JP2001265137A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent fogging at a developing part due to electrifying failure, caused by the sticking of residue toner, after transferring or the increase of its content. SOLUTION: The residue toner, after transferring remaining on the surface of a photoreceptor drum 1a without being transferred to a recording material when being transferred, is detected by a concentration sensor 15. Transfer bias applied to a transfer electrifying device 5a by a transfer bias applying power source 5e is controlled, based on the detected result by a control means 20. Thus, the quantity of transfer residue toner is decreased, and the developing part is prevented from fogging due to the change in electrical resistance of an electrifying member caused by the residue transfer toner being stuck to the electrifying member and is mixed into the toner.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer in which a developing unit also serves as a cleaning unit.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses such as electrophotographic apparatuses have been reduced in size, enhanced in function, and colorized.
On the other hand, there are increasing demands for improvement in reliability, system development, maintenance-free operation, and environmental friendliness, and various image output devices have been proposed to satisfy those requirements.

For example, JP-A-53-74037 (corresponding US Pat. No. 4,162,843) discloses that
2. Description of the Related Art An image forming apparatus has been proposed in which a plurality of photoconductors are stacked to speed up color image output, and a toner image is sequentially multiplex-transferred while a transfer material is conveyed by a belt-shaped conveyance unit.

On the other hand, recently, in particular, miniaturization of the entire apparatus, ecological measures by eliminating waste toner, extension of the life of the photosensitive member,
To reduce the amount of toner consumption per page, the developing unit also serves as a cleaning unit for the toner remaining on the photoreceptor surface after the transfer of the toner image to the recording material, eliminating the need for a cleaning unit as a dedicated device. An image forming apparatus called “simultaneous development cleaning” or “cleanerless” has also appeared (JP-A-59-133).
Nos. 573 and 62-203182 and 63-203.
Nos. 133179, 64-20587, JP-A-2-51168 and 2-302772,
JP-A-5-2287, JP-A-5-2289, and 5-
No. 53482, No. 5-61383, etc.).

In the simultaneous cleaning with development, toner remaining on the surface of the photoreceptor without being transferred onto the recording material at the time of transfer (hereinafter referred to as "transfer residual toner") is moved from the transfer portion to the development portion by rotation of the photoreceptor of the photoreceptor. A fog removal potential difference, which is a potential difference between a DC voltage applied to the developer carrier and the surface of the photoreceptor at the time of subsequent development in a developer carrier (developing member, for example, a developing sleeve) of the developing means. Vback
Is to be recovered.

According to this, the transfer residual toner can be collected by the developing means without using a cleaning device as a dedicated device, and the collected transfer residual toner is used for development in the next and subsequent steps. Therefore, waste toner can be eliminated. In addition, since a cleaning device as a dedicated device is not required, there is a great advantage in terms of space, and the device can be significantly reduced in size.

Therefore, even in an image forming apparatus described in Japanese Patent Application Laid-Open No. 53-74037, in which a plurality of photoconductors are stacked and a toner image is sequentially multiplex-transferred onto a recording material, the overall size of the apparatus is reduced. It is expected that the simultaneous development and cleaning method will be adopted in consideration of ecological measures by eliminating waste toner, extending the life of the photosensitive member, and reducing the amount of toner consumed per page.

[0008]

In an image forming apparatus in which the transfer residual toner is collected by a developing unit, when the primary charging system is a contact charging system, the transfer residual toner attached to the surface of the photoreceptor is developed from the transfer unit. The sheet is once collected by the contact transfer member on the way to the transfer section. At this time, the contact charging member is attached and mixed by the collected transfer residual toner,
The electric resistance changes. For example, if the contact charging member is a magnetic brush charger (injection charger), transfer residual toner is mixed into the magnetic brush portion, and the electric resistance thereof gradually increases. For this reason, sufficient charge cannot be transferred to the surface of the photoreceptor during the passage of the charging nip during the primary charging, and the surface potential of the photoreceptor after passing through the charging nip becomes smaller than the applied voltage. Here, assuming that the potential difference between the photosensitive member surface potential and the applied voltage is ΔV, the potential difference ΔV increases as the amount of transfer residual toner mixed into the magnetic brush unit increases. When the potential difference ΔV increases, fogging occurs in the developing section. For this reason, it is necessary to keep the amount of toner mixed in the magnetic brush portion below a certain level.

