JP2019074602A - Image forming apparatus - Google Patents

Abstract

To reduce an image defect occurring due to a reduction in surface resistance of an intermediate transfer belt, and notify a timing to replace the intermediate transfer belt while preventing unnecessary replacement of the intermediate transfer belt.SOLUTION: When a predetermined toner image on an intermediate transfer belt formed in an upstream station passes through a transfer unit in a downstream station, an image forming apparatus notifies information on replacement of the intermediate transfer belt on the basis of a charging current that is detected when an area of a photoconductor drum in the downstream station passing through the transfer unit passes through a charging area in the downstream station.SELECTED DRAWING: Figure 8

Description

  BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an image forming apparatus that uses an electrophotographic method to make an electrostatic image of an image carrier a visible image on transfer paper.

  In an image forming apparatus using an electrophotographic technology such as an electrophotographic copying machine or a laser printer, an image forming apparatus is known in which a toner image formed on a photosensitive drum is transferred to an intermediate transfer belt and then transferred to a recording material. ing. By this, it is possible to stably transfer the toner image to various recording materials.

  The intermediate transfer belt may be provided with a conductive powder-containing layer containing a conductive powder on the surface to adjust the surface resistance in order to improve the transferability. In such an intermediate transfer belt, due to the discharge in the transfer step, the chain or dispersed state of the conductive agent on the surface of the intermediate transfer member may change gradually, and the surface resistance value may change (decrease). When the surface resistance is reduced as described above, abnormal discharge is likely to occur when the toner image on the intermediate transfer belt is transferred to the transfer sheet at the secondary transfer portion. For this reason, it becomes easy to generate the image defect which an image loses in white. It is necessary to replace the intermediate transfer belt before abnormal discharge due to such a reduction in surface resistance of the intermediate transfer belt or an image defect such as "whiteout" occurs. For example, Patent Document 1 discloses that the life of the transfer belt is detected from the counter of the number of revolutions of the intermediate transfer belt, the application time of bias, and the intensity.

Japanese Patent Application Laid-Open No. 11-338271

  However, Patent Document 1 has the following problems. In the configuration of Patent Document 1, the life of the intermediate transfer belt is predicted from the counter of the number of rotations of the intermediate transfer belt, the application time of the bias, and the like. However, the surface resistance of the intermediate transfer belt is not detected. For this reason, it is not possible to appropriately grasp the timing at which an image adverse effect occurs due to the surface resistance change of the intermediate transfer belt. The surface resistance of the intermediate transfer belt is influenced by the use condition of the apparatus, the environment, individual variation of the intermediate transfer belt, and the like. Therefore, there is a limit in accurately predicting the surface resistance of the intermediate transfer belt, and it is difficult to inform the user of the replacement timing of the intermediate transfer belt correctly.

  Therefore, conventionally, the service life has to be set so that no image defect occurs even under the worst condition, and there is a problem that the intermediate transfer belt is unnecessarily replaced although it is still in a usable state. The

  Therefore, it is an object of the present invention to promote replacement of the intermediate transfer belt before an abnormal image is generated due to a reduction in the surface resistance of the intermediate transfer belt while suppressing unnecessary replacement of the intermediate transfer belt. An object of the present invention is to provide an image forming apparatus.

The present invention provides a first image forming unit for forming an image, and a second image forming unit for forming an image;
An intermediate transfer belt rotatably provided to which toner images formed by the first image forming unit and the second image forming unit are respectively transferred, and the first image forming unit and the second image forming A control unit for controlling the operation of the unit, and the first image forming unit detects an image carrier, a charging device for charging the image carrier in a charging region, and a current flowing through the charging device A current detection unit, and a transfer device for transferring a toner image formed on the image carrier to the intermediate transfer belt at a transfer region, and the first image forming unit rotates the intermediate transfer belt. The image forming apparatus is provided downstream of the second image forming unit with respect to the direction, and the control unit charges the surface of the image carrier with the charging device during non-image formation. Charged by the charging device When the surface of the image carrier passes through the transfer area, a predetermined transfer bias is applied to the transfer device, and when the predetermined transfer bias is applied, the second image forming unit A predetermined toner image formed on the intermediate transfer belt by the transfer belt to the transfer area of the first image forming unit, and the transfer area is transferred when the predetermined toner image passes the transfer area The first region of the image carrier passing through is moved toward the charging region, and the current flowing to the charging device when the first region passes the charging region is the charging current Ic. The charging current Ic is detected by the current detection unit, and an output signal for outputting information on the replacement of the intermediate transfer belt is output based on the charging current Ic.

  According to the present invention, an image capable of promoting replacement of the intermediate transfer belt before occurrence of an abnormal image due to a reduction in surface resistance of the intermediate transfer belt while suppressing unnecessary replacement of the intermediate transfer belt A forming device can be provided.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. FIG. 2 is a view for explaining a layer configuration of a charging roller and a layer configuration of a photosensitive drum of an image forming apparatus according to a first embodiment. FIG. 6 is an operation sequence diagram of the image forming apparatus according to the first embodiment. 5 is a graph showing the transition of the surface resistance of the intermediate transfer belt according to Example 1. When a solid red image is passed to the primary transfer portion of the cyan station, the charging current Ic flowing when the area of the photosensitive drum subjected to the primary transfer at the cyan station passes the charging area, the surface resistance of the intermediate transfer belt It is a schematic block diagram which shows the relationship of. FIG. 3 is a diagram showing the relationship between the post-transfer potential and the post-charge potential, which is caused by the surface resistance difference of the intermediate transfer belt according to Example 1, in (a) initial state and (b) durable state. FIG. 6 is a view for explaining a mechanism of causing a difference in post-transfer potential due to a surface resistance difference of the intermediate transfer belt according to the first embodiment. 5 is a flowchart for explaining the operation of the image forming apparatus according to the first embodiment. FIG. 6 is a view for explaining the layer configuration of a charging roller and the layer configuration of a photosensitive drum of an image forming apparatus according to a second embodiment. FIG. 5 is a schematic configuration diagram showing a relationship between a ratio of a charging current Ic to a charging current Iw and a surface resistance of an intermediate transfer belt. 6 is a flowchart for explaining the operation of the image forming apparatus according to the second embodiment. FIG. 10 is a schematic configuration diagram of an image forming apparatus according to a third embodiment. FIG. 14 is a flowchart for explaining the operation of the image forming apparatus according to the third embodiment.

