JP2004271910A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for suppressing energy consumption of a fixing device to required minimum and having sufficient color reproducibility. <P>SOLUTION: The image forming apparatus comprises a fixing condition control function for acquiring color information of an inputted image signal by a color acquisition part and for varying fixing conditions in the fixing device 9 according to acquisition of the color information. The fixing condition control function is realized by making, for example, temperature of the fixing device 9 variable. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine and a printer that forms an image by fixing a toner image on a recording medium by a predetermined process of an electrophotographic system, and more particularly to a fixing control technique of a heating type fixing device. .
[0002]
[Prior art]
In recent years, there has been a need to reduce heat energy consumed by the fixing device from the viewpoint of quick start and energy saving for environmental protection. On the other hand, as a prior art example, for example, in Patent Document 1, the thermal energy of the fixing device is reduced by using a toner having high low-temperature fixing performance.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2000-267335
[Problems to be solved by the invention]
However, the full-color image in the prior art example has low gloss, and the expressible color reproduction range is small. Therefore, there is a problem that the reproducibility of high-saturation colors is poor depending on the color original. On the other hand, it is possible to widen the color reproduction range by increasing the fixing temperature in the fixing device and sufficiently melting the toner image to enhance the glossiness, but this is not preferable from the viewpoint of energy saving.
SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus in which the energy consumption of a fixing device is minimized and the color forming capability is sufficient.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 is characterized most by an image forming apparatus having a fixing condition control function of changing a fixing condition in a fixing device according to color information of an input image signal. .
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the main feature is that the fixing condition control function is realized by making the temperature of the fixing device variable.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, an image forming apparatus having a toner adhesion amount control function of varying a toner adhesion amount in accordance with color information of an input image signal is mainly used. Characteristics.
According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the image forming apparatus further includes a gradation correcting unit that performs a gamma correction process, and the toner adhesion amount control function is realized by changing a parameter of the gamma correction process. The main feature is an image forming apparatus to be used.
According to a fifth aspect of the present invention, in the image forming apparatus according to the third or fourth aspect, the image forming apparatus has a toner amount adjusting function of adjusting a black toner amount, and the toner adhesion amount controlling function adjusts the black toner amount. The main feature is an image forming apparatus realized by making parameters variable.
According to a sixth aspect of the present invention, there is provided the image forming apparatus according to any one of the first to fifth aspects, further comprising an image processing unit for converting an input image signal into predetermined information, wherein the color information is obtained by the image processing unit. The main feature is the image forming apparatus having the obtained saturation.
According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, when the saturation is smaller than a predetermined value, the fixing condition control function performs control to lower the temperature below a predetermined value. Characteristics.
According to an eighth aspect of the present invention, in the image forming apparatus according to the sixth or seventh aspect, when the saturation is smaller than a predetermined value, the toner adhesion amount control function controls the toner adhesion amount to be lower than the predetermined value. The main feature is the image forming apparatus.
[0005]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram illustrating an image forming system of an image forming apparatus according to an embodiment of the present invention. The color image forming apparatus shown in FIG. 1 is called a tandem system, and has a configuration in which image forming units for each color are arranged in series. The image forming unit for each color is composed of a charging device 2, a developing device 4, a cleaning device 6, and the like, centering on the photoreceptor 1. An exposure device 3 and an intermediate transfer device 5 are provided for the photoreceptor 1 of each image forming unit. In addition, a paper transport unit, a paper transfer device 8, a fixing device 9, and the like are provided. Are arranged in accordance with.
Next, an operation of forming a color image will be described. An exposure device 3 such as an LD, which is driven to rotate based on an image signal, after the surface of a photosensitive member 1 serving as a latent image carrier that is driven to rotate in the direction of the arrow in the image forming unit for each color, is uniformly charged by a charging device 2. The exposure device forms an electrostatic latent image, and the developing device 4 forms a toner image of each color on the photoconductor 1 according to the electrostatic latent image.
