JP2004038091A - Calibration method for density sensor and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To calibrate the sensor output of a color density sensor without using a reference member affected by contaminatipn caused by suspended toner particles at the time of being used for a long period of time. <P>SOLUTION: After an output signal of a specular reflection sensor 301a is calibrated on the basis of an output level obtained at the time of reading a surface of a transfer carrying belt 216 (s4), a black toner patch is formed on the transfer carrying belt 216 (s5), and the quantity of specularly reflected light of the toner patch is detected by the specular reflection sensor 301a (s6), and an image formation condition is adjusted on the basis of the sensor output at this time (s7). A black toner patch is formed in the image formation condition after adjustment (s8), and the quantity of diffusely reflected light of the toner patch is detected by a diffuse reflection sensor 301b (s9). The operation condition of the diffuse reflection sensor 301b is so adjusted that the sensor output of the diffuse reflection sensor 301b at this time may be approximated to reference values preliminarily set for three primary colors of subtractive process respectively. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for calibrating a density sensor for detecting the density of a toner image formed on an image carrier such as a photoreceptor or an intermediate transfer body in an electrophotographic image forming apparatus such as a copying machine or a printer, and the calibration thereof. The present invention relates to an image forming apparatus to which the method is applied.
[0002]
[Prior art]
Since an electrophotographic image forming apparatus uses electrostatic force to form an image, the electrical characteristics of the image forming unit are liable to change depending on use conditions and surrounding environmental conditions, and the density of the formed image fluctuates. Image quality is likely to be reduced. For this reason, the conventional image forming apparatus performs image quality adjustment (process control) to adjust control conditions (charge output, exposure amount, developing bias, transfer bias, and the like) of each part of the image forming unit, and always obtains good image quality. I am trying to be.
[0003]
In this image quality adjustment, a test toner patch was formed on an image carrier such as a photoconductor, an intermediate transfer body or a transfer body at a predetermined timing not involved in image formation, and the image density of the toner patch was measured by a density sensor. Adjust the control condition based on the value. The density sensor is an optical sensor having a light emitting element and a light receiving element, and the reflected light of the light emitted from the light emitting element toward the toner patch is received by the light receiving element.
[0004]
Recently, a color image forming apparatus that forms not only an achromatic (black) toner image but also a chromatic (color) toner image on an image carrier has been widely used. In the case of a color image forming apparatus, when color image quality is adjusted using a color toner patch formed on the surface of an image carrier by a developing device, specularly reflected light from a black toner patch is detected to accurately measure the amount of adhered toner. Unlike the monochrome image quality adjustment, a method of detecting diffuse reflection from a toner patch has been proposed.
[0005]
As described above, in the color image forming apparatus that measures the density of the toner patch by different methods when adjusting the monochrome image quality and when adjusting the color image quality, a monochrome density sensor that receives specularly reflected light and a color density sensor that receives diffusely reflected light are used. Regardless of whether the density sensor is provided separately or both are provided integrally, there are the following problems in calibrating the sensor output that is affected by the change over time in the sensor performance of the density sensor.
[0006]
That is, since the density sensor for monochrome, which receives specularly reflected light, always measures the density of the toner patch based on the amount of reflected light on the surface of the image carrier, the sensor output is calibrated even if the sensor performance changes over time. It is possible to do. On the other hand, since the sensor output of the color density sensor that receives diffuse reflection light increases in proportion to the density of the toner patch, if there is no reference value of the sensor output corresponding to the known toner adhesion amount, When the sensor performance changes over time, it is difficult to calibrate the sensor output change and accurately measure the toner adhesion amount.
[0007]
Therefore, in the conventional color image forming apparatus, when adjusting the color image quality, light is emitted from the light emitting element of the color density sensor to a portion where the toner patch is not formed on the surface of the image carrier, and the diffuse reflection light is emitted. There is a type in which the sensor output is calibrated by irradiating the toner patch with light from the light emitting element with the irradiation light amount adjusted based on the sensor output when the light is detected by the light receiving element.
[0008]
[Problems to be solved by the invention]
However, in general, the amount of diffusely reflected light on the surface of the image carrier is very small. Therefore, during color image quality adjustment, the amount of diffusely reflected light on the surface of the image carrier where no toner patch is formed is determined based on the amount of diffusely reflected light received. When the sensor output of the color density sensor is calibrated, a calibration error may increase. Further, the calibration error increases due to contamination or damage of the surface of the image carrier.
[0009]
For this reason, it is conceivable to provide a reference member used for calibrating the sensor output. However, if the reference member is fixedly arranged at a position facing the density sensor, floating toner or the like inside the device adheres to the reference member itself. Staining occurs, and the optical reflection characteristics of the reference member change, making it impossible to accurately calibrate the sensor output.
