JP2003345108A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for which an appropriate electrifying bias can be easily determined. <P>SOLUTION: The image forming apparatus provided with: an electrifying member 16 electrifying the surface of an image carrier 15; a power source part 622 applying the specified electrifying bias to the electrifying member; and cleaning means 59 and 621 cleaning the electrifying member 16 at a specified timing, has a control means 600 controlling the electrifying bias based on the cleaned state of the electrifying member 16. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile, and a complex machine of these, and more particularly to a charging bias control technology for applying a charging member. .

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus such as a copying machine or a printer utilizing an electrophotographic method (electrostatic transfer method) has been widely known. One of the conditions for obtaining a good image in the image forming apparatus using these electrophotographic systems is to uniformly charge the surface of the image bearing member (photosensitive drum or the like). On the other hand, the electrical resistance value of the charging member varies depending on the environment of temperature and humidity, lot variation during manufacturing, and the like. Further, due to use for a long period of time, toner or the like adheres to change the electric resistance value of the charging member. When a constant charging bias is always applied to such a charging member, it becomes difficult to uniformly charge the surface of the image carrier.

Therefore, in JP-A-2001-201920 and JP-A-6-250504, improvements are made in which the electric resistance value of a charging member is measured at a certain timing and the charging bias to be applied is determined based on the measurement result. Technology is proposed.

[0004]

However, even with these improved techniques, if the electric resistance value of the charging member is not frequently measured, the fluctuation of the electric resistance value due to the contamination of the charging member can be reflected in the charging bias. On the other hand, frequent measurement of the electric resistance value leads to a decrease in productivity. In addition, a special configuration for measuring the electric resistance value of the charging member is required, which leads to an increase in cost of the image forming apparatus.

The present invention has been made in view of such technical problems, and an object thereof is to provide an image forming apparatus capable of easily determining an appropriate charging bias.

[0006]

That is, according to the present invention, a charging member that charges the surface of an image carrier, a power supply unit that applies a predetermined charging bias to the charging member, and the charging member are cleaned at a predetermined timing. In the image forming apparatus including the cleaning unit, the charging bias is controlled based on the cleaning status of the charging member. Here, the cleaning unit can determine the cleaning timing based on the cleaning status of the charging member. The cleaning status is determined based on either the elapsed time from the cleaning operation immediately before the charging member, the cumulative number of image formations of the image forming apparatus, the cumulative rotation speed of the image carrier, or the cumulative image pixel value. can do. Incidentally, these cleaning statuses include elapsed time measuring means, cumulative image forming number measuring means of the image forming apparatus, cumulative rotation number measuring means of the image carrier,
The image forming apparatus is provided with a cumulative image pixel value measuring means and the like, and can be measured by these.

Further, as a more specific mode of the charging bias control, the control means is configured such that, during the image forming operation during the cleaning operation, the first correction bias corresponding to the cleaning state with respect to the reference charging bias during the image forming operation. To obtain the charging bias, and immediately after the cleaning operation,
The reference bias can be the charging bias (by resetting the first correction bias). More specifically,
The control unit can control the magnitude of the charging bias to gradually (continuously) increase during the image forming operation between the cleaning operations, and the magnitude of the charging bias can be increased according to the cleaning situation. Can be controlled to increase linearly or in a quadratic curve, and the magnitude of the charging bias is (discontinuously) before and after the cleaning operation.
It can be controlled to be small, and the charging bias can always be controlled to become the reference bias immediately after the cleaning operation.

Further, the present invention may control the charging bias based on the life status of the image carrier in addition to the cleaning status of the charging member. That is, the control means can also control the charging bias based on the life status of the image carrier. Here, the life status is based on either the elapsed time from immediately before replacement of the image carrier, the cumulative number of image formations of the image forming apparatus, the cumulative rotation speed of the image carrier, or the cumulative image pixel value. You can judge.
Note that these life conditions are determined by the image forming apparatus including the elapsed time measuring means, the cumulative image forming number measuring means of the image forming apparatus, the cumulative rotational speed measuring means of the image carrier, the cumulative image pixel value measuring means, and the like. It can be measured.

Further, as a more specific aspect of the charging bias control, the control means controls the second charging operation according to the life status with respect to the reference charging bias during the image forming operation during the replacement of the image carrier. The correction bias can be added to obtain the charging bias, and the reference bias value can be set as the charging bias immediately after the replacement (by resetting the second correction bias). More specifically, the control unit can control the magnitude of the charging bias to gradually (continuously) increase during the image forming operation during the replacement (replacement interval), and the cleaning can be performed. Depending on the situation, the magnitude of the charging bias can be controlled to increase linearly or in a quadratic curve. Before and after replacement of the image carrier,
It is possible to control so that the magnitude of the charging bias becomes small (discontinuously), and immediately after the replacement of the image carrier, the charging bias can be controlled to become the reference bias.

It should be noted that the image carrier and the charging member may be included in a unit structure integrally formed and may be integrally replaced.

