JP2006184318A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and an image forming method, for detecting toner concentration with high accuracy, in an image forming apparatus for performing formation of a color image, utilizing a flash fixing method. <P>SOLUTION: Toner concentration on a recording medium 12 or on an image carrier 20 can be detected with high accuracy, by illuminating light (infrared light) in the absorption wavelength region of an infrared-absorbing agent contained in the toner as detection light 60 from an LED 62 onto a surface 12A and detecting the specularly reflected light from the surface 12A. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and an image forming method, and more particularly, to an image forming apparatus and an image forming method for forming a color image using a flash fixing method.

  In an electrophotographic image forming apparatus such as a copying machine or a printer, a toner image is electrostatically formed on the surface of a latent image carrier such as a photosensitive drum, and this is transferred onto a recording sheet by a transfer body and transferred. The toner image is fixed on the recording paper. In this series of image forming processes, it is necessary to prevent fluctuations in environmental conditions such as temperature and humidity, and fluctuations in image density due to changes over time.

  To control the image forming process, for example, a test toner patch is formed on the surface of the latent image carrier, the density of the toner patch is detected by a density sensor, and the density of the toner image is controlled based on the detection result. So-called process control is performed to control toner image density.

  In the density sensor, light is emitted from an LED emitting in the infrared region of 800 nm to 950 nm, the reflected light is detected by a light receiving element, and the current toner density is determined by the relationship between a preset amount of toner and the light receiving output. It is detected (Patent Documents 1 to 5). As shown in FIG. 8, generally, monochrome toner and color toner have different light absorption characteristics. Monochrome toner absorbs light in the infrared region, but color toner does not absorb light in the infrared region. For this reason, as shown in FIG. 9, the toner density is detected by receiving regular reflection light in the case of monochrome toner, and the toner density is detected by receiving diffuse reflection light in the case of color toner.

In recent years, there is a gradual increase in color needs for high-capacity image forming apparatuses using a flash fixing system. Color image formation by electrophotography is realized by superimposing toner images of C, M, Y (and K) colors, but the amount of toner transferred to the recording medium increases with colorization. become. In the flash fixing method, the flash lamp is intermittently turned on, and flash light emitted from the flash lamp is irradiated at the time of turning on to melt the powder toner and fix the toner image. Therefore, in a color image forming apparatus using a flash fixing method, process control for controlling the density of a toner image becomes more important.
JP-A-5-93689 JP-A-10-63048 JP 2000-39746 A JP 2000-81740 A JP 2001-108618 A

  However, as described above, the conventional color image forming apparatus receives the diffusely reflected light and detects the toner concentration, so that there is a problem that the toner concentration cannot be detected accurately. That is, since the diffuse reflected light is much less than the regular reflected light, it is necessary to greatly amplify the received light signal. However, the amplification increases the noise and decreases the S / N ratio, or the toner. Therefore, there is a problem that it is difficult to detect the output of only the toner because it is easily affected by the image carrier and the recording medium.

  Further, the conventional color image forming apparatus requires two types of density sensors, a density sensor for monochrome toner and a density sensor for color toner, and the cost is high.

  Furthermore, it is conceivable to detect the density of the color toner by irradiating light from the LED that emits light in the visible region and receiving the specularly reflected light. However, the LED that emits light in the visible region is expensive. Because the visible absorption peaks differ, light emitting elements / light receiving elements as many as the number of colors are required. When receiving visible light, the light is affected by room light. There were problems such as being necessary on the device side.

  The present invention has been made to solve the above problems, and an object of the present invention is to accurately detect toner density in an image forming apparatus that forms a color image using a flash fixing method. An object is to provide an image forming apparatus. Another object of the present invention is to provide an image forming method capable of accurately detecting the toner density in an image forming method for forming a color image using a flash fixing method.

  In order to achieve the above object, an image forming apparatus of the present invention includes a charging unit for charging an image carrier, and irradiating the image carrier charged by the charging unit with a light beam according to image data. An electrostatic latent image forming means for forming an electrostatic latent image; a developing means for developing the electrostatic latent image using a color toner containing an infrared absorber; and an image carrier developed by the developing means. A transfer unit that transfers a toner image to a recording medium; a fixing unit that flash-fixes the toner image on the recording medium transferred by the transfer unit; and an absorption wavelength region of the infrared absorbent on the image carrier or the recording medium And density detecting means for detecting the toner density on the image carrier or the recording medium by detecting the intensity of the regularly reflected reflected light.