[0010]
On the other hand, the reference member is provided to be able to advance and retreat between the exposure position and the retreat position, and the reference member is opposed to the concentration sensor at the exposure position only when it is necessary to calibrate the sensor output. There is also a proposal to store it, but a mechanism for moving the reference member between the exposure position and the retreat position is required, and the structure becomes complicated and large, which only leads to an increase in cost. Further, since the reference member is disposed in the apparatus, it is not possible to avoid contamination by floating toner during long-term use.
[0011]
SUMMARY OF THE INVENTION It is an object of the present invention to calibrate a sensor output of a color density sensor without using a reference member affected by contamination by floating toner during long-term use, and to provide a sensor for a color density sensor when sensor performance is deteriorated. An object of the present invention is to provide a method for calibrating a density sensor that can easily and accurately calibrate an output, and an image forming apparatus to which the method is applied.
[0012]
[Means for Solving the Problems]
The present invention has the following configuration in order to solve the above problems.
[0013]
(1) a step of forming a first achromatic toner pattern on an image carrier, a step of measuring the image density of the first achromatic toner pattern using a first optical sensor that detects the amount of specular reflection, A step of performing image quality adjustment for an achromatic image based on a comparison result between the image density of the chromatic toner pattern and a predetermined reference value for achromatic color, a step of forming a second achromatic toner pattern on the image carrier, and a step of diffusion. Measuring the image density of the second achromatic toner pattern using a second optical sensor for detecting the amount of reflected light; and determining the image density of the second achromatic toner pattern and a predetermined color for the three primary colors of the subtractive mixture. The step of calibrating the sensor output of the second optical sensor based on the comparison result with the reference value is performed in this order.
[0014]
In this configuration, the image density of the first achromatic toner pattern is measured using a first optical sensor that detects the amount of specular reflection, and the measurement result is compared with a predetermined reference value for achromatic color. The image quality adjustment for the achromatic image is performed, and the image density of the second achromatic toner pattern formed in the state where the image quality is adjusted is measured using the second optical sensor that detects the diffuse reflection light amount, The sensor output of the second optical sensor is calibrated based on a result of comparison between the measurement result and a predetermined reference value for the three subtractive primary colors. Therefore, by measuring the predetermined reference values for the achromatic color and the subtractive color mixture in advance, a calibration plate for calibrating the sensor output of the sensor for detecting the amount of diffuse reflection light is not required, and the image is not required. The image density sensor is accurately calibrated without being affected by the surface condition of the carrier.
[0015]
(2) a step of forming a first achromatic toner pattern on the image carrier, a step of measuring the image density of the first achromatic toner pattern using a first optical sensor that detects the amount of specular reflection, A step of performing image quality adjustment for an achromatic image based on a comparison result between the image density of the chromatic toner pattern and a predetermined reference value for achromatic color, a step of forming a second achromatic toner pattern on the image carrier, and a step of diffusion. Measuring the image density of the second achromatic toner pattern using a second optical sensor that detects the amount of reflected light; and performing a second process on the toner pattern image based on the image density of the second achromatic toner pattern. Wherein the light emission amount of the light emitting means of the optical sensor is calibrated.
[0016]
In this configuration, the image density of the first achromatic toner pattern is measured using a first optical sensor that detects the amount of specular reflection, and the measurement result is compared with a predetermined reference value for achromatic color. The image quality adjustment for the achromatic image is performed, and the image density of the second achromatic toner pattern formed in the state where the image quality is adjusted is measured using the second optical sensor that detects the diffuse reflection light amount, The light emission amount of the light emitting means of the second optical sensor is calibrated based on a result of comparison between the measurement result and a predetermined reference value for the three subtractive primary colors. Therefore, by measuring the predetermined reference values for the achromatic color and the subtractive color mixture in advance, a calibration plate for calibrating the sensor output of the sensor for detecting the amount of diffuse reflection light is not required, and the image is not required. The image density sensor is accurately calibrated without being affected by the surface condition of the carrier. In addition, the sensor output of the image density sensor is easily and accurately calibrated by calibrating the light emission amount of the light emitting means of the second optical sensor.
[0017]
(3) A first optical sensor for measuring the image density of the first achromatic toner pattern formed on the image carrier from the detection result of the amount of specularly reflected light, and a high-density second achromatic color after image quality adjustment A second optical sensor for measuring the image density of the toner pattern image from the detection result of the amount of diffusely reflected light, and comparing the image density of the first achromatic toner pattern with a predetermined reference value for the achromatic image; The image quality adjustment for the achromatic color is performed based on the image density of the second achromatic toner pattern image and the sensor of the second optical sensor based on the comparison result between the image density of the second achromatic color toner pattern image and the predetermined reference value for the three primary colors of the subtractive color mixture. Control means for calibrating the output is provided.
