JP2007041284A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of improving dot reproducibility and enhancing image quality. <P>SOLUTION: A semiconductor laser loaded to an exposure part 33 outputs laser beams, an overshoot generator loaded to the exposure part 33 makes the driving signal of the semiconductor layer overshoot, an image forming part 30 forms a density correction image, a density sensor 70 measures the density of the density correction image formed by the image forming part 30, and an overshoot time determination part 108 determines the overshoot time of the overshoot generated by the overshoot generator in accordance with the density value measured by the density sensor 70. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms toner images of different colors.

  In many cases, an electrophotographic color image forming apparatus obtains a color image by superimposing four colors of cyan, magenta, yellow, and black. In such a color image forming apparatus, a plurality of image forming units that form toner images of each color of cyan, magenta, yellow, and black are arranged in one direction, and each color is conveyed on a sheet conveyed in the arrangement direction. A so-called tandem color image forming apparatus that transfers the toner images in a superimposed manner is known.

In the above image forming apparatus, an electrostatic latent image is formed by irradiating the surface of the charged photosensitive drum with laser light, and the toner image formed by developing the electrostatic latent image with toner is recorded. 2. Description of the Related Art Laser type color image forming apparatuses that form color images by transferring and fixing on paper are known. In a laser type color image forming apparatus, it is possible to stabilize the beam diameter and maintain good image quality by intentionally overshooting the laser power of the laser beam to be irradiated (see, for example, Patent Document 1). ).
JP 2002-303814 A

  However, in an image forming apparatus having a tandem structure, the exposure device and the photosensitive drum are a pair for each color, and there is a difference in the sensitivity variation of the photosensitive drum of each color, the variation of the light emission pattern of the light source, and the variation of the characteristics of the development system. Although it is designed to be eliminated, perfect matching between image density (solid density) and dot reproducibility is extremely difficult.

  In addition, the charging level and exposure amount of the photosensitive drum can be easily changed in accordance with the characteristics of the image forming unit for each color, and correction of the image density that changes depending on the environment and state of use is actively performed. In many cases, the relationship between dot reproducibility and image density is hardly corrected. Deviations in the development characteristics of each color due to changes in the usage environment and conditions can be used to improve image quality degradation at the expense of image collapse in the high density area, gradation in the low density area, or subtle. The current situation is that the overall optimization is achieved by taking a proper balance to prevent the problem from becoming obvious.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of improving dot reproducibility and improving image quality.

  An image forming apparatus according to the present invention is an image forming apparatus that forms a color image using a plurality of toners having different colors, and generates overshoot in a light source unit that outputs a laser beam and a drive signal of the light source unit. An overshoot generating means for forming, an image forming means for forming a density correction image using a plurality of toners of different colors, a density measuring means for measuring the density of the density correction image formed by the image forming means, Overshoot time determining means for determining the overshoot time of the overshoot generated by the overshoot generating means in accordance with the density value measured by the density measuring means.

  According to this configuration, a density correction image is formed using a plurality of toners having different colors, and the density of the formed density correction image is measured. Then, the overshoot time of the overshoot generated in the drive signal of the light source means that outputs the laser beam is determined according to the measured density value. Subsequently, a drive signal having an overshoot corresponding to the determined overshoot time is output to the light source means.

  Therefore, instead of simply generating an overshoot in the drive signal of the light source means, an overshoot time corresponding to the measured density value is determined, and a drive signal having an overshoot corresponding to the determined overshoot time is output. Therefore, it is possible to adjust the overshoot time in which the optimum dot reproducibility is obtained based on the measured density value, the dot reproducibility can be improved, and the image quality can be improved.

  In the image forming apparatus, the image forming unit forms a solid image, a halftone dot image, and a line image as a density correction image, and the density measuring unit includes a solid image formed by the image forming unit, Measuring the density of a halftone dot image and a line image, and depending on the density value of the solid image, the halftone dot image and the line image measured by the density measuring means, at least one of a gamma correction value, a development bias value and an exposure condition; A color correction unit that performs a color correction process for correcting one; the overshoot time determination unit performs a halftone image measured by the density measurement unit after the color correction process is performed by the color correction unit; And the overshoot time of the overshoot generated by the overshoot generating means is determined in accordance with the density value of one of the line image and the line image. Door is preferable.

  According to this configuration, the solid image, halftone dot image, and line image are formed as the density correction image, and the density of the formed solid image, halftone dot image, and line image is measured. Then, color correction processing for correcting at least one of the gamma correction value, the development bias value, and the exposure condition is performed according to the measured density values of the solid image, the halftone dot image, and the line image. After the color correction process is performed, the overshoot time of overshoot is determined according to the density value of one of the halftone image and the line image.

  Therefore, after the color correction process that performs at least one of the gamma correction value, the development bias value, and the exposure condition is performed, the overshoot time of the overshoot is determined, so that the image density is corrected to a certain level. Image quality can be further improved.

  The image forming apparatus may further include an overshoot time storage unit that stores the overshoot time determined by the overshoot determination unit, and the overshoot generation unit stores the overshoot time storage during normal printing. It is preferable to generate an overshoot based on the overshoot time stored in the means.

  According to this configuration, the determined overshoot time is stored in the overshoot time storage unit, and overshoot based on the overshoot time stored in the overshoot time storage unit is generated during normal printing. Accordingly, during normal printing, the drive signal is controlled using the overshoot time stored in the overshoot time storage means, so there is no need to correct the overshoot time each time printing is performed, and the processing is simplified. Can do.

  The image forming apparatus may further include an overshoot amount determining unit that determines an overshoot amount of the overshoot generated by the overshoot generating unit according to the density value measured by the density measuring unit. preferable.

  According to this configuration, not only the overshoot time is changed, but also the overshoot amount corresponding to the measured concentration value is determined, and a drive signal having an overshoot corresponding to the determined overshoot amount is output. The

  Therefore, instead of simply generating an overshoot in the drive signal of the light source means, an overshoot amount corresponding to the measured density value is determined, and a drive signal having an overshoot corresponding to the determined overshoot amount is output. As a result, it is possible to adjust the overshoot amount so that the optimum dot reproducibility can be obtained based on the measured density value, the dot reproducibility can be improved, and the image quality can be improved.

  In the above image forming apparatus, the light source unit and the overshoot generating unit are disposed along a conveyance direction of the recording paper on a transfer belt that conveys the recording paper, and respectively store toner images of different colors. It is preferably provided for each of a plurality of image forming units formed individually.

