JP2015215486A - Image forming apparatus and color image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can precisely perform feedback control even when a rotary polygon mirror is contaminated.SOLUTION: An image forming apparatus includes: a laser scanner unit 122 that has a laser diode 401 that emits laser beams and polygon mirrors 123 to 126 that reflect the laser beams with a plurality of reflection surfaces; photoreceptor drums 145 to 148 that are scanned by the laser beams reflected on the rotating polygon mirrors 123 to 126 to have images formed thereon; and a transfer belt 130 to which the images formed on the photoreceptor drums 145 to 148 are transferred. When the polygon mirrors 123 to 126 are contaminated, the image forming apparatus forms an image pattern at one of both ends in the scanning direction of the transfer belt 130 according to the number of the reflection surfaces of the polygon mirrors 123 to 126.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a recorded image display apparatus, and a facsimile machine that forms an image by electrophotography.

  In general, an image forming apparatus adjusts the density or forming position of an image to be formed by feedback control. For this purpose, the image forming apparatus forms a toner pattern on an intermediate transfer member, a photosensitive member, or the like, and detects this to detect the image density or position. When an image is formed using a two-component developer composed of a carrier and a toner, the density of the image is determined by the weight mixing ratio of the carrier and the toner as an important factor. In order to keep the toner ratio to the carrier (hereinafter referred to as “toner density”) constant, the image forming apparatus detects the density of the toner pattern formed on the intermediate transfer member, and feedback of toner density based on the detection result. Take control. For this purpose, the image forming apparatus includes a light detection sensor such as a photodiode for irradiating the toner pattern with light and detecting the reflected light. The toner pattern is formed by attaching toner to an electrostatic latent image formed by scanning a photosensitive member with a light beam reflected by a rotary polygon mirror having a plurality of reflecting surfaces.

  The image forming apparatus cannot perform an image forming process based on a user instruction while performing feedback control. Therefore, it is required to improve the production efficiency of the image forming apparatus by shortening the time required for feedback control as much as possible. Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique for realizing time reduction of feedback control such as density correction and position correction. In Japanese Patent Application Laid-Open No. 2004-133620, the toner pattern for density detection is detected by a detection unit for correcting the positional deviation, and the positional deviation is corrected. Since the density correction is performed only when the toner pattern cannot be accurately detected, it is not necessary to perform an extra density adjustment, and the production efficiency of the image forming apparatus can be improved.

  The toner pattern for feedback control is formed for each color of yellow (Y), magenta (M), cyan (C), and black (K). For example, yellow and magenta toner patterns are formed at one end and cyan and black toner patterns are formed at the other end of both ends of the photoconductor in the main scanning direction. In this case, the toner pattern formation and detection time can be shortened as compared with the case where the toner patterns of the respective colors are formed side by side in the sub-scanning direction at one end.

JP 2003-280316 A

  An electrophotographic image forming apparatus forms an image using an optical scanning device. The above-mentioned rotating polygon mirror is provided in the optical scanning device. In the optical scanning device, dust may be generated by rubbing between components when assembling components. Therefore, a cleaning process for removing dust in the optical scanning apparatus is incorporated in the assembly process of the optical scanning apparatus in the factory. In the cleaning process, dust is removed with an air brush or the like. However, it is difficult to remove 100% of these dusts in the cleaning process, and a trace amount of dust may remain in the optical scanning device. Recently, air pollutants are becoming fine particles, and there is a problem that fine particles pass through the gaps in the sealed structure of the optical scanning device provided in the image forming apparatus installed in the market, and dust enters the optical scanning device. Has occurred. The dust in the optical scanning device causes dirt on the reflecting surface of the rotating polygon mirror that rotates at a high speed.

  The contamination of the rotary polygon mirror greatly affects the feedback control using the toner pattern. Therefore, the image forming apparatus cannot ignore the contamination of the rotating polygon mirror. In particular, when a toner pattern is formed on both ends of the photoconductor in the main scanning direction in order to shorten the feedback control time, the influence of contamination of the rotary polygon mirror is large, and accurate feedback control cannot be expected.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can accurately perform feedback control even when a rotating polygon mirror is dirty.

  An image forming apparatus of the present invention that solves the above problems includes a photoconductor, a light source that emits a light beam for exposing the photoconductor, and the light beam so that the light beam scans over the photoconductor. An optical scanning device comprising: a rotary polygon mirror having a plurality of reflecting surfaces; and an electrostatic latent image formed on the photosensitive member by scanning with the light beam reflected by the reflection surface of the rotary polygon mirror. An image forming unit including a developing unit that develops an image using toner, and an intermediate transfer member to which the developed toner image is transferred onto the photosensitive member, and the toner image transferred to the intermediate transfer member is recorded. Transfer means for transferring to a medium; first detection means for detecting a toner pattern transferred from the photosensitive member onto the intermediate transfer member; and the first detection device in the scanning direction of the light beam reflected by the rotary polygon mirror. Detection An image forming apparatus for controlling a toner pattern formation position, and a second detection unit that detects a toner pattern transferred from the photosensitive member onto the intermediate transfer member. A storage unit that stores the presence or absence of contamination of the rotary polygon mirror determined by the density of the test image for contamination confirmation transferred to the recording medium or the intermediate transfer member, and confirms the storage unit, When the rotary polygon mirror is not soiled, the image formation is performed such that the toner pattern transferred from the photosensitive member onto the intermediate transfer member is detected by the first detection unit and the second detection unit. Means for forming the toner pattern on the photosensitive member, and when the rotary polygon mirror is dirty, the toner pattern transferred from the photosensitive member onto the intermediate transfer member is Control means for causing the image forming means to form the toner pattern on the photoconductor so as to be detected by one of the first detecting means and the second detecting means. To do.

  According to the present invention, the formation position of the toner pattern used for feedback control is changed depending on the presence or absence of dirt on the rotary polygon mirror. Therefore, feedback control can be performed accurately even if the rotating polygon mirror is dirty.

