JP7625431B2 - Image forming device - Google Patents

Description

This relates to image density control, which controls the density of an image formed on a recording medium by an image forming device.

Electrophotographic image forming devices form images by forming an electrostatic latent image on a photoreceptor, developing the electrostatic latent image, transferring the image to a recording medium, and fixing the image to the recording medium. The density of the image formed on the recording medium varies depending on environmental conditions such as temperature and humidity, and the state of the developer (toner) used for development. For this reason, image forming devices form test images and adjust the density of the image formed by the image forming device based on the results of reading the test images with a sensor. This is called "calibration." There are two types of calibration: calibration that uses the results of reading the test image formed on the recording medium, and calibration that uses the results of measuring the test image before it is fixed to the recording medium.

The image forming device disclosed in Patent Document 1 performs calibration by forming a test image in a margin area on a recording medium on which an image (user image) in accordance with instructions from a user is formed. This allows calibration to be performed in real time. This image forming device has an advantage over conventional calibration in that the formation of the user image is not interrupted by the execution of calibration.

JP 2014-107648 A

The image forming device of Patent Document 1 can perform calibration using the results of reading a test image on a recording medium, as well as calibration using the results of measuring the test image before it is fixed to the recording medium. However, when performing calibrations using different methods like these, there is a possibility that the correction amounts determined in these calibrations will differ. This is due, for example, to differences in the sensors used for calibration, or the fact that the target values do not necessarily match for each calibration. This hinders the stability of the density of the image formed by the image forming device.

In view of the above problems, the present invention aims to stabilize the density of images formed by an image forming device.

The image forming apparatus of the present invention has an image forming means for forming an image on a recording medium based on image formation conditions for controlling image density, a reading means having a conveying path along which the recording medium is conveyed, a first reading unit for reading a pattern image formed on the recording medium conveyed along the conveying path from a first side relative to the conveying path, and a second reading unit for reading the pattern image formed on the recording medium conveyed along the conveying path from a second side opposite to the first side relative to the conveying path, an intermediate transfer body onto which a measurement image formed by the image forming means is transferred, a measuring means for measuring the measurement image transferred to the intermediate transfer body, a generating means for forming a pattern image on the recording medium by the image forming means and generating the image forming conditions based on the reading result of the pattern image by the reading means, and another generating means for generating the first conversion conditions and the second conversion conditions, and the generating means is configured to generate the first conversion conditions and the second conversion conditions based on the first reading unit. When reading a pattern image formed on the surface of the recording medium facing the first reading unit, a first reading result of the pattern image by the first reading unit is converted based on a first conversion condition, and the image formation conditions are generated based on the converted first reading result; when the second reading unit reads a pattern image formed on the surface of the recording medium facing the second reading unit, a second reading result of the pattern image by the second reading unit is converted based on a second conversion condition different from the first conversion condition, and the image formation conditions are generated based on the converted second reading result; the other generation means generates the first conversion condition based on the measurement result of the measurement image by the measurement means and the reading result of the measurement image on the recording medium read by the first reading unit, and generates the second conversion condition based on the measurement result of the measurement image by the measurement means and the reading result of the measurement image on the recording medium read by the second reading unit .

According to the present invention, it is possible to stabilize the density of an image formed by an image forming device.

Schematic cross-sectional view of an image forming apparatus Schematic cross-sectional view of a concentration sensor Control block diagram of an image forming apparatus A four-level chart to explain tone correction Schematic diagram of a gradation correction pattern formed in a first gradation correction process; Schematic diagram of a gradation correction pattern formed in the second gradation correction process; Flowchart showing the process of generating a conversion table FIG. 1 is a flowchart showing an image forming process including a gradation correction process. Illustrative diagram of a conversion table Schematic diagram of the output side setting screen FIG. 1 is a flowchart showing an image forming process including a gradation correction process. Selection screen diagram FIG. 1 is a flowchart showing an image forming process including a gradation correction process.

Example 1
(Configuration of Image Forming Apparatus)
1 is a schematic cross-sectional view of an image forming apparatus 100. The image forming apparatus 100 includes an image forming engine unit 101 (also called a printer), a reader unit 400 for reading an original, a finisher 600, and an operation panel 180. The image forming engine unit 101 has image forming stations 120, 121, 122, and 123. The image forming station 120 forms an image of yellow (Y). The image forming station 121 forms an image of magenta (M). The image forming station 122 forms an image of cyan (C). The image forming station 120 forms an image of black (Bk). A printer controller 300 for controlling each unit of the image forming apparatus 100 is housed in a controller box 104 of the image forming apparatus 100.

Image forming station 120 includes a photosensitive drum 105, a charger 111, a laser scanner unit 107, and a developer 112. The other image forming stations 121, 122, and 123 have the same configuration as image forming station 120, so the configuration of image forming station 120 will be described below.

The photosensitive drum 105 is a metal cylinder with a photosensitive layer on its surface. The photosensitive layer of the photosensitive drum 105 functions as a photoconductor. The charger 111 is a corona charger having a wire. A charging voltage is applied to the charger 111 to uniformly charge the photosensitive drum 105. Note that the charger 111 is not limited to a corona charger, and may be configured to have, for example, a charging roller that rotates while in contact with the photosensitive drum 105.

The laser scanner unit 107 has a semiconductor laser 108, a mirror 109, and a laser driver that controls the laser light emitted from the semiconductor laser 108. The laser driver drives the semiconductor laser 108 based on a laser output signal supplied from the printer controller 300. The semiconductor laser 108 of the laser scanner unit 107 exposes the photosensitive drum 105 to form an electrostatic latent image on the photosensitive drum 105.

The developer 112 of the image forming station 120 contains yellow toner and uses the yellow toner to develop the electrostatic latent image on the photosensitive drum 105. The developers 112 of the other image forming stations 121, 122, and 123 each contain a toner of a corresponding color.

The intermediate transfer body 106 is a belt that rotates in a predetermined direction as the drive roller rotates. Around the intermediate transfer body 106, there is a sensor 115 that detects the image on the intermediate transfer body 106, and a sensor 116 that detects the recording medium 110, so that the image on the intermediate transfer body 106 is transferred to the desired position on the recording medium 110. Also, around the intermediate transfer body 106, there is a density sensor 117 that detects the measurement image on the intermediate transfer body 106.

To transfer the image transferred to the intermediate transfer body 106 onto the recording medium 110, the intermediate transfer belt 106 forms a transfer nip between itself and the transfer roller 114. A transfer voltage is applied to the transfer roller 114 while the image on the intermediate transfer belt 106 and the recording medium 110 fed from the storage 113 pass through the transfer nip, so that the image on the intermediate transfer belt 106 is transferred to the recording medium 110. The recording medium 110 that has passed through the transfer nip is transported to the fixing device 105, which will be described later.