  According to this configuration, the light source unit and the overshoot generation unit are arranged on the transfer belt for transporting the recording paper along the transport direction of the recording paper, and a plurality of toner images of different colors are formed individually. Therefore, the overshoot time can be corrected for each image forming unit of each color. In addition, since the toner images of the respective colors are sequentially superimposed and transferred, the overshoot time correction process can be performed in a short time.

  In the image forming apparatus, the light source unit and the overshoot generation unit may be any of a photosensitive drum, a rotary rack on which a developing device corresponding to each of a plurality of toners is mounted, and a plurality of developing devices. A rotary rack driving means for rotating the rotary rack so that the developing roller of the developing device is positioned at a position facing the photosensitive drum, and a toner image of each color is transferred from the photosensitive drum, and a color image is obtained. It is preferable that the density measuring unit is provided in an image forming unit including an intermediate transfer body to be formed, and the density measuring unit measures the density of the density measuring image formed on the intermediate transfer body.

  According to this configuration, the image forming unit includes a photosensitive drum, a rotary rack on which a developing device corresponding to each of the plurality of toners is mounted, and a developing roller of any of the plurality of developing devices. It includes a rotary rack driving means for rotating the rotary rack so as to be positioned at a position facing the body drum, and an intermediate transfer body on which the toner image of each color is transferred from the photosensitive drum and forms a color image. A light source unit and an overshoot generation unit are provided in the image forming unit. In this case, since the photosensitive drum and the exposure apparatus including the light source unit and the overshoot generation unit are a pair, it is possible to simplify the process of correcting image variations caused by the photosensitive drum and the exposure apparatus. .

  According to the present invention, the overshoot time corresponding to the measured density value is determined, and the overshoot is determined according to the determined overshoot time, instead of simply generating an overshoot in the drive signal of the light source means. Since the drive signal is output, it is possible to adjust the overshoot time to obtain optimal dot reproducibility based on the measured density value, improve dot reproducibility, and improve image quality Can do.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing an internal configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus shown in FIG. 1 is a tandem type color printer, and is provided with a paper feed cassette 10, a transfer conveyance unit 20 provided above the paper feed cassette, and an upper part of the transfer conveyance unit 20. An image forming unit 30, a fixing unit 40 disposed on the left side of the transfer conveyance unit 20, a first conveyance path 50 for guiding the recording paper P set in the paper feed cassette 10 to the transfer conveyance unit 20, and a fixing unit And a second transport path 60 that guides the recording paper P, on which the fixing process has been performed by 40, to the discharge tray 80.

  The paper feed cassette 10 has recording paper P accumulated therein, and the deposited recording paper P is picked up one by one by a paper feed roller (not shown) and discharged to the first transport path 50 side. The image forming unit 30 includes image forming units 30K, 30Y, 30M, and 30C that form toner images of black (K), yellow (Y), magenta (M), and cyan (C), respectively. Since the image forming units 30K to 30C have the same configuration, only the black image forming unit 30K will be described.

  The black image forming unit 30K includes a photosensitive drum 31, a charging unit 32, an exposure unit 33, a developing unit 34, and a cleaner unit 35. The photosensitive drum 31 is a cylindrical member, receives a driving force from a motor (not shown), and rotates in the clockwise direction (the direction of arrow A shown in FIG. 1). The exposure unit 33 includes a light source such as a semiconductor laser, and irradiates the photosensitive drum 31 charged by the charging unit 32 with an optical signal corresponding to the image data to form an electrostatic latent image of the image data. The developing unit 34 includes a toner box 341 that stores black (K) toner, and supplies black toner to the photosensitive drum 31 on which the electrostatic latent image is formed to form a black toner image. The black toner image formed on the photosensitive drum 31 is transferred to the recording paper P or the transfer belt 21 by the transfer roller 22. The cleaner unit 35 removes toner adhering to the surface of the photosensitive drum 31 to which the black toner image is transferred.

  The transfer conveyance unit 20 includes a transfer belt 21, a transfer roller 22, a right roller 23, and a left roller 24. The right roller 23 is disposed below the image forming unit 30K, and the left roller 24 is disposed below the image forming unit 30C. The transfer belt 21 is an endless belt stretched between a right roller 23 and a left roller 24, and is fixed in a counterclockwise direction (the direction of arrow B shown in FIG. 1) by the right and left rollers 23, 24. Rotated at a speed of The transfer belt 21 is made of a heat-resistant resin material such as polyimide resin. Four transfer rollers 22 are disposed on the inner peripheral side of the transfer belt 21 and at positions facing the four photosensitive drums 31.

  The transfer roller 22 is made of a conductive rubber material or the like, and transfers the toner image of each color formed on the photosensitive drum 31 onto the recording paper P or the transfer belt 21. A density sensor 70 is provided on the outer peripheral side of the transfer belt 21 and in the vicinity of the left roller 24. The density sensor 70 is composed of, for example, a reflective photosensor, and measures the density of the toner image formed on the transfer belt 21. A temperature / humidity sensor 90 is provided in the image forming apparatus. The temperature / humidity sensor 90 measures the temperature and humidity in the image forming apparatus.

  The fixing unit 40 includes a heat shielding box 41, a fixing roller 42 having a built-in heater, and a pressure roller 43, and heats and transports the recording paper P on which the toner image is formed, thereby fixing the toner image on the recording paper P. .

  FIG. 2 is a block diagram illustrating an example of a functional configuration of the image forming apparatus illustrated in FIG. The image forming apparatus shown in FIG. 2 includes an image forming unit 30, a density sensor 70, a temperature / humidity sensor 90, and a control unit 100. In FIG. 2, the image forming units 30C, 30M, 30Y, and 30K for cyan, magenta, yellow, and black are collectively referred to as an image forming unit 30.

  The control unit 100 includes a patch image storage unit 101, a patch image forming unit 102, a density measurement unit 103, a color correction LUT (lookup table) storage unit 104, a color correction processing unit 105, a light emission control unit 106, and a light amount LUT (lookup). Table) storage unit 107, overshoot time determination unit 108, temperature / humidity measurement unit 109, environment correction table storage unit 110, and environment correction processing unit 111.

  The patch image storage unit 101 stores raster data of a patch image that is a density correction image. The patch image is a solid (full dot) patch image (solid image) in which all the dots in the patch image are printed, or a discrete dot patch image (network) printed so that the colored dots are not adjacent to each other in the diagonal direction. Point image) and a hatched patch image (line image) in which colored dots are printed in a line adjacent to each other in an oblique direction.

