Image forming apparatus

Abstract

To provide an image forming apparatus that efficiently perform density correction processing.SOLUTION: The present invention relates to an image forming apparatus. The image forming apparatus of the present invention has: exposure means that exposes a photoreceptor charged with electricity to form an electrostatic latent image; developing means that supplies developer to the electrostatic latent image on the photoreceptor to develop a developer image; image processing means that performs image processing to convert image formation data into exposable data; conveying means that conveys a medium; transfer means that transfers the developer image to the medium being conveyed by the conveying means or to the conveying means; density detection means that detects the density of the developer image on the conveying means; means that determines whether to execute density correction processing of correcting the density of the developer image developed on the photoreceptor on the basis of the density detected by the density detection means, by considering at least an element included in the image formation data; and means that, when it is determined to execute the density correction processing, controls the apparatus to execute the density correction processing.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, and can be applied to, for example, a printer that forms an image on a recording medium using an electrophotographic method. [Background technology]

[0002] Conventionally, image forming apparatuses such as color electrophotographic printers use a plurality of image forming units, each of which includes a photosensitive drum, a charging unit, an exposure unit, a developing unit, etc. In conventional image forming apparatuses, these image forming units are arranged in order, and toner images are transferred sequentially onto a transfer body or a recording medium by the image forming units of each color.

[0003] Furthermore, some conventional image forming apparatuses have a control means for correcting the density of the toner image to be formed, which means is a means for arbitrarily changing the amount of exposure energy and the developing voltage. Conventionally, an image forming apparatus having a control means for correcting the density of the toner image to be formed is disclosed in Patent Document 1.

[0004] The image forming apparatus described in Patent Document 1 has a means for correcting the process of converting print data sent from a higher-level device into data that can be exposed, as a means for controlling the correction of gradation density. Furthermore, if the image forming apparatus described in Patent Document 1 determines that density correction is necessary after receiving a print job, it performs image processing based on the density correction results after the density correction is complete, and prints from the image for which the processing has been completed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-215533 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, conventional image forming devices receive a print job and then determine whether or not to perform density correction. If necessary, they perform the density correction operation. After the density correction operation is complete, they then perform image processing on the print data based on the correction results, and print the data once the processing is complete. In such cases, conventional image forming devices can significantly increase the wait time before printing begins, making reducing this wait time a challenge. In particular, even when printing print data for which density changes have little impact on image quality, density correction can increase the wait time before printing begins, and excessive density correction can increase toner consumption.

[0007] In view of the above problems, there is a demand for an image forming apparatus that can efficiently perform density correction processing. [Means for solving the problem]

[0008] The image forming apparatus of the present invention is characterized by having an exposure means for exposing a charged photosensitive member to light to form an electrostatic latent image, a development means for supplying developer to the electrostatic latent image on the photosensitive member to develop a developer image, an image processing means for processing the image into data that can be exposed by the exposure means when image formation data is supplied, a transport means for transporting a medium, a transfer means for transferring the developer image to the medium being transported by the transport means or to the transport means, a concentration detection means for detecting the density of the developer image on the transport means, a concentration correction process execution determination means for determining whether to perform a concentration correction process to correct the density of the developer image developed on the photosensitive member based on the density detected by the concentration detection means, taking into account at least elements included in the image formation data, and a concentration correction control means for controlling the apparatus to perform the concentration correction process when the concentration correction process execution determination means determines that the concentration correction process should be performed. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an image forming apparatus that efficiently performs density correction processing. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a block diagram showing the configuration of a control system of the printer according to the embodiment. [Figure 2] 1 is a schematic side cross-sectional view of a printer according to an embodiment. [Figure 3] 1 is a schematic diagram (schematic cross-sectional view) illustrating an example of the configuration of a concentration sensor according to an embodiment. [Figure 4] FIG. 4 is a diagram showing an example of the configuration of a target gradation density value table according to the embodiment; [Figure 5] 5A and 5B are diagrams showing examples of the configuration of a tone correction value table according to the embodiment; [Figure 6] 3A to 3C are diagrams showing examples of the configuration of each table held in a mechanism control unit (storage unit) according to the embodiment. [Figure 7] 5A and 5B are diagrams showing an example of the configuration of a density detection pattern stored in a mechanism control unit (storage unit) according to the embodiment. [Figure 8] 4 is a flowchart showing a printing operation by a printer according to an embodiment. [Figure 9] 10 is a graph showing the relationship between the temperature of the photosensitive drum and the potential of the exposed portion according to the embodiment. [Figure 10] 10 is a flowchart showing the operation of a density correction process performed by a printer according to an embodiment. [Figure 11] 10A to 10C are diagrams showing examples of halftone dither patterns for each yuty used in each density detection pattern according to the embodiment. [Figure 12] 10 is a flowchart (part 1) illustrating an example of the operation of a density correction process execution determination unit according to the embodiment. [Figure 13] 10 is a flowchart (part 2) illustrating an example of the operation of the density correction process execution determining unit according to the embodiment. [Figure 14] 10 is a flowchart (part 3) illustrating an example of the operation of the density correction process execution determining unit according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] (A) Main embodiment An embodiment of an image forming apparatus according to the present invention will be described in detail below with reference to the drawings. In this embodiment, an example in which the image forming apparatus according to the present invention is applied to an electrophotographic printer capable of color printing will be described.

[0012] (A-1) Configuration of the embodiment FIG. 2 is a schematic cross-sectional side view of the printer 1 according to the embodiment.

[0013] As shown in Figure 2, printer 1 is a direct transfer color image forming device. Printer 1 has four independent printing mechanisms (image drum units, ID units) 20K, 20C, 20M, and 20Y corresponding to four colors (black, cyan, magenta, and yellow) arranged along the transport direction of transfer belt 30. Note that, hereinafter, the colors black, cyan, magenta, and yellow (toner colors) may be simply represented by the symbols K, C, M, and Y. Printing mechanism 20K is an electrophotographic LED printing mechanism for recording black (K), cyan (C), magenta (M), and yellow (Y) images. Each printing mechanism 20 includes a charging roller 21, a photosensitive drum 22 as a photosensitive body whose surface is uniformly charged by the charging roller 21, a developing roller 23 as a developing means constituting a developing section for forming a toner image, a developing blade 24, a supply roller 25, a static elimination light source 26 for eliminating static electricity from the surface of the photosensitive drum 22, a toner cartridge 27, etc.

[0014] Here, the configuration of each printing mechanism 20 will be described, using the black printing mechanism 20K as a representative. The configurations of the cyan, magenta, and yellow printing mechanisms 20C, 20M, and 20Y are the same as those of the printing mechanism 20K except for the toner color, so detailed description will be omitted. In the printing mechanism 20K, toner supplied from the toner cartridge 27 passes through the supply roller 25 and reaches the development blade 24, where it is formed into a thin layer on the circumference of the development roller 23 and reaches the contact surface with the photosensitive drum 22. As this thin layer is formed on the circumference of the development roller 23, it is rubbed strongly between the development roller 23 and the supply roller 25, causing frictional charging. At this time, the development blade 24 transports only an appropriate amount of toner to the development roller 23.

[0015] The LED heads 28, which serve as exposure means and are located above the photosensitive drums 22 of each printing mechanism 20K, 20C, 20M, and 20Y, are composed of an LED array (not shown) and a drive IC (not shown) that drives the LED array. The LED arrays emit light in response to input print data signals. The LED heads 28 of the printing mechanisms 20K, 20C, 20M, and 20Y receive color image signals, including black, cyan, magenta, and yellow image signals. The LED heads 28 emit light to expose the surface of the photosensitive drum 22, forming an electrostatic latent image on the surface of the photosensitive drum 22. Toner on the circumference of the developing roller 23 adheres to the electrostatic latent image by electrostatic force, forming an image. The toner cartridges 27 of the printing mechanisms 20K, 20C, 20M, and 20Y contain black, cyan, magenta, and yellow toner (developers), respectively. In addition, a transfer roller 29 serving as a transfer means is disposed below each photosensitive drum 22, sandwiching the transfer belt 30 therebetween. The transfer roller 29 presses the transfer belt 30 together with the photosensitive drum 22 to form a transfer nip, and transfers the toner image formed on the photosensitive drum 22 onto the transfer belt 30.

[0016] The transfer belt 30, which serves as a transport means, is stretched with a predetermined tension between a drive roller 31 and a driven roller 32. The drive roller 31 is rotated by a belt motor 83, transporting the transfer belt 30 in the direction of arrow e shown in FIG. 2. The driven roller 32 rotates along with the transfer belt 30. The outer peripheral surface of the transfer belt 30 is formed with a glossy surface, which can also be used as a reference reflector for adjusting the light-emitting current of the density sensor 33 (infrared LED 33A), which will be described later. A belt thermistor 37, which serves as a transport temperature detection means, is disposed below the transfer belt 30, and can detect the temperature of the transfer belt 30. Hereinafter, the temperature measured by the belt thermistor 37 (hereinafter referred to as the "belt temperature" or "transport temperature") will be referred to as "BT."

[0017] A paper storage cassette 11 for storing paper M as a medium (recording medium) is disposed at the bottom of the printer 1. The printer 1 is provided with a medium supply mechanism for supplying paper M stored in the paper storage cassette 11 onto the transport path (transfer belt 30), including a hopping roller 12 that feeds out paper M stored in the paper storage cassette 11, a pinch roller 13 that corrects the skew of paper M when paper M is skewed (a state in which paper M is fed obliquely is called skew), a registration roller 14 that feeds paper M to the top of the transfer belt 30, a guide 15 that guides paper M to the transfer belt 30, and media sensors 16 and 17 in front of and behind the registration roller 14 for detecting paper M.