[0018]
In this configuration, the image density of the first achromatic toner pattern is measured using a first optical sensor that detects the amount of specular reflection, and the measurement result is compared with a predetermined reference value for achromatic color. The image quality adjustment for the achromatic image is performed, and the image density of the second achromatic toner pattern formed in the state where the image quality is adjusted is measured using the second optical sensor that detects the diffuse reflection light amount, The sensor output of the second optical sensor is calibrated based on a result of comparison between the measurement result and a predetermined reference value for the three subtractive primary colors. Therefore, by measuring the predetermined reference values for the achromatic color and the subtractive color mixture in advance, a calibration plate for calibrating the sensor output of the sensor for detecting the amount of diffuse reflection light is not required, and the image is not required. The image density sensor is accurately calibrated without being affected by the surface condition of the carrier.
[0019]
(4) The control means calibrates the light emission amount of the light emitting means of the second optical sensor with respect to the toner pattern image based on the image density of the second achromatic toner pattern.
[0020]
In this configuration, the image density of the first achromatic toner pattern is measured using a first optical sensor that detects the amount of specular reflection, and the measurement result is compared with a predetermined reference value for achromatic color. The image quality adjustment for the achromatic image is performed, and the image density of the second achromatic toner pattern formed in the state where the image quality is adjusted is measured using the second optical sensor that detects the diffuse reflection light amount, The light emission amount of the light emitting means of the second optical sensor is calibrated based on a result of comparison between the measurement result and a predetermined reference value for the three subtractive primary colors. Therefore, by measuring the predetermined reference values for the achromatic color and the subtractive color mixture in advance, a calibration plate for calibrating the sensor output of the sensor for detecting the amount of diffuse reflection light is not required, and the image is not required. The image density sensor is accurately calibrated without being affected by the surface condition of the carrier. In addition, the sensor output of the image density sensor is easily and accurately calibrated by calibrating the light emission amount of the light emitting means of the second optical sensor.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a schematic front sectional view showing a configuration of a digital color copying machine which is an image forming apparatus according to an embodiment of the present invention. The copying machine body 1 according to the embodiment of the present invention includes a document table 111 and an operation panel (not shown) on an upper surface, and includes an image reading unit 110, an image forming unit 210, and a paper feeding unit 211 therein. The upper surface of the document table 111 is covered with a double-sided automatic document feeder (RADF: Reversing Automatic Document Feeder) 112 so as to be openable and closable.
[0022]
The RADF 112 conveys the document so that the first side of the document faces the image reading unit 110 at a predetermined position on the document table 111 when the double-sided reading mode is set on the operation panel of the copying machine body 1. After the image reading for the surface is completed, the front and back sides of the original are turned over, the original is conveyed such that the second surface faces the image reading unit 110 at a predetermined position on the original platen 111, and the image reading on both sides is completed. The document is discharged, and the double-sided conveyance operation for the next document is executed.
[0023]
The image reading unit 110 is arranged below the document table 111 for reading an image from a document on the document table 111 by the RADF 112. The image reading unit 110 includes first and second scanning units 113 and 114 that reciprocate in parallel along the lower surface of the document table 111, an optical lens 115, and a photoelectric conversion element (CCD) line sensor 116.
[0024]
The first scanning unit 113 has an exposure lamp for exposing the surface of the original image, and a first mirror for deflecting a reflected light image from the original in a predetermined direction. Reciprocate at scanning speed. The second scanning unit 114 has second and third mirrors for further deflecting the reflected light image from the document deflected by the first mirror of the first scanning unit 113 in a predetermined direction. Reciprocates in parallel with the lower surface of the document 111 at half the speed of the scanning unit 113 of FIG.
[0025]
The optical lens 115 reduces the reflected light image from the document deflected by the third mirror of the second scanning unit 114, and forms the reduced light image on the light receiving surface of the CCD line sensor 116.
[0026]
The CCD line sensor 116 sequentially photoelectrically converts the formed light image and outputs it as an electric signal. The CCD line sensor 116 is a three-line color CCD capable of reading a black-and-white image or a color image and outputting line data separated into R (red), G (green), and B (blue) color components. . The document image information converted into an electric signal by the CCD line sensor 116 is converted into digital data, subjected to predetermined image processing by an image processing unit (not shown), and supplied to the image forming unit 210 as image data.
[0027]
In the image forming unit 210, a transfer / conveyance belt mechanism 213 is disposed below. The transfer / transport belt mechanism 213 stretches an endless transfer / transport belt 216 between a driving roller 214 and a driven roller 215. The transfer conveyance belt 216 is an image bearing member of the present invention, and rotates the paper P in the image forming unit 210 by electrostatically adsorbing the paper P on the outer surface at the upper part in the circulation loop and rotating in the direction of the arrow Z. . A toner patch detection unit 300 is provided at a position facing the outer surface of a portion of the transfer conveyance belt 216 that contacts the drive roller 214.
