JP6935705B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

Patent Document 1 describes that in an electrophotographic image forming apparatus that forms an image using a photoconductor on which a photosensitive layer is formed via a conductive substrate, the surface of the photoconductor is charged, and after the charging, the surface of the photoconductor is charged. The surface of the photoconductor is recharged after the exposure, and after the recharge, the inflow current flowing through the photoconductor by recharging is measured by an ammeter connected to the conductive substrate, and the measured current value is measured. Is disclosed as a method for recognizing the surface potential of a photoconductor, which comprises recognizing the above as surface potential information of the photoconductor. In the surface potential recognition method according to Patent Document 1, the charging potential is partially removed and the current flowing during recharging is measured to detect the charging potential unevenness in the axial direction of the photoconductor.

Patent Document 2 describes a photoconductor that is driven to rotate, a charging means that charges the surface of the photoconductor, an exposure means that forms an electrostatic latent image on the surface of the charged photoconductor, and an electrostatic latent image with a toner. In an image forming apparatus having at least a developing means for developing, the entire surface of the photoconductor is charged by the charging current value measuring means for measuring the charging current value applied by the charging means and the charging means, and the photoconductor is subjected to the photoconductor. Each of the two or more regions divided in the longitudinal direction of the above is used as a measurement region, and at least two of the measurement regions are obtained by obtaining the charge current value measured by the charge current value measuring means when exposed by the exposure means. An evaluation value calculation means for calculating an evaluation value that evaluates a difference between the charge current value in the measurement area and the charge current value in another measurement area, and whether or not the photoconductor is in a state of failure or near failure based on the evaluation value. There is disclosed an image forming apparatus including a failure detecting device having at least a failure state determining means for determining whether or not the image is generated. In the image forming apparatus according to Patent Document 2, the charging potential is partially eliminated, the current flowing during recharging is measured, and the axial film thickness unevenness of the photoconductor is detected. However, the exposure is performed in a strip shape. The cage detection area is not continuously moved.

Japanese Unexamined Patent Publication No. 10-49008 Japanese Unexamined Patent Publication No. 2013-190626

An object of the present invention is to improve the wear detection accuracy in the exposure process when the wear of the image holder is detected from the profile of the recharge current as compared with the case of exposing while shifting the divided regions. And.

In order to achieve the above object, the image forming apparatus according to claim 1 includes an image holder that rotates about an axis of rotation, a charging means that charges the surface of the image holder, and a charge that flows during the charge. The measuring means for measuring the current, the exposure means for irradiating the surface of the charged image holder with light to expose it to form an electrostatic latent image, and the charging so as to initially charge the surface of the image holder. The means is controlled so that the surface of the charged image holder is exposed to form an exposed region while moving an irradiation region of light having a predetermined width in the direction of the rotation axis along the rotation axis. The measuring means is controlled so as to control the recharging means and measure the recharging current that flows when the exposed surface of the image holder is recharged by the charging means, and the recharging current is used to measure the recharging current. Before the image holder is initially charged by controlling the exposure means or the charging means so as to detect an abnormality of the image holder and correct an error of the recharge current due to the charging history generated in the initial charge. Includes a detection means that controls the exposure means so as to expose a predetermined area to form a correction exposure area.

Further, the invention according to claim 2 is the invention according to claim 1, wherein the detection means moves the irradiation region at a predetermined speed at a constant speed.

Further, in the invention according to claim 3, in the invention according to claim 2, the predetermined speed moves the irradiation region by the predetermined width during one rotation of the image holder. It is the speed to do.

Further, in the invention according to claim 4 , in the invention according to claim 2, the predetermined speed moves the irradiation region by the predetermined width during one rotation of the image holder. The speed is greater than the speed at which the image holder moves, and is equal to or less than the speed at which the exposure means moves by the length of the image holder in the rotation axis direction during one rotation of the image holder.

The invention according to claim 5 is the invention according to claim 1 , wherein the detection means controls the exposure means so that the correction exposure region is formed in a region that does not overlap with the exposure region. Is.

The invention according to claim 6 is the invention according to claim 5 , wherein the detection means is exposed so that the corrected exposure region is formed in a region that does not overlap with the region of the charging history of the exposure region. It further controls the means.

Further, in the invention according to claim 7 , in the invention according to claim 1 , the measurement of the recharge current is performed every one or more rotations with the rotation of the image holder, and the detection means is used. The charging means is controlled so as to recharge the initially charged region during each of the plurality of measurements of the recharging current.

The invention according to claim 8 is the invention according to claim 7 , wherein the detection means performs the initial charge for one or more rotations of the image holder until the recharge is completed. The exposure means is controlled so that the movement of the irradiation region is stopped and the next exposure after the initial charge is stopped.

According to the first aspect of the present invention, in the exposure step in the case of detecting the wear of the image holder from the profile of the recharge current, the wear detection accuracy is compared with the case of exposing while shifting the divided region. Has the effect of becoming higher.
Further, according to the first aspect of the present invention, the recharging means is not controlled so as to correct the error of the recharging current due to the charging history generated in the initial charging, as compared with the case where the detecting means does not control the exposure means or the charging means. It has the effect of improving the current measurement accuracy.
Further, according to the first aspect of the present invention, as compared with the case where the initially charged region is recharged during each of the plurality of recharge current measurements to correct the recharge current measurement error. This has the effect of reducing the number of steps for measuring the recharge current.

According to the second aspect of the present invention, an effect that a uniform exposure region can be obtained in the axial direction and the rotation direction of the image holder can be obtained as compared with the case where the exposure means is moved at a non-uniform speed. Play.

