / image processing unit 41 via the head interface unit 42 to the exposure head 31 of the image forming unit 13k. A density detection pattern for each black print duty is printed on the conveyor belt 11.

  As described above, the image forming unit 13 arranged on the downstream side of the image forming unit 13 for printing the density detecting pattern is separated from the conveying belt 11 because the printed density detecting pattern is arranged on the downstream side. This is to prevent the density from being lowered due to the reverse transfer phenomenon of the image forming unit 13 to the photosensitive drum 24, and appropriate density detection and density correction cannot be performed.

  After the black density detection pattern has passed through the separated most downstream image forming unit 13c, the main control unit 43 that has printed the black density detection pattern, as shown in FIG. The photosensitive drum 24 of the image forming unit 13y that forms a yellow toner image is brought into contact with the upper surface of the transport belt 11, and the rollers of the image forming units 13m and 13c disposed on the downstream side in the paper transport direction. The image forming unit 13k is in an empty printing state (with 0% printing duty while driving the conveying belt 11 while the photosensitive drum 24 is separated from the conveying belt 11 and the voltage applied to is turned off. That is, application of preset image forming conditions to each roller without causing the exposure head 31 of the image forming unit 13k to emit light. The image data of the density detection pattern is transmitted to the exposure head 31 of the image forming unit 13y in the same manner as described above, and the yellow print duty of each yellow print duty is transmitted to the exposure head 31 of the image forming unit 13y. After the density detection pattern is printed and after passing through the most downstream image forming unit 13c where the density detection pattern is separated, the density detection patterns of magenta and cyan print duties are sequentially printed in the same manner as described above.

  In this way, when the density detection pattern of each set color printed while driving the conveyor belt 11 moves to the position of the density sensor 35, the main control unit 43 stores the infrared LED 36 of the density sensor 35. The concentration detection pattern stored in the unit 45 emits light with the emission current for density value detection, the infrared detection light is irradiated to the density detection pattern moved to the position of the density sensor 35 by the red LED 36, and the infrared light reflected on the surface of the density detection pattern is reflected. Light is received by the specular reflection light receiving phototransistor 37 and the diffuse reflection light receiving phototransistor 38. In the case of black, the detection voltage for each print duty output from the specular reflection light receiving phototransistor 37 is read, and the other set colors. In this case, the detection voltage for each printing duty output from the phototransistor 38 for receiving diffuse reflected light is read.

  In this case, a current proportional to the received light energy of the reflected light received by the drive circuit (not shown) flows through the phototransistors 37 and 38, the current is converted into a voltage by a circuit (not shown), and the voltage value is detected voltage. Is read by the main controller 43.

  The toner of the density detection pattern of each set color printed on the conveyor belt 11 moves toward the belt cleaning blade 32 by driving the conveyor belt 11 and is scraped off into the waste toner tank 33 by the belt cleaning blade 32. Thus, the surface of the conveyor belt 11 is cleaned.

  The main control unit 43 that has read the detection voltage for each print duty of each set color converts the read detection voltage into a detection density value using the voltage density value conversion coefficient table (FIG. 4) stored in the storage unit 45. To do.

For example, when the detected voltage SDK for each black print duty is converted into the detected density value KOD, the following formula is used by using the respective black (K) coefficients A _K and B _K of the voltage density value conversion coefficient table. .

KOD _30-1 = A _K30 × SDK ₃₀ + B _K30 ... (1a)
_{KOD 70-1 = A K70 × SDK 70} + B K70 ············ (1b)
KOD _100-1 = A _K100 × SDK ₁₀₀ + B _K100 (1c)
The numbers shown in the subscripts indicate the printing duty (the same applies hereinafter), and “−1” indicates the detected density value by the first detection.

  Then, in the same manner as in the case of black (K), the main control unit 43 also applies the subscript Y, M, and C coefficients shown in FIG. 4 for yellow (Y), magenta (M), and cyan (C). Calculation is performed using A and B, and each detected density value is stored in the storage unit 45 as a first detected density value table shown in FIG.

  Step S6: The main control unit 43 storing the first detected density value stores the first detected density value table (FIG. 16) stored in the storage unit 45 in Step S5 and the density target stored in the storage unit 45. The difference for each printing duty from the value table (FIG. 6) is divided by the density value change amount per control unit of the development voltage in the development voltage adjustment amount table (FIG. 7), and these are averaged to obtain the development voltage correction amount ΔHGV. (Unit: V) is calculated.

For example, when calculating the correction amount ΔHGV _K of the developing voltage applied to the developing roller 26 of the black image forming unit 13k, it is calculated by the following equation using the density value change amount KDB of each printing duty in the developing voltage adjustment amount table. To do.

ΔHGV _K = {(KODm ₃₀ -KOD _30-1 ) / KDB ₃₀ +
(KODm ₇₀ -KOD _30-1 ) / KDB ₇₀ +
(KODm ₁₀₀ -KOD _30-1 ) / KDB ₁₀₀ } / 3 (rounded to the nearest decimal place)
(2)
The main control unit 43 then applies development voltage correction amounts ΔHGV _Y , ΔHGV _M to the yellow (Y), magenta (M), and cyan (C) image forming units 13 k in the same manner as in the case of the black image forming unit 13 k. , ΔHGV _C are also calculated using the density value change amounts of the initial letters Y, M, and C shown in FIG. 7, and each development voltage correction amount ΔHGV is transmitted to the high voltage control unit 44 so that each image forming unit 13 Instructs to increase or decrease the development voltage.

  Step S7: The main control unit 43 instructed to increase or decrease the development voltage of each image forming unit 13 acquires the detected density value for each print duty of each set color for the second time in the same manner as in Step S5, and detects each detection. The density value is stored in the storage unit 45 as a second detected density value table shown in FIG.

  In this case, a developing voltage having a value obtained by increasing or decreasing the developing voltage correction amount ΔHGV with respect to a preset image forming condition is applied to the developing roller 26 of the image forming unit 13 that prints the density detection pattern.

Note that the subscript “−2” shown in FIG. 17 indicates the detected density value by the second detection.

Step S8: The main control unit 43 that stores the second detected density value stores the second detected density value table (FIG. 17) stored in the storage unit 45 in Step S7 and the density target stored in the storage unit 45. The difference for each printing duty from the value table (FIG. 6) is divided by the density value change amount per control unit of the element driving time in the element driving time adjustment amount table (FIG. 8), and these are averaged to obtain the element driving time. A correction amount ΔHHT (unit:%) is calculated.