  In the image forming apparatus of the present invention, the charging unit charges the image carrier, and the electrostatic latent image forming unit irradiates the image carrier charged by the charging unit with a light beam in accordance with the image data. An electrostatic latent image formed with an image is formed using a color toner containing an infrared absorber. The transfer unit transfers the toner image on the image carrier developed by the developing unit to a recording medium, and the fixing unit flash fixes the toner image on the recording medium transferred by the transfer unit. Since the color toner contains an infrared absorber, the density detecting means irradiates the image carrier or the recording medium with light in the absorption wavelength region of the infrared absorber and detects the intensity of the reflected light that is regularly reflected. Thus, the toner density on the image carrier or the recording medium can be detected with high accuracy.

  In order to achieve the above object, the image forming method of the present invention transfers a toner image on an image carrier developed using a color toner containing an infrared absorber to a recording medium, and the transferred recording medium In the image forming method of forming an image by flash-fixing the toner image on the top, the image carrier or the recording medium is irradiated with light in the absorption wavelength region of the infrared absorbent, and the intensity of the reflected light that has been regularly reflected is increased. The toner density on the image carrier or the recording medium is detected by detection, and an image is formed based on the detected toner density.

  In the image forming method of the present invention, similarly to the image forming apparatus, the image carrier or the recording medium is irradiated with light in the absorption wavelength region of the infrared absorber, and the intensity of the reflected light reflected regularly is detected. The toner concentration on the carrier or the recording medium can be accurately detected.

  As described above, according to the present invention, there is an effect that the toner density can be accurately detected in the image forming apparatus that forms a color image using the flash fixing method. In addition, there is an effect that the toner density can be detected with high accuracy in an image forming method in which a color image is formed using a flash fixing method.

Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.
(Overall configuration of image forming apparatus)
FIG. 1 shows a color image forming apparatus 10 according to the present exemplary embodiment. The color image forming apparatus 10 is an apparatus that forms a color image on a recording medium 12 made of continuous paper. The recording medium 12 inserted into the body of the color image forming apparatus 10 is wound around winding rollers 14 and 16. Then, it is transported at a constant speed along a transport path formed so as to cross the body. Image forming units 18A, 18B, 18C, and 18D that form toner images of respective colors Y (yellow), M (magenta), C (cyan), and K (black) are provided below the conveyance path of the recording medium 12. It arrange | positions along the conveyance path at substantially equal intervals.

  The image forming units 18 </ b> A to 18 </ b> D have the same configuration except for the color of the toner image to be formed, and include a photoconductive drum 20 arranged so that the axis is orthogonal to the conveyance direction of the recording medium 12. The charger 22 for charging the photosensitive drum 20, the light beam scanning device 24 for irradiating the charged photosensitive drum 20 with a beam to form an electrostatic latent image, and the static on the photosensitive drum 20. A developer 26 for forming a toner image of a predetermined color on the photosensitive drum 20 by supplying toner of a predetermined color to the electrostatic latent image forming portion to develop the electrostatic latent image, and a conveyance path of the recording medium 12 sandwiched therebetween. A transfer device 28 disposed opposite to the photosensitive drum 20, a static eliminator 32 that neutralizes the photosensitive drum 20, a cleaner blade 30 and a cleaner brush 34 for removing residual toner on the photosensitive drum 20 are disposed. It is configured.

  The image forming units 18 </ b> A to 18 </ b> D form toner images of different colors on the peripheral surface of the photosensitive drum 20 by the charger 22, the light beam scanning device 24, and the developing unit 26, and then transfer the formed toner images to the transfer unit 28. To the recording medium 12. A series of processes of charging, exposure (electrostatic latent image formation), development (toner image formation), and transfer in each of the image forming units 18A to 18D is performed by the toner image formed by each of the image forming units 18A to 18D on the recording medium 12. The execution timing is controlled so as to overlap each other. As a result, a full-color toner image is formed on the recording medium 12.