Example 1
Hereinafter, preferred embodiments of the present invention will be exemplarily described in detail with reference to the drawings. However, relative arrangements, numerical values and the like of the components described in this embodiment are not intended to limit the scope of the present invention to them unless otherwise specified.

<Image forming apparatus>
FIG. 1 is a schematic cross-sectional view of the image forming apparatus 100. In the image forming apparatus 100, four image forming stations for forming toner images of respective color components are arranged in one line. Such an image forming apparatus 100 is called a tandem type image forming apparatus. In each image forming station, the image forming unit Y forms a yellow toner image, the image forming unit M forms a magenta toner image, the image forming unit C forms a cyan toner image, and the image forming unit Bk Form a black toner image. Since the image forming units Y, M, C, and Bk of each image forming station have the same configuration, the image forming unit Y that forms a yellow toner image will be described below, and the other image forming units M, C, and Bk Some of the explanations for

  The image forming unit Y includes a photosensitive drum 1a, a charging roller 2a, an exposure device 3a, a developing device 4a, a primary transfer roller 5a, and a drum cleaner 6a.

  The photosensitive drum 1a as an image carrier is a negatively chargeable organic photosensitive member (OPC) with a diameter of 30 mm, and rotates in the direction of the arrow at a process speed (circumferential speed) of 200 mm / s by driving of a driving device (not shown). It is driven. The photosensitive drum 1a is, as shown in FIG. 2, formed of a photogenerating layer 1r, a charge transport layer 1s, and a surface layer 1t containing a curable material on the surface of an aluminum cylinder (conductive drum base 1p). A photosensitive layer is provided.

  A high voltage power supply circuit (charging bias power supply) 20 is electrically connected to the charging roller 2a as the charging device. The high voltage power supply circuit (charging bias power supply) 20 includes a DC voltage generation circuit 21 and a DC voltage amplification circuit 22, and applies a charging bias generated by a combination of the DC voltage generation circuit 21 and the DC voltage amplification circuit 22 to the charging roller 2a. Do. In the present embodiment, the charging bias is −1300 V, and the potential (Vd) on the photosensitive drum 1 a is set to −700 V at the opposing position of the developing device 4 a. In FIG. 1, the DC voltage applied to the charging roller 2 a of the image forming unit Y is applied by the DC voltage generation circuit 21 a in the DC voltage generation circuit 21. Further, the magnitude of the DC voltage value is adjusted by the DC voltage amplification circuit 22 a in the DC voltage circuit 22. The direct current flowing through the direct current voltage generation circuit 21a is detected by the charging current detection circuit 101a as a current detection unit, and the detected charging current is recorded and controlled by the controller 12 as a control unit.

  The longitudinal length of the charging roller 2a is 320 mm, and as shown in FIG. 2, the lower layer 2q, the intermediate layer 2r, and the surface layer 2s are sequentially laminated from the bottom around the core metal (supporting member) 2p. It is a layer structure. The lower layer 2 q is a foam sponge layer for reducing charging noise, and the surface layer 2 s is a protective layer provided to prevent the occurrence of a leak even if there is a defect such as a pinhole on the photosensitive drum. .

More specifically, the specifications of the charging rollers 2a to 2d in the present embodiment are as follows.
Core metal 2p; 6 mm diameter stainless steel round bar lower layer 2 q; carbon dispersed foam EPDM, specific gravity 0.5 g / cm ³ , volume resistivity 10 ² to 10 ⁹ Ω, layer thickness 3.0 mm
Middle layer 2r; NBR-based rubber with carbon dispersion, volume resistivity 10 ² to 10 ⁵ Ω, layer thickness 700 μm
Surface layer 2s; dispersed tin oxide and carbon in resin of fluorine compound, volume resistivity 10 ⁷ to 10 ¹⁰ Ω, surface roughness (JIS standard 10 points average surface roughness Ra) 1.5 μm, layer thickness 10 μm

  The charging rollers 2a to 2d are urged toward the center of the photosensitive drum by a pressing spring 2t and pressed against the charging nip a with a predetermined pressing force against the surface of the photosensitive drum, and are driven by the rotational driving of the photosensitive drum And rotate in the direction of R2.

In the present embodiment, the charging roller having a total volume resistance of 1.0 × 10 ⁵ Ω was adopted.

  The exposure apparatus 3a is a laser beam scanner using a semiconductor laser, and has a light source for emitting a laser beam and an ASIC for controlling the light source based on an input image signal. The laser beam scans the surface of the photosensitive drum 1a uniformly charged to a predetermined potential, and forms an electrostatic latent image corresponding to the image signal input on the photosensitive drum 1a. In the present embodiment, the light portion potential (VL) of the photosensitive drum 1a irradiated with the laser light was set to -200V.

  The developing device 4a contains a two-component developer including toner and a carrier. Further, a developing bias in which a DC voltage (Vdc) and an AC voltage (Vac) are superimposed is applied to the developing device 4a. Specifically, the frequency of the AC voltage is 8 kHz, the DC voltage is -550 V, and the peak-to-peak voltage Vpp of the AC voltage is 1800 V.

  The primary transfer roller 5a is electrically connected to a power supply unit (not shown). The transfer power supply circuit shown in the drawing connected to the primary transfer roller 5a continuously applies transfer biases of several different voltage values to the photosensitive drum 1a charged to a desired charging potential by the charging roller 2a. And each current value is detected and the current-voltage characteristic is stored. From the obtained current-voltage characteristics, a voltage necessary to obtain a predetermined transfer current is calculated, and a transfer bias to be applied at the time of image formation is determined. The control for determining the primary transfer bias is referred to herein as primary transfer ATVC control, which is performed at the time of non-image formation.

  The drum cleaner 6a includes a plate-like elastic member for collecting the toner on the photosensitive drum 1a.