  The patch image forming unit 102 reads a predetermined patch image from the patch images stored in the patch image storage unit 101, and transfers the patch image by controlling the image forming units 30C, 30M, 30Y, and 30K. Printing is performed at a predetermined position on the belt 21. The patch image forming unit 102 prints a solid patch image, a discrete dot patch image, and a hatched patch image on the transfer belt 21 for each color of cyan, magenta, yellow, and black.

  The density measurement unit 103 causes the density sensor 70 to measure the density of the single-color solid patch image, discrete dot patch image, and oblique line patch image formed on the transfer belt 21 by the patch image forming unit 102. The color correction LUT storage unit 104 associates an optimum density value with a gamma correction value for obtaining the optimum density value for each color, and also associates the optimum density value with a development bias value for obtaining the optimum density value. A color correction LUT that associates each color with an optimum density value and an exposure condition for obtaining the optimum density value is stored.

  The color correction processing unit 105 refers to the color correction LUT stored in the color correction LUT storage unit 104 and corresponds to the density values of the solid patch image, discrete dot patch image, and oblique line patch image measured by the density measurement unit 103. , Color correction processing for correcting at least one of the gamma correction value, the development bias value, and the exposure condition is performed.

  Specifically, the color correction processing unit 105 previously planned the density of the solid patch image based on the result of the density sensor 70 detecting the solid patch image formed on the transfer belt 21 by the image forming unit 30. The development bias value is changed so that the density is the same.

  Further, the color correction processing unit 105 determines the density of the discrete dot patch image based on the result of the density sensor 70 detecting the discrete dot patch image composed of a plurality of dots formed on the transfer belt 21 by the image forming unit 30. However, the exposure condition of the exposure unit 33, for example, the pulse width of the drive signal, the magnitude of the exposure amount (laser power), or the like is changed so as to obtain the density planned in advance.

  Further, the color correction processing unit 105 previously planned the density of the hatched patch image based on the result of the density sensor 70 detecting the hatched patch image formed on the transfer belt 21 by the image forming unit 30. Change the gamma correction value so that the density is the same. The changed gamma correction value is stored in a gamma correction table (not shown).

  The light emission control unit 106 controls light emission of the semiconductor laser of the exposure unit 33. The light emission control unit 106 outputs a control signal instructing the light emission of the semiconductor laser to the exposure unit 33. The light amount LUT storage unit 107 stores a light amount LUT in which a plurality of density values are associated with an overshoot time in which optimum dot reproducibility is obtained at each density value. Overshoot is to temporarily return to a predetermined level after a predetermined level is exceeded at the rising portion of the drive signal waveform, and the time exceeding the predetermined level becomes the overshoot time, and exceeds the predetermined level. The laser power of the part becomes an overshoot amount described later.

  The overshoot time determination unit 108 refers to the light amount LUT stored in the light amount LUT storage unit 107, and determines either the discrete dot patch image or the oblique patch image formed on the transfer belt 21 by the image forming unit 30. Based on the result detected by the density sensor 70, an overshoot time in which an optimum dot reproducibility is obtained with either one of the density of the discrete dot patch image and the hatched patch image is determined.

  Note that the light amount LUT storage unit 107 in the present embodiment stores a functional expression indicating the relationship between the density value and the overshoot time at which optimum dot reproducibility is obtained at each density value, and the overshoot time determination unit 108. May calculate the overshoot time corresponding to one of the density values of the discrete dot patch image and the oblique patch image formed on the transfer belt 21 by the image forming unit 30 using the above relational expression.

  The temperature / humidity measurement unit 109 causes the temperature / humidity sensor 90 to measure the temperature and humidity in the image forming apparatus. The environment correction table storage unit 110 stores an environment correction table in which the temperature and humidity are associated with the optimum charge amount of the photosensitive drum 31 and the exposure amount to the photosensitive drum 31 at each temperature and humidity.

  The environment correction processing unit 111 refers to the environment correction table stored in the environment correction table storage unit 110, and the photosensitive drum 31 corresponding to the temperature and humidity in the image forming apparatus measured by the temperature / humidity measurement unit 109. The charge amount, the exposure amount to the photosensitive drum 31, and the like are read, and the image forming unit 30 is controlled so as to have respective values. The environmental correction processing by the environmental correction processing unit 111 is performed on the image forming units 30C, 30M, 30Y, and 30K for each color.

  FIG. 3 is a block diagram showing a detailed configuration of the exposure unit 33 shown in FIG. The exposure unit 33 shown in FIG. 3 includes a drive signal generation unit 331, an overshoot generation unit 332, an overshoot time storage unit 333, an overshoot time switching unit 334, and a semiconductor laser 335. The drive signal generation unit 331 generates a drive signal for obtaining a predetermined laser power based on the control signal output by the control unit 100.

  The overshoot generator 332 generates an overshoot for the drive signal output by the drive signal generator 331. The overshoot generator 332 includes a 0% overshoot generator 332a, a 25% overshoot generator 332b, a 50% overshoot generator 332c, and a 75% overshoot generator 332d.

  The 0% overshoot generator 332a outputs the drive signal output by the drive signal generator 331 to the overshoot time switch 334 as it is without generating an overshoot. The 25% overshoot generation unit 332b has an overshoot time in which the ratio of the drive signal output from the drive signal generation unit 331 to the total time from the rising edge to the falling edge of the driving signal is 25%. Overshoot is generated and output to the overshoot time switching unit 334.

  The 50% overshoot generation unit 332c has an overshoot time in which the ratio of the drive signal output from the drive signal generation unit 331 to the entire time from the rising edge to the falling edge of the driving signal is 50%. Overshoot is generated and output to the overshoot time switching unit 334. The 75% overshoot generator 332d has an overshoot time in which the ratio of the drive signal output from the drive signal generator 331 to the total time from the rising edge to the falling edge of the driving signal is 75%. Overshoot is generated and output to the overshoot time switching unit 334.

  The overshoot time storage unit 333 stores the overshoot time determined by the overshoot time determination unit 108 of the control unit 100. The overshoot time switching unit 334 stores the overshoot time storage unit 333 among the 0% overshoot generation unit 332a, 25% overshoot generation unit 332b, 50% overshoot generation unit 332c, and 75% overshoot generation unit 332d. It switches to the overshoot generation part which outputs the drive signal which has the same overshoot time as the overshoot time currently performed. The semiconductor laser 335 is a visible red semiconductor laser having a wavelength of 670 nm, for example, and outputs a laser beam having a laser power corresponding to the drive signal.