  In addition, the conveyance direction of the recording medium 12 is reversed by the winding rollers 38 and 40 on the downstream side of the arrangement positions of the image forming units 18A to 18D, and the space between the winding roller 40 and the subsequent winding roller 42 is reversed. In this section, the recording medium 12 is conveyed obliquely downward at an angle close to horizontal. A density sensor 100 that detects the density of the toner image formed on the recording medium 12 is provided between the winding rollers 38 and 40 and the image forming unit 18D.

  A flash fixing unit 46 having a flash lamp is disposed above the conveyance path in the section between the winding rollers 40 and 42. The winding rollers 56 and 58 are sequentially arranged at the subsequent stage of the winding roller 42, and the recording medium 12 on which the toner image is fixed by irradiating flash light from the flash fixing unit 46 is the winding roller 56. , 58 and discharged outside the body of the color image forming apparatus 10.

  In the color image forming apparatus 10 according to the present embodiment, a reference image (hereinafter referred to as “patch pattern”) as a test pattern is formed on the recording medium 12 for each color of YMCK, and the patch pattern is formed by the density sensor 100. The concentration of is measured. Then, the output image forming conditions are controlled (process control) based on the density measurement value by the density sensor 100, and an output image is formed under these forming conditions. For example, the toner density in the developing device 26, the exposure amount of the light beam scanning device 24, the developing bias potential, the charging potential of the photosensitive drum 2, and the like can be corrected.

(Configuration of concentration sensor)
FIG. 2 is a schematic configuration diagram of the density sensor 100. The density sensor 100 is disposed in the regular reflection direction of the detection light 60 by irradiating the detection light 60 to the surface 12A on which the patch pattern on the recording medium 12 is formed, and receives the regular reflection light from the surface 12A. And a light receiving element 64. When the incident angle of the detection light 60 is θ ₁ , the regular reflection light is reflected at an angle θ ₂ that is equal to θ ₁ with respect to the normal 66.

  Further, the concentration sensor 100 includes a current-voltage converter (not shown) that converts the current output from the light receiving element 64 into a voltage, and an A / D converter that converts an analog signal of the converted voltage into a digital signal. (Not shown) is provided, and the converted digital signal is output as a sensor measurement value to a controller described later.

  In image formation using the flash fixing method, an infrared absorber is contained in the toner so that the toner is melted and fixed when irradiated with flash light. FIG. 3 shows an example of the absorption characteristics of the color toner for flash fixing. FIG. 3 shows black toner absorption characteristics, heat roller fixing color toner absorption characteristics, and xenon lamp emission characteristics.

  The color toner for flash fixing contains an infrared absorber having absorption in the vicinity of 830 nm where the emission peak of a xenon lamp used as a flash lamp is present, and ranges from 700 nm to 950 nm on the longer wavelength side from the absorption peak of the colorant. Has an absorption peak.

  Accordingly, the light (infrared light) in the absorption wavelength region of the infrared absorbent contained in the toner is irradiated as the detection light 60 from the light emitting element 62 to the surface 12A, and the specularly reflected light from the surface 12A is detected. The toner density on the recording medium 12 can be detected with high accuracy.

  As the light emitting element 62, an LED that emits light with a longer wavelength than visible light can be used. An LED that emits light at a wavelength of 800 nm or more is more preferable. For example, when the absorption peak wavelength of the infrared absorber is 830 nm, an LED that emits light in the wavelength range of 800 nm to 950 nm is particularly preferable.

(Image formation control system)
FIG. 4 is a block diagram of a control system of the color image forming apparatus 10.

  The main controller 200 is connected to the density sensor 100 described above and a memory 204 that stores a target value (target value) of the toner density of the patch pattern, a conversion table for converting the sensor measurement value into the toner density, and the like. ing. The target value can be read from the memory 204 for comparison with the toner density calculated based on the sensor measurement value input from the density sensor 100.

  Further, a user interface 202 is connected, and an instruction regarding image formation or the like is given by a user's operation, and information on the image formation or the like is notified to the user. Further, a network line with an external host computer (not shown) is connected to the main controller 200 so that image data is input.