[0018] A transfer discharge sensor 18 is provided downstream of the transfer belt 30 on the drive roller 31 side to check for recording media that have failed to separate from the transfer belt 30 or to detect the trailing edge position of a recording medium that has passed through.

[0019] The paper M that has passed through the transfer belt 30 and has been printed is separated from the transfer belt 30 and conveyed to the fixing unit 40.

[0020] The fixing unit 40 is composed of a heat roller 41 and a pressure roller 43 that presses the heat roller 41. The heat roller 41 is driven by a heat motor 84, and the pressure roller 43 rotates along with the heat roller 41. The heat roller 41 incorporates a heater 42 (for example, a heat source formed from a halogen lamp or the like) as a heat source. The fixing unit 40 heats and melts the toner on the paper M, fixing the toner image onto the paper M. A thermistor 44 is disposed near the surface of the heat roller 41, and monitors the temperature of the heat roller 41.

[0021] A fixing / discharge sensor 45 is provided downstream of the fixing unit 40, and monitors for jams in the fixing unit 40 and for paper M wrapping around the heat roller 41. A guide 46 is provided downstream of the fixing / discharge sensor 45 in the paper transport direction to transport paper M to a stacker 47 on the top of the housing of the printer 1, and printed paper M is discharged into the stacker 47.

[0022] A cleaning blade 35 is disposed below the transfer belt 30 to remove residual toner remaining on the transfer belt 30. The cleaning blade 35 is made of a flexible rubber or plastic material, and scrapes off residual toner remaining on the transfer belt 30 into a waste toner storage section 36.

[0023] In addition, a density sensor 33 serving as density detection means is disposed below the transfer belt 30 at a position facing the transfer belt 30. The density sensor 33 is a reflective optical sensor with one light-emitting system and two light-receiving systems, and is used to measure the intensity of reflected light from a density detection pattern printed on the transfer belt 30 and detect the print density of the printer 1.

[0024] FIG. 3 is a schematic diagram (schematic cross-sectional view) showing an example of the configuration of the concentration sensor 33. As shown in FIG.

[0025] As shown in Figure 3(a), the density sensor 33 is composed of an infrared LED 33A, a phototransistor 33B for receiving specularly reflected light, and a phototransistor 33C for receiving diffusely reflected light, and is capable of detecting the density of both yellow, magenta, and cyan, as well as the density of black.

[0026] 3(b), when the density sensor 33 detects the densities of yellow, magenta, and cyan, the light emitted from the infrared LED 33A and diffusely reflected by the yellow toner image PY, magenta toner image PM, or cyan toner image PC printed on the transfer belt 30 is received by the diffuse reflected light receiving phototransistor 33C, and the diffuse reflected light receiving phototransistor 33C generates a voltage according to the amount of light. Therefore, if the amount of toner forming the yellow toner image PY, magenta toner image PM, or cyan toner image PC is large (=high density), the amount of diffuse reflected light received by the diffuse reflected light receiving phototransistor 33C increases.

[0027] 3(c), when the density sensor 33 detects the density of black, the light emitted from the infrared LED 33A is specularly reflected by the transfer belt 30 via the black toner image PK printed on the transfer belt 30, and is received by the specularly reflected light receiving phototransistor 33B. This causes the specularly reflected light receiving phototransistor 33B to output a voltage corresponding to the amount of light. Because the black toner image PK absorbs the light emitted from the infrared LED 33A, the less black toner there is (i.e., the lower the density), the more specularly reflected light from the transfer belt 30 that is received by the specularly reflected light receiving phototransistor 33B. Conversely, the more black toner there is (i.e., the higher the density), the less specularly reflected light there is. Therefore, to improve the detection accuracy of the specularly reflected light, the transfer belt 30 must be sufficiently glossy, have a high specular reflectance, and have a uniform specular reflectance.

[0028] A cover 34 for the density sensor 33 is disposed between the density sensor 33 and the transfer belt 30. The cover 34 is located on the density sensor 33 except during the density correction process operation, and covers the density sensor 33 to prevent it from becoming soiled with toner, paper dust, etc. During the density correction process operation, the cover 34 is moved from above the density sensor 33 by a driving means (not shown). Furthermore, as will be described later, the cover 34 is used as a reference reflector for adjusting the light emission current of the density sensor 33 (infrared LED 33A), and therefore has a surface formed thereon that diffusely reflects light corresponding to a predetermined standard.

[0029] An environmental sensor 2 is disposed in a position where the temperature and humidity of the outside air can be measured in the printer 1. Hereinafter, the temperature measured by the environmental sensor 2 (hereinafter referred to as "outside air temperature") will be referred to as "RT", and the humidity measured by the environmental sensor 2 (hereinafter referred to as "outside air humidity") will be referred to as "RH".

[0030] FIG. 1 is a block diagram showing the configuration of a control system of a printer 1 according to an embodiment.

[0031] 1, printer 1 has, as components of its control system, a communication unit 61, a command / image processing unit 62, an LED head interface unit 63, a mechanism control unit 64, a high-voltage control unit 71, and a memory unit 71A. Also, as shown in FIG. 1, printer 1 has, as components of its drive system for driving each roller, belt, etc., a hopping motor 81, a resist motor 82, a belt motor 83, a heat motor 84, and a drum motor 85. Furthermore, printer 1 has, as components of the voltage application means for applying voltages to each roller, etc., a charging voltage generation unit 72, a developing voltage generation unit 73, a supply voltage generation unit 74, and a transfer voltage generation unit 75.

[0032] The communication unit 61 functions as a physical layer interface with the host H (host computer), which is the sender of print data (image formation data) and commands. The communication unit 61 can be configured, for example, with various serial interfaces and network interfaces (for example, various communication connectors and communication chips, etc.).

[0033] The command / image processing unit 62 is responsible for interpreting commands and print data from the host H or expanding them into bitmaps (functioning as an image processing means). The command / image processing unit 62 can be configured with a microprocessor, RAM, special hardware for expansion, etc. (not shown). As shown in Fig. 1, the command / image processing unit 62 functionally has a density gradation correction control unit 62A and a memory unit 62B as density gradation correction control means.

[0034] The density gradation correction control unit 62A of the command / image processing unit 62 performs a process (hereinafter referred to as "density gradation correction process") to correct the gradation value to be output when expanded into a bitmap based on the density value detected by the density sensor 33 so that the print density of the input gradation value becomes the target value.

[0035] The memory unit 62B is a means for storing various data used in the density gradation correction process by the command / image processing unit 62, and holds a target gradation density value table 111 and a gradation correction value table 112. The target gradation density value table 111 is a control parameter used in the density gradation correction process. Furthermore, the gradation correction value table 112 holds (updates and stores) gradation values ​​corrected by the density gradation correction process (hereinafter referred to as "gradation correction values").

[0036] FIG. 4 is a diagram showing an example of the configuration of the target gradation density value table 111. As shown in FIG.

[0037] FIG. 5 is a diagram showing an example of the configuration of the tone correction value table 112. As shown in FIG.

[0038] The LED head interface unit 63 has the function of processing print data expanded into a bitmap from the command / image processing unit 62 to match the interface of the LED head 28. The LED head interface unit 63 can be configured, for example, by a semi-custom LSI and RAM (not shown).

[0039] The mechanism control unit 64, in accordance with instructions from the command / image processing unit 62, recognizes inputs from each sensor (environment sensor 2, medium sensor 16, medium sensor 17, transfer discharge sensor 18, fixing discharge sensor 45, thermistor 44, etc.), and is responsible for the control of the mechanism system and high voltage system, such as each motor (hopping motor 81, registration motor 82, belt motor 83, heat motor 84, drum motor 85, etc.), heater 42, and high voltage control unit 71. Each motor is provided with a driver (not shown) for rotating the motor in accordance with the control of the mechanism control unit 64.

[0040] The mechanism control unit 64 functionally includes a density correction process execution determination unit 64A as a density correction process execution determination unit, a density correction control unit 64B as a density correction control unit, a memory unit 64C, and a density sensor light emission amount adjustment unit 64D.

[0041] The mechanism control unit 64 controls the temperature of the heat roller 41 by controlling the heater 42 while recognizing the surface temperature of the heat roller 41 based on a detection signal from the thermistor 44. The mechanism control unit 64 also measures the temperature and humidity outside the printer 1 using the environment sensor 2, and measures the surface temperature of the transfer belt 30 using the belt thermistor 37 arranged on the transfer belt 30.

[0042] The density correction process execution determination unit 64A of the mechanism control unit 64 determines whether or not to execute a control process (density correction process) by the density correction control unit 64B (hereinafter referred to as the "density correction process execution determination") based on the operating status of the device itself, the detection results of each sensor, and the like. Hereinafter, the conditions for executing the density correction process in the density correction process execution determination are also referred to as the "density correction process execution conditions." For example, the density correction process execution determination unit 64A may determine to execute the density correction process when the power is turned on or after a predetermined number of sheets have been printed. Furthermore, for example, the density correction process execution determination unit 64A may determine to execute the density correction process when the change in the outside air temperature and humidity detected by the environmental sensor 2 exceeds a predetermined value, or when the temperature change of the transfer belt 30 detected by the belt thermistor 37 exceeds a predetermined value. Furthermore, the density correction process execution determination unit 64A may determine to execute the density correction process depending on the content of the print data to be processed. The density correction process execution determination (density correction process execution conditions) will be described in detail below.