1 is a configuration diagram of an image forming apparatus. (A), (b) is explanatory drawing of a laser scanner unit. The block diagram of a controller. 7 is a flowchart illustrating toner density feedback control processing. Explanatory drawing of the dirt of a polygon mirror. Explanatory drawing of the image formed with the dirty polygon mirror. Explanatory drawing of a dirty location. The flowchart showing the process which discriminate | determines the presence or absence of dirt. (A), (b) is an illustration figure of the screen displayed on a display panel. (A), (b) is an illustration figure of a test image. 7 is a flowchart illustrating toner density feedback control processing. FIG. 6 is an explanatory diagram of a toner pattern formation position. (A), (b) is explanatory drawing of the formation position of a toner pattern. The figure showing the positional relationship of a transfer belt and a patch detection sensor. (A)-(d) is an illustration figure of a toner pattern.

  Hereinafter, embodiments will be described in detail with reference to the accompanying drawings.

<Overall configuration of image forming apparatus>
1A and 1B are configuration diagrams of an image forming apparatus according to the present embodiment. The image forming apparatus includes a process unit 120, a primary transfer unit 121, a transfer belt 130, a secondary transfer unit 140, a laser scanner unit 122, and a fixing unit 170 for image forming processing. The image forming apparatus also includes a paper feed cassette 61, transport rollers 155 and 161, and a transport sensor 160 for transporting a recording medium such as paper on which an image is to be formed to the secondary transfer unit 140. Further, the image forming apparatus includes a transport roller 191 for discharging the recording medium to the paper discharge tray 196 via the transport path 181.

  The process unit 120 includes photosensitive drums 145 to 148 and four developing units corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (K). The process unit 120 and the laser scanner unit 122 perform image formation on the photosensitive drums 145 to 148.

  As an example, image formation on a yellow photosensitive drum 145 will be described with reference to FIG. The process unit 120 forms an image for the other colors by the same process with the same configuration. Around the photosensitive drum 145, a charging roller 101, a developing device 102, a transfer roller 103, a cleaner 104, and a pre-exposure unit 105 are provided.

  The charging roller 101 charges the surface of the photosensitive drum 145. The photosensitive drum 145 having a charged surface is a photosensitive member that is exposed to a light beam emitted from the laser scanner unit 122 to form an electrostatic latent image on the surface. The laser scanner unit 122 is an optical scanning device, and includes a laser diode as a light emitting element and a polygon mirror 123 as a rotary polygon mirror. The light beam emitted from the laser diode is reflected by the polygon mirror 123 to expose the photosensitive drum 145. As the polygon mirror 123 rotates, the light beam scans on the photosensitive drum 145 (on the photosensitive member). The laser scanner unit 122 emits a light beam according to image data representing an image to be imaged.

  The developing device 102 is supplied with yellow toner from the toner container 106. The toner is supplied when a decrease in toner density in the developing device 102 is detected. The developing device 102 develops the toner by attaching toner to the electrostatic image formed on the surface of the photosensitive drum 145. As a result, a toner image is formed on the photosensitive drum 145. The transfer roller 103 constitutes a primary transfer unit 121. The transfer roller 103 is disposed so as to sandwich the transfer belt 130 between the photosensitive drum 145 and transfers the toner image formed on the photosensitive drum 145 to the transfer belt 130. The cleaner 104 collects the toner remaining on the photosensitive drum 145 after the transfer. The pre-exposure unit 105 irradiates the surface of the photosensitive drum 145 from which the remaining toner has been collected, thereby stabilizing the charged state of the surface of the photosensitive drum 145 so that uniform charging can be performed in the subsequent charging step.

  Similarly, a magenta toner image is formed on the photosensitive drum 146, a cyan toner image is formed on the photosensitive drum 147, and a black toner image is formed on the photosensitive drum 148. The toner images of these colors are transferred to the transfer belt 130 by transfer rollers provided respectively.

  The transfer belt 130 is driven to rotate, and is an intermediate transfer body onto which toner images formed on the photosensitive drums 145 to 148 are superimposed and transferred by the primary transfer unit 121. A full-color toner image is formed on the transfer belt 130 (on the intermediate transfer member) by transferring the toner image. The transfer belt 130 rotates to convey the transferred toner image to the secondary transfer unit 140. In the secondary transfer unit 140, the toner image is transferred from the transfer belt 130 to the recording medium. A patch detection sensor 208 that detects a toner pattern formed on the transfer belt 130 is provided in the vicinity of the transfer belt 130.

  The recording medium is stored in the paper feed cassette 61. The recording medium supplied from the paper feed cassette 61 is transported to the secondary transfer unit 140 by transport rollers 155 and 161. A conveyance sensor 160 is provided between the conveyance roller 155 and the conveyance roller 161. In consideration of the timing at which the conveyance sensor 160 detects the recording medium, the conveyance roller 161 moves the recording medium so that the leading edge of the recording medium and the leading edge of the toner image on the transfer belt 130 coincide at the secondary transfer unit 140. It is conveyed to the secondary transfer unit 140. For example, when the recording medium is quickly conveyed with respect to the toner image on the transfer belt 130, the conveyance roller 161 temporarily stops conveyance of the recording medium and adjusts the conveyance timing of the recording medium.

  The recording medium is conveyed to the fixing device 170 after the toner image is transferred by the secondary transfer unit 140. The fixing device 170 heats and fixes the toner image transferred to the recording medium. The recording medium on which the toner image is fixed is discharged to a discharge tray 196 via a conveyance path 181. A conveyance sensor 171 is provided on the downstream side of the fixing device 170 in the conveyance direction. When performing double-sided printing, the recording medium is transported to the transport sensor 160 via a path on the lower side in the figure opposite to the transport path 181 after image formation on one side is completed, and an image is formed on the back surface. . Thus, the image forming apparatus is a color image forming apparatus that forms a color image on a recording medium.