  When the image data is input, the main controller 200 analyzes, for example, the print instruction information included in the image data and the image data, and converts them into a format suitable for the image forming apparatus (for example, bitmap data). Image data is sent to the image formation processing control unit 206.

  The image formation processing control unit 206 controls each of the optical scanning system control unit 208, the drive system control unit 210, the charger control unit 212, the developing device control unit 214, and the fixing unit control unit 216 based on the input image data. Synchronous control is performed to execute image formation.

  Next, a control routine for process control will be described with reference to FIG. This control routine is executed by the main controller 200, for example, when the apparatus is powered on.

  First, in step 100, a sensor measurement value is read from the density sensor 100. This sensor measurement value is a sensor measurement value corresponding to the surface concentration of the recording medium 12.

  In the next step 102, the image formation processing control unit 206 is instructed to form a patch pattern. The image formation processing control unit 206 controls each of the optical scanning system control unit 208, the driving system control unit 210, the charger control unit 212, the developing device control unit 214, and the fixing unit control unit 216, and patches on the recording medium 12. Form a pattern.

  In the next step 104, the sensor measurement value is read from the density sensor 100 again. This sensor measurement value is a sensor measurement value corresponding to the density of the patch pattern. In the next step 106, the sensor measurement value corresponding to the density of the patch pattern is corrected using the sensor measurement value corresponding to the surface density of the recording medium 12.

  In the next step 108, a conversion table for converting the sensor measurement value into the toner density is read from the memory 204, and in step 110, the sensor measurement value corrected with reference to the conversion table is converted into the toner density. The obtained density is a detection value of the toner density of the patch pattern.

  In the next step 112, the target value of the toner density corresponding to the patch pattern is read from the memory 204. In step 114, the detected value of the toner density of the patch pattern is compared with the target value. In step 116, it is determined whether or not the comparison result is within an allowable range. If the determination is affirmed, the routine is terminated.

  On the other hand, if the determination in step 116 is negative, the comparison result exceeds the allowable range, so the process proceeds to step 118, where the toner density in the developing device 26, the exposure amount of the light beam scanning device 24, and the developing bias potential Then, a correction value for correcting the charging potential of the photosensitive drum 2 is calculated and output to the image forming process control unit 206, and the process returns to step 102 to form a patch pattern for the image forming process control unit 206. Instruct.

  The image formation processing control unit 206 controls each of the optical scanning system control unit 208, the driving system control unit 210, the charger control unit 212, the developing device control unit 214, and the fixing unit control unit 216 based on the correction value. Again, a patch pattern is formed on the recording medium 12.

  As described above, the processing in steps 102 to 118 is repeated until the determination in step 116 is affirmed, so that the toner density of the patch pattern converges to the target value.

  As described above, in the color image forming apparatus according to the present embodiment, the toner density on the recording medium is detected by detecting the specularly reflected light in the density sensor, so the toner density is detected with high accuracy. And process control can be performed with high accuracy.

  In addition, it is not necessary to provide two types of density sensors, a density sensor for monochrome toner and a density sensor for color toner. In addition, since a long wavelength LED is used for the density sensor, the color image forming apparatus can be made inexpensive. Can be manufactured.

  In the above embodiment, the density sensor 100 is arranged on the downstream side of the arrangement position of the image forming units 18A to 18D. However, the density sensor is arranged for each of the image forming units 18A to 18D. Also good. For example, as shown in FIG. 6, the density sensor 102 can be arranged around the photosensitive drum 20, and the patch pattern formed on the photosensitive drum 20 can be detected by the density sensor 102. In this example, the density sensor 102 is disposed on the downstream side of the developing device 26 along the rotation direction of the photosensitive drum 20 indicated by an arrow.