[0043] The density correction control unit 64B of the mechanism control unit 64 calculates how much to increase or decrease the development voltage applied to the development roller 23 and the light emission amount (driving time) of the LED head 28 so that the density reaches the target value, based on the density value detected by the density sensor 33. In addition, the density correction control unit 64B calculates a density value to be used in the density gradation correction process, based on the density value detected by the density sensor 33.

[0044] The storage unit 64C stores a sensor detection voltage-density value conversion table 113, a target print density data table 114, a development voltage value adjustment amount table 115, and an LED drive time adjustment amount table 116 as various control parameters used in the density correction process.

[0045] FIG. 6 is a diagram showing an example of the configuration of each table held in the storage unit 64C.

[0046] 6(a) to 6(d) respectively show a sensor detection voltage-density value conversion table 113, a target print density data table 114, a development voltage value adjustment amount table 115, and an LED drive time adjustment amount table 116.

[0047] Furthermore, the storage unit 64C stores image patterns (hereinafter referred to as "density detection patterns") used in density correction processing.

[0048] FIG. 7 is a diagram showing an example of the configuration of the density detection pattern stored in the storage unit 64C.

[0049] 7(a) to 7(c) show first to third density detection patterns PAT1 to PAT3, respectively.

[0050] Furthermore, the density correction control unit 64B stores in the memory unit 64C each correction value determined in the density correction process (for example, a correction value for the voltage applied to the developing roller 23 and a correction value for the time for driving the LED head 28). After the density correction process is completed, the density correction control unit 64B also updates and stores in the memory unit 64C information such as the surface temperature of the transfer belt 30 measured by the belt thermistor 37 and the temperature and humidity outside the device measured by the environmental sensor 2.

[0051] The density sensor light emission amount adjuster 64D of the mechanism controller 64 adjusts the light emission current of the infrared LED 33A so that the output voltages of the specular reflected light receiving phototransistor 33B and the diffuse reflected light receiving phototransistor 33C become preset values ​​for a predetermined reference reflecting object (in this embodiment, the transfer belt 30 or the cover 34). Hereinafter, the adjustment of the light emission current of the infrared LED 33A will be referred to as "density sensor calibration."

[0052] High voltage control unit 71 is responsible for high voltage control (for example, control of charging voltage, developing voltage, supply voltage, transfer voltage, etc.) for each printing mechanism 20. High voltage control unit 71 can be configured, for example, by a microprocessor or custom LSI (not shown).

[0053] The charging voltage generating unit 72 has the function of applying a voltage (charging voltage) to the charging roller 21. The developing voltage generating unit 73 has the function of applying a voltage (developing voltage) to the developing roller 23. The supply voltage generating unit 74 has the function of applying a voltage (supply voltage) to the supply roller 25. The transfer voltage generating unit 75 has the function of applying a voltage (transfer voltage) to the transfer roller 29.

[0054] High voltage control unit 71 includes memory unit 71A that stores various parameters required for high voltage control. Memory unit 71A stores information such as the voltage values ​​(set voltage values) to be set in charging voltage generation unit 72, development voltage generation unit 73, supply voltage generation unit 74, and transfer voltage generation unit 75.

[0055] (A-2) Operation of the embodiment Next, the operation of the printer 1 according to this embodiment will be described.

[0056] FIG. 8 is a flowchart showing the printing operation of the printer 1.

[0057] First, it is assumed that print data is supplied from the host computer H to the printer 1 (S101). The supplied print data is received by the printer 1 via the communication unit 61.

[0058] Next, the command / image processing unit 62 determines that the print data has been received, and instructs the mechanism control unit 64 to detect (measure) the outside air temperature RT and outside air humidity RH using the environmental sensor 2, and to detect (measure) the belt temperature BT of the transfer belt 30 using the belt thermistor 37, and obtains each measurement result (S102).

[0059] Next, the density correction process execution determination unit 64A of the mechanism control unit 64 performs a density correction process execution determination (determines whether or not to execute density correction process) (S103). Only when it is determined in the density correction process execution determination of step S103 that density correction process is to be executed, the mechanism control unit 64 proceeds to step S108 and executes density correction process.

[0060] The density correction process execution determination unit 64A performs a process (hereinafter referred to as a "temperature comparison process") that compares the most recently measured temperature and humidity (outside air temperature RT, outside air humidity RH, and belt temperature BT) with the temperature and humidity measured (stored) during the previous density correction process, and determines whether to execute the density correction process based on at least the results of the temperature comparison process, etc. The density correction process execution determination unit 64A may also determine whether to execute the density correction process by taking into account other factors such as the content of the print data.

[0061] Here, the outdoor temperature RT measured during the previous density correction process is set to "RT ADC ", and the outdoor air humidity RH measured during the previous density correction process is set to "RH ADC ", and the belt temperature BT measured during the previous density correction process is set to "BT ADC " shall be expressed as ".

[0062] Here, a specific example of the density correction necessity determination process based on the temperature comparison process result will be described.

[0063] FIG. 9 is a graph showing the relationship (measurement results) between the temperature of the photosensitive drum 22 and the potential of the exposed portion (the portion on the surface of the photosensitive drum 22 exposed by the LED head 28).

[0064] In the graph of FIG. 9, the vertical axis represents the potential of the exposed portion, and the horizontal axis represents the temperature of the photosensitive drum 22.

[0065] 9, it can be seen that as the temperature of the photosensitive drum 22 drops, the absolute value of the potential does not tend to decrease even when the charged photosensitive drum 22 is exposed to light. In other words, the potential difference between the exposed portion of the photosensitive drum 22 and the developing roller 23 decreases, making it difficult for toner to adhere to the exposed portion, resulting in a lower density toner image. For example, if density correction is performed to achieve an appropriate density when the photosensitive drum 22 is warm, such as after continuous printing, and then printing is started after the photosensitive drum 22 has cooled down after being left for a while, the above-mentioned decrease in density of the toner image can occur.

[0066] Therefore, in order to prevent the above-described decrease in density of the toner image, the density correction process execution determination unit 64A of the mechanism control unit 64 determines to perform density correction process again if it determines that the temperature of the photosensitive drum 22 has decreased by a predetermined amount since the previous density correction process was performed. However, since the configuration of the printer 1 in this embodiment does not allow direct measurement of the temperature of the photosensitive drum 22, the belt temperature BT (the temperature of the transfer belt 30 in contact with each photosensitive drum 22) measured by the belt thermistor 37 is used as a substitute for the temperature of the photosensitive drum 22, but a temperature measured at another location may also be used as a substitute.

[0067] Specifically, for example, the density correction process execution determination unit 64A determines whether the following formula (1) is satisfied (the current belt temperature BT is equal to or lower than the belt temperature BT ADC , the density is determined to be significantly different from the target, and a density correction is to be performed. Note that the density correction process execution determination unit 64A is not limited to the predetermined temperature (10°C) applied to equation (1), and other values ​​may be applied. Note that the density correction process execution determination unit 64A determines whether the current belt temperature BT is lower than the belt temperature BT at the time of the previous density correction. ADC If the temperature has risen by a predetermined temperature or more (for example, by 10° C. or more) compared with the temperature of the image sensor 10, it may be determined that the density correction process should be performed. BT≦BT ADC -10…(1)

[0068] Furthermore, the density correction process execution determination unit 64A may also determine to execute the density correction process when the current outside air temperature RT and / or the outside air humidity RH has changed by a predetermined amount or more compared to the time of the previous density correction, assuming that the density of the toner image formed on the photosensitive drum 22 will change. For example, the density correction process execution determination unit 64A may determine to execute the density correction process when the current outside air temperature RT is equal to or greater than the outside air temperature RT measured at the time of the previous density correction. ADCIf the change is greater than a predetermined value (for example, 10° C. or more), the density correction process execution determination unit 64A may determine that the density correction process should be executed again. ADC If the change is greater than a predetermined value (for example, 10% or more), it may be determined that the density correction process should be performed again.

[0069] As described above, in this embodiment, the density correction process execution determination unit 64A may compare one or more of the elements of the outside air temperature RT, the outside air humidity RH, and the belt temperature BT with the previous density correction and determine that there has been a predetermined or greater change, and may determine to execute the density correction process again. Note that the density correction process execution determination unit 64A may also compare and determine only one or two of the elements of the outside air temperature RT, the outside air humidity RH, and the belt temperature BT.

[0070] Next, the command / image processing unit 62 performs preparation processing for printing on the paper M based on the supplied print data (S104). Specifically, the command / image processing unit 62 instructs the mechanism control unit 64 to warm up the heater 42, and performs print data expansion processing based on the values ​​of the gradation correction value table 112 stored in the memory unit 62B to generate bitmap data for each color. At this time, upon receiving the warm-up instruction from the command / image processing unit 62, the mechanism control unit 64 controls the heat motor 84 to drive the heat roller 41 and controls the heater 42 (halogen lamp) to adjust the fixing temperature of the fixing unit 40. When the above-described processing has met the printable conditions, i.e., when the print data for one page of each color to be printed on the recording medium is stored in the memory of the command / image processing unit 62 and the fixing temperature of the fixing unit 40 has reached the optimum temperature, the command / image processing unit 62 issues a command to the mechanism control unit 64 to start printing.

[0071] Next, in the printer 1, a process for causing each printing mechanism 20 to develop a toner image (hereinafter also referred to as a "print image forming process") is performed (S105).

[0072] Here, the print image forming process in the printer 1 will be described.