The fixing device 150 includes a fixing roller 151 having a heater, a pressure belt 152 for pressing the recording medium 110 against the fixing roller 151, and a sensor 153 for detecting when the recording medium 110 has been discharged from the fixing device 150. The recording medium 110 conveyed to the fixing device 150 is subjected to heat and pressure by the fixing roller 151 and pressure belt 152, and the toner on the recording medium 110 is melted to fix the image on the recording medium 110.

The image forming engine unit 101 includes a transport mechanism 130 that controls the transport direction of the recording medium 110 downstream of the fixing unit 150 in the transport direction in which the recording medium 110 is transported. The transport mechanism 130 has flappers 132, 133, and 134, a transport path 135, an inversion unit 136, and a sensor 137. The flapper 132 is driven to switch whether the recording medium 110 is transported to the transport path 135 or to the transport path 201. Downstream of the transport path 135 in the transport direction is the inversion unit 136. The sensor 137 detects the end of the recording medium 110. The timing for stopping the transport of the recording medium 110 is controlled based on the detection result of the sensor 137.

A line sensor 138 that reads one side of the recording medium 110 of the image forming device 100 and a line sensor 139 that reads the other side of the recording medium 110 are arranged on the conveying path 201. The recording medium 110 conveyed via the conveying path 201 is conveyed to the finisher 600 and discharged to any tray of the finisher 600.

Next, the operation of the image forming engine unit 101 to form an image will be described. The image forming apparatus 100 forms an image on the recording medium 110 based on a job. When a job is executed, the photosensitive drum 105 rotates, and the charger 111 charges the photosensitive drum 105. The laser driver controls the semiconductor laser 108 based on a laser output signal generated from image data included in the job. To form an electrostatic latent image on the photosensitive drum 105, the laser scanner unit 107 exposes the surface of the photosensitive drum 105 charged by the charger 111. The developer 112 develops the electrostatic latent image on the photosensitive drum 105 using toner. As a result, the photosensitive drum 105 carries an image visualized using toner. The toner of each color on the photosensitive drum 105 is transferred to the intermediate transfer body 106 so as to be superimposed.

The recording media 110 in the storage 113 are fed one by one by rollers (not shown) and transported to the transfer nip. When the recording media 110 and the image on the intermediate transfer body 106 pass through the transfer nip, a transfer voltage is applied to the transfer roller 114, and the image on the intermediate transfer body 106 is transferred to the recording media 110. The recording media 110 to which the image has been transferred is transported to the fixing device 150. The fixing device 150 fixes the image on the recording media 110 and transports the recording media 110 to the transport mechanism 130. The recording media 110 transported to the transport path 210 by the transport mechanism 130 is discharged to any tray of the finisher 600.

Here, for example, when an image is formed on both sides of the recording medium 110, the recording medium 110 with the image formed on the first side is transported to the transport path 135 by the flapper 132, and is transported to the inversion section 136 by the flapper 133. After the end of the recording medium 110 is detected by the sensor 137, the transport of the recording medium 110 is temporarily stopped at the position where the end of the recording medium 110 passes the sensor 137. The transport direction is then reversed by a roller (not shown). The flapper 133 transports the recording medium 110, whose transport direction has been controlled to be reversed, to the double-sided transport path. As a result, the recording medium 110 passes through the transfer nip with the front and back reversed. Then, the recording medium 110 with the image formed on the second side is transported to the transport path 201 by the flapper 132.

In addition, the image forming device 100 can control whether to eject the recording medium 110 with the image formed side facing up or with the image formed side facing down based on the print settings (paper ejection surface settings) when an image is formed on only one side. Face-up ejection is an ejection surface setting in which the recording medium 110 is ejected with the image formed side facing up, and face-down ejection is an ejection surface setting in which the recording medium 110 is ejected with the image formed side facing down.

Here, for example, when face-up discharge is performed, the recording medium 110 on which an image has been formed is transported to the transport path 201 by the flapper 132. As a result, the recording medium 110 discharged onto the tray of the finisher 600 is stacked with the image-formed surface facing upward. The transport path 201 is a common transport path through which both the recording medium 110 that has been inverted in the inversion unit 136 and the recording medium 110 that has not been inverted pass.

On the other hand, when face-down discharge is performed, the recording medium 110 on which the image has been formed is transported to the transport path 135 by the flapper 132, and after the end of the recording medium 110 is detected by the sensor 137, the transport of the recording medium 110 is temporarily stopped. The transport direction is then reversed by a roller (not shown). The recording medium 110 is then transported to the transport path 201 by the flapper 134. As a result, the recording medium 110 discharged onto the tray of the finisher 600 is stacked with the image-formed surface facing down.

(Concentration sensor)
2 is a schematic cross-sectional view of the density sensor 117. The density sensor 117 is an optical sensor that measures the measurement image formed on the intermediate transfer body 106. The density sensor 117 includes a light-emitting diode (hereinafter referred to as LED) 1171 and photodiodes (hereinafter referred to as PD) 1172 and 1173. The LED 1171 irradiates the intermediate transfer body 106 with infrared rays at an incident angle of 15°. The PD 1172 receives the reflected light from the intermediate transfer body 106 and the reflected light from the measurement image at a position with a reflection angle of 15° (specular reflection angle). The PD 1173 receives the reflected light from the intermediate transfer body 106 and the reflected light from the measurement image at a reflection angle of −35° (diffuse reflection angle). The density sensor 117 further includes a drive circuit that supplies a current to the LED 1171 in order to drive the LED 1171, and a conversion circuit that converts the current output according to the amount of light received by the PDs 1172 and 1173 into a voltage.

The density sensor 117 can measure both specularly reflected light and diffusely reflected light. PD1172, which receives specularly reflected light, is used to measure the black measurement image. The output value (voltage) of PD1172 corresponding to the reflected light from the black measurement image is converted to the density (or toner adhesion amount) value of the black measurement image. PD1173, which receives diffusely reflected light, is used to measure the color (yellow, cyan, magenta) measurement images. The output value (voltage) of PD1173 corresponding to the reflected light from the yellow measurement image is converted to the density (or toner adhesion amount) value of the yellow measurement image. The magenta measurement image and the cyan measurement image are converted in the same way. A density conversion table for converting the output value (voltage) to density (or toner adhesion amount) is prepared in advance for each color.

(Line sensor)
Line sensors 138 and 139 that read the image formed on the recording medium 110 are, for example, a CMOS sensor or a CCD. Line sensor 138 is disposed on the upper surface side of the conveying path 201, and line sensor 139 is disposed on the lower surface side of the conveying path 201, and each reads images formed on the upper surface and the lower surface of the recording medium 110 when the recording medium 110 is conveyed. Line sensors 138 and 139 output read data (luminance signal) based on the read result.

