JP6575766B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus includes an optical scanning device (optical scanning unit) that forms an electrostatic latent image by irradiating a surface of an image carrier with a light beam. The optical scanning device includes a polygon mirror that is rotationally driven by a motor, and a light source unit that emits light toward the reflecting surface of the rotating polygon mirror.

  In this type of optical scanning device, when the polygon mirror is rotated, the end portion on the downstream side in the rotation direction on the reflecting surface enters the separation region of the air flow generated at the edge portion of the polygon mirror and becomes negative pressure. For this reason, dust (for example, paper dust or scattered toner) adheres to the end portion on the downstream side in the rotation direction on the reflecting surface, and the reflectance of light at the end portion becomes lower than other portions, and as a result, the printed image There is a problem in that uneven density occurs.

  In order to solve this problem, for example, in the optical scanning device disclosed in Patent Document 1, the amount of light emitted from the light source is set according to the position in the main scanning direction based on the shading correction data stored in advance in the data storage unit. Correction (shading correction) is performed. The data storage unit stores a plurality of shading correction data with different correction characteristics, and the user or service person can select one optimal correction data from the plurality of shading correction data based on the test image. It has become.

JP 2007-83708 A

  Here, the reflectance of light on each reflecting surface varies within a predetermined range due to the processing accuracy of the reflecting surface and the degree of dust adhesion. For this reason, as shown in Patent Document 1, if the amount of light incident on each reflecting surface is corrected based on one common shading correction data, the shading accuracy varies for each reflecting surface. As a result, there is a problem that image defects such as jitter occur in the printed image at a constant period.

  The present invention has been made in view of the above points, and the object of the present invention is to cause image defects such as jitter in a printed image due to the difference in reflectance of each reflecting surface of the polygon mirror. Is to prevent.

  An image forming apparatus according to an aspect of the present invention includes a light source that emits a light beam, a polygonal mirror that includes a plurality of reflecting surfaces on a peripheral side surface, and reflects the light beam emitted from the light source on the reflecting surface; An optical scanning unit, a test image generation unit that generates a test image corresponding to each of the reflection surfaces based on the light beam reflected by each reflection surface of the polygon mirror, and a main image of each test image. A density data in the scanning direction is acquired, and based on the acquired density distribution, a correction data setting unit that sets shading correction data for each reflective surface of the polygon mirror, and is set for each reflective surface of the polygon mirror. A printing control unit that prints an image by correcting the amount of light incident on each reflecting surface based on the shading correction data according to the position in the main scanning direction.

  An image forming apparatus according to another aspect of the present invention includes: a light source that emits a light beam; a polygon mirror that includes a plurality of reflecting surfaces on a peripheral side surface and reflects the light beam emitted from the light source on the reflecting surface; , A correction data storage unit in which a plurality of shading correction data is stored in advance, and a light beam reflected by each reflection surface of the polygon mirror, corresponding to each of the reflection surfaces. A test image generation unit that generates a test image, and a selection unit that allows a user to select one correction data from the plurality of shading correction data based on the test image for each of the reflection surfaces of the polygon mirror, Based on the shading correction data selected for each reflecting surface of the polygon mirror, the amount of light incident on each reflecting surface is corrected according to the position in the main scanning direction. It includes a print controller for printing the image.

  According to the present invention, it is possible to prevent image defects such as jitter from occurring in a printed image due to differences in reflectance between the reflecting surfaces of the polygon mirror.

FIG. 1 is an overall view illustrating an image forming apparatus according to an embodiment. FIG. 2 is a plan view showing a schematic configuration of the optical scanning device. FIG. 3 is a block diagram showing the configuration of the control system. FIG. 4 is a diagram illustrating an example of shading correction data stored in the data storage unit. FIG. 5 is a diagram illustrating an example of a test image. FIG. 6 is a schematic view showing a state in which dust adheres to the downstream end portion in the rotation direction on the reflection surface of the polygon mirror. FIG. 7 is a flowchart showing the first half of the shading correction process executed by the controller. FIG. 8 is a flowchart showing the latter half of the shading correction process executed by the controller. FIG. 9 is a diagram illustrating an example of a density distribution in the main scanning direction of each test image calculated by the controller. FIG. 10 is a view corresponding to FIG. FIG. 11 is a view corresponding to FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiment.

