JP2018036312A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of stably setting an image forming condition even when a large amount of toner is replenished to a developer immediately before setting an image forming condition. An image forming apparatus has a developer 3 that houses toner and forms a toner image on a photosensitive drum 4, and transfers the toner image formed on the photosensitive drum 4 to a predetermined recording material. A printer engine 100 that forms an image on the recording material is provided. The printer engine 100 is controlled by the printer control unit 109. The developer 3 is replenished with toner from the toner cartridge at the time of image formation. When any of the predetermined amount of toner replenished immediately before forming the measurement image exceeds the predetermined amount, the printer control unit 109 drives the developer 3 for a predetermined time before forming the image of the measurement image. [Selection diagram] Fig. 3

Description

  The present invention relates to image quality stabilization control of an image forming apparatus that forms an image using a developer.

  The image forming apparatus forms an image for measurement such as a gradation pattern on a recording material such as paper, and measures this by a measuring device such as an optical sensor. The image forming apparatus feedback-controls image forming conditions for adjusting the density and gradation characteristics of the output image based on the measurement result of the measurement image. For example, Patent Document 1 discloses an image forming apparatus that forms a gradation pattern on a recording material and adjusts image formation conditions based on a result of reading the gradation pattern by a reading unit.

  2. Description of the Related Art In electrophotographic image forming apparatuses, a two-component development method in which development is performed using a developer in which a nonmagnetic toner and a magnetic carrier are mixed is widely used. In this image forming apparatus, toner in the developer is consumed by forming an image. If the toner ratio (toner concentration) in the developer in the developing device is excessively reduced, the density of the output image may be reduced, or the carrier may adhere to the photoreceptor and cause an image defect. For this purpose, the image forming apparatus includes a replenishing device that replenishes toner to the developing device when the toner density in the developing device decreases by forming an image.

JP-A-7-264411

  By the way, when a large amount of toner is supplied to the developing device immediately before forming the measurement image, the uniformity of the toner concentration in the developer and the stability of the toner charge amount are impaired. Therefore, there has been a problem that density unevenness occurs in the measurement image formed on the recording material. When the image forming condition is corrected based on the measurement result of the measurement image in which the density unevenness occurs, the image forming condition cannot be determined appropriately, and the density of the output image may not be controlled to the target density.

  Accordingly, an object of the present invention is that density unevenness occurs in the measurement image even when a large amount of toner is supplied to the developing device immediately before forming the measurement image for adjusting the image forming conditions. It is to suppress.

  The image forming apparatus of the present invention includes a developing unit that stores a developer containing toner and a carrier, an image forming unit that forms an image on a recording material using the developer in the developing unit, and the image Measuring means for measuring the measurement image formed on the recording material by the forming means; forming the measurement image on the image forming means; causing the measuring means to measure the measurement image; and measuring the measuring means A determining unit that determines an image forming condition of the image forming unit based on a result; and a replenishing unit that replenishes toner to the developing unit, the image forming unit stirring the developer in the developing unit A screw that is driven to rotate, a motor that rotates the screw, and a control unit that controls the motor. When the image forming unit forms the measurement image on the recording material, the control hand It is characterized in that control based on the rotation time of the screw, the supply amount of the supply means.

  According to the present invention, even when a large amount of toner is supplied to the developing device immediately before forming a measurement image for adjusting image forming conditions, it is possible to suppress the occurrence of density unevenness in the measurement image. .

1 is a configuration diagram of an image forming apparatus. Explanatory drawing of a reader image processing part. Explanatory drawing of a printer control part. Processing explanatory diagram of a gradation image. FIG. 4 is a four-limit chart illustrating how gradation is reproduced. 6 is a flowchart illustrating calibration processing of a printer unit. FIG. 3 is an exemplary diagram of a first test image. The figure showing a mode that the recording material was mounted. The relationship between relative drum surface potential and image density is shown. FIG. 4 is a diagram illustrating a relationship between a contrast potential and a moisture amount in the image forming apparatus. FIG. 6 is an exemplary diagram of a second test image. The figure showing a mode that the recording material was mounted. Explanatory drawing of the reading result of a 2nd test image. Explanatory drawing of a developing device. FIG. 3 is a partially cutaway view of a toner cartridge. Explanatory drawing of the circulation path of the two-component developer in a developing container. The figure showing the relationship between the toner replenishment amount per sheet and image density. 6 is a flowchart showing processing for determining a driving time of a developing device.

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

  FIG. 1 is a configuration diagram of an image forming apparatus according to the present embodiment. The image forming apparatus includes a reader unit A and a printer unit B. The reader unit A is an image reading device that reads a document image. For example, the printer unit B forms an image corresponding to the original image read by the reader unit A on the recording material 6 such as paper.

(Reader part)
The reader unit A includes a document table 102 on which the document 101 is placed, a light source 103 that emits light to the document 101 on the document table 102, an optical system 104, a light receiving unit 105, and a reader image processing unit 108. A contact member 107 and a reference white plate 106 are disposed on the document table 102. The contact member 107 is used for placing the document 101 at a correct position. The reference white plate 106 is used for white level determination and shading correction of the light receiving unit 105.

