JP2015219342A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that selectively consumes an aggregation toner while suppressing an increase in cost and size to prevent scattering of toner.SOLUTION: An image forming apparatus 900 includes: a photoreceptor drum 101; a developing device 104 that includes a developing sleeve 24 carrying a developer and develops an electrostatic image on the surface of the photoreceptor drum 101 with the developer; an attribute flag integration part 1006 that integrates, from among attributes of an image to be provided to each of pixels, the amount corresponding to the amount of the pixels to which a predetermined attribute is provided; and a CPU 800 that controls to execute a discharge control mode in which when the integrated value integrated by the attribute flag integration part 1006 reaches a predetermined integrated amount, a toner that is not used for image formation on a recording material P is transferred from the developing sleeve 24 to the photoreceptor drum 101.

Description

  The present invention relates to an image forming apparatus having a developing device.

  Patent Document 1 discloses a technique for applying a toner scattering prevention bias in order to prevent toner scattering on the downstream side in the rotation direction of the developing sleeve.

JP 2010-231017 A

  However, in the image forming apparatus described in Patent Document 1, since the scattering prevention electrode is disposed, the cost of the developing device is increased and the size thereof is increased. Further, when image formation with a low printing rate is continued in such an image forming apparatus described in Patent Document 1, toner agglomerates are generated in the developer, the influence of centrifugal force increases, and toner scattering increases.

  An object of the present invention is to provide an image forming apparatus provided with a developing device in which aggregation toner is selectively consumed and prevention of toner scattering is realized while suppressing an increase in cost and an increase in size.

  In order to achieve the above object, an image forming apparatus of the present invention includes an image carrier, an exposure unit that exposes the surface of the image carrier to form an electrostatic image, and a developer carrier that carries a developer. A developing device for developing an electrostatic image on the surface of the image carrier with a developer, and an amount corresponding to a pixel amount to which a predetermined attribute is given among attributes of an image given to each pixel. Control is performed to execute an ejection control mode for transferring the toner that is not image-formed on the recording material from the developing device to the image carrier when the integrated value integrated by the integrating device reaches a predetermined integrated amount. And a controller.

  According to the present invention, the aggregated toner is selectively consumed while suppressing the increase in the size and the increase in size, thereby preventing the toner from being scattered.

(A) is sectional drawing of the image forming apparatus which concerns on Example 1, (b) is an enlarged view of an image forming part. 2 is a block diagram of image processing inside the apparatus main body. FIG. It is a block diagram of an intermediate image processing unit. It is a block diagram etc. which show the structure of an output image process part. An example of a specific image for detecting the attribute of each image data included in the input image data described above and generating attribute flag data for identifying the attribute is shown. It is a graph which shows the example which plotted G signal among the signal values (R, G, B) which a CCD sensor reads in each area | region in the arrangement direction of CCD. An example of the attribute flag generated for the document image of FIG. It is sectional drawing which looked at the developing device from the side. It is sectional drawing which looked at the developing device from the upper part. They are a graph showing the distribution of the toner scattering amount when only the character flag is used, and a graph showing the distribution of the toner scattering amount when only the graphic flag is used. It is a flowchart which shows the toner discharge control of a controller. Here, it is a flowchart showing the scattered toner discharging operation. 6 is a graph showing the particle size distribution of toner developed on the photosensitive drum 101 when a developer that is composed only of character attribute flags and is developed at 10,000% with a printing rate of 1% is developed with various developing biases. . It is a control block diagram. It is a table | surface of the coefficient multiplied when weighting the integrated amount which concerns on Example 2 for every attribute. 6 is a flowchart illustrating toner discharge control.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, since the dimensions, materials, shapes, relative positions, etc. of the components described in this embodiment are appropriately changed depending on the configuration of the apparatus to which the invention is applied and various conditions, there is no specific description. As long as the scope of the invention is not limited to these, it is not intended.

  FIG. 1A is a cross-sectional view of the image forming apparatus 900 according to the first embodiment, and FIG. 1B is an enlarged view of the image forming unit Y. The image forming apparatus 900 includes an apparatus main body 900A. Image forming units Y, M, C, and K are arranged inside the apparatus main body 900A. The image forming units Y, M, C, and K each include a photosensitive drum 101 (101Y, 101M, 101C, and 101K) as an “image carrier”. Above the image forming portions Y, M, C, and K, an intermediate transfer device 1200 is disposed. The intermediate transfer device 1200 includes an intermediate transfer belt 121 as an intermediate transfer member. The intermediate transfer belt 121 is stretched around rollers 122, 123, and 124 and travels in the direction of the arrow.

