JP2023014913A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that reduces the entire time required for a calibration operation while maintaining the reading accuracy of an optical sensor.SOLUTION: An image forming apparatus 100 comprises: a reader 160 that reads an image formed on recording paper; a white reference plate that is used for calibration of the reader 160; and a controller 110 that performs calibration of the reader 160 with black shading adjustment performed by causing the reader 160 to read the white reference plate in a first state and white shading adjustment performed by causing the reader 160 to read the white reference plate in a second state. The controller 110 performs the black shading adjustment at a longer execution interval than the white shading adjustment.SELECTED DRAWING: Figure 1

Description

The present invention relates to an image forming apparatus that reads an image printed on a printed material and performs processing for stabilizing the quality of the image formed based on the read result.

In an image forming apparatus that forms images using an electrophotographic process, the characteristics of each process of charging, developing, transferring, and fixing change due to aging and environmental changes, and the image density and color of the image formed on the printed matter change. It can change. Therefore, image stabilization control is performed in the image forming apparatus. Image stabilization control uses an optical sensor to detect a detection image for image density detection formed on the image carrier, and based on the detection result, performs image formation so that the image printed on the printed matter has an appropriate image density. It is a control that adjusts the conditions. The image forming conditions are various settings at the time of image formation, such as the charge amount of the image carrier and the emission energy amount of the laser that scans the image carrier.

Image stabilization control is control performed based on the image density of an image before it is transferred to recording paper. Therefore, the change in image density of the image after being transferred to the recording paper is not controlled. For example, fluctuations in transfer efficiency when transferring an image from a photosensitive member or an intermediate transfer member to recording paper due to the influence of environmental fluctuations affect the image density of the image after being transferred to the recording paper. For this reason, the image stabilization control described above does not stabilize the image density of the image formed on the final printed matter.

On the other hand, Patent Document 1 discloses an image forming apparatus that forms an image for detecting image density on recording paper, detects the image for detecting with an optical sensor after the image is fixed, and adjusts the image density based on the detection result. disclose. The detection image is formed in an area on the recording paper where an image (user image) corresponding to the print job is formed. Since the detection image is formed on the same recording paper as the user image, real-time image density adjustment is possible each time image formation is performed according to a print job.

A line sensor such as a CCD (Charge Coupled Device) or a CIS (Contact Image Sensor) is employed as the optical sensor. The line sensor performs the reading operation of the detection image after the output value is adjusted by the calibration operation using the white reference plate, thereby making it possible to measure the image density with high accuracy.

JP-A-2012-53089

In a configuration in which an image formed on a recording sheet by an image forming apparatus is read by a line sensor, the line sensor is affected by heat generated by the recording sheet. When temperature fluctuations occur in the line sensor due to fanning heat, the light emission amount of the line sensor and thermal deformation of internal optical components occur. This causes a decrease in reading accuracy of the line sensor. It is possible to prevent such deterioration in reading accuracy by increasing the frequency of the calibration operation. However, the detection image cannot be read during the calibration operation. Therefore, an increase in the frequency of calibration operations leads to a decrease in real-time adjustment of image density.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a main object of the present invention is to provide an image forming apparatus that reduces the overall time required for calibration while maintaining the reading accuracy of the optical sensor.

The image forming apparatus of the present invention comprises reading means for reading an image formed on a recording sheet, a reference plate used for calibration of the reading means, and the reading means reading the reference plate in a first state. a control unit that performs the calibration of the reading unit by a first calibration operation and a second calibration operation that is performed by causing the reading unit to read the reference plate in a second state; The control means is characterized in that the first calibration operation is performed at longer execution intervals than the second calibration operation.

According to the present invention, it is possible to shorten the entire time required for the calibration operation while maintaining the reading accuracy of the reading means.