  The light source 103 irradiates the document 101 placed on the document table 102. The light receiving unit 105 receives the light reflected from the original 101 of the light emitted from the light source 103 via the optical system 104. The light receiving unit 105 generates a color component signal that is an electric signal representing each of red, green, and blue based on the received reflected light, and transmits the color component signal to the reader image processing unit 108. Such a light receiving unit 105 is constituted by, for example, a CCD (Charge Coupled Device) sensor. For example, the light receiving unit 105 includes CCD line sensors arranged in three rows corresponding to each color of red, green, and blue, and color component signals of red, green, and blue based on reflected light received by each CCD line sensor. Is generated. The light source 103, the optical system 104, and the light receiving unit 105 are a reading unit configured integrally, and are movable in the left-right direction in the drawing. The CCD line sensor of the light receiving unit 105 is aligned in the depth direction of FIG. For this purpose, the reading unit sets the depth direction in FIG. 1 as one line in the main scanning direction, and moves to read the entire original 101 sequentially one line at a time to generate a color component signal for each line.

  The reader image processing unit 108 performs image processing on each color component signal and generates image data representing an image of the original 101. The reader image processing unit 108 transmits the generated image data to the printer unit B. FIG. 2 is an explanatory diagram of the reader image processing unit 108.

  The reader image processing unit 108 acquires the color component signal of each color from the light receiving unit 105 by the analog signal processing unit 201. The analog signal processing unit 201 performs analog processing such as gain adjustment and offset adjustment of the acquired color component signal of each color. The analog signal processing unit 201 transmits analog image signals R0, G0, and B0 generated by analog processing to an A (Analog) / D (Digital) converter 202. The symbol “R” represents red, “G” represents green, and “B” represents blue. In the present embodiment, the image signal represents luminance. The A / D converter 202 converts the analog image signals R0, G0, and B0 acquired from the analog signal processing unit 201 into, for example, 8-bit digital image signals R1, G1, and B1. The A / D converter 202 transmits the image signals R1, G1, and B1 generated by digital conversion to the shading correction unit 203. The shading correction unit 203 performs known shading correction on the image signals R1, G1, and B1 acquired from the A / D converter 202 using the reading result of the reference white plate 106 for each color. The shading correction unit 203 generates image signals R2, G2, and B2 by shading correction.

  The clock generator 211 generates a clock signal CLK. In addition to the shading correction unit 203, the clock signal CLK is input to a line delay unit 204 and a line delay memory 207 described later. The clock signal CLK is input to the address counter 212. The address counter 212 counts the clock signal CLK and generates an address (main scanning address) of one line in the main scanning direction. The decoder 213 decodes the main scanning address generated by the address counter 212, and generates a CCD drive signal in units of lines such as a shift pulse and a reset pulse, a VE signal, and a line synchronization signal HSYNC. The VE signal represents an effective area corresponding to one line of the color component signal acquired from the light receiving unit 105. The address counter 212 is cleared by the line synchronization signal HSYNC, and starts counting the main scanning address of the next line.

  The line delay unit 204 receives the line synchronization signal HSYNC, corrects the spatial deviation in the sub-scanning direction with respect to the image signals R2, G2, and B2, and generates image signals R3, G3, and B3. The CCD line sensors corresponding to the respective colors provided in the light receiving unit 105 are arranged at predetermined intervals in the sub-scanning direction. The line delay unit 204 corrects a spatial shift in the sub-scanning direction caused by the predetermined interval. Specifically, the line delay unit 204 delays the image signals R2 and G2 in the sub scanning direction with reference to the image signal B2.

  The input masking unit 205 converts the reading color space determined by the spectral characteristics of the red, green, and blue filters of the CCD sensor of the light receiving unit 105 into a standard color space such as NTSC (National Television Standards Committee). As a result, the input masking unit 205 generates image signals R4, G4, and B4 from the image signals R3, G3, and B3. The input masking unit 205 calculates the image signals R4, G4, and B4 by the following matrix calculation, for example.

_{R4 = a 11 * R3 + a} 12 * G3 + a 13 * B3
_{G4 = a 21 * R3 + a} 22 * G3 + a 23 * B3
_{B4 = a 31 * R3 + a} 32 * G3 + a 33 * B3
a _{11 to} a ₁₃ , a _{21 to} a ₂₃ , and a _{31 to} a ₃₃ are constants.

  The LOG conversion unit 206 is a light amount / density conversion unit that converts the luminance represented by the image signals R4, G4, and B4 into image signals C0, M0, and Y0 that represent the density at the time of image formation. The LOG conversion unit 206 has a color conversion lookup table for converting the image signals R4, G4, and B4 into the image signals C0, M0, and Y0, and performs conversion using this. The color conversion lookup table is a multidimensional table showing the correspondence between the image signals R4, G4, B4 (input values) and the image signals C0, M0, Y0 (output values). The LOG conversion unit 206 is not limited to a configuration that converts an image signal based on a color conversion table, and may be a configuration that converts an image signal based on a mathematical expression, for example. The symbol “C” represents cyan, “M” represents magenta, and “Y” represents yellow.

  The line delay memory 207 is a line from the image signals C0, M0, and Y0 until a black character determination unit (not shown) generates determination signals such as UCR (Under Color Removal), FILTER, and SEN from the image signals R4, G4, and B4. Delay by the amount of delay. The masking / UCR unit 208 acquires the delayed image signals C1, M1, and Y1 from the line delay memory 207, and extracts an image signal K2 that represents the density of black from the three primary color image signals C1, M1, and Y1. The masking / UCR unit 208 performs processing for correcting the color turbidity of the recording material 6 in the printer unit B, and generates image signals Y2, M2, and C2. The masking / UCR unit 208 outputs the image signals Y2, M2, C2, and K2 with a predetermined bit width (8 bits in the present embodiment).