Hereinafter, the present invention will be specifically described based on examples.
Example 1
A density sensor having the configuration shown in FIG. 2 using a color toner for flash fixing containing “YKR5010” (absorption peak wavelength: 850 nm) manufactured by Yamamoto Kasei Co., Ltd. as an infrared absorber, and variously changing the toner density of the patch pattern. The light receiving output (sensor measured value) of the light receiving element was detected. As shown in Condition 1 of Table 1, the incident angle θ ₁ of the detection light of the concentration sensor was 10 °, the angle θ ₂ formed by the regular reflection light with respect to the normal line was 10 °, and the emission wavelength of the LED was 880 nm. “KL858” manufactured by Shinko Electronics Co., Ltd. was used as the LED having an emission wavelength of 880 nm, and “KS988” manufactured by Shinko Electronics Co., Ltd. was used as the light receiving element.

    When the sensor measurement values were plotted against the toner density of the patch pattern, the sensor measurement values had linearity with respect to the toner concentration as shown in FIG. The sensor measurement value had a high sensitivity difference (S / N ratio) with respect to the toner concentration. Accordingly, it is understood that when the detection light near the absorption peak wavelength of the infrared absorbent contained in the color toner is used, the regular reflection light can be detected by the density sensor, and the toner density can be detected accurately. .

(Example 2)
As shown in Condition 2 of Table 1, the same as in Example 1 except that the incident angle θ ₁ of the detection light of the density sensor is 30 ° and the angle θ ₂ formed by the regular reflection light with respect to the normal is 30 °. The sensor measurement value was detected. When the sensor measurement values were plotted against the toner density of the patch pattern, the sensor measurement values had linearity with respect to the toner concentration as shown in FIG. The sensor measurement value had a high sensitivity difference (S / N ratio) with respect to the toner concentration. Thereby, when the detection light near the absorption peak wavelength of the infrared absorbent contained in the color toner is used, even if the incident angle of the detection light is changed, the regular reflection light can be detected by the density sensor, It can be seen that the toner density can be accurately detected.

(Example 3)
Using a color toner for flash fixing containing “IRG023” (absorption peak wavelength: 1300 nm) manufactured by Nippon Kayaku Co., Ltd. as an infrared absorber, as shown in Condition 3 of Table 1, the incident angle of the detection light of the density sensor Sensor measurement values were detected in the same manner as in Example 1 except that θ ₁ was 30 °, the angle θ ₂ formed by the regular reflection light with respect to the normal was 30 °, and the emission wavelength of the LED was 1300 nm. “KL1260” manufactured by Shinko Denshi Co., Ltd. was used as the LED having an emission wavelength of 1300 nm, and “KD1263” manufactured by Shinko Denshi Co., Ltd. was used as the light receiving element.

  When the sensor measurement values were plotted against the toner density of the patch pattern, the sensor measurement values had linearity with respect to the toner concentration as shown in FIG. The sensor measurement value had a high sensitivity difference (S / N ratio) with respect to the toner concentration. As a result, even when the absorption peak wavelength of the infrared absorbent contained in the color toner changes, when the detection light near the absorption peak wavelength is used, the specular reflection light can be detected by the density sensor, and the toner concentration It can be seen that can be detected accurately.

(Comparative Example 1)
As shown in condition 4 of Table 1, the incident angle θ ₁ of the detection light of the density sensor is 30 °, the angle θ ₂ formed by the regular reflection light with respect to the normal is 30 °, and the emission wavelength of the LED is 1300 nm. The sensor measurement values were detected in the same manner as in Example 1. When the sensor measurement values were plotted against the toner density of the patch pattern, as shown in FIG. 7, the sensor measurement values were substantially zero and hardly changed. That is, the toner density cannot be detected with detection light outside the absorption wavelength region of the infrared absorbent contained in the color toner.

(Comparative Example 2)
Using a color toner for flash fixing that does not contain an infrared absorber, the toner density of the patch pattern was variously changed, and the sensor measurement values of the color density sensor shown in FIG. 9 were detected. As shown in Condition 5 in Table 1, the incident angle θ ₁ of the detection light of the density sensor is 30 °, the angle θ ₂ formed by the diffuse reflected light to be detected with respect to the normal is −60 °, and the emission wavelength of the LED is 880 nm. did.

    When the sensor measurement values are plotted against the toner density of the patch pattern, as shown in FIG. 7, the sensor measurement value has linearity with respect to the toner concentration, but the sensor measurement value is a difference in sensitivity (S / N) with respect to the toner concentration. The ratio is small. That is, in color toners that do not contain an infrared absorber, it is necessary to detect light diffusely reflected by irradiating detection light in the visible region, but in this case, the toner concentration cannot be detected accurately.

