JP2006091324A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus wherein density unevenness occurring with passage of time after the beginning is precisely detected and is suppressed by using a detection result. <P>SOLUTION: The image forming apparatus includes a latent image carrier 1a carrying a latent image on a surface thereof and a developer carrier 11 which is provided so as to face a surface of the latent image carrier 1a and carries a developer, and a developing gap being a gap between the closest surfaces of the latent image carrier 1a and the developer carrier 11 is set to a prescribed gap, and the developer carried on the surface of the developer carrier 11 is supplied to the latent image formed on the latent image carrier 1a to develop the latent image. The image forming apparatus is provided with a current detection means for detecting a current which occurs when the developer carried on the developer carrier 11 is supplied to the latent image to develop the latent image, and a developing state in a direction of a revolving shaft and/or a rotation direction on the latent image carrier 1a is determined on the basis of a detection result of the current detection means to control an exposure/development condition. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine that maintains good image quality with little density unevenness.

Conventionally, in an electrophotographic image forming apparatus, a charged latent image obtained by forming optical image information on a latent image carrier uniformly charged in advance is visualized by toner from a developing device, It is known to form an image by transferring and fixing this visible image on a transfer paper (see, for example, Patent Documents 1 and 2).
When the latent image is visualized by the developing device, left and right development unevenness occurs due to various factors. In order to suppress such density unevenness, in Patent Document 1, density sensors are provided at both ends of the rotation axis direction to detect a density difference between the left and right sides, and the charging potential is changed based on the detection result. In this method, a plurality of sensors must be provided, and the cost increases.
Japanese Patent Application Laid-Open No. 2004-228561 describes that the deviation of the developing gap due to the driving of the developer carrying member or the latent image carrying member is accurately controlled within the tolerance range by detecting the gap with an optical sensor. .
However, this method requires a plurality of optical sensors separately, and it is very difficult to accurately detect the development gap in an actual developing device filled with the developer.
Japanese Patent Laid-Open No. 05-1000053 JP 2003-162148 A

Causes of density unevenness in the direction of the rotation axis that occur during development include, for example, initial image characteristics such as latent image carrier (photoconductor) film thickness, development gap variations, and time-dependent characteristics such as uneven wear of the photoconductor. Examples thereof include a decrease in the amount of pumping up or a variation in charge amount distribution in the developer developing unit (developer carrier).
In order to suppress such density unevenness as much as possible, for example, with respect to the development gap and the photosensitive member film thickness, the tolerance width is narrowed to increase the accuracy. However, such a response only by increasing the accuracy of the component parts cannot cope with a change with time even if the initial characteristic can be dealt with up to a certain extent.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus that accurately detects density unevenness that occurs from the initial stage to the elapsed time in consideration of the above-described circumstances, and suppresses density unevenness using the result.

In order to solve the above problems, the invention described in claim 1 is a latent image carrier that carries a latent image on the surface, and a developer that is provided to face the surface of the latent image carrier. And a developing gap, which is the distance between the closest surface between the developer carrying body carrying the toner and the latent image carrying body and the developer carrying body, is set to a predetermined interval and formed on the latent image carrying body In the image forming apparatus for developing the latent image by supplying the developer carried on the surface of the developer carrier to the formed latent image, the developer carried on the surface of the developer carrier is supplied to the latent image Current detecting means for detecting a current generated when the latent image is visualized, and based on the detection result of the current detecting means, either the rotation axis direction and / or the rotation direction on the latent image carrier. An image form that determines the state of visualization and controls exposure and development conditions Apparatus characterized.
According to a second aspect of the present invention, the rotation axis direction and / or the rotation direction on the latent image carrier determined from the detection result of the current detection means is based on the visualization state of either one of the rotation axis direction and the rotation direction. A development gap control means for controlling the development gap is further provided.
According to a third aspect of the present invention, as means for correcting the development gap, gap correction is provided in the interior and moves either the latent image carrier or the developer carrier in the distance direction with respect to the other. A member is used.
According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the developer concentration fed to the developer carrying member is controlled based on the visualized state.
According to a fifth aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the developer stirring time is controlled based on the visualized state.
According to a sixth aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the developer stirring speed is controlled based on the visualized state.
According to a seventh aspect of the invention, there is provided the image forming apparatus according to the first aspect, wherein the exposure intensity is controlled based on the visualized state.
The invention according to claim 8 is the image forming apparatus according to claim 1, wherein an exposure time for one pixel is controlled based on the visualized state.

