JP2006133580A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus having a low consumption mode capable of reducing toner consumption, in which sufficient fixability is obtained even in the low consumption mode of performing area gradating processing by using a means of analyzing image data for every pixel and subjecting a solid black image etc., having relatively many pixels to be developed to dither processing and a means for forming a halftone image by controlling a laser light emission time in a 1-dot unit. <P>SOLUTION: The calorific value in fixing is increased when selecting the low consumption mode in which the area gradating processing is performed by using the means of analyzing the image data for every pixel and subjecting the solid black image etc., having the relatively many pixels to be developed to the dither processing and the means for forming the halftone image by controlling the laser light emission time in the 1-dot unit. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is an image forming apparatus that forms an electrostatic latent image on an image carrier and visualizes the electrostatic latent image with a developer, and a normal image forming mode that does not suppress consumption of the developer; By forming the electrostatic latent image on the image carrier by area gradation processing, the developer consumption is reduced and the developer consumption for developing the electrostatic latent image is reduced compared to the normal image formation mode. The present invention relates to an image forming apparatus capable of selecting a mode.

  For example, in a process cartridge detachable electrophotographic image forming apparatus, a process cartridge contains a predetermined amount of developer (hereinafter referred to as toner) in advance, and the number of sheets that can be printed is usually Correlates with the amount of stored toner. When the stored toner is used up, it is replaced with a new process cartridge. Therefore, an increasing number of users desire to reduce toner consumption of printing as much as possible to save toner and print a larger number of sheets.

  In addition, an increasing number of laser beam printers have image forming modes such as a low consumption mode and a draft mode that can automatically reduce toner consumption.

  As a means for reducing the toner consumption of printing, a method of changing the development contrast or the density of the outline portion of the image is kept as it is, and empty spots that are not printed are scattered inside the pixel collection portion such as a solid black image. There is a method of performing such area gradation processing.

Patent Document 1 discloses a means for reducing the toner consumption in an image with the same density as the outline portion of the image composed of the binary image.
JP-A-9-085993

  However, as an example of the area gradation processing, as shown in the model diagram (conceptual diagram) in FIG. 6, low toner consumption by dithering the original image G0 in (a) to the image G1 in (b). Image data composed of binary images to be printed is analyzed for each pixel, such as the mode and the original image G in (a) like the image G2 in (c), and relatively few pixels are developed. In a low toner consumption mode by controlling the laser emission time in units of one dot to form a halftone image with a line image or a character image and an image with a large development area such as a solid black image with a relatively large number of pixels to be developed. It has been found that the fixability of the toner may deteriorate.

I will explain a little about this now. In our experiments, for images with a wide development area such as a solid black image with a relatively large number of pixels to be developed,
1) When the toner consumption is suppressed by changing the contrast 2) When the toner consumption is suppressed by dithering 3) When the toner consumption is suppressed by means of modulating the laser emission time in units of one dot 7A and 7B show the respective electrostatic latent images and the cross-section of the toner image formed on the recording material P in the above three cases 1) to 3). There are other error diffusion and PWM methods for area gradation, but this example will be described with dither processing.

  FIG. 7A shows a case of a normal image forming mode (hereinafter referred to as a normal mode) in which the toner consumption is not suppressed. A toner image G0 is formed on the recording material P in accordance with the electrostatic latent image S0. The (B) is a developer low consumption image forming mode (hereinafter referred to as a low consumption mode) in which the amount of laser light is reduced and the development contrast is changed, and a toner image G3 is formed on the electrostatic latent image S3. (C) is a case of the low consumption mode by the dither processing, and the toner image G1 is formed on the electrostatic latent image S1. (D) is a case of the low consumption mode by the laser emission time modulation, and the toner image G2 is formed on the electrostatic latent image S2.

  However, in the low-consumption mode, the recording material is obtained when the dithering process is performed as shown in (c) rather than the toner image G3 formed on the recording material P when the development contrast is changed as shown in (b). The toner image G1 formed on P has a weaker binding force between the toner and the recording material or between the toners. The toner image G2 formed on the recording material P when the laser emission time is modulated as shown in (d) is the same as the toner image G3 formed when the development contrast is changed as shown in (b). In comparison, the bonding force with the recording material does not decrease so much, but the bonding force between the toners becomes weak.