A gradation correction pattern 1104 (FIG. 6) is formed on the recording medium 110 as a measurement image. When the measurement image of each color is read, the luminance signal of the measurement image is converted to a density value based on the luminance density conversion table corresponding to each color. The line sensors 138 and 139 are equipped with color filters and can extract light of Red, Green, and Blue. The density value of the measurement image of cyan is converted from the output value (luminance signal) corresponding to the luminance of the complementary color Red based on the luminance density conversion table for cyan. The density value of the measurement image of magenta is converted from the output value (luminance signal) corresponding to the luminance of the complementary color Green based on the luminance density conversion table for magenta. The density value of the measurement image of yellow is converted from the output value (luminance signal) corresponding to the luminance of the complementary color Blue based on the luminance density conversion table for yellow. The density value of the measurement image of black is converted from the output value (luminance signal) corresponding to the luminance of Green based on the luminance density conversion table for black.

(Configuration of image processing unit)
3 is a control block diagram of the image forming apparatus 100. A host computer 301 and the image forming apparatus 100 are connected by a communication line such as USB 2.0 High-Speed, 1000Base-T/100Base-TX/10Base-T (IEEE 802.3 compliant).

The printer controller CPU 314 of the printer controller 300 controls the operation of the image forming apparatus 100. The printer controller 300 includes a host I/F unit 302, which is an interface used to communicate with a host computer 301, an input/output buffer 303 used to send and receive data, and a RAM 310 that functions as a system work memory. In addition, the program ROM 304 stores the control program and control data of the printer controller CPU 314.

The printer controller CPU 314 executes the program stored in the program ROM 304 by expanding it into the RAM 310. As a result, the printer controller CPU 314 functions as an image information generation unit 305, a main-scan unevenness correction table generation unit 306, an automatic tone correction generation unit 307, a multidimensional table generation unit (ICC profile) 308, and an image defect detection unit 309.

The printer controller CPU 314 functioning as the image information generating unit 305 generates an image object based on data received from the host computer 301. The printer controller CPU 314 functioning as the main scanning unevenness correction table generating unit 306 corrects uneven density of the image formed by the image forming engine unit 101. The printer controller CPU 314 functioning as the automatic gradation correction generating unit 307 generates a γLUT for correcting the gradation characteristics of the images of the colors yellow, cyan, magenta, and black. The printer controller CPU 314 functioning as the multi-color table generating unit 308 generates a color profile for controlling the color of the mixed color image. The printer controller CPU 314 functioning as the image defect detecting unit 309 detects image defects in the output image read by the line sensor 138.

The image data transferred to the image forming apparatus 100 is subjected to image processing in the RIP unit 315, color processing unit 316, tone correction unit 317, and pseudo-halftone processing unit 318. The RIP (Raster Image Processor) unit 315 develops an image object into a bitmap image. The color processing unit 316 performs color conversion processing of the image data based on a color profile. The tone correction unit 317 converts the image data based on a γLUT to correct the tone characteristics of the image to ideal tone characteristics. The pseudo-halftone processing unit 318 performs pseudo-halftone processing on the image data. The engine I/F unit 319 transfers the image data processed by the pseudo-halftone processing unit 318 to the image forming engine unit 101. The RIP unit 315, color processing unit 316, tone correction unit 317, and pseudo-halftone processing unit 318 are realized by an ASIC.

Measurements using the line sensor 138 and density sensor 117 are controlled by the engine control CPU 102 in the image forming engine unit 101.

The table storage unit 311 stores an ICC profile as a color profile and a γLUT. The operation panel 180 has a display and functions as an interface that accepts user instruction information. The panel I/F unit 312 is electrically connected to the operation panel 180 having a display and functions as an interface that accepts user instruction information. The reader unit 400 reads an original document using an image sensor (not shown) and transfers the read image to the printer controller 300. The reader I/F unit 313 functions as an interface that accepts the read image transferred from the reader unit 400. The printer controller 300 transmits and receives information between each unit via the system bus 320.

(Explanation of tone correction)
The image processing (called gradation correction) for correcting the gradation characteristics of an image formed by the image forming apparatus 100 to ideal gradation characteristics will be described with reference to the quadrant chart shown in FIG. 4. FIG. 4 is a quadrant chart showing how gradation is reproduced. Quadrant I shows the reading characteristics of a sensor that converts the density of an original image into a density signal. Quadrant II shows the conversion characteristics (data characteristics of the γLUT) for converting the density signal into a laser output signal. Quadrant III shows the gradation characteristics (printer characteristics) of an image formed by the image forming engine unit 101. Quadrant IV shows the relationship between the density of an original image and the density of an output image. In FIG. 4, the density signal and the laser output signal are processed as 8-bit digital signals. Therefore, the number of gradations in FIG. 4 is 256.

The gradation correction unit 317 (Fig. 3) converts the laser output signal to adjust the gradation characteristics (printer characteristics) of the image formed by the image forming engine unit 101 to ideal gradation characteristics (quadrant IV). The gradation correction unit 317 (Fig. 3) uses a γLUT (quadrant II) to convert a density signal (input value) to a laser output signal (output value). The image data (laser output signal) converted based on the γLUT is sent to a laser driver that controls the driving of the laser light source 108. Then, an electrostatic latent image is formed on the photosensitive drum 105 by scanning the photosensitive drum 105 with the laser light output from the laser light source 108. This electrostatic latent image is developed to form an image of ideal density.

The image forming apparatus 100 can perform a first gradation correction process using the measurement results of the measurement image on the intermediate transfer body 106, and a second gradation correction process using the reading results of the measurement image on the recording medium 110.

(First tone correction process)
The first gradation correction process is realized by cooperation between the engine control CPU 102, which controls the density sensor 117, and the printer controller CPU 314 of the printer controller 300. When the first gradation correction process is executed, the engine control CPU 102 causes the image forming engine unit 101 to form a gradation correction pattern 1061, and causes the density sensor 117 to measure the gradation correction pattern 1061. Then, the printer controller CPU 314, which functions as the automatic gradation correction generation unit 307, generates a γLUT based on the measurement result of the gradation correction pattern 1061 by the density sensor 117.

The gradation correction unit 317 converts the image data based on the γLUT generated by the printer controller CPU 314. This makes it possible to control the gradation characteristics of the image formed by the image forming engine unit 101 to ideal gradation characteristics. The first gradation correction process is performed each time the image forming engine unit 101 forms a predetermined number of pages of images. Here, the predetermined number of pages is, for example, 100 sheets.

Figure 5 is a schematic diagram showing the gradation correction pattern 1061 formed on the intermediate transfer body 106. The gradation correction pattern 1061 is formed so that it passes through the position where the LED 1171 of the density sensor 117 irradiates light. The gradation correction pattern 1061 has multiple gradation patches with gradually different gradation values for C, M, Y, and K.