  The γ correction unit 209 uses the LUT (Look Up Table) described later to correct the tone characteristics of the image output from the printer unit B to ideal tone characteristics, and uses the image signals Y2, M2, and C2. , K2 are converted into image signals Y3, M3, C3, K3. The LUT corresponds to a conversion condition for converting an image signal, and is stored in the printer control unit 109 provided in the printer unit B. The LUT is provided for each color and is, for example, a one-dimensional table in which the correspondence between the image signal Y2 (8 bits) and the image signal Y3 (8 bits) is defined. The LUT is different from the color conversion lookup table described above. The LUT is not limited to a configuration that converts an image signal based on a one-dimensional table, and may be a configuration that converts an image signal based on a mathematical expression, for example. The output filter 210 performs edge enhancement or smoothing processing on the image signals Y3, M3, C3, and K3 by spatial filter processing. As a result, the output filter 210 generates frame-sequential image signals Y4, M4, C4, and K4 and transmits them to the printer unit B as image data.

  The processing of the reader image processing unit 108 as described above is controlled by a CPU (Central Processing Unit) 214 that controls the entire processing of the reader unit A. The CPU 214 controls the entire processing of the reader unit A by executing a computer program read from a ROM (Random Access Memory) 216 using a RAM (Random Access Memory) 215 as a work area. The operation unit 217 having the display unit 218 is connected to the reader unit A. The operation unit 217 includes a touch panel using various key buttons and a display unit 218, and functions as a user interface. The user can input various instructions by operating the operation unit 217.

(Printer part)
The printer unit B is configured to form an image on a recording material 6 such as paper. The photosensitive drum 4, which is an image carrier, the charger 8, the developing unit 3, the cleaner 9, the transfer drum 5, the fixing roller pair 7a, 7b, A laser light source 110, a polygon mirror 1, a mirror 2, and a printer control unit 109 are provided. A surface potential sensor 12 and a photosensor 40 are provided around the photosensitive drum 4.

  The photosensitive drum 4 is a drum-shaped photosensitive member, and rotates in the direction of arrow A during image formation. The surface of the photosensitive drum 4 is uniformly charged by the charger 8. The laser light source 110 scans the surface of the photosensitive drum 4 with a laser beam under the control of the printer control unit 109 with the direction perpendicular to the rotation direction of the photosensitive drum 4 (the depth direction in FIG. 1) as the main scanning direction. The printer control unit 109 acquires image data from the reader image processing unit 108 of the reader unit A, and controls blinking of the laser light emitted from the laser light source 110 based on the image data. When image data is transferred from an external device such as a personal computer, the printer control unit 109 converts the image data based on the LUT, and the laser light emitted from the laser light source 110 based on the converted image data. Control blinking. Laser light emitted from the laser light source 110 scans the uniformly charged photosensitive drum 4 through the polygon mirror 1 and the mirror 2. As a result, an electrostatic latent image based on the image data is formed on the surface of the photosensitive drum 4.

  The developing device 3 develops the electrostatic latent image formed on the photosensitive drum 4 to form a toner image. The developing device 3 is arranged around the photosensitive drum 4 in the order of the black developing device 3K, the yellow developing device 3Y, the cyan developing device 3C, and the magenta developing device 3M from the upstream in the rotation direction of the photosensitive drum 4. For example, in the case of forming a yellow toner image, the yellow developer 3Y causes the yellow developer to pass through the electrostatic latent image at the timing when the electrostatic latent image corresponding to yellow formed on the photosensitive drum 4 passes the development position. Develop by attaching to the image. The other color developing devices 3M, 3C, and 3K perform development in the same manner. Details of the configuration of the developing device 3 will be described later.

  The recording material 6 is wound around the transfer drum 5, and magenta, cyan, yellow, and black toner images are sequentially superimposed and transferred. The transfer drum 5 rotates with the recording material 6 interposed between the photosensitive drum 4 and the toner image is transferred from the photosensitive drum 4 to the recording material 6. Therefore, the transfer drum 5 rotates four times in the direction of arrow B in order to form a full-color image on one recording material 6. The recording material 6 onto which the toner image has been transferred is separated from the transfer drum 5 and conveyed to the fixing roller pair 7a and 7b. The pair of fixing rollers 7 a and 7 b fix the toner image on the recording material 6 by conveying the recording material 6 while sandwiching the recording material 6. For example, the pair of fixing rollers 7 a and 7 b heat and press the recording material 6 so that the toner image is thermocompression bonded to the recording material 6. The fixing roller pair 7a, 7b discharges the recording material 6 on which the toner image is fixed to the outside of the image forming apparatus. The toner remaining on the photosensitive drum 4 after the transfer to the recording material 6 is removed by the cleaner 9.

  The surface potential sensor 12 is provided around the photosensitive drum 4 and between the position irradiated with the laser light from the laser light source 110 and the developing device 3. The surface potential sensor 12 detects the surface potential of the photosensitive drum 4. The photo sensor 40 is provided around the photosensitive drum 4 and between the developing device 3 and the transfer drum 5. The photosensor 40 includes a light source 103 and a photodiode 11. The light source 103 irradiates the surface of the photosensitive drum 4 on which the toner image is formed with near infrared light having a dominant wavelength of about 960 [nm]. The photodiode 11 receives light reflected from the surface of the photosensitive drum 4 of the light emitted from the light source 103. Thus, the photosensor 40 can measure the amount of reflected light from the measurement toner image (hereinafter referred to as “measurement image”) formed on the photosensitive drum 4.