The toner image of each color of each color formed on the photoreceptor 1 of each image forming unit is sequentially transferred onto an intermediate transfer belt which is an intermediate transfer device 5, so that each single color toner image is formed on the intermediate transfer belt. It is piled up. The toner remaining on the photoconductor 1 after the transfer process is collected by a cleaning device 6 arranged for each image forming unit.
On the other hand, a sheet 7 as a recording material is conveyed from a sheet cassette (not shown) storing the sheet 7 to a sheet transfer device 8 by a sheet conveying unit, and the toner image superimposed on the intermediate transfer belt is a sheet. The image is transferred onto the sheet 7 by the transfer device 8. The toner image on the paper 7 is heat-fixed by the fixing device 9 to obtain a color image.
[0006]
FIG. 2 is a detailed configuration diagram of the fixing device. A rotatable fixing roller 92 having a heater 94 such as a halogen lamp therein and a pressure roller 93 are contacted with a constant pressing force by a pressing means using a spring or the like (not shown). The surface temperature of each roller is detected by 96.
By controlling the voltage applied to the heater 94 by the temperature controller 99 while detecting the temperature, each roller surface temperature can be set to a predetermined value. In addition, a release agent application roller 97, a cleaning roller 98, and the like for applying silicone oil, which is a release agent, to prevent the melted toner from adhering to the surface of the fixing roller.
When the paper 7 onto which the toner image is transferred by the paper transfer device 8 passes between the fixing roller 92 and the pressure roller 93, the toner image is fused and fixed to the paper 7 by heat and pressure. This fixing method is a so-called soft roll method in which silicone oil is applied to the surface of the fixing roller by a release agent applying roller 97, and other examples include a hard roll method using a Teflon (registered trademark) roller and a belt fixing method. is there.
The present invention is characterized in that saturation information as color information is extracted from an input signal as a document image, and fixing conditions are controlled in accordance with the saturation. An embodiment of the present invention will be described below mainly on control in an image processing unit.
[0007]
FIG. 3 is a configuration diagram of an image processing unit of the image forming apparatus according to the embodiment of the present invention. The image processing section mainly includes an input signal conversion section 11, a color conversion section 12, a gradation correction section 13, and a halftone processing section 14 as shown in FIG. It has a part.
First, an image signal sent from an input device such as a CCD 15 of a scanner enters an input signal converter 11, is appropriately converted into an RGB signal, and is sent to a color converter 12. The color conversion unit 12 generates CMYK (cyan, magenta, yellow, and black) printer color signals by performing a hue division masking process or the like as a color correction process.
Specifically, a CMYK signal is formed from the RGB signals by a matrix operation, and the coefficients of the matrix operation are optimized by a color prediction model or the like. At that time, UCR (Under Color Removal) processing for finding the optimum value of K (black) is also performed at the same time.
[0008]
A general UCR process will be described with reference to FIG. When there are C, M, and Y values as shown in FIG. 4A, the UCR process is to replace a certain ratio of a common portion of C, M, and Y (a portion below the dotted line) with K. As a result, the total amount of toner used can be reduced. Assuming that this ratio is the UCR rate, the UCR is 70% in FIG. 4 (2), the UCR is 100% in FIG. 4 (3), and the UCR is 0%.
The C, M, Y, and K signals are converted into C ′, M ′, Y ′, and K ′ signals so that desired output characteristics can be obtained by the gradation correction unit. The conversion is called gamma conversion, and the relationship between the input digital value Cin and the output digital value Cout is as shown in FIG. Here, the desired output characteristics are appropriately set according to the purpose, such as, for example, gray balance, lightness linearity, and minimum color difference. Then, after the halftone processing such as dither and error diffusion is performed by the halftone processing unit 14 for each color of the gamma-converted C ′, M ′, Y ′, and K ′ signals, the halftone processing unit 14 sends the signals to the exposure driving unit 15, The LD is driven for lighting.
