JP2012185320A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of applying an optimal transfer bias corresponding to a printed image.SOLUTION: An image forming apparatus comprises image forming means including: scanning light exposure means for forming a latent image on an image carrier synchronizing with data transmission means; developing means for developing the latent image on the image carrier to form a toner image; and transfer means for transferring the toner image to a recording medium. An image forming part comprises: image data detection means for detecting image data output from the image data transmission means; image data storage means for digitizing the image data detected by the image data detection means and storing it; and transfer control means for correcting a transfer bias to be applied to the transfer means according to the data value stored in the image data storage means.

Description

  The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer using an electrophotographic process.

  In an image forming apparatus (for example, a copying machine or a laser beam printer) provided with a contact type transfer unit, a transfer bias applied to a contact transfer member is generally controlled at a constant voltage or a constant current.

  In the case of constant voltage control, the following control is performed.

  For example, a transfer roller is used as the contact transfer member. This transfer roller is usually made by dispersing conductive particles in rubber and appropriately adjusting the volume resistance. As is well known, this type of substance has a resistance value of several orders of magnitude depending on the environment. Change. Therefore, current is insufficient and transfer failure occurs, or excessive current flows and a transfer memory is generated.

  For this reason, ATVC (Active Transfer Voltage Control) is performed in order to always apply a stable transfer bias regardless of the environment. ATVC is a control method in which constant current control is performed when no transfer material is present at the transfer site, the voltage at this time is held, and constant voltage control is performed with this voltage when the sheet passes. is there. In addition, after the leading edge of the transfer material has entered the transfer nip, before the print area of the transfer material reaches the transfer nip, control is performed to detect a leakage current by the detection circuit and change the bias by the control device. (For example, refer to Patent Document 1).

  On the other hand, the constant current control eliminates the drawbacks due to the change in the resistance value of the transfer member and transfer material as described above, and can always secure the amount of charge necessary for transfer, but allows the transfer material of small size to pass through In this case, the non-sheet passing area where the photosensitive drum and the transfer member are in direct contact with each other is widened, and most of the current flows through the non-sheet passing area, resulting in insufficient transfer charge and defective transfer. .

  For this reason, control is performed in which the target current is set to the same magnification, the coefficient is multiplied, and a constant current is applied depending on the size of the transfer material.

  The control as described above has a certain effect in preventing the occurrence of variations in transferability due to environmental fluctuations and differences in transfer material size.

Japanese Patent Laid-Open No. 11-219042

  However, the conventional example described in the background art has the following problems even if it is possible to prevent transfer variation due to environmental fluctuations or transfer material differences.

  Since the resistance value of the transfer material changes depending on the print pattern, the change of the resistance value due to the print pattern is not considered. For this reason, in the case of constant voltage control, the resistance value due to the developer becomes low in printing with a low printing rate, so that a large amount of current flows and transfer omission occurs, and in printing with a high printing rate such as solid black, it depends on the developer. Since the resistance value becomes high, current is insufficient and transfer failure occurs.

  On the other hand, in the case of constant current control, the resistance value in the main scanning direction as a whole is low for printing with a high printing rate such as solid black in a part of the main scanning direction, and the print resistance is mostly low. Transfer failure occurs.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of applying an optimum transfer bias according to a printed image.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image data generation unit that creates image data based on print data sent from an external device, and an image formation unit that forms an image on a recording medium based on the image data generated by the image data generation unit. And comprising
The image data generation unit includes an image data sending unit that sends image data to the image forming unit in synchronization with an image writing notification unit that the image forming unit reports.
The image forming unit includes a scanning exposure unit that forms a latent image on an image carrier in synchronization with the image data sending unit, a developing unit that develops the latent image on the image carrier to form a toner image, and the toner image In an image forming apparatus having an image forming means having a transfer means for transferring the image to the recording medium,
The image forming unit includes:
Image data detection means for detecting image data output from the image data transmission means;
Image data storage means for digitizing and storing image data detected by the image data detection means;
A transfer control means for correcting a transfer bias applied to the transfer means in accordance with a data value stored in the image data storage means;
An image forming apparatus comprising:

  According to the present invention, the image data generated by the image data generation unit is received, and the transfer bias is sequentially corrected according to the received image data. As a result, an optimum transfer bias can be applied even when an image whose printing rate is not stable is printed, so that it becomes possible to prevent transfer failure and transfer punch-through and improve transfer efficiency.