  The surface of the photosensitive drum 101 is charged by a charging roller type primary charging device 102 (102Y, 102M, 102C, 102K) that is contact charging. The surface of the photosensitive drum 101 is exposed by a laser 103 (103Y, 103M, 103C, 103K) driven by an exposure device 103X as an “exposure unit” to form an electrostatic image. The electrostatic image on the surface of the photosensitive drum 101 is developed with toner by the developing device 104 (104Y, 104M, 104C, 104K), and yellow, magenta, cyan, and black toner images are formed, respectively. An application unit 150 that applies a voltage to the developing sleeve 24 is connected to the developing sleeve 24 of the developing device 104.

  The toner image formed by each of the image forming portions Y, M, C, and K is transferred to a transfer roller 105 (105Y, 105M, 105C, and 105K) serving as a primary transfer unit. The image is transferred onto 121 and superimposed. The four-color toner images formed on the intermediate transfer belt 121 are transferred onto the recording material P by a secondary transfer roller 125 as a secondary transfer unit disposed to face the roller 124. The toner remaining on the intermediate transfer belt 121 without being transferred to the recording material P is removed by the cleaner 114b.

  The recording material P to which the toner image has been transferred is pressed and heated by a fixing device 130 having fixing rollers 131 and 132 to obtain a permanent image. Further, the primary transfer residual toner remaining on the photosensitive drum 101 after the primary transfer is removed by the cleaner 109 (109Y, 109M, 109C, 109K). Then, the potential on the photosensitive drum 101 is erased by the pre-exposure lamp, and the photosensitive drum 101 is again used for image formation.

  FIG. 2A is a block diagram of image processing inside the apparatus main body 900A. The selector 100 receives image information from the image scanner unit 110 and the page description language lettering unit 120. The image scanner unit 110 is a part that scans image information, and the page description language lettering unit 120 is a part that reads a page description language (PDL). The image information received by the selector 100 is subjected to image processing by the input image processing unit 200, the intermediate image processing unit 300, and the output image processing unit 400, and then output by the printer unit 500.

  FIG. 2B is a block diagram of the input image processing unit 200 in FIG. The sub-scanning color misregistration correction unit 201 is a part that corrects color misregistration in the sub-scanning direction of the input image, for example, performs a 1 × 5 matrix operation for each color of image data. The main scanning color misregistration correction unit 202 is a part that corrects color misregistration in the main scanning direction of the input image, for example, performs a 5 × 1 matrix operation for each color of the image data.

  The image area determination unit 203 as a “generating unit” is a part that generates an attribute flag indicating an image attribute for each pixel. The image area determination unit 203 identifies pixels constituting each image type, such as a photograph part / character part, chromatic part / achromatic part, etc. in the input image, for example, and sets attribute flag data indicating the type in pixel units It can be generated by Details will be described later with reference to FIGS. The filter processing unit 204 is a part that performs, for example, a 9 × 9 matrix operation that arbitrarily corrects the spatial frequency of the input image.

  The histogram unit 205 is a processing unit that samples a histogram of image data in the input image, and determines whether the input image is a color image or a monochrome image, and determines the background level of the input image. The input color correction unit 206 is an input color correction unit that corrects the color of the input image, and converts the color space of the input image into an arbitrary color space or corrects the color of the input system.

  The image data processed by the input image processing unit 200 and the attribute flag data generated by the image area determination unit 203 are transferred to the intermediate image processing unit 300. If generation of attribute flag data in the rendering unit of the page description language (PDL) 120 or image processing of the input image processing unit 200 has already been performed, the following is performed. That is, the processing of the input image processing unit 200 may be allowed to pass through, or the image data and the attribute flag data may be input to the intermediate image processing unit 300 without passing through the process.

  The input image processing unit 200 is not limited to the above-described image processing units 201, 202, 203, 204, 205, and 206, and other image processing modules may be added or deleted. Also, the order of the image processing units is not limited to this.

