JP2012046257A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that prevents deterioration of image quality by measuring a surface potential in a conveyance guiding member of a fixing lower portion and changing a resistor for grounding the conveyance guiding member based on a measured result during conveying.SOLUTION: The image forming apparatus 1 includes: a transfer device 10 that transfers a toner image to a recording material 2 to be conveyed; a conveying path 70 on which the recording material 2 with the transferred toner image is vertically conveyed; and fixing device 60 that melts and fixes the toner image on the recording material 2. The conveying path 70 includes at least one conveyance guiding member 71 between the transfer device 10 and the fixing device 60, and the conveyance guiding member 71 is grounded via the resistor 76 or without using it.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a fax machine, and more particularly to an image forming apparatus having a conveyance path between a transfer device and a fixing device.

In an image forming apparatus capable of forming a multicolor image, when the transport path from the secondary transfer unit to the fixing unit is in the vertical direction, the transport unit is provided below the fixing device for maintaining the transport stability of the recording material. A guide member is attached.
However, under conditions where the recording material is highly hydrated, transfer defects due to the transfer unit occur, and many image defects are observed. This is considered to be due to the fact that when a transfer bias is applied to the recording material, the transfer current in the transfer region flows out to the conveying guide member through the recording material with a reduced resistance.
In order to prevent the transfer current from leaking, a configuration in which the conveyance guide member is grounded through a high resistance is already known.

  Japanese Patent Application Laid-Open No. 2004-133867 discloses that “an image carrier module having an image carrier that carries a visible image of a charged color material, and a visible image carried on the image carrier of the image carrier module is transferred to a recording material. An image forming apparatus having a transfer unit and a recording material guide mechanism having a pair of guide chutes for partitioning a recording material conveyance path and guiding and conveying the recording material to a transfer area between the image carrying module and the transfer unit Discloses an image forming apparatus in which a guide chute mainly contacting a recording material is grounded via a high resistance member among recording material guiding mechanisms. In the disclosed image forming apparatus, a configuration is disclosed in which a conveying member on the side in contact with the recording material is grounded via a high-resistance body in order to avoid transfer failure due to transfer current leakage from the recording material guide mechanism. Has been. However, the problem that the transfer guide plate is charged and the transferred image causes an abnormal image due to the dust of the toner cannot be solved.

  Therefore, with the conventional conveyance guide member that is grounded via the high-resistance element, the image that the conveyance guide member is charged and transferred to the recording material is deteriorated due to toner dust. there were.

  Accordingly, the present invention has been made in view of the above-mentioned problems, and its problem is to measure the surface potential of the conveyance guide member below the fixing and to ground the conveyance guide member based on the measurement result. It is to provide an image forming apparatus that prevents deterioration in image quality by changing the image during conveyance.

The features of the present invention, which is a means for solving the above problems, are listed below.
An image forming apparatus according to the present invention includes a transfer device that transfers a toner image to a recording material to be transported, a transport path in which a recording material having the transferred toner image is transported, and a toner image on the recording material that is melted. In the image forming apparatus including the fixing device to be fixed, the transport path includes at least one transport guide member between the transfer device and the fixing device, and the transport guide member is interposed via a resistor. It is possible to change between grounding and grounding without a resistor.
The image forming apparatus of the present invention further includes a measuring unit that measures the surface potential of the conveying guide member.
The image forming apparatus of the present invention is further characterized in that the measuring device measures at least two positions of the conveying guide member.
The image forming apparatus according to the present invention is further characterized in that at least two measuring devices are arranged in the transport direction of the transport guide member.
The image forming apparatus of the present invention is further characterized in that, based on the measurement information of the measurement device, the conveyance guide member is grounded without a resistor.
The image forming apparatus of the present invention is further characterized in that the conveyance guide member is grounded via a resistor based on measurement information of the measurement device.
The image forming apparatus according to the present invention further includes at least two or more switching mechanisms for grounding through a high resistor and grounding without using a high resistor.
Further, the image forming apparatus of the present invention further determines whether or not to install a high resistance element on the transport guide member based on measurement information of the measurement apparatus after transporting a predetermined number of recording materials. It is characterized by.
The image forming apparatus of the present invention is further characterized in that the conveying guide member is a fixing entrance guide plate for introducing a recording material into the fixing device.
The image forming apparatus of the present invention is further characterized in that the conveying guide member is a transfer outlet guide plate that guides the recording material from the transfer device.
The image forming apparatus of the present invention is further characterized in that the measuring device is movable at a position where at least one is installed.