According to the third aspect of the present invention, the recharging is performed as compared with the case where the predetermined speed is faster than the speed at which the exposure means moves by the predetermined width during one rotation of the image holder. It has the effect of improving the current measurement accuracy.

According to the invention of claim 4 , the measurement time is as compared with the case where the predetermined speed is the speed at which the exposure means moves by a predetermined width during one rotation of the image holder. It has the effect of being shortened.

According to the invention of claim 5 , the correction of the error of the recharge current is more accurate than the case where the detection means controls the exposure means so as to form the correction exposure region in the region overlapping the exposure region. It has the effect of being done.

According to the invention of claim 6 , the recharging current is compared with the case where the detecting means controls the exposure means so that the corrected exposure region is formed in the region overlapping the region of the charging history by the exposure region. This has the effect that the error is corrected more accurately.

According to the invention of claim 7 , the detection means image controls the exposure means so as to expose a predetermined region to form a correction exposure region before the image holder is initially charged. This has the effect of improving the measurement accuracy.

According to the invention of claim 8 , as compared with the case where the detection means controls the exposure means so as to start the exposure after the next initial charge from a position different from the position where the exposure is stopped, the image holder It has the effect of forming a linear exposure region that is skewed on the developed view.

It is a figure which shows an example of the structure of the image forming apparatus which concerns on embodiment. (A) is a diagram showing the relationship between scanning of the exposure region and the detection region according to the present embodiment, and (b) is a graph conceptually showing changes in the recharge current and the film thickness with respect to the position in the rotation axis direction of the photoconductor. Is. In the image forming apparatus according to the first embodiment, (a) is a diagram for explaining scanning of the detection region, and (b) is a graph showing an example of the measurement result of the recharge current with respect to the position in the rotation axis direction of the photoconductor. be. In the image forming apparatus according to the second embodiment, (a) is a diagram for explaining an exposure region, and (b) is a graph showing an example of a measurement result of a recharge current with respect to a position in the rotation axis direction of the photoconductor. (A) is a diagram showing the relationship between the exposure region and the charging history, and (b) is a graph showing an example of the measurement result of the recharging current when the detection region is scanned according to (a). It is a graph which shows an example of the measurement result of the photosensitive member film thickness of the image forming apparatus which concerns on 2nd Embodiment in comparison with the measurement result of the photosensitive member film thickness of the image forming apparatus which concerns on a comparative example. In the image forming apparatus according to the third embodiment, (a) is a diagram for explaining the formation of an exposure region accompanied by a charging history, and (b) is a diagram for explaining the saturation of the charging history. It is a part of the graph which shows the exposure area of the image forming apparatus which concerns on 4th Embodiment. It is a part of the graph which shows the exposure area of the image forming apparatus which concerns on 4th Embodiment. In order to explain the occurrence of streaks in image formation due to uneven wear of the photoconductor, (a) is a graph showing the relationship between the photoconductor film thickness and white streaks, and (b) shows the uneven wear region on the photoconductor. FIG. 3C is a diagram showing white streaks on the developed view of the photoconductor. It is a figure explaining the measurement principle of a charge current. In the image forming apparatus according to the comparative example, (a) is a diagram for explaining an exposure region, and (b) is a graph showing an example of a change in the recharge current with respect to the position in the rotation axis direction of the photoconductor.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 shows a schematic view of the overall configuration of the image forming apparatus 10 to which the present invention is applied. As shown in FIG. 1, the image forming apparatus 10 includes a photoconductor 12 (image holder) that rotates at a constant speed in the direction of arrow A.

Around the photoconductor 12, a charging unit 14, an exposed unit 16, a developing unit 18, a transfer unit 20, a cleaning unit 22, and a static elimination unit 24 are arranged in this order along the rotation direction of the photoconductor 12.

That is, after the surface of the photoconductor 12 is uniformly charged to the charging potential VH predetermined by the charging unit 14, a light beam is irradiated by the exposure unit 16 to generate an electrostatic latent image on the photoconductor 12. It is formed. The potential of the region irradiated with the light beam by the exposure unit 16 is an exposure potential VL lower than the charging potential VH. However, the high-low relationship between the charging potential VH and the exposure potential VL is an example, and may be the opposite relationship.

The power supply unit 40 is connected to the charging unit 14, and the power supply unit 40 is connected to the control unit 42. The control unit 42 measures the recharging current, which will be described later. Further, the exposure unit 16 is also connected to the control unit 42, is lit by the control unit 42, and is configured to emit a light beam based on the image data. Further, the exposure unit 16 forms an exposure region according to the present embodiment described later under the control of the control unit 42.

Toner is supplied from the developing unit 18 in a state where the developing potential Vdev is applied to the electrostatic latent image formed by the exposed unit 16, and a toner image is formed on the photoconductor 12. The toner image on the photoconductor 12 is transferred to the paper 28 conveyed from a paper tray (not shown) by the transfer unit 20 including the transfer roller. The toner remaining on the photoconductor 12 after the transfer is removed by the cleaning unit 22, the photoconductor 12 is charged by the static elimination unit 24 including the erase lamp, and then charged again by the charging unit 14, and the same process is repeated. ..

On the other hand, the paper 28 on which the toner image is transferred is conveyed to the fixing portion 30 including the pressurizing roller 30A and the heating roller 30B and subjected to the fixing process. As a result, the toner image is fixed and an image based on the image data is formed on the paper 28. The paper 28 on which the image is formed is discharged to the outside of the device.