[0009]
FIG. 6 shows the relationship between the fixing temperature and the color reproduction range (a * b * plane). Here, the fixing temperature is To <Th. It can be seen that increasing the fixing temperature increases the surface gloss of the toner image and expands the color reproduction range. Considering the current energy saving, the color at the point A, which cannot be reproduced at the fixing temperature To which aims at a low gloss image, can be reproduced by setting the fixing temperature to a high Th.
On the other hand, when the color having the highest saturation in the original image is the point B, a wide color reproduction range of the fixing temperature Th is not necessary, and the color reproduction can be sufficiently performed in the color reproduction range at the fixing temperature To. is there. By controlling the fixing temperature in accordance with the saturation information of the document image in this way, it is possible to output an image with a minimum fixing energy while securing necessary color reproducibility.
In the present embodiment, as shown in FIG. 3, the color conversion section 12 includes a saturation acquisition section 16 for acquiring saturation as color information from RGB signals as image input signals. Here, the saturation C * is a color coordinate in a CIELAB space that is a color space (L *, a *, b *), and C * = ((a *) {2+ (b *) {2)}. It is represented by 0.5. Based on the saturation C * information obtained by the saturation obtaining unit 16, the histogram creating unit 17 creates a histogram in which the horizontal axis represents the saturation and the vertical axis represents the pixel count value, as shown in FIG.
[0010]
FIG. 7A shows a histogram for a pictorial image in which the original image contains many high-saturation colors, and FIG. 7B shows a histogram for a business image in which the original image has many low-saturation colors. The larger the proportion of pixels with high saturation, the greater the need for a wider color reproduction range.
In this way, it is possible to identify the size of the necessary color reproduction range according to the saturation information of the document image. Specifically, a predetermined threshold value C ′ for saturation is set, and the number of pixels in the histogram that is equal to or greater than the threshold value C ′ is counted (the shaded area in FIG. 7A), and the number of pixels is equal to or greater than a certain value. Is determined as a high-saturation image, and a control is performed to set a high fixing temperature as a fixing condition control function of the main control unit.
These controls will be described with reference to FIG. In this embodiment, the predetermined saturation thresholds are C1 and C2 (C1 <C2), the fixing temperatures are three levels T0, T1, and T2 (T0 <T1 <T2), and C1 = 40, C2 = 60, and T0 = 140 ° C. T1 = 150 ° C. T0 = 160 ° C. However, since these values depend on the toner and the system of the fixing device, the values are not limited thereto.
First, a saturation acquisition unit acquires saturation information from an input signal. The saturation information is converted into a histogram, and the frequency of the saturation in the document is obtained (S1, S2). The number of pixels N2 whose saturation is equal to or greater than C2 is counted (S3), and it is determined whether or not the ratio to the total number of pixels N is equal to or greater than a fixed value n (S4).
If the ratio of the number of pixels N2 having a saturation of C2 or more to the total number of pixels N is n or more (YES in S4), the fixing temperature is set to T2 (S5), and an image is output (S6). On the other hand, if the ratio of the number of pixels N2 having the saturation of C2 or more to the total number of pixels N is less than n (NO in S4), the number of pixels N1 having the saturation of C1 or more is counted (S7). It is determined whether or not the ratio is equal to or greater than a predetermined value n (S8). If the ratio of the number N1 of pixels having the saturation C1 or more to the total number N of pixels is not less than n (YES in S8), the fixing temperature is set to T1 (S9), and an image is output (S6). On the other hand, when the ratio of the number N1 of pixels having the saturation C1 or more to the number N of all pixels is less than n (NO in S8), the fixing temperature is set to T0 (S10), and an image is output (S6). The fixed ratio to the total number of pixels was set to 10% or more.
[0011]
By controlling the fixing temperature in accordance with the saturation information of the original image as described above, color reproduction faithful to the original can be performed, and image output can be performed with minimum fixing energy, thereby saving energy. Can be achieved.