  Next, the operation of the image forming apparatus shown in FIGS. 2 and 3 will be described. FIG. 4 is a flowchart for explaining the operation of the image forming apparatus shown in FIGS.

  First, in step S1, the control unit 100 instructs the temperature / humidity measurement unit 109 to start color correction processing. The color correction processing according to the present invention is performed, for example, when the image forming apparatus is turned on, when returning from the power saving standby state, or when an execution instruction is issued by the user from the operation panel provided in the image forming apparatus. To be executed.

  Next, in step S2, the temperature / humidity measurement unit 109 causes the temperature / humidity sensor 90 to measure the temperature and humidity in the image forming apparatus. The temperature / humidity sensor 90 measures the temperature and humidity in the image forming apparatus and outputs them to the temperature / humidity measurement unit 109. The temperature / humidity measurement unit 109 outputs the temperature and humidity output from the temperature / humidity sensor 90 to the environment correction processing unit 111.

  Next, in step S <b> 3, the environment correction processing unit 111 refers to the environment correction table stored in the environment correction table storage unit 110. In step S <b> 4, the environment correction processing unit 111 executes environment correction processing based on the temperature and humidity in the image forming apparatus measured by the temperature / humidity measurement unit 109. Specifically, the environment correction processing unit 111 sets the charging amount of the photosensitive drum 31 corresponding to the temperature and humidity in the image forming apparatus measured by the temperature / humidity measuring unit 109, the exposure amount to the photosensitive drum 31, and the like. The image forming unit 30 is read out from the correction table and controlled to have respective values.

  Next, in step S5, the patch image forming unit 102 reads the patch image stored in the patch image storage unit 101, and transfers the patch image by controlling the image forming units 30C, 30M, 30Y, and 30K. Printing is performed at a predetermined position on the belt 21.

  Here, the patch image will be described. As described above, the patch image includes a solid patch image, a discrete dot patch image, and a diagonal patch image. FIG. 5 is a diagram illustrating an example of a solid patch image, FIG. 6 is a diagram illustrating an example of a discrete dot patch image, and FIG. 7 is a diagram illustrating an example of a hatched patch image. In the solid patch image BP shown in FIG. 5, all the dots in the patch image are printed. The solid patch image BP is stored in the patch image storage unit 101 for each color of cyan, magenta, yellow, and black.

  The discrete dot patch image RP shown in FIG. 6 is printed so that the colored dots are not adjacent to each other in the diagonal direction. In this embodiment, the discrete dot patch image RP shown in FIG. 6A is used. However, the present invention is not particularly limited to this, and the discrete dot patch image RP shown in FIG. Good. Further, each dot is formed at a position that is not affected by the latent image of the adjacent dot. The discrete dot patch image RP is stored in the patch image storage unit 101 for each color of cyan, magenta, yellow, and black.

  In the hatched patch image SP shown in FIG. 7, a plurality of colored dots are printed adjacent to each other in the oblique direction. In the present embodiment, the hatched patch image SP shown in FIG. 7A is used, but the present invention is not particularly limited to this, and the hatched patch image SP shown in FIG. 7B may be used. The oblique patch image SP is stored in the patch image storage unit 101 for each color of cyan, magenta, yellow, and black.

  A patch image printed on the transfer belt 21 will be described. FIG. 8 is a diagram illustrating an example of a patch image printed on the transfer belt 21. As shown in FIG. 8, the image forming units 30C, 30M, 30Y, and 30K for each color form patch images CD, MD, YD, and KD on the transfer belt 21 at predetermined intervals, respectively. The patch images CD, MD, YD, and KD for each color are arranged on a bisector in the width direction of the transfer belt 21. Each color patch image CD, MD, YD, and KD is composed of a solid patch image BP, a discrete dot patch image RP, and a hatched patch image SP, respectively.

  Returning to FIG. 4, in step S <b> 6, the density measurement unit 103 causes the density sensor 70 to sequentially measure the density of each color solid patch image, discrete dot patch image, and diagonal line patch image formed on the transfer belt 21. The density sensor 70 measures the density of the solid patch image, discrete dot patch image, and oblique line patch image conveyed to the position of the density sensor 70 as the transfer belt 21 travels, and outputs the measured density to the density measurement unit 103. . The density measurement unit 103 samples the density value data output from the density sensor 70 and outputs the sampled data to the color correction processing unit 105 and the overshoot time determination unit 108.

  Next, in step S <b> 7, the color correction processing unit 105 reads the color correction LUT stored in the color correction LUT storage unit 104. Next, in step S8, the color correction processing unit 105 calculates the density value of the solid patch image of each color measured by the density measurement unit 103 and the density value of the optimal solid patch image of each color stored in the color correction LUT. Compare. When the density value of the solid patch image of each color measured by the density measurement unit 103 is different from the density value of the optimal solid patch image of each color stored in the color correction LUT, the color correction processing unit 105 displays the solid patch image. The development bias value at which the density value becomes the optimum density value is acquired from the color correction LUT, and the current development bias value is changed for each image forming unit 30 so as to be the acquired development bias value.

  In addition, the color correction processing unit 105 compares the density value of the discrete dot patch image of each color measured by the density measurement unit 103 with the density value of the optimum discrete dot patch image of each color stored in the color correction LUT. To do. When the density value of the discrete dot patch image of each color measured by the density measurement unit 103 is different from the density value of the optimum discrete dot patch image of each color stored in the color correction LUT, the color correction processing unit 105 Acquires the exposure amount at which the density value of the discrete dot patch image is the optimum density value from the color correction LUT, and changes the current exposure amount for each image forming unit 30 so as to obtain the acquired exposure amount.

  Further, the color correction processing unit 105 compares the density value of the hatched patch image of each color measured by the density measuring unit 103 with the density value of the optimum hatched patch image of each color stored in the color correction LUT. When the density value of the hatched patch image of each color measured by the density measuring unit 103 is different from the density value of the optimum hatched patch image of each color stored in the color correction LUT, the color correction processing unit 105 A gamma correction value at which the density value of the oblique patch image is the optimum density value is acquired from the color correction LUT, and the current gamma correction value is changed for each image forming unit 30 so as to be the acquired gamma correction value.