The present invention, which is a means for solving the above problems, has the following specific effects.
By changing the resistor grounded to the conveyance guide member to the fixing device based on the surface potential of the conveyance guide member, the transfer current leaks or the guide member is charged by the image forming apparatus of the present invention. Therefore, it is possible to prevent transfer defects due to transfer current leakage and image quality deterioration such as dust.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is an image forming apparatus according to an exemplary embodiment of the present invention, and is a schematic diagram illustrating a configuration of a conveyance path between a transfer device and a fixing device. (A) is a schematic diagram showing an example of a position for measuring the surface potential of a conveyance guide member used in the conveyance path of the image forming apparatus of the present invention, and (b) shows an example of surface potential attachment in the image forming apparatus. FIG. FIG. 6 is a diagram illustrating switching of a resistor to be grounded to a conveyance guide plate based on a specific surface potential of a fixing entrance guide plate in the image forming apparatus of the present invention. 5 is a flowchart for explaining a change of a conveyance guide member during an image forming job in the image forming apparatus of the present invention. It is an example of experimental data of surface potential and dust level.

  The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.

An embodiment of the present invention will be described. The present invention has the following characteristics when paper is conveyed to the fixing device.
In short, the resistor to be grounded to the conveyance guide member to the fixing device is changed based on the surface potential of the conveyance guide member. The features of the present invention will be described in detail with reference to the following drawings.

Embodiments of an image forming apparatus according to the present invention will be described below.
FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention.
In FIG. 1, a color image forming apparatus 1 includes a transfer device 10 having an intermediate transfer belt 11 as a transfer member for supporting a toner image, and four image forming units. Each image forming unit has an image carrier (hereinafter referred to as an image carrier). Photoconductor drums) 20Y, 20C, 20M and 20Bk, around which are dedicated charging devices 30Y, 30C, 30M and 30Bk, developing devices 50Y, 50C, 50M and 50Bk, cleaning devices 40Y, 40C and 40M, 40Bk.
A toner bottle that replenishes toner, and is filled with yellow (Y), cyan (C), magenta (M), and black (Bk) toner from the left in the drawing, and from there is a predetermined path by a conveyance path (not shown). The developing devices 50Y, 50C, 50M, and 50Bk for each color are replenished by the replenishment amount.

Regarding the operation, the recording material 2 as the recording material is fed from the paper feed cassette 81 by the paper feed roller 82, and when the leading end of the recording material 2 reaches the registration roller pair 83, it is detected by a sensor (not shown). The recording material 2 is conveyed to the nip portion between the secondary transfer roller 15 and the intermediate transfer belt 11 by the registration roller pair 83.
The photosensitive drums 20Y, 20C, 20M, and 20Bk, which are uniformly charged in advance by the charging devices 30Y, 30C, 30M, and 30Bk, are exposed and scanned by the exposure device 70 with the laser beams 71Y, 71C, 71M, and 71Bk. An electrostatic latent image of yellow (Y), cyan (C), magenta (M), and black (Bk) is formed on the drums 20Y, 20C, 20M, and 20Bk.

The electrostatic latent images are developed by the developing devices 50Y, 50C, 50M, and 50Bk for the respective colors, and yellow, cyan, magenta, and black toner images are formed on the surfaces of the photosensitive drums 20Y, 20C, 20M, and 20Bk. The intermediate transfer belt 11 having no drive starts to be driven by the frictional force with the photosensitive drums 20Y, 20C, 20M, and 20Bk as image carriers that have started rotating, and then the primary transfer rollers 12Y, 12C, 12M, and 12Bk. A voltage is applied to the photosensitive drums 20Y, 20C, 20M, and 20Bk, and the toner is sequentially transferred onto the intermediate transfer belt 11.
At this time, the image forming operation for each color is executed while shifting the timing from the upstream side toward the downstream side so that the toner image is transferred to the same position on the intermediate transfer belt 11.
The image formed on the intermediate transfer belt 11 is conveyed to the position of the secondary transfer roller 15 and is secondarily transferred to the recording material 2.