The invention according to claim 9 controls the developing gap, developer concentration, developer stirring speed, developer stirring time, exposure intensity, exposure time, or a combination thereof. Any one of the image forming apparatuses is characterized.
The invention according to claim 10 forms a latent image of a belt-like image inclined in the rotation direction of the latent image carrier, detects a current generated when the latent image is visualized, and performs exposure or The image forming apparatus according to claim 9, wherein the image forming apparatus controls development conditions.
According to an eleventh aspect of the present invention, a plurality of the belt-like images are visualized by changing the density, and a current generated during the visualization is detected to control exposure or development conditions. The image forming apparatus is characterized.
According to a twelfth aspect of the present invention, a plurality of the belt-like images are visualized at the same density, and an electric current generated during the visualization is detected to control exposure or development conditions. Features a forming device.
Further, the invention described in claim 13 visualizes a plurality of belt-like images by shifting in a stepwise manner with respect to the rotation direction of the latent image carrier, detects a current generated during the visualization, and performs exposure. Alternatively, the image forming apparatus according to claim 9 that controls development conditions.
According to a fourteenth aspect of the present invention, the belt-like image is visualized with respect to the rotation direction of the latent image carrier, the current generated during the visualization is detected, and the exposure or development conditions are controlled. 9 is an image forming apparatus.
According to the fifteenth aspect of the present invention, at the time of supplying the developer to the developer carrying member, the rotation axis direction and / or the rotating direction on the latent image carrying member are revealed from the detection result of the current detecting means. 15. The image forming apparatus according to claim 1, wherein the image forming state is determined.

  According to the present invention, there is provided current detecting means for detecting a current generated when toner adheres to the photosensitive drum, and the toner adhesion state in the rotational axis direction and the rotational direction on the photosensitive drum is estimated based on the detected result. By reflecting the estimated result in the exposure condition / development condition, a good image without density unevenness can be obtained.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing a first embodiment of an image forming apparatus. FIG. 1 shows an example of a color image forming apparatus provided with an intermediate transfer member.
In the drawing, the photosensitive drums (latent image carriers) are denoted by 1a, 1b, 1c, and 1d in order from the left. Since the image forming portion around the photosensitive drum has the same configuration for a, b, c, and d, only 1a will be described.
In FIG. 1, a developing device 2 is disposed on the left side of the photosensitive drum 1a, a cleaning device 3 is disposed on the right side, a charging device 4 is disposed on the upper center, and a writing device 5 is disposed on the upper side.
The toner image formed on the photoconductive drum 1a is transferred to the intermediate transfer body 6, and the toner image is further transferred from the photoconductive drums b, c, and d on the intermediate transfer body 6 to form a full color image. .
The full color image is transferred to a transfer material (not shown) by the transfer unit 7, and the transfer material is heated and fixed by the fixing unit 8. The method and conditions of each process of the present embodiment will be described in detail. Each photosensitive drum is charged to about −700 V in the non-image portion by the non-contact roller charging method. After exposure by the LD (writing device 5), each color is developed by the developing device.