  Next, in step S <b> 9, the overshoot time determination unit 108 reads the light amount LUT stored in the light amount LUT storage unit 107. Next, in step S <b> 10, the overshoot time determination unit 108 refers to the light amount LUT and determines an overshoot time corresponding to the density value of the discrete dot patch image of each color measured by the density measurement unit 103. The overshoot time determination unit 108 determines the overshoot time of the exposure unit 33 in the image forming unit 30 for each color. In this embodiment, the overshoot time corresponding to the density value of the discrete dot patch image of each color measured by the density measuring unit 103 is determined. However, the present invention is not particularly limited to this, and the density measurement is performed. The overshoot time corresponding to the density value of the hatched patch image of each color measured by the unit 103 may be determined.

  Here, the overshoot time will be described. FIG. 9 is a diagram for explaining the overshoot time. The vertical axis represents laser power (mW), and the horizontal axis represents time (ns).

  The laser power waveforms B1, B2, and B3 shown in FIG. 9 are obtained from the rise of the drive signal and the drive signal, respectively, in which the ratio of the overshoot time t1 to the time T from the rise to the fall of the drive signal is 25%. A drive signal in which the ratio of the overshoot time t2 to the time until the fall has an overshoot of 50%, and the drive in which the ratio of the overshoot time t3 to the time T from the rise to the fall of the drive signal has an overshoot of 75% Represents a signal. At this time, the overshoot amount is set to a constant level, and only the time for generating the overshoot is changed. The overshoot times t1, t2, and t3 represent the time from the rise to the fall of the overshoot portion at a position where the overshoot amount is halved.

  Returning to FIG. 4, next, in step S <b> 11, the overshoot time determination unit 108 stores the determined overshoot time for each color in the overshoot time storage unit 333 provided in the exposure unit 33 for each color.

  In this manner, a patch image (density correction image) is formed using a plurality of toners having different colors, and the density of the formed patch image is measured. Then, the overshoot time of the overshoot generated in the drive signal of the semiconductor laser 335 that outputs the laser beam is determined according to the measured density value. Subsequently, a drive signal having an overshoot corresponding to the determined overshoot time is output to the semiconductor laser 335.

  Therefore, instead of simply generating an overshoot in the drive signal of the light source means, an overshoot time corresponding to the measured density value is determined, and a drive signal having an overshoot corresponding to the determined overshoot time is output. Therefore, it is possible to adjust the overshoot time in which the optimum dot reproducibility is obtained based on the measured density value, the dot reproducibility can be improved, and the image quality can be improved.

  The color reproducibility on the low gradation side of color image gradation requires stabilization of dot reproducibility. In the screen or error diffusion on the low gradation side, the pattern exists as a single dot. At this time, if the dot reproducibility is uncertain and the monochromatic density may fluctuate, the color will appear clearly and color matching will be lost.

  In order to improve this, it is necessary to stabilize the presence of dots alone. As described above, 1) correction of development characteristics (gamma correction value), 2) correction of the charging bias of the photosensitive drum, and 3) correction of exposure conditions have been conventionally performed. However, in the above-described correction, the image may be crushed on the high gradation side, which may cause a gradation failure. Further, in 1) and 2), the possibility of causing image defects such as fogging, character dust, and scattering is increased. In other words, the above 1), 2), and 3) are used as means for correcting the overall change in environment correction and color correction, and are parameters for performing optimization such as image fogging and overall density. Become.

  Thus, in order to improve dot reproducibility without touching the above-mentioned anxiety material, it is conceivable to use the overshoot time of laser emission that can limit the influence of image defects only to single dots as a parameter. Overshoot is a phenomenon that occurs only at the rise during light emission. In a pattern in which a plurality of dots are arranged, the prescribed laser power becomes dominant, so that the influence of overshoot can be ignored.

  However, in any single dot, when the overshoot time is increased, the image density tends to increase at an intermediate gradation where the dot pitch is dense. For this reason, it is necessary not to increase the overshoot just because the dot reproducibility is poor, but to determine the overshoot time for each pattern based on raster data from a screen or the like.

  Therefore, in the present embodiment, in addition to the color correction, an appropriate overshoot time is obtained by comparing the reflection density of a plurality of types of patch images such as a dot pattern of a discrete pattern or a dot pattern of an oblique line and the light amount LUT. By deciding, the image quality is further improved. As described above, by performing correction that affects only a single dot, dot reproducibility can be improved without destroying a stable process state.

  Further, a solid image, a halftone dot image, and a line image are formed as a patch image (density correction image), and the density of the formed solid image, halftone dot image, and line image is measured. Then, color correction processing for correcting at least one of the gamma correction value, the development bias value, and the exposure condition is performed according to the measured density values of the solid image, the halftone dot image, and the line image. After the color correction process is performed, the overshoot time of overshoot is determined according to the density value of either the halftone image or the line image.

  Accordingly, after the color correction process for correcting at least one of the gamma correction value, the development bias value, and the exposure condition is performed, the overshoot time of the overshoot is determined, so that the image density is corrected to a certain level. Image quality can be further improved.

  Further, a plurality of semiconductor lasers 335 and overshoot generators 332 are arranged on the transfer belt 21 that conveys the recording paper along the recording paper conveyance direction, and individually form toner images of different colors. Since it is provided for each of the image forming units 30C, 30M, 30Y, and 30K, the overshoot time can be corrected for each of the color image forming units 30C, 30M, 30Y, and 30K. In addition, since the toner images of the respective colors are sequentially superimposed and transferred, the overshoot time correction process can be performed in a short time.

  Next, exposure processing by the image forming apparatus will be described. FIG. 10 is a flowchart for explaining an exposure process during printing by the image forming apparatus. First, in step S21, the control unit 100 determines whether image data to be printed has been input from a computer on the network via an I / F unit (not shown). If it is determined that image data has been input (YES in step S21), in step S22, the light emission control unit 106 sends a light emission control signal to the drive signal generation unit 331 of the exposure unit 33 of each image forming unit 30. Output.

  Next, in step S <b> 23, the overshoot time switching unit 334 reads the overshoot time stored in the overshoot time storage unit 333. Next, in step S24, the overshoot time switching unit 334 generates an overshoot corresponding to the overshoot time read from the overshoot time storage unit 333 from the plurality of overshoot generation units 332 (332a to 332e). The overshoot generator 332 to be selected is selected and switched to the selected overshoot generator 332. At this time, the overshoot time switching unit 334 connects the selected overshoot generation unit 332, the drive signal generation unit 331, and the semiconductor laser 335. For example, when the overshoot time stored in the overshoot time storage unit 333 is 25% of the maximum overshoot time, the overshoot time switching unit 334 switches to the 25% overshoot generation unit 332b, The drive signal generator 331, the 25% overshoot generator 332b, and the semiconductor laser 335 are connected.