The recording material 2 onto which the toner image of each color has been transferred is conveyed substantially vertically toward the fixing device 60 provided above.
The transport direction may not be the vertical direction, but the image forming apparatus can be downsized in the vertical direction, and the transport distance is shortened, so that the time for the image forming operation can be shortened.
The recording material 2 is conveyed to the fixing device 60 and is fixed by heat and pressure in a fixing region formed between the pressure roller 61 and the fixing roller 62, and is discharged by the paper discharge roller 84.
Thus, one image forming job is completed.
The residual toner on the photoconductive drums 20Y, 20C, 20M, and 20Bk is cleaned by the respective cleaning devices 40Y, 40C, 40M, and 40Bk, and then the charging device 30Y, in which the bias of the AC component is superimposed and applied to the direct current. 30C, 30M, and 30Bk are charged at the same time as static elimination to prepare for the next image forming job.
The residual toner on the intermediate transfer belt 11 is cleaned by the elastic intermediate transfer belt cleaning device 14 to prepare for the next image forming job.

FIG. 2 is an image forming apparatus according to an embodiment of the present invention, and is a schematic diagram illustrating a configuration of a conveyance path between a transfer device and a fixing device.
Among the color electrophotographic apparatuses that have been increasing in recent years, a diagram of a tandem type apparatus in which four image forming apparatuses are arranged and a recording material 2 being conveyed vertically is shown.
As described above, the recording material 2 is fed from the paper feed cassette 81 and comes into contact with the intermediate transfer belt 11 after passing through the registration roller 83.
The intermediate transfer belt 11 on which the color image is formed enters the nip portion with the secondary transfer roller 15 together with the recording material 2, and is transferred from the intermediate transfer belt 11 to the recording material 2 by a bias applied to the secondary transfer roller 15. Move.
Further, the recording material 2 onto which the toner image has been transferred is directed to the fixing device 60 via the conveyance path 70 and is heated and pressed by the fixing roller 62 and the pressure roller 61 to depict the image on the recording material 2. ing.

Here, as described above, an image is formed on the recording material 2 by the secondary transfer roller 15, but the conveyance path between the transfer device 10 and the fixing device 60 that forms the transfer nip portion of the secondary transfer roller 15. Since the unfixed toner may be carried on the recording material 2 being conveyed 70, the image surface side cannot be positively held.
In FIG. 2, the conveyance of the recording material 2 in the upward direction (hereinafter referred to as “vertical conveyance”) indicates the image forming apparatus 1 including the conveyance path 70 for the vertical conveyance in the substantially vertical direction.
If the image forming apparatus 1 is not the image forming apparatus 1 provided with such a vertical conveying path 70 but is conveyed in the horizontal direction (hereinafter referred to as “horizontal conveyance”), an unfixed toner image. It is also possible to feed the lower side of the recording material 2 under the condition of gravity with a conveyor belt or the like while the sheet is placed on the top. It may be disturbed, skewed, and not conveyed to the fixing nip portion between the fixing devices 60, resulting in a paper jam.

A conveyance guide member 71 is provided between the transfer nip portion of the secondary transfer roller 15 and the fixing device 60 to assist conveyance toward the non-image surface of the recording material 2, and the position of the conveyance guide member 71 is provided. The conveyance stability is maintained by adjusting. However, if the mounting position of the conveying guide member 71 is not appropriate, the recording material 2 does not hit the conveying guide member 71, or conversely, the recording material 2 strongly hits the conveying guide member 71 and the recording material 2 is conveyed. It is known that the sex becomes worse.
If the transportability of the recording material 2 is deteriorated, the image formation is disturbed at the transfer nip portion of the secondary transfer roller 15. The load causes a slight change in the transfer time of the image to the recording material 2 and disturbs the image parallelism.
In the image forming apparatus 1, the front end of the recording material 2 comes into contact with the conveyance guide member 71 and the fixing device 60 before the rear end of the recording material 2 is completely separated from the secondary transfer roller 15. Therefore, when the resistance of the recording material 2 is lowered, the current applied to the secondary transfer roller 15 is leaked, resulting in transfer failure, and an abnormal image may be generated.
Therefore, in the image forming apparatus 1 according to the present invention, the surface potential of the conveyance guide member 71 is read by a sensor and the resistor grounded to the conveyance guide member is switched. Image disturbance such as transfer dust due to charging of 71 is prevented.