  The intermediate transfer belt 7 is wound around a plurality of rollers, and is rotationally driven in the arrow direction by a drive roller. The intermediate transfer belt 7 is made of polyimide resin. In this embodiment, a polyimide resin and a predetermined amount of a resistance adjuster such as carbon are dispersed and mixed, and the center resistance of the surface resistance at 100 V application is adjusted to about 10 ^ 12 Ω. Be done. Further, as the intermediate transfer belt 7, in addition to the polyimide resin, a heat resistant high strength resin such as a polyester resin, a polyether ketone resin, and a polysulfide resin can be used.

  Around the intermediate transfer belt 7, a secondary transfer roller 8, an intermediate transfer belt cleaner 30, and a density detection sensor 50 are provided. An inner roller is provided on the opposite side of the secondary transfer roller 8 via the intermediate transfer belt 7. The secondary transfer roller 8 presses the intermediate transfer belt 7 against the inner roller, and the intermediate transfer belt 7 and the secondary transfer roller 8 form a nip. The secondary transfer roller 8 and the inner roller are electrically connected to a power supply unit (not shown), and the secondary transfer bias is determined by the secondary transfer ATVC control which is the same control as the primary transfer ATVC control.

<Image forming apparatus process>
Next, an image forming operation in which the image forming apparatus 100 forms an image on the recording material P based on the image data subjected to image processing will be described.

  In the image forming unit Y, first, the charging roller 2a uniformly charges the photosensitive drum 1a, and the exposure device 3a controls the laser light based on the image data. The laser beam of the exposure device 3a scans the photosensitive drum 1a, and an electrostatic latent image is formed on the photosensitive drum 1a. The developing device 4a develops the electrostatic latent image on the photosensitive drum 1a using yellow toner. As a result, a yellow toner image is formed on the photosensitive drum 1a. The yellow toner image is transferred from the photosensitive drum 1 a to the intermediate transfer belt 7 by applying a primary transfer bias determined by the primary transfer ATVC control by the primary transfer roller 5 a. In this embodiment, the primary transfer current is set to 20 μA by ATVC control. The toner remaining on the photosensitive drum 1a is removed by the drum cleaner 6a.

  The toner image transferred to the intermediate transfer belt 7 is conveyed to the transfer nip portion between the intermediate transfer belt 7 and the secondary transfer roller 8. At this time, the recording material P is conveyed by the registration roller 11 to the transfer nip portion so as to contact the toner image on the intermediate transfer belt 7. While the toner image on the intermediate transfer belt 7 and the recording material P pass through the transfer nip portion, the power source unit performs a secondary transfer bias determined by the secondary transfer ATVC control between the secondary transfer roller 8 and the inner roller. Supply. Thus, the toner image on the intermediate transfer belt 7 is transferred onto the recording material P. The toner remaining on the intermediate transfer belt 7 without being transferred to the recording material P is removed by the belt cleaner 30.

  The recording material P carrying the toner image is conveyed to the fixing device 9, and the heat roller 9a applies heat to the recording material P carrying the unfixed toner image at the fixing nip portion, thereby applying the toner image onto the recording material P Melt and fix. Then, the recording material P on which the toner image is fixed is discharged from the image forming apparatus 100 by a discharge roller (not shown).

<Operation Process of Image Forming Apparatus>
FIG. 3 is an operation sequence diagram of the image forming apparatus.

a. Initial rotation operation (pre-multi-rotation process)
It is a start operation period (start operation period, warming period) when the printer is started. When the power switch is turned on, the photosensitive drum is rotationally driven, and a preparation operation of predetermined process equipment such as start-up of the fixing device to a predetermined temperature is performed.

b. Print preparation rotation operation (pre-rotation process)
Print signal-This is the preparatory rotation operation period before image formation from the time when the image formation (printing) process operation is actually performed until the print operation is performed during the initial rotation operation, and is performed following the initial rotation operation when the print signal is input. Be done. When the print signal is not input, the drive of the main motor is temporarily stopped after the end of the initial rotation operation to stop the rotational drive of the photosensitive drum, and the printer is kept in the standby state until the print signal is input. When the print signal is input, the print preparation rotation operation is performed.

c. Printing process (image forming process, image forming process)
When the predetermined printing preparation rotating operation is completed, the image forming process is subsequently executed on the rotating photosensitive drum, and the toner image formed on the surface of the rotating photosensitive drum is transferred to the transfer material, and the fixing process of the toner image is performed by the fixing device. The image formation is printed out.

  In the case of the continuous printing (continuous printing) mode, the above-described printing process is repeatedly performed for a predetermined set number of printing n.

d. Paper interval process In the continuous printing mode, after the rear end of one transfer material passes the transfer position, the non-passing of the recording sheet at the transfer position occurs until the front end of the next transfer material reaches the transfer position. It is a paper condition period.

e. The post-rotation operation is a period in which the driving of the main motor is continued for a while after the printing process of the last transfer material is finished, the photosensitive drum is rotationally driven, and the predetermined post-operation is performed.

f. When the predetermined post-rotation operation is completed, the drive of the main motor is stopped and the rotational drive of the photosensitive drum is stopped, and the printer is kept in the standby state until the next print start signal is input.

  In the case of printing on only one sheet, after the printing is completed, the printer goes through a post-rotation operation and goes into a standby state.

  In the standby state, when the print start signal is input, the printer shifts to the pre-rotation step.

  The time of the printing process of c is the time of image formation (the time of transfer process), and the initial rotation operation of a, the pre-rotation operation of b, the sheet interval process of d, and the post-rotation operation of e are non-image formation. The above-described ATVC control of primary transfer and secondary transfer operates at the time of pre-multi-rotation operation of (a) or pre-rotation operation of (b) according to a predetermined frequency and timing of detection of a change in the environment. , Determine the required primary and secondary transfer biases.

<Change Characteristics of Surface Resistance of Intermediate Transfer Belt>
FIG. 4 is a graph showing the surface resistance of the intermediate transfer belt 7 as it passes through in each of the usage conditions in the tandem type image forming apparatus as described above.