  FIG. 8A shows an enlarged sectional model of the toner image G3-a before fixing the toner image G3 formed on the recording material P when the development contrast of FIG. 7B is changed, and after fixing. 3 is an enlarged cross-sectional model of a toner image G3. FIG. 7B shows an enlarged cross-sectional model of the toner image G1-a before fixing the toner image G1 formed on the recording material P when the dither processing of FIG. 7C is performed, and the toner image G1 after fixing. It is an enlarged section model.

  The unfixed toner image G1-a formed on the recording material P by performing dither processing has a height h that changes the development contrast of the unfixed toner image G3-a formed on the recording material P. A space s is generated between the toners because the height is higher than the height h and the toner formed on the recording material is thinned out. In addition, when the state of the toner image after fixing is seen, the toner image G3 when the contrast is changed has the toner t peeled off from the recording material P because the surrounding toner is melted even if there are particles t1 that are not melted in the toner image G3. Hard to fall. However, in the toner image G1 after fixing when the dither processing is performed, the toner is peeled off due to the presence of the toner t2 which is not dissolved on the surface of the recording material or the case where the toner t3 which is not dissolved exists in the toner layer. You can see that it is easier.

  As described above, in the low consumption mode, the image data is analyzed to reduce the area of the pixel where the pixels are densely compared with the means for reducing the toner consumption by changing the development contrast for the same latent image as in the normal mode. By means of gradation processing and forming an electrostatic latent image different from the normal mode to reduce toner consumption, not only the amount of toner on the recording material is reduced, but Since the state of the toner formed on the toner is different, the bonding force between the toners or between the toner and the recording material is weakened, which may affect the fixability.

  Therefore, according to the present invention, in an image forming apparatus having a low consumption mode capable of reducing the developer (toner) consumption, image data is analyzed for each pixel to obtain a solid black image having a relatively large number of pixels to be developed. Even in a low-consumption mode in which area gradation processing is performed, such as means for performing dither processing on a pixel basis or means for analyzing image data for each pixel and controlling laser emission time in units of dots to form a halftone image. The object is to obtain sufficient image fixability.

  According to the present invention, the above object is an image forming apparatus that forms an electrostatic latent image on an image carrier and visualizes the electrostatic latent image with a developer, and does not suppress the consumption of the developer. The image forming mode and the electrostatic latent image are formed on the image carrier by area gradation processing, thereby reducing the amount of developer consumption for developing the electrostatic latent image as compared with the normal image forming mode. Achieved by increasing the amount of heat at the time of fixing a developer image in the image forming apparatus capable of selecting the developer low consumption image forming mode in the developer low consumption image forming mode than in the normal image forming mode. Is done.

  Low developer image formation mode that reduces the amount of developer consumed by area gradation processing by increasing the amount of heat when fixing the developer image in the low developer image formation mode than in the normal image formation mode Even in the mode, it is possible to obtain a good image fixing property which is not different from the normal image forming mode.

(1) Example of Image Forming Apparatus FIG. 3 is a model diagram of a schematic configuration of an image forming apparatus according to the present invention. The image forming apparatus of this example is a process cartridge detachable laser beam printer using a transfer type electrophotographic process.

  Reference numeral 1 denotes a printer body. Reference numeral 2 denotes a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier (image forming carrier). The photosensitive drum 2 is formed by forming a photosensitive material such as OPC or amorphous Si on a cylindrical substrate such as aluminum or nickel, and is rotated at a predetermined peripheral speed in the clockwise direction indicated by an arrow by the driving means 2A. Driven.

  A charging means 3 uniformly charges the peripheral surface of the rotating photosensitive drum 2 with a predetermined polarity and potential. In this example, a contact charging device using a charging roller is used.

  Reference numeral 4 denotes a digital exposure apparatus (image information exposure means), which uses a laser beam scanner in this example. The laser beam scanner 4 includes a semiconductor laser, a polygon mirror, an F-θ lens, and the like, and is turned on / off according to an image signal (image information) sent from a host device (not shown) such as a computer. The modulation-controlled laser beam L is emitted, and the uniformly charged surface of the photosensitive drum 2 is scanned and exposed through the folding mirror 4a to write and form an electrostatic latent image.