<Embodiment>
FIG. 1 shows a laser printer which is an example of an image forming apparatus 1 in the present embodiment. The image forming apparatus 1 includes an image forming apparatus main body 100, a scanner device 200 attached to an upper portion of the image forming apparatus main body 100, and an operation panel 300 that can be operated by a user. In the following description, the front side and the rear side mean the front side (the side where the operation panel 300 is located) and the rear side, respectively, and the left side and the right side are viewed from the front side of the image forming apparatus 1. It means the left side and the right side.

  The image forming apparatus main body 100 has a box-shaped housing 60. The upper surface of the housing 60 is closed by the scanner device 200. Further, the upper surface portion of the front portion of the housing 60 is closed by the paper discharge tray unit 50.

  In the housing 60, the paper feeding unit 10, the image forming unit 20, and the fixing unit 40 are accommodated. A plurality of transport roller pairs 11 to 13 that sandwich and transport the paper P are disposed in the paper transport path L from the paper supply unit 10 to the paper discharge tray unit 50. Further, a reverse conveyance path L ′ that branches from the downstream side of the sheet conveyance path L and joins the upstream side is provided. Conveying roller pairs 14 to 16 are arranged in the reverse conveying path L ′.

  The paper feeding unit 10 is disposed in the lower part of the housing 60. The paper feed unit 10 includes a paper feed cassette 10a in which sheet-like paper P is accommodated, and a pickup roller 10b for taking out the paper P in the paper feed cassette 10a and sending it out of the cassette. The paper P sent out of the cassette from the paper feed cassette 10 a is supplied to the image forming unit 20 through the transport roller pair 11. In the image forming unit 20, image forming units 20Bk, 20M, 20C, and 20Y that form toner images respectively corresponding to black, magenta, cyan, and yellow are arranged in a row.

  Each of the image forming units 20Bk, 20M, 20C, and 20Y includes a photosensitive drum 21, a charging device 22, a developing device 23, and a cleaning device 24. Below the image forming units 20Bk, 20M, 20C, and 20Y, a total of four optical scanning devices (optical scanning units) 25 that irradiate the surface of each photosensitive drum 21 with laser light are arranged. . An intermediate transfer unit 26 is disposed above the image forming units 20Bk, 20M, 20C, and 20Y. The intermediate transfer unit 26 is provided with an intermediate transfer belt 27 that travels in contact with each photosensitive drum 21. A primary transfer roller 28 is provided inside the intermediate transfer belt 27 so as to sandwich the intermediate transfer belt 27 between the photosensitive drums 21. Further, a secondary transfer roller 29 is provided in contact with the surface of the intermediate transfer belt 27 on the downstream side of the image forming unit 20Bk. Above the intermediate transfer unit 26, toner containers 30Bk, 30M, 30C, and 30Y that store toner of each color to be supplied to the developing devices 23 of the image forming units 20Bk, 20M, 20C, and 20Y are arranged.

  In each of the image forming units 20Bk, 20M, 20C, and 20Y, each optical scanning device 25 irradiates the surface of each photosensitive drum 21 with laser light based on predetermined image data (for example, original image data read by the scanner device 200). Thus, an electrostatic latent image is formed, and the formed electrostatic latent image is developed by the developing device 23 to form toner images of respective colors. Each color toner image formed on the surface of each photosensitive drum 21 is transferred onto the surface of the intermediate transfer belt 27 by the primary transfer roller 28 and superimposed.