  FIG. 3 is an explanatory diagram of the printer control unit 109. The printer control unit 109 includes a CPU 28, a ROM 30, a RAM 32, a test image storage unit 31, a density conversion unit 42, a memory 25 for storing an LUT, a pulse width modulation unit 26, an LD driver 27, and a pattern generator 29. The printer control unit 109 can communicate with the reader unit A and the printer engine 100. The printer engine 100 includes a photosensitive drum 4, a charger 8, a photo sensor 40, a developing device 3, a surface potential sensor 12, a laser light source 110, and an environment sensor 33. The environmental sensor 33 detects environmental information such as temperature and humidity inside the image forming apparatus. The printer control unit 109 controls the image forming operation by the printer engine 100 having such a configuration. The CPU 28 of the printer control unit 109 controls the overall processing of the printer unit A by executing a computer program read from the ROM 30 using the RAM 32 as a work area. For example, the CPU 28 of the printer control unit 109 controls the charging bias of the charger 8 and the developing bias of the developing device 3. Note that the image forming apparatus of the present embodiment forms images for 30 sheets in A4 size per minute.

(Gradation control)
FIG. 4 is an explanatory diagram of gradation image processing. As described above, the reader image processing unit 108 of the reader unit A generates a frame sequential image signal (image data) from the color component signal acquired from the light receiving unit 105 and transmits it to the printer unit B. On the other hand, based on the LUT stored in the memory 25, the printer control unit 109 converts image data transferred from an external device such as a personal computer or a scanner into image signals Y4, M4, C4, and K4.

  FIG. 5 is a four-limit chart illustrating how the image signal is converted to correct the gradation characteristics. The first quadrant represents the reading characteristic of the reader unit A that converts the document density representing the density of the image formed on the document 101 into a density signal. The second quadrant represents a conversion characteristic of the LUT that converts the density signal into a laser output signal representing the amount of laser light output from the laser light source 110. The third quadrant represents a recording characteristic of the printer unit B that converts the laser output signal into an output density representing the density of an image formed on the recording material 6. The fourth quadrant represents the tone reproduction characteristics of the entire image forming apparatus, which represents the relationship from the image density of the original 101 to the density of the image formed on the recording material 6. In this embodiment, since the image signal is processed by an 8-bit digital signal, the number of gradations is 256 gradations.

  In the image forming apparatus of the present embodiment, in order to make the gradation characteristic of the fourth quadrant linear, the recording characteristic of the printer unit B of the third quadrant is corrected by the conversion characteristic of the LUT of the second quadrant. To do. The LUT is generated based on the calculation result described later. The image signal whose density has been converted by the CPU 28 based on the LUT is input to the pulse width modulator 26. The pulse width modulation unit 26 converts the image signal into a pulse signal corresponding to the dot width of the image to be formed, and transmits the pulse signal to the LD driver 27 that drives the laser light source 110. The pulse width modulation unit 26 converts the image signal into, for example, a PWM (Pulse Width Modulation) signal and transmits it to the LD driver 27. The LD driver 27 performs light emission control of the laser light source 110 based on the pulse signal acquired from the pulse width modulation unit 26.

  In the present embodiment, the image forming apparatus performs tone reproduction by pulse width modulation processing for all colors of yellow, magenta, cyan, and black. As described above, the laser light emitted from the laser light source 110 forms an electrostatic latent image on the photosensitive drum 4. Since the laser light source 110 is controlled to emit light based on the pulse signal, an electrostatic latent image having a predetermined gradation characteristic corresponding to a change in dot area is formed on the photosensitive drum 4. This electrostatic latent image is reproduced as a gradation image through the steps of development, transfer, and fixing.

  Processing related to stabilization of image reproduction characteristics by the reader unit A and the printer unit B will be described. FIG. 6 is a flowchart showing the calibration process of the printer unit B using the reader unit A.

  Processing in S51: The CPU 214 of the reader unit A starts calibration processing of the printer unit B when an instruction for automatic gradation correction is input from the operation unit 217. First, the CPU 214 displays a first test image output start button on the display unit 218. When the user presses the start button, the CPU 214 acquires an output instruction for the first test image, which is a measurement image. When the CPU 214 obtains the first test image output instruction, the CPU 214 instructs the CPU 28 of the printer unit B to form the first test image. The CPU 28 forms a first test image on the recording material 6 in response to an image formation instruction. Image data of the first test image is generated from the pattern generator 29. At this time, the CPU 28 determines the presence / absence of the recording material 6 for forming the first test image. When the CPU 214 is notified that there is no recording material 6, the CPU 214 displays a warning image indicating that there is no recording material 6 on the display unit 218. At the time of forming the first test image, a contrast potential described later is set to a value corresponding to the environment information detected by the environment sensor 33.

  FIG. 7 is a view showing an example of the first test image. The first test image is composed of a band-like pattern 61 having intermediate gradation densities of four colors of yellow (Y), magenta (M), cyan (C), and black (K), and a maximum density (for example, density signal value = 255). Each color patch pattern 62Y, 62M, 62C, 62K is included. The patch patterns 62Y, 62M, 62C, and 62K are formed within the size of one line read by the light receiving unit 105 of the reader unit A. The user can check the presence or absence of streak-like abnormal images, density unevenness, and color unevenness by visually inspecting the belt-like pattern 61. When there are streaky abnormal images, density unevenness, and color unevenness, the user instructs the output of the first test image again. When there are streaky abnormal images, density unevenness, and color unevenness again, the image forming apparatus needs to be repaired. Note that the reader unit A may read the belt-like pattern 61 and determine whether or not to perform the subsequent processing based on the density in the main scanning direction.