Further, the aspect of such charging bias control will be described as the operation in the cleaning interval of the charging member (shorter than the replacement interval of the image carrier), and it can be expressed as follows. That is, during the image forming operation during the cleaning operation, the control means adds the first correction bias corresponding to the cleaning status and the second correction bias corresponding to the life status to the reference charging bias to charge the image. The bias can be obtained, and the charging bias can be obtained immediately after the cleaning operation by adding the second correction bias to the reference bias value (by resetting the first correction bias).

More specifically, the control means gradually increases the magnitude of the charging bias (continuously) during the image forming operation during the cleaning operation (cleaning interval) (two consecutive times). ) It can be controlled so as to increase, and the magnitude of the charging bias can be controlled to increase linearly or in a quadratic curve according to the cleaning status. The size can be controlled to be (discontinuously) small, and immediately after the cleaning operation, the charging bias can be controlled to be the reference bias plus the second correction bias. .

Further, the present invention may control the charging bias based on the environmental condition of the image forming apparatus in addition to the cleaning condition of the charging member. That is, the control means is
The charging bias can be controlled based on the environmental conditions of the image forming apparatus. Here, the environmental condition can be determined based on the temperature and / or humidity of the image forming apparatus (inside and outside). These environmental conditions are measured by the image forming apparatus provided with a temperature sensor and / or a humidity sensor.

As a more specific aspect of the charging bias control, the control means can obtain the charging bias by adding a third correction bias corresponding to the environmental condition to the reference charging bias. Here, the third correction bias can be controlled so that the magnitude of the charging bias becomes larger in a low temperature environment and becomes smaller in a high temperature environment. The third correction bias can be controlled so that the magnitude of the charging bias becomes larger in a low humidity environment and becomes smaller in a high humidity environment.

More specifically, during the image forming operation during the cleaning operation (cleaning interval), the control means sets the first correction bias and the environmental status corresponding to the cleaning status with respect to the reference charging bias. In addition to obtaining the charging bias by adding the corresponding third correction bias, immediately after the cleaning operation, the third correction bias may be added to the reference bias (resetting the first correction bias) to obtain the charging bias. it can.

Further, during the image forming operation during the replacement of the image bearing member (replacement interval), the control means responds to the second charging bias corresponding to the life status with respect to the reference charging bias and the environmental status. The third correction bias can be added to obtain the charging bias, and immediately after replacement, the third correction bias can be added to the reference bias value (by resetting the second correction bias) to obtain the charging bias. .

Further, during the image forming operation during the cleaning operation (cleaning interval), the control means sets the first correction bias corresponding to the cleaning status with respect to the reference charging bias and the second correction bias corresponding to the life status. Correction bias and a third correction bias according to the environmental condition to obtain the charging bias, and immediately after the cleaning operation (the first correction bias is reset), the second correction bias and the second correction bias are added to the reference bias value. A charging bias can be obtained by adding a third correction bias.

As a more specific aspect of the charging bias control, the control means can control the inclination of the first correction bias with respect to the cleaning status based on the environmental status of the image forming apparatus. Here, the slope of the first correction bias may be controlled so that the magnitude of the charging bias becomes larger in the low temperature environment and becomes smaller in the high temperature environment. Therefore, it is possible to perform control so that the magnitude of the charging bias becomes larger in the low humidity environment and becomes smaller in the high humidity environment.

As a more specific aspect of the charging bias control, the control means may control the slope of the second correction bias with respect to the unit progress of the life status based on the environmental status of the image forming apparatus. it can. Here, the slope of the second correction bias may be controlled so that the magnitude of the charging bias becomes larger in the low temperature environment and becomes smaller in the high temperature environment. Therefore, it is possible to perform control so that the magnitude of the charging bias becomes larger in the low humidity environment and becomes smaller in the high humidity environment.

The maximum value of these first correction biases
The magnitude relationship among M1, the maximum value M2 of the second correction bias, and the maximum value M3 of the third correction bias is M1>M3> M2 (M1 = 30V, M2 = 10V, M3 = 15V in the embodiment). .

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a tandem type digital color printer as an image forming apparatus according to an embodiment of the present invention. FIG. 2 shows a tandem type digital color copying machine as an image forming apparatus according to the embodiment of the present invention.

1 and 2, reference numeral 1 denotes a main body of a tandem type digital color printer and a copying machine. In the case of a digital color copying machine, as shown in FIG. , An automatic document feeder (ADF) 3 for automatically feeding the originals 2 one by one
And the document 2 conveyed by the automatic document conveying device 3
A document reading device 4 for reading the image is provided. The document reading device 4 illuminates a document 2 placed on a platen glass 5 with a light source 6, and reflects a reflected light image from the document 2 into a full rate mirror 7 and half rate mirrors 8 and 9.
And a CCD through a reduction optical system including the imaging lens 10.
Scanning exposure is performed on the image reading element 11 including the above, and the color material reflected light image of the original 2 is read by the image reading element 11 at a predetermined dot density (for example, 16 dots / mm).