The multiple tone patches are each shaped like a square with sides of 10 mm. The multiple tone patches are arranged in a line parallel to the movement direction (rotation direction) of the intermediate transfer body 106. The multiple tone patches on the intermediate transfer body 106 are multiple measurement images of different tones. The density signals for forming the multiple tone patches are, for example, 16, 32, 64, 86, 104, 128, 176, 224, and 255. Note that, although the tone correction patterns 1061 are arranged in a line in FIG. 5, they may be arranged in multiple lines when multiple density sensors 117 are installed in the main scanning direction.

The gradation correction pattern 1061 on the intermediate transfer body 106 is formed at a timing when no image to be transferred to the recording medium 110 is formed. Note that, other than the timing when no image to be transferred to the recording medium 110 is formed, the gradation correction pattern 1061 may be formed after all images based on the job are formed.

Next, a method for updating the γLUT on the recording medium 110 from the density value of the gradation correction pattern 1061 on the intermediate transfer body 106 will be described. The target density of the gradation correction pattern 1061 on the intermediate transfer body 106 is stored in advance in the program ROM 304. The printer controller CPU 314 functioning as the automatic gradation correction generation unit 307 generates a γLUT so that the density value of the gradation correction pattern 1061 acquired using the density sensor 117 becomes the aforementioned target density.

(Second tone correction process)
FIG. 6 is a schematic diagram showing a gradation correction pattern 1104 formed on a recording medium 110. Here, the gradation correction pattern 1104 is formed together with a user image. A marginal area in which the gradation correction pattern 1104 is formed is called a non-image area 1102. Here, the marginal portion (non-image area 1102) on the recording medium 1101 in which the user image is not formed is cut. In other words, the gradation correction pattern 1104 formed in the marginal portion (non-image area 1102) does not remain as a final product. The cutting mark 1103 is a mark indicating the position where the cutting process is performed. The cutting mark 1103 is composed of two overlapping L-shaped marks and is formed near the four corners of the image portion 1101, and the outside of the area surrounded by the four cutting marks 1103 indicates the cutting area. For example, an operator uses a cutting device to cut the marginal portion according to the cutting marks 1103.

Note that the dots indicating the image area 1101 in FIG. 6 are shown for the purpose of explanation, and are not actually formed on the recording medium 110. Also, the recording medium 110 shown in FIG. 6 is described taking as an example a case in which the recording medium 110 is transported along the longitudinal direction of the recording medium 110.

The gradation correction pattern 1104 is formed for each of the colors C, M, Y, and K on the first surface of the recording medium 110. The first surface of the recording medium 110 is the surface (image forming surface) that comes into contact with the intermediate transfer body 106 when the recording medium 110 first passes through the transfer nip.

As shown in FIG. 6, the gradation correction pattern 1104 is preferably formed in an end region in a direction perpendicular to the transport direction in which the recording medium 110 is transported. For example, if the gradation correction pattern 1104 is formed at the end of the transport direction (i.e., the leading and trailing ends of the recording medium 110 in the transport direction), the toner may act as an adhesive and cause the recording medium 110 to wrap around the fixing roller 151 of the fixing device 150. If the gradation correction pattern 1104 is formed in an end region of the recording medium 110 in a direction perpendicular to the transport direction, the recording medium 1104 can be prevented from wrapping around the fixing roller 151.

The tone correction pattern 1104 also has a number of tone patches with gradually differing tone values for C, M, Y, and K. Each of the tone patches is a square with sides of 8 mm. The tone patches are arranged in a line parallel to the transport direction of the recording medium 110. Yellow and black tone patches are arranged in one end region, and magenta and cyan tone patches are arranged in the other end region.

The multiple gradation patches on the recording medium 110 are multiple measurement images of different gradations. The density signals for forming the multiple gradation patches are, for example, 16, 32, 64, 86, 104, 128, 176, 224, and 255. Note that the gradation patches of the gradation correction pattern 1104 are not limited to the colors C, M, Y, and K, but may be mixed-color images created from multiple colors of cyan, magenta, and yellow. Alternatively, the gradation patches of the gradation correction pattern 1104 may be gray images (called process gray or process black) made by mixing yellow, cyan, and magenta.

The gradation pattern 1104 on the recording medium 110 is read by the line sensor 138 or the line sensor 139. When face-up paper ejection is set, the gradation pattern 1104 on the recording medium 110 is read by the line sensor 138. On the other hand, when face-down paper ejection is set, the gradation pattern 1104 on the recording medium 110 is read by the line sensor 139. Even in a double-sided mode in which images are formed on both sides, the gradation pattern 1104 on the recording medium 110 is read by the line sensor 139.

When the line sensor 138 reads the gradation correction pattern 1104, the yellow and cyan gradation correction patterns 1104 on the recording medium 110 pass through the reading area of the line sensor 138. When the line sensor 138 reads the gradation correction pattern 1104, the magenta and black gradation correction patterns 1104 pass through the reading area of the line sensor 138 after the yellow and cyan gradation correction patterns 1104. On the other hand, when the line sensor 139 reads the gradation correction pattern 1104, the magenta and black gradation correction patterns 1104 on the recording medium 110 pass through the reading area of the line sensor 139. When the line sensor 139 reads the gradation correction pattern 1104, the yellow and cyan gradation correction patterns 1104 pass through the reading area of the line sensor 138 after the magenta and black gradation correction patterns 1104.

(Creating a conversion table)
In the second gradation correction process, the measurement result of the gradation correction pattern 1104 is converted into a density value of the image formed on the intermediate transfer body 106. This is because the image density is not stable if the target density of the first gradation correction process differs from the target density of the second gradation correction process. By controlling the density value acquired in the gradation correction to be the target density on the intermediate transfer body 106, it is possible to easily achieve a stable image density even when the gradation correction to be performed is switched. Therefore, the printer controller CPU 314 generates a conversion condition for converting the reading result of the measurement image on the recording medium 110 into the density of the measurement image on the intermediate transfer body 106.

The image forming apparatus 100 also has two line sensors 138 and 139. Here, there are individual differences between the line sensors 138 and 139. Therefore, in order to stabilize the image density with high accuracy, the printer controller CPU 314 generates conversion conditions for converting the reading results of the measurement image on the recording medium 110 for each line sensor 138 and 139 into the density of the measurement image on the intermediate transfer body 106. In other words, the printer controller CPU 314 generates conversion conditions for converting the reading results of the measurement image by the line sensor 138 into the measurement results of the density sensor 117, and conversion conditions for converting the reading results of the measurement image by the line sensor 139 into the measurement results of the density sensor 117.

The aforementioned conversion conditions are a conversion table that converts the luminance signal of line sensor 138 into a density value, and a conversion table that converts the luminance signal of line sensor 139 into a density value. The conversion conditions may be a conversion table that converts the luminance signal of line sensor 138 into an output value (voltage) of density sensor 117, and a conversion table that converts the luminance signal of line sensor 139 into an output value (voltage) of density sensor 117. Alternatively, the conversion conditions may be a conversion table that converts a density value calculated from the luminance signal of line sensor 138 (or line sensor 139) into a density value calculated from the output value of density sensor 117.