By the way, the image formed by the image forming apparatus 10 may have streaks due to abrasion on the surface of the photoconductor 12. There are various possible causes for the occurrence of streaks, and one example is uneven wear formed on the surface of the photoconductor 12. The principle of streak generation due to uneven wear will be described with reference to FIG.

FIG. 10A shows a change in the film thickness of the photoconductor 12 in the rotation axis direction. Reference numeral "N" in FIG. 10A indicates an initial film thickness, reference numeral "A" indicates a film thickness over time, which is a film thickness during operation, and reference numeral "E" indicates a lifetime film thickness. The film thickness of the photoconductor 12 that started operation with the initial film thickness N initially changed like the film thickness A with time as the operation continued, and the uneven wear region was particularly thin compared to other regions. Aw may occur. The uneven wear region Aw is usually formed with a certain width over the periphery of the photoconductor 12, as shown in FIG. 10 (b).

In the uneven wear region Aw, the amount of charged charge during charging by the charging unit 14 is large, so that the exposure potential during exposure by the exposure unit 16 is higher than the normal exposure potential VL. Then, since the difference between the exposure potential and the development potential Vdeve becomes small, the amount of toner adhered in the uneven wear region Aw is smaller than that in the other regions, and therefore, when viewed in the developed view P of the surface of the photoconductor 12. White streaks WL as shown in FIG. 10 (c) are generated. Since such streaks cause defects in the image formed by the image forming apparatus 10, it is desired that the image forming apparatus 10 issue a warning and perform preventive replacement before the image is visible.

It is necessary to measure the film thickness of the photoconductor film in order to predict the occurrence of an abnormality due to uneven wear of the photoconductor 12. Hereinafter, with reference to FIG. 11, an example of a method for measuring the film thickness of the photoconductor film of the photoconductor 12 (hereinafter, “photoreceptor film thickness”) will be described. FIG. 11 is a diagram showing a measurement system for the film thickness of the photoconductor, and FIG. 11 shows the photoconductor 12, the charging unit 14, the power supply unit 40 connected to the charging unit 14, and the blade as the cleaning unit 22. There is.

When the photoconductor 12 is charged by the charging unit 14, a current (charging current) flows. That is, a high-voltage power supply included in the power supply unit 40 shown in FIG. 11 is connected to the charging unit 14, and when the high-voltage power supply is applied to the charging unit 14, a charging current I flows through the photoconductor 12. Since the DC component of the charging current I depends on the film thickness d of the photoconductor 12, the film thickness d of the photoconductor 12 is estimated by measuring the charging current I with the current detection monitor. That is, the charging current I when the rotation circumferential direction of the photoconductor 12 is taken on the x-axis is obtained by the following formula (Equation 1).
I = εLΔV (dx / dt) / d ... (Equation 1)
However, d is the film thickness of the photoconductor 12, ΔV is the difference in potential on the surface of the photoconductor 12 before and after charging, ε is the permittivity of the photoconductor film, L is the length of the photoconductor 12 in the rotation axis direction, dx /. dt indicates the process speed in the rotation direction of the photoconductor 12, respectively. If the profile (distribution) of the charging current I in the rotation axis direction of the photoconductor 12 is acquired using this principle, the film thickness distribution in the rotation axis direction of the photoconductor 12 can be obtained. The position of is detected.

Reference numerals P2 and P3 in FIG. 11 schematically indicate the streak generation positions. At the position P1, uneven wear occurs on the photoconductor 12 due to the presence of the convex portion on the cleaning portion 22, and the toner TN is less likely to adhere to the photoconductor 12, and white streaks are generated. On the other hand, at the position P3, the presence of the recess in the cleaning portion 22 makes the film thickness thicker than the surroundings, and the toner TN is more likely to adhere to the surroundings, causing black streaks. As shown in position P1, the toner TN may adhere to more than the surroundings due to dirt, foreign matter, etc. generated on the photoconductor 12, and partial streaks may be generated. The streaks are streaks at position P2 or P3.

In the actual measurement of the film thickness of the photoconductor, the processes of charging by the charging unit 14, exposure by the exposure unit 16, and recharging are executed, and the charging current flowing at the time of recharging is measured to obtain the charging current obtained in advance. The charging current measured using the correspondence with the photoconductor film thickness is converted into the photoconductor film thickness. At this time, among the above-mentioned image forming processes, development, transfer, and static elimination are basically not performed, but development may be performed. In the following description, the initial charge by the charging unit 14 is referred to as "initial charge", the recharge is referred to as "recharge", and the current flowing during recharge is referred to as "recharge current".

In order to determine whether or not uneven wear has occurred on the surface of the photoconductor 12, it is necessary to acquire a profile of the photoconductor film thickness in the rotation axis direction of the photoconductor 12, and the profile of the photoconductor film thickness is acquired. In order to do so, it is necessary to acquire a recharge current profile in the direction of the rotation axis. A method of measuring the recharge current profile according to the comparative example will be described with reference to FIG. FIG. 12 (a) is a diagram showing the position of the exposure region Ae formed in the measurement of the recharge current profile according to the comparative example on the developed view P of the photoconductor 12, and FIG. 12 (b) is a diagram. 12 (a) is a graph showing a change in the recharge current flowing when the exposure region Ae shown in 12 (a) is recharged with respect to the position in the rotation axis direction of the photoconductor 12, that is, the recharge current profile.