The color material reflected light image of the document 2 read by the document reading device 4 is, for example, three-color document reflectance data of red (R), green (G), and blue (B) (each 8 bits). As IPS (Image Processing)
System) 12, and in this IPS 12,
Shading correction for reflectance data of original 2
Predetermined image processing such as positional deviation correction, lightness / color space conversion, gamma correction, frame erasing, and color / movement editing is performed. The IPS 12 is also designed to perform predetermined image processing on image data sent from a personal computer or the like.

The image data subjected to the predetermined image processing by the IPS 12 as described above is also subjected to the same IPS 12 by yellow (Y), magenta (M), cyan (C) and black (K) (8 bits each). 4 color original reproduction color material gradation data, and as described below, image forming units 13Y and 13M for yellow (Y), magenta (M), cyan (C), and black (K), respectively. 13C, 13K
ROS (Raser Output Scanne)
r) 14 and sent as ROS1 as the image exposure device
In 4, the image exposure by the laser beam LB is performed according to the document reproduction color material gradation data of a predetermined color.

In the image forming apparatus according to this embodiment, a plurality of image forming units for forming toner images of different colors are arranged in parallel, and the plurality of image forming units are arranged over the plurality of image forming units. A belt-shaped intermediate transfer member to which the toner images of the respective colors formed by the image forming units are transferred is arranged, and an image is written on the image carrier of each image forming unit below the plurality of image forming units. The image writing means for performing is arranged.

Further, in this embodiment, the transfer medium on which the toner image is transferred from the belt-shaped intermediate transfer member is conveyed from the lower side to the upper side in the vertical direction, and transferred from the belt-shaped intermediate transfer member. Secondary transfer means for transferring the toner image onto the medium is provided on the side of the intermediate transfer belt.

Further, in this embodiment, an image forming unit for forming a black toner image is arranged on the most downstream side in the moving direction of the belt-shaped intermediate transfer member among the plurality of image forming units. Is configured.

That is, inside the main body 1 of the tandem type digital color printer and copying machine, as shown in FIG. 1, four colors of yellow (Y), magenta (M), cyan (C) and black (K) are provided. Image forming units 13Y, 1
3M, 13C, and 13K are arranged in parallel in the horizontal direction at regular intervals.

These four image forming units 13Y,
The 13M, 13C, and 13K are all configured similarly and integrally, and are roughly classified into a predetermined speed (for example, 200
mm / sec), a photosensitive drum 15 as an image carrier, a charging roll 16 as a charging device for uniformly charging the surface of the photosensitive drum 15, and a surface of the photosensitive drum 15 ROS 14 as an image exposing means for exposing an image corresponding to a predetermined color to form an electrostatic latent image
A developing device 17 as a developing means for developing the electrostatic latent image formed on the photosensitive drum 15 with toner of a predetermined color,
Cleaning device 1 for cleaning the surface of the photosensitive drum 15
8 and. These photosensitive drums 15 and the image forming members arranged around the photosensitive drums 15 are integrally formed as a unit, and are separately replaceable from the printer and the copying machine main body 1.

The ROS 14, as shown in FIG.
Image forming units 13Y, 13M, 13C, 13K
The four semiconductor lasers (not shown) are modulated in accordance with the original reproduction color material gradation data of each color,
Laser beams LB-Y and LB- from these semiconductor lasers
It is configured to emit M, LB-C, and LB-K according to grayscale data. The ROS 14 may of course be individually configured for each of the plurality of image forming units. Laser light LB-Y, LB emitted from the semiconductor laser
-M, LB-C, and LB-K are irradiated onto the polygon mirror 19 through an unillustrated f-θ lens, and are deflected and scanned by the polygon mirror 19. Laser light LB-Y, LB deflected and scanned by the polygon mirror 19
-M, LB-C, and LB-K are scanned and exposed obliquely from below to an exposure point on the photoconductor drum 15 via an imaging lens (not shown) and a plurality of mirrors.

As shown in FIG. 1, the ROS 14 scans and exposes an image on the photosensitive drum 15 from below. Therefore, the ROS 14 has four image forming units 13Y, 13M and There is a risk that toner or the like will fall from the developing devices 17 of 13C and 13K and be contaminated. Therefore, the ROS 14 is hermetically sealed by the frame 20 having a rectangular parallelepiped shape, and the four laser beams LB are provided above the frame 20.
-Y, LB-M, LB-C, and LB-K are exposed on the photosensitive drums 15 of the image forming units 13Y, 13M, 13C, and 13K, so that a transparent glass window 21Y as a shield member, 21M, 21C, and 21K are provided.

From the IPS 12, yellow (Y),
Image data of each color is sequentially output to the ROS 14 provided in common to the image forming units 13Y, 13M, 13C, and 13K of each color of magenta (M), cyan (C), and black (K). Laser light LB-Y, LB-M, LB-C, LB-K emitted according to data
Is scanned and exposed on the surface of the corresponding photoconductor drum 15,
An electrostatic latent image is formed. The electrostatic latent images formed on the photosensitive drum 15 are the developing devices 17Y, 17M, 17C, 1
7K, toner images of yellow (Y), magenta (M), cyan (C), and black (K) are developed.