<Laser scanner unit>
FIG. 2 is an explanatory diagram of the laser scanner unit 122. FIG. 2A shows the configuration of the laser scanner unit 122 viewed from the front side (front side in FIG. 1) of the image forming apparatus.

  The laser scanner unit 122 includes optical scanner units 80 to 83 for each color. Each of the optical scanner units 80 to 83 includes a polygon mirror and a laser diode. The optical scanner unit 80 is used for yellow image formation. The optical scanner unit 81 is used for magenta image formation. The optical scanner unit 82 is used for forming a cyan image. The optical scanner unit 83 is used for black image formation. The configuration of the optical scanner unit 80 will be described with reference to FIG. Since the optical scanner units 80 to 83 have the same configuration, the description of the optical scanner units 81 to 83 is omitted.

  The optical scanner unit 80 includes a laser diode 401, a polygon mirror 123, a polygon motor 207, and a reflecting mirror 420. The laser diode 401 is a light source that is controlled to be turned on and off by the laser driver 210 and emits a light beam modulated according to the gradation data toward the polygon mirror 123.

  The polygon mirror 123 is a rotating polygon mirror having a plurality of reflecting surfaces. In FIG. 2, the polygon mirror 123 has five reflecting surfaces. The polygon mirror 123 is controlled to rotate in the direction of arrow A by the polygon motor 207. The light beam emitted from the laser diode 401 is reflected by the reflecting surface of the polygon mirror 123. Since the polygon mirror 123 rotates, the light beam reflected by the reflecting surface becomes reflected light whose reflection angle continuously changes. The light beam reflected by the polygon mirror 123 is reflected by the reflecting mirror 420 and scans the photosensitive drum 145 in the main scanning direction. As a result, an electrostatic latent image is formed on the photosensitive drum 145. The rotation direction of the polygon mirrors 123 to 126 may be the reverse direction of the arrow A. In this case, the main scanning direction is reversed, but the main scanning direction of each color may be the same.

<Controller>
FIG. 3 is a block diagram of a controller for controlling the operation of such an image forming apparatus. The controller is mounted on the image forming apparatus and includes an operation unit 204, a laser driver 210, a control unit 211, an image data processing unit 212, and an I / O unit 203. The control unit 211 includes a CPU (Central Processing Unit) 200, a ROM (Read Only Memory) 201, and a RAM (Random Access Memory) 202. An operation unit 204, an image data processing unit 212, and an I / O unit 203 are connected to the control unit 211. A laser driver 210 is connected to the image data processing unit 212. Polygon motors 207, 225, 226, 227, patch detection sensor 208, and toner supply motor 213 are connected to the I / O unit 203. A polygon mirror 123 is connected to the polygon motor 207. A polygon mirror 124 is connected to the polygon motor 225. A polygon mirror 125 is connected to the polygon motor 226. A polygon mirror 126 is connected to the polygon motor 227.

  The control unit 211 controls the overall operation of the image forming apparatus when the CPU 200 reads a computer program from the ROM 201 and executes the RAM 202 as a work area. The operation unit 204 is an input / output device that includes a display panel and the like.

  The image data processing unit 212 processes input image data (input image data). The input image data is generated from a document image read by a scanner unit provided in the image forming apparatus or input from an external device. The image data processing unit 212 has a data conversion table such as a gradation correction table, and gradation data for driving the light source of the light beam emitted from the laser scanner unit 122 by using the data conversion table. Convert to The laser driver 210 controls the laser scanner unit 122 according to the processing result of the image data by the image data processing unit 212, and adjusts the light emission timing and the light amount of the light beam emitted from the laser scanner unit 122. Thereby, the gradation and density of the image to be formed are adjusted.

  The I / O unit 203 performs drive control of various motors such as the polygon motors 207, 225, 226, and 227 and the toner supply motor 213 under the control of the control unit 211. Further, the I / O unit 203 acquires detection results from various sensors such as the patch detection sensor 208 and inputs the detection results to the control unit 211. The polygon motor 207 controls the rotation of the polygon mirror 123. The polygon motor 225 controls the rotation of the polygon mirror 124. The polygon motor 226 controls the rotation of the polygon mirror 125. The polygon motor 227 controls the rotation of the polygon mirror 126. The toner supply motor 213 drives and controls the toner container 106 to supply toner to the developing device.

  When the controller configured as described above receives an instruction to start an image forming operation from the operation unit 204, it drives various motors such as the polygon motors 207, 225, 226, and 227 and the toner supply motor 213 to perform image forming processing.

<Image formation processing>
The image forming apparatus performs image formation while performing feedback control of image forming conditions such as light beam emission timing and toner density. The light beam emission timing control is performed in order to correct the color misregistration by adjusting the formation position of each color toner image. In the two-component replenishment type image forming apparatus including the toner container 106, toner density control is important in order to keep the toner density in the developing device within a predetermined range. As the toner density control, there are a system in which a video count of a formed toner pattern (image pattern) is converted into a toner replenishment amount, a system in which a sensor for detecting the toner density is provided in the developing device, and the like. In the present embodiment, a color misregistration detection toner pattern for detecting a misregistration amount between the toner images of each color and a density detection toner pattern for detecting the toner density of the toner image of each color in order to correct the color misregistration. And formed on the transfer belt 130. The image forming apparatus detects these toner patterns by a patch detection sensor 208, which is an optical sensor, and feeds back the detection results to image forming conditions. Thereby, the emission timing of the light beam and the toner replenishment amount are adjusted. FIG. 4 is a flowchart showing an image forming process including such feedback control.

  The CPU 200 of the controller forms a color misregistration detection toner pattern and a density detection toner pattern on the transfer belt 130 (S101). As described above, the image forming apparatus forms the electrostatic latent images of the color misregistration detection toner pattern and the density detection toner pattern on the photosensitive drums 145 to 148 and develops them to form a toner image. The toner image of the color misregistration detection toner pattern and the density detection toner pattern is transferred to the transfer belt 130, whereby the color misregistration detection toner pattern and the density detection toner pattern are formed on the transfer belt 130.