  Process of S52: The user places the recording material 6 on which the first test image is formed on the document table 102 of the reader unit A, and causes the reader unit A to read the first test image. When the recording material 6 is placed on the document table 102, the CPU 214 of the reader unit A displays a start button for image reading on the display unit 218. When the user presses the start button, the CPU 214 performs processing for reading the first test image from the recording material 6 placed on the document table 102.

  FIG. 8 is a diagram illustrating a state where the recording material 6 on which the first test image is formed is placed on the document table 102. The wedge-shaped mark T on the upper left is an application mark for the document (recording material 6) on the document table 102. The recording material 6 is placed so that the belt-like pattern 61 is on the mark T side and the front and back sides are not mistaken. The display unit 218 displays a message so as to place the recording material 6 as shown in FIG. This prevents a control error due to misplacement. The reader unit A reads the recording material 6 on which the first test image is formed by gradually scanning from the mark T side. The reader unit A specifies the positions of the patch patterns 62Y, 62M, 62C, and 62K with reference to the position of the corner (density gap point A) of the belt-like pattern 61 where the density first changes. The reader unit A reads the image density of each patch pattern 62Y, 62M, 62C, 62K whose position has been specified.

  Specifically, the CPU 214 reads the first test image by controlling the operation of the reading unit. The light receiving unit 105 of the reading unit transmits a color component signal (reading signal value) of the first test image to the reader image processing unit 108. The reader image processing unit 108 converts the color component signal (read signal value) acquired from the light receiving unit 105 into an image density representing an optical density based on the following equation. The read signal value includes a red (R) read signal value, a green (G) read signal value, and a blue (B) read signal value.

M = −km * log ₁₀ (G / 255)
C = −kc * log ₁₀ (R / 255)
Y = −ky * log ₁₀ (B / 255)
K = −kbk * log ₁₀ (G / 255)
km, kc, ky, and kck are preset correction coefficients.

  Note that the reader image processing unit 108 may convert the color component signals into density signals M, C, Y, and K using a predetermined conversion table without using the following formula.

  Processing in S53: The CPU 214 compensates for the maximum density Dmax based on the density signals M, C, Y, and K (image signals M4, C4, Y4, and K4 in FIG. 2) obtained by the reader image processing unit 108. Calculate the potential. The contrast potential is a potential difference between the developing bias potential and the surface potential of the electrostatic latent image formed by the laser beam having the maximum level after being charged by the charger 8. FIG. 9 shows the relationship between the relative drum surface potential and the image density obtained by the processing of S52.

  In the density range of the maximum density Dmax obtained when the contrast potential is set to the potential A, the image density often changes linearly as indicated by the solid line L with respect to the relative drum surface potential. However, when developing using a two-component developer, the toner density in the developing device 3 fluctuates and decreases, so that the image density changes nonlinearly in the density range of the maximum density Dmax as indicated by the broken line N. There is. Therefore, the target value of the final maximum density Dmax is set to “1.7” in consideration of a margin from “1.6” to “0.1”. The contrast potential B for that is calculated by the following equation.

B = (A + Ka) × 1.7 / Dmax
Ka is the correction type and is set based on the type of development method.

An electrophotographic image forming apparatus cannot obtain an appropriate image density unless the contrast potential is set to a value according to the environment. Therefore, in this embodiment, the contrast potential is corrected according to the amount of water in the image forming apparatus detected by the environment sensor 33. FIG. 10 shows the relationship between the contrast potential and the amount of water in the image forming apparatus. Based on this relationship, the CPU 28 of the printer unit B corrects the contrast potential calculated by the above formula. Correction coefficient Vcont. For correcting the contrast potential. The rate is stored in the RAM 32. Correction coefficient Vcont. ratel is calculated by the following equation.
Vcont. ratel = B / A

  The image forming apparatus detects the transition of the environment (water content) every 30 minutes by the environment sensor 33, and every time the potential A is determined based on the result, A × Vcont. The rate is calculated and the contrast potential is calculated. In the process of S53, the contrast potential is set so that the maximum density Dmax is “0.1” higher than the final target value. The CPU 28 of the printer unit B sets the grid potential (the surface potential of the photosensitive drum 4 charged by the charger 8) and the developing bias potential so that such a contrast potential can be obtained.

  Processing in S54 and S55: The CPU 28 of the printer unit B determines whether or not the calculated contrast potential is within a predetermined control range. If it is out of the control range (S54: N), the CPU 28 determines that an abnormality has occurred in the developing device 3. In this case, the CPU 28 corrects the contrast potential to the limit value of the control range. Further, the CPU 28 sets the error flag to ON so that the service person can confirm the developing device 3 that has been determined to have an abnormality (S55). The CPU 28 of the printer unit B resets the grid potential (the surface potential of the photosensitive drum 4 charged by the charger 8) and the development bias potential so that the contrast potential corrected in the process of S55 is obtained.

  Processing in S56: The CPU 28 of the printer unit B controls the printer unit B based on the contrast potential and forms an image of a second test image that is a measurement image. FIG. 11 is an exemplary diagram of a second test image. The second test image includes a patch image of 64 gradations (16 columns, 4 rows) for each color of yellow (Y), magenta (M), cyan (C), and black (K). The 64 gradations of the patch image mainly include the low density gradation among the 256 gradations, and the gradation becomes smaller as the gradation becomes higher. Such a 64-gradation patch image makes it possible to satisfactorily adjust the gradation characteristics particularly in the highlight portion.