For example, when calculating the element driving time correction amount ΔHHT _K of the exposure head 31 of the black image forming unit 13k, the density value change amount KDK of each printing duty in the element driving time adjustment amount table is calculated by the following equation. To do.

ΔHHT _K = {(KODm ₃₀ -KOD _30-2 ) / KDK ₃₀ +
(KODm ₇₀ -KOD _30-2 ) / KDK ₇₀ +
(KODm ₁₀₀ −KOD _30-2 ) / KDK ₁₀₀ } / 3 (rounded to the nearest decimal place)
(3)
Then, the main control unit 43 corrects the element driving time correction amount of the exposure head 31 of the yellow (Y), magenta (M), and cyan (C) image forming unit 13 in the same manner as the black image forming unit 13k. ΔHHT _Y , ΔHHT _M , and ΔHHT _C are also calculated using the density value change amounts of the initial letters Y, M, and C shown in FIG. 8, and each element drive time correction amount ΔHHT is transmitted to the head interface unit 42. An instruction to increase or decrease the element driving time of the exposure head 31 provided in each image forming unit 13 is given.

  Thereby, each detected density value detected from the density detection pattern printed on the conveyance belt 11 is corrected so as to approach each density target value in the density target value table (FIG. 6).

  Step S9: The main control unit 43 instructing to increase / decrease the element driving time of each image forming unit 13 obtains the detected density value for each print duty of each set color when there is no reverse transfer in the same manner as in step S5. Then, each detected density value is stored in the storage unit 45 as a detected density value table when there is no reverse transfer shown in FIG.

  In this step, the developing roller 26 of the image forming unit 13 for printing the density detection pattern is applied with a developing voltage having a value obtained by increasing / decreasing the developing voltage correction amount ΔHGV with respect to the developing voltage under a preset image forming condition. Then, each light emitting element of the exposure head 31 of the image forming unit 13 is driven with an element driving time obtained by increasing / decreasing the ratio of the element driving time correction amount ΔHHT with respect to the element driving time of a preset image forming condition. .

  Note that the suffix “−A” shown in FIG. 18 indicates a detected density value by detection when there is no reverse transfer.

  Step S10: The main control unit 43 storing the detected density value when there is no reverse transfer sets each color when there is reverse transfer in order to calculate the reverse transfer amount correction rate of the reverse transfer amount in the current internal environment. The detected density value for each printing duty is acquired.

  That is, as shown in FIG. 19A, the main control unit 43 brings the photosensitive drums 24 of all the image forming units 13 into contact with the upper surface of the transport belt 11 by a contact / separation mechanism (not shown), and black toner. The image forming units 13y, 13m, and 13c arranged on the downstream side in the paper transport direction of the image forming unit 13k that forms an image are set in an empty printing state, and the exposure belt 31 of the image forming unit 13k is driven while driving the transport belt 11. In step S5, image data of the density detection pattern is transmitted in the same manner as in step S5, and the density detection pattern of each black print duty is printed on the conveyor belt 11.

  As described above, the image forming unit 13 arranged on the downstream side of the image forming unit 13 for printing the density detection pattern is brought into the blank printing state and brought into contact with the transport belt 11 because the reverse transfer phenomenon is caused by a change in the internal environment. The occurrence state varies depending on the change in the state of each part, such as the toner charge amount fluctuation due to the toner, and the resistance value fluctuation of the transport belt 11 and the transfer roller 14, so the image forming unit 13 disposed on the downstream side to the photosensitive drum 24. This is because the density reduction of the density detection pattern due to the reverse transfer phenomenon is measured, and the occurrence of reverse transfer due to the state of each part of the current printer 1 is measured.

  After the black density detection pattern has passed through the most downstream image forming unit 13c, the main control unit 43 that has printed the black density detection pattern, as shown in FIG. The image forming units 13m and 13c are disposed on the downstream side of the image forming unit 13y that forms a yellow toner image while the body drum 24 is in contact with the upper surface of the transport belt 11, and the image forming units 13m and 13c are disposed on the upstream side. The image forming unit 13k is set to the blank printing state, and the image data of the density detection pattern is transmitted to the exposure head 31 of the image forming unit 13y in the same manner as in step S5, and the density detection of each printing duty of yellow is performed on the conveyance belt 11. After the pattern is printed and the density detection pattern passes through the most downstream image forming unit 13c, the same as described above. A manner, magenta, sequentially printing the density detection pattern of each print duty of cyan.

  In this way, when the density detection pattern of each set color printed while driving the conveyor belt 11 moves to the position of the density sensor 35, the main control unit 43 stores the read detection voltage in the storage unit 45. Using the stored voltage density value conversion coefficient table (FIG. 4), in the same manner as in step S5, the detected density value for each print duty of each set color when there is reverse transfer is obtained. The values are stored in the storage unit 45 as a detected density value table when there is reverse transfer shown in FIG.

  Note that the suffix “−B” shown in FIG. 20 indicates a detected density value by detection when there is reverse transcription.

  Step S11: The main control unit 43, which stores the detected density values when there is no reverse transfer and when there is reverse transfer, reverses the detected density value table (FIG. 18) when there is no reverse transfer stored in the storage unit 45. A difference for each printing duty from the detected density value table (FIG. 20) when there is no copy is obtained, and a measured current reverse transfer amount (referred to as a density value reduced by the reverse transfer phenomenon) is calculated.

  For example, when calculating the current reverse transfer amount GK of the black image forming unit 13k, the following equation is used.

GK ₃₀ = KOD _30-A -KOD _30-B (4a)
GK ₇₀ = KOD _70-A -KOD _70-B (4b)
GK ₁₀₀ = KOD _100-A -KOD _100-B (4c)
The main control unit 43 then performs the current reverse transfer amounts GY, GM, and GC of the yellow (Y), magenta (M), and cyan (C) image forming units 13 in the same manner as the black image forming unit 13k. And the current reverse transfer amount is stored in the storage unit 45 as the current reverse transfer amount information table shown in FIG.

  Step S12: The main control unit 43 that has calculated the current reverse transfer amount of each image forming unit 13 is stored in the current reverse transfer amount information table (FIG. 21) stored in the storage unit 45 in step S11 and the storage unit 45. The ratio of the reverse transfer amount for each print duty with the set reverse transfer amount information table (FIG. 9) is calculated, and the measured reverse transfer amount correction rate (unit:%) is calculated.