  When the color misregistration detection toner pattern and the density detection toner pattern formed on the transfer belt 130 reach the detection position of the patch detection sensor 208, the patch detection sensor 208 detects them. The detection result is sent to the CPU 200 via the I / O unit 203. The CPU 200 sets image forming conditions according to the detection result of the patch detection sensor 208 (S102). The CPU 200 sets a light beam emission timing condition based on the detection result of the color misregistration detection toner pattern. The CPU 200 generates gradation correction conditions based on the detection result of the density detection toner pattern. The gradation correction condition is used for correcting a gradation correction table, for example. Further, the CPU 200 sets the amount of toner to be replenished from the toner container 106 to the developing device based on the detection result of the density detection toner pattern. As described above, the image forming conditions include light beam emission timing, gradation correction conditions, toner replenishment amount, and the like.

  The CPU 200 having set the image forming conditions performs image forming processing according to the image forming conditions (S103). The CPU 200 replenishes toner from the toner container 106 to the developing device by controlling the toner replenishment motor 213 via the I / O unit 203 according to the set toner replenishment amount. The CPU 200 transmits the light beam emission timing condition and the gradation correction condition to the image data processing unit 212. The image data processing unit 212 processes image data according to the light beam emission timing and gradation correction conditions. The image data processing unit 212 corrects a data conversion table such as a gradation correction table according to the gradation correction condition, and converts the image data into gradation data using the corrected data conversion table. The laser driver 210 performs light emission control of the laser diodes 401 to 404 of the laser scanner unit 122 according to the processing result of the image data processing unit 212. Further, the CPU 200 controls operations of various motors used for image forming processing such as various motors such as polygon motors 207, 225, 226, and 227 in order to perform image forming processing.

  When the image forming process ends, the CPU 200 determines whether or not to end the image forming process (S104). The CPU 200 determines whether or not to end the image forming process, for example, based on whether or not the image forming process on the number of recording media designated by the user has ended. When the image forming process is ended (S104: Y), the CPU 200 ends the process as it is. When the image forming process is not terminated (S104: N), the CPU 200 determines whether a predetermined number of image forming processes have been performed or whether environmental conditions of the image forming apparatus such as temperature and humidity have changed (S105). The image forming apparatus updates the image forming conditions every time a predetermined number of image forming processes are performed or when the environmental conditions change. The image forming apparatus includes a temperature sensor and a humidity sensor for detecting changes in environmental conditions.

  When the predetermined number of image forming processes have not been performed and the environmental conditions have not changed (S105: N), the CPU 200 continues the image forming process (S103). When a predetermined number of image forming processes or environmental conditions have changed (S105: Y), the CPU 200 forms a color misregistration detection toner pattern and a density detection toner pattern on the transfer belt 130 to set the image forming conditions. Start (S101).

  As described above, the image forming apparatus performs image forming processing by setting the image forming conditions by using the color misregistration detecting toner pattern and the density detecting toner pattern and adjusting the color misregistration and the toner density. By setting the image forming conditions every time a predetermined number of image forming processes are executed or when the environmental conditions of the image forming apparatus change, the image forming process is performed while optimally adjusting the color misregistration and the toner density.

<Poor polygon mirror stains>
In the toner density feedback control using the toner pattern, it is necessary to prevent deterioration of the image quality of the toner pattern in order to appropriately supply the toner. One of the causes of the deterioration of the image quality of the toner pattern is contamination of the polygon mirrors 123 to 126. FIG. 5 is an explanatory diagram of dirt on the polygon mirror 123. Since the other polygon mirrors 124 to 126 are similarly stained, the description thereof is omitted.

  When the polygon mirror 123 having five reflecting surfaces rotates in the direction A, an airflow B in the direction opposite to the direction A is generated near the apex (the corner of the reflecting surface). This is because the angle of the reflecting surface is located farthest from the center of rotation, and negative pressure is applied to the opposite side of the corner in the direction A. The dust in the laser scanner unit 122 is caught in the airflow B generated near the corner of the reflecting surface and adheres to the dirty portion C of the polygon mirror 123. In this way, the dirty portion C is soiled with dust. In such a dirty polygon mirror 123, an image as shown in FIG. 6 is formed.

  The toner image 302 formed by scanning the light beam 301 emitted from the laser scanner unit 122 is formed thinner in the region 303 than the other regions due to contamination of the polygon mirror 123. The density detection toner pattern 304 is formed in this region 303. For this reason, the density detection toner pattern 304 formed at this position is deteriorated and thinned. The controller determines that the toner amount in the developing device is small due to the thin density detection toner pattern 304. For this reason, the toner replenishment amount becomes excessive, and appropriate toner replenishment cannot be performed.

  Similarly, when correcting the gradation of an image, the density detection toner pattern 304 is detected by the patch detection sensor 208 to perform feedback control. For this reason, the contamination of the polygon mirror 123 also affects the gradation control. As described above, in a configuration in which the density detection toner pattern 304 is detected and feedback control is performed, contamination of the polygon mirror 123 interferes with appropriate feedback control and affects the use of the image forming apparatus.

  The contamination location of the polygon mirror 123 is determined according to the number of reflection surfaces of the polygon mirror 123 when the rotation speed (number of rotations) is constant. When the number of reflecting surfaces of the polygon mirror 123 becomes five or more, the polygon mirror 123 becomes nearly circular. Therefore, the distance of the reflecting surface approaches from the corner of the reflecting surface, and dust in the laser scanner unit 122 adheres to the dirt spot C on the downstream side in the rotational direction (direction A) by the air flow B as shown in FIG.