  The patch image 71 has a resolution of 200 lpi (lines / inch), and the patch image 72 has a resolution of 400 lpi. Each of the patch images 71 and 72 is formed by preparing a plurality of triangular wave cycles used by the pulse width modulation unit 26 for comparison with the image signal to be processed. The image is created with a resolution of 200 lpi, and the line image of characters or the like is created with a resolution of 400 lpi. In this embodiment, patch images 71 and 72 having the same gradation level are formed at two different resolutions. However, if the gradation characteristics differ greatly due to the difference in resolution, the previous gradation level is set according to the resolution. It is more preferable to set. The second test image is formed based on the measurement image data generated from the pattern generator 29 without using the LUT.

  Process of S57: The user places the recording material 6 on which the second test image is formed on the document table 102 of the reader unit A, and causes the reader unit A to read the second test image. When the recording material 6 is placed on the document table 102, the CPU 214 of the reader unit A displays a start button for image reading on the display unit 218. When the user presses the start button, the CPU 214 performs control for reading the second test image from the recording material 6 placed on the document table 102. Specifically, the CPU 214 reads the second test image by controlling the operation of the reading unit. The light receiving unit 105 of the reading unit transmits the read color component signal of the second test image to the reader image processing unit 108. The reader image processing unit 108 converts the color component signal (RGB signal value) acquired from the light receiving unit 105 into a density signal representing the optical density in the same manner as the process of S52. The reader unit A reads 16 points per one gradation patch image 73 of the second test image, and averages the obtained signals. The number of points to be read is optimized according to the configuration of the reader unit A and the print unit B.

  FIG. 12 is a diagram illustrating a state where the recording material 6 on which the second test image is formed is placed. The recording material 6 is placed so that the black (Bk) of the patch images 71 and 72 is applied to the contact mark T side and the front and back are not mistaken. The reader unit A reads the recording material 6 on which the second test image is formed by gradually scanning from the mark T side. The reader unit A identifies the positions of the patch images 71 and 72 with reference to the position of the black (Bk) corner (density gap point A) of the patch image 71 whose density first changes. The reader unit A reads the image density of each patch image 71 and 72 whose position has been specified.

  Processing in S58: The CPU 28 sets the LUT, the density level (density signal) of the 64-tone patch image of the second test image to the input level (density signal axis in FIG. 5), and the laser light exposure level to the output level ( It is created by replacing the coordinates with the laser output signal axis in FIG. The density signal is acquired from the result of reading the second test image by the reader unit A. The exposure amount of the laser light is a light amount corresponding to the contrast potential set when the second test image is formed. The CPU 28 calculates a value for the density level not corresponding to the patch image by interpolation processing.

  FIG. 13 is an explanatory diagram of the reading result of the second test image. In FIG. 13, the density signal (output density) obtained by converting the RGB signal value obtained by averaging the values of 16 points for each patch image 71 and 72 of the second test image is the left vertical axis, and the laser output level is Use the horizontal axis. The right vertical axis is the density level, and the base density of the paper, in this embodiment, “0.08” is normalized to 0 level, and “1.60” set as the maximum density Dmax is normalized to 255 level. If the document table 102 is dirty or the second test image is defective, the result of reading may be specifically high in density as point C or low as point D. Therefore, the inclination is limited and correction is performed so that the continuity of the read data string is preserved. Specifically, when the slope is 3 or more, the density is fixed to “3”, and when the slope is negative, the density level is the same as the previous level.

  As described above, the LUT is created by replacing the density level in FIG. 13 with the input level (density signal axis in FIG. 5) and the laser output level with the output level (laser output signal axis in FIG. 5). For density levels not supported by the patch images 71 and 72, values are obtained by interpolation calculation. At this time, the restriction condition is set so that the output level becomes 0 level with respect to the 0 level input level.

  As described above, the processing using the reader unit A completes the contrast potential control and LUT creation processing, which are image forming conditions. In this process, in order to associate the input image signal with the density of the image finally formed on the recording material 6, the exposure amount of the laser beam is controlled to set the contrast potential within a predetermined range. Therefore, very accurate control is performed, and an image having high gradation accuracy is obtained.

(Developer)
Next, the operation of the developing device 3 immediately before forming the first and second test images will be described. FIG. 14 is an explanatory diagram of the developing device 3.

  The developing device 3 contains a two-component developer composed of a non-magnetic toner and a magnetic carrier in a developing container 303, and develops with the two-component developer. In the present embodiment, the toner concentration of the two-component developer is 7 wt% in the initial state. The toner concentration should be appropriately adjusted according to the toner charge amount, the carrier particle size, the configuration of the image forming apparatus, and the like, and is not necessarily limited to this value. In the developing device 3, a developing area facing the photosensitive drum 4 is opened. The developing sleeve 301 of the developing device 3 is disposed so as to be partially exposed from the opening. The developing sleeve 301 is rotatable in the direction of the arrow in the figure. The developing sleeve 301 is made of a nonmagnetic material, and a magnet 302 is fixed inside. The developing sleeve 301 rotates during the developing operation, holds the two-component developer in the developing container 303 in a layered form, and carries and transports it to the developing area. The two-component developer conveyed to the development area is supplied to the photosensitive drum 4 and develops the electrostatic latent image formed on the surface of the photosensitive drum 4. The two-component developer remaining on the developing sleeve 301 after the development is conveyed by the rotation of the developing sleeve 301 and is collected in the developer supply unit 312 in the developing container 303.

  The developer container 303 is divided into two chambers, a developer supply unit 312 and a developer stirring unit 313, by a partition wall. The developer supply unit 312 includes a first screw 314. The developer stirring unit 313 includes a second screw 315. By rotating the first screw 314 and the second screw 315, the two-component developer is mixed and stirred while circulating in the developing container 303. The circulation direction of the two-component developer in the developing container 303 of the developing device 3 of the present embodiment is the direction from the near side to the far side in FIG. 14 in the developer supply unit 312, and in the developer stirring unit 313 in FIG. This is the direction from the back side toward the near side. The developer container 303 is supplied with toner from the toner cartridge 320 through the supply port 322.