1 is a diagram illustrating a schematic configuration of an embodiment of an image forming apparatus according to the present invention. FIG. 3 is a control block diagram illustrating an outline of control of a CPU mounted on an engine controller in the image forming apparatus according to the present invention. FIG. 3 is a block diagram illustrating a configuration of an image controller, a scanner unit, a transfer unit, and an engine controller of the image forming apparatus according to the present invention. It is a figure explaining the top view of a laser scanner unit. It is a block diagram of the scanner control part which concerns on 1st Example of this invention. 3 is a flowchart of transfer bias control during printing according to the first embodiment of the present invention. It is a block diagram of a scanner knit control part concerning the 2nd example of the present invention. It is a flowchart of the transfer bias control during printing according to the second embodiment of the present invention.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
In the first exemplary embodiment, in an image forming apparatus that performs constant voltage control of transfer when a sheet is passed, image data of an area divided in the sub-scanning direction is acquired, a print rate of the image is calculated, and transfer is performed according to the calculated print rate. Control for sequentially correcting the bias will be described.

  FIG. 1 shows an outline of the overall configuration of a laser beam printer which is an embodiment of an image forming apparatus according to the present invention.

  In this embodiment, the image forming apparatus 201 has an image forming unit for forming an image. The image forming unit includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 110 as an image carrier. The image forming unit further includes a charging roller (charging unit) 109 that charges the photosensitive drum 110 and a scanner unit (scanning exposure unit) 113 for forming an electrostatic latent image on the photosensitive drum 110. Have. Further, the image forming unit includes a developing roller (developing unit) 108 for developing the electrostatic latent image on the photosensitive drum, and a transfer for transferring the toner image obtained by the development to printing paper as a recording medium. And a roller (transfer means) 107.

  In the present exemplary embodiment, the image forming apparatus 201 is positioned below the image forming unit, and the paper feed tray 100 is disposed. The paper P placed on the paper feed tray 100 is transported to the transfer roller 107 by the paper feed roller 101 and the transport rollers 102 and 104 that transport the paper P, and the toner image is transferred onto the paper. The sheet P on which the toner image is transferred is conveyed to the fixing device 119. The sheet on which the toner image is fixed is discharged out of the apparatus by the transport rollers 120 and 122.

  FIG. 2 is a control block diagram showing an outline of control of a CPU mounted on the engine controller 202 that performs actuator control and state management of the image forming apparatus 201.

  The engine control unit 301 is a control unit that manages each control unit. When the image controller communication control unit 307 receives a print instruction from the image controller (image data generation unit) 200 (FIG. 3), the engine control unit 301 includes a paper conveyance control unit 304, a scanner control unit 303, a high pressure control unit 305, a fixing unit. An operation instruction at the time of printing is given to the control unit 306.

  The paper conveyance control unit 304 drives a conveyance motor, a photosensitive drum motor, and a fixing motor (not shown). When each motor is driven and ready to feed paper, the paper P in the paper feed tray 100 is fed, and the transport rollers 102, 104, 120, 122, the photosensitive drum 110, and the fixing pressure roller 115 are driven to feed. Control is performed to transport the printed paper to the discharge outlet. When the paper is being transported, the top edge of the paper and the rear edge of the paper are detected by the TOP sensor 105 and the fixing paper discharge sensor 114, a timer is run based on the detected timing, and the paper position is identified by monitoring the timer value. Yes.

  The scanner control unit 303 drives the polygon mirror and laser of the scanner unit 113 to perform control to form an electrostatic latent image on the photosensitive drum 110.