(Creating and selecting a conversion table)
In the image forming apparatus 100, the orientation of the gradation correction pattern 1104 formed on the recording medium 110 passing through the transport path 201 changes depending on the paper discharge surface setting. This is because the gradation correction pattern 1104 is formed on the first surface. Therefore, the printer controller CPU 314 selects whether to use the conversion table for the line sensor 138 or the conversion table for the line sensor 139 depending on the paper discharge surface setting. Furthermore, the printer controller CPU 314 controls whether to generate a conversion table for the line sensor 138 or the conversion table for the line sensor 139 depending on the paper discharge surface setting.

Next, the process of generating a conversion table will be described with reference to the flowchart in FIG. 7. When the printer controller CPU 314 receives an instruction to execute the process of generating a conversion table, it reads a program from the program ROM 304 and loads it into the RAM 310 to execute each step in FIG. 7.

First, the printer controller CPU 314 forms the gradation correction pattern 1104 on the recording medium 1104 (S70). Note that the formation of the gradation correction pattern 1104 is executed based on instructions from the engine control CPU 102, so in step S70, the printer controller CPU 314 instructs the engine control CPU 102 to form the gradation correction pattern 1104.

The gradation correction pattern 1104 formed in step S70 is a measurement image that is measured to generate a conversion table. Therefore, the gradation correction pattern 1104 formed in step S70 may be an image with a different gradation from the gradation correction pattern 1104 formed to generate the γLUT shown in FIG. 6.

Next, the printer controller CPU 314 determines whether the paper ejection side setting is set to face-up ejection (S71). Here, FIG. 10 is a setting screen for setting the paper ejection side setting displayed on the operation panel 180. The user can select face-up ejection or face-down ejection on the setting screen shown in FIG. 10. Note that if no setting has been made in the print settings, face-down ejection is selected. The printer controller CPU 314 accepts user instruction information regarding the paper ejection side setting from the operation panel 180.

If face-up paper ejection is set in step S71, the printer controller CPU 314 causes the line sensor 138 to read the gradation correction pattern 1104 (S72). In step S72, the engine control CPU 102 controls the line sensor 138 based on instructions from the printer controller CPU 314 to read the gradation correction pattern 1104 on the recording medium 110. The luminance signal of the line sensor 138 is converted to a density value A1, and the printer controller CPU 314 acquires the density value A1 sent from the engine control CPU 102.

Next, the printer controller CPU 314 forms the gradation correction pattern 1061 on the intermediate transfer body 106 (S73). Note that the formation of the gradation correction pattern 1061 is executed based on instructions from the engine control CPU 102, so in step S73, the printer controller CPU 314 instructs the engine control CPU 102 to form the gradation correction pattern 1061.

Here, the gradation correction pattern 1061 formed in step S73 is a measurement image that is measured to generate a conversion table. Therefore, the gradation correction pattern 1061 formed in step S73 may be a gradation image different from the gradation correction pattern 1061 formed to generate the γLUT shown in FIG. 5.

Next, the printer controller CPU 314 causes the density sensor 117 to read the gradation correction pattern 1106 (S74). In step S74, the engine control CPU 102 controls the density sensor 117 based on instructions from the printer controller CPU 314, and reads the gradation correction pattern 1061 on the intermediate transfer body 106. The output value (voltage) of the density sensor 117 is converted to a density value B1, and the printer controller CPU 314 acquires the density value B1 transmitted from the engine control CPU 102.

Then, the printer controller CPU 314 generates a conversion table 140140 based on the density value A1 acquired in step S72 and the density value B1 acquired in step S74 (S75). The conversion table 140 generated in step S75 is stored in the table storage unit 311, and the printer controller CPU 314 ends the conversion table generation process.

If face-down discharge is set in step S71, the engine control CPU 102 causes the transport mechanism 130 to stop the recording medium 110 at the inversion unit 136 and transport it from the inversion unit 136 to the transport path 201. This causes the recording medium 110 to be transported so that the measurement image 1104 faces the line sensor 139.

Then, the printer controller CPU 314 causes the line sensor 139 to read the gradation correction pattern 1104 (S76). In step S76, the engine control CPU 102 controls the line sensor 139 based on instructions from the printer controller CPU 314 to read the gradation correction pattern 1104 on the recording medium 110. The luminance signal of the line sensor 139 is converted to a density value A2, and the printer controller CPU 314 acquires the density value A2 sent from the engine control CPU 102.

Next, the printer controller CPU 314 forms the gradation correction pattern 1061 on the intermediate transfer body 106 (S77). Note that since the formation of the gradation correction pattern 1061 is executed based on an instruction from the engine control CPU 102, the printer controller CPU 314 instructs the engine control CPU 102 to form the gradation correction pattern 1061 in step S77.

Here, the gradation correction pattern 1061 formed in step S77 is a measurement image that is measured to generate a conversion table. Therefore, the gradation correction pattern 1061 formed in step S77 may be a gradation image different from the gradation correction pattern 1061 formed to generate the γLUT shown in FIG. 5.

Next, the printer controller CPU 314 causes the density sensor 117 to read the gradation correction pattern 1106 (S78). In step S78, the engine control CPU 102 controls the density sensor 117 based on instructions from the printer controller CPU 314 to read the gradation correction pattern 1061 on the intermediate transfer body 106. The output value (voltage) of the density sensor 117 is converted to a density value B2, and the printer controller CPU 314 acquires the density value B2 transmitted from the engine control CPU 102.

Then, the printer controller CPU 314 generates a conversion table 141 based on the density value A2 acquired in step S76 and the density value B2 acquired in step S78 (S79). The conversion table 141 generated in step S79 is stored in the table storage unit 311, and the printer controller CPU 314 ends the conversion table generation process.

In the process of generating the conversion table in FIG. 7, the gradation correction pattern 1061 is formed after the gradation correction pattern 1104 is formed, but the order in which the gradation correction pattern 1104 and the gradation correction pattern 1061 are formed is not limited to the above order. The gradation correction pattern 1601 may be formed first, and then the gradation correction pattern 1104 may be formed. In this configuration, it is sufficient to obtain user instruction information regarding the paper discharge surface settings in advance.

The conversion table 140 (or 141) is preferably generated when it is determined that the recording medium is to be used for the first time. The conversion table 140 (or 141) may be generated based on user instruction information from the operation panel 180, for example.

Figure 9 is an example diagram of conversion table 140 and conversion table 141. In Figure 9, the vertical axis is the density value obtained from the measurement result of density sensor 117, and the horizontal axis is the density value obtained from the reading result of line sensor 138 or 139. It can be seen from Figure 9 that there are individual differences between line sensor 138 and line sensor 139. In the gradation correction performed after the conversion table generation process is executed, printer controller CPU 314 converts the reading result of gradation correction pattern 1104 into a density value based on the corresponding conversion table 140 or 141.