The image forming units 13Y, 13M,
The toner images of yellow (Y), magenta (M), cyan (C), and black (K), which are sequentially formed on the photoconductor drums 15 of 13C and 13K, are formed in the respective image forming units 13.
The four primary transfer rolls 26Y, 26M, 26C, and 26K perform multiple transfer on the intermediate transfer belt 25 of the transfer unit 22 that is arranged above Y, 13M, 13C, and 13K. These primary transfer rolls 26Y,
26M, 26C, and 26K are image forming units 13
It is arranged on the back surface side of the intermediate transfer belt 25 corresponding to the Y, 13M, 13C, and 13K photosensitive drums 15. In this embodiment, a roll adjusted to a desired volume resistance value is used. Then, the primary transfer rolls 26Y, 2
A transfer bias power source (not shown in FIGS. 1 and 2) is connected to 6M, 26C, and 26K, and a transfer bias having a polarity opposite to the predetermined toner polarity (positive in this embodiment) is predetermined. Is applied at the timing of.

Further, as shown in FIG. 1, the intermediate transfer belt 25 is wound around a drive roll 27, a tension roll 24, and a backup roll 28 with a constant tension, and has a constant speed (not shown). By a drive roll 27 that is rotated by a dedicated drive motor having excellent properties, it is circularly driven at a predetermined speed in a certain direction. In FIG. 1, the intermediate transfer belt 25 is supported by four rolls including an idler roll (not shown) in addition to the drive roll 27, the tension roll (not shown), and the backup roll 28. It shows the case. The intermediate transfer belt 25
For example, a belt material (rubber or resin) whose resistance does not cause charge-up and whose resistance is adjusted is used.

Yellow (Y), magenta (M), cyan (C), which are transferred in multiple layers on the intermediate transfer belt 25,
As shown in FIG. 1, the toner image of each color of black (K) is used as a recording medium by a pressure contact force and an electric field by a secondary transfer roll 29 which is in pressure contact with a backup roll 28 arranged on the side surface of the intermediate transfer belt 25. The recording paper 30 secondarily transferred onto the recording paper 30 and having the toner images of the respective colors transferred thereto is conveyed to the fixing device 31 located above. The secondary transfer roll 29 is in pressure contact with the side of the backup roll 28, and secondarily transfers the toner image of each color onto the recording paper 30 that is conveyed from the lower side to the upper side in the vertical direction. . Then, the recording paper 30 on which the toner images of the respective colors have been transferred is subjected to a fixing process by heat and pressure by a fixing device 31, and then discharged onto a discharge tray 33 provided on the upper portion of the main body 1 by a discharge roll 32. It

The recording sheet 30 is, as shown in FIG.
A sheet feeding device 37 disposed inside the apparatus main body 1 is fed with a sheet of a predetermined size by a nudger roll 35 and a feed roll 36 for sheet separating and feeding, and the sheet feeding path 37 is separated one by one. Resist roll 38 provided in
Is once transported to and stopped. Recording paper 3 fed
The transport path 37 of 0 is vertically upward. The recording paper 30 supplied from the paper feeding device 34 is sent to the secondary transfer position of the intermediate transfer belt 35 by the registration roll 38 which rotates at a predetermined timing.

In the above digital color printer and copying machine, when making a double-sided copy such as full color, the recording paper 30 having an image fixed on one side is not directly discharged onto the discharge tray 33 by the discharge roll 32. Then, the conveyance direction is switched by a switching gate (not shown), and the sheet is conveyed to the double-sided conveyance unit 40 via the roller pair 39 for conveying the sheet. Then, in the double-sided transport unit 40, a pair of transport rollers (not shown) provided along the transport path 41 transports the recording paper 30 to the registration roll 38 again with the front and back sides thereof reversed.
This time, the image is transferred and fixed on the back surface of the recording paper 30, and then discharged onto the discharge tray 33.

In FIG. 1, 44Y, 44M, 44C, 44K
Is yellow (Y), magenta (M), cyan (C),
Toner cartridges for supplying toner of a predetermined color to the developing devices 17 for the respective colors of black (K) are shown.

FIG. 3 shows each image forming unit of the digital color printer and the copying machine.

The above-mentioned four image forming units 13Y, 13M and 13 for yellow, magenta, cyan and black.
As shown in FIG. 3, all of C and 13K have the same configuration, and these four image forming units 13Y and
In 13M, 13C, and 13K, as described above, the yellow, magenta, cyan, and black toner images are sequentially formed at predetermined timings. The image forming units 13Y, 13M,
13C and 13K are the photosensitive drums 15 as described above.
The surfaces of these photosensitive drums 15 are uniformly charged by the charging roll 16 for charging.

After that, the surface of the photosensitive drum 15 is
The laser light LB for image formation emitted from the ROS 14 according to the image data is scanned and exposed to form an electrostatic latent image corresponding to each color. The laser beam LB that is scanned and exposed on the photoconductor drum 15 is set so as to be exposed from an obliquely lower side slightly to the right of the photoconductor drum 15. The electrostatic latent image formed on the photoconductor drum 15 is the image forming unit 13Y, 13M, 13C,
The developing roller 17a of the 13K developing device 17 develops visible toner images by developing yellow toner, magenta toner, cyan toner, and black toner, respectively, and these visible toner images are intermediately transferred by the primary transfer roller 26 being charged. The images are sequentially transferred onto the belt 25 in multiple layers.