  In (a) of FIG. 4, the number of single-sided sheets of plain paper in three environments (NL: temperature 23 ° C., humidity 5%, NN: temperature 23 ° C., humidity 50% HH: temperature 30 ° C., humidity 80%) 6 is a graph showing a reduction in surface resistance of the intermediate transfer belt. As the environment is NL, that is, the environment in which the amount of water in the environment is lower, the resistance of the paper is increased, and the secondary transfer roller 8 needs a higher secondary transfer bias necessary to discharge the toner onto the paper. As the secondary transfer bias increases, the discharge at the secondary transfer portion also increases, thereby increasing the change in the chain or dispersed state of the conductive agent on the surface of the intermediate transfer member, and as a result, the surface resistance of the intermediate transfer belt 7 decreases. Promoted.

  (B) of FIG. 4 is a graph showing plain paper, single-sided sheet passing, double-sided sheet count, and reduction in surface resistance of the intermediate transfer belt. The number of sheets passed on both sides means that two sheets have passed per sheet. In the double-sided sheet passing, the paper passes through the fixing device 9, and the paper again reaches the secondary transfer roller 8, and the second side is transferred. The paper passing through the fixing device 9 evaporates the moisture in the paper and the resistance of the paper itself is increased, and the second side of the paper is a secondary transfer roller necessary for secondary transfer to discharge toner onto the paper The bias is higher. That is, the surface resistance of the intermediate transfer belt 7 is more likely to decrease when passing on both sides.

  (C) of FIG. 4 is a graph showing the number of sheets of paper on which one side of plain paper and recycled paper is passed and the decrease in surface resistance of the intermediate transfer belt. The recycled paper has lower smoothness than plain paper, and the secondary transfer roller 8 is likely to generate uneven discharge with respect to the intermediate transfer belt 7 and tends to generate strong discharge. Therefore, it is known that the surface resistance of the intermediate transfer belt 7 is more likely to be reduced with recycled paper than with plain paper.

  In the present embodiment, when the surface resistance of the intermediate transfer belt 7 is 10 7 Ω or less, when transferring the toner image on the intermediate transfer belt to the transfer sheet, a defective image is generated such that the image is blanked out due to abnormal discharge. Occurred. This white space was an image defect in which it was not possible to distinguish characters. It is appropriate to prompt the exchange of the intermediate transfer belt 7 before such a white spot image occurs.

  Here, instead of detecting the surface resistance value of the intermediate transfer belt 7 as in the prior art, it is also considered to predict the surface resistance value of the intermediate transfer belt based on the number of sheets for image formation and the like, and promote replacement of the intermediate transfer belt. Be However, the surface resistance value of the intermediate transfer belt 7 depends on the use condition, the environment, and the individual variation of the intermediate transfer belt. For this reason, it has been difficult to accurately predict the surface resistance value of the intermediate transfer belt.

  Therefore, in the present invention, attention is paid to a parameter having a correlation with the surface resistance of the intermediate transfer belt, and the timing for promoting replacement of the intermediate transfer belt 7 is determined based on the detection result of the parameter.

  The inventors of the present invention have found that the surface resistance of the intermediate transfer belt 7 has a correlation with the charging current detected under predetermined conditions as a result of the sincerity examination. That is, the case where a resistor such as a solid image formed at the upstream station is transported to the transfer portion of the downstream station is considered. In this case, it has been found that the post-transfer potential of the photosensitive drum of the downstream station which has received the primary transfer has a characteristic depending on the surface resistance of the intermediate transfer belt 7 in the transfer portion of the downstream station.

  Therefore, in the present embodiment, by utilizing this phenomenon, the surface resistance value of the intermediate transfer belt 7 is predicted from the charging current of the downstream station, and the replacement timing is determined.

<Measurement of charging current correlated to surface resistance of intermediate transfer belt>
First, in the above-described tandem type image forming apparatus, 100% printing (solid) is formed at the image forming stations of yellow (Y) and magenta (M) which are two image forming stations on the upstream side. These Y and M solid images are superimposed on the intermediate transfer belt 7 to form a red solid image which is a secondary color solid image. These solid images are formed as so-called horizontal band images formed in the printable area maximum width orthogonal to the image conveyance direction. That is, a red solid (R solid) horizontal band toner image in which the Y solid horizontal band toner image and the M solid horizontal band toner image are superimposed is formed on the intermediate transfer belt 7.

  Further, the image forming station of cyan (C), which is an image forming station one downstream, does not form the above-mentioned solid lateral band toner image, but applies the primary transfer bias in the same manner as in the normal image formation. Then, the R-solid horizontal band toner image passes through a primary transfer portion as a transfer area formed by the photosensitive drum 1c and the transfer roller 5c in a cyan image forming station (hereinafter also referred to as Cst). At this time, the R-solid-lateral-band toner image contact portion of the photosensitive drum 1c is moved to the charging region which is the contact portion with the charging roller 2c by the drive rotation of the photosensitive drum 1c. The current flowing to the charging roller 2c at this time is referred to as charging current Ic (hereinafter, also referred to as charging current Ic for R solid image). The charging current Ic is detected by the charging current detection circuit 101c. FIG. 5 is a graph showing the relationship between the charging current Ic of the R solid image and the surface resistance of the intermediate transfer belt 7. The amount of applied toner on the R solid lateral band toner image was 1.0 (mg / cm 2). Further, the charging potential of the photosensitive drum 1c of Cst was -700V.

  According to the result of FIG. 5, the charging current Ic of the R solid image has a correlation with the surface resistance value of the intermediate transfer belt 7, and the charging roller 2c of the C image forming station is decreased as the surface resistance value of the intermediate transfer belt 7 decreases. It was found that the flowing charging current decreased.

  This phenomenon will be described in detail with reference to FIG.

  FIG. 6 is a schematic cross-sectional view when the above-mentioned R solid horizontal band toner image reaches the transfer nip portion of the cyan image forming station, and shows the drum potential of the photosensitive drum 1c. On the left side of the graph showing the drum potential shown in FIG. 6, the surface potential of the photosensitive drum 1c (transfer) at the Vp position on the photosensitive drum 1c after the R solid horizontal band toner image contact portion contacts the photosensitive drum 1c The afterpotential Vp is shown. The graph shown on the right side of FIG. 6 shows the surface potential (charging potential) Vq of the photosensitive drum 1c at the position Vq after being recharged by the charging roller 2c.

