Image forming apparatus

Abstract

To perform printing according to the density of an image, while preventing extension of time required for printing.SOLUTION: An image forming apparatus 1 is provided with: an image density calculation section 58 and an image density determination section 59 that analyze the density of print data; a first image forming unit 10 that performs image formation on the basis of at least either a developing voltage value 62 or an LED light quantity value 63 as a first setting value related to the density in black; a second image forming unit 10 that performs image formation on the basis of at least either the developing voltage value 62 or the LED light quantity value 63 as a second setting value different from the first setting value and related to the density in black; and a use image forming unit determination section 51 that selects either the first image forming unit 10 or the second image forming unit 10 on the basis of results of analysis performed by the image density calculation section 58 and the image density determination section 59, and causes the selected image forming unit to perform image formation.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, and is suitable for application to an image forming apparatus that forms an image by transferring a developer image onto a recording medium. [Background technology]

[0002] Conventionally, a widely used image forming device (also called a printer) performs printing processing by forming a developer image using toner (also called a developer) in an image forming unit based on an image supplied from a computer device or the like, transferring the developer image to a medium such as paper, and then fixing the image by applying heat and pressure in a fixing unit.

[0003] The image forming unit also forms an electrostatic latent image on the surface of the photosensitive drum by irradiating the surface of the photosensitive drum with light from an exposure section that emits light for exposure, applies a charging voltage to the photosensitive drum and a developing voltage to the developing roller, and prints an image by developing the toner image by causing toner to adhere from the supply roller to the electrostatic latent image on the photosensitive drum due to the potential difference (also called bias difference) between the charging voltage and the developing voltage.

[0004] As such an image forming apparatus, one has been proposed that switches the development voltage during printing to perform printing at an appropriate density depending on the image to be printed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-37217 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in an image forming apparatus, after switching the development voltage during printing, a waiting time is required until the potential of the development roller is switched and stabilized, which results in a long time being required to complete printing.

[0007] The present invention has been made in consideration of the above points, and aims to propose an image forming apparatus that can perform printing according to the density of an image while preventing the time required for printing from increasing. [Means for solving the problem]

[0008] In order to solve this problem, the image forming apparatus of the present invention is provided with an analysis unit that analyzes the density of print data, a first image forming unit that forms an image in a first color based on a first set value related to density, a second image forming unit that forms an image in the first color based on a second set value related to density that is different from the first set value, and a control unit that selects either the first image forming unit or the second image forming unit to form an image based on the analysis results of the analysis unit.

[0009] As a result, the present invention allows image formation to be performed without switching the density setting value during image formation, by selecting multiple image forming units each having a different density setting value pre-set depending on the density of the print data, thereby preventing waiting time from occurring after switching the density setting value. [Effects of the Invention]

[0010] According to the present invention, by selecting multiple image forming units, each having a different density setting value preset thereto, according to the density of the print data and forming an image without switching the density setting value during image formation, it is possible to form an image while preventing a waiting time from occurring after switching the density setting value, and thus to realize an image forming device that can print according to the density of the image while preventing the time required for printing from increasing. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a left side view showing the overall configuration of an image forming apparatus. [Figure 2] FIG. 2 is a left side view showing the configuration of the image forming unit. [Figure 3] FIG. 2 is a block diagram showing a control configuration of the image forming apparatus. [Figure 4] FIG. 2 is a diagram illustrating the configuration of an input unit and a display unit. [Figure 5] 10 is a graph showing the relationship between print duty and density. [Figure 6] 10 is a flowchart illustrating a printing process procedure. [Figure 7] 10 is a flowchart showing a procedure for a correction value generation process according to the first embodiment. [Figure 8] 10 is a flowchart showing the procedure of an image data analysis process according to the first embodiment. [Figure 9] 10 is a flowchart showing a print image forming unit selection process procedure according to the first embodiment. [Figure 10] FIG. 2 is a diagram showing a block region according to the first embodiment. [Figure 11] FIG. 4 is a diagram illustrating an example of classification of image print duties according to the first embodiment. [Figure 12] 10 is a flowchart showing a procedure for a correction value generation process according to the second embodiment. [Figure 13] 10 is a flowchart showing the procedure of an image data analysis process according to the second embodiment. [Figure 14] 10 is a flowchart showing a print image forming unit selection process according to the second embodiment. [Figure 15] FIG. 10 is a diagram showing an image forming area according to a second embodiment. [Figure 16] FIG. 10 is a diagram showing a block region according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[0013] 1. First Embodiment [1-1. Overall configuration of image forming device] As shown in FIG. 1, image forming apparatus 1 is a color electrophotographic printer that prints a desired color image on paper P, which is a leaf-like medium. This image forming apparatus 1 has various components arranged inside a roughly box-shaped housing 2. In the following description, the right-hand end of FIG. 1 is defined as the front of image forming apparatus 1, and the up-down, left-right, and front-rear directions are defined when viewed from the front. Image forming apparatus 1 is controlled by a control unit 40. Image forming apparatus 1 is also connected wirelessly or wired to a host device (not shown) such as a computer. When a print job representing an image to be printed is provided from the host device and printing of the print job is instructed, control unit 40 executes a print process to form a print image on the surface of paper P.

[0014] A paper feed cassette 3 that stores paper sheets P is provided at the bottom of the housing 2. A pickup roller 4 is provided above and in front of the paper feed cassette 3. The pickup roller 4 has its lower portion in contact with the upper surface of the paper sheets P stored in the paper feed cassette 3, and rotates to send the uppermost sheet of paper sheets P stored therein forward.

[0015] A transport path W for transporting paper P is formed inside the housing 2. A plurality of transport rollers 5a, 5b, 5c, 5d, 5e, 5f, 5g, and 5h (hereinafter collectively referred to as transport rollers 5) are also provided inside the housing 2. The transport rollers 5 are made up of a plurality of rollers that face and contact each other across the transport path W, and transport paper P on the transport path W by rotating in a predetermined direction.

[0016] Additionally, multiple media detection sensors 6a, 6b, 6c, 6d, 6e, 6f, and 6g (hereinafter collectively referred to as media detection sensors 6) are installed inside the housing 2 at multiple locations along the conveyance path W. The media detection sensors 6 detect the presence or absence of paper P on the conveyance path W and notify the control unit 40. Based on this, the control unit 40 can recognize the presence or absence of paper P at the location on the conveyance path W where each media detection sensor 6 is installed, i.e., can grasp the position of paper P on the conveyance path W. Therefore, based on the detection results obtained from each media detection sensor 6, the control unit 40 can appropriately print an image based on image data on one or both sides of the paper P while appropriately controlling the conveyance of paper P and the operation timing of each module, and can also detect delays in paper conveyance, paper jams, etc.

[0017] Furthermore, an environmental temperature sensor 7 that measures temperature and humidity, and a belt thermistor 8 that measures the temperature of a transfer belt 21 (described later) are provided inside the housing 2. The temperature measured by the belt thermistor 8 is used as the temperature inside the housing 2.

[0018] Also provided within the housing 2 is an image forming section 9 for forming a print image by printing a color image of the print target on the surface of the paper P. The image forming section 9 comprises three image forming units 10 (image forming units 10a, 10b, and 10c) arranged in order from the front side (upstream side) to the rear side (downstream side) at the top end of the housing 2. The image forming units 10 develop electrostatic latent images representing black (K), which is a similar color component of the print image, using toner as a developer to form a toner image corresponding to the image data.

[0019] The image forming units 10a, 10b, and 10c are configured identically and use the same color toner to develop electrostatic latent images. For this reason, hereinafter, the image forming units 10a, 10b, and 10c will be collectively referred to as image forming unit 10. As shown in FIG. 2, the image forming unit 10 is made up of a toner cartridge 18, a print head 11, and a developing device 19.

[0020] The toner cartridge 18 is disposed above the developing device 19, contains toner, and is configured to be detachable from the developing device 19. The developing device 19 includes a supply roller 12, a developing roller 13, a photosensitive drum 14, a charging roller 15, a cleaning blade 16, and a drum waste toner collection container 17.

[0021] The print head 11 serving as the exposure unit is an LED (Light Emitting Diode) head, and is provided adjacent to the upper side of the photosensitive drum 14. A plurality of LED elements are aligned in the left-right direction, and each LED element is turned on or off under the control of the control unit 40. The print head 11 exposes the surface of the photosensitive drum 14, which has been charged by the application of a charging bias voltage (hereinafter also referred to as a charging voltage), which is a negative voltage, based on image data, to form an electrostatic latent image.