The surface of the photosensitive drum 15 after the toner image transfer process is completed is cleaned by a cleaning device 18 to remove residual toner and the like, and the surface is prepared for the next image forming process. The cleaning device 18 includes a cleaning blade 42, and the cleaning blade 42 removes residual toner and the like on the photosensitive drum 15. Further, as shown in FIG. 1, the surface of the intermediate transfer belt 25 after the toner image transfer step is completed is cleaned by a cleaning device 43 to remove residual toner, paper dust, and the like, to prepare for the next image forming process. The cleaning device 43 includes a cleaning brush 43a.
And a cleaning blade 43b. The cleaning brush 43a and the blade 43b remove residual toner, paper dust, and the like on the intermediate transfer belt 25.

By the way, in the embodiment of the present invention, in order to easily determine an appropriate charging bias, the following configuration is adopted.

FIG. 4 is a block diagram for explaining the control system of the digital color printer and the copying machine according to this embodiment. As shown in the figure, this control system is mainly composed of a control circuit (cleaning means, control means) 600. As a means for transmitting a measurement signal to this control circuit 600, a photosensitive drum (image carrier) ) Count circuit 611 that counts the number of rotations of 15, photosensitive drum 15 replacement detection circuit 612, environment detection circuit (temperature sensor, humidity sensor) 6 that measures the temperature and humidity inside the image forming apparatus 6)
Equipped with 13. Further, as a control signal from the control circuit 600, a contact / separation circuit (cleaning means) 621 configured to freely contact and separate the charging roll cleaning brush (cleaning means) 59 with respect to the charging roll (charging member) 15. A power supply circuit (power supply unit) 622 (including a retract mechanism) that applies a predetermined charging bias to the charging roll 15 is provided.

Here, the control circuit 600 uses the cleaning threshold TH for determining the cleaning timing in advance.
(C) is stored, and the control circuit 600 and the counting circuit 61 are stored.
1, contact / separation circuit 621, charging roll cleaning brush 5
Reference numeral 9 forms a cleaning control system for the charging roll 15. In addition, the control circuit 600 uses the environment correction table T in advance.
The control circuit 600, the counting circuit 611, the replacement detection circuit 612, the environment detection circuit 613, and the power supply circuit 62.
Reference numeral 2 forms a charging bias control system for the charging roll 15.

Each of these circuits 600, 611, 6
The functions of 12 and 613 may be realized by a wired logic circuit, but may also be realized by sharing of functions between hardware and software (control program). Further, instead of the counting circuit 611 that counts the number of rotations of the photosensitive drum (image carrier) 15, a time counter circuit that counts elapsed time (image forming time), a number counter circuit that counts the number of image formed sheets, (image It may include a pixel counter circuit that counts image pixel values (based on data). Furthermore, this power circuit 6
22 is a DC power supply circuit, but may be a superimposed power supply circuit that superimposes an AC voltage on a DC voltage. When a superposed power supply circuit is adopted, its DC component may be controlled.

First, the cleaning control operation of the charging roll 16 will be described. Each time the digital color printer or copying machine according to the present embodiment forms an image, the photosensitive drum 1
5 rotates, and the number of rotations is counted by the counting circuit 611. Then, the count number is preset to the control circuit 60.
When 0 reaches the stored threshold value TH (C), the control circuit 600 sends a control command to the contact / separation circuit 621 after the image forming job is completed, and the contact / separation circuit 62 is transmitted based on the control command.
In No. 1, the charging cleaning brush 59 is brought into contact with the charging roll 16. Then, the surface of the rotating charging roll 16 is rubbed against the brush 59, and foreign matter such as toner adhering to the surface is cleaned. On the other hand, when such a cleaning operation is performed, the cumulative number of rotations of the photoconductor drum 15 is reset, and thereafter, the number of rotations of the photoconductor drum 15 is counted again.

Next, the charging bias control operation of the charging roll 16 will be described based on each embodiment.

Embodiment 1 FIG. 5 illustrates the charging bias control operation of the image forming apparatus according to this embodiment.
FIG. 5A shows the relationship between the basic charging bias VS [-V] and the number of rotations of the photosensitive drum 15 (cleaning state). The basic charging bias VS is the photosensitive drum 15
It is constant regardless of the rotation speed of. FIG. 5B shows the relationship between the first correction bias Δ1 and the number of rotations of the photosensitive drum 15 (cleaning condition). The first correction bias Δ1 is the initial (C0) and immediately after the cleaning operation ( Each C
1) (immediately after C4), the odor is 0 [-V], but until the next cleaning operation, the size increases linearly in proportion to the number of rotations of the photosensitive drum 15, and the next cleaning operation is performed. It takes the maximum value immediately before, and becomes 0 [-V] again immediately after the next cleaning operation, and so on.