[0073] Upon receiving the command to start printing, mechanism control unit 64 controls belt motor 83 and drum motor 85 to drive drive roller 31 and photosensitive drum 22. At this time, mechanism control unit 64 also instructs high voltage control unit 71 to output high voltage. Upon receiving the high voltage output command, high voltage control unit 71 reads the set voltage values ​​of each voltage (charging voltage, developing voltage, and supply voltage) stored in memory unit 71A according to the ambient temperature RT and ambient humidity RH. High voltage control unit 71 then generates and supplies a charging voltage to charging roller 21 from charging voltage generator 72, a developing voltage to developing roller 23 from developing voltage generator 73, and a supply voltage to supply roller 25 from supply voltage generator 74. At this time, mechanism control unit 64 also reads a developing voltage correction value stored in memory unit 64C and corrects the developing voltage.

[0074] Here, the operation of each printing mechanism 20 (the operation of forming a toner image) in forming a print image will be described. Since the operation of each printing mechanism 20 differs only in the color of the toner used, the operation of each printing mechanism 20 will be described using the black printing mechanism 20K as a representative. When the charging voltage, developing voltage, and supply voltage are supplied by the high-voltage control unit 71, a charging voltage of −1100 V is supplied to the charging roller 21, charging the surface of the photosensitive drum 22 to approximately −600 V. At this time, a developing voltage of −200 V is supplied to the developing roller 23. At this time, a supply voltage of −250 V is also supplied to the supply roller 25. Furthermore, at this time, an electric field is formed in the direction from the developing roller 23 to the supply roller 25 near the contact area between the developing roller 23 and the supply roller 25. The toner cartridge 27 of the printing mechanism 20K contains black toner, and the toner supplied from the toner cartridge 27 to the developing unit is rubbed strongly at the contact area between the developing roller 23 and the supply roller 25, causing frictional charging. In this embodiment, the toner is frictionally charged to a negative polarity due to the characteristics of the developing roller 23 and the supply roller 25. As a result, the toner, which has been frictionally charged to a negative polarity, adheres to the developing roller 23 near the contact area between the developing roller 23 and the supply roller 25 due to Coulomb force from the electric field directed from the developing roller 23 to the supply roller 25. The toner adhered to the developing roller 23 is carried to the contact area between the developing roller 23 and the developing blade 24 as the developing roller 23 rotates, and is smoothed to a uniform thickness by the developing blade 24 to form a toner layer. The developing roller 23 continues to rotate, carrying the toner layer to the contact area with the photosensitive drum 22.

[0075] Meanwhile, the command / image processing unit 62 transmits bitmap data for each page to the LED head interface unit 63. The LED head interface unit 63 blinks the LED of the LED head 28 in accordance with the received bitmap data, exposes the photosensitive drum 22 charged to -600 V, discharges it to -60 V, and writes an electrostatic latent image. At this time, the LED drive time correction value stored in the memory unit 64C is read out and the LED drive time is corrected.

[0076] As the photosensitive drum 22 rotates, the electrostatic latent image written on the surface of the photosensitive drum 22 reaches the contact area with the developing roller 23. Between the developing roller 23 and the photosensitive drum 22, an electric field is formed in the direction from the photosensitive drum 22 to the developing roller 23 in the exposed portion that has been discharged to -60 V, and an electric field in the opposite direction is formed in the non-exposed portion that remains at -600 V and has not been discharged, so that toner selectively adheres only to the exposed portion from the negatively charged toner layer on the developing roller 23, and the electrostatic latent image is developed into a toner image.

[0077] As described above, the printer 1 performs the print image formation operation.

[0078] Next, in the printer 1, a process (hereinafter simply referred to as a "transfer process") is performed in which the toner images developed by the printing mechanisms 20 are transferred onto the paper M (S106).

[0079] Here, the operation of the transfer process in the printer 1 will be described.

[0080] The mechanism control unit 64 drives each printing mechanism 20 and simultaneously drives the hopping motor 81 to rotate the hopping roller 12, thereby sending only one sheet of paper M from the paper storage cassette 11 to the guide 15. The mechanism control unit 64 then monitors the output of the medium sensor 16, and when it detects that the leading edge of the paper M has reached between the registration roller 14 and the pinch roller 13, it stops the hopping motor 81. The mechanism control unit 64 then drives the registration motor 82 to rotate the registration roller 14 and transport the paper M. The mechanism control unit 64 then monitors the output of the medium sensor 17, and when it detects that the trailing edge of the paper M has reached the transfer belt 30, it stops the registration motor 82. The mechanism control unit 64 then drives the belt motor 83 to rotate the drive roller 31, and sends the paper M electrostatically attracted to the transfer belt 30 to the transfer nip, which is the contact area between the photosensitive drum 22 and the transfer belt 30. Thereafter, the sheet M is transported by the transfer belt 30, and when the leading edge of the sheet M sequentially reaches the contact area between the photosensitive drum 22 and the transfer belt 30, the high-voltage control unit 71, which receives a high-voltage output command from the mechanism control unit 64, causes the transfer voltage generation unit 75 to generate and supply a transfer voltage to the transfer roller 29. As a result, a transfer voltage of 3000 V is supplied to the transfer roller 29, forming an electric field in the direction from the transfer belt 30 toward the photosensitive drum 22, and the toner image developed on the photosensitive drum 22 is transferred to the sheet M on the transfer belt 30. The sheet M onto which the toner image has been transferred continues to be transported by the transfer belt 30 and sent to the fixing unit 40. The mechanism control unit 64 monitors the output of the transfer discharge sensor 18 to check for any sheet M that has failed to separate from the transfer belt 30, and when it detects that the trailing edge of the sheet M has reached the fixing unit, it stops the belt motor 83 and the drum motor 85. Then, upon receiving an instruction to stop high voltage output from mechanism control unit 64, high voltage control unit 71 stops the supply of charging voltage to charging roller 21 from charging voltage generating unit 72, stops the supply of developing voltage to developing roller 23 from developing voltage generating unit 73, stops the supply of supply voltage to supply roller 25 from supply voltage generating unit 74, and stops the supply of transfer voltage to transfer roller 29 from transfer voltage generating unit 75.While the belt motor 83 is driving, the toner remaining on the surface of the upper half of the transfer belt 30 is scraped off by the cleaning blade 35 into the waste toner container 36 .

[0081] As described above, the printer 1 performs the transfer process.

[0082] Next, the printer 1 applies heat and pressure to the paper M to fix the toner image (hereinafter referred to as the "fixing process") (S107), and the printing process ends. When the paper M reaches the fixing unit 40, it is sandwiched and transported between the heat roller 41, which has already reached the fixing temperature, and the pressure roller 43, which is in pressure contact with it, to heat and melt the toner on the paper M, and the toner image is fixed to the paper M. The paper M with the fixed toner image is guided by the guide 46 and discharged to the stacker 47. The mechanism control unit 64 monitors the output of the fixing discharge sensor 45 to monitor for jams in the fixing mechanism and for the paper M wrapping around the heat roller 41, and when it detects that the rear end of the paper M has reached the stacker 47, it stops the heat motor 84 and heater 42 and completes the printing operation.

[0083] Next, a specific operation of the density correction process (the process of step S108) performed by the printer 1 will be described.

[0084] FIG. 10 is a flowchart showing the operation of the density correction process performed by the printer 1.

[0085] First, the concentration sensor light emission intensity adjustment unit 64D of the mechanism control unit 64 adjusts (calibrates) the light emission current of the infrared LED 33A to absorb changes in the light emission characteristics of the infrared LED 33A due to the temperature of the concentration sensor 33 itself and variations in the light emission and light reception sensitivity of the concentration sensor 33 itself that may occur during manufacturing (S201).

[0086] Specifically, the concentration sensor light emission amount adjuster 64D adjusts (calibrates) the light emission current of the infrared LED 33A so that the output voltages of the specular reflected light receiving phototransistor 33B and the diffuse reflected light receiving phototransistor 33C in response to the light reflected by the reference reflector become preset values. In this embodiment, the light emission current adjustment range of the infrared LED 33A is 15 to 25 mV, but is not limited thereto. Also, in this embodiment, the output voltage range of the specular reflected light receiving phototransistor 33B and the diffuse reflected light receiving phototransistor 33C is 0 to 3 V, but is not limited thereto.

[0087] In this embodiment, a cover 34 disposed between the density sensor 33 and the transfer belt 30 is used as a reference reflector for calibrating the light-emitting current of the infrared LED 33A when detecting the densities of yellow, magenta, and cyan. The cover 34 has a predetermined reference diffuse reflectance, and the density sensor light emission amount adjuster 64D adjusts the light-emitting current of the infrared LED 33A so that the output voltage of the diffuse reflected light receiving phototransistor 33C becomes a set value. In this example embodiment, the set value of the output voltage of the diffuse reflected light receiving phototransistor 33C is 2.00 [V], but this is not limited to this.

[0088] In this embodiment, the transfer belt 30 is used as a reference reflector for calibrating the infrared LED 33A, which detects the density of black. The transfer belt 30 is formed with a reflective surface (a reflective surface that specularly reflects light to match a predetermined standard) that functions as a reference reflector for calibrating the infrared LED 33A. The density sensor light emission amount adjuster 64D adjusts the light emission current of the infrared LED 33A so that the output voltage of the specular reflected light receiving phototransistor 33B becomes a set value. In this embodiment, the set value of the output voltage of the specular reflected light receiving phototransistor 33B is 2.50 [V], but is not limited to this.

[0089] Next, the density correction control unit 64B of the mechanism control unit 64 sets the development voltage value and the LED drive time to predetermined initial values ​​DB0 [V] and DK0 [s] (S202).

