Image forming device

Abstract

To improve image quality, and prevent a reduction in the life and an increase in cost of an image forming unit.SOLUTION: An image forming apparatus has: an image carrier; an electrifying member; a developer carrier that attaches developer to the image carrier to form a developer image; a supply member; a transfer member; and a voltage control processing unit Pr4 that, when printing is performed in a high temperature environment, then the image forming apparatus is left standing in a low temperature environment for a predetermined time or more, and subsequently a predetermined amount or more of printing is performed in the low temperature environment, corrects development voltage applied to the developer carrier to increase the absolute value of the development voltage. The image forming apparatus can appropriately attach the developer to the image carrier in correspondence with an increase in the resistance of a surface of the developer carrier, and thereby can improve image quality. The image forming apparatus does not need to rotate the developer carrier in a non-printing period and change a finishing agent applied to the developer carrier.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Conventionally, image forming devices such as printers, copiers, facsimile machines, and multifunction devices, for example, printers, are equipped with an image forming unit, a transfer roller, a fixing device, etc., and in the image forming unit, an electrostatic latent image is formed by exposing the surface of a photosensitive drum that has been uniformly charged by a charging roller, and the electrostatic latent image is developed by a developing roller to form a toner image, which is then transferred onto a sheet of paper by the transfer roller and fixed to the sheet of paper by the fixing device.

[0003] However, if printing is performed in a high-temperature environment, and then the printer is left in a low-temperature environment, and then printing is performed in the low-temperature environment, white bands will appear in the image due to the rotation cycle of the developing roller, resulting in a decrease in image quality.

[0004] This is thought to be because when printing is performed in a high-temperature environment, toner aggregates in the printer, and the residual charge increases in the area of ​​contact with the aggregated toner on the surface of the developing roller; then, while the printer is left in a low-temperature environment, the resistance becomes high, the development efficiency becomes lower than in other areas, and the toner on the developing roller becomes less likely to adhere to the photosensitive drum.

[0005] To prevent this white band from occurring, it is conceivable to rotate the developing roller while the printer is left in a low-temperature environment, thereby changing the position of the area that comes into contact with the aggregated toner, or to change the surface treatment agent applied to the developing roller (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-89622 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the conventional printers, the developing roller is rotated when not printing, which causes wear on the developing roller, photosensitive drum, etc., shortening the life of the image forming unit and increasing the cost of the image forming unit when changing the surface treatment agent.

[0008] The present invention aims to provide an image forming apparatus that can solve the problems of the conventional printers, improve image quality, and does not shorten the life of the image forming unit or increase costs. [Means for solving the problem]

[0009] To this end, the image forming apparatus of the present invention comprises an image carrier that carries a latent image, a charging member that charges the image carrier, a developer carrier that holds developer and causes the developer to adhere to the image carrier to form a developer image, a supply member that supplies developer to the developer carrier, a transfer member that transfers the developer image on the image carrier to a medium, and a voltage control processing unit that corrects the development voltage applied to the developer carrier to increase its absolute value when printing is performed in a high-temperature environment, and then the image forming apparatus is left in a low-temperature environment for a predetermined period of time or more, and then a predetermined amount of printing is performed in the low-temperature environment. [Effects of the Invention]

[0010] According to the present invention, the image forming apparatus includes an image carrier that carries a latent image, a charging member that charges the image carrier, a developer carrier that holds developer and causes the developer to adhere to the image carrier to form a developer image, a supply member that supplies developer to the developer carrier, a transfer member that transfers the developer image on the image carrier to a medium, and a voltage control processing unit that corrects the development voltage applied to the developer carrier and increases its absolute value when printing is performed in a high-temperature environment, and then the image forming apparatus is left in a low-temperature environment for a predetermined period of time or more, and then a predetermined amount of printing is performed in the low-temperature environment.

[0011] In this case, after printing is performed in a high-temperature environment, the image forming device is left in a low-temperature environment for a predetermined time or more, and then when a predetermined amount of printing is performed in a low-temperature environment, the development voltage applied to the developer carrier is corrected and its absolute value is increased, so that the developer can be properly adhered to the image carrier in response to the increase in the resistance of the surface of the developer carrier, thereby improving image quality.

[0012] Furthermore, since there is no need to rotate the developer carrier when not printing or to change the surface treatment agent applied to the developer carrier, the life of the image forming unit is not shortened and costs are not increased. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a control block diagram of the printer according to the first embodiment of the present invention. [Figure 2] 1 is a conceptual diagram of a printer according to a first embodiment of the present invention. [Figure 3] FIG. 2 is a conceptual diagram of an image forming unit according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a diagram for explaining a risk of resistance increase in the first embodiment of the present invention. [Figure 5] FIG. 3 is a diagram showing an example of a development voltage correction value table in the first embodiment of the present invention. [Figure 6]10A and 10B are diagrams showing evaluation results of images formed on paper in a comparative example and an example, and determination results of voltage control processing. [Figure 7] FIG. 1 is a first diagram for explaining a method for evaluating images formed on paper in a comparative example and an example. [Figure 8] FIG. 2 is a second diagram for explaining the method for evaluating images formed on paper in the comparative example and the example. [Figure 9] 4 is a first flowchart showing the operation of the control device of the printer according to the first embodiment of the present invention. [Figure 10] 6 is a second flowchart showing the operation of the control device of the printer according to the first embodiment of the present invention. [Figure 11] FIG. 10 is a diagram showing the relationship between humidity and the resistance value of toner. [Figure 12] FIG. 10 is a diagram showing the relationship between toner density and toner resistance value. [Figure 13] FIG. 10 is a diagram showing the relationship between toner density and toner charge amount. [Figure 14] FIG. 10 is a diagram showing the relationship between the charge amount of toner and the number of printed sheets. [Figure 15] FIG. 11 is a diagram showing an example of a charging voltage correction value table according to the second embodiment of the present invention. [Figure 16] FIG. 10 is a diagram illustrating an example of a supply voltage correction value table according to the second embodiment of the present invention. [Figure 17] 10A and 10B are diagrams showing evaluation results of images formed on paper in a comparative example and an example, and determination results of voltage control processing. [Figure 18] 10 is a first flowchart showing the operation of the control device of the printer according to the second embodiment of the present invention. [Figure 19] 10 is a second flowchart showing the operation of the control device of the printer according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings, in which a printer as an image forming apparatus will be described.

[0015] FIG. 2 is a conceptual diagram of a printer according to the first embodiment of the present invention.

[0016] In the figure, 10 is a printer, which includes a printer main body Mb as the main body of the image forming device, a roll paper support Fd as a medium support section that supports roll paper 12 as a roll-shaped medium, and a paper feed section Sp arranged between the roll paper support Fd and the printer main body Mb.

[0017] The roll paper 12 is formed by winding a long sheet of paper (not shown) as a medium of any size (width and length) and thickness, and is held rotatably by the unwinding device 14, and the paper is fed from the roll paper support section Fd to the printer main body section Mb by the paper feed section Sp.

[0018] The paper fed from the feeding device 14 and supplied by the paper supply unit Sp is transported along a paper transport path Rt, which serves as a media transport path formed across the roll paper support unit Fd, the paper supply unit Sp, and the printer main body unit Mb.

[0019] In the paper feed unit Sp, reference numeral 16 denotes a lower guide unit that guides paper below the paper transport path Rt, and 17 denotes an upper guide unit that is arranged by a hinge hg so as to be able to swing relative to the lower guide unit 16 and that guides paper above the paper transport path Rt. The upper guide unit 17 functions as a jam release cover to open the paper transport path Rt when a paper jam occurs in the paper feed unit Sp. The paper supply section Sp is provided with a pair of conveying rollers m1 as a first conveying member, which consists of a roller ra arranged in the lower guide section 16 and a roller rb arranged in the upper guide section 17, and the paper conveyed by the pair of conveying rollers m1 is fed to the printer main body section Mb.

[0020] In the printer main body Mb, Cs is the housing of the printer main body Mb, Bd is the main body of the printer 10 formed within the housing Cs, i.e., the device main body, and 20 is a control board unit arranged at the bottom of the device main body Bd and constituting the main part of the control device of the printer 10.

[0021] The housing Cs consists of a front wall Wf, a back wall Wr, a top wall Wt, etc., and the front wall Wf is formed with a paper feed opening h1 for receiving paper fed from the roll paper support section Fd, and the back wall Wr is formed with an outlet h2 for discharging paper on which an image has been formed in the printer main body section Mb.

[0022] Furthermore, Cu is a cutter unit arranged adjacent to the front wall Wf, and the cutter unit Cu is equipped with a pair of conveying rollers m2 as a second conveying member that conveys paper fed through the paper feed port h1, and a rotary cutter 23 that is arranged downstream of the pair of conveying rollers m2 and cuts the paper to a predetermined length.

[0023] A pair of conveying rollers m3 is arranged downstream of the cutter unit Cu as a third conveying member, and a write sensor s1 is arranged downstream of the pair of conveying rollers m3 as a first medium detection unit for detecting the leading edge of the paper and setting the start position for writing the image on the paper, and an image forming unit Q1 is arranged downstream of the write sensor s1.

[0024] The image forming section Q1 includes a plurality of image forming units 21Y, 21M, 21C arranged from the upstream side to the downstream side of the paper transport path Rt, in this embodiment three image forming units 21Y, 21M, 21C for yellow, magenta, and cyan, a photosensitive drum 22 as an image carrier arranged in each of the image forming units 21Y, 21M, 21C, an LED head 24 as an exposure device arranged opposite the photosensitive drum 22, and a transfer unit u1 arranged below each of the image forming units 21Y, 21M, 21C.