  The high voltage control unit 305 controls the voltage and current applied to the charging roller 109, the developing roller 108, and the transfer roller 107, and uses the electrostatic latent image formed on the photosensitive drum 110 as a toner image, and the conveyed paper Control to transfer the toner image to P is performed.

  The fixing control unit 306 performs control to fix the toner image on the sheet by controlling the heater 118 according to the temperature of the thermistor 117 that detects the temperature of the heater installed in the fixing film 116 and adjusting the temperature.

  3 is a block diagram showing the configuration of the image controller 200, the scanner unit 113, the transfer unit 204, and the engine controller 202 of the image forming apparatus 201. is there.

  An image controller 200 as image generation means for creating image data based on print data from an external device receives a print request 10 and image data 11 from an external device such as a PC. Then, the image output permission signal 13 is received from the engine controller 202. Thereafter, the image data sending means provided in the image controller 200 synchronizes with the detection of the leading edge of the paper by the image writing notification means (TOP sensor 105), and the raster image data (14) based on the BD signal 15 from the scanner unit 113. Send.

  The engine control unit 301 receives various print requests 12 transmitted from the image controller 200. In response to the request, the scanner control instruction 20 is transmitted to the scanner control section 303, the paper conveyance control instruction 21 is transmitted to the paper conveyance control section 304, and the high pressure control instruction 22 is transmitted to the high pressure control section 305.

  Upon receiving the scanner control instruction 20, the scanner control unit 303 controls the scanner motor in the scanner unit so that a BD signal 15 that is an output reference signal of raster image data transmitted from the image controller 200 is output at a predetermined timing. . Further, the driving of the laser (mask, forced light emission, unblanking control, etc.) is controlled in accordance with the paper transport position. Further, printing rate calculation control is performed to monitor the BD signal 15 and the raster image data 14 and calculate the printing rate.

  Upon receipt of the paper conveyance control instruction 21, the paper conveyance control unit 304 drives the photosensitive drum motor, and drives the transfer roller 107 that rotates following the photosensitive drum.

  Upon receiving the high pressure control instruction 22, the high voltage control unit 305, which is a transfer control unit, performs control to set and apply a transfer bias in accordance with the passage of the paper P.

  FIG. 4 shows a plan view of the laser scanner unit 113. The scanner unit 113 includes a semiconductor laser 401 having a laser light source, a laser beam 402 emitted from the semiconductor laser 401, and a polygon mirror 403 that deflects the laser beam 402 oscillated from the semiconductor laser 401. The scanner unit 113 also includes a BD sensor (image data detection means) 404 that detects irradiation of the deflected laser beam 402 and emits a BD signal 15 detected by the BD sensor 404. Further, the scanner unit 113 includes an fθ lens 405 that corrects the scanning speed of the laser beam 402 deflected by the polygon mirror 403 on the photosensitive drum 110 to a constant speed. Further, the scanner unit 113 includes a laser driving unit 407 that controls the emission of the semiconductor laser 401 and a scanner motor driving unit 406 that controls the rotation speed of the polygon mirror. A control signal 23 for instructing acceleration and deceleration is input to the scanner motor driving unit 406, and a laser driving signal 24 for controlling light emission / extinction of the semiconductor laser and a raster transmitted from the image controller 200 are input to the laser driving unit 407. An image data signal 14 is input.

  FIG. 5 is a block diagram of the scanner control unit 303 that controls the scanner unit 113.

  When printing is started and the scanner control unit 303 receives the scanner control instruction 20 from the engine control unit 301, the scanner motor control unit 500 controls the rotation speed of the polygon mirror 403. Specifically, the control signal 23 for instructing acceleration and deceleration to the scanner motor driving unit 500 is transmitted so that the detection cycle (that is, the rotation speed) of the BD signal 15 becomes a predetermined cycle. The TOP sensor base point timer 501 starts the timer counting when the fed paper P reaches the TOP sensor 105 which is an image writing notification means.