[0022] A supply bias voltage (hereinafter also referred to as a supply voltage), which is a negative voltage, is applied to the supply roller 12, which supplies toner contained in a toner cartridge 18 to the developing roller 13. The charging roller 15 uniformly charges the surface of the photosensitive drum 14 to a negative voltage. A development bias voltage (hereinafter also referred to as a development voltage), which is a negative voltage, is applied to the developing roller 13, which serves as a developing unit, which charges the toner and electrostatically attaches it to the electrostatic latent image formed on the photosensitive drum 14, thereby forming a toner image of a certain thickness. The photosensitive drum 14 carries the electrostatic latent image and also carries a toner image obtained by developing the electrostatic latent image with toner.

[0023] The cleaning blade 16 is a blade made of urethane rubber that comes into contact with the photosensitive drum 14 downstream of the contact position with the transfer roller 22 (described later) in the rotation direction of the photosensitive drum 14, thereby scraping off and removing residual toner and waste toner remaining on the surface of the photosensitive drum 14 during the printing process and the disposal of deteriorated toner. The drum waste toner collection container 17 is a container that collects and stores the residual toner and waste toner removed by the cleaning blade 16. This drum waste toner collection container 17 is integrated with the developing device 19, and when the drum waste toner collection container 17 becomes full, the developing device 19 needs to be replaced. The developing device 19 also needs to be replaced when the photosensitive drum 14 reaches the end of its life.

[0024] In addition, in the image forming section 9 (FIG. 1), a transfer unit 20 is arranged from below the image forming unit 10a to below the image forming unit 10c, which transfers the toner images formed by the image forming units 10a, 10b, and 10c onto the surface of the paper P. The transfer unit 20 is composed of a transfer belt 21, a transfer roller 22 (FIG. 2), a belt cleaning blade 23, and a belt waste toner collection container 24.

[0025] The transfer belt 21 is an endless belt that carries the paper P on its upper surface and transports it rearward. Three transfer rollers 22 (FIG. 2) are rotatably provided inside the transfer belt 21, corresponding to the three photosensitive drums 14, facing the image forming unit 10, and a positive transfer bias voltage (hereinafter also referred to as transfer voltage) is applied to the transfer rollers 22. As a result, when forming a print image, the transfer unit 20 pinches the paper P carried by the transfer belt 21 between the upper portion of the surface of the transfer roller 22 and the lower portion of the surface of the corresponding three photosensitive drums 14, and transfers the toner image on the surfaces of the four photosensitive drums 14 to the surface of the paper P by applying a transfer voltage to the transfer roller 22.

[0026] The belt cleaning blade 23 is a blade made of urethane rubber, and by contacting the transfer belt 21, it scrapes off and removes waste toner carried by the transfer belt 21 when discarding degraded toner. The belt waste toner collection container 24 is a container that collects and stores the waste toner removed from the transfer belt 21 by the belt cleaning blade 23. This belt waste toner collection container 24 is integrated with the transfer unit 20, and when the belt waste toner collection container 24 becomes full, the transfer unit 20 needs to be replaced. The transfer unit 20 also needs to be replaced when the transfer belt 21 reaches the end of its life.

[0027] In this configuration, the image forming unit 10 performs a development process. In the development process, the image forming unit 10 rotates the photosensitive drum 14, uniformly charging the surface (surface layer) of the photosensitive drum 14 with the charging roller 15 to which a negative high voltage is applied, and then exposing the surface of the photosensitive drum 14 with the print head 11 based on image data to form an electrostatic latent image. At this time, an image signal processing unit 52 (FIG. 3) converts the image data into dot data, which is printing data, and an exposure control unit 53 (FIG. 3) controls the print head 11 based on the dot data, thereby controlling the exposure of the print head 11. Furthermore, the potential of the portion of the surface of the photosensitive drum 14 irradiated with light from the print head 11 rises to approximately 0 V, thereby forming an electrostatic latent image corresponding to the image data on the surface of the photosensitive drum 14.

[0028] Next, the image forming unit 10 supplies toner from the toner cartridge 18 to the developing device 19. The image forming unit 10 applies a developing voltage to the developing roller 13 to generate a potential difference between the developing roller 13 and the photosensitive drum 14, and forms a toner image by electrostatically attaching the toner supplied by the supply roller 12 onto the electrostatic latent image formed on the photosensitive drum 14. A supply voltage and a developing voltage, which are negative high voltages, are applied to the supply roller 12 and the developing roller 13, respectively, from a power source (not shown), and are maintained at constant voltages.

[0029] After this development process, the transfer unit 20 sandwiches the paper P transported by the transfer belt 21 between the transfer roller 22 and the photosensitive drum 14, and transfers the toner image on the surface of the photosensitive drum 14 to the surface of the paper P. In this way, the transfer unit 20 transfers a toner image of one color, black, onto the surface of the paper P, and passes the paper P with the transferred toner image to the fixing unit 26.

[0030] The image forming section 9 is provided with a fixing unit 26, which fixes the toner image to the surface of the paper P, behind the transfer unit 20. The fixing unit 26 has a paper path for passing the paper P, located approximately in the vertical center. The fixing unit 26 also has a heating roller 27 rotatably mounted above the paper path and a pressure roller 28 rotatably mounted below the paper path. Thus, when forming a print image, the fixing unit 26 takes the paper P, onto whose surface the toner image has been transferred from the transfer unit 20, into the paper path and sandwiches it between the heating roller 27 and the pressure roller 28, which rotate in opposite directions. The fixing unit 26 then fixes the toner image to the surface of the paper P by applying heat and pressure between the heating roller 27 and the pressure roller 28, which rotate in opposite directions. The fixing unit 26 fixes the black toner image to the surface of the paper P to form a print image, and delivers the paper P with the printed image formed thereon to the discharge unit 30 above or the duplex printing unit 31 below.

[0031] In this configuration, the image forming apparatus 1 transports paper P stored in a paper feed cassette 3 to the image forming unit 9 using transport rollers 5a, 5b, and 5c. In the image forming unit 9, toner is transferred onto the paper P using an image forming unit 10 while the paper P is transported using a transfer belt 21. The paper P is transported to a fixing unit 26 by the transfer belt 21. As the paper P passes through the fixing unit 26, the toner on the paper P is fixed to the paper P by high temperature. The transport direction of the paper P is switched, and the paper P is transported to an ejection unit 30 and then discharged to a media collection tray 32, or is transported to a duplex printing unit 31. The paper P transported to the duplex printing unit 31 is transported again to the image forming unit 9, where an image is formed on the opposite side of the paper, and the paper P passes through the fixing unit 26 again before being discharged to the media collection tray 32.

[0032] [1-2. Control configuration of image forming device] As shown in FIG. 3, the image forming apparatus 1 is composed of a control unit 40, a memory unit 42, an input unit 44, a display unit 46, an image forming unit 9, and a communication unit 48, and the control unit 40 controls the entire image forming apparatus 1.

[0033] [1-2-1. Control Unit Configuration] The control unit 40 is configured around a CPU (Central Processing Unit) not shown, and controls each unit to perform various processes by reading and executing predetermined programs from a program storage unit 81 in the memory unit 42. The control unit 40 also has a print management unit 50, a used image forming unit determination unit 51, an image signal processing unit 52, an exposure control unit 53, a user adjustment value determination unit 54, a correction value generation unit 55, a correction value generation determination unit 56, an adjustment value correction value reflection unit 57, an image density calculation unit 58, and an image density determination unit 59.

[0034] When the print management unit 50 receives a print instruction from an external device, it causes the user adjustment value determination unit 54 to perform a determination process as to whether or not the density setting in the image forming device 1 has been adjusted by the user. Next, if the density setting has been adjusted, the print management unit 50 causes the adjustment value correction value reflection unit 57 to apply at least one of the user setting adjustment values ​​(user setting LED light intensity adjustment value and user setting development voltage adjustment value) or the generation correction values ​​(generation development voltage correction value and generation LED light intensity correction value) to each image forming unit 10 (details will be described later). Next, the print management unit 50 executes printing.