FIG. 3 is a configuration explanatory diagram of a printing system; 1 is a configuration diagram of an image forming apparatus; FIG. FIG. 4 is an explanatory diagram of the configuration of a reader; FIG. 4 is a configuration explanatory diagram of a line sensor; Explanatory drawing of the output change of a line sensor. FIG. 4 is an exemplary diagram of an image for detecting image density; 4 is a flowchart showing image density detection processing;

Hereinafter, embodiments will be described in detail with reference to the drawings. It should be noted that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are essential to the solution of the invention.

(printing system)
FIG. 1 is a configuration explanatory diagram of a printing system including an image forming apparatus of this embodiment. A printing system 1 includes an image forming apparatus 100 and a host computer 101 . Image forming apparatus 100 and host computer 101 are communicably connected via network 105 . The network 105 is composed of a communication line such as a LAN (Local Area Network), a WAN (Wide Area Network), or a public communication line. A plurality of image forming apparatuses 100 and host computers 101 may be connected to the network 105 .

The host computer 101 is, for example, a server device, and transmits print jobs to the image forming apparatus 100 via the network 105 . A print job includes various information necessary for printing, such as image data, the type of recording paper used for printing, the number of prints, and instructions for double-sided or single-sided printing.

The image forming apparatus 100 includes a controller 110 , an operation panel 120 , a paper feeding section 140 , a printer 150 and a reader 160 . Controller 110 , operation panel 120 , paper feeder 140 , printer 150 , and reader 160 are communicably connected to each other via system bus 116 . The image forming apparatus 100 controls the operation of the printer 150 based on the print job acquired from the host computer 101 by the controller 110, and forms an image on recording paper according to the image data.

Controller 110 controls the operation of each unit of image forming apparatus 100 . The controller 110 is an information processing device that includes a ROM (Read Only Memory) 112 , a RAM (Random Access Memory) 113 , and a CPU (Central Processing Unit) 114 . The controller 110 has a communication control unit 111 and a storage 115 . Each module is communicatively connected to each other via a system bus 116 .

The communication control unit 111 is a communication interface that communicates with the host computer 101 and other devices via the network 105 . The storage 115 is a large-capacity storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive). The storage 115 stores computer programs and various data used for image forming processing (printing processing). CPU 114 executes computer programs stored in ROM 112 and storage 115 to control operations of image forming apparatus 100 . RAM 113 provides a work area when CPU 114 executes a computer program.

The operation panel 120 is a user interface and has an input interface and an output interface. The input interface is, for example, an operation button, ten keys, touch panel, or the like. The output interface is, for example, a display such as an LCD (Liquid Crystal Display), a speaker, or the like. A user can input print jobs, commands, print settings, and the like to the image forming apparatus 100 through the operation panel 120 . The operation panel 120 displays a setting screen and the state of the image forming apparatus 100 on the display.

The paper feed unit 140 includes a plurality of paper feed trays (to be described later) that accommodate recording paper. The paper feed unit 140 feeds the type of recording paper instructed by the print job from a paper feed tray that accommodates the recording paper. A plurality of sheets of recording paper (bundle of recording paper) are accommodated in the paper feed tray, and are fed in order from the topmost recording paper. The paper feed unit 140 conveys the recording paper fed from the paper feed tray to the printer 150 . Each paper feed tray may contain the same type of recording paper, or may contain different types of recording paper.

The printer 150 prints an image on recording paper supplied from the paper feed unit 140 based on the image data included in the print job to generate a printed matter. The reader 160 is an image reading device that reads an image from printed matter generated by the printer 150 and transmits the reading result to the controller 110 . The image read by the reader 160 is an image (detection image) for adjusting image forming conditions when the printer 150 forms an image. The controller 110 detects an image state such as image quality from the reading result of the detection image by the reader 160, and adjusts the image forming conditions based on the detected image state. In this embodiment, the controller 110 adjusts the image forming conditions based on the image density detected from the detection image.