  A developing device 5 develops the electrostatic latent image on the photosensitive drum 2 as a toner image. As a development method, a jumping development method, a two-component development method, or the like is used, and is often used in combination with image exposure and reversal development.

  Reference numeral 6 denotes a transfer roller as a contact charging member in the form of a rotating body having an elastic layer, which is brought into pressure contact with the photosensitive drum 2 to form a transfer nip portion N (an image forming portion for a recording material). It is rotationally driven at a predetermined peripheral speed in the clockwise direction indicated by the arrow by means 6A.

  The toner image formed on the photosensitive drum 2 is electrostatically sequentially applied to the recording material P (transfer material) fed from the cassette paper feeding portion 9 or the manual paper feeding portion 12 to the transfer nip portion N. Transcribed.

  In the sheet feeding from the cassette sheet feeding unit 9, the recording material P of the sheet feeding unit is separated and fed by the rotation of the sheet feeding roller 10 and conveyed through the sheet path 11, and the sheet feeding from the manual sheet feeding unit 12 is performed. The recording material P of the paper feed unit is separated and fed by the rotation of the paper feed roller 13 and is conveyed through the sheet path 14. After waiting temporarily by the pre-feed sensor 15, the registration roller 16, the registration sensor 17, The paper passes through the pre-transfer guide 18 and is fed to the transfer nip N. The recording material P is synchronized with the toner image formed on the surface of the photosensitive drum 2 by the registration sensor 17 and is supplied to a transfer nip N formed by the photosensitive drum 2 and the transfer roller 6.

  The recording material P that has received the transfer of the toner image at the transfer nip portion N and has passed through the transfer nip portion N is separated from the surface of the photosensitive drum 2 and conveyed to the fixing device 20 through the sheet path 19. The fixing device 20 in the printer of this example is a film heating type fixing device composed of a pressure contact body of a heating film unit 20a and a pressure roller 20b, and the recording material P holding a toner image is the heating film unit 20a and the pressure roller. The toner image is fixed on the recording material P as a permanent image by being nipped and conveyed by the fixing nip portion T which is a pressure contact portion 20b and being heated and pressurized.

  The recording material P on which the toner image has been fixed is changed in route by the flapper 21, and if discharge to the face-up discharge tray 24 is selected, it passes through the sheet path 22 to the tray 24 by the discharge roller 23. Discharged. If discharge to the face-down discharge tray 27 is selected, the sheet passes through the sheet path 25 and is discharged to the tray 27 by the discharge roller 26.

  On the other hand, the surface of the photosensitive drum 2 after the transfer of the toner image onto the recording material P in the transfer nip N is cleaned by the cleaning device 7 after removal of the transfer residual toner, and is repeatedly used for image formation. The cleaning device 7 of this example is a blade cleaning device, and 7a is the cleaning blade.

  In the printer of this example, the four process devices of the photosensitive drum 2, the charging roller 3, the developing device 5, and the cleaning device 7 are collectively made into a process cartridge 8 that can be attached to and detached from the printer main body 1. When the developer toner stored in the container of the developing device 4 is used up, it is replaced with a new process cartridge.

(2) Low Consumption Mode Next, an outline of image processing in the low consumption mode will be described with reference to the block diagram of the control system in FIG. 1 and the control flowchart in FIG.

  In FIG. 1, reference numeral 100 denotes a host device such as a computer connected to the printer main body 1. Various electrical information is exchanged between the host device 100 and the main body control unit (main body CPU) 30 on the printer main body 1 side. Reference numerals 101 and 102 denote input image signals and input print mode signals transmitted from the host apparatus 100 side to the main body control unit 30 on the printer main body 1 side. In this example, the print mode can be selected from four modes, the normal mode in which toner consumption is not suppressed and the first to third low consumption modes, on the host device 100 side. The selected print mode signal is transmitted to the main body control unit 30 on the printer main body 1 side.