  FIG. 3 is a block diagram of the intermediate image processing unit 300. The image data from the input image processing unit 200 and the attribute flag data obtained by determination by the image area determination unit are transferred to the intermediate image processing unit 300 and subjected to the following processing.

  The attribute flag replacement unit 301 replaces or adds attribute flag data. The details will be described with reference to FIG. 6, but before or after the compression processing after 303, the attribute flag data generated by the image area determination unit 203 in the input image processing unit 200 is replaced as necessary. Or processing for adding attribute flag data. Image data and attribute flag data pass through the image bus 302.

  The compressed block line buffer 303 divides the image data and attribute flag data into tiles. Then, for each tile M × N pixel (where the size of the tile is M × N), color information encoding, discrete cosine transform encoding (JPEG), and attribute flag data information encoding run Encoding is performed by dividing into length encoding.

  However, M and N must be multiples of the window size for discrete cosine transform coding. In this embodiment, the case of the JPEG compression method will be described. In the JPEG compression method, the window size for compression is 8 × 8 pixels. Therefore, for example, if M = N = 32, the 32 × 32 pixel tile is further divided into 16 8 × 8 pixels, and JPEG compression is performed in units of 8 × 8 pixels (hereinafter described as M = N = 32). But of course not limited to that value).

  The image data encoding unit 304 quantizes the 16 8 × 8 pixel windows included in the 32 × 32 pixel tile image by performing a known DCT transform. The quantization coefficient used at this time (referred to as a quantization matrix) can be switched and set for each tile.

  For switching, the determination unit 305 refers to attribute flag data of 32 × 32 pixels corresponding to certain predetermined image data 32 × 32 pixels per tile. For example, if the attribute flag data of 32 × 32 pixels includes an attribute indicating a character even in one pixel, the image data 1 tile composed of the 32 × 32 pixels is regarded as a character tile, and the image The data 1 tile is compressed by the encoding coefficient for characters.

  If even one pixel does not contain an attribute indicating a character, the image data 1 tile is regarded as a photo tile, and the image data 1 tile is quantized so that the image data 1 tile is compressed with a photo coding coefficient. A command is issued to 306. The quantization matrix selection unit 306 selects a predetermined encoding coefficient, sets it to the image data encoding unit 304, and compresses the image data with a compression coefficient that is different for each tile.

  The attribute flag data is compressed by the attribute flag encoding unit 307. The encoded image data and attribute flag data are stored as compressed image data and compressed attribute flag data in the hard disk 309 via the compression memory 308.

  When the stored image is output from the printer unit, or when the attribute flag data replacement process is performed by the attribute flag replacement unit 301, the image data and the attribute flag data stored in the hard disk 309 are read out. Decrypt and output in the procedure of First, the compressed and stored image data and attribute flag are extracted to the compression memory 310, and the attribute flag data for M × N pixels is decoded by the attribute flag decoding unit 314. This compression memory 310 may be the same as the previous compression memory 308.

  The determination unit 312 performs attribute determination processing based on the attribute flag data decoding result to determine whether one tile of each image data is a character tile or a photo tile from the attribute flag data, and the quantization matrix selection unit 313 Send a command to select a compression decoding factor for each tile. The quantization matrix selection unit 313 selects a compression decoding coefficient to be used for each tile and sends it to the image data decoding unit 311. The image data decoding unit 311 switches the coefficient for each tile to change the image data. Is decoded and then output to the line buffer 315.

  The determination unit 305 and the determination unit 312 make exactly the same determination, and the attribute flag data is compressed by a lossless compression method such as run-length encoding that does not deteriorate the data, so that it is the same during encoding and decoding. The determination results corresponding to the tiles are exactly the same. Therefore, even if quantization is performed with a different quantization coefficient for each tile, an appropriate inverse quantization coefficient is set at the time of decoding, so that correct decoded image data can be obtained.

  The image data encoding unit 304 and the image data decoding unit 311 will be further described with reference to FIG. 3, and the attribute flag encoding unit 307, which is a run-length encoder for attribute flag data, will be further described with reference to FIG. To do. Further, the configuration in the intermediate image processing unit 300 is not limited to the configuration described above, and other image processing modules may be added or deleted, and the configuration is not limited thereto.