  The toner image transferred onto the intermediate transfer belt 27 is transferred onto the paper P supplied from the paper supply unit 10 by the secondary transfer roller 29. The sheet P after the transfer is supplied to the fixing unit 40. The fixing unit 40 fixes the toner image on the paper P by pressing the paper P supplied from the image forming unit 20 between the fixing roller 40a and the pressure roller 40b. Then, the paper P on which the toner image is fixed by the fixing unit 40 is sent out to the downstream side by the fixing roller 40a and the pressure roller 40b. The paper P sent out from the fixing unit 40 is discharged to the paper discharge tray unit 50 through a plurality of conveying roller pairs 12 and 13. When toner images are formed on both sides of the paper P, the paper P is switched back by the transport roller pair 13 and transported to the reverse transport path L ′.

  The scanner device 200 includes a document reading unit 201 and a document cover 220. A scanner unit (not shown) is accommodated in the document reading unit 201. The upper surface of the document reading unit 201 constitutes a document placement surface on which a document is placed. A substantially rectangular opening (not shown) is formed on the document placement surface, and contact glass is fitted into the opening.

  The scanner unit housed in the document reading unit 201 optically reads a document placed on the contact glass on the document placement surface and generates image data thereof. The scanner unit 210 transmits the generated image data to the data storage unit 258 (see FIG. 3) for storage.

  Next, each optical scanning device 25 will be described in detail with reference to FIG. A total of four optical scanning devices 25 are provided corresponding to four colors of yellow, magenta, cyan, and black. Since the configuration of each optical scanning device 25 is the same, only one of the optical scanning devices 25 will be described, and description of the other optical scanning devices 25 will be omitted.

  The optical scanning device 25 includes a light source 251, a collimator lens 252, a cylindrical lens 253, a polygon mirror 254, an fθ lens 255, a polygon motor 256, and a BD sensor 257 as a synchronization detection sensor. The BD sensor 257 detects the light beam from the light source 251 before starting the writing of the image data, and outputs an output signal (for example, a voltage signal) corresponding to the detected light amount of the light beam as a synchronization detection signal. In the present embodiment, the BD sensor 257 is configured to increase the output signal value as the light amount of the received light beam increases.

  The light source 251 includes a laser diode (LD) that converts a current signal into laser light, and is electrically connected to the controller 150. The controller 150 controls the writing start timing of the image data by the light source 251 based on the synchronization detection signal from the BD sensor 257.

  The light beam emitted from the light source 251 is converted into parallel light by the collimator lens 252 and then condensed on the respective reflecting surfaces r1 to r5 of the polygon mirror 254 by the cylindrical lens 253.

  The polygon mirror 254 is formed in a polygonal shape (in this embodiment, for example, a pentagonal shape) having a plurality of reflecting surfaces r1 to r5 on the peripheral side surface. The polygon mirror 254 is rotationally driven by a polygon motor 256, and reflects the light beam emitted from each light source 251 to the axial direction of the photosensitive drum 21 (the main scanning direction X, which is the vertical direction in FIG. 2). ).

  The fθ lens 255 is disposed between the polygon mirror 254 and the photosensitive drum 21. The fθ lens 255 converts the scanning light reflected by the polygon mirror 254 at a constant speed and forms an image on the peripheral surface of the photosensitive drum 21. As a result, electric charges on the peripheral surface of the photosensitive drum 21 are removed, and an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 21.

  The controller 150 includes a microcomputer having a CPU, a ROM, a RAM, and the like. The controller 150 controls the light amount of each light source 251 based on the operation signal received from the operation panel 300.

  As shown in FIG. 3, the controller 150 is connected to the operation panel 300 and the data storage unit 258.

  The operation panel 300 includes a display unit 300a for displaying a message and an operation unit 300b that can be operated by a user with a finger. The user can select either the job print mode or the test print mode by operating the operation unit 300b. The job print mode is a mode for executing a print job accepted by the accepting unit of the image forming apparatus 1. The test print mode is a mode for printing the test images G1 to G5 for shading correction.

  Further, the user can select one correction data from a plurality of shading correction data D1 to D5 described later by operating the operation unit 300b.