[0025] Each of the LED heads 24 exposes the photosensitive drum 22 based on print data, selectively irradiating the surface of the photosensitive drum 22 with light, and forms an electrostatic latent image as a latent image.

[0026] A fixing unit 30 is disposed downstream of the image forming unit Q1 on the paper transport path Rt and includes a heating roller 31 as a first fixing member and a pressure roller 32 as a second fixing member.

[0027] Downstream of the fixing unit 30 on the paper transport path Rt, a pair of discharge rollers m4 serving as discharge members is arranged adjacent to the spine wall Wr, and downstream of the pair of discharge rollers m4, a discharge sensor s2 serving as a second media detection unit for detecting the rear end of the paper is arranged.

[0028] Next, the image forming units 21Y, 21M, and 21C will be described.

[0029] Fig. 3 is a conceptual diagram of an image forming unit according to the first embodiment of the present invention. Note that image forming units 21Y, 21M, and 21C have the same structure except for the color of the toner used as the developer, which will be described later, and therefore only image forming unit 21Y is shown in Fig. 3.

[0030] The image forming units 21Y, 21M, and 21C each include a main body of the image forming units 21Y, 21M, and 21C, that is, a unit main body 33, and a toner storage device Ct formed integrally with each unit main body 33 as a developer storage device.

[0031] The toner storage device Ct includes a toner storage chamber (not shown) as a first developer storage section that stores new toner (not shown) of each color, and a waste toner box Bx (not shown) as a second developer storage section that is disposed adjacent to the toner storage chamber and stores waste toner as waste developer.

[0032] In addition, the image forming units 21Y, 21M, and 21C are equipped with a drum counter Cd (FIG. 1) described below, and when the count value of the drum counter Cd reaches an upper limit value or the waste toner box Bx becomes full, the operator is prompted to replace the image forming units 21Y, 21M, and 21C.

[0033] In this embodiment, the toner is composed of toner particles having an average particle size of 7 μm, which are formed by a pulverization method from a polyester resin, a colorant, a charge control agent, and a release agent, and an external additive such as hydrophobic silica added to the toner particles.

[0034] The unit main body 33 is provided with the photosensitive drum 22, which is rotatably arranged, a charging roller 34 as a charging device, which is rotatably arranged in contact with the photosensitive drum 22, a developing roller 36 as a developer carrier, which is rotatably arranged in contact with the photosensitive drum 22 and carries toner, a supply roller 38 as a supply member, which is rotatably arranged in contact with the developing roller 36, a developing blade 39 as a developer regulating member, which is arranged in pressure contact with the developing roller 36, a cleaning blade 41 as a first cleaning member, which is arranged in contact with the photosensitive drum 22, a transport coil 43 as a waste developer transport member, which is rotatably arranged below the cleaning blade 41 and transports the waste toner to the waste toner box Bx, and a cleaning roller 44 as a second cleaning member, which is arranged in contact with the charging roller 34 and removes toner adhering to the charging roller 34.

[0035] The photosensitive drum 22 is rotated in the direction of arrow A by driving a belt motor M1 (FIG. 1) serving as a drive unit, which will be described later.

[0036] The charging roller 34 uniformly charges the surface of the photosensitive drum 22. To this end, a charging voltage Vch serving as a first process voltage is applied to the charging roller 34 by a charging voltage control unit Ea serving as a first voltage control unit, which will be described later.

[0037] The developing roller 36 is formed of a metal shaft and an elastic body made of semiconductive urethane rubber with a rubber hardness of 70° (Asker C) arranged on the outer periphery of the shaft, and develops the electrostatic latent image formed on the surface of the photosensitive drum 22 by exposure to light from the LED head 24, by adhering toner to the electrostatic latent image, thereby forming a toner image as a developer image of each color, which is a visible image. To this end, a developing voltage Vdb is applied to the developing roller 36 as a second process voltage by a developing voltage control unit Eb as a second voltage control unit, which will be described later.

[0038] The supply roller 38 is rotated in the same direction as the developing roller 36, supplies the toner supplied from the toner storage chamber to the unit body 33 to the developing roller 36, and frictionally charges the toner. To this end, a supply voltage Vsp is applied to the supply roller 38 as a third process voltage by a supply voltage control unit Ec as a third voltage control unit, which will be described later.

[0039] The developing blade 39 thins the toner supplied to the developing roller 36 by the supply roller 38 to form a toner layer as a developer layer. To this end, a regulated voltage Vre as a fourth process voltage is applied to the developing blade 39 by a regulated voltage control unit Ed as a fourth voltage control unit described later.

[0040] The cleaning blade 41 scrapes off toner remaining on the photosensitive drum 22, toner that has deteriorated and adhered to the photosensitive drum 22 by the developing roller 36, and the like, and removes it as waste toner.

[0041] Next, the transfer unit u1 will be described.

[0042] The transfer unit u1 includes a drive roller R1, a driven roller R2, a belt 26 that is stretched so as to be freely movable between the drive roller R1 and the driven roller R2 and that transports paper as it moves, a transfer roller 27 as a transfer member that is rotatably arranged opposite each photosensitive drum 22 via the belt 26, and a cleaning blade 28 as a third cleaning member that is arranged opposite the belt 26.

[0043] The transfer roller 27 transfers the toner image of each color formed on the photosensitive drum 22 onto a sheet of paper.

[0044] For this purpose, a transfer voltage Vtr serving as a fifth process voltage is applied to the transfer roller 27 by a transfer voltage control unit Ee serving as a fifth voltage control unit, which will be described later.

[0045] The cleaning blade 28 scrapes off and removes toner and other particles adhering to the belt 26 .

[0046] Next, the operation of the printer 10 having the above configuration will be described.

[0047] At the roll paper support section Fd, paper is fed onto the paper transport path Rt by the feeding device 14, transported by the transport roller pair m1, and fed to the printer main body Mb by the paper feed section Sp. Inside the printer main body Mb, the paper is transported by the transport roller pair m2 and sent to the cutter unit Cu, where it is cut at the specified timing.

[0048] The cut paper is sent to the image forming section Q1 by the conveying roller pair m3, and is transported by the belt 26 in the image forming section Q1, and is transported between the photosensitive drum 22 of each image forming unit 21Y, 21M, 21C and the transfer roller 27 of the transfer unit u1.

[0049] In each of the image forming units 21Y, 21M, and 21C, the surface of the photosensitive drum 22 is uniformly charged by the charging roller 34 and exposed by the LED head 24, whereby an electrostatic latent image is formed on the photosensitive drum 22.

[0050] In addition, in each image forming unit 21Y, 21M, 21C, the toner supplied from each toner storage device Ct into the unit main body 33 is charged as the supply roller 38 rotates and then supplied to the developing roller 36, where it is formed into a thin layer by the developing blade 39 and electrostatically attached to the electrostatic latent image on the photosensitive drum 22 to form a toner image of each color.

[0051] Then, in the transfer unit u1, as the transfer voltage Vtr is applied to each transfer roller 27, the toner images of each color formed on each photosensitive drum 22 are transferred onto the paper in succession by electrostatic force, forming a color toner image on the paper.

[0052] The paper is then sent to the fixing device 30, where the color toner image is heated by the heating roller 31 and fixed by being pressed against the paper by the pressure roller 32, forming a color image on the paper. The paper is discharged from the fixing device 30 by the discharge roller pair m4 and out of the device body Bd through the discharge port h2.

[0053] However, if printing is performed in a high-temperature environment, and then the printer 10 is left in a low-temperature environment, and then printing is performed in the low-temperature environment, white bands (horizontal white bands) will form in the image with the rotation cycle of the developing roller 36, resulting in a decrease in image quality.

[0054] In particular, when the printer 10 is used for a long period of time and the cumulative number of printed sheets reaches 10,000 or more, the formation of white bands becomes noticeable.

[0055] Therefore, in this embodiment, when printing is performed in a high-temperature environment, the printer 10 is left in a low-temperature environment, and then printing is performed in the low-temperature environment, the development voltage Vdb applied to the development roller 36 is corrected and its absolute value is increased.

[0056] Next, the control device of the printer 10 will be described.

[0057] FIG. 1 is a control block diagram of a printer according to a first embodiment of the present invention.

[0058] In the figure, reference numeral 10 denotes a printer, and a PC denotes a host computer as an information input device and as a higher-level device connected to the printer 10 via a wired or wireless LAN or the like.

[0059] Further, 50 is a control unit, IF is an interface unit as a communication unit that connects the printer 10 and the host computer PC and receives print jobs consisting of print data, print commands (control commands), etc. from the host computer PC and transmits status information of the printer 10 to the host computer PC, 53 is a ROM (Read Only Memory) as a first storage unit, and 54 is a RAM (Random Access Memory) as a second storage unit. Reference numeral 56 denotes an operation panel serving as an operation and display unit; s3 denotes a temperature sensor serving as a first temperature detection unit and as a first environmental information acquisition unit that detects the temperature inside the device main body Bd (FIG. 2) as an internal device temperature T1 described below; s4 denotes a humidity sensor serving as a second environmental information acquisition unit and as a humidity detection unit that detects the humidity inside the device main body Bd as internal device humidity; and s5 denotes a belt temperature sensor serving as a third environmental information acquisition unit and as a second temperature detection unit that detects the temperature of the belt 26 as a belt temperature.

[0060] The belt temperature sensor s5 is disposed adjacent to a predetermined image forming unit in the running direction of the belt 26, in this embodiment downstream of the image forming unit 21C, and the temperature sensor s3 and humidity sensor s4 are disposed near the image forming unit 21C.