[0035] The image forming unit to be used determination section 51 determines the image forming unit to be used to print each duty block area (high-duty block area, medium-duty block area, and low-duty block area) in the image. Here, the high-duty block area indicates a block area with high image density, the low-duty block area indicates a block area with low image density, and the medium-duty block area indicates a block area with image density between the high-duty block area and the low-duty block area (details will be described later). Hereinafter, the high-duty block area, medium-duty block area, and low-duty block area will also be collectively referred to as duty block areas. Also, below, the image forming unit 10 that prints the high-duty block area will also be referred to as the image forming unit for printing the high-duty block area, the image forming unit 10 that prints the medium-duty block area will also be referred to as the image forming unit for printing the medium-duty block area, and the image forming unit 10 that prints the low-duty block area will also be referred to as the image forming unit for printing the low-duty block area. Furthermore, in the following description, the high-duty block area printing image forming unit, the medium-duty block area printing image forming unit, and the low-duty block area printing image forming unit are also collectively referred to as duty block area printing image forming units.

[0036] The image signal processing unit 52 converts image data into dot data, which is print data. The exposure control unit 53 controls the print head 11 based on the dot data converted from the image data by the image signal processing unit 52, thereby performing exposure control of the print head 11.

[0037] The user adjustment value determination unit 54 determines whether the density setting in the image forming apparatus 1 has been adjusted by the user with respect to 0, which is the reference value, on the density setting screen DIP (Fig. 4).

[0038] The correction value generation unit 55 generates a generated correction value (described later) based on a user setting adjustment value (described later) corresponding to a user density adjustment value (described later). The correction value generation unit 55 also sets either both the user setting adjustment value and the generated correction value or only the user setting adjustment value in each duty block area printing image forming unit.

[0039] The correction value generation determination unit 56 determines whether at least one of the user setting LED light amount adjustment value or the user setting developing voltage adjustment value has been calculated according to the user density adjustment value. The adjustment value correction value reflection unit 57 applies at least one of the user setting adjustment value corresponding to the user density adjustment value or the generated correction value based on the user setting adjustment value corresponding to the user density adjustment value to each image forming unit 10.

[0040] The image density calculation unit 58 calculates the image density for each block area from the dot data converted from the image data by the image signal processing unit 52. The image density determination unit 59 determines all the block areas using the image density thresholds T1 and T2 (where T1 < T2) pre-recorded in the ROM 80, and classifies all the block areas into three types: a high-duty block area, a medium-duty block area, or a low-duty block area according to the image density.

[0041] [1-2-2. Configuration of the storage unit] The storage unit 42 includes a RAM (Random Access Memory) 60, a ROM (Read Only Memory) 80, and a flash memory (not shown).

[0042] [1-2-2-1. RAM configuration] The RAM 60 has a used image forming unit storage section 61, a development voltage value 62, an LED light quantity value 63, and an image density storage section 64. The used image forming unit storage section 61 stores the print image forming units for each duty block area determined by the used image forming unit determination section 51.

[0043] The developing voltage value 62 is a value indicating the developing voltage for each image forming unit 10, and remains at a reference value when developing voltage correction is not performed, but is changed and updated when developing voltage correction is performed. The LED light quantity value 63 is a value indicating the LED light quantity for each image forming unit 10, and remains at a reference value when LED light quantity correction is performed, but is changed and updated when LED light quantity correction is performed. The image density storage unit 64 stores the image density calculated for each block area (described below) based on the dot data.

[0044] [1-2-2-2. ROM configuration] In addition to a program storage section 81, the ROM 80 has a user adjustment value storage section 82, a print duty history recording section 83, and a discard dot count 84. The user adjustment value storage section 82 stores a user density adjustment value, which is a value for adjusting the density setting value in the image forming apparatus 1 and is set by the user by operating the operation button section 45 of the input section 44, for example.

[0045] The print duty history recording unit 83 indicates the cumulative value of the print duty for printing performed up to now by the image forming apparatus 1. The waste dot count 84 is calculated based on the dot count, and indicates the cumulative value of the amount of deteriorated toner accumulated in each image forming unit 10. When the image forming apparatus 1 discards deteriorated toner, the value is subtracted from the waste dot count 84.

[0046] [1-2-3. Configuration of input unit, display unit, image forming unit and communication unit] Input unit 44 generally comprises, for example, a touch sensor or an operation keyboard, and accepts operations from the user. In this embodiment, input unit 44 has an operation button unit 45 as shown in Fig. 4. Display unit 46 comprises, for example, a display panel 47 as shown in Fig. 4, and displays the status of image forming apparatus 1.

[0047] When the image forming apparatus 1 is in a standby state or other state where it can accept user operations, in response to a user's operation of the operation button unit 45, the image forming apparatus 1 displays the status and setting items of the image forming apparatus 1 on the display panel 47. In addition, the image forming apparatus 1 allows the user to change the device settings for some setting items.

[0048] The image forming unit 9 (FIG. 3) mainly includes the toner cartridge 18, the photosensitive drum 14, the charging roller 15, the print head 11, the supply roller 12, the developing roller 13, the cleaning blade 16, the transfer roller 22, and the fixing unit 26.

[0049] The communication unit 48 is an interface that executes wireless network communication using a wired LAN (Local Area Network) system or a wireless LAN system, and performs communication such as sending and receiving data with the outside.

[0050] [1-3. How to adjust image density] Here, we will explain how to adjust the density of an image in the development process. There are roughly two types of methods for adjusting the density of an image to be printed in the development process.

[0051] The first is development voltage correction, a method in which the image forming apparatus 1 adjusts the development voltage, which is the voltage applied to the development roller 13, to adjust the thickness of the developer adhering to the electrostatic latent image. Specifically, when the development voltage difference, which is the potential difference between the development voltage of the development roller 13 and the charging voltage of the photosensitive drum 14, increases, the thickness of the developer adhering to the electrostatic latent image increases, and the density of the printed image increases. On the other hand, when the development voltage difference decreases, the thickness of the developer adhering to the electrostatic latent image decreases, and the density of the printed image decreases.

[0052] The second is LED light intensity correction, a method in which the image forming apparatus 1 adjusts the area of ​​developer adhesion on the photosensitive drum 14 by adjusting the irradiation time (i.e., light intensity) of light from the print head 11 (hereinafter also referred to as LED light intensity). Specifically, when the LED light intensity increases, the area (i.e., the unit area of ​​one dot) of the electrostatic latent image on the photosensitive drum 14 seen at the dot level increases, the amount of developer adhering to the photosensitive drum 14 increases, and the density of the printed image increases. On the other hand, when the LED light intensity decreases, the area (i.e., the unit area of ​​one dot) of the electrostatic latent image on the photosensitive drum 14 seen at the dot level decreases, the amount of developer adhering to the photosensitive drum 14 decreases, and the density of the printed image decreases. In this type of LED light intensity correction, it is also possible to increase the LED light intensity only for dots whose density is to be increased.

[0053] Figure 5 shows the relationship between print duty and density, and the change in density with development voltage correction and LED light intensity correction. Here, print duty (print rate) refers to image density, and is the ratio of the area of ​​an image actually formed on paper P to the area when a solid image is formed in the image formation area when viewed on one page of paper P. In other words, print duty is the ratio of the count value of actually printed dots to the case where dots are formed over the entire surface of an area within a specified area on paper P, when viewed on one page, assuming that the state when dots are formed over the entire surface of an area within a specified area on paper P is 100%.

[0054] 5 shows the density relative to the print duty when neither development voltage correction nor LED light intensity correction is performed. Development voltage correction line L2 shows the density relative to the print duty when the development voltage is corrected by a predetermined value and the development voltage value 62 is not the reference value. LED light intensity correction line L3 shows the density relative to the print duty when the LED light intensity is corrected by a predetermined value and the LED light intensity value 63 is not the reference value.

[0055] From Figure 5, it can be seen that in the case of development voltage correction, the higher the print duty, the greater the change in density, even if the development voltage is corrected by the same value, and in the case of LED light intensity correction, the closer the print duty is to the intermediate band, the greater the change in density, even if the LED light intensity is corrected by the same value.

[0056] [1-4. User density settings] Although the density of the image printed by the image forming device 1 is generally corrected in a density correction process by the image forming device 1, the user can adjust (change) the density setting value, which is the set value for the density setting, using the operation button section 45 (Figure 4) of the input section 44.

[0057] In this case, the user operates the operation button unit 45 according to the display on the display panel 47 (FIG. 4), causes the display panel 47 to display the density setting item among the various setting items, and selects the density setting item. In response, the control unit 40 displays on the display panel 47 a density setting screen DIP as shown in FIG. 4, which allows the density setting of the image forming apparatus 1 to be adjusted to seven levels from -3 to +3. The user can change the density adjustment value displayed on the display panel 47 using the operation button unit 45. In FIG. 4, for example, +2 is selected as the density adjustment value.