As shown in FIG. 12A, in the method for measuring the recharge current profile according to the comparative example, the exposure portion 16 positions the rectangular exposure region Ae with respect to the surface of the photoconductor 12 as the photoconductor 12 rotates. Form while shifting. The white arrows with the symbol "Ds" shown in FIG. 12A indicate the rotation direction of the photoconductor 12, and the white arrows with the symbol "Dm" indicate the rotation axis direction of the photoconductor 12. There is. When the exposed region Ae formed as shown in FIG. 12 (a) is recharged and the recharge current is measured, the recharge current profile as shown in FIG. 12 (b) is obtained.

However, when divided exposure is performed as in the exposed region Ae, the recharge current becomes an average value for each divided region, and a detailed recharge current profile cannot be obtained. For example, in the example of FIG. 12B, only eight recharge currents can be obtained. On the other hand, if the number of divisions is increased in order to obtain a detailed recharge current profile, that is, if the width of the exposure region Ae is narrowed, the measurement time becomes long.
That is, in the method for measuring the recharge current profile according to the comparative example, the acquisition of the detailed recharge current profile and the measurement time are incompatible.

Further, when the intervals between the exposure regions Ae are brought closer in order to shorten the measurement time, the positions where the exposure regions Ae are adjacent to each other as shown by the black arrows in FIG. 12 (b) (the positions indicated by the black arrows in FIG. 12 (a)). ) Causes spike-like current fluctuations. This is because the latent image portion of the exposed region Ae does not disappear instantly at the peripheral edge portion, but disappears with a skirt having a certain width. Due to the increase in current. When such a current fluctuation occurs, the recharge current profile cannot be measured accurately.

Therefore, in the present invention, an exposure region that moves diagonally with the rotation of the photoconductor 12 is formed with a predetermined width, and the recharge current in this exposure region is measured. As a result, the continuous recharge current profile is measured in a short time, and the acquired recharge current profile also suppresses spike-like current fluctuations as shown in FIG. 12 (b).

The method for measuring the recharge current profile according to the present embodiment will be described in more detail with reference to FIG. FIG. 2A is a diagram showing an exposure region Ae formed on the surface of the photoconductor 12 by the exposure step by the exposure unit 16 according to the present embodiment on the developed view P of the photoconductor 12. However, the developed view P is not limited to the developed view for one rotation of the photoconductor 12, and may show the developed view for a plurality of rotations. The exposure region Ae shown in FIG. 2A is formed by, for example, in the case of a laser-type exposure portion, an irradiation region having a predetermined width is moved in the rotation axis direction of the photoconductor by a scanning device. Further, in the case of an LED printhead using an LED (Light Emitting Diode), the LEDs are sequentially turned on and controlled to move an irradiation region having a predetermined width in the direction of the rotation axis of the photoconductor. At this time, if the irradiation region is moved at a constant velocity, a linear (band-shaped) exposure region Ae as shown in FIG. 2A is formed, which is desirable from the viewpoint of measuring the recharge current profile. Not limited to this, it may be moved at a fluctuating speed.

The reference numeral “Ad” shown in FIG. 2 conceptually represents a detection region when the recharge current of the strip-shaped exposure region Ae is measured by the current detection monitor (see FIG. 11) included in the power supply unit 40.
The detection region Ad can be regarded as moving along the exposure region Ae in the scanning direction indicated by the reference numeral “D1”. FIG. 2B shows changes in the recharge current and the film thickness with respect to the position in the rotation axis direction when the exposure region Ae is formed as shown in FIG. 2A. Further, the codes [1], [2], and [3] shown in FIG. 2 (b) are located at the positions of the detection areas Ad shown by the codes [1], [2], and [3] shown in FIG. 2 (a). It shows the position on the corresponding graph.

The position [1] indicates the position where the measurement of the recharge current is started. In the present embodiment, the measurement of the recharge current starts from the exposure start position (the position at the left end of the exposure region Ae). When the position of the detection region Ad moves along the scanning direction D1 and begins to overlap the uneven wear region Aw at the position [2], the recharge current starts to increase. The recharge current shows a constant value at the position [3] until the detection region Ad deviates from the uneven wear region Aw, and after that, it starts to decrease to the original value. At this time, the width of the constant value after the increase of the recharge current is substantially equal to the width f of the scanning direction D1 of the detection region Ad. As shown in FIG. 2B, since the uneven wear region Aw in which the film thickness of the photoconductor is thin is included in the width f of the recharge current, the position of the uneven wear region Aw is estimated from the recharge current profile ( Detected). Therefore, from the viewpoint of resolution in detecting the uneven wear region Aw, the width of the detection region Ad in the rotation axis direction Dm, that is, the width of the exposure region Ae in the rotation axis direction Dm is larger than the width of the uneven wear region Aw in the rotation axis direction Dm. It is preferable that it is wide and as close as possible to the width of the uneven wear region Aw in the rotation axis direction Dm.

Next, an actual measurement example of the recharge current profile will be described with reference to FIG. FIG. 3A is a diagram showing the exposed region Ae on the developed view P when the photoconductor 12 is rotated a plurality of times. In the measurement of the recharge current according to the present embodiment, the detection region Ad is scanned in the scanning direction D1. Move to. FIG. 3B shows an example of the recharge current profile obtained by performing the measurement method shown in FIG. 3A.