In the image forming apparatus 1 of the present invention, the disturbance of the balance of the recording material 2 is read by the surface potential meter 79 with the surface potential of the conveying guide member 71, and the conveying guide member 71 is read via the high resistance 76 or the high resistance. By grounding without passing through the body 76, it is possible to prevent image disturbance such as transfer failure due to transfer current leakage or toner dust on the recording material 2.
3A is a schematic diagram showing an example of a position for measuring the surface potential of a conveyance guide member used in the conveyance path of the image forming apparatus of the present invention, and FIG. It is the schematic which shows an example.
In the image forming apparatus of the present invention, the surface for measuring the surface potential of the fixing entrance guide plate 711 with respect to the upward conveyance of the recording material 2 conveyed to the portion between the secondary transfer roller 15 and the fixing device 60. An electrometer 79 is provided.
As shown in (a), the surface electrometer 79 is disposed at a position where the upper and lower portions of the central portion of the fixing entrance guide plate 711 can be measured. The measured detection result is input to the control unit 77.
For example, a surface electrometer 79 is prepared and the positions of A and B are measured. At this time, two surface electrometers 79 may be prepared and all may be fixed.
Alternatively, as shown in (b), one surface electrometer 79 may be prepared and moved to measure the positions of A and B, respectively. As a movable structure, for example, a motor and a rack and pinion are combined and moved in the transport direction.
By doing so, measurement places A and B in the same transport direction can be measured with one electrometer.

FIG. 4 is a diagram for explaining switching of the resistor to be grounded to the conveyance guide plate based on the specific surface potential of the fixing entrance guide plate in the image forming apparatus of the present invention.
The surface potential of the fixing entrance guide plate 711 was measured by measuring the surface potentials of A and B (hereinafter referred to as absolute values by omitting the sign of polarity) VA1 and VB1 before passing, and after passing a certain number of sheets, For example, after passing 50 sheets, the surface potential at each position is again measured (hereinafter, the sign of the polarity is omitted to be an absolute value) VA2, VB2.
It should be noted that the resistor has the high resistor 76 grounded before the sheet passing before the image forming operation. This is because whether the fixing entrance guide plate 711 is charged by contact with the recording material 2 is caused by the image forming operation. Therefore, before the image forming operation, the fixing entrance guide plate 711 is grounded to the high resistance 76. Yes.
The high resistance body 76 may be any material as long as the leakage of the transfer current is within an allowable range via the recording material 2 having a low resistance, and is generally selected to be about 180 to 220 (MΩ).
Then, the surface potential changes VA2-VA1, VB2-VB1 before passing the recording material 2 and after passing a certain number of sheets are passed through a high resistor 76 that is grounded to the fixing entrance guide plate 711, or the high resistor 76 is attached. Decide whether or not to intervene.
In the present embodiment, the measured surface potential data is input to the control unit 77, and the control unit 77 determines whether or not the high resistance body 76 is passed through the data based on the data. . In that case, the control unit 77 controls the changeover switch 75 to control whether the high resistance body 76 is used or not.
Specifically, when the surface potential changes VA2-VA1 and VB2-VB1 of the fixing entrance guide plate 711 are lower than the respective threshold values α and β, the fixing entrance guide plate 711 is not charged. May remain the high resistance 76.
On the contrary, when the changes VA2-VA1 and VB2-VB1 of the surface potential of the fixing entrance guide plate 711 are higher than the threshold values α and β, the conveyance guide plate 71 is charged and thus is a resistor. The fixing entrance guide plate 711 is grounded without using the high resistor 76.
Thereafter, when the surface potential becomes lower than α and β, the fixing entrance guide plate 711 is grounded through the high resistance 76 again.

The switching of the high resistor 76 as described above is performed during the job or at the end of the job.
FIG. 5 is a flowchart for explaining the change of the conveying guide member during the image forming job in the image forming apparatus of the present invention.
First, two positions A and B of the conveyance guide member 71, here, the fixing inlet guide member 711 are selected, and the respective surface potentials VA1 and VB1 are measured (step S1).
Next, during a job for image formation, a job for forming a predetermined number of images is performed, for example, 50 images are formed and the recording material is passed (step S2).
It is determined whether or not the image forming operation exceeds the predetermined number (step S3).
However, if the image forming operation is finished before the predetermined number of sheets is exceeded, the fixing entrance guide member 711 is grounded via the high resistor 76 for the next image forming operation (step S9). . Here, this completes the image forming operation.
If the image forming operation has not been completed even though the predetermined number has been exceeded, the two positions A and B of the fixing inlet guide member 711 are set after passing the predetermined number. Each surface potential VA2 and VB2 is measured (step S4).
The measured potential is transmitted to the control unit 77 (step S5).
Then, it is determined whether the surface potential changes VA2-VA1 and VB2-VB1 are larger or smaller than the predetermined values of α and β (step S6).
At this time, if it is smaller than the respective threshold values α and β, it means that the potentials at the two positions A and B of the fixing inlet guide member 711 are not high in the recording material 2. In this case, if it is determined that VA2-VA1 and VB2-VB1 are smaller than the predetermined threshold values α and β, the contact with the recording material 2 in the image forming operation is also possible. It is determined that the fixing inlet guide member 711 is not charged, and the fixing inlet guide member 711 is grounded via the high resistor 76, and the next image forming operation is performed while preventing leakage of the transfer current. (Step S7) Here, an image forming operation can be further performed (Step S2).
On the other hand, when it is determined that the fixing inlet guide member 711 is grounded without passing through the high resistance body 76, the fixing inlet guide member 711 is grounded through the high resistance body 76 (step S8). In addition, an image forming operation can be further performed (step S2).
Further, when determining whether the surface potential changes VA2-VA1 and VB2-VB1 are larger or smaller than the predetermined threshold values α and β (step S6), the respective threshold values α are determined. If it is larger than β, it is determined that the fixing inlet guide member 711 is charged by contact with the recording material 2 by the image forming operation, and is grounded without the high resistor 76 (step S10). In addition, an image forming operation can be further performed (step S2).