[0061] Also, in the figure, Ea is a charging voltage control unit that applies the charging voltage Vch to the charging roller 34, Eb is a developing voltage control unit that applies the developing voltage Vdb to the developing roller 36, Ec is a supply voltage control unit that applies the supply voltage Vsp to the supply roller 38, Ed is a regulating voltage control unit that applies the regulating voltage Vre to the developing blade 39, Ee is a transfer voltage control unit that applies the transfer voltage Vtr to the transfer roller 27, Dr1 is an exposure control unit that drives the LED head 24, and Dr2 is a motor control unit that drives the belt motor M1.

[0062] When the belt motor M1 is driven, the drive roller R1 is driven to run the belt 26 and rotate the photosensitive drum 22, which in turn rotates the charging roller 34 in unison with the rotation of the photosensitive drum 22. In this embodiment, gears (not shown) for transmitting rotation are provided at one end of the photosensitive drum 22, the developing roller 36, and the supply roller 38, and the gears of the developing roller 36 and the supply roller 38 are meshed with the gear of the photosensitive drum 22. Therefore, when the photosensitive drum 22 is rotated, the developing roller 36 and the supply roller 38 are rotated in unison.

[0063] The control unit 50 includes a CPU (Central Processing Unit) (not shown) as an arithmetic device, an input / output port (not shown), a drum counter Cd that counts the cumulative number of rotations of the photosensitive drum 22, and the like, and controls the entire printer 10 and performs various processes based on programs (software), control data, etc. recorded in ROM 53.

[0064] In addition to the programs, the ROM 53 stores not only setting values, threshold values, etc. required for the control unit 50 to perform the various processes, but also stores resistance increase determination information (described later), which is information acquired by the information processing unit Pr2 (described later), and tables such as the development voltage correction value table Tb1 (Figure 5) (described later) for correcting the development voltage Vdb.

[0065] In this embodiment, a rewritable flash ROM or the like is used as the ROM 53.

[0066] The RAM 54 temporarily stores image data generated based on the print data for printing, as well as various information generated as the program is executed and the resistance increase determination information.

[0067] The RAM 54 functions as a work area when the CPU performs calculations.

[0068] The operation panel 56 includes an operation unit 58 consisting of switches, keys, etc., with which the operator inputs instructions to the printer 10, and a display unit 59 consisting of an LED screen, etc., for displaying the status of the printer 10. If the operation panel 56 is formed of a touch panel, the display unit 59 also functions as an operation unit.

[0069] The control unit 50 includes a print processing unit Pr1, an information processing unit Pr2, a resistance increase determination processing unit Pr3, a voltage control processing unit Pr4, and the like.

[0070] The print processing unit Pr1 performs print processing, and when it receives a print job from the host computer PC, it converts the print data for each print job into image data, drives the LED head 24 based on the image data to form an image on paper, and performs printing.

[0071] The information processing unit Pr2 performs information processing, and each time it receives a print job from the host computer PC, it acquires resistance increase determination information for determining whether the resistance of the surface of the developing roller 36 is increasing, and records the resistance increase determination information in or reads it from ROM 53.

[0072] The resistance increase determination information consists of the date and time measured by the timing device 55, the temperature inside the device detected by the temperature sensor s3, the humidity inside the device detected by the humidity sensor s4, the belt temperature detected by the belt temperature sensor s5, and the cumulative number of printed sheets represented by the cumulative count value counted by the drum counter Cd.

[0073] In this embodiment, the print job currently received by the interface unit IF from the host computer PC is defined as the current print job job(n) (n≧3), the print job received immediately before the current print job job(n) is defined as the previous print job job(n-1), and the oldest print job received within a predetermined period of time, in this embodiment not exceeding 10 hours, going back from the time when reception of the previous print job job(n-1) was completed is defined as the preceding print job job(n-(1+m)) (m: any number equal to or greater than 1).

[0074] The interface unit IF current Print job job( n When the first timing is when the print processing unit Pr1 receives a print job (n-1)), the second timing is when the print processing unit Pr1 finishes printing the previous print job (n-(1+m)), and the third timing is when the print processing unit Pr1 finishes printing the preceding print job (n-(1+m)), the information processing unit Pr2 acquires, at the first timing, resistance increase determination information consisting of date and time D1, in-apparatus temperature T1, in-apparatus humidity H1, and belt temperature t1 at the first timing; when the second timing is when the information processing unit Pr2 acquires, at the second timing, resistance increase determination information consisting of date and time D2, in-apparatus temperature T2, in-apparatus humidity H2, belt temperature t2, and cumulative number of printed sheets Pn1 at the second timing; and when the third timing is when the information processing unit Pr2 acquires, at the third timing, date and time D3, in-apparatus temperature T3, in-apparatus humidity H3, belt temperature t3, and cumulative number of printed sheets Pn2 at the third timing.

[0075] The resistance increase determination processing unit Pr3 performs the resistance increase determination processing, and the cumulative number of printed sheets Pn 1 , Pn 2When the number of sheets reaches a predetermined amount, in this embodiment, 10,000 sheets or more, it is determined whether the resistance of the surface of the developing roller 36 has increased based on the resistance increase determination information acquired by the information processing unit Pr2.

[0076] For this purpose, the resistance increase determination processing unit Pr3 subtracts the cumulative number of printed sheets Pn2 from the cumulative number of printed sheets Pn1 to obtain the number of printed sheets ΔPn ΔPn=Pn1-Pn2 (sheets) and subtract the date and time D2 from the date and time D1 to obtain the unused time ΔD of the printer 10 from the date and time D2 to the date and time D1. ΔD=D1-D2 [time] Calculate the temperature difference t by subtracting the belt temperature t1 from the belt temperature t2. t=t2-t1 Calculate the humidity difference h by subtracting the humidity H1 from the humidity H2 inside the device. h=H2-H1 Calculate.

[0077] The resistance increase determination processing unit Pr3 then determines whether the number of printed sheets ΔPn is 1000 or more, whether the left-standing time ΔD is 24 or more hours, and whether the temperature difference t is 20°C or more. If the number of printed sheets ΔPn is 1000 or more, the left-standing time ΔD is 24 or more hours, and the temperature difference t is 20°C or more, it determines that the resistance of the developing roller 36 has increased because the printer 10 was left in a low-temperature environment for a predetermined time or longer after printing a predetermined amount or more in a high-temperature environment.

[0078] In addition, if the standing time ΔD is less than 24 hours or the temperature difference t is less than 20°C, or if the temperature difference t is 10°C or more and the humidity difference h is 15% or more, the resistance increase determination processing unit Pr3 also determines that the resistance of the developing roller 36 has increased.

[0079] When the resistance increase determination processing unit Pr3 determines that the resistance of the surface of the developing roller 36 is increasing, the voltage control processing unit Pr4 performs voltage control processing to correct the developing voltage Vdb applied to the developing roller 36 and increase its absolute value.

[0080] For this purpose, the voltage control processing unit Pr4 refers to the development voltage correction value table Tb1, corrects the development voltage Vdb in accordance with the temperature difference t and humidity difference h, and increases the absolute value.

[0081] In addition, the voltage control processing unit Pr4 changes the developing voltage Vdb to the value before correction when a predetermined amount of printing, in this embodiment, 200 sheets or more, has been performed after printing with the corrected developing voltage Vdb has begun.

[0082] Next, the possibility that the resistance of the surface of the developing roller 36 increases due to changes in the environment in which the printer 10 is placed, or due to the printer 10 being left unused, that is, the risk of an increase in resistance, will be described.

[0083] FIG. 4 is a diagram for explaining the risk of resistance increase in the first embodiment of the present invention.

[0084] As can be seen from the diagram, when the number of printed sheets ΔPn (sheets) is small, the thickness of the toner layer on the developing roller 36 is less likely to increase, the nip pressure applied to the toner at the nip between the photosensitive drum 22 and the developing roller 36 is correspondingly lower, and the toner is less likely to coagulate, so the resistance of the surface of the developing roller 36 is less likely to increase. Therefore, the risk of resistance increase is low.

[0085] Furthermore, if the number of printed sheets ΔPn [sheets] is large, the temperature inside the device T1 is high, the standing time ΔD in a low temperature environment is long, the temperature inside the device T2 is low, and the temperature difference t is small, the temperature change near the image forming units 21Y, 21M, and 21C is small, so they are not subject to the resistance increase judgment processing by the resistance increase judgment processing unit Pr3, and the risk of resistance increase is low.

[0086] Furthermore, if the number of printed sheets ΔPn [sheets] is large, the temperature inside the device T1 is high, the standing time ΔD in a low-temperature environment is long, the temperature inside the device T2 is high, and the temperature difference t is large, the temperature change near the image forming units 21Y, 21M, and 21C is large, so the risk of resistance increasing is high.

[0087] Furthermore, when the number of printed sheets ΔPn [sheets] is large, the temperature inside the device T1 is high, the standing time ΔD in a low-temperature environment is long, the temperature inside the device T2 is high, the temperature difference t is small, and the humidity difference h is large, the temperature change near the image forming units 21Y, 21M, and 21C is small but the humidity change is large, so the risk of resistance increasing is high.

[0088] Furthermore, when the number of printed sheets ΔPn [sheets] is large, the temperature T1 inside the device is high, the standing time ΔD in a low temperature environment is long, the temperature T2 inside the device is high, the temperature difference t is small, and the humidity difference h is small, the temperature change and humidity change near the image forming units 21Y, 21M, and 21C are small, so the risk of resistance increase is low.