(Image forming device)
FIG. 2 is a configuration diagram of the image forming apparatus 100. As shown in FIG. The image forming apparatus 100 includes paper feed trays 140a to 140e, a printer 150, a reader 160, and a finisher 190 in order from the upstream side in the recording paper transport direction. The paper feed trays 140 a to 140 e constitute the paper feed section 140 . The finisher 190 is a post-processing device that performs post-processing on printed matter generated by the printer 150 . The finisher 190 performs, for example, staple processing, sort processing, or cutting processing (to be described later) on a plurality of printed materials.

Printer 150 includes a plurality of image forming units that form images of different colors. The printer 150 of this embodiment includes four image forming units to form four-color images of yellow (Y), magenta (M), cyan (C), and black (K). Each image forming unit differs only in the color of the image to be formed, and performs the same operation with the same configuration.

One image forming unit includes a photosensitive drum 153 , charger 220 , exposure device 223 and developer 152 . The photosensitive drum 153 is a drum-shaped photosensitive member having a photosensitive layer on its surface, and is rotationally driven in an arrow R1 direction by a motor (not shown) about a drum shaft. The charger 220 charges the surface (photosensitive layer) of the rotating photosensitive drum 153 . The exposure device 223 exposes the charged surface of the photosensitive drum 153 with laser light. The laser light scans the surface of the photosensitive drum 153 in the axial direction of the photosensitive drum 153 . The direction in which the laser beam scans the surface of the photosensitive drum 153 is the main scanning direction of the printer 150 (depth direction in FIG. 2). An electrostatic latent image is thereby formed on the surface of the photosensitive drum 153 . The developing device 152 develops the electrostatic latent image using developer (toner). As a result, an image (toner image) in which the electrostatic latent image is visualized is formed on the surface of the photosensitive drum 153 .

The printer 150 includes an intermediate transfer belt 154 onto which toner images produced by each image forming unit are transferred. The intermediate transfer belt 154 is rotationally driven in the arrow R2 direction. A toner image of each color is transferred from the photosensitive drum 153 at timing according to the rotation of the intermediate transfer belt 154 . As a result, a full-color toner image is formed on the intermediate transfer belt 154 in which the toner images of the respective colors are superimposed. The full-color toner image is conveyed to the nip formed by the intermediate transfer belt 154 and the transfer roller 221 as the intermediate transfer belt 154 rotates. A full-color toner image is transferred to the recording paper by the nip portion.

Recording paper is housed in paper feed trays 140a, 140b, 140c, 140d, and 140e of paper feed section 140, and is fed according to the timing of image formation by each image forming unit. The paper feed source from which the recording paper is fed is specified by the print job. The recording paper is conveyed to the nip portion at the timing when the full-color toner image is conveyed to the nip portion formed by the intermediate transfer belt 154 and the transfer roller 221 . As a result, the toner image is transferred to a predetermined position on the recording paper. The conveying direction of the recording paper is the sub-scanning direction perpendicular to the main scanning direction.

The printer 150 includes a first fixing device 155 and a second fixing device 156 that fix the toner image on the recording paper by applying heat and pressure. The first fixing device 155 includes a fixing roller containing a heater and a pressure belt for pressing the recording paper against the fixing roller. The fixing roller and pressure belt are driven by a motor (not shown) to nip and convey the recording paper. The second fixing device 156 is arranged downstream of the first fixing device in the recording paper transport direction. The second fixing device 156 is used to increase the gloss of the image on the recording paper that has passed through the first fixing device 155 and to secure fixability. The second fixing device 156 includes a fixing roller containing a heater and a pressure roller containing a heater. The second fixing device 156 is not used depending on the type of recording paper. In this case, the recording paper is not conveyed to the second fixing device 156 but is conveyed to the conveying path 130 . Therefore, a flapper 131 is provided downstream of the first fixing device 155 to guide the recording paper to either the conveying path 130 or the second fixing device 156 .