  For example, when calculating the reverse transfer amount correction rate ΔGK of the black image forming unit 13k, the calculated reverse transfer amount GKs of each print duty in the set reverse transfer amount information table is calculated by the following equation.

ΔGK ₃₀ = (GK ₃₀ / GKs ₃₀ ) × 100 (5a, rounded off after decimal point)
ΔGK ₇₀ = (GK ₇₀ / GKs ₇₀ ) × 100 (5b, rounded off after decimal point)
ΔGK ₁₀₀ = (GK ₁₀₀ / GKs ₁₀₀ ) × 100 (5c, rounded off after decimal point)
The main control unit 43 then performs reverse transfer amount correction rates ΔGY, ΔGM, yellow (Y), magenta (M), and cyan (C) image forming units 13 in the same manner as in the case of the black image forming unit 13k. ΔGC is also calculated, and each reverse transfer amount correction rate is stored in the storage unit 45 as a reverse transfer amount correction rate table shown in FIG.

  This reverse transfer amount correction rate table is continuously used until it is determined in step S1 that the next environmental correction process needs to be executed. When printing on the paper P, the reverse transfer amount correction rate table is used. This is used to correct the image forming condition of the image to be formed into an image forming condition suitable for the current internal environment.

  In this way, the environment correction process in the print density correction process by the printer 1 of this embodiment is executed, and when the process is completed, the main control unit 43 returns to step S1 and continues the standby in steps S1 to S3.

  Step S13: The main control unit 43 that has determined execution of printing on the paper P in the above step S2 uses the paper-specific density correction processing function of the print density correction processing program for each paper at the time of printing before starting the printing process. In order to start execution of the density correction process and acquire the medium reverse transfer amount as the medium reverse transfer amount information of the paper P based on the volume resistivity ρ as the resistance information of the paper P to be printed, The resistance information acquisition unit 47 reads the medium setting information set in advance by the user from the received print data, and reads the type of the paper P and the classification for each type included in the medium setting information.

  As shown in the volume resistivity correction coefficient table (FIG. 10) and the reference medium reverse transfer amount information table (FIG. 11), the types of paper P in this embodiment are “quality paper”, “plain paper”, and “film paper”. The classification for each type includes “no selection”, “low resistance”, and “high resistance”, and the main control unit 43 uses the medium reverse transfer amount calculation means 48 based on the type of the read sheet P and its classification. The medium reverse transfer based on the volume resistivity ρ of the paper P to be printed using the volume resistivity correction coefficient table (FIG. 10) and the reference medium reverse transfer amount information table (FIG. 11) stored in the storage unit 45. Calculate the amount.

  For example, the medium reverse transfer amount PGK for each black print duty when the type “quality paper” and the paper “P” of the category “not selected” are set is the volume resistivity correction of black in the volume resistivity correction coefficient table. Using the coefficient KR1 and the reference medium reverse transfer amount KG1 for black high-quality paper in the reference medium reverse transfer amount information table, calculation is performed according to the following equation.

PGK ₃₀ = KG1 ₃₀ × KR1 (6a)
PGK ₇₀ = KG1 ₇₀ xKR1 (6b)
PGK ₁₀₀ = KG1 ₁₀₀ × KR1 (6c)
Then, the main control unit 43 performs the medium reverse transfer amounts PGY and PGM of yellow (Y), magenta (M), and cyan (C) in the type “quality paper” and the category “not selected” in the same manner as in the case of black. , PGC are also calculated using the volume resistivity correction coefficients of the initial letters Y, M, and C shown in FIGS. 10 and 11 and the reference medium reverse transfer amount, and the medium reverse transfer amounts shown in FIG. It is stored in the storage unit 45 as a copy amount table.

  In this way, the main control unit 43 calculates the medium reverse transfer amount of the paper P based on the volume resistivity ρ that is resistance information of the paper P to be printed.

  Step S14: The main control unit 43 that stores the medium reverse transfer amount calculates a development voltage correction amount and an element driving time correction amount at the time of printing, which are used in the printing process shown in the next step.

  In this case, the correction of the density change due to the reverse transfer phenomenon is performed by correcting the developing voltage correction amount and the element driving time correction amount at a ratio of 1: 1. For example, if the density change amount is −X, + X / 2 is corrected by the development voltage and the remaining + X / 2 is corrected by the element driving time.

  That is, the main control unit 43 reverses the reverse transfer amount correction rate table (FIG. 22) stored in the storage unit 45 in step S12 to the medium reverse transfer amount for each print duty in the medium reverse transfer amount table (FIG. 23). The value obtained by multiplying the exposure correction rate is halved, and this value is halved in the development voltage adjustment amount table (FIG. 7) in the density value change amount per control unit or in the element drive time adjustment amount table (FIG. 8). Dividing by the amount of change in the density value per control unit of the element driving time and averaging these, the development voltage correction amount ΔHGVp (unit: V) and the element driving time correction amount ΔHHTp (unit:%) at the time of printing are calculated.

For example, when calculating the correction amount ΔHGVp _K of the developing voltage applied to the developing roller 26 of the black image forming unit 13k, the reverse transfer amount correction rate ΔGK of each print duty in the reverse transfer amount correction rate table, the developing voltage adjustment amount The density value change amount KDB for each printing duty in the table is used to calculate the following equation.

ΔHGVp _K = [{(PGK ₃₀ × ΔGK ₃₀ ) / 2} / KDB ₃₀ +
{(PGK ₇₀ × ΔGK ₇₀ ) / 2} / KDB ₇₀ +
{(PGK ₁₀₀ × ΔGK ₁₀₀ ) / 2} / KDB ₁₀₀ ] / 3 (7)
When calculating the element driving time correction amount ΔHHTp _K of the exposure head 31 of the black image forming unit 13k, the reverse transfer amount correction rate ΔGK of each printing duty in the reverse transfer amount correction rate table, the element driving time adjustment amount table The density value change amount KDK of each print duty is calculated by the following equation.