  FIG. 15 is a partially cutaway view of the toner cartridge 320. The toner cartridge 320 has a substantially cylindrical shape and can be detached from the main body of the image forming apparatus. The replenishing port 322 is opened by inserting the toner cartridge 320 from the front side of the image forming apparatus and rotating the toner cartridge 320 to the right by the handle 321. When the toner cartridge 320 is detached from the image forming apparatus, the supply port 322 is closed by rotating the handle 321 to the left. Therefore, toner that is powder from the toner cartridge 320 does not leak outside. In the toner cartridge 320, a stirring member 324 for conveying the toner inside is provided. The agitating member 324 is formed so that a resin film or the like is formed in a spiral shape and is rotationally driven by a rigid shaft. As the agitating member 324 rotates, the toner in the toner cartridge 320 is transported to the developing container 303 side to assist replenishment. The toner consumed by the image formation is supplied from the toner cartridge 320 through the supply port 322 to the developing container 303 by the rotational force of the stirring member 324 and gravity. The developing device 3 includes a supply screw 308 in the vicinity of the supply port 322. The replenishing screw 308 supplies the toner replenished by rotating into the developing container 303.

  FIG. 16 is an explanatory diagram of the circulation path of the two-component developer in the developing container 303. As shown in FIGS. 14 and 16, the developer stirring unit 313 is inclined with respect to the horizontal direction. In the developing device 3 of the present embodiment, the developer stirring unit 313 is inclined by 5 degrees with respect to the horizontal direction. In the first connection unit 316 that transfers the developer from the developer stirring unit 313 to the developer supply unit 312, the bottom surface of the developer stirring unit 313 and the bottom surface of the developer supply unit 312 are in the same position in the vertical direction. In the second connecting unit 317 that transfers the developer from the developer supply unit 312 to the developer stirring unit 313, the bottom surface of the developer stirring unit 313 is positioned vertically below the bottom surface of the developer supply unit 312. Therefore, the first connecting portion 316 can smoothly deliver the developer. In the second connecting portion 316, the developer is transferred by the dropping operation of the developer, so that the developer can be smoothly transferred.

  The first screw 314 and the second screw 315 of this embodiment both have an axial diameter of 6 [mm], and spiral-shaped conveyance members 318 having a diameter of 16 [mm] are spaced on the axial peripheral surface at an interval of 15 [mm]. It is arranged and arranged. A return member is provided at each downstream end in the developer transport direction. The return member pushes back the developer in the direction opposite to the developer transport direction, and smoothes the delivery of the developer at the first connecting portion 316 and the second connecting portion 317. The first screw 314 and the second screw 315 are rotationally driven by a drive source such as a motor.

  In the developing device 3 of this embodiment, the time until the toner replenished from the toner cartridge 320 to the toner replenishing portion T passes through the developer agitating portion 313 and the developer supplying portion 312 and returns to the toner replenishing portion T again. 20 seconds. Since the number of output sheets per minute in the image forming apparatus according to the present embodiment is 30 sheets in A4 size, the toner replenished to the toner replenishing unit T during the image formation of 10 sheets in A4 size is stirred by the developer. The unit 313 is reached.

  FIG. 17 is a diagram illustrating the relationship between the toner replenishment amount per sheet and the image density during image formation. The image density is an image density at the time when the two-component developer supplied with a predetermined amount of toner in the toner supply unit T circulates in the developing container 303 and reaches the developer supply unit 312. In FIG. 17, the horizontal axis represents the image signal, and the vertical axis represents the image density.

As shown in the drawing, in the developing device 3 of the present embodiment, the image density increases when the toner replenishment amount exceeds a predetermined amount, that is, 0.3 [g] in the present embodiment, by forming one image. This indicates that the toner and carrier are not sufficiently charged by friction with the stirring ability of the second screw 315 in the developer stirring section 313 because the amount of toner replenishment is large. In the image forming apparatus of the present embodiment, the toner amount per unit area on the photosensitive drum 4 for forming an image with the maximum density is 0.55 [mg / cm ² ]. Accordingly, a toner amount of 0.3 [g] corresponds to a toner consumption amount when an image having a maximum density is formed on an area of about 87% of an A4 size recording material. Even when the toner replenishment amount is 0.3 [g], the image density does not increase when the two-component developer replenished with toner reaches the developer supply unit 312 for the second time. This is because the stirring by the first screw 314 and the second screw 315 is advanced by further circulating in the developing container 303, and the replenished toner and carrier are sufficiently frictionally charged.

  FIG. 18 is a flowchart showing a process for determining the driving time of the developing device 3 immediately before starting the image formation of the test image (measurement image) according to the history of the toner supply amount. The first screw 314 and the second screw 315 are rotationally driven for a rotational time corresponding to the driving time. By driving the developing device 3 for a predetermined time before the test image is formed, the two-component developer circulates in the developing container 303 and the toner and the carrier are frictionally charged. This process is started when a mode setting instruction for automatic gradation correction is input from the operation unit 217.