A transport path 135 and an ejection path 139 are provided downstream of the position where the transport paths 130 join on the downstream side of the second fixing device 156 . For this reason, a flapper 132 for guiding the recording paper to either the transport path 135 or the discharge path 139 is provided downstream of the second fixing device 156 at the position where the transport path 130 joins. The flapper 132 guides the recording paper with the image formed on the first side to the transport path 135 in, for example, the double-sided printing mode. The flapper 132 guides the recording paper with the image formed on the first side to the ejection path 139 in, for example, the face-up ejection mode. The flapper 132 guides the recording paper with the image formed on the first side to the transport path 135 in, for example, the face-down paper discharge mode.

The recording paper conveyed to the conveying path 135 is conveyed to the reversing section 136 . The recording paper conveyed to the reversing section 136 is switched back to reverse the conveying direction after the conveying operation is temporarily stopped. The recording paper is guided from the reversing section 136 to either the transport path 135 or the transport path 138 by the flapper 133 . The flapper 133 guides the switched-back recording paper to the transport path 138 for printing the image on the second side, for example, in the double-sided printing mode. The recording paper conveyed to the conveying path 138 is conveyed toward the nip portion between the intermediate transfer belt 154 and the transfer roller 221 . As a result, the recording paper is turned upside down when passing through the nip portion, and image formation is performed on the second surface. The flapper 133 guides the switched back recording paper to the transport path 135 in, for example, the face-down paper discharge mode. The recording paper transported to transport path 135 by flapper 133 is guided to discharge path 139 by flapper 134 .

A recording sheet on which an image has been formed by the printer 150 is conveyed from the ejection path 139 to the reader 160 . The reader 160 is an image reading device that reads an image for detecting image density formed on recording paper. A user image corresponding to the print job is printed on the recording paper together with the detection image. The recording paper conveyed from the printer 150 to the reader 160 is conveyed through a conveying path 313 inside the reader 160 . The reader 160 includes a document detection sensor 311 and line sensor units 312 a and 312 b on a transport path 313 . Between the line sensor unit 312a and the transport path 313, a scanning glass 314a and a white reference plate 315a are arranged. Between the line sensor unit 312b and the transport path 313, a scanning glass 314b and a white reference plate 315b are arranged. The reader 160 reads the detection image printed on the recording paper by means of the line sensor units 312 a and 312 b while conveying the recording paper to the conveyance path 313 .

The document detection sensor 311 is, for example, an optical sensor having a light emitting element and a light receiving element. A document detection sensor 311 detects the leading edge of the recording paper conveyed on the conveying path 313 in the conveying direction. A detection result of the leading edge of the recording paper by the document detection sensor 311 is transmitted to the controller 110 . The controller 110 starts the reading operation by the reader 160 (line sensor units 312 a and 312 b ) based on the detection timing of the leading edge of the recording paper by the document detection sensor 311 .

The line sensor units 312a and 312b read the detection image formed on the recording paper being conveyed. The detection image is printed on both the front and back sides of the recording paper. The line sensor units 312a and 312b are provided at positions sandwiching the transport path 313 in order to read the detection images formed on both sides of the sheet in one pass. When performing image density adjustment, the image forming apparatus 100 reads detection images by the line sensor units 312a and 312b, and detects image densities of both the front side and the back side from the reading result. The controller 110 controls the image forming process based on the detection result of the image density so that the image printed on the printed material to be output has an appropriate image density. The line sensor units 312a and 312b are driven by a drive unit (not shown) to move the white reference plates 315a and 315b to a readable position during a calibration operation, which will be described later, and move the recording paper to a readable position during image density detection. do.

(leader)
FIG. 3 is an explanatory diagram of the configuration of the reader 160. As shown in FIG. The reader 160 includes an image memory 303 and an image density detection processing section 305 in addition to the line sensor units 312 a and 312 b and the document detection sensor 311 . The CPU 114 of the controller 110 controls the operations of the line sensor units 312a and 312b, the image memory 303, the image density detection processor 305, and the document detection sensor 311. FIG.