The present invention does not limit the toner or the developing system. For example, in the case of a one-component magnetic toner, a BMT (bipolar magnetic toner) method in which the toner is charged by frictional charging between the toners and conveyed to the developing region by rotation of the mag roller and the sleeve, or on the developing sleeve For example, a jumping method is used in which a thin toner layer is formed, and the toner layer is brought close to the photosensitive drum and the toner is ejected by an AC bias for development.
Regarding non-magnetic toner, NSP (Non-Magnetic Single-Component Development Process) method that transports toner to the development area by attaching toner to conductive or surface-insulated development roller, non-magnetic toner For the toner jumping method and the two-component toner, a magnetic brush developing method or the like is applied.
Among these development methods, the experiment this time was conducted by the two-component magnetic brush development method. The toner image on the photosensitive drum developed by the two-component magnetic brush development method is transferred to the intermediate transfer member 6.
In the experiment according to the present invention, the intermediate transfer member 6 was a seamless belt (volume resistance 8E9 Ωcm) formed of a polyvinylidene fluoride resin film sheet, and the primary transfer bias was 1300 V under constant voltage control.
As the belt material, a film made of a dielectric resin such as a polyethylene terephthalate resin film sheet (PET sheet) or a polyurethane resin film sheet is widely used. Of course, an appropriate applied bias value varies depending on the material of the belt and its resistance value.
The primary transfer process from the photosensitive drum to the intermediate transfer member (intermediate transfer belt) 6 is performed for each of the colors Y, M, C, and K, and a color superimposed image is formed on the intermediate transfer belt 6. , And transferred onto a transfer material at a transfer portion denoted by reference numeral 7.
In FIG. 1, the transfer unit 7 is exemplified by a transfer belt that also serves as a conveyance belt, but secondary transfer can be performed by using a roller or a corona charger instead of the belt.

FIG. 2 is a partial sectional view showing a schematic configuration around the development used in the image forming apparatus according to the present invention. The developing device (developing unit) 2 includes main body cases 9 and 10 that are disposed on the side of a cylindrical photosensitive drum 1a and that have openings toward the photosensitive drum 1a.
The developing device 2 is also partly exposed from the opening and is conveyed onto the developing roller 11 as a developer carrying member that carries a developer composed of toner and a magnetic powder carrier on its surface. It includes a doctor blade 12 as a developer regulating member that regulates the amount of developer that has developed, and a stirring screw 13 that is arranged in parallel to the developing roller 11.
The developing roller 11 is composed of a cylindrical developing sleeve made of a nonmagnetic material and a magnet 14 of a magnet roller as a magnetic field generating means fixed inside, and the developing sleeve freely rotates around this magnet. be able to.
In the magnet 14, a main pole (P1 pole) is arranged at a position opposite to the photosensitive drum 1a, and an S pole and an N pole are alternately arranged in the counterclockwise direction, but in order to peel the developer from the developing sleeve. In addition, magnetic poles of the same polarity are arranged adjacent to each other at a downstream position in the rotation direction of the developing sleeve (developing roller) 11 from the portion facing the photosensitive drum 1a.
In this embodiment, the developing sleeve is made of aluminum and the surface is sandblasted. Paying attention to the process around the developing sleeve, the developer is frictionally charged by the stirring action in the developing device 2, and negatively charged toner is attached around the positively charged carrier.
When the paddle is rotated counterclockwise by a motor (not shown), the developer inside the main body case is conveyed to the developing sleeve by the paddle. At this time, the developer is attracted to the surface of the developing sleeve by the magnetic force generated by the magnet 14 inside the developing roller to form a magnetic brush.
Next, the developer whose layer thickness is regulated by the doctor blade 12 is conveyed to a portion closest to the photosensitive drum 1a, and the toner is electrically attached to the electrostatic latent image. Not all the toner conveyed to the developing unit is developed, and the toner remaining on the developing sleeve without being developed is stirred again.
Hereinafter, the features of the present invention will be described in which density unevenness is accurately detected and suppressed. Although the toner is electrically attached to the electrostatic latent image and developed, an electric current is generated according to the amount of toner to be developed.