[0089] Furthermore, when the number of printed sheets ΔPn (sheets) is large, the temperature T1 inside the device is high, and the standing time ΔD in a low temperature environment is short, the device body Bd does not cool down, so the risk of resistance increase is low.

[0090] Thus, it can be seen that the risk of resistance increase increases when the printer 10 is left in a low-temperature environment for a long time ΔD and the temperature difference t or humidity difference h is large, and when the printer 10 is left in a low-temperature environment for a predetermined time or longer after printing in a high-temperature environment.

[0091] Therefore, in this embodiment, under conditions where the risk of resistance increase in FIG. 4 is deemed high, the voltage control processing unit Pr4 corrects the development voltage Vdb in accordance with the temperature difference t and humidity difference h in the development voltage correction value table Tb1, and forms images Im1 and Im2 (FIGS. 7 and 8) with a solid color of 100% and a dot density of 50%, as described below, and measures the density of the images Im1 and Im2 to quantitatively confirm whether or not a white band has been formed due to an increase in the resistance of the development roller 36.

[0092] FIG. 5 is a diagram showing an example of a development voltage correction value table in the first embodiment of the present invention.

[0093] In the figure, Tb1 is a development voltage correction value table, and in the development voltage correction value table Tb1, the temperature difference t is t<10 (℃) 10 (℃)≦t<15 (℃) 15 (℃)≦t<20 (℃) 20 (℃)≦t<25 (℃) 25 (℃)≦t<30 (℃) 30 [℃] ≦ t The humidity difference h is h<5% 5%≦h<10% 10%≦h<15% 15%≦h<20% 20%≦h<25% 25%≦h A correction value ΔVdb of the development voltage Vdb is set for each range.

[0094] It is assumed that the risk of resistance increase increases as the temperature difference t and humidity difference h increase, so the correction value ΔVdb is set to be larger as the temperature difference t and humidity difference h increase.

[0095] Since the developing voltage Vdb takes a negative value, when the correction value ΔVdb is added, the absolute value of the developing voltage Vdb becomes larger. For example, when the reference developing voltage Vdb is −200 [V], the correction value ΔVdb is δVdb=-15 [V] Then, the corrected development voltage Vdb is Vdb=-200+(-15) =-215 (V) becomes.

[0096] In this embodiment, in the development voltage correction value table Tb1, the correction value ΔVdb is calculated based on the temperature difference τ τ=T2-T1 The correction value ΔVdb is set in accordance with the temperature difference t and the humidity difference h, rather than in accordance with the temperature difference t and the humidity difference h. However, compared with the internal device temperatures T1 and T2, the belt temperatures t1 and t2 take longer to change in response to changes in the environment, are maintained at low temperatures for a longer period of time, and are therefore more suitable for determining whether or not resistance is increasing. In addition, the distance between the developing roller 36 and the belt 26 is short, so the correction value ΔVdb is set in accordance with the temperature difference t and the humidity difference h.

[0097] Next, we will explain comparative examples 1-1 to 1-4 in which the images Im1 and Im2 were formed on paper without correcting the development voltage Vdb by the voltage control processing unit Pr4 in the range of temperature difference t and humidity difference h where the risk of resistance increase is high, and examples 1-1 to 1-24 in which the development voltage Vdb was corrected based on the correction value ΔVdb to form images Im1 and Im2 on paper. Comparative Example 1-1 The temperature difference t and humidity difference h t<10 (℃) 25%≦h When the developing voltage Vdb was within the range of , the developing voltage Vdb was not corrected. Comparative Example 1-2 The temperature difference t and humidity difference h 10 (℃)≦t<15 (℃) 15%≦h<20% When the developing voltage Vdb was within the range of , the developing voltage Vdb was not corrected. Comparative Examples 1-3 The temperature difference t and humidity difference h 20 (℃)≦t<25 (℃) h<5% When the developing voltage Vdb was within the range of , the developing voltage Vdb was not corrected. Comparative Examples 1-4 The temperature difference t and humidity difference h 20 (℃)≦t<25 (℃) 5%≦h<10% When the developing voltage Vdb was within the range of , the developing voltage Vdb was not corrected. Example 1-1 The temperature difference t and humidity difference h 10 (℃)≦t<15 (℃) 15%≦h<20% When the developing voltage Vdb was within the range of Example 1-2 The temperature difference t and humidity difference h 10 (℃)≦t<15 (℃) 20%≦h<25% When the developing voltage Vdb was within the range of Examples 1-3 The temperature difference t and humidity difference h 10 (℃)≦t<15 (℃) 25%≦h When the developing voltage Vdb was within the range of Examples 1-4 The temperature difference t and humidity difference h 15 (℃)≦t<20 (℃) 15%≦h<20% When the developing voltage Vdb was within the range of Examples 1-5 The temperature difference t and humidity difference h 15 (℃)≦t<20 (℃) 20%≦h<25% When the developing voltage Vdb was within the range of Examples 1-6 The temperature difference t and humidity difference h 15 (℃)≦t<20 (℃) 25%≦h When the developing voltage Vdb was within the range of Examples 1-7 The temperature difference t and humidity difference h 20 (℃)≦t<25 (℃) h<5% When the developing voltage Vdb was within the range of Examples 1-8 The temperature difference t and humidity difference h 20 (℃)≦t<25 (℃) 5%≦h<10% When the developing voltage Vdb was within the range of Examples 1-9 The temperature difference t and humidity difference h 20 (℃)≦t<25 (℃) 10%≦h<15% When the developing voltage Vdb was within the range of Examples 1-10 The temperature difference t and humidity difference h 20 (℃)≦t<25 (℃) 15%≦h<20% When the developing voltage Vdb was within the range of Examples 1-11 The temperature difference t and humidity difference h 20 (℃)≦t<25 (℃) 20%≦h<25% When the developing voltage Vdb was within the range of Examples 1-12 The temperature difference t and humidity difference h 20 (℃)≦t<25 (℃) 25%≦h When the developing voltage Vdb was within the range of Examples 1-13 The temperature difference t and humidity difference h 25 (℃)≦t<30 (℃) h<5% When the developing voltage Vdb was within the range of Examples 1-14 The temperature difference t and humidity difference h 25 (℃)≦t<30 (℃) 5%≦h<10% Examples 1-15 The temperature difference t and humidity difference h 25 (℃)≦t<30 (℃) 10%≦h<15% When the developing voltage Vdb was within the range of Examples 1-16 The temperature difference t and humidity difference h 25 (℃)≦t<30 (℃) 15%≦h<20% When the developing voltage Vdb was within the range of Examples 1-17 The temperature difference t and humidity difference h 25 (℃)≦t<30 (℃) 20%≦h<25% When the developing voltage Vdb was within the range of [Examples 1-18] The temperature difference t and humidity difference h 25 (℃)≦t<30 (℃) 25%≦h When the developing voltage Vdb was within the range of Examples 1-19 The temperature difference t and humidity difference h 30 [℃] ≦ t h<5% When the developing voltage Vdb was within the range of Examples 1-20 The temperature difference t and humidity difference h 30 [℃] ≦ t 5%≦h<10% When the developing voltage Vdb was within the range of [Example 1-21] The temperature difference t and humidity difference h 30 [℃] ≦ t 10%≦h<15% When the developing voltage Vdb was within the range of [Example 1-22] The temperature difference t and humidity difference h 30 [℃] ≦ t 15%≦h<20% When the developing voltage Vdb was within the range of [Example 1-23] The temperature difference t and humidity difference h 30 [℃] ≦ t 20%≦h<25% When the developing voltage Vdb was within the range of Examples 1-24 The temperature difference t and humidity difference h 30 [℃] ≦ t 25%≦h When the developing voltage Vdb was within the range of

[0098] Next, the evaluation method and results of the images formed on the paper in the comparative examples 1-1 to 1-4 and the examples 1-1 to 1-24, as well as the results of the voltage control process will be described.

[0099] FIG. 6 is a diagram showing the evaluation results of images formed on paper in the comparative example and the example and the judgment results of the voltage control process, FIG. 7 is a first diagram for explaining the evaluation method of images formed on paper in the comparative example and the example, and FIG. 8 is a second diagram for explaining the evaluation method of images formed on paper in the comparative example and the example.

[0100] In this case, A4 size paper "PPR-DA4TDB_55 [kg] paper" (manufactured by Oki Electric Industry Co., Ltd.) was fed horizontally to form a cyan image, and the density of the image was measured using a densitometer "X-rite528" (manufactured by X-Rite), and the image was evaluated using evaluation methods A and B.

[0101] In the figure, P denotes an A4 size sheet of paper that is fed horizontally, and the width Wp of the sheet of paper P is 297 mm, and the length Lp is 210 mm.

[0102] In evaluation method A, a 100% solid image Im1 as shown in FIG. 7 is formed, and it is visually confirmed whether or not a white band Wb1 is formed at a circumferential pitch Lr represented by the circumference of the developing roller 36 (FIG. 3), and the density OD1 of the portion Ar1 where the white band Wb1 is formed and the density OD2 of the portion Ar2 where the white band Wb1 is not formed are measured, and the density difference ΔODa ΔODa=OD2-OD1 was calculated.

[0103] When the density difference ΔODa is less than 0.05, the formation of the white band Wb1 cannot be visually confirmed, so the image Im1 is deemed to be good, and the evaluation result A is rated as ○.

[0104] Furthermore, when the density difference ΔODa is 0.05 or more and less than 0.10, the formation of the white band Wb1 can be confirmed by squinting, and the formation of the white band Wb1 is not bothersome, so the image Im1 is deemed to be within the acceptable range, and the evaluation result A is rated as △.