(Gradation correction control)
The second gradation correction process is realized by the cooperation of the engine control CPU 102, which controls the line sensors 138 and 139, and the printer controller CPU 314. When the second gradation correction process is executed, the printer controller CPU 314, which functions as the automatic gradation correction generation unit 307, generates a γLUT based on the reading result of the gradation correction pattern 1104 by the line sensor 138 or 139. Then, the gradation correction unit 317 converts image data (density signal) based on the γLUT generated by the automatic gradation correction generation unit 307. Then, the image forming engine unit 101 forms an image based on the image data (laser output signal) converted by the gradation correction unit 317. As a result, the gradation characteristics of the image formed by the image forming engine unit 101 are controlled to ideal gradation characteristics. In the second gradation correction process, the gradation correction pattern 1104 is repeatedly formed on a plurality of recording media 110. Then, a γLUT is generated based on an average value of the density values of the gradation correction patterns 1104 formed on a plurality of recording media 110 .

Next, the image forming process including the gradation correction process will be described with reference to the flowchart in FIG. 8. When the image forming apparatus 100 receives an instruction to execute the image forming process for forming an image based on a job, the printer controller CPU 314 reads the program from the program ROM 304 and loads it in the RAM 310 to execute each step in FIG. 8.

First, the printer controller CPU 314 instructs the engine control CPU 102 to start image formation processing and starts job printing (S81). The printer controller CPU 314 determines whether execution of the second gradation correction process is enabled or disabled based on user instruction information regarding gradation correction input from the operation panel 180 (S82). If execution of the second gradation correction process is permitted in step S82, the printer controller CPU 314 checks the settings of the paper discharge surface setting (S83). The printer controller CPU 314 determines whether a conversion table corresponding to the paper discharge surface setting confirmed in step S83 is stored in the table storage unit 311 (S84).

If a conversion table corresponding to the paper discharge side setting is not stored in the table storage unit 311 in step S84, the printer controller CPU 314 executes the conversion table generation process shown in FIG. 7 (S85). In step S85, a conversion table corresponding to the currently set paper discharge side setting is stored in the table storage unit 311. After the conversion table generation process is executed, the printer controller CPU 314 increments the count value that counts the number of output sheets by 1 and transitions to step S86 described below.

On the other hand, if a conversion table corresponding to the paper discharge surface setting is stored in the table storage unit 311 in step S84, the printer controller CPU 314 forms the gradation correction pattern 1104 on the recording medium 110 together with the user image based on the job (S86). In step S86, the printer controller CPU 314 sends a laser output signal to the engine control CPU 102 that controls the image forming engine unit 101 to form the user image and the gradation correction pattern 1104 on the recording medium 110.

The printer controller CPU 314 causes the line sensor 138 or 139 to read the gradation correction pattern 1104 (S87). In step S86, the engine control CPU 102 controls the line sensor 138 or 139 based on instructions from the printer controller CPU 314 to read the gradation correction pattern 1104 on the recording medium 110. The luminance signal of the line sensor 138 or 139 is converted to a density value. The printer controller CPU 314 acquires the density value transmitted from the engine control CPU 102. Then, the printer controller CPU 314 converts the density value based on the conversion table 140 or 141 corresponding to the line sensor 138 or 139 that read the gradation correction pattern 1104 (S88).

The printer controller CPU 314 generates a γLUT based on the density values converted in step S88 (S89), and determines whether the count value of the number of output sheets has reached the number of output sheets set in the job (S90). If the count value has reached the number of output sheets set in the job in step S90, it is determined that the last image based on the job has been formed, and the printer controller CPU 314 ends the image formation process.

On the other hand, if the count value has not reached the number of output sheets set in the job in step S90, the printer controller CPU 314 transitions the process to step S86. As a result, the image forming device 100 continues to repeatedly form the gradation correction pattern 1104 on the recording medium 110 together with the user image until the count value reaches the number of output sheets set in the job.

If execution of the second gradation correction process is not permitted in step S82, the printer controller CPU 314 forms the gradation correction pattern 1061 at a predetermined timing in order to execute the first gradation correction process (S90). The predetermined timing is, for example, the timing when 20 pages of images are formed. In step S90, the printer controller CPU 314 transmits a laser output signal for the gradation correction pattern 1061 to the engine control CPU 102 that controls the image forming engine unit 101 so that the engine control CPU 102 forms the gradation correction pattern 1061.

The printer controller CPU 314 causes the density sensor 117 to measure the gradation correction pattern 1061 (S92). In step S92, the engine control CPU 102 controls the density sensor 117 based on instructions from the printer controller CPU 314 to measure the gradation correction pattern 1061 on the recording medium 110. The output value (voltage) of the density sensor 117 is converted into a density value. The printer controller CPU 314 acquires the density value sent from the engine control CPU 102.

The printer controller CPU 314 generates a γLUT based on the density value acquired in step S92 (S93), and transitions the process to step S90. If the count value in step S90 has not reached the number of output sheets set in the job, the printer controller CPU 314 transitions the process to step S91. As a result, the image forming apparatus 100 forms the gradation correction pattern 1061 at each predetermined timing until the count value reaches the number of output sheets set in the job.

The gradation correction pattern 1104 is formed in the non-image area 1102 of the recording medium 110 (the edge area in the direction perpendicular to the transport direction in which the recording medium 110 is transported), so the formation of the user image is not interrupted for gradation correction. This makes it possible to reduce downtime in the second gradation correction process. The density values acquired in the second gradation correction process are converted into the measurement results of the measurement image on the intermediate transfer body 106, and a γLUT is generated based on the converted density values. This makes it easy to achieve stable image density regardless of the type of gradation correction.

It is also preferable to reacquire the conversion table depending on various conditions. The control parameters for each process of image transfer and fixing are changed according to the environmental conditions (temperature and humidity) in which the image forming apparatus 100 is installed. The control parameters are, for example, the value of the transfer voltage and the fixing temperature. This may cause a change in the correspondence relationship between the density of the image on the recording medium 110 (toner adhesion amount) and the density of the image on the intermediate transfer body 106 (toner adhesion amount). Therefore, the printer controller CPU 314 executes a conversion table generation process to update the conversion table, for example, every time 10,000 pages of images are formed.

In the image forming process shown in FIG. 8, only one of the first tone correction process and the second tone correction process is executed. However, the printer controller CPU 314 may control whether to execute only the first tone correction process without executing the second tone correction process, or whether to execute both the first tone correction process and the second tone correction process. If the execution of the second tone correction process is permitted in step S82, the printer controller CPU 314 executes both the first tone correction process and the second tone correction process. On the other hand, if the execution of the second tone correction process is not permitted in step S82, the printer controller CPU 314 executes only the first tone correction process. Since the target density of the first tone correction process and the target density of the second tone correction process are the same, even if both the first tone correction process and the second tone correction process are executed, it is possible to suppress a change in image density when the tone correction process is switched.