[0028]
A fixing device 217 having a pair of a heating roller and a pressure roller is disposed downstream of the transfer and transport belt mechanism 213. The sheet P to which the toner image has been transferred during the transfer by the transfer and transfer belt 216 is heated and pressed in the fixing device 217, and the toner image is melted and pressed to be fixed firmly on the sheet P. The sheet P that has passed through the fixing device 217 is discharged through a switching gate 218 by a discharge roller 219 onto a discharge tray 220 attached to the outer wall of the copying machine main body 1.
[0029]
The switching gate 218 selectively switches the transport path of the sheet P after passing through the fixing device 217 toward the discharge tray 220 or the switchback transport path 221. When forming an image on the first side of the sheet P in the double-sided image forming mode in which images are formed on both sides of the sheet, the switching gate 218 switches the sheet conveying path after passing through the fixing device 217 toward the switchback conveying path 221. The sheet P on which an image is formed on one side is re-conveyed into the image forming unit 210 with the front and back sides reversed, after the front and rear ends of the sheet P are reversed in the switchback conveyance path 221.
[0030]
Above the transfer belt mechanism 213 in the image forming unit 210, first to fourth image forming stations Pa to Pd are arranged in order from the upstream side to the downstream side of the sheet conveying path. Each of the image stations Pa to Pd has substantially the same configuration. As an example, each image station Pa is provided with a photosensitive drum 222a rotatably in the direction of arrow F, and uniformly covers the surface of the photosensitive drum 222a around the photosensitive drum 222a along the rotation direction of the photosensitive drum 222a. Charger 223a, a developing device 224a for developing an electrostatic latent image formed on the surface of the photosensitive drum 222a into a toner image, and a transfer device for transferring the toner image carried on the surface of the photosensitive drum 222a to the paper P And a cleaning device that removes toner remaining on the surface of the photosensitive drum 222a. Above the photosensitive drum 222a, a laser scanning unit (LSU) 227a is provided. The LSU 227a is a semiconductor laser (not shown) that irradiates a laser beam modulated based on image data supplied from the image processing unit of the image reading unit 110, and outputs a laser beam from the semiconductor laser at a constant angular velocity in the main scanning direction. It comprises a polygon mirror 240a that deflects, an fθ lens 241a that deflects the laser light deflected by the polygon mirror 240a at a constant speed, and mirrors 242 and 243 that distribute the deflected laser light to the surface of the photosensitive drum 222a. ing.
[0031]
In each of the image stations Pa to Pd, each of LSUs 227a to 227d is supplied with image data of a black component, a cyan component, a magenta component, and a yellow component of document image information. And yellow toner are stored. Accordingly, in each of the image stations Pa to Pd, an electrostatic latent image of a black component, a cyan component, a magenta component, and a yellow component is formed on the surface of each of the photosensitive drums 222a to 222d, and black, cyan, magenta, and yellow toners are respectively formed. Developed into an image.
[0032]
Further, between the registration roller 212 and the first image forming station Pa in the paper transport path, a paper suction charger 228 is provided. The paper suction charger 228 charges the surface of the transfer conveyance belt 216. The paper P supplied from the paper feeding mechanism 211 is attracted to the surface of the transfer / transport belt 216 by electrostatic force, and is transported in a stable state between the first image forming station Pa and the fourth image forming station Pd.
[0033]
Prior to the image forming operation in each of the image forming stations Pa to Pd, the sheet feeding unit 211 separates the sheets P stored in the sheet cassette one by one and conveys the sheets P toward the image forming unit 210. Feed paper on the road. The fed sheet P is temporarily stopped in a state where the front ends thereof are brought into contact with a pair of registration rollers 212 which stop rotating before the image forming unit 210. The registration roller 212 starts rotating at a timing synchronized with the image forming operation in each of the image forming stations Pa to Pd, and the front end of the paper P is transferred to each of the photosensitive drums 222 a to 222 d in each of the image forming stations Pa to Pd. And the front ends of the toner images carried on the surfaces of the photosensitive drums 222a to 222d. The toner images of the respective colors are sequentially superimposed on the surface of the sheet P that is electrostatically attracted onto the transfer conveyance belt 216 and passes through the image stations Pa to Pd.
[0034]
In the above configuration, the LSUs 227a to 227d are used as writing means for irradiating a laser beam modulated by image data to form an electrostatic latent image on the surface of the photosensitive drums 222a to 222d. An LED head including a light emitting diode array and an imaging lens array may be used. The LED head is smaller in size than the LSU, and has no moving parts, so it is silent. Therefore, it can be suitably used in an image forming apparatus such as a tandem type digital color copying machine which requires a plurality of writing means.