[0105] If the density difference ΔODa is 0.10 or more, the formation of the white band Wb1 can be visually confirmed, so the image Im1 is determined to be defective and the evaluation result A is set to ×.

[0106] On the other hand, in evaluation method B, the developing voltage Vdb is corrected to form a 50% halftone image Im2 as shown in FIG. 8, and it is visually confirmed whether or not a white band Wb2 is formed at a circumferential pitch Lr represented by the circumference of the developing roller 36 of 39.7 mm. The density OD3 of a portion Ar3 where the white band Wb2 is formed and the density OD4 of a portion Ar4 where the white band Wb2 is not formed are measured, and the density difference ΔODb ΔODb = OD4 - OD3 was calculated.

[0107] When the density difference ΔODb is less than 0.05, the formation of the white band Wb2 cannot be visually confirmed, so the image Im2 is deemed to be good, and the evaluation result B is rated as ○.

[0108] Furthermore, when the density difference ΔODa is 0.05 or more and less than 0.10, the formation of the white band Wb1 can be confirmed by squinting, and the formation of the white band Wb2 is not noticeable, so the image Im2 is deemed to be within the acceptable range and the evaluation result is △.

[0109] If the density difference ΔODb is 0.10 or more, the formation of the white band Wb2 can be visually confirmed, so the image Im2 is determined to be defective and the evaluation result B is set to ×.

[0110] If the evaluation results A and B were both ○, it was determined that the correction of the development voltage Vdb was effective, and the overall judgment of the voltage control process was ◎; if either the evaluation results A or B was ×, it was determined that the correction of the development voltage Vdb was ineffective, and the overall judgment of the voltage control process was ×; and if either the evaluation results A or B was △, it was not possible to completely prevent the formation of the white bands Wb1 and Wb2, but it was determined that the correction of the development voltage Vdb was effective, and the overall judgment of the voltage control process was ○.

[0111] Next, the operation of the control device of the printer 10 will be described.

[0112] Fig. 9 is a first flowchart showing the operation of the printer control device in the first embodiment of the present invention, Fig. 10 is a second flowchart showing the operation of the printer control device in the first embodiment of the present invention, Fig. 11 is a diagram showing the relationship between humidity and toner resistance, Fig. 12 is a diagram showing the relationship between toner density and toner resistance, Fig. 13 is a diagram showing the relationship between toner density and toner charge amount, and Fig. 14 is a diagram showing the relationship between toner charge amount and the number of printed pages. In Fig. 11, the horizontal axis represents humidity and the vertical axis represents toner resistance, in Fig. 12, the horizontal axis represents toner density and the vertical axis represents toner resistance, in Fig. 13, the horizontal axis represents toner density and the vertical axis represents toner charge amount, and in Fig. 14, the horizontal axis represents the number of printed pages and the vertical axis represents toner charge amount.

[0113] First, when the interface unit IF receives the current print job job(n) from the host computer PC (step S1), the information processing unit Pr2 obtains the resistance increase determination information at the first timing when the interface unit IF receives the current print job job(n), i.e., the date and time D1, the temperature inside the device T1, the humidity inside the device H1, and the belt temperature t1, by reading them from the timing device 55, the temperature sensor s3, the humidity sensor s4, and the belt temperature sensor s5, respectively, and records them in the ROM 53 (step S2).

[0114] Next, the information processing unit Pr2 reads out from ROM 53 the resistance increase determination information at the second timing when printing of the previous print job job(n-1) is completed, i.e., the date and time D2, the temperature inside the device T2, the humidity inside the device H2, the belt temperature t2, and the cumulative number of printed sheets Pn1 (step S3), and also reads out from ROM 53 the resistance increase determination information at the third timing when printing of the preceding print job job(n-(1+m)) is completed, i.e., the date and time D3, the temperature inside the device T3, the humidity inside the device H3, the belt temperature t3, and the cumulative number of printed sheets Pn2 (step S4).

[0115] Then, the resistance increase determination processing unit Pr3 determines the number of printed sheets ΔPn ΔPn=Pn1-Pn2 (sheets) is calculated, and it is determined whether the first resistance increase condition is met based on whether a certain amount of printing, equal to or greater than the threshold value Pth, in this embodiment, 1000 sheets or more, has been performed between date and time D3 and date and time D2, i.e., whether the number of printed sheets ΔPn is 1000 sheets or more (step S5).

[0116] In Figure 11, L1 is the line that shows the relationship between humidity and toner resistance at a low temperature of 10°C, and L2 is the line that shows the relationship between humidity and toner resistance at a high temperature of 32°C. As shown in Figure 11, the toner resistance, at which humidity is nearly equal at high and low temperatures, is 10.0 log Ω. Therefore, if the toner resistance is 8.0 log Ω, which is lower than 10.0 log Ω, the toner will be less susceptible to the moisture content in the air and less likely to aggregate. Therefore, as can be seen from Figure 12, in order to lower the toner resistance below 8.0 log Ω, the toner density needs to be 0.450 g cm -3 As can be seen from Figure 13, it is preferable to set the toner density to 0.450 [g cm -3 To lower the charge to the toner to -15.0 [μC g -1 As can be seen from Figure 14, it is preferable to make the toner charge less than -15.0 [μC g -1In order to reduce the number of prints to less than 1000, it is preferable to reduce the number of prints to less than 1000.

[0117] For this reason, in this embodiment, the threshold value Pth of the number of prints ΔPn for determining whether the first resistance increase condition is met is set to 1000. In fact, in experiments, when the number of prints ΔPn was set to less than 1000, no white bands were formed in the image.

[0118] If the number of printed sheets ΔPn is 1000 or more and the first resistance increase condition is met, the resistance increase determination processing unit Pr3 determines whether the printer 10 is left unused for a certain period of time ΔD ΔD=D1-D2 is calculated, and it is determined whether the second resistance increase condition is met depending on whether the standing time ΔD is equal to or greater than a predetermined threshold ΔDth, which is 24 hours in this embodiment (step S6).

[0119] If the unused time ΔD is 24 hours or more and the second resistance increase condition is met, the resistance increase determination processor Pr3 determines whether the third resistance increase condition is met by determining whether the temperature difference t is greater than or equal to the first threshold value ta, which in this embodiment is 20°C (Step S7). If the temperature difference t is greater than or equal to 20°C and the third resistance increase condition is met, the voltage control processor Pr4 references the development voltage correction value table Tb1, reads out the correction value ΔVdb corresponding to the temperature difference t and humidity difference h, and corrects the development voltage Vdb (Step S8). Next, the print processor Pr1 performs a print process in which the development voltage Vdb is corrected, i.e., a correction mode print process (Step S9).

[0120] Next, the resistance increase determination processing unit Pr3 determines whether the first voltage correction end condition is met based on whether a predetermined amount of printing, in this embodiment, 200 or more sheets, has been performed since the correction mode printing process began (step S10).If 200 or more sheets have been printed and the first voltage correction end condition is met, the voltage control processing unit Pr4 changes the development voltage Vdb to the value before correction (step S11), and the printing processing unit Pr1 performs normal mode printing process without correcting the development voltage Vdb, i.e., normal mode printing process (step S12).

[0121] Then, the information processing unit Pr2 updates the resistance increase determination information (step S13) and records the resistance increase determination information at the first timing when the interface unit IF receives the current print job job(n) in ROM53 as the resistance increase determination information at the second timing when the print processing unit Pr1 finishes printing the previous print job job(n-1).

[0122] On the other hand, if the number of printed sheets ΔPn is less than 1000 (sheets) and the first resistance increase condition is not met, the print processing unit Pr1 performs printing processing in the normal mode (step S12).

[0123] Furthermore, if the number of printed sheets ΔPn is 1000 or more and the first resistance increase condition is met, but the printer 10 has been left unused for less than 24 hours and the second resistance increase condition is not met, the resistance increase determination processing unit Pr3 determines whether the fourth resistance increase condition is met based on whether the temperature difference t is greater than or equal to the second threshold value tb, in this embodiment, 10°C (step S14).

[0124] If the temperature difference t is 10°C or more and the fourth resistance increase condition is met, the resistance increase determination processor Pr3 determines whether the fifth resistance increase condition is met based on whether the humidity difference h is greater than or equal to a threshold value hth, which in this embodiment is 15% or more (step S15). If the humidity difference h is 15% or more and the fifth resistance increase condition is met, the voltage control processor Pr4 references the development voltage correction value table Tb1, reads out the correction value ΔVdb corresponding to the temperature difference t and humidity difference h, and corrects the development voltage Vdb (step S8). If the temperature difference t is less than 10°C and the fourth resistance increase condition is not met, or if the humidity difference h is less than 15% and the fifth resistance increase condition is not met, the print processor Pr1 performs normal mode printing (step S12).

[0125] Furthermore, if 200 or more sheets have not been printed since the start of the correction mode printing process and the first voltage correction end condition is not met, the resistance increase determination processor Pr3 determines whether a second voltage correction end condition is met based on whether a predetermined time, in this embodiment, 3 hours or more, has elapsed since the first timing when the interface unit IF received the current print job job(n) (step S16). If 3 hours or more have elapsed since the first timing and the second voltage correction end condition is met, the print processor Pr1 performs the normal mode printing process (step S12). If 3 hours or more have not elapsed since the first timing and the second voltage correction end condition is not met, the voltage control processor Pr4 references the development voltage correction value table Tb1, reads out the correction value ΔVdb corresponding to the temperature difference t and humidity difference h, and corrects the development voltage Vdb (step S8).