  The data storage unit 258 is configured by a memory such as a ROM or a RAМ, and includes an image data storage unit 258a and a correction data storage unit 258b. The image data storage unit 258a stores image data read by the scanner device 200 and image data received from an external terminal such as a personal computer. The correction data storage unit 258b stores a plurality of (five in this embodiment) shading correction data D1 to D5 having different correction characteristics.

  As shown in FIG. 4, each shading correction data D1 to D5 is, for example, data in a graph data format, and the vertical axis of the graph represents a light quantity correction coefficient, and the horizontal axis represents a position in the main scanning direction X. .

  In each of the shading correction data D1 to D5, correction coefficients are set so as to suppress density unevenness caused by a decrease in reflectance at the downstream end portions of the respective reflecting surfaces r1 to r5 of the polygon mirror 254. That is, each of the shading correction data D1 to D5 has a correction coefficient at one end in the main scanning direction (side corresponding to the downstream end of the reflection surface of the polygon mirror) larger than the correction coefficient at the other end. Is set to When the controller 150 executes the shading correction process, the light quantity is emitted from each light source 251 assuming that the theoretical light amount of each light source 251 (the reflectance of each reflecting surface r1 to r5 of the polygon mirror 254 is constant in the main scanning direction). The light amount obtained by multiplying the light amount) by the correction coefficient is set as the light amount of each light source 251.

  If the controller 150 determines that the job print mode is set based on a signal from the operation unit 300b, the controller 150 includes an image included in the print job received by the data receiving unit (not shown) of the image forming apparatus 1. Execute the data printing process. When printing the image data, the controller 150 determines the light amount of the light beam emitted from the light source 251 of each optical scanning device 25 (the light beam incident on each reflecting surface r1 to r5) according to the scanning position in the main scanning direction X. To correct (shading correction). The controller 150 executes the shading correction process based on the shading correction data previously selected by the user for each reflection surface of the polygon mirror 254. The user selects shading correction data in the test print mode.

  When it is determined that the test print mode is set based on signals from the controller 150 and the operation unit 300b, first, predetermined test images G1 to G5 are printed. FIG. 5 is an example of test images G1 to G5 printed in the test print mode. In this example, a test image printed by the black image forming unit 20Bk is shown, but actually, not only black but also magenta, yellow, and cyan test images are printed.

  As shown in FIG. 5, a total of five test images G1 to G5 are printed. Each of the test images G1 to G5 is associated with each of the reflection surfaces r1 to r5 of the polygon mirror 254, and is generated based on the light beam reflected by each of the reflection surfaces r1 to r5. Each of the test images G1 to G5 is a half image composed of a plurality of (four in the present embodiment) image lines arranged at intervals in the vertical direction of the paper P, for example.

  In the example of FIG. 5, the density of each image line is drawn constant in the main scanning direction, but actually, the density at one side edge of each image line in the main scanning direction is lower than the other parts. Yes. This decrease in density occurs because the reflectance at the downstream end in the rotational direction of each of the reflection surfaces r1 to r5 is lower than that of the other portions. That is, the downstream end portions of the reflecting surfaces r1 to r5 enter the separation region of the air flow generated at the edge portion of the polygon mirror 254 and become negative pressure, so that dust (scattered toner, paper dust, etc.) adheres to the reflection rate. (See FIG. 6). Therefore, the density at one end of the light beam that has passed through the dust adhesion region F in the main scanning direction is lowered.

  By the way, the size and shape of the dust adhesion area F on each of the reflection surfaces r1 to r5 of the polygon mirror 254 vary due to processing errors of the polygon mirror 254, uneven rotation speed of the polygon motor 256, and the like. For this reason, when the light amount of the light beam incident on each of the reflection surfaces r1 to r5 is corrected based on one common shading correction data, the correction accuracy differs for each light beam. As a result, there is a problem that image defects such as jitter occur in the printed image at a constant period. In order to solve this problem, in this embodiment, the user can select the optimum shading correction data for each of the reflection surfaces r1 to r5 of the polygon mirror 254 by looking at the print results of the test images G1 to G5. Here, the “optimal correction data” is correction data that minimizes density unevenness in the main scanning direction X of the print image among the plurality of shading correction data D1 to D5, in other words, the plurality of shadings. Among the correction data D1 to D5, the correction data has the highest shading correction accuracy.