As is clear from the profile in the dotted line frame of FIG. 3 (b), the spike-shaped current fluctuation as shown in FIG. 12 (b) does not occur in the recharge current profile according to the present embodiment. Therefore, a continuous recharge current profile corresponding to the photoconductor film thickness distribution is measured. Further, in the method of measuring the recharge current profile according to the comparative example shown in FIG. 12, when the uneven wear region Aw exists over the vicinity of the boundary of the adjacent exposure region Ae, the signal components corresponding to the uneven wear region Aw are adjacent to each other. It may be difficult to specify the position of the uneven wear region Aw by separating it into the exposure region Ae. This is because the recharge current is measured as an average value in both of the two adjacent exposure regions Ae. However, in the method for measuring the recharge current profile according to the present embodiment, since the exposure region Ae is continuous, such a problem does not occur in principle, and even if the uneven wear region Aw occurs at any position. The position of the uneven wear region Aw is specified under the same conditions.

[Second Embodiment]
The image forming apparatus according to the present embodiment will be described with reference to FIGS. 4 to 6. The image forming apparatus according to the present embodiment is a form in which the influence of the charging history by the charging unit 14 is suppressed in the image forming apparatus according to the above embodiment. Therefore, since the image forming apparatus itself is the same as the image forming apparatus 10 according to the above embodiment, detailed description thereof will be omitted by referring to the drawings described above as necessary.

First, with reference to FIG. 5, the influence of the charging history on the measurement of the recharging current profile will be described. FIG. 5A is a developed view showing the state of the surface of the photoconductor 12 for three rotations. Reference numerals "R1", "R2", and "R3" shown in FIG. 5A are additional numerals indicating the number of rotations of the photoconductor 12, and indicate the first, second, and third rotations, respectively. Hereinafter, they will be referred to as "first rotation R1". Reference numeral "S" shown in FIG. 5A indicates the peripheral length of the photoconductor 12.

The charging history refers to a phenomenon in which the charging potential becomes lower than the charging potential VH when a predetermined exposure or static elimination is not performed when the battery is charged once, then exposed and further charged. FIG. 5A shows the charging histories Ag1 and Ag2 generated when the exposed region Ae is formed by the method according to the above embodiment. The color depths of the charging histories Ag1 and Ag2 indicate that the darker the color, the greater the decrease in the charging potential. The charge history Ag1 shows the charge history generated in the rotation of the second lap with respect to the exposure region Ae, and the charge history Ag2 shows the charge history generated in the rotation of the third lap with respect to the exposure region Ae. In this case, in the measurement of the recharge current of the second rotation R2, the recharge current according to the charge history Ag1 is superimposed in addition to the recharge current of the exposure region Ae that is originally desired to be measured. This is because the potential of the charge history Ag1 is also lower than the potential of the surroundings excluding the exposure region Ae.

Similarly, in the third rotation R3, in addition to the recharge current in the exposure region Ae, the recharge current flowing in the charge history Ag1 and the charge history Ag2 is also measured. In this way, if the recharge current due to the charge history Ag1 and Ag2 is superimposed on the recharge current of the exposure region Ae that is originally desired to be measured, an accurate recharge current cannot be obtained, and as a result, accurate measurement of the photoconductor film thickness is performed. May be hindered. Therefore, it is preferable to eliminate the influence of the charging history as much as possible. However, as will be described later, among the charging histories generated with the rotation of the photoconductor 12, the charging history Ag1 of the second rotation R2 is dominant, and the charging history Ag2 and thereafter of the third rotation R3 are substantially. It can be ignored.

FIG. 5B shows a recharge current profile when the photoconductor 12 having a uniform photoconductor film thickness is rotated four times. As shown in FIG. 5B, the first rotation R1 is not affected by the charging history, but since the recharging current due to the charging history is added after the second rotation R2, the first rotation R1 and the second rotation A current gap ΔI in which the recharge current fluctuates greatly is generated between R2 and later. In this respect, such a current gap ΔI hardly occurs after the second rotation R2. Since the occurrence of the current gap ΔI causes an error in the accurate measurement of the photoconductor film thickness d, it is preferable to eliminate it as much as possible.

An image forming apparatus according to the present embodiment in which the influence of the charging history is suppressed will be described with reference to FIG. In the present embodiment, the pre-exposure region is formed before the originally intended exposure region Ae is formed to suppress the influence of the charging history.

FIG. 4A is a diagram showing a method of forming the exposure region Ae according to the present embodiment on a developed view of the photoconductor 12 for four rotations. In the present embodiment, the measurement of the recharge current is started from the second rotation R2, and the pre-exposure is performed in the first rotation R1 one rotation before the measurement to form the pre-exposure region Aep. The shape of the pre-exposure area Aep is the same as the shape of one rotation of the exposure area Ae. The region on the photoconductor 12 forming the pre-exposure region Aep is the charging history of the pre-exposure region Aep and the pre-exposure region Aep. Perform in a region that does not overlap with Ag1 and Ag2. If the charging history Ag1 and Ag2 are not a problem, the pre-exposure region Aep may be set to a region overlapping the charging history Ag1 and Ag2. Further, in the present embodiment, a mode in which pre-exposure is performed one rotation before forming the exposure region Ae will be described as an example, but the present invention is not limited to this, and as a mode in which pre-exposure is continuously performed from two or more rotations before. May be good. This pre-exposure area Aep corresponds to the "correction exposure area" according to the present invention.