  FIG. 7 is an explanatory diagram of dirt spots generated on the polygon mirror 123 having four reflecting surfaces. When there are four reflecting surfaces, the downstream side in the rotation direction of the corners of the reflecting surface is a negative pressure. However, the negative pressure is small, and the resulting vortex is also less involved. Therefore, the curvature of the generated airflow D increases. The position where the airflow D of the reflecting surface collides becomes a dirty portion C, and dust adheres.

<Polygon mirror stain detection>
FIG. 8 is a flowchart showing processing for determining whether or not the polygon mirrors 123 to 126 are dirty. FIG. 9 is a view showing an example of a screen displayed on the display panel 701 of the operation unit 204 during the process of determining whether or not the polygon mirrors 123 to 126 are dirty.

  The control unit 211 displays an operation screen 702 (FIG. 9A) for instructing the user to determine whether or not the polygon mirrors 123 to 126 are dirty on the display panel 701 of the operation unit 204 (S200). When the user operates (presses) the “Yes” button 703 on the operation screen 702, an instruction to start processing for determining whether the polygon mirrors 123 to 126 are dirty is input to the image forming apparatus. Thus, the control unit 211 starts a process for determining whether or not the polygon mirrors 123 to 126 are dirty (S210: Y). When the “NO” button 704 is operated (pressed), the image forming apparatus ends the process without performing the discrimination process (S210: N).

  First, the control unit 211 forms a test image for checking dirt on the recording medium by the image forming process described above, and displays the input screen 705 for the test image check result shown in FIG. The information is displayed on the panel 701 (S201, S202). FIG. 10 is an exemplary diagram of a recording medium on which a test image for checking dirt is formed. 10 is a halftone image formed on one surface of the recording medium in the main scanning direction. In addition to the halftone image, an image that can easily detect stains on the polygon mirrors 123 to 126, such as a darker image or a lighter image, can be used as a test image for checking dirt. FIG. 10A shows a test image for confirming a stain in which density unevenness and missing are not generated in the main scanning direction of the recording medium. In this case, the user can determine that the polygon mirrors 123 to 126 are not soiled. FIG. 10B shows a test image in which density unevenness and missing are generated in a predetermined region 1001 (one end portion) in the main scanning direction of the recording medium. In this case, the user can determine that the polygon mirrors 123 to 126 are soiled.

  The user confirms the smear confirmation test image with the recording medium discharged from the image forming apparatus, and inputs the confirmation result from the input screen 705. When the user confirms a decrease in density at the edge of the image such as the area 1001, the user presses a “Yes” button 706. As a result, it is input from the operation unit 204 to the control unit 211 that the polygon mirrors 123 to 126 are contaminated, and the control unit 211 determines that there is contamination (S203: Y). If there is dirt, the control unit 211 stores the fact that the polygon mirrors 123 to 126 are dirty (dirty) in the storage unit 205 (S204).

  The user presses a “NO” button 707 in the case where density reduction such as the area 1001 cannot be confirmed on the recording medium discharged from the image forming apparatus. As a result, it is input from the operation unit 204 to the control unit 211 that the polygon mirrors 123 to 126 are not dirty, and the control unit 211 determines that there is no contamination (S203: N). When there is no dirt, the control unit 211 stores in the storage unit 205 that the polygon mirrors 123 to 126 are not dirty (no dirt) (S205).

  Note that it is also possible to determine whether or not the polygon mirrors 123 to 126 are dirty without the user's operation. For example, an image reading unit such as an optical sensor that detects the density of a test image for confirming a stain formed on a recording medium is provided in the image forming apparatus. The presence or absence of dirt on the mirrors 123 to 126 may be determined. Further, the density of the test image for confirming dirt may be detected when it is formed on the transfer belt 130 to determine whether or not the polygon mirrors 123 to 126 are dirty. In this case, a line sensor is provided near the transfer belt 130 to detect the image density.

  Further, when determining the presence or absence of contamination on the polygon mirrors 123 to 126 from the image formation result, it may be separated from other factors that degrade the image quality of the test images such as the photosensitive drums 145 to 148. For example, when forming a test image for checking dirt, the test image may be formed by changing the voltage applied to the photosensitive drums 145 to 148 in addition to the test image for checking dirt. By comparing these test images, it is possible to identify and specify the deterioration factor of the image quality.

<Toner pattern formation position>
The toner pattern used for feedback control is formed at both ends of the transfer belt 130 in the main scanning direction. As described above, the end in the main scanning direction is affected by the contamination of the polygon mirrors 123 to 126. Therefore, in the present embodiment, the toner pattern forming position used for feedback control is changed according to whether the polygon mirrors 123 to 126 are dirty. FIG. 11 is a flowchart showing processing for performing feedback control of toner density by changing the toner pattern formation position in accordance with the presence or absence of contamination on the polygon mirrors 123 to 126.

  The CPU 200 of the controller confirms whether it is time to correct the toner density (S300). The timing for correcting the toner density is before or after the image forming process is started or after a predetermined number of image forming processes. When it is time to correct the toner density (S300: Y), the CPU 200 confirms whether or not the polygon mirrors 123 to 126 are dirty according to the storage contents of the storage unit 205 (S301).

When the polygon mirrors 123 to 126 are dirty (S301: Y), the control unit 211 uses the image data processing unit 212 to acquire image data having a toner pattern used for feedback control at one end in the main scanning direction. The controller 211 controls the laser scanner unit 122 with the laser driver 210 to form a toner pattern according to the acquired image data (S302). Which of the two end portions the toner pattern is formed on is determined by the number of reflecting surfaces of the polygon mirrors 123 to 126. When the number of reflection surfaces of the polygon mirrors 123 to 126 is five or more, a toner pattern is formed on the upstream side with respect to the rotation direction of the polygon mirrors 123 to 126. When the number of reflecting surfaces of the polygon mirrors 123 to 126 is 4 or less, a toner pattern is formed on the downstream side with respect to the rotation direction of the polygon mirrors 123 to 126. The storage unit 205 stores image data corresponding to the number of reflection surfaces of the polygon mirrors 123 to 126.
When the polygon mirrors 123 to 126 are not dirty (S301: N), the control unit 211 forms toner patterns used for feedback control at both ends in the main scanning direction (S303).