  Next, details of the shading correction processing in the controller 150 will be described with reference to FIGS. 7 and 8.

  In step SA1, it is determined whether or not the current mode of the image forming apparatus 1 is the test print mode based on the operation information from the operation unit 300b. If this determination is NO, the process proceeds to step SA11 and YES. If so, the process proceeds to step SA2.

  In step SA2, one of the four image forming units 20Bk, 20M, 20C, and 20Y of black, magenta, cyan, and yellow is sequentially selected.

  In step SA3, the light amount of the light source 251 corresponding to the selected image forming unit is controlled to a preset set light amount.

  In step SA4, test images G1 to G5 corresponding to the reflecting surfaces r1 to r5 are printed based on the light beams reflected by the reflecting surfaces r1 to r5 of the polygon mirror 254.

  In step SA5, a message prompting the user to read the test images G1 to G5 into the scanner device 200 is displayed on the display unit 300a.

  In step SA6, it is determined whether or not reading of the test images G1 to G5 by the scanner device 200 has been completed. If this determination is NO, the process returns to step SA5 to continue displaying the message. If there is, the process proceeds to step SA7.

  In step SA7, the density distribution in the main scanning direction X of each of the test images G1 to G5 read in step S6 is calculated (acquired) and converted into graph data, and the graph data is displayed on the display unit 300a. FIG. 9 is an example of the graph data. Lines P1 to P5 in the graph data represent the density distributions of the test images G1 to G5, respectively. In addition, the vertical axis | shaft of FIG. 9 shows a reflection absolute density. According to this graph data, it can be seen that there is some variation in the density value at one end of the main scanning direction X of each test image. In the present invention, the “density distribution” is not limited to continuous graph data as shown in FIG. 9, but is discrete data composed of density values at a plurality of locations (for example, 2 locations or 3 locations) arranged in the main scanning direction. It may be.

  In step SA8, the plurality of shading correction data D1 to D5 shown in FIG. 4 are displayed in a graph format on the display unit 300a of the operation panel 300. Then, by displaying a predetermined message on the display unit 300a, the user is prompted to select optimum shading correction data for each of the reflection surfaces r1 to r5 of the polygon mirror 254.

  In step SA9, it is determined whether or not the user has selected the optimum shading correction data for all the reflecting surfaces r1 to 5 of the polygon mirror 254 in step SA8. If this determination is NO, the process proceeds to step SA8. On the other hand, if YES, the process proceeds to step SA10. This determination is made based on a signal from the operation unit 300b on which the user has performed a shading correction data selection operation.

  In step SA10, it is determined whether or not printing of test images G1 to G5 has been completed for all four colors of black, magenta, cyan, and yellow. If this determination is NO, the process returns to step SA2 while YES. If there is, return.

  In step SA11 which proceeds when the determination in step SA1 is NO, it is determined that the current mode of the image forming apparatus 1 is the job print mode. Then, it is determined whether or not there is a print request to the image forming apparatus 1. If this determination is NO, the process returns. On the other hand, if YES, the process proceeds to step SA12.

  In Step SA12, the light amount of the light beam emitted from each light source 251 of the four optical scanning devices 25 is corrected based on the shading correction data D1 to D5 selected for each reflection surface r1 to r5 of the polygon mirror 254. The image data is printed. Then, the process returns after the printing of the image data is completed.

  As described above, in this embodiment, the user can select optimum shading correction data for each of the reflection surfaces r1 to r5 of the light source 251 of the optical scanning device 25 (steps SA8 and SA9). Therefore, even if the reflectance of each of the reflecting surfaces r1 to r5 of the polygon mirror 254 differs due to the degree of dust adhesion, the processing accuracy of the polygon mirror 254, and the like, image defects such as jitter occur in the printed image. Can be reliably prevented.