  Next, in step S <b> 25, the drive signal generation unit 331 generates a drive signal for driving the semiconductor laser based on the light emission control signal and outputs the drive signal to the overshoot generation unit 332. This drive signal is a rectangular wave without overshoot. The drive signal generated by the drive signal generation unit 331 is output to a plurality of overshoot generation units 332 (332a to 332e). Of the plurality of overshoot generation units 332 (332a to 332e), the drive signal is output only from the overshoot generation unit 332 switched by the overshoot time switching unit 334, and the drive signal having the overshoot is the semiconductor laser 335. Is input.

  Next, in step S26, the semiconductor laser 335 outputs a laser beam corresponding to the drive signal having an overshoot, and exposure is started. Note that the processing in steps S23 to S26 is performed in the image forming unit 30 for each color.

  Thus, the determined overshoot time is stored in the overshoot time storage unit 333, and overshoot based on the overshoot time stored in the overshoot time storage unit 333 is generated during normal printing. Accordingly, during normal printing, the drive signal is controlled using the overshoot time stored in the overshoot time storage unit 333. Therefore, it is not necessary to correct the overshoot time each time printing is performed, and the processing is simplified. be able to.

  Next, an experiment regarding the relationship between the overshoot time and the dot reproducibility will be described. In the following experiment, the pulse width of one dot is 79 nsec, and a Macbeth reflection densitometer is used as the density sensor.

  FIG. 11 is a diagram showing experimental results regarding dot reproducibility that changes in accordance with environmental fluctuations. FIG. 11A shows an experiment regarding dot reproducibility when printing is performed using black magnetic one-component toner. FIG. 11B is a diagram showing experimental results of dot reproducibility when printing is performed using magenta non-magnetic one-component toner.

  11A and 11B, dot reproducibility was evaluated when the overshoot time was changed to 0 ns, 10 ns, 22 ns, 39 ns, and 60 ns in a normal temperature and normal humidity environment and a high temperature and high humidity environment. In a normal temperature and humidity environment, the temperature is set to 23 degrees and the humidity is set to 45% RH. In a high temperature and high humidity environment, the temperature is set to 30 degrees and the humidity is set to 80% RH.

  As shown in FIG. 11A, when printing using a black magnetic one-component toner, if an overshoot with an overshoot time of 22 ns, 39 ns, or 60 ns is generated in a room temperature and normal humidity environment, the density value is increased. The values are 0.80, 0.94, and 1.05, respectively, and relatively good dot reproducibility can be obtained. Also, in an environment of high temperature and high humidity, if an overshoot with an overshoot time of 39 ns or 60 ns is generated, the density values are 0.80 and 0.98, and relatively good dot reproducibility can be obtained.

  Similarly, as shown in FIG. 11B, when printing using magenta non-magnetic one-component toner, an overshoot with an overshoot time of 22 ns, 39 ns, and 60 ns is generated in a normal temperature and humidity environment. The density values are 0.83, 0.97, and 1.10, respectively, and relatively good dot reproducibility can be obtained. In addition, in an environment of high temperature and high humidity, if an overshoot with an overshoot time of 39 ns or 60 ns is generated, the density values become 0.94 and 1.02, respectively, and relatively good dot reproducibility can be obtained. In this way, it is possible to maintain sufficient dot reproducibility by correcting the overshoot time without performing environmental correction of development settings according to environmental changes.

  FIG. 12 is a diagram showing an experimental result of dot reproducibility that changes with time. FIG. 12A shows an experiment of dot reproducibility when printing is performed using black magnetic one-component toner. FIG. 12B is a diagram showing experimental results of dot reproducibility when printing is performed using magenta non-magnetic one-component toner.

  As shown in FIG. 12A, when printing is performed using black magnetic one-component toner, in the initial state, when an overshoot with an overshoot time of 39 ns and 60 ns is generated, the density value becomes 0.85 respectively. 0.99, and relatively good dot reproducibility can be obtained. In the initial state, when an overshoot with an overshoot time of 22 ns was generated, improvement in dot reproducibility was confirmed although it was insufficient.

  In addition, in the 50K print volume, when an overshoot with an overshoot time of 60 ns is generated, the density value becomes 0.95, and relatively good dot reproducibility can be obtained. Note that 50K print volume represents a state after printing 50,000 sheets. In addition, in 50K print volume, when an overshoot with an overshoot time of 39 ns was generated, an improvement in dot reproducibility was confirmed although it was insufficient.

  Further, in the case of 50K print volume and when color correction processing is executed (50Kpv color calib. On), when an overshoot with an overshoot time of 39 ns and 60 ns is generated, the density values are 0.83 and 0.96, respectively. Thus, relatively good dot reproducibility can be obtained.

  Similarly, as shown in FIG. 12B, when printing is performed using magenta non-magnetic one-component toner, in the initial state, if an overshoot with an overshoot time of 22 ns, 39 ns, or 60 ns is generated, The values are 0.66, 0.94, and 1.11 respectively, and relatively good dot reproducibility can be obtained.

  In addition, in the 50K print volume, when an overshoot with an overshoot time of 39 ns and 60 ns is generated, the density values become 0.85 and 0.95, respectively, and relatively good dot reproducibility can be obtained. Further, when 50K print volume is used and color correction processing is executed (50Kpv color calib. On), if an overshoot with an overshoot time of 39 ns and 60 ns is generated, the density values are 0.88 and 1.03, respectively. Thus, relatively good dot reproducibility can be obtained.

  As described above, in the image pattern in which the density transition due to the dot reproducibility is larger than the density transition of the solid patch image and the dot reproducibility affects the image quality depending on the use state, the image quality is maintained by changing the overshoot time. be able to. Also, the dot reproducibility may vary depending on the developer specifications. Since the dot reproducibility is slightly different between black and magenta as in the above experiment, it is possible to maintain a good balance of image quality by setting an overshoot time for each color.