In addition, according to the image forming device 100, the reading results of the line sensor 138 or 139 are converted based on a conversion table corresponding to the paper discharge surface setting, so that the density of the image formed by the image forming device 100 can be controlled with high precision.

Example 2
The image forming apparatus 100 of this embodiment is similar to that of the embodiment 1. The image forming apparatus 100 of this embodiment creates and selects a conversion table in response to a user's selection of a line sensor to be used, rather than in response to a setting of the discharge surface of the recording medium 110.

The output of line sensors 138 and 139 decreases when, for example, toner or paper dust adheres to them. If toner or paper dust adheres to line sensors 138 and 139 and high-precision measurements cannot be performed, it is possible to adopt a configuration in which a usable line sensor is used.

At this time, as described in the first embodiment, regardless of the paper discharge surface setting selected by the user, it is necessary to create and select a conversion table corresponding to line sensor 138 or 139.

When one of the line sensors is unavailable and the conversion table for the available line sensor is valid, the image forming device 100 selects the conversion table corresponding to the available line sensor. In addition, the conversion table corresponding to the available line sensor may be retaken due to a change in the environment where the image forming device 100 is installed or an update to the control parameters of the image forming device 100. In this case, a density value conversion table corresponding to the available line sensor is created regardless of the paper output surface setting selected by the user.

The image formation process including the gradation correction process will be described with reference to the flowchart in FIG. 11. Note that steps S101 and S102 shown in FIG. 11 are the same as steps S81 and S82 shown in FIG. 8. Also, steps S105 to S110 and step S118 shown in FIG. 11 are the same as steps S84 to S90 shown in FIG. 8. Furthermore, steps S119 to S121 shown in FIG. 11 are the same as steps S91 to S93 shown in FIG. 8. Therefore, the description of each of the above steps will be omitted.

If execution of the second gradation correction process is permitted in step S102, the printer controller CPU 314 determines whether both line sensors 138 and 139 are available (S103). If both line sensors 138 and 139 are available in step S103, the printer controller CPU 314 checks the paper discharge side setting (S104).

On the other hand, if both line sensors 138 and 139 are not available in step S103, printer controller CPU 314 determines whether either line sensor 138 or 139 is available (S111). If line sensor 138 or 139 is available in step S111, printer controller CPU 314 checks the paper discharge surface setting (S112). Then, printer controller CPU 314 determines whether line sensor 138 or 139 used in the selected paper discharge surface setting can read gradation correction pattern 1104 (S113). If line sensor 138 or 139 used in step S113 can read gradation correction pattern 1104, printer controller CPU 314 transitions the process to step S105.

If neither line sensor 138 nor line sensor 139 can be used in step S111, printer controller CPU 314 causes operation panel 180 to display a screen notifying the user that the second gradation correction process (on-paper correction) cannot be performed (S114). Then printer controller CPU 314 transitions the process to step S119 and executes the first gradation correction process.

Also, if the gradation correction pattern 1104 cannot be read in step S113, the printer controller CPU 314 displays a selection screen on the operation panel 180 for selecting whether or not to perform the second gradation correction process (S115). The selection screen is a screen on which the user can select whether or not to change the paper discharge surface setting. The image forming apparatus 100 cannot perform the second gradation correction process unless the paper discharge surface setting is changed. The user can select on the selection screen whether to not perform the second gradation correction process or to change the paper discharge surface setting.

Next, the printer controller CPU 314 obtains user instruction information regarding the content selected by the user on the selection screen from the operation panel 180, and determines whether the second gradation correction process (on-paper correction) has been prioritized (S116). If the second gradation correction process (on-paper correction) has not been prioritized in step S116, that is, if a change to the paper output surface setting has not been instructed, the printer controller CPU 314 transitions the process to step S119 and executes the first gradation correction process.

On the other hand, if the second gradation correction process (on-paper correction) is prioritized in step S116, that is, if an instruction to change the paper discharge surface setting is given, the printer controller CPU 314 determines whether or not a conversion table is stored in the table storage unit 311 (S117). If the conversion table 140 or 141 for the usable line sensor 138 or 139 is not stored in the table storage unit 311 in step S117, the printer controller CPU 314 transitions the process to step S118. This causes the conversion table generation process to be executed, and the conversion table for the usable line sensor 138 or 139 is stored in the table storage unit 311.

Also, if conversion table 140 or 141 for usable line sensor 138 or 139 is stored in table storage unit 311 in step S117, printer controller CPU 314 transitions the process to step S106.

When the reading accuracy of one of line sensors 138 and 139 cannot be compensated for, image forming apparatus 100 notifies the user that the second gradation correction process cannot be performed with the paper discharge surface setting selected by the user. Furthermore, the user can select whether to perform the second gradation correction process using the other available line sensor in the subsequent operation, or to perform the image formation process by prioritizing the paper discharge surface setting, making it possible to perform an operation according to the situation. As described above, according to image forming apparatus 100 described in this embodiment, it is possible to display to the user the option of prioritizing the paper discharge surface setting or the second gradation correction process.

Example 3
The image forming apparatus 100 described in the first and second embodiments is described only in the case where a user image and a gradation correction pattern 1104 are formed on one side of the recording medium 110. In other words, only a job in which the image forming apparatus 100 forms an image on one side of the recording medium 100 (hereinafter referred to as a single-sided job) is described. However, the image forming apparatus 100 can also form images on both sides of the recording medium 110. Therefore, hereinafter, a gradation correction process when an image is formed based on a job in which the image forming apparatus 100 forms images on both sides of the recording medium 110 (hereinafter referred to as a double-sided job) will be described.

Here, in a single-sided job, the recording medium 110 passes through the fixing device 150 only once, whereas in a double-sided job, the recording medium 110 passes through the fixing device 150 twice. In other words, the effect of heat from the fixing device 150 differs between a single-sided job and a double-sided job. Therefore, the gradation correction pattern 1104 and the density of the user image may also differ between a single-sided job and a double-sided job. Therefore, the image forming apparatus 100 of this embodiment is characterized by having a single-sided conversion table and a double-sided conversion table in order to control the density of the output image with high precision for both a single-sided job and a double-sided job.

The process of generating the double-sided conversion table is performed when the recording medium 110 is output for the first time by the image forming apparatus 100. First, based on the instruction of the printer controller CPU 314, the engine control CPU 102 causes the image forming engine unit 101 to form a gradation adjustment pattern 1061 on the intermediate transfer body 106. Next, based on the instruction of the printer controller CPU 314, the engine control CPU 102 causes the density sensor 117 to measure the gradation correction pattern 1061 on the intermediate transfer body 106. As a result, the printer controller CPU 314 acquires the density value B of the gradation correction pattern 1061. Then, based on the instruction of the printer controller CPU 314, the engine control CPU 102 causes the image forming engine unit 101 to form a gradation correction pattern 1104 on the first side of the recording medium 110. When a double-sided job is executed, the conveying mechanism 130 conveys the recording medium 110 to the double-sided conveying path. As a result, the first side of the recording medium 110 conveyed on the conveying path 201 is read by the line sensor 139. Based on instructions from the printer controller CPU 314, the engine control CPU 102 causes the line sensor 139 to read the gradation correction pattern 1104 on the recording medium 110. The printer controller CPU 314 acquires the density value A of the gradation correction pattern 1104. The printer controller CPU 314 generates a double-sided density conversion table T3 based on the density value A and the density value B. When a double-sided job is executed, the printer controller CPU 314 converts the reading result of the gradation correction pattern 1104 into a density value based on the double-sided conversion table T3, and generates a γLUT based on the converted density value.

