JP7797891B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

Conventionally, image forming devices such as printers, copiers, facsimile machines, and multifunction devices, for example, printers, are equipped with an image forming unit, transfer roller, fuser, etc. In the image forming unit, the surface of a photosensitive drum, which has been uniformly charged by a charging roller, is exposed to light to form an electrostatic latent image. This electrostatic latent image is then developed by a developing roller to form a toner image. This toner image is then transferred onto paper by the transfer roller and fixed to the paper in the fuser.

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

This is thought to be because when printing is performed in a high-temperature environment, toner aggregates in the printer, and residual charge increases in areas on the surface of the developing roller that come into contact with the aggregated toner. Then, when the printer is left in a low-temperature environment, the resistance increases, resulting in lower development efficiency than other areas and making it difficult for toner on the developing roller to adhere to the photosensitive drum.

To prevent this white band from occurring, one possible solution is 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 by changing the surface treatment agent applied to the developing roller (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2008-89622

However, in the conventional printers mentioned above, 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 surface treatment agents.

The present invention aims to provide an image forming device that solves the problems of conventional printers, improves image quality, and does not shorten the life of the image forming unit or increase costs.

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, the image forming apparatus is left in a low-temperature environment for a predetermined period of time, and then a predetermined amount of printing is performed in the low-temperature environment.

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 to increase its absolute value when printing is performed in a high-temperature environment, the image forming apparatus is left in a low-temperature environment for a predetermined period of time, and then a predetermined amount of printing is performed in the low-temperature environment.

In this case, after printing in a high-temperature environment, the image forming device is left in a low-temperature environment for a predetermined time or longer, and then when a predetermined amount of printing is performed in the low-temperature environment, the development voltage applied to the developer carrier is corrected and its absolute value is increased. This allows the developer to adhere to the image carrier appropriately in response to the increase in the resistance of the developer carrier's surface, improving image quality.

In addition, there is no need to rotate the developer carrier when not printing, or to change the surface treatment agent applied to the developer carrier, so the lifespan of the image forming unit is not shortened and costs are not increased.

FIG. 2 is a control block diagram of the printer according to the first embodiment of the present invention. 1 is a conceptual diagram of a printer according to a first embodiment of the present invention. FIG. 2 is a conceptual diagram of an image forming unit according to the first embodiment of the present invention. FIG. 10 is a diagram for explaining a risk of resistance increase in the first embodiment of the present invention. FIG. 4 is a diagram showing an example of a development voltage correction value table according to the first embodiment of the present invention. 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. FIG. 10 is a first diagram for explaining a method for evaluating images formed on paper in the comparative example and the example. FIG. 10 is a second diagram for explaining the method for evaluating images formed on paper in the comparative example and the example. 4 is a first flowchart showing the operation of the control device of the printer according to the first embodiment of the present invention. 10 is a second flowchart showing the operation of the control device of the printer according to the first embodiment of the present invention. FIG. 10 is a diagram showing the relationship between humidity and the resistance value of toner. FIG. 10 is a diagram showing the relationship between toner density and toner resistance value. FIG. 10 is a diagram showing the relationship between toner density and toner charge amount. FIG. 10 is a diagram showing the relationship between the charge amount of toner and the number of printed sheets. FIG. 11 is a diagram illustrating an example of a charging voltage correction value table according to the second embodiment of the present invention. FIG. 11 is a diagram illustrating an example of a supply voltage correction value table according to the second embodiment of the present invention. 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. 10 is a first flowchart showing the operation of a control device of a printer according to a second embodiment of the present invention. 10 is a second flowchart showing the operation of the control device of the printer according to the second embodiment of the present invention.

Embodiments of the present invention will be described in detail below with reference to the drawings. In this case, a printer will be described as an image forming device.

Figure 2 is a conceptual diagram of a printer in the first embodiment of the present invention.

In the figure, reference numeral 10 denotes a printer. The printer 10 comprises a printer main body Mb as the main body of the image forming device, a roll paper support Fd as a medium support unit that supports roll paper 12 as a roll-shaped medium, and a paper feed unit Sp disposed between the roll paper support Fd and the printer main body Mb.

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

Paper fed from the feeding device 14 and supplied by the paper supply unit Sp is transported along the paper transport path Rt, which serves as a media transport path extending through the roll paper support unit Fd, the paper supply unit Sp, and the printer main body Mb.

In the paper feed section Sp, reference numeral 16 denotes a lower guide section that guides paper below the paper transport path Rt, and reference numeral 17 denotes an upper guide section that is arranged by a hinge hg so as to be able to swing relative to the lower guide section 16 and that guides paper above the paper transport path Rt. The upper guide section 17 functions as a jam release cover to open the paper transport path Rt when a paper jam occurs in the paper feed section Sp.
The paper supply section Sp is provided with a pair of conveying rollers m1 as a first conveying member, consisting 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.

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 the control board unit located at the bottom of the device main body Bd and making up the main part of the printer 10's control device.