ΔHHTp _K = [{(PGK ₃₀ × ΔGK ₃₀ ) / 2} / KDK ₃₀ +
{(PGK ₇₀ × ΔGK ₇₀ ) / 2} / KDK ₇₀ +
{(PGK ₁₀₀ × ΔGK ₁₀₀ ) / 2} / KDK ₁₀₀ ] / 3 (8)
The main control unit 43 then develops the development voltage correction amounts ΔHGVp _Y and ΔHGVp _{M of} the yellow (Y), magenta (M), and cyan (C) image forming units 13 in the same manner as the black image forming unit 13k. , ΔHGVp _C , and element driving time correction amounts ΔHHTp _Y , ΔHHTp _M , and ΔHHTp _C of the exposure head 31 are also calculated using the density value variation of the initial letters Y, M, and C shown in FIGS. Each development voltage correction amount ΔHGVp is transmitted to the high voltage control unit 44 to instruct increase / decrease of the development voltage of each image forming unit 13, and each element drive time correction amount ΔHHTp is transmitted to the head interface unit 42. An instruction to increase or decrease the element driving time of the exposure head 31 provided in the image forming unit 13 is given, and the process proceeds to step S15.

  In this way, before the image formation on the paper P by the image forming unit 13, the preset image forming conditions are corrected to the image forming conditions suitable for the current internal environment and the paper P to be printed.

  Step S15: The main control unit 43 instructing the high voltage control unit 44 and the head interface unit 42 by using the development voltage correction amount ΔHGVp and the element driving time correction amount ΔHHTp of each image forming unit 13 as the increase / decrease amounts thereof, according to the print processing program The printing operation is started, and the paper P corresponding to the type of the paper P in the medium setting information is fed out from the paper P stored in the paper feed storage cassette 3 by the hopping roller 6, and the image forming unit 13 through the paper transport path 2. Transport in the direction of.

  In parallel with this, the main controller 43 rotates the photosensitive drum 24 and the charging roller 25 of each image forming unit 13 and uniformly charges the photosensitive drum 24 with the charging roller 25 having a predetermined charge. The image data generated by the head interface unit 42 according to each set color based on the print data received by the command / image processing unit 41 via the host interface unit 40 is sent to each exposure head 31. Light is emitted from the light emitting element onto the surface of the photosensitive drum 24 to form an electrostatic latent image of each set color on the surface of each photosensitive drum 24, and the developing blade 27 presses with a predetermined pressing force to develop. A thin layer of toner formed on the surface of the roller 26 is attached to the electrostatic latent image on the rotating photosensitive drum 24 while being in contact with the toner, and developed on the photosensitive drum 24 according to the set color. To form a toner image.

  In this case, the developing roller 26 of each image forming unit 13 is applied with a corrected developing voltage having a value obtained by increasing or decreasing the developing voltage correction amount ΔHGVp with respect to a preset image forming condition. Each light emitting element of the thirteen exposure heads 31 is driven with a corrected element driving time in which the ratio of the element driving time correction amount ΔHHTp is increased or decreased with respect to the element driving time set based on the image data.

  The main control unit 43 sequentially transfers the toner images of the set colors formed on the photosensitive drums 24 onto the paper P conveyed to the image forming unit 13 by the conveying belt 11 by the transfer roller 14. The color image transferred onto the paper P is formed by transfer, the color image transferred onto the paper P is fixed by the fixing device 17, and the paper P after the fixing is further conveyed through the paper conveyance path 2 to be stacked in the stacker 4 of the printer 1. Drain up.

  In this case, if the print data includes a plurality of pieces of image data, the remaining number is printed by repeating the printing operation in step S15, and when all the image data has been printed, the process proceeds to step S1. It returns and continues the standby by step S1-S3.

  Hereinafter, the print density correction processing of the present embodiment will be described using specific numerical values shown in FIGS.

  In the following description, only black (K) is shown, but the same applies to yellow (Y), magenta (M), and cyan (C).

  In the following description, the detected density value detected from the density detection pattern printed on the conveyor belt 11 in steps S4 to S8 in the environment correction process shown in FIG. 13 is the numerical value of the density target value shown in FIG. The development voltage correction amount and the element driving time correction amount are calculated so as to approach each other. As a result, in step S10, each numerical value of the detection density value table shown in FIG. 25 is acquired as the detection density value when there is no reverse transfer. In step S11, description will be made assuming that each numerical value of the detected density value table shown in FIG. 26 is acquired as the detected density value when there is reverse transfer.

  In this case, the numerical values shown in FIGS. 27 and 28 are used as the development voltage adjustment amount and the head drive voltage adjustment amount.

In step S11, when obtaining the current reverse transfer amount GK of black, using equations (4a) to (4c),
GK ₃₀ = KOD _30-A -KOD _30-B
= 0.392-0.368 = 0.024
GK ₇₀ = KOD _70-A -KOD _70-B
= 1.023-0.982 = 0.041
GK ₁₀₀ = KOD _100-A -KOD _100-B
= 1.489-1.415 = 0.074
Each numerical value is calculated and stored in the storage unit 45 as the numerical value of the current reverse transfer amount information table shown in FIG.

In step S11, when obtaining the black reverse transfer amount correction rate ΔGK, each numerical value of the set reverse transfer amount GKs shown in FIG. 30 and the equations (5a) to (5c) are used.
ΔGK ₃₀ = (GK ₃₀ / GKs ₃₀ ) × 100
= (0.024 / 0.012) x 100 = 200 [%]
ΔGK ₇₀ = (GK ₇₀ / GKs ₇₀ ) × 100
= (0.041 / 0.031) x 100 = 133 [%]
ΔGK ₁₀₀ = (GK ₁₀₀ / GKs ₁₀₀ ) × 100
= (0.074 / 0.045) x 100 = 167 [%]
Each numerical value is calculated and stored in the storage unit 45 as a numerical value in the reverse transfer amount correction rate table shown in FIG.

  In this description, the measured reverse transfer amount is increased due to the change in the state of each part due to the change in the internal environment.

  Next, the density correction processing for each sheet at the time of printing will be described. In this description, it is assumed that “high quality paper” is set as the type of paper P and “low resistance” is set as the category in the medium setting information preset by the user.

When obtaining the black medium reverse transfer amount PGK in step S13, the numerical value of the volume resistivity correction coefficient KR1 _Low shown in FIG. 32, the numerical values of the reference medium reverse transfer amount GKs shown in FIG. 33, and the equation (6a) Using ~ (6c)
PGK ₃₀ = KG1 ₃₀ × KR1 _Low
= 0.012 x 120 [%] = 0.014
PGK ₇₀ = KG1 ₇₀ x KR1 _Low
= 0.030 x 120 [%] = 0.036
PGK ₁₀₀ = KG1 ₁₀₀ x KR1 _Low
= 0.045 x 120 [%] = 0.054
Each numerical value is calculated and stored in the storage unit 45 as the numerical value of the medium reverse transfer amount table shown in FIG.