FIG. 3 is a diagram showing an example of an image pattern for density unevenness detection created by obliquely shifting a belt-like image in the rotation axis direction in the rotation direction. Therefore, in the present invention, as shown in FIG. 3, a belt-like image in the direction of the rotation axis is created while being obliquely shifted in the rotation direction, and the current flowing during development is monitored by a current detection means (not shown).
FIG. 4 is a graph showing the result of monitoring the detected current. When looking at FIG. 4, which is the result of monitoring in FIG. 3, the value of the current that flows when developing the strip-shaped image inclined in the rotation direction is downwardly sloping. That is, it can be detected that the development amount on the back side of the machine is small (right side = back side in this experiment).
FIG. 5 is a schematic diagram showing the configuration of the developing gap correcting means according to the present invention. A method of suppressing density unevenness by controlling the development gap based on the detection result described above will be described.
In the embodiment shown in FIG. 5, as gap correction means, a spring 15 for applying tension in the direction of separating the photosensitive drum 1a and the developing sleeve (developing roller) 11 from each other, and the developing sleeve 11 as the photosensitive drum 1a. And a cam 18 as a gap correction member for moving in the distance direction.
One end of the spring 15 is abutted and supported by a receiving portion 17 provided on the photosensitive drum 1 a and the other end is supported by a receiving portion 16 provided on the developing sleeve 11. Further, the developing sleeve 11 is supported inside the developing unit 2 so as to be movable in the distance direction with respect to the photosensitive drum 1a, and the cam 18 is on the back side facing the side where the spring 15 of the receiving portion 16 on the developing sleeve 11 side abuts. Abut.
With the above configuration, tension is applied between the photosensitive drum 1 a and the developing sleeve 11 in the separating direction by the spring 15, and the receiving portion 17 is moved by the swinging of the cam 18 around the cam shaft 19. The distance to the photosensitive drum 1a moves.
The cam 18 is driven by calculating a cam drive amount from a current detection result generated during development by the cam drive motor 20 fitted to the cam shaft 19 and rotating the cam 18 stepwise.
A developing gap correcting means is provided, and the developing gap is corrected based on the toner adhering state in the rotational axis direction on the photosensitive drum 1a estimated from the current generated by the toner adhering at the time of development. No good image can be obtained.
By controlling the distance to either one of the photosensitive drum 1a or the developing sleeve 11 as the developing gap control means, the developing gap can be corrected with a simple configuration.

FIG. 6 is a graph showing a change in the detected current amount due to exposure intensity control. FIG. 6 shows the relationship between the development potential and the development amount (toner adhesion amount on the photosensitive drum 1a) when the development gap is largely changed. By providing such a relationship as a control table in advance, the man-hours required for control can be shortened.
The development unevenness can be suppressed by controlling the exposure intensity. Depending on the amount of development unevenness detected from the current generated during development, a portion where the density is reduced can be dealt with by increasing the exposure intensity. FIG. 6 shows changes in the development current of the belt-like image pattern inclined obliquely in the rotation direction before and after exposure intensity control.
By controlling the developer concentration in the developing unit 2 based on the toner adhesion state in the rotation direction of the photosensitive drum 1a estimated from the current caused by toner adhesion during development, the development follow-up property is improved and the rotation direction is improved. Therefore, it is possible to obtain a good image without uneven density.