[0058] When the user changes the density setting value from the reference value of 0, the control unit 40 records the changed user density adjustment value (for example, +2) in the user adjustment value storage unit 82. When control involving printing is performed, the control unit 40 refers to the user density adjustment value stored in the user adjustment value storage unit 82 and adjusts the density of the image by setting adjustment values ​​for the development voltage, the LED light intensity, or both the development voltage and the LED light intensity.

[0059] Specifically, the control unit 40 performs a development voltage correction, for example, by applying a ±15 V correction to the development voltage for each ±1 V change in the user density adjustment value. Hereinafter, the development voltage adjustment value calculated by the control unit 40 in accordance with the user density adjustment value is also referred to as a user-defined development voltage adjustment value. The control unit 40 updates the development voltage value 62 by adding or subtracting the user-defined development voltage adjustment value to or from a reference value of the development voltage value 62. The control unit 40 may also calculate a user-defined LED light intensity adjustment value, which is an adjustment value for the LED light intensity, instead of the user-defined development voltage adjustment value in accordance with the user density adjustment value. The control unit 40 updates the LED light intensity value 63 by adding or subtracting the user-defined LED light intensity adjustment value to or from a reference value of the LED light intensity value 63. Furthermore, the control unit 40 may calculate both the user-defined development voltage adjustment value and the user-defined LED light intensity adjustment value in accordance with the user density adjustment value. Hereinafter, the user-defined development voltage adjustment value and the user-defined LED light intensity adjustment value are collectively referred to as user-defined adjustment values.

[0060] [1-5. Stabilization time for high-pressure components] Next, the stabilization wait time for high-voltage members will be explained. The image forming unit 9 has multiple members (high-voltage members) to which a high voltage is applied, such as the developing roller 13. When these members are used in print control, for example, they are not used for control immediately after the application of high voltage, but rather after some time has passed since the start of application. This is because a wait time is required until the surface potential of the developing roller 13 or the photosensitive drum 14 reaches a target value and stabilizes. If control involving printing is performed without ensuring the stabilization wait time for these high-voltage members, printing will be performed using members that have not yet reached the target voltage value originally used in control, resulting in unstable density of the printed image and reduced print quality.

[0061] [1-6. Printing process] Next, specific processing procedures for print processing by the control unit 40 will be described in detail using the flowcharts shown in Figures 6, 7, 8, and 9. When the image forming apparatus 1 is powered on, the control unit 40 starts print processing procedure RT1 by reading and executing a print processing program from the storage unit 42, and proceeds to step SP1. In step SP1, the control unit 40 receives a print instruction together with a print job from the outside via the print management unit 50, and proceeds to step SP2.

[0062] In step SP2, the control unit 40 instructs the user adjustment value determination unit 54 via the print management unit 50 to perform a determination process to determine whether or not the density setting in the image forming device 1 has been adjusted by the user, and the user adjustment value determination unit 54 determines whether or not the density setting in the image forming device 1 has been adjusted by the user. If a positive result is obtained here, this indicates that development voltage correction and LED light intensity correction need to be performed in accordance with the user density adjustment value, and the control unit 40 then proceeds to step SP3.

[0063] In step SP3, the control unit 40 instructs the correction value generation unit 55 from the print management unit 50 to perform the correction value generation process described below, and after going through the correction value generation process procedure SRT1 shown in Figure 7, generates a generated correction value based on the user adjustment value and sets at least one of the user-set adjustment value or the generated correction value to each duty block area printing image forming unit, and then proceeds to step SP4.

[0064] In step SP4, the control unit 40 applies (i.e., adds or subtracts) at least one of the user-set adjustment value or the generated correction value set in the correction value generation process to each image forming unit 10 (i.e., each image forming unit for printing in the duty block area) using the adjustment value correction value reflection unit 57, and then proceeds to step SP5. In step SP5, the control unit 40 starts printing using the print management unit 50 using the image forming unit 10 to which the user-set adjustment value and the generated correction value have been applied and the development voltage and LED light intensity have been appropriately changed, and then proceeds to step SP6.

[0065] In step SP6, the control unit 40 instructs the image density calculation unit 58 from the print management unit 50 to perform the image data analysis process described below, and after going through the image data analysis process procedure SRT2 shown in Figure 8, calculates the image density of each block area within the image formation area AR within one page of image data, and allocates each block area to a high duty block area, medium duty block area, or low duty block area based on the image density, and then proceeds to step SP7.

[0066] In step SP7, the control unit 40 instructs the print management unit 50 to the image forming unit determination unit 51 to perform the print image forming unit selection process described below, and after going through the print image forming unit selection process procedure SRT3 shown in Figure 9, determines which image forming unit 10 will print each duty block area in the image, and then proceeds to step SP8.

[0067] In step SP8, the control unit 40 uses the determined image forming unit 10 to print on paper P using the print management unit 50, and then proceeds to step SP9. In step SP9, the control unit 40 determines whether all pages in the print job have been printed using the print management unit 50. If a negative result is obtained here, this means that there are still unprinted pages remaining in the print job, and in this case the control unit 40 returns to step SP6 and repeats the above-mentioned processing.

[0068] On the other hand, when all pages in the print job have been printed, the control unit 40 obtains a positive result in step SP9, moves to step SP10, and when the print management unit 50 ends printing, moves to step SP12, and ends the print processing procedure RT1.

[0069] On the other hand, if a negative result is obtained in step SP2, this indicates that neither development voltage correction nor LED light intensity correction is required in accordance with the user density adjustment value, and in this case the control unit 40 proceeds to step SP11 to start printing. When all pages in the print job have been printed, the control unit 40 proceeds to step SP10, and when printing is completed by the print management unit 50, the control unit 40 proceeds to step SP12 to end the print processing procedure RT1.

[0070] [1-7. Correction value generation process] Next, the specific processing procedure of the correction value generation process by the control unit 40 will be described with reference to the flowchart in Fig. 7. The control unit 40 starts the correction value generation processing procedure SRT1 shown in Fig. 7 in step SP3 of the printing processing procedure RT1 (Fig. 6), and proceeds to step SP21.

[0071] In step SP21, the control unit 40 determines the image forming unit for printing, indicating which image forming unit 10 will be used to print each of the high duty block area, medium duty block area, and low duty block area, using the image forming unit to be used determination unit 51, records the result in the image forming unit to be used memory unit 61, and proceeds to step SP22.

[0072] At this time, the image forming unit to be used determination section 51 refers to, for example, the waste dot count 84, and determines the image forming units 10 with the largest amounts of waste toner as the image forming units for printing in the order of high duty block area, medium duty block area, and low duty block area, thereby causing the image forming units 10 with the largest waste dot count 84 to use toner and making it difficult for waste toner to accumulate. Alternatively, the image forming unit to be used determination section 51 refers to, for example, the print duty history recording section 83, and determines the image forming units 10 with the smallest cumulative print duty values ​​(past print history) as the image forming units for printing in the order of high duty block area, medium duty block area, and low duty block area.

[0073] In step SP22, the control unit 40 determines whether or not the user-set LED light intensity adjustment value has been calculated in accordance with the user-set density adjustment value using the correction value generation determination unit 56. If a negative result is obtained here, this indicates that only the user-set developing voltage adjustment value has been calculated in accordance with the user-set density adjustment value, and the control unit 40 then proceeds to step SP23.

[0074] In step SP23, the control unit 40 references the user-set developing voltage adjustment value and generates a generated LED light intensity correction value, which is a correction value for the LED light intensity that is expected to result in a similar increase or decrease in density, using the correction value generation unit 55. At this time, for example, if the user-set developing voltage adjustment value is +15 [V], the correction value generation unit 55 generates a generated LED light intensity correction value of -12 [%].

[0075] Next, the correction value generation unit 55 sets the user-set development voltage adjustment value to the development voltage value 62 of the image forming unit for printing the high-duty block area. The correction value generation unit 55 also sets the generated LED light intensity correction value to the LED light intensity value 63 of the image forming unit for printing the medium-duty block area and the LED light intensity value 63 of the image forming unit for printing the low-duty block area.

[0076] Next, the control unit 40 proceeds to step SP27, ends the correction value generation processing procedure SRT1, and proceeds to step SP4 of the printing processing procedure RT1 (FIG. 6).

[0077] On the other hand, if a positive result is obtained in step SP22, this indicates that either only the user-set LED light intensity adjustment value or both the user-set development voltage adjustment value and the user-set LED light intensity adjustment value have been calculated according to the user density adjustment value, and in this case the control unit 40 proceeds to step SP24.