When the development voltage correction amount ΔHGVp _K (unit: V) and the element driving time correction amount ΔHHTp _K (unit:%) during black printing are obtained in step S14, the reverse transfer amount shown in FIG. 31 obtained in step S12. Using the numerical value of the correction rate table, the numerical value of the medium reverse transfer amount table shown in FIG. 34 obtained in step S13, and equations (7) and (8),
ΔHGVp _K = [{(PGK ₃₀ × ΔGK ₃₀ ) / 2} / KDB ₃₀ +
{(PGK ₇₀ × ΔGK ₇₀ ) / 2} / KDB ₇₀ +
{(PGK ₁₀₀ × ΔGK ₁₀₀ ) / 2} / KDB ₁₀₀ ] / 3 = 11 [V]
ΔHHTp _K = [{(PGK ₃₀ × ΔGK ₃₀ ) / 2} / KDK ₃₀ +
{(PGK ₇₀ × ΔGK ₇₀ ) / 2} / KDK ₇₀ +
{(PGK ₁₀₀ × ΔGK ₁₀₀ ) / 2} / KDK ₁₀₀ ] / 3 = 13 [%]
And the development voltage correction amount ΔHGVp _K is transmitted to the high voltage control unit 44 to instruct increase / decrease of the development voltage of the image forming unit 13k, and the element driving time correction amount ΔHHTp _K is sent to the head interface unit 42. The print processing is executed by instructing to increase / decrease the element driving time of the exposure head 31 of the image forming unit 13k.

  The same applies to the yellow (Y), magenta (M), and cyan (C) image forming units 13y, 13m, and 13c.

  FIG. 35 shows the effect of this embodiment. As shown in FIG. 35, a conventional printed matter (a printed matter that has not been subjected to the print density correction processing of the present embodiment), that is, a printed matter that has been corrected using only the reverse transfer amount that was estimated in advance in the design (set reverse transfer amount information table (FIG. 9)). In this case, the print density value is reduced by about 3 to 10% compared to the target density value due to the reverse transfer phenomenon. However, when the print density correction processing of this embodiment is performed, In comparison, the print density value can be suppressed within 3% of the error.

  In this embodiment, the table values in the volume resistivity correction table (FIG. 10) and the reference medium reverse transfer amount table (FIG. 11) are experimental values of the medium reverse transfer amount due to the actual reverse transfer phenomenon on each paper P. The table values of the volume resistivity correction table and the reference medium reverse transfer amount table may be values calculated by simulation or the like.

  As described above, in this embodiment, the medium reverse transfer amount calculated based on the reverse transfer amount correction rate in the current state obtained from the density detection pattern printed directly on the conveyance belt and the volume resistivity ρ of the paper P. Are used to calculate the respective correction amounts of the development voltage and the element driving time, and the image forming conditions set in advance before the image formation on the paper P are corrected by these correction amounts. It is possible to prevent a decrease in density due to the reverse transfer phenomenon caused by the type of P and the like and always obtain a stable printing density.

  Hereinafter, the printer of this embodiment will be described with reference to FIGS. In addition, the same part as the said Example 1 attaches | subjects the same code | symbol, and abbreviate | omits the description.

  In FIG. 36, reference numeral 50 denotes a medium resistance measuring mechanism as a resistance information measuring unit, which is disposed in the paper conveyance path 2 between the hopping roller 6 and the registration roller 7 on the upstream side in the paper conveyance direction. 3 has a function of measuring the resistance value of the paper P fed from the hopping roller 6 to 3, and also has a function of measuring the thickness of the paper P.

  As shown in FIG. 37, the medium resistance measuring mechanism 50 includes an electrode 51 and an electrode 52 arranged to face each other, and the electrode 51 is attached to one end of a lever 53 that rotates about a rotation fulcrum 53a. Yes.

  The lever 53 is provided with a spring member 54 such as a compression coil spring for biasing the electrode 51 in the direction of the electrode 52 at the end on the electrode 51 side, and on the opposite side across the rotation fulcrum 53a of the electrode 51. A cam 55 that rotates about a rotation fulcrum 55a is disposed, and the electrode 51 moves with the rotation of the cam 55 so that the electrode can move toward and away from the electrode 52. 51 and the electrode 52 can be sandwiched.

  Further, a distance sensor 56 for measuring the amount of vertical movement of the end portion of the lever 53 on the opposite side of the electrode 51 is arranged so that the thickness of the paper P can be measured.

  FIG. 38 shows a circuit diagram for measuring the electric resistance of the paper P by the electrodes 51 and 52 of the medium resistance measuring mechanism 50. As shown in FIG. 38, the electrode 52 is grounded and connected to a DC power source 57. In addition, a variable resistor 58 is connected to the DC power source 57, and a terminal 59 is provided between the variable resistor 58 and the electrode 51.

  In FIG. 39, reference numeral 61 denotes resistance information acquisition means, which calculates a current value flowing through the paper P from the resistance value of the variable resistor 58 and the potential of the terminal 59, and determines the resistance of the paper P from the current value and the voltage drop due to the paper P The volume resistivity ρ is calculated from the resistance value, the thickness of the paper P measured by the distance sensor 56 and the contact area of the electrodes 51 and 52 with the paper P, and the resistance information of the paper P is acquired. It is functional means formed by software having a function and the main control unit 43.

  Reference numeral 62 denotes medium reverse transfer amount calculation means, which has a function of calculating the medium reverse transfer amount of the paper P using the logarithmic approximation formula based on the volume resistivity ρ of the paper P acquired by the resistance information acquisition means 47. And functional means formed by the main control unit 43.

  The storage unit 45 of the printer 1 according to the present embodiment has a print density correction processing program having functions such as environment correction processing and paper-based density correction processing similar to those in the first embodiment, and functions similar to those in the first embodiment. A print job execution program including a print processing program and the like is stored in advance, and each functional unit of the printer 1 of the present embodiment is formed by steps of the print job execution program executed by the main control unit 43.

  The storage unit 45 also has the same image forming conditions as in the first embodiment, the image data of the density detection pattern (FIG. 14), the voltage density value conversion coefficient table (FIG. 4), and the density target value table (FIG. 6). The development voltage adjustment amount table (FIG. 7), the element drive time adjustment amount table (FIG. 8), and the set reverse transfer amount information table (FIG. 9) are preset and stored. The resistivity reverse transfer amount conversion coefficient table shown in FIG. 40 used for the density correction processing for each sheet in the density correction processing is preset and stored.