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

Cu denotes a cutter unit arranged adjacent to the front wall Wf. This cutter unit Cu includes a pair of transport rollers m2 as a second transport member that transports paper fed through the paper feed port h1, and a rotary cutter 23 arranged downstream of the pair of transport rollers m2 that cuts paper to a predetermined length.

A third transport member, a pair of transport rollers m3, is located downstream of the cutter unit Cu. A first media detection unit, a write sensor s1, is located downstream of the pair of transport rollers m3 and serves as the first media detection unit for detecting the leading edge of the paper and setting the position where the image should be written onto the paper. An image forming unit Q1 is located downstream of the write sensor s1.

The image forming unit Q1 includes multiple image forming units 21Y, 21M, and 21C (three in this embodiment, yellow, magenta, and cyan) arranged from upstream to downstream on the paper transport path Rt; a photosensitive drum 22 serving as an image carrier arranged in each of the image forming units 21Y, 21M, and 21C; an LED head 24 serving 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, and 21C.

Each LED head 24 exposes the photosensitive drum 22 based on print data, selectively irradiating the surface of the photosensitive drum 22 with light to form an electrostatic latent image.

The reference numeral 30 denotes a fixing unit, which serves as a fixing device and is disposed downstream of the image forming unit Q1 on the paper transport path Rt. The fixing unit 30 includes a heating roller 31 as a first fixing member and a pressure roller 32 as a second fixing member.

Downstream of the fixing unit 30 on the paper transport path Rt, a pair of discharge rollers m4 serving as a discharge member is disposed 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 that detects the trailing edge of the paper is disposed.

Next, we will explain the image forming units 21Y, 21M, and 21C.

Figure 3 is a conceptual diagram of an image forming unit in the first embodiment of the present invention. Note that image forming units 21Y, 21M, and 21C all have the same structure, except for the color of the toner used as the developer (described below), so only image forming unit 21Y is shown in Figure 3.

Image forming units 21Y, 21M, and 21C each include a main body 33, i.e., a unit main body, and a toner storage device Ct, which serves as a developer storage device and is integrally formed with each unit main body 33.

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

The image forming units 21Y, 21M, and 21C are also equipped with a drum counter Cd (Figure 1), which will be described later. When the count value of the drum counter Cd reaches its upper limit or the waste toner box Bx becomes full, the operator is prompted to replace the image forming unit 21Y, 21M, or 21C.

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

The unit main body 33 includes the rotatably arranged photosensitive drum 22, a charging roller 34 as a charging device rotatably arranged in contact with the photosensitive drum 22, a developing roller 36 as a developer carrier that is rotatably arranged in contact with the photosensitive drum 22 and carries toner, a supply roller 38 as a supply member rotatably arranged in contact with the developing roller 36, a developing blade 39 as a developer regulating member that is pressed against the developing roller 36, a cleaning blade 41 as a first cleaning member that is arranged in contact with the photosensitive drum 22, a transport coil 43 as a waste developer transport member that 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 that is arranged in contact with the charging roller 34 and removes toner adhering to the charging roller 34.

The photosensitive drum 22 is rotated in the direction of arrow A by driving a belt motor M1 (Figure 1) which serves as a drive unit, as described below.

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, which serves as a first voltage control unit described below.

The developing roller 36 is formed from a metal shaft and an elastic body made of semi-conductive urethane rubber with a rubber hardness of 70° (Asker C) arranged around the outer periphery of the shaft. It develops the electrostatic latent image formed on the surface of the photosensitive drum 22 by exposure to light from the LED head 24, by attaching toner to the image, forming a visible toner image as a developer image of each color. 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, which serves as a second voltage control unit (described below).

The supply roller 38 rotates in the same direction as the developing roller 36, supplying toner supplied from the toner storage chamber to the unit main body 33 to the developing roller 36 and frictionally charging 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, which serves as a third voltage control unit described below.

The developing blade 39 thins the toner supplied to the developing roller 36 by the supply roller 38, forming 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 below.

The cleaning blade 41 scrapes off residual toner on the photosensitive drum 22, as well as degraded toner that has been adhered to the photosensitive drum 22 by the developing roller 36, and removes it as waste toner.

Next, we will explain the transfer unit u1.

The transfer unit u1 includes a drive roller R1, a driven roller R2, a belt 26 that is stretched and freely movable between the drive roller R1 and the driven roller R2 and 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.

The transfer roller 27 transfers the toner images of each color formed on the photosensitive drum 22 onto paper.

To this end, a transfer voltage Vtr serving as a fifth process voltage is applied to the transfer roller 27 by the transfer voltage control unit Ee, which serves as a fifth voltage control unit described below.

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

Next, we will explain the operation of the printer 10 configured as described above.

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. Within 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.

The cut paper is sent to image forming unit Q1 by transport roller pair m3, where it is transported by belt 26 between the photosensitive drums 22 of image forming units 21Y, 21M, and 21C and the transfer roller 27 of transfer unit u1.

In each image forming unit 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, forming an electrostatic latent image on the photosensitive drum 22.