  The image output permission signal control unit 502 sets the transfer nip position b by the distance from the laser irradiation position a (FIG. 1) to the transfer nip position b (FIG. 1) on the circumference of the drum when the leading edge of the paper P is in the conveyance path 140. The image output permission signal 13 is transmitted to the image controller 200 when it is time to reach a position going back to the upstream side (hereinafter referred to as “conveying path laser irradiation position”).

  The laser drive signal control unit 503 sets the laser drive signal 24 to the image mask release setting at the timing when the leading edge of the paper reaches the conveyance path laser irradiation position. Thereafter, the sheet is conveyed, and the laser drive signal 24 is set to the mask at the timing when the trailing edge of the sheet reaches the conveyance path laser irradiation position. Thereafter, the image controller 200 that has received the image output permission signal 13 transmits the raster image data 14 based on the BD signal 15 output from the scanner unit.

  When the dot count control unit 510 receives the image output permission signal 13, it clears the BD line number counter 511, the dot number counter 512, and the ON dot number counter 513 as image data detection means. Thereafter, every time the BD signal 15 is received, the BD line number counter 511 is incremented. Further, the dot number counter 512 is incremented every time the raster image data 14 from the image sending means of the image controller 200 is monitored, and the ON dot number counter 513 is incremented every time the raster image data is ON when monitored. When scanning is performed for the designated number of lines, the printing rate calculation control unit (printing rate calculation means) 514 calculates the printing rate from the calculation formula of “(ON dot number counter 513) ÷ (dot number counter 512) × 100”. . The calculated printing rate is stored in a printing rate recording unit (image data storage unit) 516 that stores the image data value digitized by the memory controller 515.

FIG. 6 shows a flowchart of transfer bias control during printing. The image forming apparatus 201 used in this embodiment is 600 DPI, and the resistance value of the transfer roller 107 is 1.4 × 10 ⁸ Ω (temperature 23 ° C., humidity 60% (referred to as N / N environment)). Resistance value when 2.5 KV is applied to the transfer roller 107), the width of the transfer nip TN is 1.5 mm, the length from the laser irradiation position a to the transfer nip position b on the drum is 40 mm, and the process speed is 186 mm did.

  When printing is started, the high voltage control unit 305 starts transfer ATVC control (S601). Specifically, by applying a constant current to the dark part (VD part) of the photosensitive drum and monitoring the generated voltage, the applied bias is controlled by combining the voltage with the same magnification, coefficient multiplication, constant voltage, etc. To do.

  When the transfer ATVC control is started, constant current control is performed to control the applied bias so that a predetermined target current value (8.0 μA in this embodiment) is obtained (S602), and the target current value is supplied to the transfer roller 107. A value Vt0 obtained by holding the output voltage value is determined (S603).

  When the constant current control is completed and the first sheet reaches the conveyance path laser irradiation position a, the image output permission signal 13 is transmitted to the image controller 200 and latent image formation is started (S604). When the latent image formation is started, the printing rate calculation control is started (S605). The printing rate calculation control unit 514 controls the transfer nip width data (35 lines in this embodiment) as one data block, calculates the printing rate for each block, and stores it in the printing rate recording unit 516 sequentially. Do. The data for one block is 35 lines (1.5 mm on the drum), and the data is stored at a timing advanced by 1.5 mm from the laser irradiation position a, and then held until the transfer nip position b is reached. Since one block of data is 1.5 mm and the transfer nip position is 40 mm from the laser irradiation position, a sufficient time can be secured for correcting the transfer bias after storing the data.