  When the toner pattern formed on the transfer belt 130 reaches the detection position of the patch detection sensor 208, the patch detection sensor 208 detects the density of the toner pattern. The detection result is sent to the CPU 200 (S304). The CPU 200 compares the detection result of the patch detection sensor 208 with a reference density value, and determines the density of the toner pattern relative to the reference. The CPU 200 calculates the toner replenishment amount to the developing device from the result of the density determination (S305). The CPU 200 drives and controls the toner supply motor 213 according to the calculated toner supply amount, and supplies toner from the toner bottle to the developing device (S306).

  12 and 13 are explanatory diagrams of toner pattern formation positions. FIG. 12 shows a case where toner patterns are formed at both ends in the main scanning direction. FIG. 13 shows a case where a toner pattern is formed at one end in the main scanning direction. 13A shows a case where the number of reflection surfaces of the polygon mirror 123 is five, and FIG. 13B shows a case where the number of reflection surfaces of the polygon mirror 123 is four.

  When forming toner patterns at both ends in the main scanning direction, separate the toner patterns corresponding to each color, for example, yellow and magenta toner patterns at one end and cyan and black toner patterns at the other end. Form. As a result, the toner pattern formation and detection time is shortened as compared with the case where toner patterns of each color are formed side by side in the sub-scanning direction at one end.

  When the number of reflective surfaces is 5 or more, the downstream side with respect to the rotation direction of the polygon mirror 123 is a dirty portion C. Therefore, in this case, if toner patterns are formed at both ends in the main scanning direction, the images “Y” and “M” are affected. Therefore, a toner pattern is formed in a region 601 that is an end in the main scanning direction that is upstream (upstream in the main scanning direction) with respect to the rotation direction of the polygon mirror 123.

  When the number of reflecting surfaces is 4 or less, the upstream side with respect to the rotation direction of the polygon mirror 123 is a dirt spot C. Therefore, in this case, if toner patterns are formed at both ends in the main scanning direction, the images “C” and “K” are affected. Therefore, a toner pattern is formed in a region 602 that is an end portion in the main scanning direction that is downstream (downstream in the main scanning direction) with respect to the rotation direction of the polygon mirror 123.

  As described above, the position where the toner pattern is formed is changed according to the number of reflection surfaces of the polygon mirror 123.

  The toner pattern is formed (transferred) on the transfer belt 130 and then detected by the patch detection sensor 208. FIG. 14 is a diagram illustrating the positional relationship between the transfer belt 130 and the patch detection sensor 208. As described above, the toner pattern for feedback control of the toner density is formed at the upstream end or the downstream end in the main scanning direction. On the transfer belt 130, these are both ends in the width direction. For this purpose, the patch detection sensor 208 is provided in the vicinity of both ends in the width direction of the transfer belt 130 (patch detection sensor 208F, patch detection sensor 208R). The patch detection sensors 208 </ b> F and 208 </ b> R are provided on the downstream side of the primary transfer unit 121 in the rotation direction of the transfer belt 130. Therefore, the patch detection sensors 208 </ b> F and 208 </ b> R can detect the toner pattern immediately after being formed (transferred) on the transfer belt 130 by the primary transfer unit 121.

  FIG. 15 is an illustration of a toner pattern. FIG. 15A shows a toner pattern for color misregistration detection. 15B, 15C, and 15D show toner patterns for toner density detection.

  The color misregistration detection toner patterns 53 are formed at both ends in the width direction of the transfer belt 130 (FIG. 15A). The color misregistration detection toner pattern 53 includes yellow, magenta, cyan, and black images 53Y, 53M, 53C, and 53K that are continuously arranged in the rotation direction of the transfer belt 130. Since the color misregistration detection toner patterns 53 are arranged at both ends of the transfer belt 130 in the width direction, the color misregistration detection toner patterns 53 can be detected by either of the patch detection sensors 208F and 208R. The color misregistration correction is performed according to the image forming positions of the respective color images 53Y, 53M, 53C, and 53K included in the color misregistration detection toner pattern 53. Therefore, the density change of the color misregistration detection toner pattern 53 hardly affects the color misregistration correction. That is, even if the density of the toner pattern 53 changes due to the reflecting surface of the polygon mirror 123 becoming dirty, the influence on the color misregistration correction is small. Further, since substantially the same position of each reflection surface of the polygon mirror 123 is uniformly soiled, the detection accuracy of the toner pattern 53 is within an allowable range.

  The toner pattern 52 for detecting the toner density is formed at both end portions (FIG. 15B) in the width direction of the transfer belt 130 or at either one end portion (FIGS. 15C and 15D). In FIG. 15B, yellow and magenta images 52Y and 52M are formed at one end, and cyan and black images 52C and 52K are formed at the other end. In order to form the toner pattern 52 for detecting the toner density separately for each of the two colors at both ends, the toner is compared with the case where the images 52Y, 52M, 52C, and 52K of each color are arranged at one end. The formation time and detection time of the density detection toner pattern 52 can be shortened.

  FIGS. 15C and 15D show the toner density detection toner pattern 52 in which images 52Y, 52M, 52C, and 52K of yellow, magenta, cyan, and black are continuously arranged in the rotation direction of the transfer belt 130. Is configured. Since the toner pattern 52 for detecting the toner density is arranged on at least one of both ends in the width direction of the transfer belt 130, it is detected by one of the patch detection sensors 208F and 208R. Therefore, even if the reflection surface of the polygon mirror 123 is dirty, one of the patch detection sensors 208F and 208R can accurately detect the toner pattern 52.