  In the present embodiment, the overshoot time is changed according to the concentration value measured by the concentration measurement unit 103, but the present invention is not particularly limited to this, and even if the overshoot amount is changed. Good. In this case, the control unit 100 illustrated in FIG. 2 further includes an overshoot amount determining unit that determines an overshoot amount that causes overshoot.

  FIG. 13 is a diagram for explaining the amount of overshoot. The vertical axis represents laser power (mW), and the horizontal axis represents time (ns). Laser power waveforms A1, A2, and A3 shown in FIG. 13 each have a drive signal having an overshoot amount of 25% of a preset maximum overshoot amount and an overshoot amount of 75% of the maximum overshoot amount. The drive signal represents a drive signal having an overshoot amount (maximum overshoot amount) of 100%. As shown in FIG. 13, the difference between the laser power value X when no overshoot occurs and the maximum laser power values Y1, Y2, Y3 when overshoot occurs is the overshoot amounts Z1, Z2, Z3. It becomes.

  For example, when the overshoot time determined by the overshoot time determination unit 108 exceeds a preset time, for example, the time from the rise to the fall of the drive signal, the overshoot amount determination unit refers to the light amount LUT 107. The overshoot amount is determined while maintaining the overshoot time for a preset time. At this time, the light amount LUT 107 further stores a light amount LUT in which the density value and the overshoot amount are associated with each other.

  Thus, not only the overshoot time is changed, but also the overshoot amount corresponding to the measured density value is determined, and a drive signal having an overshoot corresponding to the determined overshoot amount is output. Therefore, instead of simply generating an overshoot in the drive signal of the light source means, an overshoot amount corresponding to the measured density value is determined, and a drive signal having an overshoot corresponding to the determined overshoot amount is output. As a result, it is possible to adjust the overshoot amount so that the optimum dot reproducibility can be obtained based on the measured density value, the dot reproducibility can be improved, and the image quality can be improved.

  In the image forming apparatus according to the present embodiment, a plurality of image forming units that form toner images of each color of cyan, magenta, yellow, and black are arranged in one direction, and each color is conveyed on a sheet conveyed in the arrangement direction. Although described as a tandem type color image forming apparatus that transfers toner images in a superimposed manner, the present invention is not particularly limited to this, and toner images of each color of cyan, magenta, yellow, and black are sequentially superimposed on an intermediate transfer member. In this case, a four-cycle color image forming apparatus may be used in which the toner images of four colors on the intermediate transfer member are collectively transferred to a sheet.

  FIG. 14 is a diagram schematically showing an internal configuration of an image forming apparatus according to another embodiment of the present invention. The image forming apparatus illustrated in FIG. 14 is a four-cycle color printer, and includes a paper feed cassette 201, a recording paper transport unit 202, an image forming unit 300, and a density sensor 207. The paper feed cassette 201 is attached to the main body of the image forming apparatus so that it can be pulled out, and stores a bundle of recording paper.

  The recording paper transport unit 202 includes a pickup roller 221, a transfer roller 222, transport rollers 223 and 224, and transports the recording paper along the recording paper transport path and discharges it from the recording paper discharge port 225. The pickup roller 221 picks up one sheet of recording paper from the recording paper bundle stored in the paper feed cassette 201 and conveys it to the transfer roller 222. The transfer roller 222 transfers the color toner image formed on the intermediate transfer belt 261 onto a recording sheet. The conveyance rollers 223 and 224 convey the recording paper picked up by the pickup roller 221 along the paper conveyance path.

  The image forming unit 300 includes an exposure unit 203, a rotary rack 204, a photosensitive unit 205, and an intermediate transfer unit 206. The exposure unit 203 converts the modulation signal generated based on the image data of the document into laser light and outputs it, and forms an electrostatic latent image for each color on the photosensitive drum 251.

  The photosensitive unit 205 includes a photosensitive drum 251, a charging unit 252 disposed around the photosensitive drum, a cleaning blade 253, and a fur brush 254. The charging unit 252 uniformly charges the surface of the photosensitive drum 251 that rotates in the direction of the arrow. The cleaning blade 253 contacts the surface of the photosensitive drum 251 with a predetermined contact pressure and scrapes off residual toner on the drum surface. The fur brush 254 cleans the surface of the photosensitive drum 251.

  The rotary rack 204 is a cylindrical device that is mounted so as to be able to rotate in the direction of arrow A by receiving a driving force from the rotary rack motor 208, and includes a developing device 204Y that forms a yellow toner image and cyan toner. The image forming apparatus includes a developing device 204C that forms an image, a developing device 204M that forms a magenta toner image, and a developing device 204K that forms a black toner image.

  Since the developing devices 204Y to 204K have the same configuration, only the developing device 204Y will be described. The developing device 204Y includes a toner tank 241, a toner supply roller 242, a developing roller 243, and a developing blade 244. The toner tank 241 stores yellow toner. The toner supply roller 242 rotates in the direction of the arrow and supplies the toner stored in the toner tank 241 to the developing roller 243. The developing blade 244 forms a toner thin film on the surface of the developing roller 243. The developing roller 243 rotates in the direction of the arrow and supplies thin film toner formed on the surface to the photosensitive drum 251.

  The rotary rack 204 is positioned so that the developing roller 243 of the developing device 204Y faces the photosensitive drum 251 when forming a yellow toner image. Further, when a cyan toner image is formed on the photosensitive drum 251, the developing roller 243 of the developing device 204 </ b> C is positioned so as to face the photosensitive drum 251. Further, when a magenta toner image is formed on the photosensitive drum 251, the developing roller 243 of the developing device 204 </ b> M is positioned so as to face the photosensitive drum 251. Further, when the black toner image is formed on the photosensitive drum 251, the developing roller 243 of the developing device 204 </ b> K is positioned so as to face the photosensitive drum 251.

  The intermediate transfer unit 206 includes an intermediate transfer belt 261, five rollers 262, and a cleaner 263. The intermediate transfer belt 261 is an endless belt, and is rotated in the direction of the arrow in response to a driving force from a roller 262 disposed on the inner periphery. The toner images for each color formed on the photosensitive drum 251 are sequentially transferred to form a color toner image on the belt surface.

  A cleaner 263 and a density sensor 207 are disposed around the intermediate transfer belt 261. A cleaner 263 cleans the surface of the intermediate transfer belt 261. The density sensor 207 has the same configuration as the density sensor 70 shown in FIG. 1, and irradiates the intermediate transfer belt 261 with light and receives reflected light, thereby forming a toner image (patch image) formed on the intermediate transfer belt 261. Measure the concentration. A temperature / humidity sensor 209 is provided in the image forming apparatus. The temperature / humidity sensor 209 has the same configuration as the temperature / humidity sensor 90 shown in FIG.