However, when the simultaneous development and cleaning method is employed in the image forming apparatus, the following problems can be considered.

The transfer efficiency, that is, the ratio of the toner transferred to the recording material to the toner forming a toner image on the surface of the photosensitive member may decrease due to the aging and durability deterioration of the transfer member. In this case, the amount of adhesion and mixing of the transfer residual toner once collected by the contact charging member to the contact charging member increases, and the electrical resistance value of the contact charging member changes, thereby causing fogging in the developing unit. There was such a problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in an image forming apparatus employing a simultaneous development and cleaning method, it is possible to prevent the occurrence of fogging in a developing section due to a decrease in transfer efficiency, and to always obtain a good image. It is an object to provide an image forming apparatus capable of forming.

[0012]

According to a first aspect of the present invention, there is provided an image bearing member, wherein the surface of the image bearing member is charged by a charging member in contact with the surface of the image bearing member. Charging means, an exposure means for exposing the charged surface of the image carrier to form an electrostatic latent image, a developing means for adhering toner to the electrostatic latent image and developing it as a toner image, and the toner Transfer means for transferring an image to a recording material, and after the transfer residual toner remaining on the surface of the image carrier not transferred to the recording material at the time of transfer is once collected by the charging member, the toner is discharged from the charging member. A transfer bias applying power source for applying a transfer bias to the transfer unit when transferring the toner image on the image carrier to the recording material, wherein the toner for the recording material is And density detecting means for detecting the concentration of toner remaining on the image bearing member surface after the transfer of,
Control means for controlling a transfer bias applied to the transfer means by the transfer bias application power supply based on a detection result of the density detection means.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, when the charging member discharges the transfer residual toner once collected from the charging member, the time when the surface of the image carrier is charged is changed. A different bias is applied to the charging member.

According to a third aspect of the present invention, there is provided the first or second aspect.
In the image forming apparatus, the control unit may detect the density of the residual toner at predetermined time intervals, and the control unit may control the transfer bias based on the detection result. Features.

According to a fourth aspect of the present invention, in the image forming apparatus of the third aspect, the predetermined time interval is required for the recording material carrier that carries and conveys the recording material to rotate by a predetermined number of rotations. Time.

According to a fifth aspect of the present invention, in the image forming apparatus of the third aspect, the predetermined time interval is a time required for the image carrier to rotate by a predetermined number of rotations.
It is characterized by the following.

According to a sixth aspect of the present invention, in the image forming apparatus of the third aspect, the predetermined time interval is a time required for forming an image on a predetermined number of the recording materials. Features.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 shows an example of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG.
This is a four-color full-color image forming apparatus provided with four image forming stations as image forming units, and FIG. 1 is a longitudinal sectional view showing a schematic configuration thereof.

The image forming apparatus shown in FIG.
7c is suspended by a drive power supply (not shown)
A transfer belt 7a as a recording material carrier that travels (rotates) in the direction, and a transfer belt 7 is disposed above the transfer belt 7a.
There are four image forming stations Pa, Pb, Pc and Pd arranged in order from the upstream side in the rotation direction of a.

Image forming stations Pa, Pb, Pc,
Pd has a cylindrical electrophotographic photosensitive member (hereinafter, referred to as a “photosensitive drum”) serving as an image carrier, which is driven to rotate in the direction of arrow R1 by driving means (not shown) in contact with the above-described transfer belt 7a.
1a, 1b, 1c, and 1d.