  FIG. 4A is a block diagram illustrating a configuration of the output image processing unit 400. The background removal unit 401 is a part that removes the background color of image data and removes unnecessary background fogging. For example, the background removal unit 401 performs background removal by 3 × 8 matrix calculation or one-dimensional LUT.

  The monochrome generation unit 402 is a part that converts color image data, for example, RGB data into Gray single color when the color image data is converted into monochrome data and printed as a single color. For example, it is composed of a 1 × 3 matrix operation that multiplies RGB by an arbitrary constant to obtain a Gray signal. The output color correction unit 403 is a part that performs color correction in accordance with the characteristics of the printer unit that outputs image data. For example, it includes processing by 4 × 8 matrix calculation or direct mapping.

  The filter processing unit 404 is a part that arbitrarily corrects the spatial frequency of the image data, and includes, for example, a process of performing a 9 × 9 matrix operation. The gamma correction unit 405 is a part that performs gamma correction in accordance with the characteristics of the output printer unit. The gamma correction unit 405 is a color balance adjustment that adjusts the density balance of each color of CMYK and a density that can be adjusted to increase or decrease the overall density. Adjustment and the like are usually realized by a one-dimensional LUT. The halftone processing unit 406 is a part that performs arbitrary halftone processing according to the number of gradations of the printer unit to be output, and is a part that performs arbitrary screen processing such as binarization and binarization and error diffusion processing. It is.

  Up to this point, the input image processing unit, the intermediate image processing unit, and the output image processing unit have been described with reference to FIGS. 2 (a) to 4 (a). In each image processing unit, together with the image data, attribute flag data generated by the image region determination unit 203 for identifying the image type in the input image described with reference to FIG. Thereafter, each processing unit flows together. In accordance with the attribute flag data, image processing with an optimum processing coefficient is performed on each image region. Further, the HDD 309 has an integration means for integrating attribute flags.

  In the filter processing unit 404 of the output image processing unit in FIG. 4A, the high frequency component of the image is emphasized with respect to the character region to enhance the sharpness of the character, and so-called low-pass filter processing is applied to the halftone dot region. And removing the moire component peculiar to the digital image. In this way, each processing module can perform high-quality image processing by performing optimal processing on the image area in accordance with the attribute flag data.

  FIG. 4B is a block diagram of the image data encoding unit 304 and the image data decoding unit 311 described in FIG. The attribute flag data will be described in detail with reference to FIG.

  The image data signal 500 is an input signal. In the case of a color signal, the image data signal 500 is an image data signal of three colors of red (R), green (G), and blue (B). The color converter 501 converts the RGB signal into a luminance color difference signal (YCbCr). A discrete cosine transform (DCT) 502 performs a spatial frequency transform (DCT transform) on each luminance / chrominance signal in units of 8 × 8 pixels.

  The quantizer 503 reduces the amount of data by quantizing the DCT coefficients using the set quantization matrix. A variable length encoder (VLC) 504 further reduces data by performing a Huffman encoding process on the quantized value. The above is the color image encoder unit, and the compressed image data is stored in the compression memory 505. The compression memory 505 corresponds to the compression memory 308 described with reference to FIG.

  The image data stored in the compression memory 308 is stored in the mass storage device HDD 309 and is stored in the compression memory 310 at the time of decoding, and then the decoding process is performed. The compression memory 308, HDD 309, and compression memory 310 in FIG. 3 correspond to the compression memory 505 in FIG. Data stored in the compression memory 505 is decoded in the following procedure.

  A variable length decoder (VLD) 506 performs Huffman decoding. The inverse quantizer 507 returns the DCT coefficient value to the set inverse quantization matrix. The IDCT 508 performs inverse DCT inverse transformation to return to a luminance / color difference signal. The color converter 509 returns the luminance color difference signal to the RGB signal. The color image signal 510 is output to the outside as a result of the above compression and decoding processes.

  FIG. 4C is a block diagram of the attribute flag encoding unit 307, which is a run-length encoder for attribute flag data described with reference to FIG. In the figure, a determination unit 600 determines whether the value of the previous pixel and the value of the current pixel of the input attribute flag data are the same. If the values are the same, the determination is performed by the RL code generation unit 601. Switch to send data.