  6A shows the case of the intermediate transfer belt 7 in the initial state where the surface resistance value is high, and FIG. 6B shows the intermediate state in the durable state in which the surface resistance value is lowered due to sheet passing. The case of the transfer belt 7 is shown.

  The vertical axis of each graph represents the surface potential of the photosensitive drum 1c, and in the present embodiment, the arrow direction indicates a negative potential.

  Reference is made to FIG. 6A showing the case of the intermediate transfer belt 7 in the initial stage. In this case, the post-transfer potential Vp on the photosensitive drum 1c of the portion in contact with the R solid horizontal band toner image has an absolute value larger than the post-transfer potential Vp on the photosensitive drum 1c in the contact portion with the non-toner image portion. . The post-transfer potential of the photosensitive drum 1c is higher on the part where the R solid horizontal band toner image contacts, than on the part where the toner image is not present. In this embodiment, as shown in FIG. 6A, the post-transfer potential Vp of the photosensitive drum 1c is -200 V at the contact portion with the toner image free portion (also referred to as solid white portion or solid white region). The contact portion with the horizontal band toner image bearing portion was -300V. This is because the R solid horizontal band toner image serves as a resistor at the R solid horizontal band toner image contact portion. Therefore, the inflow current to the photosensitive drum 1c when the primary transfer bias is applied decreases, and the post-transfer potential Vp of the photosensitive drum 1c does not drop compared to the solid white contact portion.

  Thereafter, the photosensitive drum 1c is recharged to the target charging potential Vq at the time of image formation by the charging roller 2c. However, since the post-transfer potential Vp is higher at the R-solid horizontal band toner image contact portion than at the solid white contact portion, the potential difference with the charging potential Vq decreases. As a result, compared to the solid white contact portion, the charging current at the solid red toner image contact portion decreases. In FIG. 6A, the post-transfer potential Vp of the photosensitive drum 1c at the R solid horizontal band toner image contact portion is -300 V, the charging potential Vq is -700 V, and the potential difference thereof is 400 V. It is stated that the charging current was 10 .mu.A.

  FIG. 6 (b) similarly shows the case of the intermediate transfer belt 7 in which the surface resistance value after passing paper has been lowered. When the surface resistance value of the intermediate transfer belt 7 is low, the post-transfer potential Vp of the photosensitive drum 1c at the R solid area toner image contact portion is higher than when the surface resistance value is high. The post-transfer potential Vp of the intermediate transfer belt 7 at which the surface resistance value has been lowered was -200 V at the solid white contact portion and -500 V at the R solid lateral band toner image contact portion.

  Thereafter, similarly, the photosensitive drum 1c is recharged to the target charging potential Vq at the time of image formation by the charging roller 2c. However, since the potential difference between the post-transfer potential Vp and the charging potential Vq of the photosensitive drum 1c at the R solid horizontal band toner image contact portion is 200 V, the charging current detected by the charging current detection circuit 101c is also reduced to 5 μA.

  As described above, when the surface resistance value of the intermediate transfer belt 7 is lowered due to the sheet feeding durability, the post-transfer potential Vp of the R solid horizontal band toner image contact portion is increased and the potential difference with the charging potential Vq is decreased. As a result, the charging current flowing to the charging roller 2c is reduced.

  FIG. 7 is a mechanism diagram for explaining the above-mentioned phenomenon. In the case of the intermediate transfer belt 7 having a high surface resistance as in the initial stage, as shown in FIG. 7, the toner of the R solid horizontal band toner image becomes a resistor, and the current flowing from the transfer roller 5c to the photosensitive drum 1c Decrease. Further, in the case of the intermediate transfer belt 7 whose surface resistance value is lowered due to the paper passage durability, as shown in FIG. I will. One is a current flowing from the transfer roller 5c in the direction of the photosensitive drum 1c, and the other is a current flowing across the surface of the intermediate transfer belt 7 having a low surface resistance value. As a result, the transfer current corresponding to the current flowing to the photosensitive drum 1c is decreased, so that the post-transfer potential Vp of the photosensitive drum 1c does not easily decrease, and as a result, the charging current is decreased.

  Therefore, in the present embodiment, when a toner image (for example, R solid horizontal band toner image) with a large amount of applied toner as a resistor passes through the transfer portion of the downstream station, the inflow current from the transfer roller to the photosensitive drum decreases. Use the phenomenon that The resistance value of the intermediate transfer belt 7 is measured indirectly, noting that the post-transfer potential after passing through the transfer nip changes according to the surface resistance value of the intermediate transfer belt 7.

<Intermediate Transfer Belt Replacement Display>
FIG. 8 shows an operation flowchart (detection mode) of this embodiment.

  The timing for measuring the surface resistance of the intermediate transfer belt 7 was once for every 1000 sheets.

  First, the controller 12 executes the detection mode of the present embodiment after performing the pre-rotation operation in the pre-rotation process of FIG. 3. The pre-rotation operation rotates the photosensitive drums 1 a to 1 d and the intermediate transfer belt 7. Then, in each of the image forming sections, the photosensitive drums 1a to 1d are charged by the charging rollers 2a to 2d as in the case of the normal image formation. Then, the primary transfer bias is applied to the transfer rollers 5a to 5d when the respective regions of the charged photosensitive drums 1a to 1d pass through the portions facing the transfer rollers 5a to 5d. During the detection mode, charging and transfer bias are continuously applied.

  Next, the controller 12 causes the R (solid yellow) toner image to be formed on the intermediate transfer belt 7 by the yellow (Y) image forming unit and the magenta (M) image forming unit. (S101) At this time, the exposure device of the cyan image forming unit is turned off so as not to perform image exposure. That is, solid white is formed on the cyan image forming portion. Here, the application amount of the R solid horizontal belt toner image is 1.0 (mg / cm 2), the width in the longitudinal direction is the maximum developable width, and the width in the rotational direction of the intermediate transfer belt is 10 mm.