After the photosensitive layers on the surfaces of the photosensitive drums 1a, 1b, 1c and 1d are uniformly charged by primary chargers (eg, magnetic brush chargers) 2a, 2b, 2c and 2d as charging members, Exposure devices (exposure means) 3a, 3b, 3
Light images of yellow, magenta, cyan, and black components of the original image are exposed by c and 3d, respectively, and electrostatic latent images are formed on the photosensitive drums 1a, 1b, 1c, and 1d. The electrostatic latent image is moved by the rotation of the photosensitive drums 1a, 1b, 1c, and 1d to form developing units (developing units) 4a, 4b, 4
c and 4d, and reaches the developing position where yellow supplied from the developing units 4a, 4b, 4c and 4d,
Magenta, cyan, and black toners are attached and developed as a toner image.

The above-described toner images of each color are transferred to the photosensitive drum 1
a, 1b, 1c, 1d, a blade-shaped transfer charger (transfer means) 5a in which conductive rubber is processed into a plate shape with rotation of
It reaches the transcription position (transcription site) where 5b, 5c, and 5d are arranged. On the other hand, the recording material P stored in the sheet cassette is fed by a sheet feeding roller 8a, conveyed by a conveying roller 8b, and temporarily stopped by a registration roller 8c. The recording material P is supplied onto the transfer belt 7a by the registration roller 8c so as to match the timing of each color toner image on each of the photosensitive drums 1a, 1b, 1c, and 1d, and is carried on the surface of the transfer belt 7a. Is done. The recording material P is sequentially conveyed to the transfer position of each color by the rotation of the transfer belt 7a in the direction of the arrow R7. At the transfer position of each color, the transfer bias application power supplies 5e, 5e
The toner images of each color on the photosensitive drums 1a, 1b, 1c, and 1d are sequentially transferred onto the recording material P by the transfer bias applied by f, 5g, and 5h. Thereby, the four color toner images are superimposed on the recording material P. In addition,
The transfer bias applied to each transfer bias application power source 5e, 5f, 5g, 5h is controlled by the control unit 20.

The untransferred toner remaining on the photosensitive drums 1a, 1b, 1c, and 1d without being transferred onto the recording material P at the time of the transfer is once collected by the primary chargers 2a, 2b, 2c, and 2d, and is temporarily recovered. After the tribo is re-applied by the carrier constituting the upper 2b, 2c, 2d, the tribo is discharged onto the photosensitive drums 1a, 1b, 1c, 1d, and the developing devices 4a,
4b, 4c and 4d. That is, the image forming apparatus shown in FIG. 1 does not have a cleaning device as a dedicated device, and the developing devices 4a, 4b, 4c, and 4d also serve as a cleaning device. Is adopted.

By adopting such a configuration, almost 100% of the transfer residual toner can be reused without being discarded, so that the running cost can be reduced and environmental problems can be satisfactorily dealt with.

On the other hand, the recording material P to which the four color toner images have been transferred is discharged by the separating / discharging device 9 and separated from the transfer belt 7a.
b is transported to the fixing device 10 having b. The recording material P is heated and pressurized in the fixing nip between the two rollers to mix and fix the toner images of the respective colors, and is discharged out of the apparatus as a full-color permanent image.

On the other hand, the transfer belt 7a after the recording material P is separated is moved by the inner static eliminator 11 and the outer static eliminator 12
The charge received during the transfer is eliminated. In addition, the cleaning blade 14 and the backup member 13 provided on the downstream side in the rotation direction further adhere to the surface of the cleaning blade 14 and the backup member 13, that is, foreign matters such as fog toner, flying toner, and paper dust. Is removed and cleaned, and is provided for the next image formation.

Hereinafter, the density of the transfer residual toner on the photosensitive drum (hereinafter referred to as "residual toner density")
That. ) Will be described.

FIG. 2 is a schematic diagram showing a cross section of a yellow image forming station Pa of the image forming apparatus according to the present embodiment and a periphery of a transfer portion thereof.

Assuming that a nip portion formed between the photosensitive drum 1a and the transfer belt 7a is a transfer position N, the transfer position N along the rotation direction (direction of arrow R1) of the photosensitive drum 1a.
A density sensor 15 as a density detecting means is disposed downstream from the apparatus. The density sensor 15 is of a reflection type, and an LED is provided for the toner image on the photosensitive drum 1a.
Irradiates light, and the density of the toner image is detected by the reflected light. The detection result of the density sensor 15 is sent to the control means 20. The control means 20 controls the transfer bias application power supplies 5e, 5f, 5g,
5h is controlled to adjust the toner transferred from the photosensitive drums 1a, 1b, 1c, and 1d to the recording material P, thereby adjusting the residual toner concentration.