  The RL code generation unit 601 counts the number of times the same as the previous pixel data until different data comes out, and finally outputs the repeated data. The LT code generation unit 602 counts the number of cases where the data is different from the previous pixel, and outputs the code word corresponding to the count number and the minimum number of constituent bits of the actual data by the count number. The synthesizer 603 synthesizes the output data of the RL code generator 601 and the output data of the LT code generator 602 and outputs the result as a code 604.

  FIG. 5 shows an example of a specific image for detecting the attribute of each image data included in the input image data described above and generating attribute flag data for identifying the attribute. In the original document image data 701 showing an input example, a silver halide photograph region 702, a black character region 703, a halftone dot region 704, and a color graphic region 705 are mixed. Here, the scanner unit scans the original image with a color CCD sensor and reads it as a color digital signal (R, G, B) for each pixel. The read RGB signal has a characteristic determined by an attribute for each region of the image.

  FIG. 6 is a graph showing an example in which G signals among signal values (R, G, B) read by the CCD sensor in each region are plotted in the CCD arrangement direction. This figure shows the characteristic of the read signal value when each image attribute is read by the CCD sensor.

  Areas 820, 830, 840, and 850 in the graph of FIG. 5 are examples of characteristics that appear characteristically when the areas from 702 to 705 in FIG. 5 are read. The horizontal axis represents the pixel position in the CCD and the vertical direction, the vertical axis represents the read signal value, and the pixel is closer to white (brighter) as it goes upward. The characteristics of each region will be described below.

  Since the area 820 is a photographic area, the change due to the position of the image signal to be read is relatively gentle, and the difference 821 between the pixel values at a short distance is a small value. The area 830 is a characteristic of the black character region 703. Since black characters are written on a white background, the plot of the signal value has such a characteristic that the read signal value changes rapidly from the white background portion 831 to the character portion 832. .

  The area 840 is a characteristic of the halftone dot region 704. The halftone dot region is a repetition of the white background 841 and the halftone dot 842 printed thereon, so that the signal value plotted is white as shown in the figure. Black is a characteristic that repeats at a high frequency (frequency). Area 850 is a plot of the graph area. The graphic edge portion 851 has a signal value that suddenly decreases, and the internal colored portion 852 has a characteristic that a certain intermediate level continues.

  In order to determine these attributes, the characteristics for each region as described above may be read and detected from the signal value. For this purpose, the amount of change in the image data in the vicinity of the pixel of interest or the integrated value of the amount of change within a certain interval, the luminance value of the surrounding pixels (whether white or colored background), white to black of the image data within the certain interval A feature extraction method using a well-known method such as the number of times of change is used. Also, a well-known attribute discrimination method based on it can be used.

  FIG. 7 shows an example of an attribute flag generated for the document image of FIG. This figure shows an example of attribute flag data of the input image 201 described in FIG. In the figure, three types of flags, a character flag, a graphic flag, and a halftone flag, are generated as attribute flag data. However, the present invention is not limited to this.

  In the character flag 901, the pixel represented by black in the figure has a pixel attribute, character flag = 1 is generated, and the character flag = 0 (the white part in the figure) is otherwise. The graphic flag 902 is an area that becomes 1 in the graphic area and 0 otherwise. The halftone dot flag 903 is an area that becomes 1 in the halftone area and 0 otherwise. Since the graphic area 904 (photo area) does not correspond to any of the above-described 901, 902, and 903, that is, it can be treated as an area other than characters, graphics, and dots, so all the flags are 0. In the example of 5, it is all white.

  When these are collected as 3-bit (bit2, bit1, bit0) signals, the following relationship is obtained.

Value bit2 bit1 bit0
One character graphic halftone dot
Other than 0 characters Other than graphics Other than halftone dots

  As in this example, it may be distinguished by binary system, for example, character 100, non-character 000, graphic 010, non-graphic 000, halftone dot 001, halftone dot 000, non-character 000, non-graphic 000, other than halftone dot 000 can also be a photo.

  When the attribute of the image is detected for each pixel by the above image area separation process, as described above, the image processing according to the image attribute is performed by each image processing unit. As mentioned earlier, the high-frequency component of the image is emphasized for the character area to enhance the sharpness of the character, and the so-called low-pass filter processing is applied to the dot area, so that the moire component peculiar to digital images Can be performed. These processes can be switched in units of pixels according to the attribute flag data generated by the image area determination unit 203.