  The CPU 28 of the printer unit B supplies the toner replenishment amount Tn replenished to the developing device 3 at the time of image formation up to the predetermined number of sheets from the RAM 32, here up to ten sheets (n is a natural number, and represents the number of sheets from the present time. 1 to 10) are read (S61). The CPU 28 stores the amount of toner replenished to the developing device 3 at the time of image formation in the RAM 32 as a toner replenishment amount each time. Here, the toner replenishment amount T1 represents the toner replenishment amount one sheet before (when the previous image is formed), and the toner replenishment amount T10 represents the toner replenishment amount when the image ten times before is formed. The CPU 28 determines whether any of the toner replenishment amount Tn exceeds a predetermined amount, for example, 0.3 [g] (S62). If it does not exceed 0.3 [g] (S62: Y), the CPU 28 ends this processing and starts image formation of a test image.

When exceeding 0.3 [g] (S62: N), the CPU 28 determines the pre-driving time Tp (seconds) according to the latest number n (S63). For example, the CPU 28 calculates the pre-driving time Tp according to the following equation. The pre-drive time Tp is a time for driving the developing device 3 before the start of image formation, that is, a rotation time for the first screw 314 and the second screw 315. The developing device 3 conveys the internal developer while being agitated.
Tp = (10−n) × 2

  After driving the developing device 3 for the calculated pre-driving time Tp (S64, S65: Y), the CPU 28 ends this process and starts image formation of a test image. In this embodiment, the driving speed of the developing device 3 during pre-driving (the rotational speed of the first screw 314 and the second screw 315) is the same speed as during image formation. By driving the developing device 3 for the pre-driving time Tp before image formation of the test image, it is possible to prevent an increase in the image density of the test image.

  As described above, in the developing device 3 of the present embodiment, the time required for the toner supplied to the toner supply unit T to circulate through the developer stirring unit 313 and the developer supply unit 312 and return to the toner supply unit T is 20 times. Seconds. Further, the number of images formed per minute by the image forming apparatus is 30 sheets in A4 size. For this purpose, the toner replenished in the toner replenishing portion T circulates once around the inside of the developing device 3 and reaches the developer agitating portion 313 while forming 10 images in A4 size. Accordingly, the toner replenished during the image formation of n sheets before (a predetermined number of sheets) passes through the developer supply unit 312 and reaches the developer stirring unit 313 after the pre-driving time Tp. That is, by driving the developing device 3 for the pre-driving time Tp, the toner replenished at the time of n-th previous image formation is not used for image formation of the test image. Therefore, even if the toner supply exceeding 0.3 [g] is performed before n sheets, by driving the developing device 3 for the pre-driving time Tp, an increase in the image density of the test image can be suppressed and stable. An image forming condition, in this embodiment, an LUT can be created. Further, in S61, how many sheets of toner supply amount Tn at the time of image formation is read out is determined according to the time during which the developer circulates in the developing device 3 once.

  In addition, since the pre-driving time Tp is calculated by using the most recent number n from the time when the toner replenishment amount exceeds 0.3 [g], the pre-driving time Tp is shortened and the test image is formed. The time to start can be shortened.

  In the image forming apparatus according to the present embodiment, the number of sheets output by image formation for one minute is 30 sheets of A4 size, but is not limited to this. By calculating the pre-driving time as appropriate based on the present embodiment, it is possible to obtain the same effect regardless of the number of output sheets per minute of the image forming apparatus.

  The driving speed of the developing device 3 at the time of pre-driving is described as the same speed as at the time of image formation, but is not limited to this. For example, by shortening the driving speed of the developing device 3 during pre-driving (the rotational speeds of the first screw 314 and the second screw 315) than during image formation, the pre-driving time is shortened, that is, the test image is formed. The time until the start can be shortened. For example, if the driving speed of the developing device 3 at the time of pre-driving is twice that at the time of image formation, the pre-driving time can be reduced to half.

  The image forming apparatus according to the present embodiment as described above does not cause unevenness in the density of the gradation pattern even when a large amount of toner is replenished immediately before the gradation correction control is performed, and stable image forming conditions. Can be corrected.

Claims (8)

An image forming unit having a developer containing a developer containing toner and a carrier, and forming an image on a recording material using the developer in the developer;
Measuring means for measuring a measurement image formed on the recording material by the image forming means;
A determination unit that causes the image forming unit to form the measurement image, causes the measurement unit to measure the measurement image, and determines an image forming condition of the image forming unit based on a measurement result of the measurement unit;
Replenishing means for replenishing toner to the developing unit,
The image forming unit includes a screw that is rotationally driven to stir the developer in the developing device, a motor that rotates the screw, and a control unit that controls the motor.
When the image forming unit forms the measurement image on the recording material, the control unit controls the rotation time of the screw based on the supply amount of the supply unit.
Image forming apparatus. The screw rotation time is a time for the motor to rotate the screw before the image forming means forms the measurement image.
The image forming apparatus according to claim 1. When the image forming unit forms the measurement image on the recording material, the control unit forms an image on a predetermined number of recording materials before the rotation time of the screw is formed. And controlling based on the amount of toner replenished to the developing device by the replenishing means during
The image forming apparatus according to claim 1. The control means determines the rotation time of the screw according to the number of sheets since the toner exceeding a predetermined amount has been replenished.
The image forming apparatus according to claim 1. The control means determines the rotation time of the screw according to the number of sheets since the toner exceeding the predetermined amount is supplied.
The image forming apparatus according to claim 4. The control means determines the rotation time of the screw according to the time for which the toner circulates in the developing device once.
The image forming apparatus according to claim 1. The control means drives the screw at the same speed as that when the image forming means forms an image before forming the measurement image.
The image forming apparatus according to claim 1. The control means drives the screw at a speed faster than the speed at which the image forming means drives when forming an image before image formation of the measurement image.
The image forming apparatus according to claim 1.

Images