Further, in the present invention, in addition to the above-described functions, the main control unit of the image forming apparatus is provided with a toner adhesion amount control function of controlling the amount of toner adhesion according to color information of an image, so that heat energy consumption during fixing can be improved. Is further suppressed.
The energy required for fixing depends on the maximum amount of toner adhering to the image. To set the fixing temperature low, it is necessary to further reduce the maximum amount of toner adhering. In the present embodiment, the function of reducing the maximum amount of adhered toner is realized by changing the parameters of the gamma correction process and the UCR process in the image processing.
Here, simply reducing the maximum amount of toner adhesion only reduces the color reproduction range. In the present embodiment, the amount of adhered toner is controlled according to the saturation obtained by the saturation obtaining unit 16. Specifically, when a high-saturation color is not used in the original image, the necessary color reproduction range may be small. Therefore, when performing the gamma conversion by the gradation correcting unit 13 (gradation correcting unit), FIG. 9) to 9 (2), the parameters are variably set so as to lower the maximum density, so that the maximum amount of toner adhesion can be reduced and the fixing temperature can be lowered.
Furthermore, by increasing the UCR rate in accordance with the saturation obtained by the saturation acquisition unit 16, the maximum amount of toner adhesion can be reduced, and the fixing temperature can be further reduced. The change in the UCR rate is expressed in claims as black toner amount adjustment, and the main control unit of the image forming apparatus variably sets a black toner amount adjustment parameter. However, there is a possibility that a change in tint may be increased by increasing the UCR rate. Therefore, it is desirable to perform the processing on an image with low saturation.
[0012]
These controls will be described with reference to FIG. In the present embodiment, the predetermined saturation thresholds are C1 and C2 (C1 <C2), the fixing temperatures are three levels T0, T1, and T2 (T0 <T1 <T2), and C1 = 40, C2 = 60, and T0 ′ = 130. ° C, T1 '= 140 ° C, and T0 = 160 ° C. However, since these values depend on the toner and the system of the fixing device, the values are not limited thereto.
First, the saturation acquisition unit 16 acquires saturation information from an input signal. The saturation information is converted into a histogram, and the frequency of the saturation in the document is obtained (S1, S2). The number of pixels N2 whose saturation is equal to or greater than C2 is counted (S3), and it is determined whether or not the ratio to the total number of pixels N is equal to or greater than a fixed value n (S4).
If the ratio of the number of pixels N2 having a saturation of C2 or more to the total number of pixels N is not less than a fixed value n (YES in S4), the fixing temperature is set to T2 (S5), and an image is output (S6). On the other hand, when the ratio of the number N2 of pixels having a saturation of C2 or more to the number N of all pixels is less than the fixed value n (NO in S4), the parameter of the gamma conversion is changed in the direction of decreasing the maximum density setting (S7). Next, the number of pixels N1 whose saturation is equal to or greater than C1 is counted (S8), and it is determined whether or not the ratio to the total number of pixels N is equal to or greater than a fixed value n (S9).
If the ratio of the number N1 of pixels having a saturation of C1 or more to the number N of all pixels is equal to or more than a fixed value n (YES in S9), the fixing temperature is set to T1 '(S10), and an image is output (S6). On the other hand, if the ratio of the number N1 of pixels having a saturation of C1 or more to the number N of all pixels is less than the fixed value n (NO in S9), the UCR rate is changed to be increased (S11). The fixing temperature is set to T0 '(S12), and an image is output (S6). The ratio to the total number of pixels was set to 10% or more.
As described above, by reducing the maximum amount of toner adhered in accordance with the saturation information of the original image and controlling the fixing temperature, color reproduction faithful to the original can be performed, and with the minimum fixing energy. Energy saving can be achieved by enabling image output.
[0013]
【The invention's effect】
According to the first aspect of the present invention, color reproduction faithful to a document can be performed with the minimum necessary energy consumption of the fixing device, so that there is an effect that both good color reproducibility and energy saving can be achieved.