  Also, in the output from the application via the driver, image area information is generated on the application side and processed by rendering in the page description language. The image area separation means is not limited to this. As a result, various known means may be used as long as the attribute flag data can be generated.

  For example, a Microsoft WORD may have the following in information in an image for one sheet. First, there is information on the number of pixels (pixel amount) of the character associated with the number of pixels (pixel amount) to which the character attribute assigned to the character area is assigned. Second, there is information on the number of pixels (pixel amount) of a graphic associated with the number of pixels (pixel amount) to which an attribute of a graphic (for example, drawing by a power point) given to the graphic area is given. Third, there is information on the number of pixels (pixel amount) of halftone dots associated with the number of pixels (pixel amount) to which the halftone dot attribute assigned to the halftone dot region is assigned. Note that a flag is not set because there is no information on the number of pixels in the attribute of the graphic (eg, photo) assigned to the graphic area.

  In this case, the CPU 800 of the image forming apparatus 900 receives the number of pixels (pixel amount) corresponding to the character, graphic, and halftone dot attributes, and creates a character flag, graphic flag, halftone dot, and the like.

  Note that the operation of the CPU 800 varies depending on the following usage conditions. When the user uses the image forming apparatus 900 as a copying machine, the image area determination unit 203 as “generating means” generates an attribute flag indicating the attribute of the image (character, graphic, halftone dot) for each pixel. To do. Then, an attribute flag integrating unit 1006 as “integrating means” integrates the amount corresponding to the pixel amount indicating a predetermined attribute among the attribute flags generated by the image area determining unit 203.

  On the other hand, when the user uses the image forming apparatus 900 as a printer, the image area determination unit 203 does not generate an attribute flag. This is because an attribute flag is assigned to information data such as WORD and the image area determination unit 203 does not need to generate an attribute flag. Then, an attribute flag integrating unit 1006 as “integrating means” integrates an amount corresponding to a pixel amount to which a predetermined attribute is given among attributes of an image given to each pixel of information data such as WORD. .

  FIG. 8 is a cross-sectional view of the developing device 104 as viewed from the side. FIG. 9 is a cross-sectional view of the developing device 104 as viewed from above. The developing device 104 includes a developing container 20 as a “storage unit” that stores the developer. In the developing container 20, a two-component developer containing toner as a developer and a carrier is accommodated. Further, a developing sleeve as a “developer carrying member” that is disposed in the opening of the developing container 20 and carries the developer in the developing container 20 in order to develop the electrostatic image on the surface of the photosensitive drum 101 with the developer. 24 is arranged. Further, a regulating blade 25 that regulates the ears of the developer carried on the developing sleeve 24 is disposed in the developing container 20.

  The interior of the developing container 20 is divided into a developing chamber 21a and a stirring chamber 21b on the left and right in the horizontal direction by a partition wall 23 extending in a direction perpendicular to the surface of this paper. It is accommodated in the chamber 21b.

  In the developing chamber 21a and the agitating chamber 21b, first and second screws 22a and 22b, which are conveying members as developer agitating and conveying means, are arranged, respectively. The first screw 22a is disposed substantially parallel to the bottom of the developing chamber 21a along the axial direction of the developing sleeve 24, and rotates to convey the developer in the developing chamber 21a in one direction along the axial direction. To do. The second screw 22b is disposed at a bottom portion in the stirring chamber 21b substantially in parallel with the first screw 22a, and conveys the developer in the stirring chamber 21b in the opposite direction to the first screw 22a.

  As described above, the developer is agitated with the developing chamber 21a through the openings (that is, the communicating portions) 26 and 27 (see FIG. 9) at both ends of the partition wall 23 by the conveyance by the rotation of the first and second screws 22a and 22b. It circulates between chambers 21b. In the present embodiment, the developing chamber 21a and the stirring chamber 21b are arranged on the left and right in the horizontal direction. However, in the developing device in which the developing chamber 21a and the stirring chamber 21b are arranged up and down, or in other forms of developing devices, The present invention is applicable.

  In this embodiment, there is an opening at a position corresponding to the developing area A of the developing container 20 facing the photosensitive drum 101, and the developing sleeve 24 is partially exposed in the photosensitive drum direction at this opening. It is rotatably arranged.