[0078] In step SP24, the control unit 40 determines whether or not the user-set developing voltage adjustment value has been calculated in accordance with the user-set density adjustment value using the correction value generation determination unit 56. If a negative result is obtained here, this indicates that only the user-set LED light intensity adjustment value has been calculated in accordance with the user-set density adjustment value, and the control unit 40 then proceeds to step SP25.

[0079] In step SP25, the control unit 40 generates a generated development voltage correction value, which is a correction value for the development voltage that is expected to increase or decrease the density to the same extent, by referring to the user-set LED light amount adjustment value, using the correction value generation unit 55. Hereinafter, the generated development voltage correction value and the generated LED light amount correction value will also be collectively referred to as generated correction values.

[0080] Next, the correction value generation unit 55 sets a generated development voltage correction value to the development voltage value 62 of the image forming unit for printing the high-duty block area. The correction value generation unit 55 also sets a user-defined LED light intensity adjustment value to the LED light intensity value 63 of the image forming unit for printing the medium-duty block area and the LED light intensity value 63 of the image forming unit for printing the low-duty block area.

[0081] Next, the control unit 40 proceeds to step SP27, ends the correction value generation processing procedure SRT1, and proceeds to step SP4 of the printing processing procedure RT1 (FIG. 6).

[0082] On the other hand, if a positive result is obtained in step SP24, this indicates that both the user-set development voltage adjustment value and the user-set LED light intensity adjustment value have been calculated according to the user density adjustment value, and the control unit 40 then proceeds to step SP26.

[0083] In step SP26, the control unit 40 sets user-defined developing voltage adjustment values ​​for the development voltage value 62 of the image forming unit for printing the high-duty block area, the development voltage value 62 of the image forming unit for printing the medium-duty block area, and the development voltage value 62 of the image forming unit for printing the low-duty block area, using the correction value generation unit 55. The correction value generation unit 55 also sets user-defined LED light intensity adjustment values ​​for the LED light intensity value 63 of the image forming unit for printing the high-duty block area, the LED light intensity value 63 of the image forming unit for printing the medium-duty block area, and the LED light intensity value 63 of the image forming unit for printing the low-duty block area.

[0084] Next, the control unit 40 proceeds to step SP27, ends the correction value generation processing procedure SRT1, and proceeds to step SP4 of the printing processing procedure RT1 (FIG. 6).

[0085] [1-8. Image data analysis methods] Next, the image data analysis means will be described. Image density calculation unit 58 calculates image density D from the dot data converted from image data by image signal processing unit 52. Image density D is an index showing the proportion of dots exposed by print head 11 within a specified area, and is calculated by image density D = (number of exposed dots / number of pixels in specified area) x 100 [%].

[0086] In the first embodiment, the image density calculation unit 58 divides the image into block regions and calculates the image density Dij for each block region. For example, the length from the leftmost LED element to the rightmost LED element of the print head 11, i.e., the length of the print head 11 in the left-to-right direction (main scanning direction), is defined as the print head length L1, and the length of the image in the front-to-back direction (sub-scanning direction) perpendicular to the main scanning direction is defined as the image sub-scanning direction length L2. The area on the paper P formed by the print head length L1 in the main scanning direction and the image sub-scanning direction length L2 in the sub-scanning direction is also referred to as the image formation area AR on the paper P where an image can be formed. 10, the image forming area AR is divided into n equal parts along lines in the sub-scanning direction so that the areas with the print head length L1 are aligned in the main scanning direction, and into m equal parts along lines in the main scanning direction so that the areas with the image sub-scanning length L2 are aligned in the sub-scanning direction. Each area enclosed by adjacent lines in the sub-scanning direction and adjacent lines in the main scanning direction is defined as a block area gij (where 1≦i≦m, 1≦j≦n). The image density Dij in each block area gij is calculated as follows: image density Dij=(number of exposed dots in block area gij / number of pixels in block area gij)×100[%]. Thus, in the first embodiment, each block area gij is square, and when viewed as a whole, the image forming area AR is divided into a grid pattern.

[0087] [1-9. Image data analysis processing] Next, the specific processing procedure of the image data analysis process by the control unit 40 will be described using the flowchart of FIG. 8. The control unit 40 starts the image data analysis processing procedure SRT2 shown in FIG. 8 in step SP6 of the printing processing procedure RT1 (FIG. 6), and moves to step SP31. In step SP31, the control unit 40 converts the image data into dot data by the image signal processing unit 52, and moves to step SP32. In step SP32, the control unit 40 calculates the image density Dij of each block region gij based on the dot data as described above by the image density calculation unit 58, records the image density Dij in the image density storage unit 64, and moves to step SP33.

[0088] In step SP33, the control unit 40 determines all the block regions gij using the threshold values T1 and T2 (where T1 < T2) of the image density Dij recorded in the ROM 80 in advance by the image density determination unit 59, and classifies all the block regions gij into three types: a high-duty block region, a medium-duty block region, or a low-duty block region according to the image density Dij.

[0089] For example, when the threshold value T1 = 20 and the threshold value T2 = 80, the image density determination unit 59 determines that when the image density Dij in the block region gij of the image is 80[%] ≦ Dij ≦ 100[%], since it is a high printing duty, the block region gij is a high-duty block region. Also, the image density determination unit 59 determines that when the image density Dij in the block region gij of the image is 0[%] ≦ Dij < 20[%], since it is a low printing duty, the block region gij is a low-duty block region. Further, the image density determination unit 59 determines that when the image density Dij in the block region gij of the image is 20[%] ≦ Dij < 80[%], since it is a medium printing duty between the high-duty block region and the low-duty block region, the block region gij is a medium-duty block region.

[0090] Fig. 11 shows an example of classification of image print duties when i = 8 and j = 6. In Fig. 11, block areas gij marked with H indicate high-duty block areas, block areas gij marked with M in Fig. 11 indicate medium-duty block areas, and block areas gij marked with L in Fig. 11 indicate low-duty block areas.

[0091] Next, the control unit 40 proceeds to step SP34, ends the image data analysis processing procedure SRT2, and proceeds to step SP7 of the printing processing procedure RT1 (FIG. 6).

[0092] [1-10. Print image forming unit selection process] Next, a specific procedure for the print image forming unit selection process by the control unit 40 will be described with reference to the flowchart in Fig. 9. The control unit 40 starts the print image forming unit selection process procedure SRT3 shown in Fig. 9 in step SP7 of the print process procedure RT1 (Fig. 6), and then proceeds to step SP41.

[0093] In step SP41, the control section 40 sets the image forming unit to be used determination section 51 so that the dot data for the high-duty block area is printed by the image forming unit for printing the high-duty block area, and then proceeds to step SP42.

[0094] In step SP42, the control section 40 sets the image forming unit to be used determination section 51 so that the dot data for the medium duty block area is printed by the image forming unit for printing the medium duty block area, and then proceeds to step SP43.

[0095] In step SP43, the control section 40 sets the image forming unit to be used determination section 51 so that the dot data for the low-duty block area is printed by the image forming unit for printing the low-duty block area.

[0096] When the image forming units 10 to be used for all block areas gij have been determined, the control section 40 proceeds to step SP44, ends the print image forming unit selection processing procedure SRT3, and proceeds to step SP8 of the print processing procedure RT1 (FIG. 6).

[0097] [1-11. Effects, etc.] In the above configuration, the image forming apparatus 1 is provided with a plurality of image forming units 10 each equipped with a toner cartridge 18 containing toner of the same color (e.g., black). The image forming apparatus 1 also applies a user-set adjustment value and a generation correction value based on a user-set user density adjustment value to each of the image forming units for printing duty block areas (the image forming unit for printing high-duty block areas, the image forming unit for printing medium-duty block areas, and the image forming unit for printing low-duty block areas). Furthermore, the image forming apparatus 1 switches the image forming units for printing duty block areas for each block area gij according to the image density Dij of each block area gij to perform printing.

[0098] In this way, the image forming apparatus 1 does not switch the development voltage value 62 or the LED light intensity value 63 during image formation, but instead selects from a plurality of image forming units 10, each having a different development voltage value 62 or LED light intensity value 63 preset thereto, according to the density of the image data, to form an image.

[0099] Therefore, the image forming apparatus 1 can perform image formation while preventing a waiting time from occurring after switching at least one of the development voltage value 62 and the LED light amount value 63 during image formation. This allows the image forming apparatus 1 to perform printing at an appropriate density according to the image density Dij of each block area gij while preventing the time required to complete printing from becoming too long.