The line sensor units 312a, 312b include line sensors 301a, 301b, memories 300a, 300b, and AD converters 302a, 302b. Line sensors 301a and 301b are, for example, CIS. The memories 300a and 300b store correction information such as variations in the amount of light between pixels of the corresponding line sensors 301a and 301b, steps between pixels, and distances between pixels. AD converters 302a and 302b acquire analog signals that are results of reading by line sensors 301a and 301b. The AD converters 302 a and 302 b convert the acquired analog signals into digital signals and transmit the digital signals to the image density detection processing unit 305 . The digital signal is R (red), G (green), and B (blue) image data.

The image density detection processing unit 305 calculates the average value (average luminance value) of the RGB luminance values of the detection image portion from the RGB image data acquired from the line sensor units 312a and 312b. The image density detection processing unit 305 transmits the calculated average luminance value to the CPU 114 . The image density detection processing unit 305 is composed of a semiconductor device such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). An image memory 303 stores image data necessary for image processing in the CPU 114 .

(line sensor)
FIG. 4 is an explanatory diagram of the configuration of the line sensor 301a. The line sensor 301b also has a similar configuration. The line sensor 301a is an optical sensor that includes light emitting units 400a and 400b, light guides 402a and 402b, a lens array 403a, and a sensor chip group 401. FIG. The line sensor 301a has a substantially rectangular parallelepiped shape and reads an image with its longitudinal direction as the main scanning direction.

The light emitting units 400a and 400b are light sources configured by, for example, LEDs (Light Emitting Diodes) that emit white light. The light guide 402a has a light emitting portion 400a disposed at its end, and irradiates the recording paper with light emitted from the light emitting portion 400a. The light guide 402b has a light emitting portion 400b arranged at its end, and irradiates the recording paper with light emitted from the light emitting portion 400b. The light guides 402a and 402b are formed linearly in the main scanning direction. Therefore, the line sensor 301 irradiates light linearly in the main scanning direction. The main scanning direction of the line sensor unit 312 and the main scanning direction of the printer 150 are the same.

The lens array 403a is an optical system that guides the reflected light from the recording paper of the light emitted from the light emitting units 400a and 400b to the sensor chip group 401a. The sensor chip group 401a is a light receiving unit in which a plurality of photoelectric conversion elements (sensor chips) are arranged linearly in the main scanning direction. One sensor chip reads an image of one pixel. The plurality of sensor chips of this embodiment has a 3-line configuration. One line is coated with an R (red) color filter, another line is coated with a G (green) color filter, and another line is coated with a B (blue) color filter. be done. The light guided by the lens array 403a forms an image on the light receiving surface of each sensor chip of the sensor chip group 401a.

The light emitted from the light emitting portions 400a and 400b diffuses inside the light guides 402a and 402b, and is emitted from the curved portions to illuminate the entire area of the recording paper in the main scanning direction. The light guides 402a and 402b are arranged with the lens array 403a interposed therebetween in the sub-scanning direction perpendicular to the main scanning direction. For this reason, the line sensor 301a has a double-side illumination configuration that irradiates the lens array 403a (image reading line) with light from two directions in the sub-scanning direction. The sub-scanning direction of the line sensor unit 312a and the sub-scanning direction of the printer 150 are the same.

(Calibration operation)
A calibration operation of the line sensors 301a and 301b will be described. Although the calibration operation for the line sensor 301a will be described here, the calibration operation for the line sensor 301b is also performed in the same manner.

There are two types of calibration operations depending on the states of the light emitting units 400a and 400b (here, light emitting states).
In the first calibration operation, the white reference plate 315a is read while the light emitting units 400a and 400b emit light to irradiate the white reference plate 315a, and the output value of each pixel (sensor chip) becomes the target value. This is an operation to correct as follows. In this embodiment, such calibration performed by emitting light from the light emitting units 400a and 400b is referred to as "white shading adjustment". There are three types of correction methods: adjustment of the light emission time of the light emitting units 400a and 400b, adjustment of the reading time of the line sensor 301a, and correction using a digital correction value (difference from the target value). In this embodiment, the light emission time of the light emitting units 400a and 400b and the reading time of the line sensor 301a are set in advance. Therefore, in the white shading adjustment, correction is performed using a digital correction value.