FIG. 7 is a graph showing the relationship between the development potential in each development gap and the toner adhesion amount on the photosensitive drum. As shown in FIG. 7, when the exposure intensity is controlled, it is possible to cope with not only density unevenness biased left and right but also density reduction at both ends that occurs when the amount of pumping up and down is reduced. It becomes.
Similarly to the above, it is possible to control the exposure time per image (exposure duty). When the normal writing has a duty of 100%, the integrated intensity can be lowered by reducing the duty, and the density can be adjusted.
By adjusting the exposure power based on the rotation axis direction on the photosensitive drum 1a and the toner adhesion state in the rotation direction estimated from the current generated by toner adhesion during development, a good image with no density unevenness can be obtained. Can do.
By controlling the developer agitation time based on the toner adhesion state in the rotation direction of the photosensitive drum estimated from the current generated by toner adhesion during development, the charging rise is insufficient, such as immediately after toner replenishment. In such a case, it is possible to increase the charging and improve the development followability.
A combination of correction by the development gap and correction by the exposure condition is an effective correction method. As shown in FIG. 7, the variation in the adhesion amount due to the change in the development gap is very sensitive, so that it can be corrected with very high accuracy by using it together with fine adjustment according to the exposure conditions.
In this embodiment, the development current is detected by tilting the belt-shaped image pattern in the rotation direction to detect left and right unevenness. However, the development current is detected by arranging a plurality of belt-shaped images tilted in the rotation direction having different densities. By performing the control, a uniform image can be obtained on both the left and right sides of the gradation pattern as well as a solid, and a good image can be obtained.
FIG. 8 is a diagram showing an example of an image pattern for detecting density unevenness. FIG. 9 is a graph showing an example of the detection current result monitored in the image pattern example of FIG. From FIG. 9, it can be seen that the development amount is reduced on the back side for each gradation.
By controlling the development gap based on this current result, left and right unevenness can be eliminated for each gradation. Depending on the current detection result, the control under the exposure condition is also effective as described above.
By controlling a plurality of strip-like images tilted in the rotation direction with the same density and detecting the development current, it is possible to see not only the left and right unevenness but also the follow-up performance of the development in the rotation direction. By detecting the development current using a band-like image inclined in the rotation direction, the density unevenness in the axial direction can be detected accurately and smoothly.

FIG. 10 is a diagram illustrating an example of an image pattern for detecting density unevenness. FIG. 11 is a graph showing an example of the detection current result monitored in the image pattern example of FIG. Referring to FIG. 11, it can be seen from the current detection result that a density drop occurs at the rear end portion of the image simultaneously with the left-right unevenness.
The left and right unevenness can be controlled by the development gap, but the followability cannot be controlled by the development gap. As a countermeasure when it is not possible to follow, increase the toner concentration in the developer, or if the toner charge does not rise immediately after replenishment, increase the toner charge amount by increasing the stirring time to follow up. Sex can be secured. Further, if the rotation speed of the stirring member of the developing unit is variable, it is possible to ensure followability by increasing the rotation speed.
FIG. 12 is a diagram showing an image pattern obtained by dividing the belt-like image in the axial direction and shifting it in a staircase shape in the rotational direction. If a belt pattern is always formed at the time of developing current detection, toner consumption is intense. For example, by detecting and controlling only the left and right widths and the center, the amount of toner consumption required for detection can be suppressed.
By detecting / determining the state of toner adhesion to the photosensitive drum during toner replenishment, the developer stirring state in the axial direction can be determined without directly measuring the density. Then, it is possible to prevent image output in a state where stirring is insufficient immediately after toner replenishment.
According to the present invention, the development follow-up property is improved by controlling the stirring speed of the developer based on the toner adhesion state estimated from the current caused by the toner adhesion during development, thereby improving the density unevenness. A good image with no image can be obtained.
According to the present invention, the density unevenness in the axial direction can be accurately and smoothly detected by detecting the developing current using a strip-like image inclined in the rotation direction. Further, by detecting the development current using a plurality of strip-like images inclined in the rotation direction and changing the density, it is possible to detect the left-right unevenness with high accuracy and smoothness for each gradation.
By forming a plurality of belt-like images in a staircase pattern and detecting the development current, it is possible to detect density unevenness with a small amount of toner consumption and with high accuracy.