[0035]
In order to obtain a high-quality full-color image in a tandem-type electrophotographic digital color copying machine as shown in FIG. 1, it is required that the image density of each color is appropriate and stable. For this reason, in addition to the normal image forming mode, a mode (hereinafter, referred to as a process control mode) for appropriately setting the image density of each color is provided.
[0036]
In the process control mode, the image carrier (here, the transfer conveyance belt 2165 includes an intermediate transfer body such as a photoconductor, an intermediate transfer drum or an intermediate transfer belt, or a transfer body such as a transfer drum or a transfer belt). A toner patch serving as a density reference is formed thereon, and the density (toner adhesion amount) of the toner patch is detected by an image density sensor as an optical detecting means. Based on the detected density, the charging potential and the exposure intensity are determined. Feedback is applied to parameters (image forming conditions) that affect image density, such as a developing bias potential, a transfer voltage, and a toner replenishing amount (in the case of a two-component developer).
[0037]
That is, in the process control mode, an electrostatic latent image of a toner patch, which is a pattern having a constant area of, for example, about 20 mm square, is formed on the photosensitive drums 222a to 222d, and is developed with a predetermined developing contrast voltage. Then, the obtained toner patches are transferred to the surface of the transfer and conveyance belt 216 for each color, and the density of the toner patches of each color formed on the transfer and conveyance belt 216 is detected by the toner patch detection unit 300.
[0038]
FIG. 2 is a diagram showing a configuration of a main part of an image forming unit in the digital color copying machine. As described above, in the digital color copying machine 1, the toner patch detection unit 300 is disposed to face the surface of the transfer belt 216 and at a predetermined distance from the surface. In the process control mode, the toner patch detection unit 300 detects the amount of toner attached to the toner patch T, which is a test toner image formed on the surface of the transfer belt 216.
[0039]
The toner patch detection unit 300 includes a regular reflection type image density sensor (regular reflection type sensor) 301a as a first optical sensor of the present invention and a diffuse reflection type as a second optical sensor on a circuit board 302. The image density sensor (diffuse reflection type sensor) 301b is mounted. Each of the regular reflection sensor 301a and the diffuse reflection sensor 302b is an LED having a center wavelength of 970 nm, which is a light emitting element for irradiating the toner patch T on the transfer conveyance belt 216 with light, and a light receiving element for receiving the reflected light. It is a known optical sensor having a photodiode.
[0040]
As shown in FIG. 3A, the regular reflection sensor 301a receives a regular reflection light amount, which decreases with an increase in the image density of the toner patch T of the light of the light emitting element 311a, by the light receiving element 312a. As shown in FIG. 3B, the diffuse reflection type sensor 301b decreases in the case of black toner and increases in the case of color toner as the image density of the toner patch T of light from the light emitting element 311b increases. The amount of reflected light is received and detected by the light receiving element 312b. Light incident on the photodiodes of the reflection sensor 301a and the diffuse reflection sensor 302b generates a current depending on the amount of received light, and the photodiode outputs a voltage signal corresponding to the current.
[0041]
In this embodiment, the density detection of the patch image is performed using the transfer conveyance belt. However, the present invention is not limited to this, and the present invention can be applied to an intermediate transfer type image forming apparatus. Further, the density of the patch image may be detected on a photosensitive drum (image carrier) instead of the transfer / conveying belt.
[0042]
3C, a light emitting element 311c for irradiating the toner patch T with light, a light receiving element 312c for detecting the amount of regular reflection light, and a diffuse reflection light, as shown in FIG. It is also possible to use a single optical sensor 301c in which the light receiving element 313c for detecting the amount of light is integrated.
[0043]
FIG. 4 is a diagram illustrating a relationship between the image density of the toner patch and the output of the image density sensor. FIG. 4A shows the specular reflection component density Da based on the element output of the specular reflection type image density sensor (specular reflection sensor) and the diffuse reflection component density Db based on the element output of the diffuse reflection type image density sensor. And the image density of the toner pattern (toner adhesion amount). The regular reflection light component density Da indicated by a solid line in the drawing decreases as the toner adhesion amount increases, and tends to be saturated when the toner adhesion amount exceeds a predetermined amount.
[0044]
FIG. 4B shows the saturation characteristics of the element output based on the regular reflection light of the toner patches of Y (yellow), M (magenta), C (cyan) and K (black). For any of the colors, when the toner adhesion amount increases, the element output of the specular reflection light saturates, and therefore, when trying to detect the toner adhesion amount based only on the specular reflection component concentration, the dynamic range becomes smaller. I have.