  The input image signal 101 is held in the main body control unit 30 or a storage device (not shown), and transmits image information to the image processing control unit 31. The sent image data is analyzed, and image processing is performed according to the selected input print mode. After the image processing is performed, the image data is transmitted again to the main body control unit 30, and is transmitted to the laser drive control unit 32 as a processed image after the image processing, and is used for laser emission control of the laser beam scanner 4.

  The memory unit of the main body control unit 30 stores in advance an optimum fixing temperature table for each print mode. The main body control unit 30 controls the heater drive control unit 33 so that the fixing temperature of the fixing device 20 becomes an optimum fixing temperature corresponding to the selected input print mode. That is, the temperature of the fixing device 20 is controlled so that the temperature detected by the thermistor 20c that detects the temperature of the heating film unit 20a of the fixing device 20 is maintained at the fixing temperature on the fixing temperature table corresponding to the input print mode.

  In this embodiment, in the normal mode, the fixing temperature of the fixing device 20 is set to 200 ° C., and the recording material P passes through the fixing nip T of the fixing device 20 with a throughput of 20 ppm.

  In the low-consumption mode, image data composed of binary images is analyzed for each pixel, and the laser emission time is set in units of one dot for an image pattern with a wide development area such as a solid black image having a relatively large number of pixels to be developed. Means for controlling and halftone imaging were used.

  Specifically, when the image data to be printed is analyzed and there is a dense dot pattern of 3x3 dots in the data, the laser emission time of the central dot is modulated, and the modulation degree is 1 dot emission in the normal mode Three modes were set to be 70%, 50%, and 30% of the time, respectively, and a first low consumption mode, a second low consumption mode, and a third low consumption mode were set. The first low-consumption mode, the second low-consumption mode, and the third low-consumption mode are performed in order of decreasing degree of toner loading. More toner can be reduced in the third low consumption mode than in the first low consumption mode.

  In each of the four print modes, the normal mode and the first to third low-consumption modes, the fixing temperature detected by the thermistor 20c is changed, and the A4 size is changed at each set temperature. A solid image of 3 cm square was printed in the center of the recording paper, and the fixing property was examined. The fixing level was evaluated as follows: when printing was rubbed with a finger after printing, ◯: hardly dropped, Δ: slightly dropped, x: well dropped. Table 1 shows the fixability in each print mode.

  It can be seen from Table 1 that sufficient fixing properties cannot be obtained in the first to third low consumption modes at the same fixing temperature as in the normal mode. In addition, when the fixing temperature is too high or too low for each optimum fixing temperature in each print mode, problems of hot offset and cold offset occur.

  From the results shown in Table 1, the optimum fixing temperature in each print mode was set within a set temperature range in which problems such as offset did not occur. This is shown in Table 2.

  As shown in Table 2, a table in which the fixing temperature is set so as to obtain the optimum fixing heat amount for each of the normal mode and the first to third low consumption mode print modes is created and mounted in the main body control unit or the like. It is stored in advance in a storage device, and an optimum fixing temperature is set according to the selected print mode.

  As described above, by controlling the print mode selected by the user so that the fixing temperature detected by the thermistor 20c becomes the fixing temperature based on the table, the normal mode and the first to third low consumption modes are performed. In any print mode, stable fixing properties can be obtained. In other words, in the low consumption mode, the amount of heat applied when the toner image is fixed to the recording material is appropriately increased as compared with that in the normal mode. By appropriately increasing the amount of heat at the time of thermal fixing of the toner image, stable fixing properties can be obtained in any print mode.

  A control flow of the fixing temperature in the low consumption mode in this embodiment will be described with reference to FIG.

  Image information and the selected print mode are transmitted from a host device 100 such as a computer connected to the printer body 1 (step ST1). After determining whether all image signals have been received (ST2), the designated print mode is checked (ST3). In the normal mode, the normal fixing temperature setting for the normal mode is set (ST4), and the image forming process is executed (ST5).

  When the first, second, or third low consumption mode is selected (ST6), image processing is performed according to each mode (ST7), and the fixing temperature is set according to a preset table (ST7). After that, an image forming process is executed (ST5). When image formation is performed, laser drive control is performed according to each mode, an electrostatic latent image different from the normal mode is formed on the photosensitive drum, and an image is formed by the development contrast formed by the development bias. . Thereafter, end processing is performed, and all printing operations are ended (ST9).