FIG. 5C shows the relationship between the charging bias V [-V] applied to the charging roll 16 and the rotation speed (cleaning condition) of the photosensitive drum 15, where the charging bias V = reference charging. Bias VS + first correction bias Δ
It is 1. VS [-V] is set in the case where the charging roll 16 is relatively less contaminated at the initial stage (C0) and immediately after the cleaning operation (immediately after each of C1 to C4), but is the photosensitive drum until the next cleaning operation. The size linearly increases in proportion to the rotation speed of 15 (V = VS + Δ1) to compensate for the decrease in charging efficiency due to dirt on the charging roll 16, and the dirt on the charging roll 16 is removed immediately after the next cleaning operation. Then, the charging bias V = VS again
[-V], and so on.

Modification Example FIG. 6 shows the relationship between the first correction bias Δ1 and the rotation speed (cleaning state) of the photosensitive drum 15 in the image forming apparatus of Modification Example 1-1. The bias Δ1 is 0 [− at the initial stage (C0) and immediately after the cleaning operation (immediately after each of C1 to C4).
V], the size increases linearly in proportion to the number of rotations of the photoconductor drum 15 until the next cleaning operation, and reaches the maximum value immediately before the next cleaning operation. Immediately after the cleaning operation of 0, the voltage becomes 0 [-V] again, and so on. Note that other configurations and operations are the same as those of the first embodiment including the point that the charging bias V = the reference charging bias VS + the first correction bias Δ1, and therefore the description thereof is omitted.

FIG. 7 shows the relationship between the first correction bias Δ1 and the number of rotations (cleaning state) of the photosensitive drum 15 in the image forming apparatus of modification 1-2. Is that in the initial (C0) and immediately after the cleaning operation (immediately after each of C1 to C4) and the next cleaning operation, the size increases linearly in proportion to the rotation speed of the photosensitive drum 15. Same as Example 1, but different from Example 1 in that the inclination changes depending on the environment.

[0054]

[Table 1] That is, as shown in Table 1, when the detection result by the environment detection circuit 613 is a low temperature and low humidity environment (L / L environment),
As shown in FIG. 7A, when the charging roll 16 is in the initial (C
0) or immediately after cleaning (for example, immediately after C1), Δ1 (C0) = 10 [−V]. When the charging roll 16 is immediately before cleaning (for example, immediately before C1), Δ1 (immediately before C1) = 30 [−V]. That is, the first correction bias varies by 20 [V] within the range of 10 to 30 [-V]. On the other hand, when the detection result by the environment detection circuit 613 is a high temperature and high humidity environment (H / H environment), as shown in FIG. 7B, the charging roll 16 is initially (C0) or immediately after cleaning (for example, C1). Immediately after), Δ1 (C0) = − 5 [−V]. Also,
When the charging roll 16 is immediately before cleaning (for example, immediately before C1), Δ1 (immediately before C1) = 5 [−V]. That is, the first correction bias is -5 to +5 [-V].
In the range of 10 [V].

Embodiment 2 FIG. 8 illustrates a charging bias control operation of the image forming apparatus according to this embodiment.
8A shows the basic charging bias V as in FIG. 5A.
The relationship between S [-V] and the number of rotations of the photosensitive drum 15 (cleaning status) is shown. FIG. 8 (b) shows FIG.
Similar to (b), the relationship between the first correction bias Δ1 and the rotation speed (cleaning status) of the photosensitive drum 15 is shown.

FIG. 8C shows the relationship between the third correction bias Δ3 and the number of rotations of the photosensitive drum 15 (cleaning condition), and between the cleaning operation C2 and the next cleaning operation C3. The value of the third correction bias Δ3 when the environment changes from the normal environment (N environment) to the low temperature and low humidity environment (L / L environment) is shown. That is, under the N environment, the third correction bias Δ3 = 0 [-V], but L /
Under the L environment, the third correction bias Δ3 = 10 [−V].

FIG. 8D shows the relationship between the charging bias V [-V] applied to the charging roll 16 and the rotation speed (cleaning condition) of the photosensitive drum 15, where the charging bias V = reference charging. Bias VS + first correction bias Δ
1 + third correction bias Δ3. Initial (C
0) and immediately after the cleaning operation (immediately after each of C1 to C4) when the charging roll 16 is relatively dirty, VS + Δ3 [−V] (Δ1 = 0), but until the next cleaning operation. The size increases linearly in proportion to the rotation speed of the photosensitive drum 15 (V =
VS + Δ1 + Δ3) The deterioration of the charging efficiency due to the dirt on the charging roll 16 is compensated, and when the dirt on the charging roll 16 is removed immediately after the next cleaning operation, the charging bias V = VS again.
It becomes + Δ3 [−V] (Δ1 = 0). In addition, the third correction bias Δ3 changes from 0 to 10 [-V] between the cleaning operation C2 and the next cleaning operation C3. The description of the same configuration and operation as in the first embodiment will be omitted.