In each image forming unit 21Y, 21M, and 21C, 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. The toner is then thinned by the developing blade 39 onto the developing roller 36 and electrostatically adhered to the electrostatic latent image on the photosensitive drum 22 to form a toner image of each color.

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.

The paper is then sent to the fixing device 30, where the color toner image is heated by the heating roller 31 and pressed against the paper by the pressure roller 32, fixing the image to form a color image on the paper. The paper is then ejected from the fixing device 30 by the pair of ejection rollers m4, and is then discharged from the device body Bd through the ejection port h2.

However, if 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, white bands (horizontal white bands) will appear in the image with each rotation of the developing roller 36, resulting in a decrease in image quality.

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.

In this embodiment, therefore, if 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.

Next, we will explain the printer 10's control device.

Figure 1 is a control block diagram of a printer in the first embodiment of the present invention.

In the diagram, 10 is the printer, and the PC is a host computer that acts as an information input device and higher-level device connected to the printer 10 via a wired or wireless LAN.

50 is a control unit, IF is an interface unit that connects the printer 10 to the host computer PC and serves as a communication unit that receives print jobs consisting of print data, print commands (control commands), etc. from the host computer PC and transmits printer 10 status information to the host computer PC, 53 is ROM (Read Only Memory) as a first storage unit, and 54 is RAM (Random Access Memory) as a second storage unit. Memory), 55 is a timing device (timer) that measures the date and time consisting of the year, month, day, and time, and measures elapsed time, 56 is an operation panel that serves as an operation and display unit, s3 is a temperature sensor that serves as a first temperature detection unit and as a first environmental information acquisition unit that detects the temperature inside the device main body Bd (Figure 2) as an internal device temperature T1 (described below), s4 is a humidity sensor that serves 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 is a belt temperature sensor that serves as a third environmental information acquisition unit and as a second temperature detection unit that detects the temperature of the belt 26 as the belt temperature.

The belt temperature sensor s5 is located downstream of a specific image forming unit (in this embodiment, image forming unit 21C) in the direction of travel of the belt 26, and is adjacent to the belt 26. The temperature sensor s3 and humidity sensor s4 are located near the image forming unit 21C.

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.

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, developing roller 36, and supply roller 38, and the gears of the developing roller 36 and supply roller 38 mesh with the gear of the photosensitive drum 22. Therefore, when the photosensitive drum 22 is rotated, the developing roller 36 and supply roller 38 are rotated in unison.

The control unit 50 includes a CPU (Central Processing Unit) (not shown) as a calculation device, input/output ports (not shown), a drum counter Cd that counts the cumulative number of rotations of the photosensitive drum 22, and other components, and controls the entire printer 10 while also performing various processes based on programs (software), control data, etc. stored in ROM 53.

In addition to the programs, the ROM 53 stores setting values, thresholds, etc. necessary for the control unit 50 to perform the various processes. It also stores resistance increase determination information (described below), which is information acquired by the information processing unit Pr2 (described below), and tables such as the development voltage correction value table Tb1 (Figure 5) (described below) for correcting the development voltage Vdb.

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

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

RAM 54 functions as a work area when the CPU performs calculations.

The operation panel 56 includes an operation unit 58 consisting of switches, keys, etc. that the operator uses to input instructions to the printer 10, and a display unit 59 consisting of an LED screen, etc. that displays 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.

The control unit 50 also includes a print processing unit Pr1, an information processing unit Pr2, a resistance increase determination processing unit Pr3, and a voltage control processing unit Pr4.

The print processing unit Pr1 performs printing processing. 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, and forms an image on paper, thereby printing.

The information processing unit Pr2 processes information and acquires resistance increase determination information to determine whether the resistance of the surface of the developing roller 36 is increasing each time a print job is received from the host computer PC, and records the resistance increase determination information in or reads it from ROM 53.

The resistance increase determination information consists of the date and time measured by the timing device 55, the internal device temperature detected by the temperature sensor s3, the internal device humidity 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.

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 (n) (n≧3), the print job received immediately before the current print job (n) is defined as the previous print job (n-1), and the oldest print job received within a specified period of time (in this embodiment, not exceeding 10 hours) going back from the time when reception of the previous print job (n-1) was completed is defined as the previous print job (n-(1+m)) (m: any number equal to or greater than 1).

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

The resistance increase determination processing unit Pr3 performs a resistance increase determination process, and when the cumulative number of printed sheets Pn1 , Pn2 reaches a predetermined amount, in this embodiment, 10,000 sheets or more, it determines whether the resistance of the surface of the developing roller 36 has increased based on the resistance increase determination information obtained by the information processing unit Pr2.

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 subtracting 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]
The temperature difference t is calculated by subtracting the belt temperature t1 from the belt temperature t2.
t = t2 - t1
The humidity difference h is calculated by subtracting the humidity H1 inside the device from the humidity H2 inside the device.
h = H2 - H1
Calculate.

The resistance increase determination processor 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 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, and therefore the resistance of the developing roller 36 has increased.