  This resistivity reverse transfer amount conversion coefficient table shows the coefficients AL and BL in the logarithmic approximation formula for calculating the medium reverse transfer amount of the paper P from the volume resistivity ρ of the paper P calculated by the resistance information acquisition means 47. Store.

  In this embodiment, the coefficients AL and BL in the resistivity reverse transfer amount conversion coefficient table are the relationship between the actual medium reverse transfer amount experimentally obtained using various types of paper P and the volume resistivity ρ of the paper P. For example, the relationship between the volume resistivity ρ of the paper P and the black medium reverse transfer amount is as shown in FIG. 41 for each printing duty.

  In the density correction processing for each sheet according to the present embodiment, the resistance information acquisition method and the medium reverse transfer amount calculation method for the sheet P are different from those in the first embodiment. For this reason, in this embodiment, the storage of the volume resistivity correction coefficient table (FIG. 10) and the reference medium reverse transfer amount information table (FIG. 11) of Embodiment 1 is omitted.

  The print job processing by the printer 1 having the above-described configuration will be described according to the steps indicated by SA using the flowchart shown in FIG.

  The standby operation in steps SA1 to SA3 and the environmental correction process in steps SA4 to SA12 in the present embodiment are the standby operation in steps S1 to S3 in the first embodiment, and the environmental correction process in steps S4 to S12. Since it is the same, the description is abbreviate | omitted.

  Step SA13: In step SA2, the main control unit 43 that has determined execution of printing on the paper P starts a printing operation by the print processing program, and sets the volume resistivity ρ as resistance information of the paper P to be printed. In order to obtain this, the cam 55 of the medium resistance measuring mechanism 50 is rotated to separate the electrode 51 and the electrode 52, and the type of the sheet P of the medium setting information from among the sheets P stored in the sheet supply storage cassette 3. The paper P corresponding to the above is fed by the hopping roller 6 and conveyed to the medium resistance measuring mechanism 50 to stop it, and the printing operation is temporarily interrupted. In this case, the feeding amount of the paper P is controlled by monitoring the rotational speed of the hopping motor 6a.

  The main control unit 43 that interrupted the printing operation rotates the cam 55 by the resistance information acquisition unit 61 in order to execute the density correction processing for each paper at the time of printing by the density correction processing function for each paper of the print density correction processing program. Thus, the sheet P is sandwiched between the electrode 51 and the electrode 52, the displacement of the end of the lever 53 is detected from the output of the distance sensor 56, and the thickness d of the sheet P is measured. In this case, since the positional relationship between the lever 53, its rotation center 53a, and the distance sensor 56 is known, the displacement amount of the electrode 51, that is, the thickness d of the paper P is determined from these dimensions and the displacement detection value by the distance sensor 56. Can be requested.

The main control unit 43 that has measured the thickness d of the paper P applies a predetermined voltage _VDC from the DC power source 57 in a state where the paper P is sandwiched between the electrode 51 and the electrode 52, and the voltage at the terminal 59 is predetermined. by controlling the variable resistor 58 to be in the range of, calculated from the potential V _Er of the resistance value R _r and the terminal 59 of the variable resistor 58 at that time, the current value I _DC flowing through the variable resistor 58 by the following formula .

I _DC = VEr / Rr (9)
From Kirchhoff's law, the current flowing through the sheet P between the electrode 51 and the electrode 52 of the calculated current value I _DC and medium resistance measurement mechanism 50 are equal, the contact area S of the electrode 51 and electrode 52 is known Therefore, the main control unit 43 calculates the resistance value R ₁ of the contact area S of the paper P from the applied voltage V _DC and current value I _DC and the potential V _{Er of the} terminal 59 by the following equation.

R ₁ = (V _DC -V _Er ) / I _DC (10)
Then, the main control unit 43 calculates the volume resistivity ρ of the paper P from the contact area S and the measured thickness d of the paper P by the following equation.

ρ = R ₁ S / d (11)
In this way, the main control unit 43 acquires the volume resistivity ρ, which is resistance information of the paper P to be printed, by the resistance information acquisition unit 61.

  Step SA14: The main control unit 43 that has acquired the volume resistivity ρ uses the medium reverse transfer amount calculation unit 62 to store the resistivity reverse transfer amount conversion coefficient stored in the storage unit 45 based on the acquired volume resistivity ρ. Using the table (FIG. 40), the medium reverse transfer amount based on the volume resistivity ρ of the paper P to be printed is calculated.

For example, each medium reverse transfer amount PGK for each black print duty is calculated by the following equation using the coefficients AL _K and BL _K of the resistivity reverse transfer amount conversion coefficient table.

PGK ₃₀ = AL _K30 × Ln (ρ) + BL _K30 (12a)
PGK ₇₀ = AL _K70 × Ln (ρ) + BL _K70 (12b)
PGK ₁₀₀ = AL _K100 × Ln (ρ) + BL _K100 (12c)
Then, the main control unit 43 also applies the medium reverse transfer amounts PGY, PGM, and PGC of yellow (Y), magenta (M), and cyan (C) on the paper P having the volume resistivity ρ in the same manner as in the case of black. 40, and the respective media reverse transfer amounts are stored in the storage unit 45 as the medium reverse transfer amount table shown in FIG.

  In this way, the main control unit 43 calculates the medium reverse transfer amount of the paper P based on the volume resistivity ρ that is resistance information of the paper P to be printed.

  Step SA15: The main control unit 43 that stores the medium reverse transfer amount table uses the expressions (7) and (8) to calculate the development voltage correction amount ΔHGVp at the time of printing, as in step S14 of the first embodiment. The element driving time correction amount ΔHHTp is calculated, and each developing voltage correction amount ΔHGVp is transmitted to the high voltage controller 44 to instruct increase / decrease of the developing voltage of each image forming unit 13, and each element driving time correction amount ΔHHTp is used as the head interface. The unit 42 is instructed to increase / decrease the element driving time of the exposure head 31 provided in each image forming unit 13, and the process proceeds to Step SA16.

  In this way, before the image formation on the paper P by the image forming unit 13, the preset image forming conditions are corrected to the image forming conditions suitable for the current internal environment and the paper P to be printed.

  Step SA16: The main control unit 43 that has instructed the high voltage control unit 44 and the head interface unit 42 to increase or decrease the development voltage correction amount ΔHGVp and the element driving time correction amount ΔHHTp of each image forming unit 13 has been interrupted. In order to resume the printing operation, the cam 55 of the medium resistance measuring mechanism 50 is rotated to release the pinching of the paper P by the electrode 51 and the electrode 52, and the paper P is moved in the direction of the image forming unit 13 through the paper transport path 2. Transport to.