  The controller 150 is configured to calculate the density distribution in the main scanning direction X of each of the test images G1 to G5, convert the calculated density distribution into graph data, and display the graph data on the display unit 300a. Therefore, the user can select the optimum shading correction data for each of the reflection surfaces r1 to r5 of each polygon mirror 254 by operating the operation unit 300b based on the graph data.

<< Embodiment 2 >>
FIG. 10 shows the second embodiment. In this embodiment, the first half of the shading correction process executed by the controller 150 is different from that of the first embodiment. That is, in this embodiment, the controller 150 automatically generates optimal shading correction data instead of the user selecting optimal shading correction data for each of the reflection surfaces r1 to r5 of the polygon mirror 254 as in the first embodiment. (Setting).

  In the first step SB1, whether or not the current mode of the image forming apparatus 1 is the test print mode is determined based on the operation signal from the operation unit 300b. If this determination is NO, the process of the first embodiment is performed. The same process as the process after step SA11 is executed. If YES, the process proceeds to step SB2.

  In step SB2, one of the four image forming units 20Bk, 20M, 20C, and 20Y of black, magenta, cyan, and yellow is sequentially selected.

  In step SB3, test images G1 to G5 are printed for each of the reflection surfaces r1 to r5 of the polygon mirror 254 of the optical scanning device 25 corresponding to the selected image forming unit. At this time, among the four image lines of each of the test images G1 to G5, the light quantity of the light source 251 is set as the first light quantity for the upper two lines, and the light quantity of the light source 251 is different from the first light quantity for the lower two lines. Printing is performed under the control of the second light quantity.

  In step SB4, a predetermined message is displayed on the display unit 300a of the operation panel 300, thereby prompting the user to cause the scanner device 200 to read the test images G1 to G5 printed in step SB3.

  In step SB5, it is determined whether or not reading of the test images G1 to G5 by the scanner device 200 has been completed. If this determination is NO, the process returns to step SB4 to continue displaying the message, while YES. If there is, the process proceeds to step SB6.

  In step SB6, optimum shading correction data is calculated for each of the reflection surfaces r1 to r5 of each polygon mirror based on the test images G1 to G5 read in step SB5. Specifically, first, the density difference between the upper two image lines and the lower two image lines is calculated at each position in the main scanning direction X, and the main scanning direction X is calculated based on the calculated density difference. The density change rate with respect to the light quantity change is calculated at each of the positions. For example, in one of the four image lines arbitrarily selected, the density difference between the density at each position in the main scanning direction X of the image line and the maximum density is calculated using the maximum density as a reference. Then, the light amount change amount (in this embodiment, the light amount magnification factor) necessary to make this density difference zero at each position in the main scanning direction X is calculated based on the density change rate. The light quantity change rate thus calculated is stored in the correction data storage unit 258b as shading correction data D1 to D5. The shading correction data D1 to D5 are stored in the correction data storage unit 258b in association with the reflecting surfaces r1 to r5 of the polygon mirror 254.

  In step SB7, it is determined whether or not the printing of the test images G1 to G5 has been completed for all four colors of black, magenta, cyan, and yellow. If this determination is NO, the process returns to step SB2, while YES. If there is, return.

  As described above, in the second embodiment, the controller 150 generates, in each of the test images G1 to G5, an image when the light amount of the light source 251 is set to the first light amount and an image when the light amount is set to the second light amount. (Step SB3), the optimum shading correction data D1 to D5 are automatically calculated for each of the reflection surfaces r1 to r5 of the polygon mirror 254 based on the density difference between the two images (step SB6). .

  Therefore, it is possible to save the user from manually selecting the optimum shading correction data D1 to D5. In addition, the optimum shading correction data D1 to D5 can be calculated for each of the reflection surfaces r1 to r5 of the polygon mirror 254 by calculation without depending on the user's sense. Therefore, it is possible to increase the shading correction accuracy for each of the reflection surfaces r1 to r5 as much as possible and suppress the occurrence of image defects such as jitter.