  The toner density detection toner pattern 52 may be formed at both ends of the transfer belt 130 in the same manner as the color misregistration detection toner pattern 53. In this case, the controller preferentially uses the detection result of one of the patch detection sensors 208F and 208R to detect the toner density. Which detection result of the patch detection sensors 208F and 208R is prioritized is determined by the number of reflection surfaces of the polygon mirror 123.

  As described above, when the reflection surface of the polygon mirror 123 becomes dirty, a toner pattern for feedback control is formed according to the number of reflection surfaces of the polygon mirror 123. Therefore, feedback control can be performed without being affected by contamination of the polygon mirror 123. The present embodiment can be applied to any feedback control as long as it detects toner patterns such as tone correction control in addition to toner density control and performs control according to the detection result. .

  DESCRIPTION OF SYMBOLS 122 ... Laser scanner unit, 123-126 ... Polygon mirror, 130 ... Transfer belt, 145-148 ... Photosensitive drum, 207 ... Polygon motor, 208 ... Patch detection sensor, 213 ... Toner supply motor, 401 ... Laser diode, 420-425 …Reflector

Claims (14)

A photoreceptor,
An optical scanning comprising: a light source that emits a light beam for exposing the photosensitive member; and a rotary polygon mirror having a plurality of reflecting surfaces that reflect the light beam so that the light beam scans on the photosensitive member. Equipment,
An image forming unit including a developing unit that develops the electrostatic latent image formed on the photosensitive member by scanning with the light beam reflected by the reflecting surface of the rotary polygon mirror using toner;
A transfer unit that includes an intermediate transfer member to which the developed toner image is transferred onto the photosensitive member, and that transfers the toner image transferred to the intermediate transfer member to a recording medium;
First detecting means for detecting a toner pattern transferred from the photosensitive member onto the intermediate transfer member;
Second detection for detecting a toner pattern transferred from the photosensitive member onto the intermediate transfer member, which is disposed at a position different from the first detection unit in the main scanning direction of the light beam reflected by the rotary polygon mirror. Means,
An image forming apparatus for controlling the formation position of the toner pattern,
Storage means for storing the presence or absence of dirt on the rotary polygon mirror determined by the density of a test image for dirt confirmation transferred to the recording medium or the intermediate transfer member;
When the rotating polygon mirror is not contaminated by checking the storage means, the toner pattern transferred from the photosensitive member onto the intermediate transfer member is detected by the first detection means and the second detection means. As described above, when the image forming unit forms the toner pattern on the photoconductor and the rotating polygon mirror is soiled, the toner pattern transferred from the photoconductor onto the intermediate transfer body is Control means for causing the image forming means to form the toner pattern on the photoconductor so as to be detected by one of the first detection means and the second detection means. ,
Image forming apparatus. The storage means stores image data for forming the toner pattern at one end in the main scanning direction according to the number of reflection surfaces of the rotary polygon mirror,
The image forming unit forms an image corresponding to the image data on the photoconductor when the rotating polygonal mirror is dirty.
The image forming apparatus according to claim 1. An operation means for inputting a result of confirming whether or not the rotating polygon mirror is soiled by the recording medium on which the stain confirmation test image is transferred by a user operation,
The control means causes the storage means to store the presence or absence of dirt on the rotary polygon mirror in response to an input from the operation means.
The image forming apparatus according to claim 1. Comprising image reading means for detecting the density of the test image for confirmation of contamination formed on the recording medium,
The control means determines the presence or absence of dirt on the rotary polygon mirror based on the detection result of the image reading means, and stores the presence or absence of dirt on the rotary polygon mirror in the storage means.
The image forming apparatus according to claim 1. A line sensor for detecting the density of the test image for confirmation of dirt formed on the intermediate transfer member,
The control means determines the presence or absence of dirt on the rotary polygon mirror based on the detection result of the line sensor, and stores the presence or absence of dirt on the rotary polygon mirror in the storage means.
The image forming apparatus according to claim 1. The image forming unit forms the toner pattern on one end of the photoconductor in the main scanning direction if the number of the reflecting surfaces is 4 or less when the rotating polygon mirror is soiled. If the number of the reflective surfaces is 5 or more, the toner pattern is formed on the other end of the photoconductor in the main scanning direction.
The image forming apparatus according to claim 1. If the rotating polygon mirror is soiled and the number of the reflecting surfaces is 4 or less, the image forming means may be the main scanning that is downstream of the rotation direction of the rotating polygon mirror of the photoconductor. If the toner pattern is formed at the end in the direction and the number of reflecting surfaces is 5 or more, the end in the main scanning direction on the upstream side with respect to the rotation direction of the rotary polygon mirror of the photoconductor Forming the toner pattern,
The image forming apparatus according to claim 6. A first photoreceptor;
A second photoreceptor,
A third photoreceptor;
A fourth photoreceptor;
A first light source that emits a first light beam for exposing the first photosensitive member; a second light source that emits a second light beam for exposing the second photosensitive member; A third light source that emits a third light beam for exposing the third photosensitive member; a fourth light source that emits a fourth light beam for exposing the fourth photosensitive member; A first rotating polygon mirror having a plurality of reflecting surfaces for reflecting the first light beam so that the first light beam scans on the first photoconductor; and A second rotary polygon mirror having a plurality of reflecting surfaces for reflecting the second light beam so as to scan on the second photosensitive member; and the third light beam scans on the third photosensitive member. A third rotating polygon mirror having a plurality of reflecting surfaces for reflecting the third light beam, and the fourth light beam A fourth rotary polygon mirror having a plurality of reflecting surfaces for reflecting the fourth light beam to scan the serial fourth photoreceptor above, an optical scanning device comprising a,