  Since the subsequent printing operation is the same as step S15 in the first embodiment, the description thereof is omitted.

  In this case, when a plurality of pieces of image data are included in the print data, steps SA13 and SA14 are omitted, and the electrode 51 and the electrode 52 of the medium resistance measuring mechanism 50 are separated from each other, and the paper feed is accommodated. The sheet P fed from the cassette 3 is transported in the direction of the image forming unit 13 through the medium resistance measuring mechanism 50, and the remaining number of sheets is used as in step S15 of the first embodiment using the corrected image forming conditions. The same printing operation may be repeated, or after printing on one sheet P, the process returns to step SA13 and steps SA13 to SA16 may be repeated to print the remaining number of sheets.

  When all the image data has been printed, the process returns to step SA1 to continue the standby in steps SA1 to SA3.

  Hereinafter, the print density correction processing according to the present embodiment will be described with reference to specific numerical values shown in FIGS.

  In the following description, only black (K) is shown, but the same applies to yellow (Y), magenta (M), and cyan (C).

  Further, in the following description, the reverse transfer amount correction rate is calculated by steps SA4 to SA12 in the environment correction process shown in FIG. 42, and each numerical value is stored as a value of the reverse transfer amount correction rate table shown in FIG. The volume resistivity ρ calculated by the resistance information acquisition unit 61 in step SA13 in the density correction processing for each paper at the time of printing according to the present embodiment is 2.58E + 10 [Ω · cm]. .

In step SA14, when the black medium reverse transfer amount PGK is obtained, the numerical values of the coefficients AL _K and BL _{K in} the resistivity reverse transfer amount conversion coefficient table shown in FIG. 44 and the equations (12a) to (12c) are obtained. make use of,
PGK ₃₀ = AL _K30 × Ln (ρ) + BL _K30 = 0.019
PGK ₇₀ = AL _K70 × Ln (ρ) + BL _K70 = 0.045
PGK ₁₀₀ = AL _K100 × Ln (ρ) + BL _K100 = 0.065
Each numerical value is calculated and stored in the storage unit 45 as the numerical value of the medium reverse transfer amount table shown in FIG.

When obtaining the development voltage correction amount ΔHGVp _K (unit: V) and the element driving time correction amount ΔHHTp _K (unit:%) during black printing in step SA15, the values in the reverse transfer amount correction rate table shown in FIG. And using the numerical values of the medium reverse transfer amount table shown in FIG. 45 obtained in step SA14, the equations (7), and (8),
ΔHGVp _K = [{(PGK ₃₀ × ΔGK ₃₀ ) / 2} / KDB ₃₀ +
{(PGK ₇₀ × ΔGK ₇₀ ) / 2} / KDB ₇₀ +
{(PGK ₁₀₀ × ΔGK ₁₀₀ ) / 2} / KDB ₁₀₀ ] / 3 = 14 [V]
ΔHHTp _K = [{(PGK ₃₀ × ΔGK ₃₀ ) / 2} / KDK ₃₀ +
{(PGK ₇₀ × ΔGK ₇₀ ) / 2} / KDK ₇₀ +
{(PGK ₁₀₀ × ΔGK ₁₀₀ ) / 2} / KDK ₁₀₀ ] / 3 = 15 [%]
And the development voltage correction amount ΔHGVp _K is transmitted to the high voltage control unit 44 to instruct increase / decrease of the development voltage of the image forming unit 13k, and the element driving time correction amount ΔHHTp _K is sent to the head interface unit 42. The print processing is executed by instructing to increase / decrease the element driving time of the exposure head 31 of the image forming unit 13k.

  The same applies to the yellow (Y), magenta (M), and cyan (C) image forming units 13y, 13m, and 13c.

  FIG. 46 shows the effect of this embodiment. As shown in FIG. 46, conventionally, the print density value is reduced by about 3 to 12% compared to the target density value due to the reverse transfer phenomenon, but when the print density correction processing of this embodiment is performed, Compared with the target density value, the print density value can be suppressed within 4% of the error.

  In this embodiment, each table value of the resistivity reverse transfer amount conversion coefficient table (FIG. 40) is obtained based on the medium reverse transfer amount due to the actual reverse transfer phenomenon in various types of paper P obtained experimentally. The table value of the resistivity reverse transfer amount conversion coefficient table may be a value calculated by simulation or the like.

  As described above, in this embodiment, the volume calculated from the reverse transfer amount correction rate in the current state obtained from the density detection pattern printed directly on the conveyance belt and the resistance value of the paper P measured by the medium resistance measurement mechanism. Using the medium reverse transfer amount calculated based on the resistivity ρ, the correction amounts of the development voltage and the element driving time are calculated, and the image formation set in advance before the image formation on the paper P by the correction amounts. Since the conditions are corrected, it is possible to prevent a decrease in density due to the reverse transfer phenomenon caused by the internal environment of the printer, the type of the paper P, etc., and always obtain a stable printing density.

  In each of the above embodiments, the resistance information of the paper P is described as the volume resistivity ρ, but is not limited to the above, and may be, for example, a resistance value.

  In each of the above embodiments, the element driving time of the exposure head is increased or decreased to correct the density change due to the reverse transfer phenomenon. However, the present invention is not limited to the above, and the current value supplied to the light emitting element Alternatively, the drive voltage may be increased or decreased.

  Further, in each of the above embodiments, the development voltage applied to the development roller has been described as increasing and decreasing to correct the density change due to the reverse transfer phenomenon. However, the present invention is not limited thereto, and the drum potential, charging voltage, supply voltage, etc. You may make it increase / decrease, and you may make it control combining these and development voltage.

  Further, in each of the embodiments described above, the correction of the density change due to the reverse transfer phenomenon has been described as correcting the development voltage correction amount and the element driving time correction amount at a ratio of 1: 1, but is not limited thereto. .

  Further, in each of the above embodiments, the exposure head is described as using an element array composed of a plurality of light emitting elements as a light source. However, the present invention is not limited to the above, and a laser light source or the like is used as a light source. May be.

  Further, in each of the above embodiments, the image forming unit is described as being arranged in the order of black, yellow, magenta, and cyan from the upstream side in the paper conveyance direction. However, the present invention is not limited to the above. In the case of having a plurality of image forming units, cyan may be the most upstream in the arrangement order of the image forming units, for example.