The second calibration operation reads the white reference plate 315a with the light emitting units 400a and 400b turned off, and corrects the output value of each pixel (sensor chip) to a predetermined value (for example, 0 [V]). This is an operation called correction. In the present embodiment, such calibration performed with the light emitting units 400a and 400b turned off is referred to as "black shading adjustment". By performing the white shading adjustment and the black shading adjustment, the line sensor 301a can accurately detect the image density.

White shading adjustment and black shading adjustment are performed before reading the detection image. The controller 110 executes white shading adjustment and black shading adjustment at predetermined time intervals. During such calibration (white shading adjustment and black shading adjustment), the detection image reading operation is stopped. Therefore, the real-time performance of image density adjustment is degraded.

FIG. 5 is an explanatory diagram of output changes of the line sensor 301a when white shading adjustment is performed after black shading adjustment. When shading adjustment is required, the line sensor unit 312a moves to the reading position of the white reference plate 315a, and black shading adjustment is performed with the light emitting units 400a and 400b turned off. After that, the line sensor unit 312a performs white shading adjustment by turning on the light emitting units 400a and 400b. Immediately after the light emitting units 400a and 400b are turned on, the output of the line sensor 301a fluctuates because the amount of light emitted is not stable. Therefore, the white shading adjustment needs to be performed after a predetermined time has passed since the light emitting units 400a and 400b are turned on. This waiting time increases the time required for the calibration operation.

On the other hand, black shading adjustment is less affected by environmental changes than white shading adjustment. Although this depends on the structure of the line sensor 301a, white shading adjustment has more factors related to components of the line sensor 301a than black shading. Therefore, black shading adjustment need not be performed as frequently as white shading adjustment. Therefore, by lengthening the time interval for black shading adjustment compared to white shading adjustment, it is possible to reduce the time required for the calibration operation. For example, white shading adjustment is performed every 5 minutes, and black shading adjustment is performed every 10 minutes. This makes it possible to reduce the overall time required for the calibration operation compared to the case where the black shading adjustment and the white shading adjustment are performed at the same time intervals.

(Image for detection of image density)
FIG. 6 is an exemplary diagram of an image for detecting image density formed on a recording sheet. In this embodiment, a detection image is added to the user image corresponding to the print job. When image formation is performed according to a print job, the line sensor units 312a and 312b read detection images from all recording sheets. The controller 110 adjusts the image density based on the reading results of the detection images by the line sensor units 312a and 312b. Therefore, it is possible to adjust the image density in real time.

The shaded area is the print area for the user image. A detection image is formed along the edge of the recording paper. In FIG. 6, detection images are formed on both ends of the recording paper in the main scanning direction. As for the detection image, two-color test images 601 and 602 are formed along one side, and other two-color test images 603 and 604 are formed along the other side. The test images 601 to 604 of this embodiment are four colors of yellow, magenta, cyan, and black, but are not limited to this. Test images 601 to 604 for each color are printed with priority over the user image.

Test images 601 to 604 are formed by combining images whose image densities are changed stepwise. In FIG. 6, each of test images 601 to 604 is configured by arranging seven images in the sub-scanning direction. The images at both ends in the sub-scanning direction have the same image density, and the image density is the highest. The areas where the test images 601 to 604 are formed are the areas that are finally cut by the finisher 190 . Therefore, the detection image is not printed on the final printed matter.

A predetermined range around the test images 601 to 604 is a white background. In the white background portion, the distance from the user image to the test images 601 to 604 is longer in the sub-scanning direction than in the main scanning direction. That is, the white background portion in the conveying direction of the recording paper is larger than the white background portion in the reading direction of the recording paper. As a result, the influence of reflection from the user image when the detection image is read becomes constant. Note that the positions of the test images 601 to 604 in FIG. 6 are just an example, and are not limited to this.