(Comparative Example 3)
Various toner densities of the patch pattern were changed, and the sensor measurement values of the color density sensor shown in FIG. 9 were detected. As shown in Condition 6 of Table 1, the incident angle θ ₁ of the detection light of the density sensor was 30 °, and the angle θ ₂ formed by the diffuse reflected light to be detected with respect to the normal was −60 °.

    When the sensor measurement values were plotted against the toner density of the patch pattern, as shown in FIG. 7, the sensor measurement values were substantially zero and hardly changed. That is, even if the detection light near the absorption peak wavelength of the infrared absorbent contained in the color toner is used, the toner density cannot be detected if the diffusely reflected light is detected.

  The results are summarized in Table 1.

1 is a schematic diagram illustrating a configuration of a color image forming apparatus according to an exemplary embodiment. It is a schematic block diagram of the concentration sensor which concerns on this Embodiment. FIG. 4 is a diagram illustrating an example of absorption characteristics of a color toner for flash fixing. 2 is a block diagram of a control system of the color image forming apparatus according to the present embodiment. FIG. It is a flowchart which shows the control routine of process control. It is a figure which shows another example of arrangement | positioning of a density sensor. It is a diagram which shows the correlation between a sensor measured value and toner density. FIG. 4 is a diagram illustrating light absorption characteristics of a monochrome toner and a color toner. It is a schematic block diagram of the conventional density | concentration sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Color image forming apparatus 12 Recording medium 12A Surface 14, 16 Rolling roller 18A, 18B, 18C, 18D Image forming part 20 Photosensitive drum 22 Charging device 24 Light beam scanning device 26 Developer 28 Transfer device 30 Electric discharger 32 Cleaner blade 34 Cleaner Brush 38 Winding Roller 40 Winding Roller 42 Winding Roller 46 Flash Fixing Unit 56, 58 Winding Roller 60 Detection Light 66 Normal 40, 42 Rolling Roller 100 Density Sensor 102 Density Sensor 200 Main Controller 202 User Interface 204 Memory 206 Image formation processing control unit 208 Optical scanning system control unit 210 Drive system control unit 212 Charger control unit 214 Developing device control unit 216 Fixing unit control unit

Claims (5)

Charging means for charging the image carrier;
An electrostatic latent image forming unit that forms an electrostatic latent image by irradiating the image carrier charged by the charging unit with a light beam according to image data;
Developing means for developing the electrostatic latent image using a color toner containing an infrared absorber;
Transfer means for transferring the toner image on the image carrier developed by the developing means to a recording medium;
Fixing means for flash-fixing the toner image on the recording medium transferred by the transfer means;
The toner density on the image carrier or the recording medium is detected by irradiating the image carrier or the recording medium with light in the absorption wavelength region of the infrared absorbing agent and detecting the intensity of the reflected light that is regularly reflected. Concentration detecting means for
An image forming apparatus.   Control for controlling at least one of a charging potential of the charging unit, a light beam intensity of the electrostatic latent image forming unit, and a developing bias potential of the developing unit based on the toner density detected by the density detecting unit The image forming apparatus according to claim 1, further comprising means.   The image forming apparatus according to claim 1, wherein the infrared absorber has an absorption wavelength peak on a longer wavelength side than 800 nm.   The density detecting means includes a light emitting element that emits light at a wavelength of 800 nm to 950 nm, and irradiates the image carrier or the recording medium with light in an absorption wavelength region of the infrared absorbent by the light emitting element. The image forming apparatus according to any one of the above. In an image forming method in which a toner image on an image carrier developed using a color toner containing an infrared absorber is transferred to a recording medium, and the toner image on the transferred recording medium is flash-fixed to form an image. ,
The toner density on the image carrier or the recording medium is detected by irradiating the image carrier or the recording medium with light in the absorption wavelength region of the infrared absorbing agent and detecting the intensity of the reflected light that is regularly reflected. And forming an image based on the detected toner density.

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