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 greater and the humidity difference h is 15% or greater, the resistance increase determination processor Pr3 also determines that the resistance of the developing roller 36 has increased.

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, corrects the developing voltage Vdb applied to the developing roller 36, and increases its absolute value.

To achieve this, the voltage control processing unit Pr4 references 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.

In addition, the voltage control processing unit Pr4 changes the development 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 development voltage Vdb corrected has begun.

Next, we will explain the possibility that the resistance of the surface of the developing roller 36 may increase due to changes in the environment in which the printer 10 is placed, or due to the printer 10 being left unused, i.e., the risk of increased resistance.

Figure 4 is a diagram explaining the risk of resistance increase in the first embodiment of the present invention.

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 clump, so the resistance of the surface of the developing roller 36 is less likely to increase. Therefore, the risk of resistance increase is low.

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

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

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

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

Furthermore, if the number of printed sheets ΔPn (sheets) is large, the internal device temperature T1 is high, and the leaving time ΔD in a low-temperature environment is short, the device body Bd does not cool down, so the risk of resistance increasing is low.

As such, it can be seen that the risk of resistance increasing increases when the printer 10 is left in a low-temperature environment for a long time ΔD, the temperature difference t or humidity difference h is large, or when the printer 10 is left in a low-temperature environment for a predetermined period of time or longer after printing in a high-temperature environment.

In this embodiment, under conditions where the risk of resistance increase is deemed high in Figure 4, 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 (Figures 7 and 8) with a solid color of 100% and a dot density of 50%, as described below.The densities of the images Im1 and Im2 are measured, and it is quantitatively confirmed whether white bands have formed due to an increase in the resistance of the development roller 36.

Figure 5 shows an example of a development voltage correction value table in the first embodiment of the present invention.

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 [°C]
10°C≦t<15°C
15°C≦t<20°C
20°C≦t<25°C
25°C≦t<30°C
30 [°C] ≦ t
The humidity difference h is divided into the range:
h<5%
5%≦h<10%
10%≦h<15%
15%≦h<20%
20%≦h<25%
25%≦h
The correction value δVdb of the development voltage Vdb is set for each range.

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 increased as the temperature difference t and humidity difference h increase.

Since the developing voltage Vdb is a negative value, when the correction value δVdb is added, the absolute value of the developing voltage Vdb becomes larger. For example, if 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.

In this embodiment, in the development voltage correction value table Tb1, the correction value δVdb is set to the temperature difference τ
τ = T2 - T1
The correction value δVdb is set to correspond to the temperature difference t and humidity difference h, rather than to the temperature difference t and humidity difference h. However, compared with the temperatures T1 and T2 inside the device, 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, and the distance between the developing roller 36 and the belt 26 is short, so the correction value δVdb is set to correspond to the temperature difference t and humidity difference h.

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
Temperature difference t and humidity difference h are 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 are 10°C≦t<15°C.
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 are 20°C≦t<25°C.
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 are 20°C≦t<25°C.
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 are 10°C≦t<15°C.
15%≦h<20%
When the developing voltage Vdb was within the range of
Example 1-2
The temperature difference t and humidity difference h are 10°C≦t<15°C.
20%≦h<25%
When the developing voltage Vdb was within the range of
[Examples 1-3]
The temperature difference t and humidity difference h are 10°C≦t<15°C.
25%≦h
When the developing voltage Vdb was within the range of
Examples 1-4
The temperature difference t and humidity difference h are 15°C≦t<20°C.
15%≦h<20%
When the developing voltage Vdb was within the range of
Examples 1-5
The temperature difference t and humidity difference h are 15°C≦t<20°C.
20%≦h<25%
When the developing voltage Vdb was within the range of
[Examples 1-6]
The temperature difference t and humidity difference h are 15°C≦t<20°C.
25%≦h
When the developing voltage Vdb was within the range of
Examples 1-7
The temperature difference t and humidity difference h are 20°C≦t<25°C.
h<5%
When the developing voltage Vdb was within the range of
[Examples 1-8]
The temperature difference t and humidity difference h are 20°C≦t<25°C.
5%≦h<10%
When the developing voltage Vdb was within the range of
Examples 1-9
The temperature difference t and humidity difference h are 20°C≦t<25°C.
10%≦h<15%
When the developing voltage Vdb was within the range of
[Examples 1-10]
The temperature difference t and humidity difference h are 20°C≦t<25°C.
15%≦h<20%
When the developing voltage Vdb was within the range of
[Examples 1-11]
The temperature difference t and humidity difference h are 20°C≦t<25°C.
20%≦h<25%
When the developing voltage Vdb was within the range of
[Example 1-12]
The temperature difference t and humidity difference h are 20°C≦t<25°C.
25%≦h
When the developing voltage Vdb was within the range of
Example 1-13
The temperature difference t and humidity difference h are 25°C≦t<30°C.
h<5%
When the developing voltage Vdb was within the range of
Example 1-14
The temperature difference t and humidity difference h are 25°C≦t<30°C.
5%≦h<10%
Example 1-15
The temperature difference t and humidity difference h are 25°C≦t<30°C.
10%≦h<15%
When the developing voltage Vdb was within the range of
Example 1-16
The temperature difference t and humidity difference h are 25°C≦t<30°C.
15%≦h<20%
When the developing voltage Vdb was within the range of
Example 1-17
The temperature difference t and humidity difference h are 25°C≦t<30°C.
20%≦h<25%
When the developing voltage Vdb was within the range of
Example 1-18
The temperature difference t and humidity difference h are 25°C≦t<30°C.
25%≦h
When the developing voltage Vdb was within the range of
Example 1-19
Temperature difference t and humidity difference h are 30 [℃] ≦ t
h<5%
When the developing voltage Vdb was within the range of
Example 1-20
Temperature difference t and humidity difference h are 30 [℃] ≦ t
5%≦h<10%
When the developing voltage Vdb was within the range of
Example 1-21
Temperature difference t and humidity difference h are 30 [℃] ≦ t
10%≦h<15%
When the developing voltage Vdb was within the range of
Example 1-22
Temperature difference t and humidity difference h are 30 [℃] ≦ t
15%≦h<20%
When the developing voltage Vdb was within the range of
Example 1-23
Temperature difference t and humidity difference h are 30 [℃] ≦ t
20%≦h<25%
When the developing voltage Vdb was within the range of
Example 1-24
Temperature difference t and humidity difference h are 30 [℃] ≦ t
25%≦h
When the developing voltage Vdb was within the range of