By performing the pre-exposure in this way, in the second rotation R2, the recharge current in the exposure region Ae and the charge history Agp1 is measured. In the third rotation R3 and the fourth rotation R4, the charging history Agp2 in the second rotation can be ignored, so the recharging current due to the charging history Ag1 in the exposure region Ae and the exposure region Ae is measured. That is, in the measurement of the recharged electric profile according to the present embodiment from the second rotation R2 onward, the measurement is performed in a state where the recharged current by the charging history Ag1 is superimposed in addition to the recharged current by the exposure region Ae. Therefore, in the measurement of the recharge current in the exposure region Ae, the recharge current of the same shape is always applied, so that the error of the recharge current due to the charge history is reduced and the current gap ΔI is generated. It is suppressed.
As a result, according to the image layering apparatus according to the present embodiment, the influence of the charging history is suppressed, and the photoconductor film thickness d can be measured more accurately than in the above-described embodiment.

FIG. 4B shows a recharge current profile measured by applying the above measurement method. As shown in FIG. 4 (b), according to the method for measuring the recharge current profile according to the present embodiment, it can be seen that the occurrence of the current gap ΔI as shown in FIG. 5 (b) is suppressed.

Next, with reference to FIG. 6, the measurement result of the photoconductor film thickness by the recharge current profile according to the present embodiment and the comparison result between the actual photoconductor film thickness (FIG. 6A) and the comparative example are shown. A comparison result (FIG. 6 (b)) with the measurement result of the photoconductor film thickness by the recharge current profile will be described.

The curve C1 shown in FIG. 6A shows the measurement result of the photoconductor film thickness by the recharge current profile according to the present embodiment, and the curve C2 shows the actual photoconductor film thickness. In the example shown in FIG. 6A, uneven wear occurs at the positions P4 and P5 of the photoconductor 12 in the rotation axis direction, but according to the measurement result of the photoconductor film thickness according to the present embodiment, this is caused. It can be seen that uneven wear at positions P4 and P5 has been detected.

The curve C3 shown in FIG. 6B shows the measurement result of the photoconductor film thickness by the method for measuring the recharge current profile according to the comparative example shown in FIG. Further, the curve C4 is obtained by forming each of the exposure regions Ae shown in FIG. 12A in a strip shape around the entire periphery of the photoconductor 12 as a modification of the method for measuring the recharge current profile according to the comparative example. The measurement results of the photoconductor film thickness by the charging current profile are shown respectively. As shown by the curve C3, in the measurement result of the photoconductor film thickness according to the comparative example, a step in the photoconductor film thickness due to the current gap ΔI due to the charging history appears at the position P6. Further, at positions P7, P8, and P9, a decrease in the photoconductor film thickness due to spike-like current fluctuations at the boundary of the adjacent exposure regions Ae indicated by the black arrows in FIG. 12B appears.
It can be seen that it is difficult to obtain the actual photoconductor film thickness shown in the curve C2 due to these fluctuations in the photoconductor film thickness. Further, as is clear by comparing the curves C4 and C2, the uneven wear at the positions P4 and P5 cannot be detected in the measurement of the photoconductor film thickness by the recharge current profile according to the modified example of the comparative example.

[Third Embodiment]
The image forming apparatus according to the present embodiment will be described with reference to FIG. 7. Similar to the above embodiment, the present embodiment is also an embodiment aimed at suppressing the influence of the charging history, but in the above embodiment, the recharging current due to the charging history of the same magnitude is always superimposed. However, the present embodiment is a form in which the charging history is saturated (almost eliminated) and the influence of the charging history is suppressed. Saturation of the charging history means that the charging potential rises to almost a predetermined charging potential VH by recharging the once formed charging history region.

First, the saturation of the charging history will be described in more detail with reference to FIG. 7 (b). FIG. 7B shows the circulation of the photoconductor 12 when the charging unit 14 is operated, in which the operations of the transfer unit 20 and the static elimination unit 24, which the photoconductor is in electrical contact with other than the charging unit 14, are stopped. It shows the change in charging potential. That is, in FIG. 7B, the region where the first charge was performed in the first rotation R1 is charged for the second time in the second rotation R2, and then in the third rotation R3 for the third time and in the fourth rotation R4. The fourth charge is performed with.

As shown in FIG. 7B, the potential of the charging history gradually approaches the predetermined charging potential VH from the exposure potential VL, that is, approaches saturation as the number of times of passing through the charging unit 14 increases. However, the potential difference ΔV between the charging potential in the first rotation R1 and the charging potential in the second rotation R2 is much larger than the potential difference in the other rotations. The charging current itself due to the potential difference ΔV is also a value of about 1/10 of the charging current corresponding to the initial charging potential VH1. In other words, the potential difference after the potential difference between the charging potential of the second rotation R2 and the charging potential of the third rotation R3 is as small as a negligible level. That is, almost no charging current flows after the second rotation. In this embodiment, this phenomenon is applied.

In the present embodiment, during the measurement cycle of the recharge current in the rotation cycle of the photoconductor 12, a refresh cycle is provided in which the exposure unit 16 does not perform exposure (does not draw an image) and charges the photoconductor 12 until the charge history is saturated. , The influence of charging history is suppressed. More specifically, in the present embodiment, the rotation cycle of the measurement cycle and the rotation cycle of the refresh cycle are alternately set in the rotation cycle of the photoconductor 12. In the measurement cycle, the recharge current of the formed exposure region Ae is measured, and in the refresh cycle, the movement of the irradiation region by the exposure unit 16 is stopped to form the exposure region Ae, and the exposure region Ae is charged in the immediately preceding rotation cycle. Saturate history.