  The R solid horizontal band toner image arrives at the transfer nip portion between the photosensitive drum 1c and the transfer roller 5c in the cyan (C) image forming portion (S102). Then, the charging current Ic detected by the charging current detection circuit 101c is measured when the portion (first region) of the photosensitive drum 1c in contact with the R solid horizontal belt toner image reaches the charging roller 2c (S103).

Next, the controller 12 determines whether the charging current Ic is less than 5 μA (less than a predetermined value) (S104). When the charging current Ic is less than 5 μA, the controller 12 displays (notifies) information on the replacement of the intermediate transfer belt (a message prompting the replacement of the intermediate transfer belt) on the operation unit 13. (S105)
When the charging current Ic is 5 μA or more in (S104), the flow is ended.

  With the above-described configuration, it is possible to properly promote the exchange of the intermediate transfer belt before the end of the life when the whiteout image occurs under various use conditions. In addition, since the intermediate transfer belt can be used to the end of its life, an image forming apparatus with low running cost can be provided.

  In the present embodiment, the configuration for causing the operation unit 13 to display information prompting replacement of the intermediate transfer belt 7 has been described as an example, but the present invention is not limited to this. For example, it may be displayed on an external device or the like connected to the main body. In this case, an output signal for causing the external device to display information on replacement is output to the external device.

Example 2
The second embodiment is the same as the first embodiment except that the configuration of the photosensitive drum is different. Therefore, the description will be omitted and only the parts different from the first embodiment will be described. In addition, the parts not described in particular are the same as in Example 1 described above. Since the image forming units Y, M, C, and Bk of each image forming station have the same configuration, the image forming unit Y that forms a yellow toner image will be described below, and the other image forming units M, C, and Bk Some of the explanations for

  In Example 1, the surface layer 1t of the photosensitive drum 1a contains a curable material. For this reason, a long-lived photosensitive drum was adopted, in which the scraping amount of the photosensitive drum 1a was extremely low, that is, the capacity fluctuation of the photosensitive drum was hardly caused.

  Therefore, if the charging potential and the transfer current are constant, the pre-charging potential is constant, and the current flowing to the charging roller 2a is constant when solid white passes.

  In the present embodiment, the photosensitive drum 1a is, for example, the photosensitive drum without the surface layer 1t shown in FIG.

  As shown in FIG. 9, the photosensitive drum 1a includes an undercoat layer 1q for suppressing light interference and improving adhesion of the upper layer, and a photogenerating layer 1r on the surface of an aluminum cylinder (conductive drum base) 1p. The charge transport layer 1s is formed by applying three layers in order from the bottom.

  In such a configuration, the charge transport layer 1s is worn out along with the paper passage durability. That is, even if the potential before charging is constant, the absolute value of the charging current flowing to the charging roller when solid white passes increases as the photosensitive drum is scraped, even though the capacity of the photosensitive drum fluctuates.

In addition, even if the transfer current is constant, the post-transfer potential also changes as the capacity of the photosensitive drum fluctuates. As the photosensitive drum is scraped, the amount of decrease in the post-transfer potential decreases (the charge removal effect in transfer decreases)
That is, in a system in which the capacity of the photosensitive drum fluctuates, as in Example 1, when the solid R is formed on the intermediate transfer belt 7, the intermediate transfer belt 7 is the absolute value of the charging current in the cyan image forming portion. It is difficult to measure the surface resistance of

  Therefore, in the present embodiment, in addition to the charging current Ic of the R solid image as in the first embodiment, the measurement is performed in a state in which the R solid image described in the first embodiment is replaced with a white solid image (white solid area). Use the charging current Iw. That is, an area (solid white area) in which a toner image is not formed is formed on the intermediate transfer belt 7, and the white solid area is allowed to pass through the transfer portion of the cyan station. At this time, when the area of the photosensitive drum 1c of the cyan station passing the transfer portion of the cyan station reaches the charging area in contact with the charging roller 2c, the charging current flowing to the charging roller 2c is taken as the charging current Iw. The charging current Iw is detected by the charging current detection circuit 101c. Then, based on the charging current Ic of the R solid image and the charging current Iw of the white solid image, the decrease in the surface resistance of the intermediate transfer belt 7 was determined. In this embodiment, the ratio (Ic / Iw) of the charging current Ic of the R solid image and the charging current Iw of the white solid image is used as information correlated with the surface resistance of the intermediate transfer belt 7.

  As described above, by using (Ic / Iw), it is possible to cancel the influence of the fluctuation of the capacity of the photosensitive drum and to detect the surface resistance of the intermediate transfer belt 7 with high accuracy.

  FIG. 10 is a graph showing the relationship when the surface resistance of the intermediate transfer belt 7 is taken along the horizontal axis, with the ratio of the charging current Ic of the R solid image and the charging current Iw of the white solid image as the vertical axis. The loading amount of R solid was 1.0 (mg / cm 2). Further, the charging potential of the photosensitive drum 1c of Cst was -700V.

  From FIG. 10, (R solid image charging current Ic) / (white solid image charging current Iw) has a correlation with the surface resistance of the intermediate transfer belt 7. That is, it was found that (R solid image charging current Ic) / (white solid image charging current Iw) decreases as the surface resistance of the intermediate transfer belt 7 decreases.

  Therefore, in the present embodiment, the surface resistance of the intermediate transfer belt 7 is detected from (charging current Ic of solid R image) / (charging current Iw of white solid image) in FIG.

  FIG. 11 shows an operation flowchart of this embodiment.

  The timing for measuring the surface resistance of the intermediate transfer belt 7 was once for every 1000 sheets. First, the controller 12 rotates the photosensitive drums 1 a to 1 d and the intermediate transfer belt 7 in the pre-rotation step of FIG. 3. Then, in each of the image forming sections, the photosensitive drums 1a to 1d are charged by the charging rollers 2a to 2d as in the case of the normal image formation. Then, the primary transfer bias is applied to the transfer rollers 5a to 5d when the respective regions of the charged photosensitive drums 1a to 1d pass through the portions facing the transfer rollers 5a to 5d.

  Next, the controller 12 causes the R (solid yellow) toner image to be formed on the intermediate transfer belt 7 by the yellow (Y) image forming unit and the magenta (M) image forming unit. (S201) At this time, the exposure device of the cyan image forming unit is turned off so as not to perform image exposure. That is, solid white is formed on the cyan image forming portion.