<< Embodiment 3 >>
FIG. 11 shows the third embodiment. In this embodiment, the latter half of the shading correction process executed by the controller 150 is different from the above embodiments. That is, in the present embodiment, the dust adhesion region F of each of the reflection surfaces r1 to r5 of the polygon mirror 254 overlaps the region of the reflection surfaces r1 to r5 that reflects the light beam toward the BD sensor 257. In consideration of the above, the execution / non-execution of the shading correction process is switched according to the output signal value of the BD sensor 257. Specific processing contents will be described below.

  In step SC11 that proceeds when the determination in step SA1 is NO, it is determined that the current mode of the image forming apparatus 1 is the job printing mode. Then, it is determined whether or not there is a print request to the image forming apparatus 1. If this determination is NO, the process returns. On the other hand, if YES, the process proceeds to step SC12.

  In step SC12, it is determined whether or not the output signal value of the BD sensor 257 is equal to or smaller than a preset initial setting threshold value. If this determination is NO, the process proceeds to step SC17. If YES, the process proceeds to step SC17. Proceed to SC13.

  In step SC13, it is determined whether or not the output signal value of the BD sensor 257 is equal to or less than the current set threshold value (set threshold value updated in step SC16 described later). If this determination is NO, the process proceeds to step SC18. On the other hand, if YES, the process proceeds to step SC14.

  In step SC14, a predetermined message is displayed on the display unit 300a to prompt the user to switch the print mode of the image forming apparatus 1 from the print job mode to the test print mode.

  In step SC15, it is determined whether or not the switching from the job print mode to the test print mode is completed based on the signal from the operation unit 300b. If this determination is NO, the process proceeds to step SC19 while YES. If YES, go to Step SC16.

  In step SC16, the setting threshold value of the BD sensor 257 is updated to a new threshold value lower than the current value, and then the process returns.

  In step SC17 which proceeds when the determination in step SC12 is NO, printing of image data is executed without performing shading correction, and then the process returns.

  In step SC18 that proceeds when the determination in step SC13 is NO, as in step SA12 in the first embodiment, correction processing is performed based on the shading correction data selected for each of the reflection surfaces r1 to r5 of the polygon mirror 254. To print the image data.

  In step SC19, which proceeds when the determination in step SC15 is NO, a warning message to the effect that there is a risk of image defects such as jitter in the printed image is displayed on the display unit 300a. Instead of displaying a warning message in this step SC19, execution of a print job (image data printing process) may be prohibited.

  In step SC20, the image data printing process is forcibly executed based on the shading correction data currently selected for each of the reflection surfaces r1 to r5 of the polygon mirror 254, and then the process returns.

  As described above, in this embodiment, the controller 150 executes the shading correction process when the output signal value of the BD sensor 257 is equal to or smaller than the initial setting threshold value (YES in step SC12), while the output signal value is equal to the initial setting threshold value. Is exceeded (NO in step SB12), the shading correction process is not executed.

  Therefore, when dust of a predetermined amount or more adheres to the downstream end in the rotation direction of each of the reflecting surfaces r1 to r5 of the polygon mirror 254, that is, when the light reflectance at the downstream end becomes less than a predetermined value. The shading correction process by the controller 150 is executed only when the determination at step SC12 is YES. Therefore, it is possible to prevent the shading correction process by the controller 150 from being performed unnecessarily and increasing the printing time of the image data.

<< Other embodiments >>
In the above-described embodiment, each of the test images G1 to G5 is a half image, but is not limited thereto, and may be a solid image, for example.

  The present invention is not limited to the first to third embodiments, and the present invention includes a configuration in which these first to third embodiments are appropriately combined.

  As described above, the present invention is useful for an image forming apparatus.