In the example shown in FIG. 7A, the recharge current in the exposure region Ae1 is measured in the first rotation R1.
In the second rotation R2, the exposure region Ae is not formed, and only the charging history Ag1 corresponding to the exposure region Ae1 is charged to saturate the charging history Ag1. In the subsequent third rotation R3, the recharge current in the exposure region Ae2 is measured. At this time, since the charging history Ag2 corresponding to the exposure region Ae1 is charged twice, it is almost saturated and almost no recharging current flows.

Similarly, in the fourth rotation R4, only charging is performed to saturate the charging history Ag3 corresponding to the exposure region Ae2, and in the fifth rotation R5, the recharge current of the exposure region Ae3 is measured. At that time, the charge history Ag4 corresponding to the exposure region Ae2 is saturated to a negligible level. That is, in the example shown in FIG. 7A, the first rotation R1, the third rotation R3, and the fifth rotation R5 are measurement cycles, and the second rotation R2 and the fourth rotation R4 are refresh cycles. ..

In short, in the present embodiment, the exposure region Ae is moved in the axial direction in the measurement cycle while alternately executing the measurement cycle and the refresh cycle. That is, in the present embodiment, the charging history is saturated, and the recharging current in the exposure region Ae is measured together with the charging history on the second lap after exposure at a level where the recharging current is almost negligible. Therefore, for example, even if the initial charging history fluctuates within the first rotation cycle of the photoconductor 12, it is not affected by the fluctuation. This embodiment requires a large number of cycles for measurement, but is a method for measuring a recharge current profile that is suitable, for example, when more accurate measurement is required.

[Fourth Embodiment]
The image forming apparatus according to the present embodiment will be described with reference to FIG. In each of the above embodiments, the moving speed of the photoconductor 12 in the irradiation region by the exposure unit 16 in the rotation axis direction vs. the width W of the exposure region Ae in the rotation axis direction Dm is variable. .. Since the moving speed vs. the moving speed of the irradiation region is equal to the moving speed of the exposure region Ae when the exposure region Ae is formed by skewing, it is hereinafter referred to as the moving speed vs. the exposure region Ae. Further, the moving speed vs. the moving speed is expressed by the moving distance (m / rotation) in the rotation axis direction per circumference of the photoconductor 12.

First, the relationship between the pattern of the exposure region Ae on the peripheral surface of the photoconductor 12 and the moving speed vs. the movement speed of the exposure region when the rotation speed of the photoconductor 12 and the width W of the exposure region Ae (irradiation region) are constant will be described. do. The pattern of the exposure area Ae depends on the movement speed vs. When the movement speed vs. is slowed down, the pattern of the exposure area Ae has a small inclination angle with respect to the rotation direction Ds and becomes a densely packed form. It becomes a form. Therefore, the moving speed vs. the width W of the exposure area Ae needs to be determined by the trade-off between the resolution and the measurement time in specifying the position of the streak.

In FIGS. 8 and 9, the width of the exposure region Ae (irradiation region) is W, the movement speed of the exposure region Ae is vs, the length of the photoconductor 12 in the rotation axis direction is L, and the movement speed vs is changed. It shows the change of the pattern of the exposure area Ae in the case of. In each figure, <1> is a diagram showing the exposure region Ae on the developed view of the peripheral surface of the photoconductor 12, and <2> is a diagram showing the exposed region Ae in each rotation aggregated on one developed view. It is a figure.

FIG. 8A shows the pattern of the exposure region Ae when vs = W. As shown in FIG. 8A <2>, the exposure area Ae in this case is arranged without any gap. Of course, the moving speed vs. the speed of vs = W or less may be intentionally overlapped with the adjacent exposure regions Ae, but here, vs = W is defined as the minimum speed of vs = vsmin. In the case of the minimum speed vsmin, the length of the formed exposure region Ae in the rotation direction Ds is maximized, which is preferable from the viewpoint of detecting the uneven wear region Aw, but the measurement time is long. Further, in the present embodiment, since the exposure region Ae and the exposure region Ae are adjacent to each other, the width of the exposure region Ae in the rotation axis direction Dm is set to the rotation axis of the uneven wear region Aw in consideration of the skirt in the latent image described above. It is preferable that the width is equal to or less than the width of the direction Dm.

FIG. 9B shows a mode in which the movement speed vs. L = L, that is, the exposure region Ae moves from one end to the other end of the photoconductor 12 while the photoconductor 12 makes one round. As shown in FIG. 9B <2>, the number of exposed regions Ae formed in this case is one. Of course, it is possible to make the moving speed vs. L faster than vs = L, but since the length of the rotation direction Ds of the exposure area Ae becomes extremely narrow, this moving speed vs = L is the moving speed vs. It is defined as maximum speed vs = vsmax. In the case of the maximum speed vsmax, the measurement time is shortened, but the length of the formed exposure region Ae in the rotation direction Ds is shortened, so that the detection accuracy of the uneven wear region Aw is lowered.