Embodiment 3 FIG. 9 illustrates the charging bias control operation of the image forming apparatus according to this embodiment.
FIG. 9A shows the relationship between the basic charging bias VS [-V] and the rotation speed (cleaning state) of the photosensitive drum 15, as in FIGS. 5A and 8A. Figure 9
5B shows the relationship between the first correction bias Δ1 and the rotation speed (cleaning condition) of the photosensitive drum 15, as in FIGS. 5B and 8B. FIG. 9D is the same as FIG.
Similar to (c), the relationship between the third correction bias Δ3 and the rotation speed (cleaning status) of the photosensitive drum 15 is shown.

FIG. 9C shows the relationship between the second correction bias Δ2 and the number of rotations of the photosensitive drum 15 (cleaning condition). The second correction bias Δ2 is initially (C).
0) and immediately after the photoconductor drum 15 is replaced (immediately after R), it is 0 [-V], but until the next replacement operation, the magnitude is linearly proportional to the rotation speed of the photoconductor drum 15. Becomes larger immediately before the next replacement of the photosensitive drum 15, and becomes 0 [-V] again immediately after the next replacement operation, and so on. The replacement of the photosensitive drum 15 is detected by the replacement detection circuit 612 when the unit 13 is replaced.

FIG. 9E shows the relationship between the charging bias V [-V] applied to the charging roll 16 and the rotation speed (cleaning condition) of the photosensitive drum 15, where the charging bias V = reference charging. Bias VS + first correction bias Δ
1 + second correction bias + third correction bias Δ3. In the case where there is relatively little dirt on the charging roll 16 in the initial stage (C0) and immediately after the cleaning operation (each C1 to C4), VS + Δ2 + Δ3 [−V] (Δ1 =
However, until the next cleaning operation, the size of the photosensitive drum 15 increases linearly in proportion to the rotation speed of the photosensitive drum 15 (V = VS + Δ1 + Δ3). Immediately after the next cleaning operation, if the dirt on the charging roll 16 is removed, the charging bias becomes V = VS + Δ2 + Δ3 [−V] again (Δ1 = 0). Further, between the cleaning operation C2 and the next cleaning operation C3, the third correction bias Δ3
Is from 0 to 10 It changes to [-V].

Further, the initial (C0) and the photosensitive drum 15
Immediately after replacement (immediately after R) or the like, when the wear of the photosensitive drum 15 is relatively small, VS + Δ3 [−V] (Δ1 =
0, Δ2 = 0), but until the next replacement, the size increases linearly in proportion to the rotation speed of the photosensitive drum 15 (V = VS + Δ1 + Δ2 (≠ 0) + Δ
3) Compensation for the decrease in charging efficiency due to abrasion of the photosensitive drum 15, and after the next photosensitive drum 15 is replaced, the charging bias V
= VS + Δ3 [−V] (Δ1 = 0, Δ2 = 0).
The description of the same configuration and operation as in the first embodiment will be omitted.

Modified Example FIG. 10 shows the relationship between the second correction bias Δ2 and the rotation speed (cleaning state) of the photosensitive drum 15 in the image forming apparatus of the modified example 3-1. The bias Δ2 is 0 [-V] in the initial stage (C0) and immediately after the photoconductor drum 15 is replaced (immediately after R).
However, until the next replacement, the size increases in a quadratic linear manner in proportion to the rotation speed of the photoconductor drum 15, takes a maximum value immediately before the next replacement, and immediately after the next replacement. It becomes 0 [-V] again, and so on. Note that the charging bias V = reference charging bias VS + first correction bias Δ1
Other configurations and operations are the same as those of the third embodiment including the point of + second correction bias Δ2 + third correction bias Δ3, and therefore description thereof is omitted.

FIG. 11 shows the relationship between the second correction bias Δ2 and the number of rotations (cleaning state) of the photosensitive drum 15 in the image forming apparatus of Modification 3-2. The second correction bias Δ2 is shown in FIG. Is 0 [-V] in the initial stage (C0) and immediately after the photoconductor drum 15 is exchanged (immediately after R), but is stepwise in proportion to the rotation speed of the photoconductor drum 15 until the next exchange. The size becomes large, takes a maximum value immediately before the next exchange, becomes 0 [-V] again immediately after the next exchange, and so on. Where the second correction bias Δ
2 increases stepwise with each cleaning operation (each C1 to C4) as a trigger. Note that the other configurations and operations are the same as those in the third embodiment, including that the charging bias V = the reference charging bias VS + the first correction bias Δ1 + the second correction bias Δ2 + the third correction bias Δ3. The description is omitted.

FIG. 12 shows the relationship between the second correction bias Δ2 and the rotation speed (cleaning condition) of the photosensitive drum 15 in the image forming apparatus of Modification 3-3. In the initial (C0) and immediately after the replacement of the photosensitive drum 15 (immediately after R) to the next replacement, the size linearly increases in proportion to the rotation speed of the photosensitive drum 15. Same as example 3 (see FIG. 9)
(See (c)), but differs from Example 1 in that the inclination changes depending on the environment.