  The functional configuration of the 4-cycle image forming apparatus shown in FIG. 14 is the same as that of the tandem image forming apparatus shown in FIG. The density sensor 70, the temperature / humidity sensor 90, the image forming unit 30, the photosensitive drum 31, the charging unit 32, the exposure unit 33, and the developing unit 34 illustrated in FIG. , Corresponding to the image forming unit 300, the photosensitive drum 251, the charging unit 252, the exposure unit 203, and the rotary rack 204 (developing devices 204Y to 204K).

  The functional configuration of the exposure unit 203 in the 4-cycle image forming apparatus shown in FIG. 14 is substantially the same as the functional configuration of the exposure unit 33 in the tandem image forming apparatus shown in FIG. However, in the tandem image forming apparatus, the exposure unit 33 is provided for each color, but in the four-cycle image forming apparatus, only one exposure unit 203 is provided.

  Therefore, the overshoot time storage unit 333 of the exposure unit 203 stores the overshoot time for each color, and the overshoot time switching unit 334 is stored in the overshoot time storage unit 333 every time each color is printed. The overshoot time is read and the overshoot generators 332a to 332e to be connected are switched. The operation of the 4-cycle image forming apparatus shown in FIG. 14 is almost the same as that of the tandem image forming apparatus shown in FIG.

  As described above, the image forming unit 300 includes any one of the photosensitive drum 251, the rotary rack 204 in which the developing devices 204 </ b> C, 204 </ b> M, 204 </ b> Y, and 204 </ b> K corresponding to each of the plurality of toners are mounted. The developing roller 243 of the developing device is positioned at a position facing the photosensitive drum 251, and a rotary rack motor 208 that rotates the rotary rack 204, and a toner image of each color is transferred from the photosensitive drum 251, and a color image is transferred. And an intermediate transfer belt 261 to be formed. A semiconductor laser 335 and an overshoot generator 332 are provided in the image forming unit 300. In this case, since the photosensitive drum 251 and the exposure unit 203 including the semiconductor laser 335 and the overshoot generation unit 332 are a pair, a process of correcting image variations caused by the photosensitive drum 251 and the exposure unit 203 is performed. It can be simplified.

1 is a diagram schematically illustrating an internal configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating an example of a functional configuration of the image forming apparatus illustrated in FIG. 1. FIG. 3 is a block diagram showing a detailed configuration of an exposure unit shown in FIG. 2. 4 is a flowchart for explaining an operation of the image forming apparatus shown in FIGS. 2 and 3. It is a figure which shows an example of a solid patch image. It is a figure which shows an example of a discrete dot patch image. It is a figure which shows an example of a diagonal patch image. It is a figure which shows an example of the patch image printed on the transfer belt. It is a figure for demonstrating overshoot time. 6 is a flowchart for explaining an exposure process during printing by the image forming apparatus. It is a figure which shows the experimental result about the dot reproducibility which changes according to environmental fluctuations. It is a figure which shows the experimental result about the dot reproducibility which changes according to a time-dependent change. It is a figure for demonstrating the amount of overshoots. FIG. 5 is a diagram schematically showing an internal configuration of an image forming apparatus according to another embodiment of the present invention.

Explanation of symbols

30 (30K, 30Y, 30M, 30C) Image forming unit 31 Photosensitive drum 32 Charging unit 33 Exposure unit 34 Developing unit 70 Density sensor 90 Temperature / humidity sensor 100 Control unit 101 Patch image storage unit 102 Patch image forming unit 103 Density measurement unit 104 color correction LUT storage unit 105 color correction processing unit 106 light emission control unit 107 light intensity LUT storage unit 108 overshoot time determination unit 109 temperature / humidity measurement unit 110 environment correction table storage unit 111 environment correction processing unit 331 drive signal generation unit 332 overshoot Generation unit 333 Overshoot time storage unit 334 Overshoot time switching unit 335 Semiconductor laser

Claims (6)

An image forming apparatus for forming a color image using a plurality of toners having different colors,
Light source means for outputting a laser beam;
Overshoot generating means for generating an overshoot in the drive signal of the light source means;
Image forming means for forming a density correction image using a plurality of toners of different colors;
Density measuring means for measuring the density of the density correction image formed by the image forming means;
An image forming apparatus comprising: an overshoot time determining unit that determines an overshoot time of an overshoot generated by the overshoot generating unit according to a density value measured by the density measuring unit. The image forming unit forms a solid image, a halftone dot image, and a line image as a density correction image,
The density measuring means measures the density of a solid image, a halftone dot image and a line image formed by the image forming means;
Color correction for performing color correction processing for correcting at least one of a gamma correction value, a development bias value, and an exposure condition in accordance with the density values of the solid image, the halftone dot image, and the line image measured by the density measuring unit. Further comprising means,
The overshoot time determining means, after the color correction processing by the color correction means is performed, according to the density value of either one of the halftone image and the line image measured by the density measuring means, 2. The image forming apparatus according to claim 1, wherein an overshoot time of the overshoot generated by the overshoot generating means is determined. An overshoot time storage means for storing the overshoot time determined by the overshoot determination means;
The image forming apparatus according to claim 1, wherein the overshoot generation unit generates an overshoot based on an overshoot time stored in the overshoot time storage unit during normal printing.   2. The image according to claim 1, further comprising an overshoot amount determining means for determining an overshoot amount of the overshoot generated by the overshoot generating means in accordance with a density value measured by the density measuring means. Forming equipment.   The light source unit and the overshoot generating unit are arranged along a conveyance direction of the recording paper on a transfer belt that conveys the recording paper, and each of the plurality of image forming units individually forms toner images of different colors. The image forming apparatus according to claim 1, wherein the image forming apparatus is provided for each. The light source means and the overshoot generating means include a photosensitive drum, a rotary rack on which a developing device corresponding to each of a plurality of toners is mounted, and a developing roller of any of the developing devices. An image including a rotary rack driving means for rotating the rotary rack so as to be positioned at a position facing the photosensitive drum, and an intermediate transfer member for transferring a color toner image from the photosensitive drum to form a color image. Provided in the forming unit,
The image forming apparatus according to claim 1, wherein the density measuring unit measures a density of a density measuring image formed on the intermediate transfer member.

Images