[0090] Next, the density correction control unit 64B of the mechanism control unit 64 reads the data of each table (sensor detection voltage-density value conversion table 113, target print density data table 114, development voltage value adjustment amount table 115, LED drive time adjustment amount table 116) stored in the memory unit 64C (S203).

[0091] Next, upon receiving the signal to perform density detection, the density correction control unit 64B of the mechanism control unit 64 performs the process of printing and detecting the first density detection pattern PAT1 (S204).

[0092] Specifically, the density correction control unit 64B reads the density detection pattern PAT1 (pattern shown in FIG. 7(a)) stored in advance in the memory unit 64C and starts printing it on the transfer belt 30. In the density detection pattern PAT1, rectangular areas are formed for each toner color (developer) from the downstream side in the transport direction, with the toner development area ratio (the ratio of the toner image developed on the transfer belt 30 to a specified area, hereinafter referred to as "duty") being 100%. Hereinafter, each area in the density detection pattern (each area corresponding to a combination of color and duty) will be referred to as a "block."

[0093] In the following, combinations of color (toner color) and duty will be expressed using a symbol representing the color (either K, C, M, or Y) and a numerical value indicating the duty (in [%]), such as "K100%" (combination of black and duty 100%) or "Y50%" (combination of yellow and duty 50%).

[0094] In the density detection pattern PAT1 shown in Figure 7(a), from the downstream side in the transport direction, there are arranged a block PY100 of Y100%, a block PM100 of M100%, a block PC100 of C100%, and a block PK100 of K100%. Note that the dimension (length) in the transport direction of each block that makes up the density detection pattern PAT1 is Lp [mm], and there is no gap (0 [mm]) between adjacent blocks in the transport direction. Note that the pattern used for density detection is not limited to this pattern, and the order of colors and the combination of duties may be changed as needed.

[0095] FIG. 11 is a diagram showing an example of halftone dither patterns for each duty used in each of the density detection patterns PAT1 to PAT3.

[0096] 11(a) to 11(f) show examples of halftone dither patterns with a duty of 15%, 30%, 50%, 70%, 85%, and 100%, respectively. In each pattern in FIG. 11, pixel areas to which toner has adhered are shown with hatched (diagonal lines). Note that, although the screen angle in each halftone dither pattern shown in FIG. 11 is 45°, different screen angles may be applied to each color.

[0097] Since the duty of each block constituting the density detection pattern PAT1 is 100%, toner adheres to all pixel areas as shown in FIG. 11(f).

[0098] The mechanism control unit 64 activates the infrared LED 33A of the density sensor 33 in accordance with the color of the pattern being read, irradiating the density detection pattern PAT1 with infrared light. The specular reflected light receiving phototransistor 33B and the diffuse reflected light receiving phototransistor 33C are driven by a circuit (not shown) to pass a current proportional to the received light energy. This current is converted to a voltage by a circuit (not shown) and read by the mechanism control unit 64. The mechanism control unit 64 reads the output voltage of the diffuse reflected light receiving phototransistor 33C when the read pattern is yellow, magenta, or cyan, and reads the output voltage of the specular reflected light receiving phototransistor 33B when the read pattern is black. In this embodiment, the first pattern detected is block PY100, so the output voltage of the diffuse reflected light receiving phototransistor 33C is read. Next, the transfer belt 30 is driven and moved by the density detection pattern length Lp [mm] to align the center of block PM100 (magenta, duty 100%) with the detection position of the density sensor 33, and the output voltage of the diffuse reflected light receiving phototransistor 33C is read. Thereafter, the mechanism control unit 64 performs similar control processing to sequentially read the output voltage for all blocks of the density detection pattern PAT1.

[0099] The mechanism control unit 64 converts the read output voltage into a concentration value based on a sensor detection voltage-to-concentration value conversion table 113. The table values ​​of the sensor detection voltage-to-concentration value conversion table 113 are experimentally determined optimal values ​​of coefficients A and B, which are coefficients of a linear approximation equation that shows the relationship between the sensor detection voltage and the concentration value. As shown in FIG. 6(a), in the sensor detection voltage-to-concentration value conversion table 113 of this embodiment, the coefficient A corresponding to K, Y, M, and C is K(A), Y(A), M(A), and C(A), respectively. Also, as shown in FIG. 6(B), in the sensor detection voltage-to-concentration value conversion table 113 of this embodiment, the coefficient B corresponding to K, Y, M, and C is K(B), Y(B), M(B), and C(B), respectively.

[0100] Here, the sensor detection voltage read for block PY100 is expressed as YV 100 Then, the density value YOD corresponding to Y100%100 can be calculated using the following equation (2-1): 100 is the sensor test voltage YV 100 can be calculated by multiplying the coefficient Y(A) and adding the coefficient Y(B). Therefore, the sensor inspection voltages of blocks PM100, PC100, and PK100 are calculated as MV 100 , CV 100 , K.V. 100 Then, the density value MOD corresponding to M100% 100 , COD concentration value corresponding to C100% 100 , the concentration value KOD corresponding to K100% 100 can be expressed by the following equations (2-2) to (2-3), respectively. YOD 100 =Y(A)×YV 100 +Y(B)…(2-1) MOD 100 =M(A)×MV 100 +M(B)…(2-2) COD 100 =C(A)×CV 100 +C(B)…(2-3) KOD 100 =K(A)×KV 100 +K(B)…(2-4)

[0101] Next, the mechanism control unit 64 compares the density values ​​read in the density correction process flow S204 with the target print density data table 114, and calculates how much to increase or decrease the development voltage value for each color based on the difference (S205).

[0102] For this calculation, the mechanism control unit 64 uses the development voltage value adjustment amount table 115 stored in the memory unit 64C to create the target print density data table 114. The table values ​​in the development voltage value adjustment amount table 115 indicate the amount of change in density value for each combination of color and duty when the development voltage value changes by 1 [V]. In the development voltage value adjustment amount table 115 shown in FIG. 6(c), the amounts of change in K100%, Y100%, M100%, C100%, K50%, Y50%, M50%, and C50% are respectively ΔKDB 100 , ΔYDB 100 , ΔMDB100 , ΔCDB 100 , ΔKDB 50 , ΔYDB 50 , ΔMDB 50 , ΔCDB 50 It states that:

[0103] In each printing mechanism 20, changing the development voltage can change the thickness of the developed toner layer, which can be used to increase or decrease the density from low-duty areas to high-duty areas. In this embodiment, if the development voltage control amount for Y is YDB(A), YDB(A) can be calculated using the following equation (3-1). Similarly, if the development voltage control amount for M is MDB(A), the development voltage control amount for C is CDB(A), and the development voltage control amount for K is KDB(A), MDB(A), CDB(A), and KDB(A) can be calculated using the following equations (3-2) to (3-4), respectively. YDB(A)=(YOD 100 -YOD T100 ) / ΔYDB 100 …(3-1) MDB(A)=(MOD 100 -MOD T100 ) / ΔMDB 100 …(3-2) CDB(A)=(COD 100 -COD T100 ) / ΔCDB 100 …(3-3) KDB(A)=(KOD 100 -K.O.D. T100 ) / ΔKDB 100 …(3-4)

[0104] The mechanism control unit 64 instructs the high voltage control unit 71 to increase or decrease the development voltage based on the development voltage correction results for each color obtained in density correction process flow S205. Then, as shown in the following equation (4-1), the development voltage generation unit 73 obtains a development voltage value YDB1 [V] as a correction result by adding a development voltage correction value YDB(A) to an initial value (hereinafter referred to as the "initial development voltage") YDB0 of the development voltage supplied to Y (the development roller 23 of the printing mechanism 20Y) during printing operation. The development voltage generation unit 73 then supplies the obtained development voltage value YDB1 [V] to the development roller 23 of the printing mechanism 20Y. If the initial development voltages for M, C, and K are MDB0, CDB0, and KDB0, respectively, the development voltage values ​​MDB1, CDB1, and KDB1 can be obtained using the following equations (4-2) to (4-4), respectively. YDB1[V]=YDB0+YDB(A)…(4-1) MDB1[V]=MDB0+MDB(A)…(4-2) CDB1[V]=CDB0+CDB(A)…(4-3) KDB1[V]=KDB0+KDB(A)…(4-4)

[0105] Next, upon receiving the signal to perform density detection, the density correction control unit 64B of the mechanism control unit 64 performs the process of printing and detecting the second density detection pattern PAT2 (S206).

[0106] Specifically, the density correction control unit 64B reads the density detection pattern PAT2 (the pattern shown in FIG. 7(b)) stored in advance in the memory unit 64C, and starts printing it on the transfer belt 30. In the density detection pattern PAT2, a block area with a duty of 50% is formed for each color from the downstream side in the transport direction.

[0107] In the density detection pattern PAT2 shown in Figure 7(b), from the downstream side in the transport direction, there are arranged a block PY50 of Y 50%, a block PM50 of M 50%, a block PC50 of C 50%, and a block PK50 of K 50%. Note that the dimension (length) in the transport direction of each block that makes up the density detection pattern PAT2 is Lp [mm], and there is no gap (0 [mm]) between adjacent blocks in the transport direction. Note that the pattern used for density detection is not limited to this pattern, and the order of colors and the combination of duties may be changed as needed.

[0108] The development voltage values ​​for each color used to print the density detection pattern PAT2 are the development voltage values ​​YDB1, MDB1, CDB1, and KDB1 corrected in step S204.

[0109] Since the duty of each block constituting the density detection pattern PAT2 is 50%, toner adheres to half of the entire pixel area, as shown in Fig. 11(c). Note that although the screen angle is set to 45° in the halftone dither pattern shown in Fig. 11(c), the screen angle of each block applied to the density detection pattern PAT2 may be changed depending on the color.