(Image density detection processing)
FIG. 7 is a flowchart showing image density detection processing. This processing is performed when image forming processing is performed. Here, the process is started when the user inputs instructions such as the document size and the print mode from the operation panel 120 .

The CPU 114 acquires an instruction from the operation panel 120, and based on the instruction, sets information necessary for a print job to each device, and saves various parameters included in the instruction in the RAM 113, thereby performing mode setting. (S500). After setting the mode, the CPU 114 waits for a copy start instruction from the operation panel 120 (S501: N).

When the CPU 114 acquires the copy start instruction (S501: Y), it starts print processing. After starting the printing process, the CPU 114 initializes the page count value P to 0 (S502). The page count value P represents the number of sheets of recording paper on which the image is printed. Next, the CPU 114 performs calibration operations (black shading adjustment and white shading adjustment) for the line sensor units 312a and 312b (S503). When the calibration operation ends, the CPU 114 initializes both the first timer T1 for white shading adjustment and the second timer T2 for black shading adjustment to 0 (S504). After the initialization, the CPU 114 starts clocking by the first timer T1 and the second timer T2.

In the copy process, the image forming apparatus 100 reads an image of a document using a scanner (not shown). The CPU 114 causes the printer 150 to print the document image read by the scanner on recording paper together with the detection image (S505). The recording paper on which the image is formed is conveyed from printer 150 to reader 160 . A document detection sensor 311 of the reader 160 detects the leading edge of the recording paper conveyed from the printer 150 . The signal value of the output signal of the document detection sensor 311 changes by detecting the leading edge of the recording paper. The CPU 114 increments the page count value P by 1 according to the change in the signal value of the output signal of the document detection sensor 311 (S506).

Triggered by a change in the signal value of the output signal of the document detection sensor 311, the CPU 114 uses the line sensor units 312a and 312b and the image density detection processing unit 305 to detect the image density of the detection image printed on the recording paper. (S507). Note that the luminance value may be detected instead of the image density here. Based on the detected image density, the CPU 114 derives a correction value for correcting the density deviation of the image density (S508). Based on this correction value, the image forming conditions are adjusted to stabilize the image density in the next printing. The correction value is the difference in the detected image density with respect to the reference image density value.

The CPU 114 that derived the correction value determines whether or not the time measured by the first timer T1 is equal to or longer than the first predetermined time Ttar1 (S509). When the time measured by the first timer T1 is less than the first predetermined time Ttar1 (S509: N), the CPU 114 determines whether the page count value P is equal to or greater than the predetermined image density detection end number Pmax ( S511). The detection end number Pmax is a preset number. If the page count value P is less than the image density detection end number Pmax (S511: N), the CPU 114 repeats the processing from S505. If the page count value P is greater than or equal to the image density detection completion number Pmax (S511: Y), the CPU 114 terminates the process.

When the time measured by the first timer T1 is equal to or longer than the first predetermined time Ttar1 (S509: Y), the CPU 114 determines whether or not the time measured by the second timer T2 is equal to or longer than the second predetermined time Ttar2 (S510). ). The second predetermined time Ttar2 is longer than the first predetermined time Ttar2.

When the time measured by the second timer T2 is equal to or longer than the second predetermined time Ttar2 (S510: Y), the CPU 114 executes black shading adjustment and white shading adjustment (S512). After executing the black shading adjustment and the white shading adjustment, the CPU 114 initializes the first timer T1 and the second timer T2 to 0 (S513), and performs the process of S511.

When the time counted by the second timer T2 is less than the second predetermined time Ttar2 (S510: N), the CPU 114 executes only white shading adjustment (S514). After executing the white shading adjustment, the CPU 114 initializes the first timer T1 to 0 (S515) and performs the processing of S511.