  The amount of R solid was 1.0 (mg / cm 2), the width in the longitudinal direction was the maximum image forming width (maximum developable area width), and the width in the rotational direction of the intermediate transfer belt was 10 mm.

Next, in (S201), the R solid horizontal band toner image and the white solid area formed on the intermediate transfer belt 7 reach the transfer nip portion formed by the photosensitive drum 1c and the transfer roller 5c of the cyan image forming portion. (S202)
Next, the controller 12 controls the charging current Ic flowing to the charging roller 2c by the charging current detection circuit 101c when the portion of the photosensitive drum 1c in contact with the R solid horizontal band toner image comes to the charging area contacting the charging roller 2c. To detect. (S203)
Similarly, the controller 12 controls the charging current Iw flowing through the charging roller 2c when the portion (second region) of the photosensitive drum 1c in contact with the white solid region comes in the charging region contacting the charging roller 2c. It detects with 101c. (S203)
Next, the controller 12 determines whether the ratio Ic / Iw of the charging current is less than 0.3 (S204). When Ic / Iw is less than 0.3, the controller 12 causes the operation unit 13 to display a message prompting replacement of the intermediate transfer belt. (S205)
If Ic / Iw is 0.3 or more in (S204), the flow is ended.

  According to the above configuration, even when the photosensitive drum is easily scraped and the volume fluctuation is large, the effect of the intermediate transfer belt can be properly promoted before the lifetime where the white spot image occurs under various use conditions. In addition, since the intermediate transfer belt can be used to the end of its life, an image forming apparatus with low running cost can be provided.

  In this embodiment, an example in which the replacement timing of the intermediate transfer belt 7 is determined based on the ratio of Iw to Ic has been described, but the difference between Iw and Ic may be used.

[Example 3]
In this embodiment, an image forming apparatus having a discharging unit on the photosensitive drum will be described. The present embodiment 3 has the same configuration as that of the embodiment 1 except that the charge removing means is provided, and therefore the description thereof is omitted, and only the portions different from the embodiment 1 will be described. In addition, the parts not described in particular are the same as in Example 1 described above. Since the image forming units Y, M, C, and Bk of each image forming station have the same configuration, the image forming unit Y that forms a yellow toner image will be described below, and the other image forming units M, C, and Bk Some of the explanations for

  FIG. 12 is a schematic block diagram showing a full color image forming apparatus of this embodiment.

  In this embodiment, a pre-exposure device 10a as a charge removing unit is provided between the drum cleaning device 6a and the transfer roller 5a.

  The pre-exposure device 10a includes an arrayed light source (hereinafter simply referred to as "LED") in which a plurality of LEDs are aligned in the rotational axis direction of the photosensitive drum 1, and the voltage applied to the LEDs is controlled to adjust the light amount. Be done. In the present embodiment, the pre-exposure device 10a has a light source wavelength peak at 400 nm to 800 nm, and can be controlled in the range of the light amount (pre-exposure light amount) 0 Lux · sec to 40 Lux · sec on the surface of the photosensitive drum 1a. . In the present embodiment, the amount of pre-exposure light is set to 30 Lux · sec in order to discharge the potential after transfer to around 0 V.

  As described above, in the image forming apparatus provided with the pre-exposure device, the potential after transfer of the photosensitive drum can be lowered to around 0 V by performing pre-exposure. As in the first and second embodiments, when the R solid toner to be a resistor comes to the Cst transfer nip portion and at other times as well, the pre-charge potential is around 0 V in both cases. The current is constant without the influence of the upstream toner.

  That is, when there is a pre-exposure device and the exposure operation of the pre-exposure device is ON as in the case of normal image formation, toner is formed on the upstream st as in the first and second embodiments. The life of the intermediate transfer belt 7 can not be determined by the charging current.

  Therefore, a flowchart in the present embodiment is shown in FIG.

  The timing for measuring the surface resistance of the intermediate transfer belt 7 was once for every 1000 sheets.

  First, in the pre-rotation step of FIG. 3, the controller 12 turns off the pre-exposure irradiation of the pre-exposure device 10 c of Cst. (S301) Incidentally, the pre-exposure device 10c is kept off until the end of the flow. Next, the controller 12 rotates the photosensitive drums 1a to 1d and the intermediate transfer belt 7 in the pre-rotation step of FIG. Then, in each of the image forming sections, the photosensitive drums 1a to 1d are charged by the charging rollers 2a to 2d as in the case of the normal image formation. Then, the primary transfer bias is applied to the transfer rollers 5a to 5d when the respective regions of the charged photosensitive drums 1a to 1d pass through the portions facing the transfer rollers 5a to 5d.

  Next, the controller 12 causes the R (solid yellow) toner image to be formed on the intermediate transfer belt 7 by the yellow (Y) image forming unit and the magenta (M) image forming unit. (S302) At this time, the exposure device of the cyan image forming unit is turned off so as not to perform image exposure. That is, solid white is formed on the cyan image forming portion. (S302) The amount of R solid was 1.0 (mg / cm 2), the width in the longitudinal direction was a developable area, and the width in the rotational direction of the intermediate transfer belt was 10 mm.

  The R solid reaches the transfer nip portion between the photosensitive drum 1 c and the transfer roller 5 c in the C image forming portion. (S303) Next, the controller 12 measures the charging current Ic flowing to the charging current detection circuit 101c when the R solid contact portion of the photosensitive drum 1c reaches the charging region in contact with the charging roller 2c (S304) ).

Next, the controller 12 determines whether the charging current Ic is less than 5 μA (S305). When the charging current Ic is less than 5 μA, the controller 12 causes the operation unit 13 to display a message prompting replacement of the intermediate transfer belt (S306).
When the charging current Ic is 5 μA or more in (S305), the flow is ended.

  According to the above configuration, even in the image forming apparatus having the pre-exposure device, the effect of the intermediate transfer belt can be properly promoted before the life of the whiteout image under various use conditions. In addition, since the intermediate transfer belt can be used to the end of its life, an image forming apparatus with low running cost can be provided.