[0110] The density sensor 33 reads the output voltage of each color pattern, and the mechanism control unit 64 converts it into a density value using the sensor detection voltage-density value conversion table 113. The sensor detection voltage of the block PY50 is converted into YV' 50 Then, the density value YOD' corresponding to Y50% 50 can be calculated using the following formula (5-1): Similarly, the density values ​​MOD' corresponding to M50%, C50%, and K50% 50 , COD' 50 , K.O.D.' 50 can be calculated using the following equations (5-2) to (5-4). YOD' 50 =Y 50 (A)×YV' 50 +Y 50 (B)…(5-1) MOD' 50 =M 50(A)×MV' 50 +M 50 (B)…(5-2) COD' 50 =C 50 (A) × CV' 50 +C 50 (B)…(5-3) KOD' 50 =K 50 (A)×KV' 50 +K 50 (B)…(5-4)

[0111] Next, the mechanism control unit 64 compares the density value read in step S105 with the target print density value registered in the target print density data table 114, and calculates how much to increase or decrease the individual LED drive time of the LED head 28 of each color from the difference (S207).

[0112] The target print density is set for each combination of color and duty in the target print density data table 114. In the target print density data table 114 shown in FIG. 6(b), the target print densities of K100%, Y100%, M100%, C100%, K50%, Y50%, M50%, and C50% are respectively set as KOD 100 , YOD 100 , MOD 100 , COD 100 , K.O.D. 50 , YOD 50 , MOD 50 , COD 50 It states that:

[0113] Furthermore, the mechanism control unit 64 uses the LED drive time adjustment amount table 116 stored in the storage unit 64C for the calculation in step S207. The table values ​​in the LED drive time adjustment amount table 116 indicate the amount of change in density value when the LED drive time (the time during which the LED head 28 exposes the photosensitive drum 22) changes by 1 [%], for each combination of color and duty. In the LED drive time adjustment amount table 116 shown in FIG. 6(d), the amounts of change in K 100%, Y 100%, M 100%, C 100%, K 50%, Y 50%, M 50%, and C 50% are respectively expressed as ΔKDK 100 , ΔYDK100 , ΔMDK 100 , ΔCDK 100 , ΔKDK 50 , ΔYDK 50 , ΔMDK 50 , ΔCDK 50 It states that:

[0114] By changing the LED drive time, it is possible to increase or decrease the density mainly from the low-duty to the medium-duty area. In this embodiment, the LED drive time control amount for Y is defined as YDK(A), which can be calculated using the following formula (6-1). Similarly, if the LED drive time control amounts for M, C, and K are defined as MDK(A), CDK(A), and KDK(A), MDK(A), CDK(A), and KDK(A) can be calculated using the following formulas (6-2) to (6-4), respectively. YDK(A)=(YOD' 50 -YOD T50 ) / ΔYDK 50 …(6-1) MDK(A)=(MOD' 50 -MOD T50 ) / ΔMDK 50 …(6-2) CDK(A)=(COD' 50 -COD T50 ) / ΔCDK 50 …(6-3) KDK(A)=(KOD' 50 -K.O.D. T50 ) / ΔKDK 50 …(6-4)

[0115] Based on the LED drive time correction results for each color, the mechanism control unit 64 instructs the LED head interface unit 63 to increase or decrease the drive time of the LED head 28 corresponding to each color. Then, as shown in the following equation (7-1), the LED head interface unit 63 calculates the LED drive time YDK1 [s] as a correction result by adding the value obtained by multiplying the LED drive time correction value YDK(A) by YDK0 to the initial value (hereinafter referred to as the "LED drive time initial value") YDK0 of the LED drive time set for Y (the LED head 28 corresponding to the printing mechanism 20Y) during printing operation. Then, the mechanism control unit 64 controls the LED head 28 corresponding to the printing mechanism 20Y during printing operation so that it exposes for the calculated LED drive time YDK1 [s]. Similarly, if the initial LED drive times for M, C, and K are MDK0, CDK0, and KDK0, respectively, the LED drive times MDK1, CDK1, and KDK1 can be calculated using the following equations (7-2) to (7-4), respectively. YDK1[s]=YDK0+YDK0×YDK(A)…(7-1) MDK1[s]=MDK0+MDK0×MDK(A)…(7-2) CDK1[s]=CDK0+CDK0×CDK(A)…(7-3) KDK1[s]=KDK0+KDK0×KDK(A)…(7-4)

[0116] Next, upon receiving the signal to perform density detection, the density correction control unit 64B of the mechanism control unit 64 performs the process of printing and detecting the third density detection pattern PAT3 (S208).

[0117] Specifically, the density correction control unit 64B reads the density detection pattern PAT3 (pattern shown in FIG. 7C) stored in advance in the memory unit 64C and starts printing it on the transfer belt 30. In the density detection pattern PAT3, six sets of blocks (sets of four blocks) are arranged in the order Y, M, C, and K from the downstream side in the transport direction (six sets of four blocks, for a total of 24 blocks). The duties of the sets constituting the density detection pattern PAT3 are 15%, 30%, 50%, 70%, 85%, and 100%, respectively, from the downstream side in the transport direction. Therefore, as shown in Figure 7(c), the density detection pattern PAT3 is arranged in the following order from downstream in the transport direction: Y15 (block PY15), M15 (block PM15), C15 (block PC15), K15 (block PK15), Y30 (block PY30), ..., Y50 (block PY50), ..., Y70 (block PY70), ..., Y85 (block PY85), ..., Y100 (block PY100), M100 (block PM100), C100 (block PC100), and K100 (block PK100). Like the density detection pattern PAT1, the density detection pattern PAT3 is printed with a pattern length Lp [mm], with no gap between the end of each pattern and the next density detection pattern. The dot arrangement for each duty of the blocks constituting the density detection pattern PAT3 is as shown in Figure 11. That is, the dot arrangements of each duty (15%, 30%, 50%, 70%, 85%, 100%) that make up the density detection pattern PAT3 are as shown in Figures 11(a) to 11(f). Note that the screen angles of the dot arrangements shown in Figure 11 are all 45°, but this is not limiting and various screen angles may be set.

[0118] When printing the density detection pattern PAT3, the mechanism control unit 64 uses the development voltage value KDB1 [V] after development voltage correction as the development voltage value, and the LED drive time KDK1 [s] after LED drive time correction as the LED drive time.

[0119] The mechanism control unit 64 reads the output voltage for each block of the density detection pattern PAT3 from the density sensor 33 and converts it into a density value based on the sensor detection voltage-density value conversion table 113. Here, the sensor detection voltages read by the mechanism control unit 64 for the blocks PY15, PY30, PY50, PY70, PY85, and PY100 are respectively expressed as YV 15 , YV” 30 , YV” 50 , YV” 70 , YV” 85 , YV” 100 Here, the density values ​​corresponding to Y15%, Y30%, Y50%, Y70%, Y85%, and Y100% are defined as YOD. 15 , YOD” 30 , YOD” 50 , YOD” 70 , YOD” 85 , YOD” 100 Then, YOD” 15 , YOD” 30 , YOD” 50 , YOD” 70 , YOD” 85 , YOD” 100 can be calculated using the following equations (8) to (13), respectively. YOD” 15 =Y 15 (A)×YV” 15 +Y 15 (B)…(8) YOD” 30 =Y 30 (A)×YV” 30 +Y 30 (B)…(9) YOD” 50 =Y 50 (A)×YV” 50 +Y 50 (B)…(10) YOD” 70 =Y 70 (A)×YV” 70 +Y 70 (B)…(11) YOD” 85 =Y 85 (A)×YV” 85 +Y 85 (B)…(12) YOD” 100 =Y 100 (A)×YV” 100 +Y 100 (B)…(13)

[0120] As with Y, the mechanism control unit 64 reads the output voltage for each block of the density detection pattern PAT3 using the density sensor 33 for M, C, and K, and converts it into a density value based on the sensor detection voltage-density value conversion table 113.

[0121] Next, the density gradation correction control unit 62A of the command / image processing unit 62 calculates a gradation density value for each combination of color and duty, and performs processing to update the gradation correction value table 112 (S209).

[0122] Here, the process by which the density tone correction control unit 62A calculates the gradation density value will be described in detail.

[0123] First, the density gradation correction control unit 62A of the command / image processing unit 62 calculates the density values ​​YOD" of the duty 15%, 30%, 50%, 70%, 85%, and 100% patterns of the density detection pattern PAT3 read by the mechanism control unit 64 in the density correction process flow S208. 15 , YOD” 30 , YOD” 50 , YOD” 70 , YOD” 85 , YOD” 100 The density gradation correction control unit 62A calculates density values ​​for 256 gradation levels from the density values ​​of each of the received fill factors.