  As described above, by setting an appropriate fixing temperature for each print mode and switching the fixing temperature in accordance with the selected print mode, the laser emission time is controlled in units of one dot and a halftone image. Even in the low consumption mode in which the area gradation process using the converting means is performed to form an electrostatic latent image different from the normal mode, good fixability that is the same as the normal mode can be obtained.

  The low consumption mode and the fixing temperature set value described in the present embodiment are not limited to this. Further, the number of low consumption modes is not limited to this.

  Needless to say, the image forming apparatus main body 1 can also be provided with a selection unit for the print mode (normal mode, first to third low consumption modes).

  In the first embodiment, when the low consumption mode is selected, the fixing temperature of the fixing device 20 is increased to a more appropriate temperature than in the normal mode, thereby increasing the amount of heat applied to the toner and the recording material, and stable fixing even in the low consumption mode. I was able to get sex.

  In this embodiment, when the low consumption mode is selected, the amount of heat is increased by increasing the time during which the recording material passes through the fixing device 20 by lowering the recording material conveyance speed than in the normal mode. By reducing the throughput so as to obtain an appropriate amount of fixing heat when the low consumption mode is selected, the amount of heat applied to the toner and the recording material is increased, and a low consumption mode with stable fixing property is provided.

  This embodiment will be described based on the block diagram of the control system in FIG. The difference from the first embodiment is that the recording material conveyance speed is controlled as heat quantity control. Accordingly, the outline of the image processing in the low consumption mode is the same as that of the first embodiment, but in this embodiment, the fixing roller drive control circuit 34, the recording material conveyance drive control unit 35, the photosensitive member drive control unit 36, the transfer drive control. The scanner scanning drive in the unit 37 and the laser drive control unit 32 is controlled, and the recording material conveyance speed in the printer is lowered so that a sufficient amount of heat can be obtained at the time of fixing according to each print mode. In this way, control is performed so that the optimum recording material conveyance speed is obtained in order to obtain stable fixing properties even in the low consumption mode.

  The fixing temperature in the normal mode is set to 200 ° C., the recording material conveyance speed is changed in the normal mode setting and the low consumption mode setting similar to that in the first embodiment, and the same image pattern as in the first embodiment is printed with the throughput corresponding thereto. The fixing property was examined. Table 3 shows the throughput and the fixability in each print mode when the recording material conveyance speed is changed.

  From the results in Table 3, a throughput is set so that a sufficient amount of heat can be obtained when each low consumption mode is selected, as in Example 1, and Table 4 shows.

  As described above, by controlling the print mode selected by the user so as to achieve the throughput based on the table shown in Table 4, a sufficient amount of fixing heat can be obtained, and stable fixability even in the low consumption mode. Can be obtained.

  A control flow of the fixing temperature in the low consumption mode in this embodiment will be described with reference to FIG.

  Image information and the selected print mode are transmitted from a host device 100 such as a computer connected to the printer body 1 (step ST1). After determining whether all image signals have been received (ST2), the designated print mode is checked (ST3). In the normal mode, the normal throughput setting for the normal mode is set (ST4), and the image forming process is executed (ST5).

  When the first, second, or third low consumption mode is selected (ST6), image processing is performed according to each mode (ST7), and the throughput is set according to a preset table (ST8). Thereafter, an image forming process is executed (ST5). When image formation is performed, laser drive control is performed according to each mode, an electrostatic latent image different from the normal mode is formed on the photosensitive drum, and an image is formed by the development contrast formed by the development bias. . Thereafter, end processing is performed, and all printing operations are ended (ST9).

  As described above, an appropriate throughput is set for each print mode, and the laser emission time is controlled in units of dots by switching the throughput (recording material conveyance speed) according to the selected print mode. Even in the low power consumption mode in which an electrostatic latent image different from the normal mode is formed by performing area gradation processing using a means for forming a halftone image, good fixability that is the same as the normal mode is obtained. be able to.

  The set values of the low consumption mode, the recording material conveyance speed, and the throughput described in the present embodiment are not limited thereto. Further, the number of low consumption modes is not limited to this.