(Others)
In Example 2, the method of detecting the life of the intermediate transfer belt from the ratio of the charging current at the time of the R solid of Cst and the charging current at the time of the solid white, uses a curable material for the surface layer of Examples 1 and 3. The present invention is also effective for the photosensitive drum used with almost no capacity fluctuation.

  In the present embodiment, a four-color tandem system of Y, M, C, and Bk is exemplified, but, for example, three colors of Y, M, and C may be used. Even when the image forming portion for developing toners other than Y, M, C and Bk increases, the life of the intermediate transfer belt is detected from the charging current when the upstream secondary color toner passes the downstream station Doing is also effective.

  In Examples 1 to 3, the tandem system of Y, M, C, and Bk in order is taken as an example, R which is a secondary color of Y and M is transferred, and the value of the charging current of Cst is measured. An example is to detect the life of the transfer belt. However, it is equally effective to transfer R and measure the value of Bkst charging current.

  It is also obvious that measuring the charging current with Bkst has the same effect on G (green), which is the secondary color of Y and C, and B (blue), which is the secondary color of M and C. It is.

  In this embodiment, it is a representative example that the upstream secondary color solid is placed on the intermediate transfer belt and the charging current of the downstream st is detected. The reason is that the larger the amount of toner as the resistor, the more the change of the charging current in the downstream st, and the higher the accuracy. Also, since the secondary color solid usually becomes the upper limit of the toner amount formed by the image forming apparatus in many cases, the density control of the normal image forming apparatus is also used to specify the toner amount to be placed on the intermediate transfer belt shape. It is recommended that the surface resistance detection control of this embodiment be performed with a solid secondary color. However, even though the accuracy is low, even if the primary color solid is not intended to be transferred onto paper, for example, it is also possible to place the third color and measure the charging current at the final st to determine the life of the intermediate transfer belt. It is available.

  In the present embodiment, a so-called DC charging method in which a direct current voltage is applied to the charging roller and a potential is applied to the photosensitive drum is taken as an example. However, even in the AC charging method in which an AC voltage is superimposed on a DC voltage on a charging roller, the difference between the potential before charging and the potential after charging is detected as a DC current. It is obvious.

  In this embodiment, control is performed to transfer the horizontal band of the solid secondary color at a timing of once per 1000 sheets. However, this lateral band is not only transferred for this embodiment, but, for example, lateral band formation for maintaining the surface property of the photosensitive drum CLN and the transfer belt CLN, and the developer life in the developing device For maintenance, it can be used in combination with control for discharging toner. By doing so, it is also possible to reduce the amount of toner used only for this control.

Reference Signs List 1 photosensitive drum 2 charging device 3 exposure device 4 developing device 5 primary transfer roller 6 drum cleaner 7 intermediate transfer belt 8 secondary transfer portion 9 fixing device 20 high voltage power supply circuit (charging bias power supply)
100 Image forming device P Recording material

Claims (6)

A first image forming unit for forming an image;
A second image forming unit for forming an image;
An intermediate transfer belt provided rotatably and to which the toner images formed by the first image forming unit and the second image forming unit are respectively transferred;
A control unit that controls operations of the first image forming unit and the second image forming unit;
The first image forming unit includes an image carrier, a charging device for charging the image carrier in a charging region, a current detection unit for detecting a current flowing to the charging device, and the image carrier. A transfer device for transferring the transferred toner image to the intermediate transfer belt in a transfer area, and the first image forming unit is downstream of the second image forming unit with respect to the rotational direction of the intermediate transfer belt. An image forming apparatus provided,
The controller charges the surface of the image carrier with the charging device during non-image formation, and the surface of the image carrier charged by the charging device passes through the transfer area. A predetermined transfer bias is applied to the transfer device, and when the predetermined transfer bias is applied, the predetermined toner image formed on the intermediate transfer belt by the second image forming unit is used as the first toner image. The first area of the image carrier which passes through the transfer area of the image forming unit and passes the transfer area when the predetermined toner image passes through the transfer area is moved toward the charging area The charging current Ic is detected by the current detection unit when the charging current Ic is a current flowing through the charging device when the first area passes through the charging area, and the charging current Ic is detected based on the charging current Ic. Previous Image forming apparatus and outputs an output signal for outputting information about the replacement of the intermediate transfer belt.   The image forming apparatus further includes a third image forming unit disposed upstream of the second image forming unit with respect to the rotational direction of the intermediate transfer belt and forming a toner image on the intermediate transfer belt, wherein the predetermined toner image is 2. The image forming apparatus according to claim 1, wherein the solid image formed by the second image forming unit and the solid image formed by the third image forming unit are superimposed.   The image forming apparatus according to claim 1, wherein the control unit outputs the output signal when the charging current Ic is less than a predetermined value.   In the detection mode for detecting the charging current Ic, when the predetermined transfer bias is applied, the controller controls the white solid area where the toner image is not formed in the area of the intermediate transfer belt. A second area of the first image carrier that passes through the transfer area of the first image forming unit and passes the transfer area when the white solid area passes through the transfer area; The charging current Iw is detected by the current detection unit, and the charging current Iw is moved when the charging current Iw is moved while the second region is passing through the charging region. The image forming apparatus according to any one of claims 1 to 3, wherein the output signal is output based on Iw and the charging current Ic.   The image bearing member is a photosensitive member, and the first image forming unit is provided downstream of the charging device and upstream of the transfer device in the rotational direction of the photosensitive member, and latent on the photosensitive member. 5. The exposure apparatus according to claim 1, further comprising an exposure device for forming an image, wherein the exposure device is controlled not to form a latent image in the area of the photosensitive member where the detection of the charging current Ic is performed. An image forming apparatus according to any one of the items.   The image bearing member is a photosensitive member, and the first image forming unit is provided downstream of the transfer device and upstream of the charging device with respect to the rotational direction of the photosensitive member. A pre-exposure device for exposing the surface is provided, and control is performed so that the exposure operation by the pre-exposure device is not performed when the area of the photosensitive member where the detection of the charging current Ic is performed passes the pre-exposure device. The image forming apparatus according to any one of claims 1 to 5, wherein:

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