When it is time for the leading edge of the sheet to reach the transfer nip TN (S606), a transfer print bias Vt (kV) is calculated (S607). The transfer print bias Vt (kV) is calculated by the following (formula 1).
Vt = 1.4 × Vt0 + 0.8 (Expression 1)

When the transfer print bias Vt is determined, the print rate of the first data block stored in the image print rate recording unit 516 is acquired (S608), and the image process condition (transfer bias) is corrected according to the print rate. The correction voltage value (kV) is calculated by the following (Formula 2).
Correction voltage value = 0.5 × (print rate (%) ÷ 100) (Expression 2)

  In the above equation, 0.5 (kV) is a correction voltage value when a solid black image is passed. The transfer current value when a solid white image paper is passed through the transfer nip TN and 2.5 kV is applied is 13.3 μA, and a solid black image paper is passed through the transfer nip TN when 2.5 kV is applied. The transfer current value was 11.0 μA. This phenomenon is a phenomenon in which when the toner carried on the drum 110 is transferred, it becomes a resistance, and the current value flowing through the transfer decreases. In order to flow 13.3 μA in the case of a solid black image, it is necessary to apply 3.0 kV, and in the case of a solid black image, it is necessary to correct 0.5 kV. That is, the transfer current value is increased as the printing rate calculated by the printing rate calculation means increases. For images where the printing rate is between a solid white image and a solid black image, the correction rate is calculated according to the printing rate as shown in (Equation 2) because the printing rate and the resistance value of the toner are linear. it can. The correction voltage value is added to the transfer print bias Vt to determine a new transfer print bias (S609), and the transfer bias is applied (S610).

  When the transfer time corresponding to the transfer nip width has elapsed (S611), the printing rate of the next data block stored in the image printing rate recording unit 516 is acquired in the same manner as in S607, S608, and S609 (S612), and according to the printing rate. The correction is performed (S613), the transfer bias is determined, and the transfer bias is applied (S614). When S611 to S614 are repeatedly performed and the trailing edge of the sheet passes through the transfer nip TN (S615), a bias between the transfer sheets is applied, and the printing rate calculation control is ended (S616).

  If there is no next reservation and printing is completed (S617), the transfer bias is turned off (S618). If printing continues (S617), ATVC control is performed between sheets (S619 to S621), and then the process returns to S605 to repeatedly perform transfer control.

  The above is the embodiment of the first embodiment. By performing this embodiment, the printing rate with the image data of the transfer nip width as one block is calculated and stored until the latent image portion reaches the transfer portion, and the transfer bias is sequentially corrected. Even in the case of an image with a printing rate, it is possible to apply an optimal transfer bias, and as a result, it is possible to prevent transfer failure and transfer punch-through and improve transfer efficiency.

Example 2
In the first embodiment, in an image forming apparatus that performs constant voltage control of transfer when a sheet is passed, an area in the sub-scanning direction is divided, image data divided in the sub-scanning direction is acquired, and an image printing rate is calculated. The control for sequentially correcting the transfer bias according to the printing rate described above has been described. In the second embodiment, in an image forming apparatus that performs constant current control of transfer when a sheet is passed, in addition to area division in the sub-scanning direction, area division is also performed in the main scanning direction, and a printing rate for each divided area is calculated. The control for sequentially correcting the transfer target current value according to the calculated printing rate will be described.

  The image forming apparatus in this embodiment has the same configuration as the image forming apparatus described in Embodiment 1 described with reference to FIG. Therefore, the description of the image forming apparatus uses the description of the first embodiment, and the description thereof is omitted here. Similarly, in the first embodiment, the outline of the CPU mounted on the engine controller 202 described with reference to FIG. 2, the image controller 200 described with reference to FIG. 3, the scanner unit 113 of the image forming apparatus, and the transfer unit 204. The configuration of the engine controller 202 and the plan view of the laser scanner unit 113 described with reference to FIG. 4 are also employed in the present embodiment, and the description of the first embodiment is incorporated. Therefore, the re-explanation here is omitted.

  FIG. 7 shows a block diagram of the scanner control unit 303 in the second embodiment. Since the scanner motor control unit 500, the TOP sensor base point timer 501, the image output permission signal control unit 502, and the laser drive signal control unit 503 are the same as the description of FIG. 5 of the first embodiment, the description of the first embodiment is used. The re-explanation here is omitted.