Next, we will explain the evaluation method and results of the images formed on paper in Comparative Examples 1-1 to 1-4 and Examples 1-1 to 1-24, as well as the judgment results of the voltage control process.

Figure 6 shows the evaluation results of images formed on paper in the comparative example and the working example, as well as the judgment results of the voltage control process. Figure 7 is the first figure for explaining the evaluation method of images formed on paper in the comparative example and the working example. Figure 8 is the second figure for explaining the evaluation method of images formed on paper in the comparative example and the working example.

In this case, A4-sized 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-rite 528" (manufactured by X-Rite), and the image was evaluated using evaluation methods A and B.

In the figure, P represents an A4-sized sheet of paper being fed horizontally, with a width Wp of 297 mm and a length Lp of 210 mm.

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 a portion Ar1 where the white band Wb1 is formed and the density OD2 of a portion Ar2 where the white band Wb1 is not formed are measured, and the density difference ΔODa
ΔODa=OD2-OD1
was calculated.

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 given a ○.

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 noticeable, so the image Im1 is deemed to be within the acceptable range, and the evaluation result A is rated as △.

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

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.

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 given a ○.

Furthermore, when the density difference ΔODa is 0.05 or greater 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 image Im2 is deemed to be within the acceptable range and the evaluation result is rated as △.

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

If both evaluation results A and B are ○, the correction of the development voltage Vdb was deemed effective and the overall judgment of the voltage control process was ◎. If either evaluation result A or B is ×, the correction of the development voltage Vdb was deemed ineffective and the overall judgment of the voltage control process was ×. If either evaluation result A or B is △, although it was not possible to completely prevent the formation of the white bands Wb1 and Wb2, the correction of the development voltage Vdb was deemed effective and the overall judgment of the voltage control process was ○.

Next, we will explain the operation of the printer 10's control device.

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

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 received the current print job job(n), i.e., the date and time D1, the internal device temperature T1, the internal device humidity 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).

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

Then, the resistance increase determination processing unit Pr3 determines the number of printed sheets ΔPn
ΔPn = Pn1 - Pn2 (sheets)
and determines 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).

In Fig. 11, L1 is a line representing the relationship between humidity and toner resistance at a low temperature of 10° C., and L2 is a line representing the relationship between humidity and toner resistance at a high temperature of 32° C. As shown in Fig. 11, the resistance of the toner at which humidity is approximately equal at high and low temperatures is 10.0 log Ω. Therefore, when the resistance of the toner becomes 8.0 log Ω, which is lower than 10.0 log Ω, it is thought that the toner will be less susceptible to the amount of moisture contained in the air and will be less likely to aggregate. Therefore, as can be seen from Figure 12, in order to reduce the toner resistance value to less than 8.0 [log Ω], it is preferable to reduce the toner density to less than 0.450 [g·cm ^-3 ]; as can be seen from Figure 13, in order to reduce the toner density to less than 0.450 [g·cm ^-3 ], it is preferable to reduce the toner charge to less than -15.0 [μC·g ^-1 ]; and as can be seen from Figure 14, in order to reduce the toner charge to less than -15.0 [μC·g ^-1 ], it is preferable to reduce the number of printed sheets to less than 1000 [sheets].

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 [sheets]. In fact, in experiments, when the number of prints ΔPn was set to less than 1000 [sheets], no white bands were formed in the image.

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 value ΔDth, which is 24 hours in this embodiment (step S6).