The electrostatic latent image formed on the first photosensitive member by being scanned by the first light beam reflected by the reflecting surface of the first rotary polygon mirror is developed using toner. An electrostatic latent image formed on the second photosensitive member by scanning with the second light beam reflected by the reflecting surface of the first developing unit and the second rotary polygon mirror, A second developing means that develops the image using the light and a third light beam reflected by the reflecting surface of the third rotary polygon mirror, and the static light formed on the third photoconductor by scanning with the third light beam. The fourth photosensitive member is scanned by the third developing means for developing the electrostatic latent image with toner and the fourth light beam reflected by the reflecting surface of the fourth rotary polygon mirror. A fourth developing hand for developing the electrostatic latent image formed thereon with toner; When the image forming means comprising a
An intermediate transfer member to which a developed toner image is transferred to each of the first photosensitive member, the second photosensitive member, the third photosensitive member, and the fourth photosensitive member; Transfer means for transferring the toner image transferred to the recording medium;
First detecting means for detecting a toner pattern transferred onto the intermediate transfer member from each of the first photosensitive member, the second photosensitive member, the third photosensitive member, and the fourth photosensitive member. When,
The first detector in the main scanning direction of the light beam reflected by the first rotary polygon mirror, the second rotary polygon mirror, the third rotary polygon mirror, and the fourth rotary polygon mirror; Detecting toner patterns that are arranged at different positions and transferred from the first photosensitive member, the second photosensitive member, the third photosensitive member, and the fourth photosensitive member onto the intermediate transfer member. Second detecting means for
A color image forming apparatus for controlling the formation position of the toner pattern,
The first rotating polygon mirror, the second rotating polygon mirror, the third rotating polygon mirror, and the first rotation polygon mirror determined by the density of a test image for confirmation of dirt transferred to the recording medium or the intermediate transfer member; Storage means for storing the presence or absence of dirt on the fourth rotating polygon mirror;
If the first rotating polygon mirror, the second rotating polygon mirror, the third rotating polygon mirror, and the fourth rotating polygon mirror are not contaminated after checking the storage means, The toner pattern transferred onto the intermediate transfer member from each of the photosensitive member, the second photosensitive member, the third photosensitive member, and the fourth photosensitive member is the first detecting unit and the second detecting member. The toner pattern is applied to each of the first photoconductor, the second photoconductor, the third photoconductor, and the fourth photoconductor on the image forming unit. When the first rotating polygon mirror, the second rotating polygon mirror, the third rotating polygon mirror, and the fourth rotating polygon mirror are soiled, the first photosensitive member, 2 photoconductors, the third photoconductor, and the fourth photoconductor The toner pattern is transferred to the image forming unit so that the toner pattern transferred onto the intermediate transfer member is detected by one of the first detection unit and the second detection unit. And a control unit formed on each of the second photoconductor, the second photoconductor, the third photoconductor, and the fourth photoconductor.
Color image forming apparatus. The storage means performs the main scanning according to the number of reflecting surfaces of each of the first rotating polygon mirror, the second rotating polygon mirror, the third rotating polygon mirror, and the fourth rotating polygon mirror. Storing image data for forming the toner pattern at one end in the direction;
The image forming unit responds to the image data when the first rotating polygon mirror, the second rotating polygon mirror, the third rotating polygon mirror, and the fourth rotating polygon mirror are dirty. Forming an image on the photoreceptor,
The color image forming apparatus according to claim 8. The first rotating polygon mirror, the second rotating polygon mirror, the third rotating polygon mirror, and the fourth rotation of the recording medium on which the stain confirmation test image is transferred by a user operation. Provided with operation means for inputting the confirmation result of contamination of the polygon mirror,
In response to an input from the operation means, the control means stores the first rotary polygon mirror, the second rotary polygon mirror, the third rotary polygon mirror, and the fourth rotary polygon in the storage means. Memorize the presence or absence of dirt on the mirror,
The color image forming apparatus according to claim 8 or 9. Comprising image reading means for detecting the density of the test image for confirmation of contamination formed on the recording medium,
The control means determines whether the first rotary polygon mirror, the second rotary polygon mirror, the third rotary polygon mirror, and the fourth rotary polygon mirror are dirty according to the detection result of the image reading means. It is discriminated, and the storage means stores the presence / absence of contamination on the first rotary polygon mirror, the second rotary polygon mirror, the third rotary polygon mirror, and the fourth rotary polygon mirror. And
The color image forming apparatus according to claim 8 or 9. A line sensor for detecting the density of the test image for confirmation of dirt formed on the intermediate transfer member,
The control means determines whether or not the first rotary polygon mirror, the second rotary polygon mirror, the third rotary polygon mirror, and the fourth rotary polygon mirror are contaminated based on a detection result of the line sensor. The storage means stores the presence / absence of contamination on the first rotary polygon mirror, the second rotary polygon mirror, the third rotary polygon mirror, and the fourth rotary polygon mirror. To
The color image forming apparatus according to claim 8 or 9. When the rotating polygon mirror is soiled and the number of the reflecting surfaces is 4 or less, the image forming unit is configured such that the first photoconductor, the second photoconductor, the third photoconductor, If the toner pattern is formed at one end in the main scanning direction of each of the fourth photoconductors and the number of reflection surfaces is 5 or more, the first photoconductor, the second photoconductor The toner pattern is formed at the other end in the main scanning direction of each of the photoconductor, the third photoconductor, and the fourth photoconductor.
The color image forming apparatus according to claim 8. When the rotating polygon mirror is soiled and the number of the reflecting surfaces is 4 or less, the image forming unit is configured such that the first photoconductor, the second photoconductor, the third photoconductor, And downstream of the rotation direction of the first rotating polygon mirror, the second rotating polygon mirror, the third rotating polygon mirror, and the fourth rotating polygon mirror of each of the fourth photosensitive members. If the toner pattern is formed at the end in the main scanning direction and the number of reflection surfaces is 5 or more, the first photoconductor, the second photoconductor, the third photoconductor, And upstream of the rotation direction of the first rotary polygon mirror, the second rotary polygon mirror, the third rotary polygon mirror, and the fourth rotary polygon mirror of each of the fourth photosensitive members. The toner pattern is formed at an end in the main scanning direction.
The color image forming apparatus according to claim 13.