Hereinafter, a control sequence of the transfer bias based on the residual toner density will be described with reference to a flowchart shown in FIG.

As shown in step 1 (hereinafter referred to as "S1"), after a series of image formation is completed, the photosensitive drum 1a is moved to a position passing the density sensor 15 in the same manner as a normal image forming operation. Through the process, a solid image of a predetermined size (hereinafter, referred to as “patch image”) is formed. This patch image is directly transferred to the surface of the transfer belt 7a by the transfer charger 5a (S2). At this time, as the value of the bias applied to the transfer charger 5a, a set value previously determined by an experiment is used in an initial state of the apparatus so that optimum transfer to the transfer belt 7a can be performed.

The patch image that has not been completely transferred onto the transfer belt 7a remains on the surface of the photosensitive drum 1a and passes through a position facing the density sensor 15. At this time, the density sensor 15
As a result, the density of the patch image that cannot be completely transferred is obtained as a voltage signal.

Control means (C included in the image forming apparatus)
PU) 20 based on the signal value obtained by the residual toner sensor 15 when passing the patch image.
It is determined whether or not the density of the patch image remaining on a (the patch image density Dm measured by the density sensor 15) is equal to or higher than the set density threshold Dt (S4).

If Dm ≦ Dt, the sequence ends (S5).

On the other hand, when Dm> Dt, the transfer bias value T is increased by +1 [μA], and the above-described steps 1 to 3 and steps 6 and 9 are performed until Dm becomes equal to or less than the threshold value Dt.
Is repeated, and then the sequence ends (S
5).

However, the adjustment of the set value of the transfer bias value T is limited to the initial value T1 + 5 [μA] of the transfer bias, and when the Dm does not fall below the threshold value Dt even when adjusted to the initial value T1 + 5 [μA]. Then, a message prompting replacement of consumable parts of the image forming station (image forming unit) of that color is displayed on the operation panel of the image forming apparatus (S7), and the sequence is terminated (S8).

By employing the above configuration and sequence, the conventional problems can be solved. That is, conventionally, when the simultaneous development and cleaning method is adopted, the transfer efficiency (the recording material P with respect to the toner formed on the photosensitive drum 1a) is changed due to the aging and durability deterioration of the transfer charging member.
Of the toner transferred to the contact charging member, the amount of adhesion and mixing of the transfer residual toner once collected by the contact charging member to the contact charging member increases. Has been changed to cause fogging in the developing section, but this problem can be solved.

<Second Embodiment> In the second embodiment, prior to the control sequence of the transfer bias based on the residual toner concentration described in the first embodiment, the operation of discharging the toner collected by the charging member is performed. Are characteristically different, and will be described below.

The configuration and the image forming operation of the image forming apparatus according to the second embodiment are substantially the same as those of the first embodiment, so that the description thereof will be omitted as appropriate.

FIG. 4 shows a flowchart of a transfer bias control sequence based on the residual toner concentration in the second embodiment, which will be described below.

After the transfer of the toner image to the recording material P by the last image forming station Pd is completed, the driving means (not shown) is used for a while before the transfer bias control sequence based on the residual toner density. By continuing driving, the photosensitive drums 1a, 1b, 1c, and 1d are rotationally driven to stop the application of the AC component of the charging bias, so that the photosensitive drums 1a, 1b, 1c, and 1d are temporarily recovered by a primary charger (for example, a magnetic brush charger). Transfer residual toner is transferred to the photosensitive drums 1a, 1b, 1
c, 1d. That is, as shown in FIG. 4, a forced discharge operation is provided as Step S2A between Step 1 (S1) and Step 2 (S2) in the flowchart of FIG.