  When the dot count control unit 510 receives the image output permission signal 13, it clears the BD line number counter (first image data detecting means) 511, the BD base point timer 517, the dot number counter 512, and the ON dot number counter 513. Thereafter, every time the BD signal 15 is received, the BD line number counter 511 is incremented, and the BD base point timer 517 is started. The dot number counter 512 and the ON dot number counter 513 have counters (second image data detection means) (512-N, 513-N) for each area obtained by dividing the main scanning direction into a predetermined number N. . The M-th (M = 1, 2,... N) counters are a dot number counter M (512-M) and an ON dot number counter M (513-M), respectively.

  The BD base point timer (517) determines in which area the position of the N-divided area is present. In the Mth area, the dot number counter M (512-512) is monitored every time the raster image data 14 is monitored. M) is incremented and the ON dot number counter M (513-M) is incremented every time the raster image data is ON when monitored. When scanning is performed for the designated number of lines, the printing rate calculation control unit 10 calculates the first to Nth from the calculation formula of “ON dot number counter M (513-M) ÷ dot number counter M (512-M) × 100”. The printing rate of the area is calculated. The calculated printing rate of each area is stored in the printing rate recording unit 516 by the memory controller 515.

  FIG. 8 is a flowchart showing an embodiment of transfer bias control during printing in the second embodiment.

  When printing is started and the first sheet reaches the conveyance path laser irradiation position, an image output permission signal 13 is transmitted to the image controller 200, and latent image formation is started (S801). When the latent image formation is started, the printing rate calculation control is started (S802). The print rate calculation control unit 514 sets the width of the transfer nip TN (35 lines in this embodiment) as one block, sets one block as N areas in the main scanning direction, and sets the print rate for each area. Control to calculate and sequentially store in the printing rate recording unit 516 is performed. When it is time to reach the transfer nip (S803), the printing rate data is acquired (S804), the correction current value is added to the transfer target current value It (13.3 μA in this embodiment), and a new target is obtained. Determine the current value. The correction current value is calculated by the following (Equation 3) by obtaining an average printing rate which is an average value of the printing rate of the 1st to N areas among the maximum printing rate in one block.

In the following description, in the present embodiment, the printing rate calculation control unit 514 serves as a maximum printing rate calculation unit and an average printing rate calculation unit, and further, a printing rate comparison for comparing the average printing rate with the maximum printing rate. Functions as a means.
Correction current value = 2.7 μA × ((maximum printing rate−average printing rate) ÷ 100) (Equation 3)

  2.7 μA in the above formula is a correction current value when the average printing rate is very small but there is only a part of the solid black image. When the entire area is a solid black image, the voltage value when the constant current control is 13.3 μA is 3.0 kV. When only one area is the solid black image, the voltage value when the constant current control is 13.3 μA. The voltage value was 2.5 kV. This phenomenon becomes a resistance when the toner carried on the photosensitive drum 110 is transferred to the paper P, but even when only one area is an image with a high printing rate, the resistance value of the entire area is small and the applied voltage value. Is a phenomenon that becomes smaller. If only one area is a solid black image, the target current value needs to be 16.0 μA in order to apply 3.0 kV, and if only one area is a solid black image, it needs to be corrected by 2.7 μA. is there. In order to linearly correct the target current value according to the difference between the maximum printing rate and the average printing rate, a correction current value is calculated as shown in (Equation 3) (S805). The target current value of the constant current control is increased as the difference between the average printing rate calculated by the average printing rate calculation unit and the maximum printing rate calculated by the maximum printing rate calculation unit increases.

  Thereafter, constant current control for controlling the applied bias so as to achieve the determined target current value is started (S806).

  When the transfer nip width has elapsed (S807), the print rate data is acquired (S808) as in S804 and S805, and the print rate of the next data block stored in the image print rate recording unit 516 is obtained. Accordingly, correction is performed and a target current value is determined (S809). When S807 to S809 are repeated and the trailing edge of the sheet passes through the transfer nip TN (S810), a bias between the transfer sheets is applied, and the printing rate calculation control ends (S811). If there is no next reservation and printing is completed (S812), the transfer bias is turned off (S813). If printing continues, the process returns to S802 and the transfer control is repeated.