[0045]
FIG. 4C shows the influence of contamination of the light receiving surface on the output of the image density sensor on the toner patch detection unit. Since the image density sensor of the toner patch detection unit 300 detects the density of the unfixed toner image, there is a high possibility that the light receiving surface of the image density sensor is stained by floating toner or the like. When the light receiving surface of the image density sensor becomes dirty, the element output of the regular reflection type image density sensor decreases from Da to Da ', and the element output of the diffuse reflection type image density sensor decreases from Db to Db'.
[0046]
FIGS. 5A and 5B show the relationship between the image density (the amount of toner attached to the toner patch) and the sensor output of the regular reflection type image density sensor and the diffuse reflection type sensor for the color toner patch and the black toner patch. FIG. As shown in FIG. 5A, in the regular reflection type image density sensor, when the toner adhesion amount of the color toner patch increases by a certain amount or more, the sensor output does not change. Further, as shown in FIG. 5B, in the diffuse reflection type sensor, the change in the sensor output of the black toner patch is small irrespective of the toner adhesion amount.
[0047]
FIG. 6 is a block diagram of a control unit of the digital color copying machine. The control unit 2 of the digital color copying machine 1 includes a density calculation unit 31, a developing unit control unit 32, an image density control unit 35, a light amount controller 36, a reference pattern signal generator 38, and a signal processing unit 39. The density calculation unit 31 calculates a corrected density signal containing no error by performing a predetermined calculation on the density signal output from the regular reflection type sensor 301a and the diffuse reflection type sensor 301b of the toner patch detection unit 300.
[0048]
The developing device controller 32 generates a control signal for controlling the developing condition of the toner image based on the corrected density signal output from the density calculator 31 and rotates the developing roller of the developing device 6 at a predetermined rotation speed. The driving motor 33 and a dispenser motor 34 for adjusting the toner supply amount from the dispenser containing unused toner to the developing device 6 to a predetermined amount are output.
[0049]
The image density control unit 35 creates a control signal for controlling the forming condition of the electrostatic latent image based on the corrected density signal output from the density calculation unit 31, and controls the light amount controller 36, the grid power supply 37 and the reference pattern signal generator 38. Output to The light amount controller 36 controls the light amount of the laser light emitted from the LSUs 242a to 242d based on a control signal output from the image density control unit 35. The grid power supply 37 applies a voltage to grids of the chargers 223a to 223d based on a control signal output from the image density controller 36. The reference pattern signal generator 38 generates a reference pattern signal for forming a 20 mm × 20 mm toner patch on the photosensitive drums 222 a to 222 d based on the control signal output from the image density control unit 35.
[0050]
In the normal image forming processing mode, the control unit 2 performs predetermined image processing on the input image data in the signal processing unit 39, and supplies the image data after the image processing to the LSUs 242a to 242d.
[0051]
FIG. 7 is a flowchart showing a processing procedure of the control unit of the digital color copying machine. When a predetermined initialization process after the power is turned on is completed, the control unit 2 of the digital color copying machine 1 waits for an instruction input to execute an image forming process, and determines whether it is time to execute process control during the standby. A determination is made (s1, s2). The execution timing of the process control refers to the time after the power is turned on, before the start of the first image forming process, and when the predetermined number of image forming processes are completed or when the number of rotations of the developing roller in the image forming process reaches the predetermined number. Etc. are predetermined timings.
[0052]
If it is the execution timing of the process control, the control unit 2 first activates a process control program for a black image (s3), and sets the output level when the surface of the transfer conveyance belt 216 is read by the regular reflection sensor 301a. After calibrating the output signal of the specular reflection sensor 301a based on the calibration (s4), a black toner patch is formed on the transfer conveyance belt 216 (s5). The control unit 2 detects the regular reflection light amount of the black toner patch formed on the transfer conveyance belt 216 by the regular reflection sensor 301a (s6), and forms an image based on the sensor output of the regular reflection sensor 301a at this time. The conditions are adjusted (s7).
[0053]
Next, the control unit 2 forms a black toner patch used for calibrating the sensor output of the diffuse reflection sensor 301b under the adjusted image forming conditions (s8), and uses the diffuse reflection light amount in the toner patch as the diffuse reflection sensor. Detected by 301b (s9). The control unit 2 adjusts the operating conditions of the diffuse reflection sensor 301b so that the sensor output of the diffuse reflection sensor 301b at this time approaches the preset reference value for each of the three subtractive primary colors (s10). ).
[0054]
Note that the correlation between the sensor output in s9 and the reference values for the three primary colors of subtractive color mixing, that is, after the detection result of the black toner patch by the regular reflection sensor 301a and after the image forming conditions are adjusted using black Is determined by repeating measurement and the like in advance.