FIG. 6 is an example of experimental data of surface potential and dust level. Since the threshold values α and β vary depending on the surface material of the conveying guide member 71 and the number of sheets to be passed, for example, the threshold value α is set with reference to experimental data as shown in FIG.
In this way, when the recording material 2 has a low resistance in a high temperature and high humidity environment by being grounded to the fixing entrance guide plate 711 via the high resistance body 76, the transfer is performed via the recording material 2 reaching the transfer region. It is possible to effectively avoid the situation where the current leaks to the conveying guide member 71, effectively prevent the transfer failure due to the transfer current leakage, and maintain good image quality.
Further, when the conveyance guide member 71 is charged, image dust accompanying charging of the conveyance guide member 71 can be effectively avoided, and good image quality can be maintained.

1 Image forming apparatus 2 Recording material
10 Transfer device
11 Intermediate transfer belt
12 Tension roller
13 Primary transfer roller
14 Belt cleaning device
15 Secondary transfer roller 20 Photosensitive drum 21 Exposure device 30 Charging device 40 Cleaning device
50 Developer
51 Development sleeve
60 Fixing device
61 Pressure roller
62 Fixing roller
70 Conveying path 71 Conveying guide member 711 Fixing entrance guide plate 712 Transfer exit guide plate 75 Changeover switch 76 High resistance body 77 Control unit 79 Surface potential meter 79
80 Paper feeder
81 Paper cassette
82 Paper feed roller
83 Registration Roller
84 Paper discharge roller

JP2001-139185

Claims (11)

A transfer device for transferring a toner image to a recording material to be conveyed;
A conveyance path through which a recording material having a transferred toner image is conveyed;
In an image forming apparatus including a fixing device that melts and fixes a toner image on a recording material,
The conveyance path has at least one conveyance guide member between the transfer device and the fixing device, and the conveyance guide member is grounded via a resistor or not via a resistor. Or an image forming apparatus that can be changed. The image forming apparatus according to claim 1, wherein the image forming apparatus includes a measuring unit that measures a surface potential of the conveyance guide member. The image forming apparatus according to claim 1, wherein the measuring device measures at least two positions of the conveyance guide member. The image forming apparatus according to claim 1, wherein at least two measuring devices are arranged in a transport direction of the transport guide member. The image forming apparatus according to claim 1, wherein the conveyance guide member is grounded without using a resistor based on measurement information of the measurement apparatus. The image forming apparatus according to claim 1, wherein the conveyance guide member is grounded via a resistor based on measurement information of the measurement apparatus. The image forming apparatus according to any one of claims 1 to 6, wherein the image forming apparatus includes at least two or more switching mechanisms for grounding via a high resistor and for grounding without a high resistance. apparatus. The image forming apparatus determines whether or not to install a high-resistance body on the conveyance guide member based on measurement information of the measurement apparatus after conveyance of the recording material for each predetermined number of sheets. The image forming apparatus according to any one of 1 to 7. The image forming apparatus according to claim 1, wherein the conveyance guide member is a fixing entrance guide plate for introducing a recording material into the fixing device. The image forming apparatus according to claim 1, wherein the conveyance guide member is a transfer outlet guide plate that guides a recording material from a transfer device. The image forming apparatus according to claim 1, wherein at least one of the measuring devices is movable.

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