[0100] According to the above configuration, the image forming device 1 is provided with an image density calculation unit 58 and an image density determination unit 59 that analyze the image density Dij as the density of the print data, a first image forming unit 10 that is one of the image forming units 10 that form an image based on at least one of a development voltage value 62 or an LED light intensity value 63 as a first setting value related to density for black as a first color, a second image forming unit 10 that is the other of the image forming units 10 that form an image based on at least one of a development voltage value 62 or an LED light intensity value 63 as a second setting value related to density for black that is different from the first setting value, and a used image forming unit determination unit 51 that selects either the first image forming unit 10 or the second image forming unit 10 to form an image based on the analysis results of the image density calculation unit 58 and the image density determination unit 59.

[0101] As a result, the image forming device 1 can perform image formation by selecting multiple image forming units 10, each having a different development voltage value 62 or LED light intensity value 63 preset thereto, according to the density of the print data, without switching the development voltage value 62 or LED light intensity value 63 during image formation, thereby preventing a waiting time from occurring after switching the development voltage value 62 or LED light intensity value 63.

[0102] 2. Second Embodiment [2-1. Configuration of image forming device] Image forming apparatus 101 (FIGS. 1 and 3) according to the second embodiment differs from image forming apparatus 1 according to the first embodiment in that it has a control unit 140 instead of control unit 40, but is otherwise configured similarly. Control unit 140 according to the second embodiment differs from control unit 40 according to the first embodiment in that it has a used image forming unit determination unit 151, a correction value generation unit 155, an image density calculation unit 158, and an image density determination unit 159 instead of used image forming unit determination unit 51, correction value generation unit 55, image density calculation unit 58, and image density determination unit 59, respectively, but is otherwise configured similarly. This control unit 140 executes a different printing process compared to control unit 40.

[0103] The image forming unit to be used determination section 151 determines which image forming unit 10 will print each page (high-duty page, medium-duty page, and low-duty page). Here, a high-duty page refers to a page with a high image density, a low-duty page refers to a page with a low image density, and a medium-duty page refers to a page with an image density between that of a high-duty page and that of a low-duty page. Hereinafter, an image forming unit 10 that prints high-duty pages will also be referred to as an image forming unit for printing high-duty pages, an image forming unit 10 that prints medium-duty pages will also be referred to as an image forming unit for printing medium-duty pages, and an image forming unit 10 that prints low-duty pages will also be referred to as an image forming unit for printing low-duty pages. Hereinafter, the image forming unit for printing high-duty pages, the image forming unit for printing medium-duty pages, and the image forming unit for printing low-duty pages will also be referred to collectively as image forming units for printing duty pages.

[0104] The correction value generation unit 155 generates a generated correction value based on a user-set adjustment value corresponding to the user density adjustment value. The correction value generation unit 155 also sets both the user-set adjustment value and the generated correction value, or only the user-set adjustment value, for each duty page printing image forming unit.

[0105] The image density calculation unit 158 calculates the image density D for each page from the dot data converted by the image signal processing unit 52 from the image data. The image density determination unit 159 determines all pages using the thresholds T1 and T2 (where T1 < T2) of the image density D recorded in the ROM 80 in advance, and classifies all pages into three types: high-duty pages, medium-duty pages, or low-duty pages according to the image density D.

[0106] [2-2. Printing Process] Next, the specific processing procedure of the printing process by the control unit 140 will be described in detail using the flowcharts shown in FIGS. 6, 12, 13, and 14. When the power of the image forming apparatus 101 is turned on, the control unit 140 reads out and executes the printing process program from the storage unit 42, starts the printing process procedure RT101, and moves to step SP1. In step SP1, the control unit 140 receives a printing instruction together with a printing job from the outside by the printing management unit 50, and moves to step SP2.

[0107] In step SP2, the control unit 140 instructs the user adjustment value determination unit 54 from the printing management unit 50 to perform a determination process on whether the density setting in the image forming apparatus 101 has been adjusted by the user, and the user adjustment value determination unit 54 determines whether the density setting of the image forming apparatus 101 has been adjusted by the user. When an affirmative result is obtained here, this indicates that it is necessary to perform developing voltage correction and LED light amount correction according to the user density adjustment value. At this time, the control unit 140 moves to step SP103.

[0108] In step SP103, the control unit 140 instructs the correction value generation unit 155 from the printing management unit 50 to perform a correction value generation process described later. Through the correction value generation process procedure SRT101 shown in FIG. 12, a generated correction value is generated based on the user setting adjustment value, and at least one of the user setting adjustment value or the generated correction value is set in each duty page printing image forming unit, and then moves to step SP4.

[0109] In step SP4, the control unit 140 applies (i.e., adds or subtracts) at least one of the user-set adjustment value or the generated correction value set in the correction value generation process to each image forming unit 10 (i.e., each duty page printing image forming unit) using the adjustment value correction value reflection unit 57, and then proceeds to step SP5. In step SP5, the control unit 140 starts printing using the print management unit 50 using the image forming unit 10 to which the user-set adjustment value and the generated correction value have been applied and the development voltage and LED light intensity have been appropriately changed, and then proceeds to step SP106.

[0110] In step SP106, the control unit 140 instructs the image density calculation unit 158 ​​from the print management unit 50 to perform the image data analysis process described below, and after going through the image data analysis process procedure SRT102 shown in Figure 13, calculates the image density D within the image formation area AR within one page of the image data, and allocates each page to a high duty page, medium duty page, or low duty page based on the image density D, and then proceeds to step SP107.

[0111] In step SP107, the control unit 140 instructs the print management unit 50 to the image forming unit determination unit 151 to perform the print image forming unit selection process described below, and after going through the print image forming unit selection process procedure SRT103 shown in Figure 14, determines which image forming unit 10 will print each page, and proceeds to step SP8.

[0112] In step SP8, the control unit 140 uses the determined image forming unit 10 to print on paper P using the print management unit 50, and then proceeds to step SP9. In step SP9, the control unit 140 determines whether all pages in the print job have been printed using the print management unit 50. If a negative result is obtained here, this means that there are still unprinted pages remaining in the print job, and in this case the control unit 140 returns to step SP106 and repeats the above-mentioned processing.

[0113] On the other hand, when all pages in the print job have been printed, the control unit 140 obtains a positive result in step SP9, moves to step SP10, and when the printing manager 50 ends printing, moves to step SP12, and ends the print processing procedure RT101.

[0114] On the other hand, if a negative result is obtained in step SP2, this indicates that neither development voltage correction nor LED light intensity correction is necessary in accordance with the user density adjustment value, and in this case the control unit 140 proceeds to step SP11 to start printing. When all pages in the print job have been printed, the control unit 140 proceeds to step SP10, and when printing is completed by the print management unit 50, the control unit 140 proceeds to step SP12 to end the print processing procedure RT101.

[0115] [2-3. Correction value generation process] Next, the specific processing procedure of the correction value generation process by the control unit 140 will be described using the flowchart of Fig. 12, in which the same steps as in Fig. 7 are assigned the same reference numerals. The control unit 140 starts the correction value generation processing procedure SRT101 shown in Fig. 12 in step SP103 of the printing processing procedure RT101 (Fig. 6), and proceeds to step SP121.

[0116] In step SP121, the control unit 140 determines the image forming unit for printing, indicating which image forming unit 10 will be used to print each of the high-duty pages, medium-duty pages, and low-duty pages, using the image forming unit used determination unit 151, records the result in the image forming unit used memory unit 61, and proceeds to step SP22.

[0117] At this time, the image forming unit to be used determination section 151 refers to, for example, the waste dot count 84, and determines the image forming unit 10 with the largest amount of waste toner as the image forming unit for printing high-duty pages, medium-duty pages, and low-duty pages in that order, thereby causing the image forming unit 10 with the largest waste dot count 84 to use toner and making it difficult for waste toner to accumulate. Alternatively, the image forming unit to be used determination section 151 refers to, for example, the print duty history recording section 83, and determines the image forming unit 10 with the smallest cumulative print duty value (past print history) as the image forming unit for printing high-duty pages, medium-duty pages, and low-duty pages in that order.

[0118] If a negative result is obtained in step SP22, the control unit 140 proceeds to step SP123. In step SP123, the control unit 140 causes the correction value generation unit 155 to generate a generated LED light intensity correction value, which is a correction value for the LED light intensity that is expected to result in a similar increase or decrease in density, by referencing the user-set developing voltage adjustment value. Next, the correction value generation unit 155 sets the user-set developing voltage adjustment value to the developing voltage value 62 of the image forming unit for printing high-duty pages. The correction value generation unit 155 also sets the generated LED light intensity correction value to the LED light intensity value 63 of the image forming unit for printing medium-duty pages and the LED light intensity value 63 of the image forming unit for printing low-duty pages.