(Gradation correction control)
Next, the image forming process including the gradation correction process will be described with reference to the flowchart of Fig. 13. When the image forming apparatus 100 accepts an instruction to execute the image forming process based on a job, the printer controller CPU 314 reads out a program from the program ROM 304 and loads it in the RAM 310 to execute each step of Fig. 13.

Note that the processes in steps S901 and S902 shown in FIG. 13 are the same as the processes in steps S81 and S82 shown in FIG. 8. Also, the processes in steps S908 to S915 shown in FIG. 13 are the same as the processes in steps S86 to S93 shown in FIG. 8. Therefore, a description of each of the above steps will be omitted.

If execution of the second gradation correction process is permitted in step S902, the printer controller CPU 314 determines whether or not it is a double-sided job (S903). Note that the user selects whether it is a single-sided job or a double-sided job in the print settings when sending the job to the image forming device 100. The printer controller CPU 314 can determine whether it is a double-sided job or a single-sided job by obtaining information indicating whether it is a single-sided job or a double-sided job.

If it is determined in step S903 that it is a double-sided job, the printer controller CPU 314 determines whether or not the double-sided conversion table T3 is stored in the table storage unit 311 (S904). If the double-sided conversion table T3 is stored in the table storage unit 311 in step S904, the printer controller CPU 314 transitions the process to step S908. As a result, the image forming engine unit 101 forms a user image and a gradation correction pattern 1104 on the recording medium 1104 based on the double-sided job.

On the other hand, if the double-sided conversion table T3 is not stored in the table storage unit 311 in step S904, the printer controller CPU 314 executes the above-mentioned process of generating the double-sided conversion table T3. As a result, the double-sided conversion table T3 is stored in the table storage unit 311. Then, the printer controller CPU 314 transitions the process to step S908.

If it is determined in step S903 that the job is a single-sided job, the printer controller CPU 314 determines whether a conversion table (single-sided conversion table) corresponding to the paper discharge side setting described in the first embodiment is stored in the table storage unit 311 (S906). If a single-sided conversion table is stored in the table storage unit 311 in step S906, the printer controller CPU 314 transitions the process to step S908. As a result, the image forming engine unit 101 forms a user image and a gradation correction pattern 1104 on the recording medium 1104 based on the single-sided job.

On the other hand, if a single-sided conversion table is not stored in the table storage unit 311 in step S906, the printer controller CPU 314 executes the conversion table generation process shown in FIG. 7. This causes the single-sided conversion table to be stored in the table storage unit 311. The printer controller CPU 314 then transitions the process to step S908.

According to the image forming device 100 described in the third embodiment, both a single-sided conversion table and a double-sided conversion table are generated, so that the image density can be controlled with high precision, taking into account the density fluctuations caused by the heat of the fixing unit 150.

In addition, in the image forming apparatus 100 described in Example 3, the density value converted based on the single-sided conversion table is the same as the density value converted based on the double-sided conversion table. This makes it possible to suppress fluctuations in image density using the single-sided conversion table and the double-sided conversion table, even when an image is formed based on a job that includes a mixture of single-sided and double-sided jobs.

106 Intermediate transfer body 110 Recording medium 138 Line sensor 139 Line sensor 140 Conversion table 141 Conversion table 314 Printer controller CPU
1061 Gradation correction pattern 1104 Gradation correction pattern

Claims (5)

an image forming means for forming an image on a recording medium based on image forming conditions for controlling image density;
a reading means including a conveying path along which the recording medium is conveyed, a first reading unit that reads a pattern image formed on the recording medium conveyed on the conveying path from a first side with respect to the conveying path, and a second reading unit that reads the pattern image formed on the recording medium conveyed on the conveying path from a second side opposite to the first side with respect to the conveying path;
an intermediate transfer body onto which a measurement image formed by the image forming means is transferred;
a measuring means for measuring the measurement image transferred to the intermediate transfer body;
a generating unit that causes the image forming unit to form a pattern image on the recording medium and generates the image forming conditions based on a reading result of the pattern image by the reading unit;
another generating means for generating the first conversion condition and the second conversion condition;
having
The generating means includes:
When the first reading unit reads a pattern image formed on a surface of the recording medium facing the first reading unit, a first reading result of the pattern image by the first reading unit is converted based on a first conversion condition, and the image forming condition is generated based on the converted first reading result;
when the second reading unit reads a pattern image formed on a surface of the recording medium facing the second reading unit, a second reading result of the pattern image by the second reading unit is converted based on a second conversion condition different from the first conversion condition, and the image forming condition is generated based on the converted second reading result ;
The other generating means is
generating the first conversion condition based on a measurement result of the measurement image by the measurement means and a reading result of the measurement image on the recording medium read by the first reading unit;
generating the second conversion condition based on a measurement result of the measurement image by the measuring means and a reading result of the measurement image on the recording medium read by the second reading unit;
1. An image forming apparatus comprising: The image forming apparatus according to claim 1, characterized in that the reading means is disposed downstream of the image forming means in the transport direction in which the recording medium is transported. the image forming unit is capable of switching between face-up paper ejection, in which the surface on which the image is formed faces upward, and face-down paper ejection, in which the surface on which the image is formed faces downward;
the first reading unit reads the pattern image of the recording medium when the face-up paper ejection is performed;
3. The image forming apparatus according to claim 2 , wherein the second reading section reads the pattern image on the recording medium when the face-down paper ejection is performed. the image forming means has a fixing section that heats the recording medium to fix the image on the recording medium,
When the image forming unit executes a double-sided job for forming images on both sides of the recording medium, the pattern image on the recording medium passes through the fixing unit twice,
the generating means, when the second reading unit reads the pattern image of the recording medium in the double-sided job, converts a second reading result of the pattern image by the second reading unit based on a third conversion condition, and generates the image forming condition based on the converted second reading result;
2. The image forming apparatus according to claim 1, wherein the third conversion condition is different from both the first conversion condition and the second conversion condition. the image forming means has an image processing section which performs image processing on image data based on a gradation correction condition, and forms the image based on the image data which has been subjected to the image processing by the image processing section;
2. The image forming apparatus according to claim 1, wherein the image forming conditions are the tone correction conditions.

Images