[0126] Next, the flowchart will be described. Step S1: The interface unit IF receives the current print job job(n) from the host computer PC. Step S2: The information processing section Pr2 reads and acquires resistance increase determination information at the first timing, and records it in the ROM 53. Step S3: The information processing section Pr2 reads out from the ROM 53 the resistance increase determination information at the second timing. Step S4: The information processing section Pr2 reads out from the ROM 53 the resistance increase determination information at the third timing. In step S5, the resistance increase determination processor Pr3 determines whether the number of printed sheets ΔPn is equal to or greater than 1000. If the number of printed sheets ΔPn is equal to or greater than 1000, the process proceeds to step S6; if the number of printed sheets ΔPn is less than 1000, the process proceeds to step S12. In step S6, the resistance increase determination processor Pr3 determines whether the left-standing time ΔD is 24 hours or more. If the left-standing time ΔD is 24 hours or more, the process proceeds to step S7, and if the left-standing time ΔD is less than 24 hours, the process proceeds to step S14. In step S7, the resistance increase determination processing unit Pr3 determines whether the temperature difference t is 20° C. or more. If the temperature difference t is 20° C. or more, the process proceeds to step S8, and if the temperature difference t is less than 20° C., the process proceeds to step S14. In step S8, the voltage control processing unit Pr4 corrects the developing voltage Vdb. In step S9, the print processing unit Pr1 performs the correction mode print processing. In step S10, the resistance increase determination processor Pr3 determines whether or not 200 or more sheets have been printed. If 200 or more sheets have been printed, the process proceeds to step S11. If 200 or more sheets have not been printed, the process proceeds to step S16. In step S11, the voltage control processing unit Pr4 changes the developing voltage Vdb to the value before correction. In step S12, the print processing unit Pr1 performs normal mode print processing. In step S13, the information processing section Pr2 updates the resistance increase determination information, and the process ends. In step S14, the resistance increase determination processing unit Pr3 determines whether the temperature difference t is 10° C. or more. If the temperature difference t is 10° C. or more, the process proceeds to step S15, and if the temperature difference t is less than 10° C., the process proceeds to step S12. In step S15, the resistance increase determination processing unit Pr3 determines whether the humidity difference h is 15% or more. If the humidity difference h is 15% or more, the process proceeds to step S8. If the humidity difference h is less than 15%, the process proceeds to step S12. In step S16, the resistance increase determination processor Pr3 determines whether or not three hours have elapsed since the first timing. If three hours or more have elapsed since the first timing, the process proceeds to step S12. If three hours or more have not elapsed since the first timing, the process returns to step S8.

[0127] In this manner, in the present embodiment, after printing has been performed in a high-temperature environment, the printer 10 is left in a low-temperature environment for a predetermined time or longer, and then when a predetermined amount of printing or more is performed in the low-temperature environment, the developing voltage Vdb applied to the developing roller 36 is corrected and its absolute value is increased, so that toner can be properly adhered to the photosensitive drum 22 in response to the increase in the resistance of the surface of the developing roller 36, thereby improving image quality.

[0128] Furthermore, since there is no need to rotate the developing roller 36 when not printing or to change the surface treatment agent of the developing roller 36, the life of the image forming units 21Y, 21M, 21C is not shortened and the cost is not increased.

[0129] Furthermore, when a predetermined amount of printing has been performed after printing with the corrected developing voltage Vdb has started, the developing voltage Vdb is changed to the value before correction, so the absolute value of the developing voltage Vdb does not remain large after the resistance of the surface of the developing roller 36 stops increasing, and the image density does not become excessively high or the amount of toner consumed does not increase.

[0130] In the present embodiment, when it is determined that the resistance of the surface of the developing roller 36 is increasing, the developing voltage Vdb applied to the developing roller 36 is corrected. However, when the correction value ΔVdb becomes large, the density of the formed image, particularly the density of the halftone image, increases, and the difference in density between the areas where a white band is formed and the areas where a white band is not formed increases. This not only reduces the image quality but also causes toner to adhere to the non-printing areas where no image is formed, resulting in contamination such as background fogging.

[0131] Normally, the surface potential of the non-exposed portions of the photosensitive drum 22 that are not exposed by the LED head 24 is higher than the potential of the toner on the developing roller 36, so toner does not adhere to the non-exposed portions. However, if the absolute value of the developing voltage Vdb is increased to increase the surface resistance of the developing roller 36, for example, from -180 V to -210 V, the potential of the toner on the developing roller 36 appears to be higher, causing toner to adhere to the non-exposed portions, resulting in this contamination.

[0132] Normally, the surface potential on the photosensitive drum 22 changes depending on the development voltage Vdb, so in the first embodiment, the surface potential on the photosensitive drum 22 changes by the amount of correction of the development voltage Vdb, i.e., by the correction value ΔVdb, and the amount of toner adhering to the photosensitive drum 22 changes.

[0133] Therefore, it is conceivable to stabilize the amount of toner adhering to the photosensitive drum 22 by changing the surface potential of the photosensitive drum 22 by correcting the charging voltage Vch applied to the charging roller 34, or by changing the amount of toner supplied to the developing roller 36 by correcting the supply voltage Vsp applied to the supply roller 38.

[0134] Next, a second embodiment of the present invention will be described, in which not only the development voltage Vdb but also the charging voltage Vch and the supply voltage Vsp are corrected in accordance with the risk of an increase in resistance. Note that the same reference numerals are used for components having the same structure as in the first embodiment, and the effects of the invention resulting from having the same structure are incorporated into the effects of the first embodiment.

[0135] In this embodiment, as in the first embodiment, under conditions where the risk of resistance increase in FIG. 4 is deemed high, the developing voltage Vdb, charging voltage Vch, and supply voltage Vsp are corrected in accordance with the temperature difference t and humidity difference h, and images Im1 and Im2 with a solid color of 100% and a dot density of 50% are formed, and the densities OD1 to OD4 of the images Im1 and Im2 are measured to quantitatively confirm whether white bands Wb1 and Wb2 due to an increase in the resistance of the developing roller 36 have occurred in the images Im1 and Im2.

[0136] In addition, in this embodiment, the development voltage correction value table Tb1, and the charging voltage correction value table Tb2 (FIG. 15) and supply voltage correction value table Tb3 (FIG. 16) described later are recorded in ROM 53 as a first storage unit, and when the resistance increase determination processing unit Pr3 determines that the resistance of the surface of the development roller 36 as a developer carrier has increased, the voltage control processing unit Pr4 refers to the development voltage correction value table Tb1, charging voltage correction value table Tb2 and supply voltage correction value table Tb3 to correct the development voltage Vdb, charging voltage Vch and supply voltage Vsp and increase their absolute values.

[0137] FIG. 15 is a diagram showing an example of a charge voltage correction value table in the second embodiment of the present invention, and FIG. 16 is a diagram showing an example of a supply voltage correction value table in the second embodiment of the present invention.

[0138] In the figure, Tb2 is the charging voltage correction value table, and Tb3 is the supply voltage correction value table. In both the charging voltage correction value table Tb2 and the supply voltage correction value table Tb3, similarly to the development voltage correction value table Tb1 (FIG. 5), the temperature difference t is t<10 (℃) 10 (℃)≦t<15 (℃) 15 (℃)≦t<20 (℃) 20 (℃)≦t<25 (℃) 25 (℃)≦t<30 (℃) 30 [℃] ≦ t The humidity difference h is h<5% 5%≦h<10% 10%≦h<15% 15%≦h<20% 20%≦h<25% 25%≦h A correction value ΔVch for the charging voltage Vch and a correction value ΔVsp for the supply voltage Vsp are set for each range.

[0139] It is assumed that the risk of resistance increase increases as the temperature difference t and humidity difference h increase, so the correction values ​​ΔVch and ΔVsp are set to be larger as the temperature difference t and humidity difference h increase.