[0119] Next, the control unit 140 proceeds to step SP27, ends the correction value generation processing procedure SRT101, and proceeds to step SP4 of the printing processing procedure RT101 (FIG. 6).

[0120] On the other hand, if a positive result is obtained in step SP22, then the control unit 140 proceeds to step SP24. If a negative result is obtained in step SP24, then the control unit 140 proceeds to step SP125. In step SP125, the control unit 140 causes the correction value generation unit 155 to generate a target development voltage correction value, which is a correction value for the development voltage that is expected to result in a similar increase or decrease in density, by referencing the user-set LED light intensity adjustment value. Next, the correction value generation unit 155 sets the target development voltage correction value to the development voltage value 62 of the image forming unit for printing high-duty pages. The correction value generation unit 155 also sets the user-set LED light intensity adjustment value to the LED light intensity value 63 of the image forming unit for printing medium-duty pages and the LED light intensity value 63 of the image forming unit for printing low-duty pages.

[0121] Next, the control unit 140 proceeds to step SP27, ends the correction value generation processing procedure SRT101, and proceeds to step SP4 of the printing processing procedure RT101 (FIG. 6).

[0122] On the other hand, if a positive result is obtained in step SP24, then the control unit 140 proceeds to step SP126. In step SP126, the control unit 140 causes the correction value generation unit 155 to set the user-defined developing voltage adjustment values ​​for the developing voltage value 62 of the image forming unit for printing high-duty pages, the developing voltage value 62 of the image forming unit for printing medium-duty pages, and the developing voltage value 62 of the image forming unit for printing low-duty pages. The correction value generation unit 155 also sets the user-defined LED light intensity adjustment values ​​for the LED light intensity value 63 of the image forming unit for printing high-duty pages, the LED light intensity value 63 of the image forming unit for printing medium-duty pages, and the LED light intensity value 63 of the image forming unit for printing low-duty pages.

[0123] Next, the control unit 140 proceeds to step SP27, ends the correction value generation processing procedure SRT101, and proceeds to step SP4 of the printing processing procedure RT101 (FIG. 6).

[0124] [2-4. Image data analysis methods] Next, the image data analysis means will be described. The image density calculation unit 158 calculates the image density D from the dot data obtained by the image signal processing unit 52 converting the image data. In the second embodiment, the image density calculation unit 158 obtains the image density D of the entire page (that is, the entire image formation area AR as shown in FIG. 15) without dividing the image into block areas. The image density D of the entire image formation area AR is calculated by the formula: image density D = (number of exposed dots / number of pixels in the entire image formation area AR) × 100 [%].

[0125] [2-5. Image Data Analysis Processing] Next, the specific processing procedure of the image data analysis processing by the control unit 140 will be described using the flowchart of FIG. 13 with the same reference numerals as the corresponding steps in FIG. 8. The control unit 140 starts the image data analysis processing procedure SRT102 shown in FIG. 13 in step SP106 of the printing processing procedure RT101 (FIG. 6), and moves to step SP31. In step SP31, the control unit 140 converts the image data into dot data by the image signal processing unit 52, and moves to step SP132. In step SP132, the control unit 140 calculates the image density D of the image formation area AR of all pages based on the dot data as described above by the image density calculation unit 158, and records the image density D in the image density storage unit 64, and moves to step SP133.

[0126] In step SP133, the control unit 140 determines all pages by the image density determination unit 159 using the thresholds T1 and T2 (where T1 < T2) of the image density D recorded in the ROM80 in advance, and classifies all pages into three types: high-duty pages, medium-duty pages, or low-duty pages according to the image density D.

[0127] For example, if threshold value T1=20 and threshold value T2=80, when image density D over the entire image forming area AR of a page is 80[%]≦D≦100[%], the image density determination unit 159 determines that the page is a high-duty page because the print duty is high. Also, when image density D over the entire image forming area AR of a page is 0[%]≦D<20[%], the image density determination unit 159 determines that the page is a low-duty page because the print duty is low. Furthermore, when image density D over the entire image forming area AR of a page is 20[%]≦D<80[%], the image density determination unit 159 determines that the page is a medium-duty page because the print duty is somewhere between a high-duty page and a low-duty page.

[0128] Next, the control unit 140 proceeds to step SP34, ends the image data analysis processing procedure RT102, and proceeds to step SP107 of the printing processing procedure RT101 (FIG. 6).

[0129] [2-6. Print image forming unit selection process] Next, a specific processing procedure for the print image forming unit selection process by the control unit 140 will be described using the flowchart of Fig. 14, in which the same steps as in Fig. 9 are assigned the same reference numerals. In step SP107 of the print processing procedure RT101 (Fig. 6), the control unit 140 starts the print image forming unit selection processing procedure SRT103 shown in Fig. 14, and proceeds to step SP141.

[0130] In step SP141, the control section 140 sets the image forming unit to be used to print the dot data of the high-duty page using the image forming unit for printing high-duty pages, by the image forming unit to be used 151, and then proceeds to step SP142.

[0131] In step SP142, the control section 140 sets the image forming unit to be used determination section 151 so that the dot data for the medium duty block area is printed by the image forming unit for printing the medium duty block area, and then proceeds to step SP143.

[0132] In step SP143, the control section 140 sets the image forming unit to be used determination section 151 so that the dot data for the low-duty block area is printed by the image forming unit for printing the low-duty block area.

[0133] When the image forming units 10 to be used for all pages have been determined, the control section 140 proceeds to step SP44, ends the print image forming unit selection processing procedure SRT103, and proceeds to step SP8 of the print processing procedure RT101 (FIG. 6).

[0134] [2-7. Effects, etc.] In the above configuration, the image forming apparatus 101 applies the user-set adjustment value and the generated correction value based on the user density adjustment value set by the user to each page (high-duty page, medium-duty page, and low-duty page). Furthermore, the image forming apparatus 101 switches the image forming unit for printing each duty page for each page according to the image density D of each page to perform printing.

[0135] In this way, the image forming apparatus 101 does not switch the development voltage value 62 or the LED light intensity value 63 during image formation, but instead selects from a plurality of image forming units 10, each having a different development voltage value 62 or LED light intensity value 63 preset thereto, according to the density of the image data, to form an image.

[0136] Therefore, the image forming apparatus 101 can perform image formation while preventing a waiting time from occurring after switching at least one of the development voltage value 62 and the LED light amount value 63 during image formation. As a result, the image forming apparatus 101 can perform printing at an appropriate density according to the image density D of each page while preventing the time required to complete printing from becoming too long.

[0137] Furthermore, compared to the image forming apparatus 1 according to the first embodiment, the image forming apparatus 101 can speed up processing and improve the consistency of print results for each page in the same duty classification, for example, for high duty pages.

[0138] In other respects as well, image forming apparatus 101 according to the second embodiment can achieve the same effects as image forming apparatus 1 according to the first embodiment.

[0139] 3. Other Embodiments In the first embodiment described above, the image forming apparatus 1 applies the user-set adjustment value and the generation correction value based on the user-set user density adjustment value set by the user to each of the image forming units for printing duty block areas (the image forming unit for printing high-duty block areas, the image forming unit for printing medium-duty block areas, and the image forming unit for printing low-duty block areas), and performs printing by switching the image forming units for printing duty block areas for each block area gij according to the image density Dij of each block area gij. The present invention is not limited to this. The image forming apparatus 1 may apply different development voltage values ​​62 to each of the image forming units for printing duty block areas, regardless of the density setting by the user, and may perform printing by switching the image forming units for printing duty block areas for each block area gij according to the image density Dij of each block area gij. The same applies to the LED light intensity value 63. The same applies to the second embodiment.

[0140] In the first embodiment described above, the image forming apparatus 1 corrects the development voltage value 62 by ±15 [V] and the LED light amount value 63 by ±12 [%] in response to a change in the user density adjustment value by 1. The present invention is not limited to this, and the image forming apparatus 1 may correct the development voltage value 62 and the LED light amount value 63 by various other values ​​in response to a change in the user density adjustment value by 1. The same applies to the second embodiment.

[0141] Furthermore, in the first embodiment described above, the image forming apparatus 1 generates a generated LED light intensity correction value when only the user-set developing voltage adjustment value is calculated according to the user density adjustment value, and generates a generated developing voltage correction value when only the user-set LED light intensity adjustment value is calculated according to the user density adjustment value. The present invention is not limited to this. The image forming apparatus 1 may generate a generated developing voltage correction value or a generated LED light intensity correction value, or only a generated developing voltage correction value when only the user-set developing voltage adjustment value is calculated according to the user density adjustment value, or may generate a generated developing voltage correction value or a generated LED light intensity correction value, or only a generated LED light intensity correction value when only the user-set LED light intensity adjustment value is calculated according to the user density adjustment value. The same applies to the second embodiment.