[0055]
This association is performed by the following first to fourth procedures. In the first procedure, the regular reflection sensor 301a is adjusted so that the regular reflection sensor 301a detects the regular reflection light of the base of the transfer / transport belt 216, and the sensor output at this time becomes a value corresponding to the density 0. The light output of the regular reflection sensor 301a is adjusted by controlling the current value of the light emitting element 311a in the regular reflection sensor 301a.
[0056]
As a process control for a black image, which is a second procedure, a plurality of black toner patches are formed on the transfer / conveying belt 216 in a state where image forming conditions such as a developing bias voltage and / or a charging grid voltage are gradually changed. The regular reflection type sensor 301a of the light emission output determined in the first procedure detects the regular reflection light amount from the toner patch.
[0057]
As a third procedure, based on the image forming conditions in which a plurality of black toner patches are created in the second procedure, a sensor output (target reflection output) having a predetermined ratio to the sensor output from the substrate of the transfer conveyance belt 216 is formed. ) Is calculated by calculation. That is, in FIG. 8A, the sensor output V0 and the target reflection output Vn (n = 1, 2, 3) when the density of the toner patch is “0” (the base of the transfer conveyance belt 216) have a predetermined ratio. Therefore, the developing bias voltage VBn and / or the charging grid voltage VGn required to realize the toner patch density IDn for obtaining the target reflection output Vn are calculated.
[0058]
The sensor output obtained from the plurality of toner patches in the second procedure is only an approximate value of the target reflection output Vn, and is not always an accurate target reflection output. However, since there is a correlation between the density of the toner patch, which is an approximate value thereof, and the image forming conditions such as the developing bias voltage and / or the charging grid voltage, the image forming conditions corresponding to the target reflection output are calculated backward. You can ask. For example, since it is known from the data table of FIG. 8B that the target reflection output appears near any one of V1 to V3, the corresponding charging grid VG and / or developing bias voltage VB are proportionally changed. It can be obtained by distribution or the like.
[0059]
As adjustment of the sensor output of the diffuse reflection type sensor 301b which is the fourth procedure, a black toner patch is formed on the transfer conveyance belt 216 under the image forming conditions determined in the third procedure, and the diffuse reflection type sensor 301b performs The amount of diffuse reflection is detected, and the current value of the light emitting element 311b in the diffuse reflection sensor 301b is adjusted to control the light emission output of the diffuse reflection sensor 301b so that a target diffuse reflection output is obtained. The amount of diffuse reflection of the black toner patch to be actually detected by the diffuse reflection sensor 301b is very small, and the amount of information obtained is small. For this reason, in order to prevent a reading error from occurring, the current value to be applied to the light emitting element 311b is increased by m times (for example, about 3 times), and when the process control for the color image is executed, the current value is obtained. A current that is (1 / m) times the current value supplied is supplied to the light emitting element 311b, and the diffuse reflection sensor 301b detects the amount of diffuse reflection light.
[0060]
Thereafter, the control unit 2 activates a process control program for a color image which is a subtractive color mixture of three primary colors (s11), and forms toner patches of the subtractive color mixture of the three primary colors (s12). The controller 2 detects the amount of diffusely reflected light of the toner patches of the three subtractive primary colors formed on the transfer / conveyor belt 216 by the diffuse reflection type sensor 301b (s13), and based on the sensor output, performs subtractive color mixture. The image forming conditions for the three primary colors are adjusted (s14).
[0061]
When the process control for the black image and the color image is completed by the above processing, the control unit 2 returns to a state of waiting for the input of the execution command of the image forming process (s14 → s1), and the execution command of the image forming process is input. Then, the image forming process is executed (s15).
[0062]
As described above, after adjusting the image forming conditions of the black image by the black process control using the regular reflection sensor 301a, the density of the black toner patch created again is detected using the diffuse reflection sensor 301b, The operating condition of the diffuse reflection sensor 301b (specifically, the light emission amount of the light emitting element 311b of the diffuse reflection sensor 301b) is determined based on the relationship between this detection result and the density of the black toner patch detected using the regular reflection sensor 301a. ) Is adjusted (the diffuse reflection sensor 301b is calibrated), and then the color image forming conditions are adjusted by creating a color toner patch and detecting its density with the diffusion sensor 301b. Calibration of the diffuse reflection sensor 301b in which the calibration (calibration) error becomes large can be performed without using a calibration plate.
[0063]
【The invention's effect】
According to the present invention, the following effects can be obtained.