1 is a schematic diagram illustrating a first embodiment of an image forming apparatus. FIG. 2 is a partial cross-sectional view showing a schematic configuration around development used in the image forming apparatus according to the present invention. It is a figure which shows an example of the image pattern for density nonuniformity detection produced by shifting the strip | belt-shaped image of a rotating shaft direction diagonally to a rotating direction. It is a figure which shows the monitoring result of a detection current with a graph. It is the schematic which shows the structure of the development gap correction means by this invention. It is a figure which shows the change of the detection electric current amount by exposure intensity control with a graph. It is a figure which shows the relationship between the developing potential in each developing gap, and the toner adhesion amount on a photoreceptor drum. It is a figure which shows the example of an image pattern for density unevenness detection. It is a figure which shows the example of a detection electric current result monitored with the image pattern example of FIG. 8 with a graph. It is a figure which shows the example of an image pattern for density unevenness detection. It is a figure which shows the example of a detection electric current result monitored with the image pattern example of FIG. 10 with a graph. It is a figure which shows the image pattern which divided | segmented the strip | belt-shaped image into the axial direction, and shifted to the rotation direction stepwise.

Explanation of symbols

1a Latent image carrier (photosensitive drum)
2 Development device (development unit)
11 Developer carrier (developing roller, developing sleeve)
15 Gap correction means (spring)
16 Gap correction means (receiving part)
17 Gap correction means (receiving part)
18 Gap correction means (cam, gap correction member)

Claims (15)

  A latent image carrier that carries a latent image on the surface, a developer carrier that is provided to face the surface of the latent image carrier and that carries a developer on the surface, the latent image carrier and the developer The developing gap, which is the distance between the surfaces closest to the carrier, is set to a predetermined interval, and the developer carried on the surface of the developer carrier is supplied to the latent image formed on the latent image carrier. Then, in the image forming apparatus that visualizes the latent image, a developer carried on the surface of the developer carrying member is supplied to the latent image to detect a current generated when the latent image is visualized. Provided with current detection means, and based on the detection result of the current detection means, determines the visualization state of the rotation axis direction and / or rotation direction on the latent image carrier, and controls the exposure / development conditions. An image forming apparatus.   Further provided is a development gap control means for controlling the development gap on the basis of the state of visualization in either the rotation axis direction or the rotation direction on the latent image carrier determined from the detection result of the current detection means. The image forming apparatus according to claim 1, wherein:   The gap correcting member provided inside and moving either one of the latent image carrier and the developer carrier in the distance direction with respect to the other is used as the means for correcting the development gap. 3. The image forming apparatus according to 1 or 2.   The image forming apparatus according to claim 1, wherein a developer concentration sent to the developer carrying member is controlled based on the visualized state.   The image forming apparatus according to claim 1, wherein a developer stirring time is controlled based on the visualized state.   2. The image forming apparatus according to claim 1, wherein a developer stirring speed is controlled based on the visualized state.   2. The image forming apparatus according to claim 1, wherein exposure intensity is controlled based on the visualized state.   The image forming apparatus according to claim 1, wherein an exposure time for one pixel is controlled based on the visualized state.   9. The method according to claim 1, wherein the development gap, the developer concentration, the developer stirring speed, the developer stirring time, the exposure intensity, and the exposure time are controlled in any one or combination. Image forming apparatus.   A latent image of a belt-like image tilted in the rotation direction of the latent image carrier is formed, a current generated when the latent image is visualized is detected, and exposure or development conditions are controlled. Item 10. The image forming apparatus according to Item 9.   The image forming apparatus according to claim 10, wherein a plurality of the belt-like images are visualized at different densities, a current generated during the visualization is detected, and exposure or development conditions are controlled.   The image forming apparatus according to claim 10, wherein a plurality of the belt-like images are visualized at the same density, a current generated during the visualization is detected, and exposure or development conditions are controlled.   A plurality of strip images are visualized by shifting in a stepwise manner with respect to the rotation direction of the latent image carrier, and a current generated during the visualization is detected to control exposure or development conditions. The image forming apparatus according to claim 9.   The image forming apparatus according to claim 9, wherein the belt-like image is visualized with respect to the rotation direction of the latent image carrier, a current generated during the visualization is detected, and exposure or development conditions are controlled. .   At the time of supplying the developer to the developer carrying member, an operation for determining the visualization state of the rotation axis direction and / or the rotation direction on the latent image carrier from the detection result of the current detection unit is performed. The image forming apparatus according to any one of claims 1 to 14.

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