8 (b) and 9 (a) show the pattern of the exposure region Ae when the moving speed vs. the moving speed is set between the minimum speed vs min and the maximum speed vs max. FIG. 8B shows a pattern of the exposure region Ae formed when the moving speed is vs = vsmid1, and FIG. 9A shows a pattern of the exposure region Ae formed when the moving speed is vs = vsmid2, respectively. Shown. Further, vsmid1 <vsmid2. That is, the relationship between the moving speeds and the movement speeds in each of FIGS. 8 and 9 is as follows.
W = vsmin <vsmid1 <vsmid2 <vsmax = L

As shown in FIGS. 8 (b) <2> and 9 (a) <2>, when the moving speed vs. is between the minimum speed vs min and the maximum speed vs max, a plurality of exposure regions Ae are formed. As the moving speed vs. becomes faster, the inclination angle of the exposure region Ae becomes larger, and the gap between the exposure regions Ae becomes wider. From the viewpoint of the detection accuracy of the uneven wear region Aw, the form of FIG. 8B is preferable, and from the viewpoint of the measurement time, the form of FIG. 9A is preferable. Further, in the present embodiment, since there is a gap between the exposure region Ae and the exposure region Ae, the influence of the hem on the latent image described above is suppressed, so that the width of the exposure region Ae in the rotation axis direction Dm is biased. It may be equal to or larger than the width of the wear region Aw in the rotation axis direction Dm.

Here, in the above description, for ease of understanding, a mode in which the moving speed vs. is changed with the width W of the exposure region Ae as a given one is illustrated, but conversely, the moving speed vs. the given one is given. The width W of the exposure region Ae may be changed, and this form is preferable from the viewpoint of practicality. In this case, if the width W of the exposure region Ae is widened, the measurement time is shortened, but the width of the exposure region Ae as the detection region with respect to the width of the uneven wear region Aw in the rotation axis direction Dm is also widened, so that the uneven wear region Aw The position accuracy in the detection of is reduced. On the other hand, when the width W of the exposure region Ae is made equal to the moving speed vs. the movement speed vs. the exposure region Ae is arranged precisely without any gap as shown in FIG. 8A, so-called two-dimensional mapping can be obtained.

However, since the present embodiment is premised on the uneven wear region Aw formed over the entire circumference of the photoconductor 12 as shown in FIG. 10B, two-dimensional mapping is not always necessary. Therefore, in consideration of the measurement time, the width W of the exposure region Ae is made shorter than the moving distance in the rotation axis direction Dm per rotation indicated by the moving speed vs. that is, that is, FIG. 8 (b) or FIG. 9 (a). The measurement time may be shortened by forming the exposure region Ae as shown by. It is preferable that the width W of the exposure region Ae is set to about ½ of the moving distance in the rotation axis direction Dm per rotation from the viewpoint of both measurement accuracy and measurement time. However, in practice, the moving speed vs. the moving speed of the exposure region Ae needs to be equal to or lower than the speed determined by the response speed of the recharge current measurement system.

10 Image forming device 12 Photoreceptor 14 Charging unit 16 Exposing unit 18 Developing unit 20 Transfer unit 22 Cleaning unit 24 Static elimination unit 28 Paper 30 Fixing unit 30A Pressurizing roller 30B Heating roller 40 Power supply unit 42 Control unit Ad Detection area Ae Exposure area Aep Pre-exposure area Ag1 to Ag4, Agp1, Agp2 Charging history Aw Uneven wear area d Thickness f Width D1 Scanning direction Dm Rotation axis direction Ds Rotation direction I Charging current L Length S Peripheral length P Development view N Initial film thickness A Time-lapse film Thickness E Life thickness P1 to P9 Position R1 1st rotation R2 2nd rotation R3 3rd rotation R4 4th rotation R5 5th rotation TN Toner VL Exposure potential VH Charging potential Vdev Development potential vs Moving speed W Width WL White streak ΔI Current Gap ΔV potential difference

Claims (8)

An image holder that rotates around the axis of rotation,
A charging means for charging the surface of the image holder and
A measuring means for measuring the charging current flowing during charging, and
An exposure means for forming an electrostatic latent image by irradiating the surface of the charged image holder with light to expose the image holder.
The charging means is controlled so as to initially charge the surface of the image holder, and the image holding is charged while moving an irradiation region of light having a predetermined width in the direction of the rotation axis along the rotation axis. The exposure means is controlled so as to expose the surface of the body to form an exposure region, and the recharge current that flows when the exposed surface of the image holder is recharged by the charging means is measured. The exposure means or the charging means so as to control the measuring means, detect the abnormality of the image holder by using the recharging current, and correct the error of the recharging current due to the charging history generated in the initial charging. An image forming apparatus including means for controlling the means and detecting means for controlling the exposure means so as to expose a predetermined region before initial charging the image holder to form a correction exposure region. The image forming apparatus according to claim 1, wherein the detection means moves the irradiation region at a constant speed at a predetermined speed. The image forming apparatus according to claim 2, wherein the predetermined speed is a speed at which the irradiation region moves by the predetermined width during one rotation of the image holder. The predetermined speed is larger than the speed at which the irradiation region moves by the predetermined width during one rotation of the image holder, and the exposure means is said to be the exposure means during one rotation of the image holder. It is equal to or less than the speed at which the image holder moves by the length in the rotation axis direction.
The image forming apparatus according to claim 2. The detection means controls the exposure means so that the correction exposure region is formed in a region that does not overlap with the exposure region.
The image forming apparatus according to claim 1. The detection means further controls the exposure means so that the correction exposure region is formed in a region that does not overlap with the region of the charging history of the exposure region.
The image forming apparatus according to claim 5. The measurement of the recharge current is performed every one or more rotations with the rotation of the image holder, and the detection means is used for the initially charged region during each of the plurality of measurements of the recharge current. The charging means is controlled so as to recharge the battery.
The image forming apparatus according to claim 1. The detection means stops the movement of the irradiation region until the recharge is completed after performing the initial charge for one or a plurality of rotations of the image holder, and stops the next exposure after the initial charge. The exposure means is controlled so as to start from a vertical position.
The image forming apparatus according to claim 7.

Images