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 based on whether the temperature difference t is greater than or equal to the first threshold value ta (20°C in this embodiment) (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 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 with the development voltage Vdb corrected, i.e., a correction mode print process (step S9).

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

Then, the information processing unit Pr2 updates the resistance increase determination information (step S13) and records in ROM 53 the resistance increase determination information at the first timing when the interface unit IF receives the current print job job(n) 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).

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

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 ΔD 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, which in this embodiment is 10°C (step S14).

If the temperature difference t is 10°C or greater 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 the threshold value hth (15% in this embodiment) (step S15). If the humidity difference h is 15% or greater and the fifth resistance increase condition is met, the voltage control processor Pr4 references the development voltage correction value table Tb1, reads 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).

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 the 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 (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 the correction value δVdb corresponding to the temperature difference t and humidity difference h, and corrects the development voltage Vdb (step S8).

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 unused time ΔD is 24 hours or more. If the unused time ΔD is 24 hours or more, the process proceeds to step S7. If the unused time ΔD is less than 24 hours, the process proceeds to step S14.
In step S7, the resistance increase determination processor Pr3 determines whether the temperature difference t is equal to or greater than 20° C. If the temperature difference t is equal to or greater than 20° C., the process proceeds to step S8, and if the temperature difference t is less than 20° C., the process proceeds to step S14.
Step S8: The voltage control processing section Pr4 corrects the development voltage Vdb.
Step S9: The print processing unit Pr1 performs 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 section Pr4 changes the developing voltage Vdb to the value before correction.
Step S12: The print processing unit Pr1 performs normal mode print processing.
Step S13: The information processing section Pr2 updates the resistance increase determination information, and the process ends.
In step S14, the resistance increase determination processor 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 processor 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 or more have passed since the first timing. If three hours or more have passed since the first timing, the process proceeds to step S12. If three hours or more have not passed since the first timing, the process returns to step S8.

In this manner, in this embodiment, after printing 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 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. This allows toner to adhere appropriately to the photosensitive drum 22 in response to the increase in surface resistance of the development roller 36, thereby improving image quality.

In addition, since there is no need to rotate the developing roller 36 when not printing or to change the surface treatment agent on the developing roller 36, the lifespan of the image forming units 21Y, 21M, and 21C is not shortened and costs are not increased.

Furthermore, if a predetermined amount of printing has been performed since printing began with the development voltage Vdb corrected, the development voltage Vdb is changed to the value before correction. This prevents the absolute value of the development voltage Vdb from remaining high after the resistance of the surface of the development roller 36 stops increasing, preventing excessively high image density and excessive toner consumption.

In this embodiment, the development voltage Vdb applied to the development roller 36 is corrected when it is determined that the surface resistance of the development roller 36 is increasing. However, if the correction value δVdb becomes large, the density of the formed image, particularly the density of half-tone images, increases, and the density difference between areas where white bands are formed and areas where white bands are not formed increases. This not only reduces image quality, but also causes toner to adhere to non-printing areas where no image is formed, resulting in contamination such as background fogging.

This contamination occurs because the surface potential of the non-exposed areas of the photosensitive drum 22, i.e., the areas not exposed to light by the LED head 24, is normally higher than the potential of the toner on the developing roller 36, so toner does not adhere to the non-exposed areas. 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 areas.

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

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.

Next, we will explain a second embodiment of the present invention, in which not only the development voltage Vdb but also the charging voltage Vch and supply voltage Vsp are corrected in accordance with the risk of resistance increase. Note that components having the same structure as in the first embodiment are given the same reference numerals, and the effects of the invention resulting from having the same structure are incorporated in the same manner as in the first embodiment.

In this embodiment, as in the first embodiment, under conditions deemed to be at high risk of resistance increase in Figure 4, the development 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 100% solid color and a 50% dot density are formed. The densities OD1 to OD4 of images Im1 and Im2 are measured, and it is quantitatively confirmed whether white bands Wb1 and Wb2 have appeared in images Im1 and Im2 due to an increase in the resistance of the developing roller 36.

In addition, in this embodiment, the development voltage correction value table Tb1, the charging voltage correction value table Tb2 (Figure 15), and the supply voltage correction value table Tb3 (Figure 16), which will be described later, are recorded in ROM 53, which serves as the first storage unit. When the resistance increase determination processing unit Pr3 determines that the resistance of the surface of the development roller 36, which serves 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, and corrects the development voltage Vdb, charging voltage Vch, and supply voltage Vsp to increase their absolute values.

Figure 15 shows an example of a charge voltage correction value table for the second embodiment of the present invention, and Figure 16 shows an example of a supply voltage correction value table for the second embodiment of the present invention.

In the figure, Tb2 is a charging voltage correction value table, and Tb3 is a 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 [°C]
10°C≦t<15°C
15°C≦t<20°C
20°C≦t<25°C
25°C≦t<30°C
30 [°C] ≦ 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.

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 increased as the temperature difference t and humidity difference h increase.