[0140] Next, we will explain comparative examples 2-1 to 2-4 in which images Im1 and Im2 were formed on paper P as a medium without correcting the development voltage Vdb, charging voltage Vch, and supply voltage Vsp by the voltage control processing unit Pr4 in the range of temperature difference t and humidity difference h where the risk of resistance increase is high, and examples 2-1 to 2-24 in which images Im1 and Im2 were formed on paper P by correcting the development voltage Vdb based on the correction value ΔVdb, correcting the charging voltage Vch based on the correction value ΔVch, and correcting the supply voltage Vsp based on the correction value ΔVsp. Comparative Example 2-1 The temperature difference t and humidity difference h t<10 (℃) 25%≦h In the range, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were not corrected. Comparative Example 2-2 The temperature difference t and humidity difference h 10 (℃)≦t<15 (℃) 15%≦h<20% In the range, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were not corrected. Comparative Example 2-3 The temperature difference t and humidity difference h 20 (℃)≦t<25 (℃) h<5% In the range, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were not corrected. Comparative Example 2-4 The temperature difference t and humidity difference h 20 (℃)≦t<25 (℃) 5%≦h<10% In the range, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were not corrected. Example 2-1 The temperature difference t and humidity difference h 10 (℃)≦t<15 (℃) 15%≦h<20% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-2 The temperature difference t and humidity difference h 10 (℃)≦t<15 (℃) 20%≦h<25% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-3 The temperature difference t and humidity difference h 10 (℃)≦t<15 (℃) 25%≦h When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. [Example 2-4] The temperature difference t and humidity difference h 15 (℃)≦t<20 (℃) 15%≦h<20% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-5 The temperature difference t and humidity difference h 15 (℃)≦t<20 (℃) 20%≦h<25% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. [Example 2-6] The temperature difference t and humidity difference h 15 (℃)≦t<20 (℃) 25%≦h When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. [Example 2-7] The temperature difference t and humidity difference h 20 (℃)≦t<25 (℃) h<5% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. [Example 2-8] The temperature difference t and humidity difference h 20 (℃)≦t<25 (℃) 5%≦h<10% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-9 The temperature difference t and humidity difference h 20 (℃)≦t<25 (℃) 10%≦h<15% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-10 The temperature difference t and humidity difference h 20 (℃)≦t<25 (℃) 15%≦h<20% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-11 The temperature difference t and humidity difference h 20 (℃)≦t<25 (℃) 20%≦h<25% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-12 The temperature difference t and humidity difference h 20 (℃)≦t<25 (℃) 25%≦h When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-13 The temperature difference t and humidity difference h 20 (℃)≦t<30 (℃) 30%≦h When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-14 The temperature difference t and humidity difference h 25 (℃)≦t<30 (℃) h<5% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-15 The temperature difference t and humidity difference h 25 (℃)≦t<30 (℃) 10%≦h<15% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-16 The temperature difference t and humidity difference h 25 (℃)≦t<30 (℃) 15%≦h<20% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-17 The temperature difference t and humidity difference h 25 (℃)≦t<30 (℃) 20%≦h<25% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-18 The temperature difference t and humidity difference h 25 (℃)≦t<30 (℃) 25%≦h When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-19 The temperature difference t and humidity difference h 30 [℃] ≦ t h<5% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-20 The temperature difference t and humidity difference h 30 [℃] ≦ t 5%≦h<10% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-21 The temperature difference t and humidity difference h 30 [℃] ≦ t 10%≦h<15% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-22 The temperature difference t and humidity difference h 30 [℃] ≦ t 15%≦h<20% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-23 The temperature difference t and humidity difference h 30 [℃] ≦ t 20%≦h<25% When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected. Example 2-24 The temperature difference t and humidity difference h 30 [℃] ≦ t 25%≦h When the voltage Vdb is within the range of Vcc, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are corrected.

[0141] Next, the evaluation methods and evaluation results of the images formed on the paper in the comparative examples 2-1 to 2-4 and examples 2-1 to 2-24 will be described.

[0142] FIG. 17 is a diagram showing the evaluation results of images formed on paper in the comparative example and the example, and the determination results of the voltage control process.

[0143] In this case, as in Comparative Examples 1-1 to 1-4 and Examples 1-1 to 1-24 in the first embodiment, A4 size paper "PPR-DA4TDB_55 [kg] paper" (manufactured by Oki Electric Industry Co., Ltd.) was fed horizontally as paper P to form a cyan image, and the density of the image was measured using a densitometer "X-rite528" (manufactured by X-Rite), and the image was evaluated using evaluation methods A and B.

[0144] In evaluation method A, a 100% solid image Im1 as shown in Figure 7 was formed on paper P, and it was visually confirmed whether a white band Wb1 had been formed.The density OD1 of the portion Ar1 where the white band Wb1 had been formed and the density OD2 of the portion Ar2 where the white band Wb1 had not been formed were measured, and the density difference ΔODa was calculated.

[0145] When the density difference ΔODa is less than 0.05, the formation of the white band Wb1 cannot be visually confirmed, so the image Im1 is deemed to be good, and the evaluation result A is rated as ○.

[0146] Furthermore, when the density difference ΔODa is 0.05 or more and less than 0.10, the formation of the white band Wb1 can be confirmed by squinting, and the formation of the white band Wb1 is not bothersome, so the image Im1 is deemed to be within the acceptable range, and the evaluation result A is rated as △.

[0147] If the density difference ΔODa is 0.10 or more, the formation of the white band Wb1 can be visually confirmed, so the image Im1 is determined to be defective and the evaluation result A is set to ×.

[0148] On the other hand, in evaluation method B, a 50% halftone image Im2 as shown in Figure 8 was formed, and it was visually confirmed whether or not a white band Wb2 had formed.The density OD3 of the portion Ar3 where the white band Wb2 had formed and the density OD4 of the portion Ar4 where the white band Wb2 had not formed were measured, and the density difference ΔODb was calculated.

[0149] When the density difference ΔODb is less than 0.05, the formation of the white band Wb2 cannot be visually confirmed, so the image Im2 is deemed to be good, and the evaluation result B is rated as ○.

[0150] Furthermore, when the density difference ΔODa is 0.05 or more and less than 0.10, the formation of the white band Wb1 can be confirmed by squinting, and the formation of the white band Wb2 is not noticeable, so the image Im2 is deemed to be within the acceptable range, and the evaluation result B is rated as △.

[0151] If the density difference ΔODb is 0.10 or more, the formation of the white band Wb2 can be visually confirmed, so the image Im2 is determined to be defective and the evaluation result B is set to ×.

[0152] If the evaluation results A and B were both ○, it was determined that the corrections to the development voltage Vdb, charging voltage Vch, and supply voltage Vsp were effective, and the overall judgment of the voltage control process was ◎; if either the evaluation results A or B was ×, it was determined that the corrections to the development voltage Vdb, charging voltage Vch, and supply voltage Vsp were ineffective, and the overall judgment of the voltage control process was ×; and if either the evaluation results A or B was △, it was not possible to completely prevent the formation of the white bands Wb1 and Wb2, but it was determined that the corrections to the development voltage Vdb, charging voltage Vch, and supply voltage Vsp were effective, and the overall judgment of the voltage control process was ○.

[0153] Next, the operation of the control device of the printer 10 as an image forming apparatus will be described.

[0154] FIG. 18 is a first flowchart showing the operation of the printer control device in the second embodiment of the present invention, and FIG. 19 is a second flowchart showing the operation of the printer control device in the second embodiment of the present invention.

[0155] First, when the interface unit IF as a communication unit receives the current print job job(n) from the host computer PC as an information input device and as a higher-level device (step S21), the information processing unit Pr2 acquires the resistance increase determination information at the first timing when the interface unit IF received the current print job job(n), i.e., the date and time D1, the temperature inside the device T1, the humidity inside the device H1, and the belt temperature t1, by reading them from the timing device 55, the temperature sensor s3 as a first environmental information acquisition unit and as a first temperature detection unit, the humidity sensor s4 as a second environmental information acquisition unit and as a humidity detection unit, and the belt temperature sensor s5 as a third environmental information acquisition unit and as a second temperature detection unit, and records them in ROM 53 (step S22).

[0156] Next, the information processing unit Pr2 reads out from ROM 53 the resistance increase determination information at the second timing when printing of the previous print job job(n-1) is completed, i.e., the date and time D2, the temperature inside the device T2, the humidity inside the device H2, the belt temperature t2, and the cumulative number of printed sheets Pn1 (step S23), and also reads out from ROM 53 the resistance increase determination information at the third timing when printing of the preceding print job job(n-(1+m)) is completed, i.e., the date and time D3, the temperature inside the device T3, the humidity inside the device H3, the belt temperature t3, and the cumulative number of printed sheets Pn2 (step S24).

[0157] Then, the resistance increase determination processing unit Pr3 determines the number of printed sheets ΔPn ΔPn=Pn1-Pn2 (sheets) is calculated, and it is determined whether the first resistance increase condition is met depending on whether the number of printed sheets ΔPn is equal to or greater than a threshold value Pth, which is a certain amount, in this embodiment, 1000 sheets (step S25).

[0158] When the number of printed sheets ΔPn is 1000 or more and the first resistance increase condition is met, the resistance increase determination processing unit Pr3 determines whether the printer 10 is left unused for a certain period of time ΔD ΔD=D1-D2 is calculated, and it is determined whether the second resistance increase condition is met depending on whether the standing time ΔD is equal to or greater than a predetermined threshold ΔDth, which is 24 hours in this embodiment (step S26).

[0159] If the unused time ΔD is 24 hours or more and the second resistance increase condition is met, the resistance increase determination processor Pr3 determines whether the third resistance increase condition is met by determining whether the temperature difference t is equal to or greater than the first threshold value ta (20°C in this embodiment) (step S27). If the temperature difference t is equal to or greater than 20°C and the third resistance increase condition is met, the voltage control processor Pr4 references the development voltage correction value table Tb1, the charge voltage correction value table Tb2, and the supply voltage value table Tb3, reads out the correction values ​​ΔVdb, ΔVch, and ΔVsp corresponding to the temperature difference t and the humidity difference h, and corrects the development voltage Vdb, the charge voltage Vch, and the supply voltage Vsp (step S28). Next, the print processor Pr1 performs a print process in which the development voltage Vdb, the charge voltage Vch, and the supply voltage Vsp are corrected, i.e., a correction mode print process (step S29).

[0160] Next, the resistance increase determination processing unit Pr3 determines whether the first voltage correction end condition is met based on whether a predetermined amount, in this embodiment, 200 or more sheets, have been printed since the correction mode printing process began (step S30).If 200 or more sheets have been printed and the first voltage correction end condition is met, the voltage control processing unit Pr3 changes the development voltage Vdb to the value before correction (step S31), and the printing processing unit Pr1 performs normal mode printing process in which the development voltage Vdb, charging voltage Vch, and supply voltage Vsp are not corrected, i.e., normal mode printing process (step S32).

[0161] Then, the information processing unit Pr2 updates the resistance increase determination information (step S13) and records the resistance increase determination information at the first timing when the interface unit IF receives the current print job job(n) in ROM53 as the resistance increase determination information at the second timing when the print processing unit Pr1 finishes printing the previous print job job(n-1).

[0162] On the other hand, if the number of printed sheets ΔPn is less than 1000 (sheets) and the first resistance increase condition is not met, the print processing unit Pr1 performs print processing in the normal mode (step S32).