[0124] Here, if each duty of 15%, 30%, 50%, 70%, 85%, and 100% is expressed in 256 gradation levels from 0 to 255, duty 0% is 0 gradation level, duty 15% is 38 gradation level, duty 30% is 77 gradation level, duty 50% is 128 gradation level, duty 70% is 179 gradation level, duty 85% is 217 gradation level, and duty 100% is 255 gradation level. The density value of the 0 gradation level is YODG0, and the density value of the 38 gradation level is YODG38 , the density value of 77 gradation levels is YODG 77 , 128 gradation level density values ​​YODG 128 , 179 gradation level density values ​​YODG 179 , 217 gradation level density values ​​YODG 217 , 255 gradation level density values ​​YODG 255 Then, YODG0, YODG 38 , YODG 77 , YODG 128 , YODG 179 , YODG 217 , YODG 255 The concentration values ​​of can be expressed by the following equations (14) to (20), respectively. YODG0=0…(14) YODG 38 =YOD” 15 …(15) YODG 77 =YOD” 30 …(16) YODG 128 =YOD” 50 …(17) YODG 179 =YOD” 70 …(18) YODG 217 =YOD” 85 …(19) YODG 255 =YOD” 100 …(20)

[0125] Here, the density value of the l gradation level (l=1 to 37) between the 1st gradation level and the 37th gradation level is expressed as YODG l , the density value of m gradation levels (m=39~76) between 39 gradation levels and 76 gradation levels is YODG m , the density value of n gradation levels (n=78~127) between 78 gradation level and 127 gradation level is YODG n , the density value of the o gradation level (o=129~178) between the 129 gradation level and the 178 gradation level is YODG o , the density value of p gradation levels (p=180~216) between 180 gradation level and 216 gradation level is YODGp , the density value of the q gradation level (q=218~254) between the 218 gradation level and the 254 gradation level is YODG q Then, YODG l , YODG m , YODG n , YODG o , YODG p , YODG q can be calculated using the following equations (21) to (26), respectively. YODG l =YODG0 +{(YODG 38 -YODG0) / 38}×l…(21) YODG m =YODG 38 +{(YODG 77 -YODG 38 ) / (77-38)}×(m-38)…(22) YODG n =YODG 77 +{(YODG 128 -YODG 77 ) / (128-77)}×(n-77)…(23) YODG o =YODG 128 +{(YODG 179 -YODG 128 ) / (179-128)}×(o-128)…(24) YODG p =YODG 179 +{(YODG 217 -YODG 179 ) / (217-179)}×(p-179)…(25) YODG q =YODG 217 +{(YODG 255 -YODG 217 ) / (255-217)}×(q-217)…(26)

[0126] Then, the density gradation correction control unit 62A of the command / image processing unit 62 compares the calculated density values ​​of each of the 256 gradation levels with the target gradation density values ​​set in the target gradation density value table 111, finds out from each of the calculated 256 gradation levels a gradation level that matches the density value of each of the 256 gradation levels in the target gradation density value table 111, and updates the gradation correction value table 112 by setting the gradation levels in the target gradation density value table 111 as input gradation values ​​and setting each of the calculated 256 gradation levels that matches the density value in the target gradation density value table 111 as output gradation values.

[0127] The density gradation correction control unit 62A of the command / image processing unit 62 calculates the gradation density value for each combination of color and duty for M, C, and K, as in the example of Y above, and performs processing to update the gradation correction value table 112.

[0128] 4, the target gradation density value is registered for each combination of color and gradation value in the target gradation density value table 111. In FIG. 4, the target gradation density values ​​of K corresponding to gradation values ​​0 to 255 are set as KOD H0 ~KOD H255 , the target gradation density value of Y corresponding to the gradation value 0 to 255 is set as YOD H0 ~YOD H255 , the target gradation density value of M corresponding to the gradation value 0 to 255 is MOD H0 ~MOD H255 , the target gradation density value of C corresponding to the gradation value 0 to 255 is COD H0 ~COD H255 is illustrated as

[0129] 5, the output tone values ​​for each combination of color and input tone value are registered in the tone correction value table 112. In FIG. 4, the output tone values ​​of K corresponding to tone values ​​0 to 255 are KCV0 to KCV 255 , the Y output gradation values ​​corresponding to gradation values ​​0 to 255 are YCV0 to YCV 255 , the output gradation values ​​of M corresponding to gradation values ​​0 to 255 are MCV0 to MCV 255 , the C output gradation values ​​corresponding to gradation values ​​0 to 255 are CCV0 to CCV 255 is illustrated as

[0130] Next, a specific example of density gradation correction control by the density gradation correction control unit 62A will be described. For example, suppose that the gradation level (one of the 256 gradation levels) that matches the density value of the 100 gradation level at the target gradation density value is the 90 gradation level. In this case, the calculated density value of the 100 gradation level at each of the 256 gradation levels is darker than the density value of the 100 gradation level at the target gradation density value. Therefore, if an input signal at the 100 gradation level is printed as an output signal at the 100 gradation level, the density value when actually printed will be darker than the target density value. Therefore, the density gradation correction control unit 62A replaces the input signal at the 100 gradation level with the calculated 90 gradation level that matches the density value of the 100 gradation level at the target gradation density value as an output signal and performs printing processing, thereby correcting the density value when actually printed to the target density value.

[0131] When the density correction process is completed, the mechanism control unit 64 (density correction control unit 64B) detects the temperature and humidity RT of the outside air detected by the environment sensor 2 at that time. ADC and the belt temperature BT measured by the belt thermistor 37. ADC is measured and updated and stored in the storage unit 64C (S210), and the process ends.

[0132] The above is the description of the normal density correction processing flow.

[0133] Next, the density correction process execution determination in step S103 will be described in detail.

[0134] 12 to 14 are flowcharts showing an example of the density correction process execution determination process performed by the density correction process execution determination unit 64A.

[0135] First, the density correction process execution determination process shown in FIG. 12 will be described.

[0136] In the flowchart of FIG. 12, the density correction process execution determination unit 64A first determines whether to execute the density correction process by temperature comparison processing (S301), and then ultimately determines whether to "execute the density correction process" or "not execute the density correction process" based solely on this determination (S302, S303).

[0137] That is, in the density correction process execution determination shown in FIG. 12, the final density correction process execution determination is made only based on the result of the density correction process execution determination by the temperature comparison process.

[0138] Next, the density correction process execution determination process shown in FIG. 13 will be described.

[0139] The flowchart in Fig. 13 differs from the flow in Fig. 12 in that step S304 has been added. The flowchart in Fig. 13 will be described below, focusing on the differences from the flowchart in Fig. 12.

[0140] 13, density correction process execution determination unit 64A first determines whether to execute density correction process by temperature comparison processing in step S301, and if the result of this determination is "to execute density correction process," it proceeds to step S304, where it analyzes the contents of the print data (the contents of the print data received in step S101) and determines whether the objects included in the print data are only character data (text data). If the contents of the print data are composed of only character data, density correction process execution determination unit 64A proceeds to step S303, where it finally determines that "density correction process should be executed," and if not, it proceeds to step S302, where it finally determines that "density correction process should not be executed."

[0141] In other words, in the flowchart of FIG. 13, the density correction process execution determination unit 64A skips the density correction process if the print data contains only text data. Generally, in printed matter, text often does not require printing with as accurate a density as photographs, multi-color images, or other imagery. Therefore, for users who do not place as much importance on density variations in text as they do on imagery, skipping the density correction process when the print data contains only text data will not have a significant impact. While this embodiment illustrates an example in which the print data contains only text data, the present invention is not limited to this, and the print data may be considered to be essentially composed of text data only. For example, data other than text data may account for less than 10% of the printable area. This type of print data is print data composed of text data.

[0142] Next, the density correction process execution determination process shown in FIG. 14 will be described.

[0143] The flowchart in Fig. 14 differs from the flowchart in Fig. 13 in that step S305 is added. The flowchart in Fig. 14 will be described below, focusing on the differences from the flowchart in Fig. 13.

[0144] 14, the density correction process execution determination unit 64A, as in the case of Fig. 13, first performs a density correction process execution determination based on the result of the temperature comparison process in step S301, and if the result is "to execute density correction process," it further performs a process of confirming whether all objects included in the print data are character data in step S304. Then, if all objects included in the print data are character data, the density correction process execution determination unit 64A proceeds to step S305, where it performs a density correction process execution determination based on information about the density correction process performed last time (hereinafter referred to as "previous density correction process information"), and only if the result of the determination is "to execute density correction process," it proceeds to step S303, where it finally determines that "density correction process should be executed," and if not, it proceeds to step S302, where it finally determines that "density correction process should not be executed."

[0145] Here, an example of density correction process execution determination using previous density correction process information will be described.

[0146] The previous density correction processing information is, for example, information from the previous density correction processing (e.g., the corrected development voltage value, the outside air temperature RT, the outside air humidity RH, the temperature of the photosensitive drum 22, etc.). For example, a case will be described in which the density correction processing execution determination unit 64A uses the corrected development voltage value as the previous density correction processing information. Here, it is assumed that the density correction control unit 64B has previously stored in the memory unit 64C each piece of information from the previous density correction processing (previous density correction processing information). Then, in the processing of step S305, the density correction processing execution determination unit 64A performs a density correction processing execution determination based on the previous density correction processing information stored in the memory unit 64C. For example, the density correction process execution determination unit 64A may check whether the development voltage value at the time of the previous density correction process (e.g., the corrected development voltage value for any of the printing mechanisms 20 or the average value of the corrected development voltage values ​​for all of the printing mechanisms 20) is within a predetermined range (a range defined by an upper limit and / or a lower limit), and if it is within the predetermined range, determine that "the density correction process will not be executed" and proceed to step S302, or if it is not within the predetermined range, determine that "the density correction process will be executed" and proceed to step S303. Also, for example, the density correction process execution determination unit 64A may check whether the temperature corresponding to the photosensitive drum 22 at the time of the previous density correction process (e.g., the temperature of the belt temperature BT) is within a predetermined range (a range defined by an upper limit and / or a lower limit), and if it is within the predetermined range, determine that "the density correction process will not be executed" and proceed to step S302, or if it is not within the predetermined range, determine that "the density correction process will be executed" and proceed to step S303. Furthermore, for example, the density correction process execution determination unit 64A may determine that "the density correction process is not to be executed" when the temperature of the photosensitive drum 22 (for example, the temperature of the belt temperature BT) at the time of the previous density correction process is higher than the outside air temperature RT at the time of the previous correction process by a predetermined value or more. Note that the threshold values ​​(upper limit value and / or lower limit value) for the above-mentioned predetermined range used in step S305 may be stored in advance in the storage unit 64C.