  Furthermore, in each of the embodiments described above, the number of image forming units is four. However, the number of image forming units is not limited to the above, and the image forming unit includes two or more, three or less, or five or more image forming units. Even when applied to a forming apparatus, the same effects as described above can be obtained.

DESCRIPTION OF SYMBOLS 1 Printer 2 Paper conveyance path 3 Paper feed accommodation cassette 4 Stacker 6 Hopping roller 6a Hopping motor 7 Registration roller 7a Registration motor 8 Pinch roller 9 Drive roller 9a Belt motor 10 Tension roller 11 Conveyance belt 12 Adsorption roller 13, 13k, 13y, 13m , 13c Image forming unit 14 Transfer roller 14a Transfer voltage generator 15 Heat roller 15a Heater motor 16 Pressure roller 17 Fixing device 18a, 18b, 18c, 18d Conveyance monitoring sensor 20 Heater 21 Thermistor 23 Toner cartridge 24 Photosensitive drum 24a Drum motor DESCRIPTION OF SYMBOLS 25 Charging roller 25a Charging voltage generating part 26 Developing roller 26a Developing voltage generating part 27 Developing blade 28 Supply roller 28a Supply voltage generating part 29 Static elimination light source 31 Dew Head 32 belt cleaning blade 33 a waste toner tank 35 concentration sensor 36 red LED
37 Phototransistor for specular reflection light reception 38 Phototransistor for diffuse reflection light reception 40 Host interface unit 41 Command / image processing unit 42 Head interface unit 43 Main control unit 44 High voltage control unit 45 Storage unit 47, 61 Resistance information acquisition means 48, 62 Medium reverse transfer amount calculation means 50 Medium resistance measurement mechanism 51, 52 Electrode 53 Lever 53a Rotation fulcrum 54 Spring member 55 Cam 55a Rotation fulcrum 56 Distance sensor 57 DC power supply 58 Variable resistance 59 Terminal

Claims (10)

In an image forming apparatus that forms a density detection pattern on a conveyor belt to perform density correction and forms an image on a medium.
Means for obtaining resistance information of the medium;
Means for acquiring medium reverse transfer amount information of the medium based on the acquired resistance information;
An image forming apparatus comprising: means for correcting an image forming condition when an image is formed on a medium based on the acquired medium reverse transfer amount information. The image forming apparatus according to claim 1.
Based on the acquired resistance information, instead of means for acquiring medium reverse transfer amount information of the medium,
Medium reverse transfer amount information storage means for storing medium reverse transfer amount information corresponding to the resistance information of the medium;
An image forming apparatus comprising: means for acquiring the medium reverse transfer amount information from the medium reverse transfer amount information storage unit based on the acquired resistance information. The image forming apparatus according to claim 1, wherein:
An image forming apparatus comprising: a density detection unit that detects a density value of the density detection pattern. The image forming apparatus according to claim 1, wherein:
The image forming apparatus is characterized in that the correction of the image forming condition is performed by changing a developing voltage. The image forming apparatus according to claim 1, wherein:
The image forming apparatus corrects the image forming condition by changing a driving time of a light emitting element of an exposure head. The image forming apparatus according to claim 1, wherein:
A plurality of image forming units configured to be able to contact and separate from each other are provided to the conveyor belt,
An image forming apparatus comprising: a means for forming the density detection pattern by bringing the image forming unit into contact with the transport belt. The image forming apparatus according to claim 1.
The image forming apparatus, wherein the resistance information is acquired from input medium setting information. The image forming apparatus according to claim 1.
A resistance information measurement unit that measures resistance information of the medium is provided.
The resistance information is acquired by the resistance information measuring unit. A transport belt for transporting the medium;
A plurality of image forming units that are arranged along the medium conveyance direction of the medium on the conveyance belt and configured to form a developer image of a set color on the medium, each configured to be able to contact and separate from the conveyance belt; ,
A density detector that detects a density value of a density detection pattern formed on the conveyor belt;
In an image forming apparatus comprising: a reference medium reverse transfer amount information storage unit that stores a medium reverse transfer amount of a reference medium corresponding to the resistance information of the medium;
One of the image forming units is brought into contact with the transport belt, and the density detection pattern is formed on the transport belt in a state where the image forming unit on the downstream side in the medium transport direction is separated from the transport belt, Means for detecting a density value of the density detection pattern by the density detector;
Means for bringing all of the image forming units into contact with the conveyor belt, forming the density detection pattern on the conveyor belt by one of them, and detecting the density value of the density detection pattern by the density detector; ,
Each set color is based on the difference in detected density value between when the image forming unit downstream in the medium conveying direction is separated from the conveying belt and when all the image forming units are in contact with the conveying belt. Means for calculating the reverse transfer amount correction rate of
When forming a developer image on the medium,
Means for reading a reference medium reverse transfer amount of a medium on which an image is to be formed from the reference medium reverse transfer amount information storage means based on the input resistance information of the medium, and calculating a medium reverse transfer amount of the medium;
An image forming apparatus comprising: means for correcting an image forming condition when an image is formed on a medium based on the acquired medium reverse transfer amount and the reverse transfer amount correction rate. A transport belt for transporting the medium;
A plurality of image forming units that are arranged along the medium conveyance direction of the medium on the conveyance belt and configured to form a developer image of a set color on the medium, each configured to be able to contact and separate from the conveyance belt; ,
A density detector that detects a density value of a density detection pattern formed on the conveyor belt;
In an image forming apparatus including a resistance information measuring unit that measures resistance information of a medium,
One of the image forming units is brought into contact with the transport belt, and the density detection pattern is formed on the transport belt in a state where the image forming unit on the downstream side in the medium transport direction is separated from the transport belt, Means for detecting a density value of the density detection pattern by the density detector;
Means for bringing all of the image forming units into contact with the conveyor belt, forming the density detection pattern on the conveyor belt by one of them, and detecting the density value of the density detection pattern by the density detector; ,
Based on the difference in detected density value between when the image forming unit on the downstream side in the medium conveying direction is separated from the conveying belt and when all the image forming units are in contact with the conveying belt, the reverse transfer amount Means for calculating a correction factor;
When forming a developer image on the medium,
Means for acquiring resistance information of a medium on which an image is to be formed by the resistance information measuring unit;
Means for calculating a medium reverse transfer amount of the medium based on the measured resistance information;
An image forming apparatus comprising: means for correcting an image forming condition when an image is formed on a medium based on the calculated medium reverse transfer amount and the reverse transfer amount correction rate.

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