D1 Shading correction data D2 Shading correction data D3 Shading correction data D4 Shading correction data D5 Shading correction data G1 Test image G2 Test image G3 Test image G4 Test image G5 Test image r1 Reflective surface r2 Reflective surface r3 Reflective surface r4 Reflective surface r5 Reflective surface X main scanning direction 1 image forming device 25 optical scanning device (optical scanning unit)
150 controller (test image generator, correction data generator, print controller)
251 Light source 254 Polygon mirror 256 Polygon motor 257 BD sensor (synchronous detection sensor)
258 Correction data storage unit 300b Operation unit (selection unit)

Claims (3)

An optical scanning unit comprising: a light source that emits a light beam; and a polygon mirror that includes a plurality of reflection surfaces on a peripheral side surface and reflects the light beam emitted from the light source on the reflection surface;
A reception unit for receiving print jobs;
A mode setting unit for setting one of a job print mode for executing a print job received by the reception unit and a test print mode;
When the test print mode is set in the mode setting unit, a test for generating a test image corresponding to each reflective surface based on the light beam reflected by each reflective surface of the polygon mirror An image generator;
When the test print mode is set by the mode setting unit, the density distribution in the main scanning direction of each test image generated by the test image generation unit is acquired, and the acquired density distribution is based on the acquired density distribution. A correction data setting unit for setting shading correction data for each reflecting surface of the polygon mirror,
Print control for printing the image of the print job by correcting the amount of light incident on each reflection surface according to the position in the main scanning direction based on the shading correction data set for each reflection surface of the polygon mirror. comprises a part, the,
A test image corresponding to each of the reflection surfaces of the polygon mirror includes a first image line formed by scanning a light beam in the main scanning direction with the light amount of the light source set to the first light amount, and the first image line. A second image line formed by scanning the light beam in the main scanning direction with the light amount of the light source as the second light amount at a sub-scanning position different from the one image line,
The correction data setting unit calculates a density difference between the first image line and the second image line at each position in the main scanning direction for the test image corresponding to each of the reflection surfaces. The density change rate with respect to the light quantity change is calculated based on the density difference, and then the main scanning direction of the image line is determined with reference to the maximum density in one of the first image line and the second image line. A density difference from the maximum density at each position is calculated, and an amount of change in light amount necessary to reduce the calculated density difference to 0 at each position in the main scanning direction is expressed as the density difference and the density change rate. An image forming apparatus configured to generate and set shading correction data by calculation based on the above . The image forming apparatus according to claim 1 .
It also has a display that can display information,
The optical scanning unit further includes a synchronization detection sensor that detects a light beam reflected from a downstream end portion in a rotation direction of each reflection surface of the polygon mirror and outputs a synchronization detection signal.
The print control unit controls the writing start timing of the image data by the light source based on the synchronization detection signal output from the synchronization detection sensor,
In a state where the job print mode is set by the mode setting unit , the print control unit is configured to notify the user when the output signal value from the synchronization detection sensor is equal to or less than a preset initial set threshold value . Information that prompts the user to switch to the test print mode is displayed on the display unit, and when the switching is detected, the setting threshold value of the synchronization detection sensor is updated to a value lower than the current setting value. After the update, when the synchronization detection signal output from the synchronization detection sensor exceeds the current setting threshold and is equal to or less than the initial setting threshold, the correction data setting unit at the present time Based on the set shading correction data for each reflecting surface, the amount of light incident on each reflecting surface is corrected according to the position in the main scanning direction and A display unit that prompts the user to switch to the test print mode when the job image is printed and when the synchronization detection signal output from the synchronization detection sensor is equal to or lower than the set threshold value after the update. The image forming apparatus is configured to execute control to update the setting threshold value of the synchronization detection sensor to a value lower than the current setting value when it is detected that the switching is completed. The image forming apparatus according to claim 2 .
In the case where the job print mode is set by the mode setting unit, the print control unit is configured to output the shading correction data when the output signal value from the synchronization detection sensor exceeds the preset initial threshold value. An image forming apparatus configured to execute printing of an image of the print job without performing correction based on the above.

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