[0147] (A-3) Effects of the embodiment According to this embodiment, the following effects can be achieved.

[0148] In the printer 1 of this embodiment, after receiving print data, the execution of the density correction process is skipped before printing starts depending on the result of the density correction necessity determination, so it is possible to reduce the time until printing starts (for example, if the density correction process takes 30 seconds, the time is reduced by 30 seconds) while suppressing a reduction in print quality. Also, in the printer 1 of this embodiment, after receiving print data, the execution of the density correction process is skipped before printing starts depending on the configuration of the print data and the status of the previous density correction process, etc., so it is possible to reduce the consumption of toner and power consumed in the density correction process.

[0149] For example, if the printer 1 receives print data and then determines whether to perform density correction processing using only the temperature comparison results, as in the flowchart of FIG. 12, the printer 1 will determine to perform density correction processing even in cases where density changes are not considered important, such as when printing text data only. This means that the time from when the image forming device receives the print data to when the printing operation begins will be significantly longer than when density correction is not performed, due to the time it takes to perform the density correction operation. Since users who print text only are likely to not consider density changes important, the increased time before printing due to density correction processing can be extremely stressful. On the other hand, if the objects comprising the print data received by the printer 1 are all text data, as in the flowchart of FIG. 13, skipping the density correction processing can shorten the time before printing begins, thereby improving user satisfaction.

[0150] However, in the case of the processing in the flowchart of Fig. 13, if the print data consists only of character data, the density correction processing is always skipped, and if there has been a significant change in the environment around or inside the printer 1 since the previous density correction processing, there is a risk that the image printed on the paper M will be darker or lighter than specified. In contrast, in the processing in the flowchart of Fig. 14, even if the print data consists only of character data, a process is added (processing in step S305) that takes into account the previous density correction information to determine whether to perform the density correction processing, thereby suppressing a deterioration in print quality by performing the density correction processing when an environmental change of a predetermined magnitude or more has occurred as described above (an environmental change of a predetermined magnitude or more has occurred since the previous density correction processing).

[0151] (B) Other embodiments The present invention is not limited to the above-described embodiments, and may include modified embodiments such as those exemplified below.

[0152] (B-1) The present invention is not limited to the above-described embodiments, and various modifications are possible based on the spirit of the present invention, and these modifications are not excluded from the scope of the present invention.

[0153] (B-2) In the above embodiment, an example was described in which the image forming apparatus of the present invention is applied to a printer, but it may also be applied to other multifunction peripherals (MFPs), facsimiles, copiers, etc. Also, in the above embodiment, the image forming apparatus of the present invention may also be applied to an intermediate transfer type printer.

[0154] (B-3) In the density correction process of the printer 1 of the above embodiment, the density detection patterns PAT1 to PAT3 shown in FIGS. 7 and 11 are used, but this is not limited to this, and the type and configuration of the dither pattern, the combination of duties, the order of colors, the length and spacing of each pattern, etc. may be changed as needed.

[0155] (B-4) In step S304 of the flowcharts in Figures 13 and 14, the density correction process execution determination unit 64A analyzes the contents of the print data and determines to skip the density correction process if the print data consists of only character data. This is because it is assumed that users do not place importance on density changes when printing characters, but there are also types of objects other than character data for which users are not expected to place importance on density changes. For example, it is assumed that users do not place importance on density changes in graphic data consisting only of lines and characters, such as graphs and shapes (graphic data consisting of vectorized objects), just as with characters.

[0156] Therefore, in step S304 of the flowcharts of Figures 13 and 14, the density correction process execution determination unit 64A may be configured to determine whether to skip the density correction process if the print data is composed of at least one or both of character data and graphic data (any of the patterns of "character data only," "graphic data only," or "character data and graphic data only").

[0157] Furthermore, even if the print data includes image data in addition to text data and graphics data, if the area corresponding to the image data is less than a predetermined value (for example, if "the proportion of the image image that occupies the printing surface of the paper M is less than a predetermined threshold value" or "the area of ​​the image image is less than a predetermined value"), it is assumed that even if there is a density change in the image image portion, the overall impact on print quality is small (the user does not place importance on density changes in the image data). Therefore, in step S304 of the flowcharts in Figures 13 and 14, the density correction process execution determination unit 64A may determine to skip the density correction process if the area of ​​the image image corresponding to the image data is less than a predetermined value, even if the print data includes image data (objects other than text data and graphics data).

[0158] (B-5) In step S305 of the flowchart in FIG. 14, the density correction process execution determination unit 64A determines whether to skip the density correction process based on the previous density correction information, but the determination may be made based on other conditions. For example, in step S305 of the flowchart in FIG. 14, the density correction process execution determination unit 64A may determine to perform the density correction process if the density correction process has been skipped a predetermined number of times or more since the previous density correction process was performed (if the density correction determination ultimately outputs a determination result that the density correction process will not be performed). Also, for example, in step S305 of the flowchart in FIG. 14, the density correction process execution determination unit 64A may determine to perform the density correction process even if the number of sheets printed since the previous density correction process was performed is a predetermined number or more. [Explanation of symbols]

[0159] 1... printer, 2... environment sensor, 11... paper storage cassette, 12... hopping roller, 13... pinch roller, 14... registration roller, 15... guide, 15... block PC, 16... media sensor, 17... media sensor, 18... transfer discharge sensor, 20, 20C, 20K, 20M, 20Y... printing mechanism, 21... charging roller, 22... photosensitive drum, 23... developing roller, 24... developing blade, 25... supply roller, 26... static elimination light source, 27... toner cartridge Ridge, 28...LED head, 29...transfer roller, 30...transfer belt, 31...drive roller, 32...driven roller, 33...density sensor, 33A...infrared LED, 33B...phototransistor for receiving specular reflected light, 33C...phototransistor for receiving diffuse reflected light, 34...cover, 35...cleaning blade, 36...waste toner storage section, 37...belt thermistor, 40...fixing section, 41...heat roller, 42...heater, 43...pressure roller, 44... Thermistor, 45...fixing discharge sensor, 46...guide, 47...stacker, 50...block PC, 61...communication unit, 62...command / image processing unit, 62A...density gradation correction control unit, 62B...storage unit, 63...LED head interface unit, 64...mechanism control unit, 64A...density correction process execution determination unit, 64B...density correction control unit, 64C...storage unit, 64D...density sensor light emission amount adjustment unit, 71...high voltage control unit, 71A...storage unit, 72...charging voltage generation unit, 3...developing voltage generating unit, 74...supply voltage generating unit, 75...transfer voltage generating unit, 81...hopping motor, 82...registration motor, 83...belt motor, 84...heat motor, 85...drum motor, 100...block PC, 111...target gradation density value table, 112...gradation correction value table, 113...density value conversion table, 114...target print density data table, 115...developing voltage value adjustment amount table, 116...LED drive time adjustment amount table

Claims

1. an exposure means for exposing a charged photosensitive member to light to form an electrostatic latent image; a developing means for supplying a developer to the electrostatic latent image on the photosensitive member to develop a developer image; an image processing means for processing the image into data that can be exposed by the exposure means when image formation data is supplied; a conveying means for conveying the medium; a transfer means for transferring the developer image onto the medium being transported by the transport means or onto the transport means; a density detecting means for detecting the density of the developer image on the conveying means; a density correction process execution determination means for determining whether or not to execute a density correction process for correcting the density of the developer image developed on the photosensitive member based on the density detected by the density detection means, taking into consideration at least elements included in the image formation data; a density correction control unit that controls the device itself to execute the density correction process when the density correction process execution determination unit determines that the density correction process is to be executed; An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, wherein the density correction process execution determining unit determines not to execute the density correction process when the image formation data is composed of character data.

3. 2. The image forming apparatus according to claim 1, wherein the density correction process execution determination means determines not to execute the density correction process when the image formation data is composed of at least one or both of character data and graphic data.

4. The image forming apparatus according to claim 1, characterized in that the density correction process execution determination means determines not to execute the density correction process if the area corresponding to the image image data is smaller than a predetermined value, even if the image formation data includes image image data.

5. the density correction control means holds density correction processing information relating to the state of the device itself when the density correction processing is executed, The density correction process execution determining means determines whether or not to execute the density correction process, taking into consideration the content of the density correction process information when the density correction control means previously executed the density correction process.

5. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

6. Further provided is a conveying temperature detection means for detecting a conveying temperature of the conveying means, the density correction control means holds, as the density correction processing information, the conveying temperature detected by the conveying temperature detection means when the density correction processing is executed; The density correction process execution determining means determines not to execute the density correction process if the conveying temperature when the density correction control means previously executed the density correction process is within a predetermined range.

6. The image forming apparatus according to claim 5,

7. The image forming apparatus according to claim 2, characterized in that the density correction process execution determination means determines to execute the density correction process if the number of times it has been determined not to execute the density correction process since the previous density correction process was performed is equal to or greater than a predetermined number, even if the image formation data is composed of character data.

8. The image forming apparatus according to claim 2, characterized in that the density correction process execution determination means determines to execute the density correction process if the number of media that have undergone image formation processing by the apparatus since the last time the density correction process was performed is greater than or equal to a predetermined number, even if the image formation data is composed of character data.

Images