[0142] Furthermore, in the first embodiment described above, the image forming apparatus 1 refers to the waste dot count or the cumulative value of the print duty to determine the image forming units for printing in each of the high-duty block areas, medium-duty block areas, and low-duty block areas. However, the present invention is not limited to this, and the image forming apparatus 1 may refer to various other information such as the consumable usage status to determine the image forming units for printing in each of the high-duty block areas, medium-duty block areas, and low-duty block areas.

[0143] Furthermore, since the toner stored in the image forming units 10 arranged near the fixing unit 26 tends to be easily deteriorated by the heat generated by the fixing unit 26, the image forming apparatus 1 may determine the high-duty block area, the medium-duty block area, and the low-duty block area as the image forming units for printing in the order from the image forming unit 10c located near the fixing unit 26 and downstream in the transport direction of the paper P toward the image forming unit 10a located upstream. In this case, the image forming apparatus 1 can make the image forming unit 10 located downstream in the transport direction use more toner, thereby making it less likely for waste toner to accumulate. The same applies to the second embodiment.

[0144] Furthermore, in the first embodiment described above, the image forming apparatus 1 classifies the block areas gij into three categories: high-duty block areas, medium-duty block areas, and low-duty block areas. However, the present invention is not limited to this, and the image forming apparatus 1 may classify the block areas gij into various numbers of categories, such as two, four, or more. In this case, it is sufficient to determine the image density Dij of each block area gij using the number of image density Dij thresholds corresponding to the number of categories of the block areas gij. The same applies to the second embodiment.

[0145] Furthermore, in the first embodiment described above, the image forming apparatus 1 divides the image formation area AR (FIG. 10) into a grid of square block areas gij and calculates the image density Dij for each block area gij. However, the present invention is not limited to this. As shown in FIG. 16, the image forming apparatus 1 may divide the image formation area AR along lines along the main scanning direction into m equal areas, each with a sub-scanning direction length L2, aligned in the sub-scanning direction, and define each area surrounded by adjacent lines along the main scanning direction as a block area gij (where 1≦i≦m). In this case, the image density Di in each block area gij is calculated by the formula: Image density Di = (number of exposed dots in block area gij / number of pixels in block area gij) × 100 [%]. Thus, each block area gij in other embodiments is a rectangle (strip) extending in the main scanning direction.

[0146] Furthermore, in the first embodiment described above, the image forming apparatus 1 has been described as displaying "Density Setting" on the display panel 47 as the name of the setting item that allows the user to set the density. However, the present invention is not limited to this, and the image forming apparatus 1 may display various other display names on the display panel 47 as the name of the setting item that allows the user to set the density.

[0147] Furthermore, in the first embodiment described above, the image forming apparatus 1 has been described as having the input unit 44 configured by the operation button unit 45 and the display unit 46 configured by the display panel 47. However, the present invention is not limited to this, and the image forming apparatus 1 may have other input devices and output devices such as a touch panel or an operation keyboard as the input unit 44 and the display unit 46.

[0148] Furthermore, in the above-described embodiment, the present invention has been described as being applied to an image forming apparatus 1 or 101 having three image forming units 10 corresponding to black toner. However, the present invention is not limited to this, and may be applied to image forming apparatuses having various numbers of image forming units, such as two or less or four or more. Furthermore, the present invention may be applied to image forming apparatuses having multiple image forming units 10 corresponding to toners of various colors other than black.

[0149] Furthermore, in the above-described embodiment, the present invention has been described as being applied to the image forming apparatus 1 or 101 that writes a latent image onto the photosensitive drum 14 using the print head 11, which is an LED head. However, the present invention is not limited to this, and may be applied to image forming apparatuses that write a latent image using various other types of print head 11, such as a laser head.

[0150] Furthermore, the present invention is not limited to the above-described embodiments and other embodiments. That is, the scope of application of the present invention also extends to embodiments in which the above-described embodiments are combined in part or in whole with any of the above-described other embodiments. The scope of application of the present invention also extends to embodiments in which part of the configuration described in any of the above-described embodiments and other embodiments is extracted and used as part of the configuration of any of the above-described embodiments and other embodiments, or in which part of the extracted configuration is added to any of the above-described embodiments.

[0151] Furthermore, in the above-described first embodiment, the image forming apparatus 1 is configured as an image forming apparatus by the image density calculation unit 58 and the image density determination unit 59 as analysis units, one of the image forming units 10 as a first image forming unit, the other of the image forming units 10 as a second image forming unit, and the used image forming unit determination unit 51 as a control unit. However, the present invention is not limited to this, and the image forming apparatus may be configured by an analysis unit, a first image forming unit, a second image forming unit, and a control unit having various other configurations. [Industrial Applicability]

[0152] The present invention can be used in a printer provided with a plurality of image forming units that form images using toner of the same color. [Explanation of symbols]

[0153] 1...image forming apparatus, 2...casing, 3...paper feed cassette, 4...pickup roller, 5...conveyor roller, 6...media detection sensor, 7...ambient temperature sensor, 8...belt thermistor, 9...image forming section, 10...image forming unit, 11...print head, 12...supply roller, 13...developing roller, 14...photosensitive drum, 15...charging roller, 16...cleaning blade, 17...drum waste toner collection container, 18...toner cartridge, 19...developing device, 20...transfer unit, 21...transfer belt, 22...transfer roller, 23...belt cleaning blade, 24...belt waste toner collection container, 26...fixing unit, 27...heating roller, 28...pressure roller, 30...ejection unit, 31...duplex printing unit, 32...media collection tray, W ......Conveying path, 40......Control unit, 42......Memory unit, 44......Input unit, 45......Operation button unit, 46......Display unit, 47......Display panel, 48......Communication unit, 50......Printing management unit, 51, 151......Image forming unit to be used determination unit, 52......Image signal processing unit, 53......Exposure control unit, 54......User adjustment value determination unit, 55, 155......Correction value generation unit, 56......Correction value generation determination unit, 57......Adjustment value correction value reflection unit, 58, 158......Image density calculation unit, 59, 159......Image density determination unit, 60......RAM, 61......Image forming unit to be used memory unit, 62......Developing voltage value, 63......LED light intensity value, 64......Image density memory unit, 80......ROM, 81......Program storage unit, 82......User adjustment value memory unit, 83......Printing duty history recording unit, 84......Waste dot count, AR......Image forming area.

Claims

1. an analysis unit that analyzes the density of the print data; a first image forming unit that forms an image in a first color based on a first setting value related to density; a second image forming unit that forms an image based on a second set value for the first color and a density different from the first set value; a control unit that selects either the first image forming unit or the second image forming unit based on the analysis result of the analysis unit and causes the selected unit to perform image formation; An image forming apparatus comprising:

2. The first image forming unit includes: a first photosensitive drum on which an electrostatic latent image is formed, and a first developing unit that develops the first photosensitive drum with a developer of the first color, and performs image formation with a first bias difference between the first photosensitive drum and the first developing unit based on the first set value; The second image forming unit includes: The image forming device includes a second photosensitive drum on which an electrostatic latent image is formed, and a second developing unit that develops the second photosensitive drum with a developer of the first color, and forms an image with a second bias difference between the second photosensitive drum and the second developing unit that is different from the first bias difference based on the second set value.

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

3. The first image forming unit includes: a first exposure unit that forms an electrostatic latent image on a first photosensitive drum, and forms an image in the first color by forming an electrostatic latent image on the first photosensitive drum with a first exposure amount from the first exposure unit based on the first set value; The second image forming unit includes: a second exposure unit that forms an electrostatic latent image on a second photosensitive drum, and forms an image in the first color by forming an electrostatic latent image on the second photosensitive drum with a second exposure amount that is different from the first exposure amount from the second exposure unit based on the second set value; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. The control unit The first image forming unit or the second image forming unit is selected according to the density of the image for each area obtained by dividing the page of the print data, and the image is formed.

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

5. The control unit The first image forming unit or the second image forming unit is selected according to the density of the image for each page of the print data and is made to perform image formation.

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

6. an image formed based on the second set value has a higher density than an image formed based on the first set value; The second image forming unit is provided downstream of the first image forming unit in a conveying direction of a medium on which an image is formed.

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

Images