<Others>
1) Although the laser beam scanner 4 which is a digital exposure device is used as the means for forming an electrostatic latent image on the photosensitive drum which is the image carrier, the digital exposure device is not limited to the laser beam scanner, but the LED. It is possible to use a light emitting element array such as an array, or another digital exposure apparatus including a combination of a fluorescent lamp and a liquid crystal shutter.

  2) Further, the image bearing member is not limited to the electrophotographic photosensitive member, and may be a dielectric or an insulator having no photosensitivity. In this case, as a means for forming an electrostatic latent image on the image carrier, the surface of the image carrier is subjected to an image signal by a non-exposure type charging / discharging means such as a charging element array, a neutralizing element array, or an electron gun device. A method of drawing an electrostatic latent image by selectively charging or discharging can be used.

  3) Further, the image forming apparatus forms an electrostatic latent image on the image carrier as in 1) and 2) above, develops the electrostatic latent image with a developer, and transfers the developer image to a recording material. The transfer method is not limited to the transfer method in which the image is fixed by the fixing means, but is a direct method, that is, a sheet such as photosensitive paper or electrostatic recording paper is used as an image carrier, and an electrostatic latent image is formed on the sheet. Can be developed with a developer, and the developer image is directly fixed on a sheet by a fixing means.

2 is a block diagram of a control system of an image forming unit and a fixing heat amount control unit according to Embodiment 1. FIG. 3 is a flowchart regarding control in the first embodiment. 1 is a schematic diagram of an image forming apparatus in Embodiment 1. FIG. 6 is a block diagram of a control system of an image forming unit and a fixing heat amount control unit according to Embodiment 2. FIG. 10 is a flowchart regarding control in the second embodiment. It is the schematic about the image processing at the time of a low consumption mode. FIG. 4 is a diagram illustrating an electrostatic latent image in each of a normal mode and a low consumption mode and a state of toner formed on a recording material. FIG. 8 is an enlarged model diagram of the toner on the recording material and the toner after fixing in FIG. 7.

Explanation of symbols

  2 .... Photosensitive drum (image carrier) 3 .... Charging roller 4 .... Laser beam scanner (digital exposure device) 20 .... Fixing device

Claims (8)

An image forming apparatus that forms an electrostatic latent image on an image carrier and visualizes the electrostatic latent image with a developer, and has a normal image forming mode that does not suppress consumption of the developer, and an image carrier. Select a developer-low-consumption image formation mode that reduces the amount of developer consumption for developing an electrostatic latent image by forming an electrostatic latent image by area gradation processing, compared to the normal image formation mode. In an image forming apparatus capable of
An image forming apparatus characterized in that, in the developer low-consumption image forming mode, the amount of heat at the time of fixing a developer image is increased as compared with that in a normal image forming mode.   2. The image according to claim 1, wherein the increase in the amount of heat is performed by changing a setting fixing temperature of the developer image fixing unit to a temperature higher than a setting fixing temperature in a normal image forming mode. Forming equipment.   The image forming apparatus according to claim 1, wherein the increase in the amount of heat is performed by lowering a throughput of the image forming apparatus below a set throughput in a normal image forming mode.   The amount of heat at the time of fixing a developer image in the developer low-consumption image forming mode is changed according to a plurality of developer low-consumption image forming modes having different ratios for reducing the developer consumption amount. Item 4. The image forming apparatus according to any one of Items 1 to 3.   5. The digital exposure apparatus according to claim 1, wherein the electrostatic latent image forming means for the image carrier is a digital exposure device that irradiates the image carrier with light that is on-off modulated in accordance with an image signal. The image forming apparatus according to any one of the above.   The area gradation processing of the electrostatic latent image in the developer low-consumption image forming mode uses means for modulating the lighting width corresponding to each pixel in the image signal of the digital exposure apparatus. The image forming apparatus according to claim 5.   The image forming apparatus according to claim 5, wherein the digital exposure apparatus is a laser beam scanner or a light emitting element array.   The means for forming an electrostatic latent image on the image carrier is a non-exposure type charging / discharging means such as a charging element array, a neutralization element array, or an electron gun device, and the surface of the image carrier is selectively charged according to an image signal. The image forming apparatus according to claim 1, wherein an electrostatic latent image is drawn by removing electricity.

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