[0163] Furthermore, if the number of printed sheets ΔPn is 1000 or more and the first resistance increase condition is met, but the standing time ΔD is less than 24 hours and the second resistance increase condition is not met, the resistance increase determination processing unit Pr3 determines whether the fourth resistance increase condition is met based on whether the temperature difference t is greater than or equal to the second threshold value tb, in this embodiment, 10°C (step S34).

[0164] If the temperature difference t is 10°C or more and the fourth resistance increase condition is met, the resistance increase determination processor Pr3 determines whether the fifth resistance increase condition is met by determining whether the humidity difference h is greater than or equal to a threshold value hth (15% in this embodiment) (step S35). If the humidity difference h is 15% or more and the fifth resistance increase condition is met, the voltage control processor Pr4 references the development voltage correction value table Tb1, the charge voltage correction value table Tb2, and the supply voltage value table Tb3, reads out the correction values ​​ΔVdb, ΔVch, and ΔVsp corresponding to the temperature difference t and the humidity difference h, and corrects the development voltage Vdb, the charge voltage Vch, and the supply voltage Vsp (step S28). If the temperature difference t is less than 10°C and the fourth resistance increase condition is not met, or if the humidity difference h is less than 15%, and the fifth resistance increase condition is not met, the print processor Pr1 performs normal mode printing (step S32).

[0165] Furthermore, if 200 or more sheets have not been printed since the start of the correction mode printing process and the first voltage correction termination condition is not met, the resistance increase determination processing unit Pr3 determines whether a second voltage correction termination condition is met based on whether a predetermined time (3 hours or more in this embodiment) has elapsed since the first timing when the interface unit IF received the current print job (n) (step S36). If 3 hours or more have elapsed since the first timing and the second voltage correction termination condition is met, the print processing unit Pr1 performs normal mode printing (step S32). If 3 hours or more have not elapsed since the first timing and the second voltage correction termination condition is not met, the voltage control processing unit Pr4 references the development voltage correction value table Tb1, the charge voltage correction value table Tb2, and the supply voltage value table Tb3, reads out the correction values ​​ΔVdb, ΔVch, and ΔVsp corresponding to the temperature difference t and the humidity difference h, and corrects the development voltage Vdb, the charge voltage Vch, and the supply voltage Vsp (step S28).

[0166] Next, the flowchart will be described. In step S21, the interface unit IF receives the current print job job(n) from the host computer PC. In step S22, the information processing section Pr2 reads and acquires resistance increase determination information at the first timing, and records it in the ROM 53. In step S23, the information processing section Pr2 reads out from the ROM 53 the resistance increase determination information at the second timing. In step S24, the information processing section Pr2 reads out from the ROM 53 the resistance increase determination information at the third timing. In step S25, the resistance increase determination processor Pr3 determines whether the number of printed sheets ΔPn is 1000 or more. If the number of printed sheets ΔPn is 1000 or more, the process proceeds to step S26; if the number of printed sheets ΔPn is less than 1000, the process proceeds to step S32. In step S26, the resistance increase determination processor Pr3 determines whether the left-standing time ΔD is 24 hours or more. If the left-standing time ΔD is 24 hours or more, the process proceeds to step S27, and if the left-standing time ΔD is less than 24 hours, the process proceeds to step S34. In step S27, the resistance increase determination processing unit Pr3 determines whether the temperature difference t is 20° C. or more. If the temperature difference t is 20° C. or more, the process proceeds to step S28, and if the temperature difference t is less than 20° C., the process proceeds to step S34. In step S28, the voltage control processing unit Pr4 corrects the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp. In step S29, the print processing unit Pr1 performs the correction mode print processing. In step S30, the resistance increase determination processor Pr3 determines whether 200 or more sheets have been printed since the start of the correction mode printing process. If 200 or more sheets have been printed since the start of the correction mode printing process, the process proceeds to step S31. If 200 or more sheets have not been printed since the start of the correction mode printing process, the process proceeds to step S36. In step S31, the voltage control processing unit Pr3 changes the developing voltage Vdb to the value before correction. In step S32, the print processing unit Pr1 performs normal mode print processing. In step S33, the information processing section Pr2 updates the resistance increase determination information, and the process ends. In step S34, the resistance increase determination processing unit Pr3 determines whether the temperature difference t is 10° C. or more. If the temperature difference t is 10° C. or more, the process proceeds to step S35, and if the temperature difference t is less than 10° C., the process proceeds to step S32. In step S35, the resistance increase determination processing unit Pr3 determines whether the humidity difference h is 15% or more. If the humidity difference h is 15% or more, the process proceeds to step S28, and if the humidity difference h is less than 15%, the process proceeds to step S32. In step S36, the resistance increase determination processor Pr3 determines whether or not three hours or more have passed since the first timing. If three hours or more have passed since the first timing, the process proceeds to step S32, and if three hours or more have not passed since the first timing, the process returns to step S28.

[0167] In this manner, in the present embodiment, not only the developing voltage Vdb but also the charging voltage Vch and the supply voltage Vsp are corrected, so that the correction value ΔVdb can be prevented from being unnecessarily large. Therefore, it is possible to prevent the density of the formed image, particularly the density of halftone images, from becoming unnecessarily high, and the density difference between the areas where white bands are formed and the areas where white bands are not formed does not become large, thereby improving image quality. Furthermore, it is possible to prevent toner from adhering to non-printing areas where no image is formed, and to prevent stains such as background fogging from occurring.

[0168] Furthermore, the range of the printing environment for suppressing an increase in the resistance of the surface of the developing roller 36, for example, the range of the temperature difference t and the humidity difference h, can be widened.

[0169] In each of the above-described embodiments, the amount of toner that is deposited from the developing roller 36 onto the photosensitive drum 22 is increased by increasing the absolute value of the developing voltage Vdb. However, the amount of toner that is deposited from the developing roller 36 onto the photosensitive drum 22 can also be increased by decreasing the absolute value of the surface potential of the photosensitive drum 22, for example, by changing from -50 V to -25 V.

[0170] In addition, since the amount of charge remaining on the surface of the developing roller 36 increases as the amount of wear on the surface of the developing roller 36 increases or as the surface of the developing roller 36 deteriorates, the developing voltage Vdb can also be corrected depending on the usage conditions of the image forming units 21Y, 21M, and 21C.

[0171] Furthermore, in each of the above embodiments, a small printer 10 using three colors of toner has been described, but the present invention can also be applied to a printer having a black image forming unit in addition to three image forming units of yellow, magenta, and cyan, a printer having a white or transparent image forming unit, a monochrome printer, etc.

[0172] The present invention can also be applied to printers of an intermediate transfer type, or to large printers such as label printers that use roll paper for labels.

[0173] Although the present embodiment has been described with reference to the printer 10, the present invention can also be applied to image forming devices such as copying machines, facsimile machines, and multifunction machines.

[0174] The present invention is not limited to the above-described embodiment, and various modifications are possible based on the spirit of the present invention, and these modifications are not excluded from the scope of the present invention. [Explanation of symbols]

[0175] 10 Printers 22 Photosensitive drum 27 Transfer roller 34 Charging roller 36 Developing roller 38 Supply roller P paper Pr4 Voltage control processing section Vdb Development voltage

Claims

1. (a) an image carrier that carries a latent image; (b) a charging member for charging the image bearing member; (c) a developer carrier that holds a developer and causes the developer to adhere to the image carrier to form a developer image; (d) a supply member for supplying developer to the developer carrier; (e) a transfer member for transferring the developer image on the image carrier to a medium; (f) a conveyor belt for conveying the medium; (g) a voltage control processing unit that, when the image forming apparatus is left in a low-temperature environment for a predetermined time or longer after a certain amount of printing has been performed in a high-temperature environment, corrects the developing voltage applied to the developer carrier by a correction value set in accordance with a temperature difference between the temperature of the conveyor belt after printing has been performed in the high-temperature environment and the temperature of the conveyor belt before printing has been performed in the low-temperature environment, thereby increasing the absolute value of the developing voltage; have An image forming apparatus characterized by:

2. The correction value is set corresponding to the temperature difference and the humidity difference, which is the difference between the humidity inside the image forming device after printing in the high-temperature environment and the humidity inside the image forming device before printing in the low-temperature environment. The image forming apparatus according to claim 1 .

3. 2. The image forming apparatus according to claim 1, wherein the voltage control processing unit corrects at least one of the charging voltage and the supply voltage to increase the absolute value when correcting the developing voltage to increase the absolute value.

4. a correction value for correcting the developing voltage and at least one of the charging voltage and the supply voltage, The temperature difference is set in accordance with the temperature difference and the humidity difference between the humidity inside the image forming apparatus after printing has been performed in the high-temperature environment and the humidity inside the image forming apparatus before printing has been performed in the low-temperature environment. The image forming apparatus according to claim 3 .

5. The voltage control processing unit 5. The image forming apparatus according to claim 1, wherein the developing voltage is changed to a value before correction when a predetermined amount of printing for which the developing voltage is corrected is performed.

6. An image forming apparatus according to any one of claims 1 to 5, wherein the first timing is when a reference print job is received from a host device, the second timing is when printing of the print job immediately before the reference print job is completed, and the third timing is when printing of a specified print job immediately before the immediately previous print job is completed, and the image forming apparatus is left unattended between the first and second timings, and printing is performed in a high-temperature environment between the second and third timings.

7. 7. The image forming apparatus according to claim 1, wherein the voltage control processing section corrects the developing voltage to increase its absolute value when the cumulative number of printed sheets reaches or exceeds a predetermined value.

Images