According to the second aspect of the present invention, the fixing temperature is controlled so as to minimize the energy consumption of the fixing device according to the document, and color reproduction faithful to the document can be performed. There is an effect that both energy savings can be achieved.
According to the third aspect of the present invention, the amount of toner adhered is controlled so as to minimize the energy consumption of the fixing device according to the original, and color reproduction faithful to the original can be performed. And there is an effect that further energy saving can be achieved.
According to the fourth aspect of the present invention, since the gamma correction process is performed so as to minimize the energy consumption of the fixing device according to the original and color reproduction faithful to the original can be performed, good color reproducibility can be obtained. And there is an effect that further energy saving can be achieved.
According to the fifth aspect of the present invention, since the UCR process is performed so as to minimize the energy consumption of the fixing device according to the document and color reproduction faithful to the document can be performed, good color reproducibility and There is an effect that further energy saving can be achieved.
According to the sixth aspect of the present invention, by extracting the saturation as the color information of the original, color reproduction faithful to the original can be performed with the minimum required energy consumption of the fixing device. And energy saving can be achieved at the same time.
According to a seventh aspect of the present invention, an image can be formed with low energy consumption in a fixing device for a document having a saturation smaller than a predetermined value, and faithful color reproduction is performed for a high-saturation document. Therefore, there is an effect that both good color reproducibility and energy saving can be achieved.
According to the eighth aspect of the present invention, an image can be formed with less energy consumption in a fixing device for a document having a saturation smaller than a predetermined value, and faithful color reproduction can be performed for a document having a high saturation. Therefore, there is an effect that both good color reproducibility and energy saving can be achieved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram illustrating an image forming system of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a detailed configuration diagram of a fixing device.
FIG. 3 is a configuration diagram of an image processing unit of the image forming apparatus according to the embodiment of the present invention.
FIG. 4 is a diagram showing a UCR process.
FIG. 5 is a diagram showing a relationship between an input digital value and an output digital value.
FIG. 6 is a diagram illustrating a relationship between a fixing temperature and a color reproduction range.
FIG. 7 is a diagram showing a histogram.
FIG. 8 is a flowchart illustrating a first control example of the present invention.
FIG. 9 is a diagram illustrating gamma conversion.
FIG. 10 is a flowchart illustrating a second control example of the present invention.
[Explanation of symbols]
Reference Signs List 11 input signal conversion unit 12 color conversion unit 13 gradation correction unit 14 halftone processing unit 16 saturation acquisition unit 17 histogram creation unit

Claims (8)

An image forming apparatus having a fixing condition control function for changing a fixing condition in a fixing device according to color information of an input image signal. 2. The image forming apparatus according to claim 1, wherein the fixing condition control function is realized by changing a temperature of the fixing device. 3. The image forming apparatus according to claim 1, further comprising a toner adhesion amount control function for varying a toner adhesion amount in accordance with color information of an input image signal. 4. The image forming apparatus according to claim 3, further comprising: a gradation correction unit that performs a gamma correction process, wherein the toner adhesion amount control function is realized by changing a parameter of the gamma correction process. Forming equipment. 5. The image forming apparatus according to claim 3, further comprising a toner amount adjustment function for adjusting a black toner amount, wherein the toner adhesion amount control function is realized by changing a parameter for adjusting the black toner amount. An image forming apparatus, comprising: 6. The image forming apparatus according to claim 1, further comprising an image processing unit that converts an input image signal into predetermined information, wherein the color information is a saturation obtained by the image processing unit. Characteristic image forming apparatus. 7. The image forming apparatus according to claim 6, wherein when the saturation is smaller than a predetermined value, control for lowering the temperature below the predetermined value is performed in the fixing condition control function. 8. The image forming apparatus according to claim 6, wherein when the saturation is smaller than a predetermined value, a control to reduce the toner adhesion amount to a predetermined value is performed in the toner adhesion amount control function. .

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