[0064]
(1) The image density of the first achromatic toner pattern is measured using a first optical sensor that detects the amount of specular reflection, and the measurement result is compared with a predetermined reference value for achromatic color to determine the achromatic color. The image quality of the image is adjusted, and the image density of the second achromatic toner pattern formed with the image quality adjusted is measured using a second optical sensor that detects the amount of diffusely reflected light. A calibration plate is required to calibrate the sensor output of the sensor that detects the amount of diffusely reflected light by calibrating the sensor output of the second optical sensor based on the result of comparison with a predetermined reference value for the three mixed colors. It is possible to accurately calibrate the sensor output of the image density sensor without being influenced by the surface condition of the image carrier, and to always obtain a high-quality image by always improving the image forming state. But Kill.
[0065]
(2) The image density of the first achromatic toner pattern is measured using a first optical sensor for detecting the amount of specular reflection, and the measurement result is compared with a predetermined reference value for achromatic color to compare the achromatic color. The image quality of the image is adjusted, and the image density of the second achromatic toner pattern formed with the image quality adjusted is measured using a second optical sensor that detects the amount of diffusely reflected light. Calibration for calibrating the sensor output of the sensor for detecting the amount of diffusely reflected light by calibrating the light emission amount of the light emitting means of the second optical sensor based on the result of comparison with the predetermined reference value for the three mixed colors. A plate is not required, and the image density sensor can be accurately calibrated without being influenced by the surface state of the image carrier, and the image forming state can always be improved, so that a high-quality image can be stably obtained. Further, by calibrating the light emission amount of the light emitting means of the second optical sensor, it is possible to easily and accurately calibrate the sensor output of the image density sensor.
[Brief description of the drawings]
FIG. 1 is a schematic front sectional view showing a configuration of a digital color copying machine which is an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram showing a configuration of a main part of an image forming unit in the digital color copying machine.
FIG. 3 is a diagram showing a configuration of an image density sensor used in a toner patch detection unit of the digital color copying machine.
FIG. 4 is a diagram illustrating a relationship between an image density of a toner patch and an output of an image density sensor.
FIG. 5 is a diagram illustrating a relationship between an image density (amount of toner attached to the toner patch) and sensor outputs of a regular reflection type image density sensor and a diffuse reflection type sensor for a color toner patch and a black toner patch.
FIG. 6 is a block diagram of a control unit of the digital color copying machine.
FIG. 7 is a flowchart showing a processing procedure of a control unit of the digital color copying machine.
FIG. 8 is a diagram illustrating a relationship between a toner patch density and a sensor output of a diffuse reflection sensor, and a relationship between a sensor output of the diffuse reflection sensor and image forming conditions.
[Explanation of symbols]
1- Digital color copier (image forming apparatus)
2-Control unit (control means)
216-Transfer Conveying Belt (Image Carrier)
300-toner patch detection unit
301a-Specular reflection sensor (first optical sensor)
301b—Diffuse reflection sensor (second optical sensor)

Claims (4)

Forming a first achromatic toner pattern on the image carrier, measuring an image density of the first achromatic toner pattern using a first optical sensor for detecting the amount of specular reflection, achromatic toner pattern Performing image quality adjustment for an achromatic image based on a comparison result between the image density of the image and a predetermined reference value for achromatic color, forming a second achromatic toner pattern on the image carrier, Measuring the image density of the second achromatic toner pattern using the second optical sensor to be detected; and determining the image density of the second achromatic toner pattern and a predetermined reference value for the three primary colors of subtractive color mixing. A step of calibrating the sensor output of the second optical sensor based on the comparison result in the above order. Forming a first achromatic toner pattern on the image carrier, measuring an image density of the first achromatic toner pattern using a first optical sensor for detecting the amount of specular reflection, achromatic toner pattern Performing image quality adjustment for an achromatic image based on a comparison result between the image density of the image and a predetermined reference value for achromatic color, forming a second achromatic toner pattern on the image carrier, Measuring the image density of the second achromatic toner pattern using the second optical sensor to be detected, and using the second optical sensor for the toner pattern image based on the image density of the second achromatic toner pattern A method for calibrating an optical sensor, comprising calibrating a light emission amount of a light emitting unit of the sensor. A first optical sensor that measures the image density of the first achromatic toner pattern formed on the image carrier from the detection result of the amount of specularly reflected light, and a high-density second achromatic toner pattern image after image quality adjustment A second optical sensor for measuring the image density of the first achromatic toner pattern from the detection result of the amount of diffused reflected light, based on a comparison result between the image density of the first achromatic toner pattern and a predetermined reference value for the achromatic image. The image quality adjustment for coloring is performed, and the sensor output of the second optical sensor is calibrated based on a comparison result between the image density of the second achromatic toner pattern image and a predetermined reference value for the three subtractive primary colors. An image forming apparatus, comprising: 5. The image forming apparatus according to claim 4, wherein the control unit calibrates a light emission amount of the light emitting unit of the second optical sensor with respect to the toner pattern image based on an image density of the second achromatic toner pattern. 6. apparatus.

Images