That is, when the detection result of the environment detection circuit 613 is the low temperature and low humidity environment (L / L environment), FIG.
As shown in (a), the linear linear inclination proportional to the rotation speed of the photosensitive drum 15 is relatively large. On the other hand, when the detection result of the environment detection circuit 613 is a high temperature and high humidity environment (H / H environment), as shown in FIG. 12B, a linear linear inclination proportional to the rotation speed of the photoconductor drum 15 is obtained. Is relatively small.

[0066]

As described above in detail, according to the present invention, it is possible to provide an image forming apparatus capable of easily determining an appropriate charging bias.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a color printer according to an embodiment.

FIG. 2 is a schematic cross-sectional view of the copying machine according to the embodiment.

FIG. 3 is a schematic sectional view of an image forming unit of a color printer and a copying machine according to the embodiment.

FIG. 4 is a block diagram illustrating a control system of the color printer and the copying machine according to the embodiment.

FIG. 5 is a graph illustrating a charging bias control operation of the image forming apparatus according to the first exemplary embodiment.

FIG. 6 is a graph illustrating a charging bias control operation of the image forming apparatus according to Modification 1-1.

FIG. 7 is a graph illustrating a charging bias control operation of the image forming apparatus according to Modification 1-2.

FIG. 8 is a graph illustrating a charging bias control operation of the image forming apparatus according to the second exemplary embodiment.

FIG. 9 is a graph illustrating a charging bias control operation of the image forming apparatus according to the third exemplary embodiment.

FIG. 10 is a graph illustrating a charging bias control operation of the image forming apparatus according to Modification 3-1.

FIG. 11 is a graph illustrating a charging bias control operation of the image forming apparatus according to Modification 3-2.

FIG. 12 is a graph illustrating a charging bias control operation of the image forming apparatus according to Modification 3-3.

[Explanation of symbols]

13 ... Image forming unit, 15 ... Photosensitive drum (image carrier), 16 ... Charging roll (charging member), 600 ... Control circuit (control means, cleaning means), 611 ... Counting circuit, 612 ... Exchange detection circuit, 613 ... environment detection circuit (temperature sensor, humidity sensor), 59 ... charging roll cleaning brush (cleaning means), 621 ... contact / separation circuit (cleaning means), 622 ... power supply circuit (power supply section)

Continued front page    F-term (reference) 2H027 DA11 DA14 DA33 DA38 DA45                       DB01 DE07 EA01 EC06 ED03                       EE07 EE08 EF09                 2H200 FA02 FA08 FA18 GA23 GA30                       HA03 HA29 HB12 HB22 LB02                       LB08 LB12 PA05 PA10 PB05                       PB27 PB28 PB33 PB34 PB35

Claims (11)

[Claims] 1. An image forming apparatus comprising: a charging member that charges the surface of an image carrier; a power supply unit that applies a predetermined charging bias to the charging member; and a cleaning unit that cleans the charging member at a predetermined timing. The image forming apparatus according to claim 1, further comprising control means for controlling the charging bias based on the cleaning status of the charging member. 2. The cleaning status is the elapsed time from the cleaning operation immediately before the charging member, the cumulative number of image formations of the image forming apparatus, or the cumulative rotation speed of the image carrier,
The image forming apparatus according to claim 1, wherein the image forming apparatus is determined based on either the accumulated image pixel value. 3. The control means obtains a charging bias by adding a first correction bias corresponding to the cleaning condition to the reference charging bias during the image forming operation during the cleaning operation, and immediately after the cleaning operation. Has
The image forming apparatus according to claim 1, wherein the reference bias is a charging bias (by resetting the first correction bias). 4. The image forming apparatus according to claim 1, wherein the control unit controls the charging bias based on the life status of the image carrier. 5. The life status is one of an elapsed time from immediately before replacement of the image carrier, a cumulative number of image formations of the image forming apparatus, a cumulative rotation speed of the image carrier, or a cumulative image pixel value. The image forming apparatus according to claim 4, wherein the image forming apparatus is judged based on the above. 6. The control means obtains a charging bias by applying a second correction bias corresponding to a life condition to a reference charging bias during an image forming operation during replacement of an image carrier. The image forming apparatus according to claim 4, wherein the reference bias value is set to the charging bias immediately after replacement. 7. The control means sets a first correction bias corresponding to a cleaning status and a second correction bias corresponding to a life status to a reference charging bias during an image forming operation between cleaning operations. 7. The image forming apparatus according to claim 4, wherein the charging bias is additionally obtained, and the charging bias is obtained immediately after the cleaning operation by adding the second correction bias to the reference bias value. 8. The image forming apparatus according to claim 1, wherein the control unit controls the charging bias based on an environmental condition of the image forming apparatus. 9. The image forming apparatus according to claim 8, wherein the control unit obtains the charging bias by adding a third correction bias according to an environmental condition to the reference charging bias. 10. The image forming apparatus according to claim 8, wherein the control unit controls the inclination of the first correction bias with respect to the cleaning status based on the environmental status of the image forming apparatus. 11. The image forming apparatus according to claim 8, wherein the control unit controls the inclination of the second correction bias with respect to the life status based on the environmental status of the image forming apparatus.