By this operation, the charged state of the photosensitive drums 1a, 1b, 1c, 1d becomes unstable due to the influence of the transfer residual toner collected in the primary chargers (magnetic brush chargers) 2a, 2b, 2c, 2d. , And more accurate transfer bias adjustment can be performed.

The conventional problems can be solved by adopting the above configuration and sequence in the image forming apparatus. In other words, conventionally, when the simultaneous development and cleaning method is adopted, the transfer efficiency (the ratio of the toner transferred to the recording material P to the toner formed on the photosensitive drum 1a) is reduced due to the aging and durability deterioration of the transfer charging member. As a result, the amount of transfer residual toner once collected by the contact charging member adheres to and mixes into the contact charging member, thereby changing the electrical resistance value of the contact charging member and causing fogging in the developing unit. However, we were able to solve this problem.

Third Embodiment In the third embodiment, the timing for executing the transfer bias control sequence based on the residual toner density described in the first embodiment is
Embodiment 2 is different from Embodiment 1 in that the image forming operation is not performed after the end of the normal image forming operation but is performed periodically at predetermined time intervals in accordance with the number of rotations of the transfer belt 7a. Note that, in the present embodiment, a description of the same configuration and operation as those of the above-described first embodiment will be appropriately omitted.

FIG. 5 is a perspective view showing the periphery of the transfer belt of the image forming apparatus according to the third embodiment.

The transfer belt 7a as a recording material carrier is
It is suspended between a pair of rollers 7b and 7c, and travels (rotates) in the direction of arrow R7 by a driving means (not shown).
A white position mark 1 is provided inside the transfer belt 7a.
6 is attached, for example, by gluing. Further, a position sensor 17 is disposed at a position facing the position mark 16.

In this embodiment, the position mark 16
Uses a high-density polyethylene excellent in slipperiness and durability, but the color and shape of the mark may be determined by using an optimal means depending on the type of the transfer belt 7a and the position sensor 17. Further, instead of the position mark 16, a through hole may be provided in the transfer belt 7a, and this may be detected by a light transmission type sensor.

When the transfer belt 7a rotates, the position mark 16 passes the position facing the position sensor 17 for each rotation, and the number of rotations of the transfer belt 7a is counted. This value is stored in a storage device (RAM, etc.) in the image forming apparatus.
(Not shown).

When the value of the count reaches a predetermined value,
At the end of the image forming operation, the sequence of FIG. 1 described in the first embodiment is executed, and the value of the counter is returned to zero.

As a result, toner consumption due to the transfer bias control sequence based on the residual toner density can be suppressed.

The conventional problems can be solved by employing the above configuration and sequence in the image forming apparatus. In other words, conventionally, when the simultaneous development and cleaning method is adopted, the transfer efficiency (the ratio of the toner transferred to the recording material P to the toner formed on the photosensitive drum 1a) is reduced due to the aging and durability deterioration of the transfer charging member. As a result, the amount of transfer residual toner once collected by the contact charging member adheres to and mixes into the contact charging member, thereby changing the electrical resistance value of the contact charging member and causing fogging in the developing unit. However, we were able to solve this problem.

In the above description, the number of rotations of the transfer belt 7a is counted. However, instead of this, a sensor for detecting the number of discharged recording materials P is provided, and the discharge of the recording material P detected by this sensor is provided. Even when the control sequence similar to the above is executed when the number of sheets reaches the predetermined number, substantially the same effects as in the third embodiment can be obtained.
Instead of detecting the rotation speed of the transfer belt 7a, the rotation speeds of the photosensitive drums 1a, 1b, 1c, and 1d may be detected.

More preferably, the third embodiment should be combined with the second embodiment. That is,
Prior to the control sequence of the transfer bias based on the residual toner concentration, the operation of forcibly discharging the toner collected in the primary chargers 2a, 2b, 2c, and 2d is performed.
Similarly, the photosensitive drums 1a, 1b, 1d are affected by the transfer residual toner collected in the primary chargers 2a, 2b, 2c, 2d.
It is possible to prevent the charging states of c and 1d from becoming unstable, and to more accurately adjust the transfer bias.