  The above is the embodiment of the second embodiment. By performing this embodiment, the printing rate for each area obtained by dividing the image data of the transfer nip width by N before the latent image portion reaches the transfer portion is calculated and stored, and the transfer target current is determined according to the printing rate. By sequentially correcting the values, it is possible to apply an optimum transfer bias even if there is a bias in the image, and as a result, it is possible to prevent an image transfer failure with a bias in the printing rate.

  It should be noted that the form of the means for correcting the image bias in the present embodiment can also be applied to the image forming apparatus that performs the constant voltage control described in the first embodiment.

105 TOP sensor (image writing notification means)
107 Transfer roller (transfer means)
108 Developing roller (developing means)
109 Charging roller (charging means)
110 Photosensitive drum (image carrier)
113 Scanner unit (scanning exposure means)
200 Image controller (image data generator)
201 Image forming apparatus 202 Engine controller 305 High pressure control unit (transfer control means)
404 BD sensor (image data detection means)
511 BD line number counter (image data detection means)
512 dot number counter (second image data detection means)
513 ON dot number counter (second image data detection means)
514 Print rate calculation control unit (print rate calculation means)
516 Print rate recording unit (image data storage means)

Claims (6)

An image data generation unit that creates image data based on print data sent from an external device, and an image formation unit that forms an image on a recording medium based on the image data generated by the image data generation unit,
The image data generation unit includes an image data sending unit that sends image data to the image forming unit in synchronization with an image writing notification unit that the image forming unit reports.
The image forming unit includes a scanning exposure unit that forms a latent image on an image carrier in synchronization with the image data sending unit, a developing unit that develops the latent image on the image carrier to form a toner image, and the toner image In an image forming apparatus having an image forming means having a transfer means for transferring the image to the recording medium,
The image forming unit includes:
Image data detection means for detecting image data output from the image data transmission means;
Image data storage means for digitizing and storing image data detected by the image data detection means;
A transfer control means for correcting a transfer bias applied to the transfer means in accordance with a data value stored in the image data storage means;
An image forming apparatus comprising: An image data detecting means for dividing an area in the sub-scanning direction of the scanning exposure means into data blocks having a predetermined number of lines, and detecting image data for each data block;
A printing rate calculating means for calculating a printing rate from the image data for each data block;
The image forming apparatus according to claim 1, wherein the transfer bias is corrected by the transfer control unit in accordance with the printing rate. A first image data detecting unit that divides an area in the sub-scanning direction of the scanning exposure unit into data blocks having a predetermined number of lines, and detects image data for each data block;
A second image data detection unit that divides an area in the main scanning direction of the scanning exposure unit into a predetermined number and detects image data for each divided area;
Average printing rate calculation means for calculating an average value of printing rates of all areas divided in the main scanning direction of the scanning exposure means for each data block divided in the sub-scanning direction of the scanning exposure means;
Maximum printing rate calculating means for calculating the maximum printing rate of all areas for each divided data block in the sub-scanning direction of the scanning exposure unit;
A printing rate comparison unit for comparing the results of the average printing rate calculation unit and the maximum printing rate calculation unit;
The image forming apparatus according to claim 1, wherein the transfer bias is corrected by the transfer control unit in accordance with a result of comparison by the printing rate comparison unit.   The image forming apparatus according to claim 1, wherein the transfer control unit is a unit that performs constant voltage control or constant current control.   The image forming apparatus according to claim 2, wherein the transfer control unit is a unit that performs constant voltage control, and increases the transfer current value as the printing rate calculated by the printing rate calculation unit increases.   The transfer control unit is a unit that performs constant current control, and the constant current increases as the difference between the average printing rate calculated by the average printing rate calculation unit and the maximum printing rate calculated by the maximum printing rate calculation unit increases. The image forming apparatus according to claim 3, wherein a target current value for control is increased.

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