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
Temperature difference t and humidity difference h are t<10 [℃]
25%≦h
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are within the above range, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are not corrected.
Comparative Example 2-2
The temperature difference t and humidity difference h are 10°C≦t<15°C.
15%≦h<20%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are within the above range, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are not corrected.
Comparative Example 2-3
The temperature difference t and humidity difference h are 20°C≦t<25°C.
h<5%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are within the above range, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are not corrected.
Comparative Example 2-4
The temperature difference t and humidity difference h are 20°C≦t<25°C.
5%≦h<10%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are within the above range, the developing voltage Vdb, the charging voltage Vch, and the supply voltage Vsp are not corrected.
Example 2-1
The temperature difference t and humidity difference h are 10°C≦t<15°C.
15%≦h<20%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-2
The temperature difference t and humidity difference h are 10°C≦t<15°C.
20%≦h<25%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-3
The temperature difference t and humidity difference h are 10°C≦t<15°C.
25%≦h
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-4
The temperature difference t and humidity difference h are 15°C≦t<20°C.
15%≦h<20%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-5
The temperature difference t and humidity difference h are 15°C≦t<20°C.
20%≦h<25%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-6
The temperature difference t and humidity difference h are 15°C≦t<20°C.
25%≦h
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-7
The temperature difference t and humidity difference h are 20°C≦t<25°C.
h<5%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-8
The temperature difference t and humidity difference h are 20°C≦t<25°C.
5%≦h<10%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-9
The temperature difference t and humidity difference h are 20°C≦t<25°C.
10%≦h<15%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-10
The temperature difference t and humidity difference h are 20°C≦t<25°C.
15%≦h<20%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-11
The temperature difference t and humidity difference h are 20°C≦t<25°C.
20%≦h<25%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-12
The temperature difference t and humidity difference h are 20°C≦t<25°C.
25%≦h
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-13
The temperature difference t and humidity difference h are 20°C≦t<30°C.
30%≦h
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-14
The temperature difference t and humidity difference h are 25°C≦t<30°C.
h<5%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-15
The temperature difference t and humidity difference h are 25°C≦t<30°C.
10%≦h<15%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-16
The temperature difference t and humidity difference h are 25°C≦t<30°C.
15%≦h<20%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-17
The temperature difference t and humidity difference h are 25°C≦t<30°C.
20%≦h<25%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-18
The temperature difference t and humidity difference h are 25°C≦t<30°C.
25%≦h
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-19
Temperature difference t and humidity difference h are 30 [℃] ≦ t
h<5%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-20
Temperature difference t and humidity difference h are 30 [℃] ≦ t
5%≦h<10%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-21
Temperature difference t and humidity difference h are 30 [℃] ≦ t
10%≦h<15%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-22
Temperature difference t and humidity difference h are 30 [℃] ≦ t
15%≦h<20%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-23
Temperature difference t and humidity difference h are 30 [℃] ≦ t
20%≦h<25%
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.
Example 2-24
Temperature difference t and humidity difference h are 30 [℃] ≦ t
25%≦h
When the voltage Vdb, the charging voltage Vch, and the supply voltage Vsp were within the range of Vdb, Vch, and Vsp, respectively, the voltage Vdb, Vch, and Vsp were corrected.

Next, we will explain the evaluation methods and results of the images formed on paper in Comparative Examples 2-1 to 2-4 and Examples 2-1 to 2-24.

Figure 17 shows the evaluation results of images formed on paper in the comparative example and the example, as well as the judgment results of the voltage control process.

In this case, as in Comparative Examples 1-1 to 1-4 and Examples 1-1 to 1-24 in the first embodiment, A4-sized 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 image density was measured using a densitometer "X-rite 528" (manufactured by X-Rite), and the image was evaluated using Evaluation Methods A and B.

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 formed. The density OD1 of the portion Ar1 where the white band Wb1 had formed and the density OD2 of the portion Ar2 where the white band Wb1 had not formed were measured, and the density difference ΔODa was calculated.

If 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 given a ○.

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 noticeable, so the image Im1 is deemed to be within the acceptable range, and the evaluation result A is rated as △.

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

On the other hand, in evaluation method B, a 50% halftone image Im2 as shown in Figure 8 was created, 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.

If 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 given a ○.

Furthermore, when the density difference ΔODa is 0.05 or greater 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 image Im2 is deemed to be within the acceptable range, and the evaluation result B is rated as △.

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

If evaluation results A and B are both ○, the corrections to the development voltage Vdb, charging voltage Vch, and supply voltage Vsp were deemed effective, and the overall judgment of the voltage control process was ◎. If either evaluation result A or B is ×, the corrections to the development voltage Vdb, charging voltage Vch, and supply voltage Vsp were deemed ineffective, and the overall judgment of the voltage control process was ×. If either evaluation result A or B is △, although it was not possible to completely prevent the formation of the white bands Wb1 and Wb2, 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 ○.

Next, we will explain the operation of the control device of the printer 10 as an image forming device.