In the first to third embodiments, four image forming stations Pa and P are used as image forming apparatuses.
Although the image forming apparatus having b, Pc, and Pd has been described, the present invention is not limited to this, and is applicable to any image forming apparatus that transfers a toner image formed on an image carrier to a recording material. Can achieve the same effect. For example, the present invention is also applicable to an image forming apparatus that forms a single-color toner image (such as a black-and-white copying machine).

[0056]

As described above, according to the present invention,
The transfer residual toner remaining on the surface of the image carrier without being transferred to the recording material at the time of transfer is detected by the density detecting means, and the control means controls the transfer bias based on the detection result, so that the transfer residual toner adheres to the charging member. It is possible to prevent fogging in the developing unit due to the change in the electrical resistance of the charging member due to mixing, and it is possible to always perform good image formation.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment.

FIG. 2 is an enlarged view of one image forming station.

FIG. 3 is a flowchart illustrating a control sequence of a transfer bias based on a residual toner density in the first embodiment.

FIG. 4 is a flowchart illustrating a control sequence of a transfer bias based on a residual toner density according to the first embodiment.

FIG. 5 is a perspective view showing a transfer belt, a position mark, and a position sensor according to a third embodiment.

[Explanation of symbols]

1a, 1b, 1c, 1d Image carrier (photosensitive drum) 2a, 2b, 2c, 2d Charging member (primary charger, magnetic brush charger) 3a, 3b, 3c, 3d Exposure means (exposure device) 4a, 4b 4c, 4d developing means (developing device) 5a, 5b, 5c, 5d transfer means (transfer charger) 5e, 5f, 5g, 5h transfer bias applying power source 7a recording material carrier (transfer belt) 15 density detecting means (density sensor) ) 20 control means (CPU) P recording material

Continued on front page F-term (reference) 2H003 AA11 BB11 CC04 DD00 2H027 DA10 DA39 DA41 DA43 DE02 EA03 EC03 ED24 EF09 2H032 AA05 BA01 BA03 BA27 CA02 CA13 CA15 2H077 AA37 AC16 AD35 CA19 DA03 DA47 DB15 9A001 HH34 JJ09 KK35

Claims (6)

[Claims] An image carrier, a charging unit for charging the surface of the image carrier by a charging member in contact with the surface of the image carrier, and an electrostatic latent image formed by exposing the surface of the image carrier after charging. An exposure unit for forming a toner image, a developing unit for attaching a toner to the electrostatic latent image to develop the toner image as a toner image, and a transfer unit for transferring the toner image to a recording material, wherein the toner image is not transferred to the recording material during transfer. In the image forming apparatus, after the transfer residual toner remaining on the surface of the image carrier is once collected by the charging member, and then discharged from the charging member and collected by the developing unit, the toner image on the image carrier is A transfer bias application power source for applying a transfer bias to the transfer unit when transferring to the recording material; and detecting a density of a transfer residual toner remaining on the surface of the image carrier after the transfer of the toner image onto the recording material. A degree detecting means, based on a detection result of the density detection means, and control means for controlling the transfer bias said transfer bias application voltage source is applied to the transfer means, that the image forming apparatus according to claim. 2. The method according to claim 1, wherein a bias different from that when the surface of the image bearing member is charged is applied to the charging member when the charging member discharges the collected transfer residual toner from the charging member. Item 2. The image forming apparatus according to Item 1. 3. The control unit, wherein at a predetermined time interval, the density detection unit detects the density of the residual toner, and the control unit controls the transfer bias based on the detection result. The image forming apparatus according to claim 1. 4. The image according to claim 3, wherein the predetermined time interval is a time required for a recording material carrier that carries and conveys the recording material to rotate by a predetermined number of rotations. Forming equipment. 5. The image forming apparatus according to claim 3, wherein the predetermined time interval is a time required for the image carrier to rotate by a predetermined number of rotations. 6. The image forming apparatus according to claim 3, wherein the predetermined time interval is a time required to form an image on a predetermined number of the recording materials.