Thus, when the second predetermined time Ttar2 longer than the first predetermined time Ttar1 has passed, black shading adjustment and white shading adjustment are performed. When a time longer than the first predetermined time Ttar1 and shorter than the second predetermined time Ttar2 has elapsed, only white shading adjustment is performed. That is, the white shading adjustment is performed at intervals of the first predetermined time Ttar1, and the white shading adjustment and the black shading adjustment are performed at intervals of the second predetermined time Ttar2.

In this way, the white shading adjustment execution interval is set shorter than the black shading adjustment execution interval. Therefore, the number of times of black shading adjustment is reduced and the overall time required for calibration is shortened compared to the case where black shading adjustment and white shading adjustment are performed each time calibration is performed. On the other hand, in this embodiment, the white shading adjustment is more susceptible to environmental changes than the black shading adjustment. Since the white shading adjustment is performed more frequently than the black shading adjustment, the influence of environmental changes on the line sensor units 312a and 312b is suppressed. Therefore, the image density adjustment is performed based on the accurate detection result of the detection image by the line sensor units 312a and 312b, and accurate image density adjustment is realized.

In this embodiment, an example in which the white shading adjustment execution interval is shorter than the black shading adjustment execution interval has been described, but this relationship may be reversed. That is, the execution interval of black shading adjustment may be shorter than the execution interval of white shading adjustment. This also reduces the overall time required for calibration.

Which of the execution intervals of the black shading adjustment and the white shading adjustment is to be shortened is determined by the degree of influence of environmental changes on the detection accuracy of the line sensor units 312a and 312b. By shortening the execution interval and frequently performing the shading adjustment that is more influenced by the environmental change, the influence of the environmental change on the detection accuracy of the line sensor units 312a and 312b is reduced.

Although the image density adjustment has been described in the present embodiment, the present embodiment can be applied even when other image forming conditions are adjusted. That is, (1) the printer 150 forms a detection image for image forming condition adjustment on recording paper. (2) The detection image formed on the recording paper is detected by the line sensor units 312a and 312b. (3) Adjust the image forming conditions based on the detection results of the detection images by the line sensor units 312a and 312b. As long as the image forming conditions are adjusted by the processes (1) to (3) above, the application of the present embodiment enables high-precision adjustment in a short period of time.

Claims (7)

reading means for reading the image formed on the recording paper;
a reference plate used for calibration of the reading means;
The reading means performs a first calibration operation by causing the reading means to read the reference plate in a first state and a second calibration operation to be performed by causing the reading means to read the reference plate in a second state. and a control means for performing the calibration of
The control means performs the first calibration operation at a longer execution interval than the second calibration operation,
Image forming device. The reading means comprises light emitting means and light receiving means,
The reading means reads the reference plate in a state in which the light emitting means emits light to irradiate the reference plate with light in the first state, and reads the reference plate in a state in which the light emitting means is extinguished in the second state. characterized by reading a board,
The image forming apparatus according to claim 1. The reading means comprises light emitting means and light receiving means,
The reading means reads the reference plate in the first state with the light emitting means turned off, and reads the reference plate in the second state with the light emitting means emitting light and irradiating the reference plate with light. characterized by reading a board,
The image forming apparatus according to claim 1. further comprising image forming means for forming an image on the recording paper based on predetermined image forming conditions;
The control means derives a correction value used for adjusting the image forming conditions based on a reading result of the detection image for adjusting the image forming conditions formed on the recording paper by the reading means. characterized by
The image forming apparatus according to any one of claims 1 to 3. The control means causes the image forming means to form the detection image and an image corresponding to the print job on the recording paper, and causes the reading means to read the detection image formed on the recording paper. characterized by
5. The image forming apparatus according to claim 4. The image forming means forms the detection image with priority over the image corresponding to the print job on the recording paper,
6. The image forming apparatus according to claim 5. It further comprises cutting means for cutting the area where the detection image is formed from the recording paper after the detection image is read by the reading means,
The image forming apparatus according to any one of claims 4 to 6.

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