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

First, when the interface unit IF, acting as a communications unit, receives the current print job job(n) from the host computer PC, acting as both an information input device and a higher-level device (step S21), the information processing unit Pr2 acquires 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 internal device temperature T1, the internal device humidity H1, and the belt temperature t1, by reading them from the timing device 55, the temperature sensor s3, acting as both a first environmental information acquisition unit and a first temperature detection unit, the humidity sensor s4, acting as both a second environmental information acquisition unit and a humidity detection unit, and the belt temperature sensor s5, acting as both a third environmental information acquisition unit and a second temperature detection unit, and records the information in ROM 53 (step S22).

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

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).

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 value ΔDth, which is 24 hours in this embodiment (step S26).

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 (20°C in this embodiment) (step S27). 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, charge voltage correction value table Tb2, and supply voltage value table Tb3, reads the correction values δVdb, δVch, and δVsp corresponding to the temperature difference t and humidity difference h, and corrects the development voltage Vdb, charge voltage Vch, and supply voltage Vsp (step S28). Next, the print processor Pr1 performs a print process in which the development voltage Vdb, charge voltage Vch, and supply voltage Vsp are corrected, i.e., a correction mode print process (step S29).

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 has been performed since the start of the correction mode printing process (in this embodiment, 200 or more sheets) (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 print processing unit Pr1 performs normal mode printing processing without correcting the development voltage Vdb, charging voltage Vch, and supply voltage Vsp, i.e., normal mode printing processing (step S32).

Then, the information processing unit Pr2 updates the resistance increase determination information (step S13) and records in ROM 53 the resistance increase determination information at the first timing when the interface unit IF receives the current print job job(n) 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).

On the other hand, if the number of printed sheets ΔPn is less than 1,000 and the first resistance increase condition is not met, the print processing unit Pr1 performs printing in normal mode (step S32).

Furthermore, if the number of printed sheets ΔPn is 1000 or more and the first resistance increase condition is met, but the unused 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, which in this embodiment is 10°C (step S34).

If the temperature difference t is 10°C or greater 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 the threshold value hth (15% in this embodiment) (step S35). If the humidity difference h is 15% or greater 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 the correction values δVdb, δVch, and δVsp corresponding to the temperature difference t and 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).

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

Next, the flowchart will be described.
Step S21: The interface unit IF receives the current print job job(n) from the host computer PC.
In step S22, the information processing unit Pr2 reads and acquires resistance increase determination information at the first timing, and records the information in the ROM 53.
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 resistance increase determination information at the third timing from the ROM 53.
In step S25, 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 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 unused time ΔD is 24 hours or more. If the unused time ΔD is 24 hours or more, the process proceeds to step S27, and if the unused time ΔD is less than 24 hours, the process proceeds to step S34.
In step S27, the resistance increase determination processor Pr3 determines whether the temperature difference t is equal to or greater than 20° C. If the temperature difference t is equal to or greater than 20° C., 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.
Step S29: The print processing unit Pr1 performs 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 section 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 processor 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 processor 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. If three hours or more have not passed since the first timing, the process returns to step S28.

In this manner, in the present embodiment, not only the development 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, the density of the formed image, particularly the density of halftone images, can be prevented from being unnecessarily high, and the density difference between the areas where the white bands are formed and the areas where the 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.

Furthermore, the range of the printing environment, such as the temperature difference t and humidity difference h, can be widened to prevent an increase in the surface resistance of the developing roller 36.

In each of the above 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 development 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, from -50 V to -25 V.

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

Furthermore, while the above embodiments have been described as a small printer 10 using three colors of toner, the present invention can also be applied to printers that have a black image forming unit in addition to three image forming units (yellow, magenta, and cyan), printers that have a white or transparent image forming unit, monochrome printers, etc.

The present invention can also be applied to intermediate transfer printers and large printers such as label printers that use roll paper for labels.

In this embodiment, a printer 10 has been described, but the present invention can also be applied to image forming devices such as copiers, facsimile machines, and multifunction peripherals.

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.

10 Printer 22 Photosensitive drum 27 Transfer roller 34 Charging roller 36 Development roller 38 Supply roller P Paper Pr4 Voltage control processing unit Vdb Development voltage

Claims (7)

(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) An image forming apparatus characterized by having 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 development voltage applied to the developer carrier by an amount corresponding to a correction value set in accordance with the temperature difference between the temperature of the conveying belt after printing has been performed in the high-temperature environment and the temperature of the conveying belt before printing has been performed in the low-temperature environment, thereby increasing the absolute value, until the certain amount of printing has been performed in the low-temperature environment. The correction value is set in accordance with the temperature difference and the humidity difference between the humidity inside the image forming apparatus after printing in the high-temperature environment and the humidity inside the image forming apparatus before printing in the low-temperature environment.
The image forming apparatus according to claim 1 . 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 development voltage to increase the absolute value. 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 . 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. 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. The image forming apparatus according to claim 1 , wherein the voltage control processing unit corrects the developing voltage to increase its absolute value when the cumulative number of printed sheets reaches or exceeds a predetermined value.