  In this embodiment, the developing sleeve 24 has a diameter of 20 mm, the photosensitive drum 101 has a diameter of 30 mm, and the closest region between the developing sleeve 24 and the photosensitive drum 1 is set to a distance of about 300 μm. With this configuration, the developer conveyed to the development area A is set so that development can be performed in a state where the developer is in contact with the photosensitive drum 101. The developing sleeve 24 is made of a nonmagnetic material such as aluminum or stainless steel, and a magnet roller 24m, which is a magnetic field means, is installed in a non-rotating state inside the developing sleeve 24.

  With the above configuration, the developing sleeve 24 rotates in the direction indicated by the arrow (counterclockwise) during development, and carries the two-component developer whose layer thickness is regulated by the cutting of the magnetic brush by the regulating blade 25. The developing sleeve 24 conveys the developer whose layer thickness is regulated to the developing area A facing the photosensitive drum 101, supplies the developer to the electrostatic image formed on the photosensitive drum 101, and outputs the electrostatic image. Develop.

  At this time, in order to improve the developing efficiency, that is, the toner application rate to the electrostatic image, a developing bias voltage in which a DC voltage and an AC voltage are superimposed is applied to the developing sleeve 24 from a power source. In this example, a DC voltage of −500 V, a peak-to-peak voltage Vpp of 1800 V, and an AC voltage having a frequency f of 12 kHz were used. However, the DC voltage value and the AC voltage waveform are not limited to this.

  In general, in the two-component magnetic brush development method, when an AC voltage is applied, the development efficiency increases and the image becomes high-quality, but conversely, fogging easily occurs. For this reason, fogging is prevented by providing a potential difference between the DC voltage applied to the developing sleeve 24 and the charged potential of the photosensitive drum 1 (that is, the white background potential).

  The regulation blade 25 that is a ear cutting member is formed of a nonmagnetic member formed of plate-like aluminum or the like extending along the longitudinal axis of the developing sleeve 24. Further, the regulating blade 25 is disposed upstream of the photosensitive drum 101 in the developing sleeve rotation direction. Then, both the developer toner and the carrier pass between the tip of the regulating blade 25 and the developing sleeve 24 and are sent to the developing area A.

By adjusting the gap between the regulating blade 25 and the surface of the developing sleeve 24, the amount of the developer magnetic brush carried on the developing sleeve 24 is regulated and the amount of developer conveyed to the developing region is adjusted. Is done. In this embodiment, the developer coating amount per unit area on the developing sleeve 24 is regulated to 30 mg / cm ² by the regulating blade 25. The gap between the regulating blade 25 and the developing sleeve 24 is set to 200 to 1000 μm, preferably 300 to 700 μm. In this embodiment, it is set to 500 μm.

  In the developing area A, the developing sleeve 24 of the developing device 104 is moved in both the moving direction and the forward direction of the photosensitive drum 101, and the peripheral speed ratio is 1.80 times that of the photosensitive drum 101. Yes. The peripheral speed ratio is set between 0 and 3.0 times, and preferably any number as long as it is set between 0.5 and 2.0 times. The larger the moving speed ratio, the higher the development efficiency. However, if the movement speed ratio is too large, problems such as toner scattering and developer deterioration occur. Therefore, the moving speed ratio is preferably set within the above range.

<Developer replenishment method>
Next, a developer replenishing method in this embodiment will be described. Above the developing device 104, a hopper 31 that contains a two-component developer for replenishment in which toner and carrier are mixed (usually toner / replenishment developer = 100% to 80%) is disposed. The hopper 31 constituting the toner replenishing means includes a screw-shaped replenishing member, that is, a replenishing screw 32 at a lower portion, and one end of the replenishing screw 32 is provided at a developer replenishing port 30 provided at a rear end portion of the developing device 104. Extends to position.

  The toner consumed by the image formation passes through the developer supply port 30 from the hopper 31 and is supplied into the developing container 20 by the rotational force of the supply screw 32 and the gravity of the developer. The amount of replenishment developer replenished from the hopper 31 to the developing device 104 in this way is roughly determined by the number of rotations of the replenishment screw 32. The number of rotations is determined by a toner replenishment amount control unit (not shown) based on a video count value of image data, a detection result of a toner density detection unit (not shown) installed in the developing container 20, and the like.

<Overview of developer in developing device>
Here, the two-component developer 1 composed of toner and carrier housed in the developing container 20 of the developing device 104 of this embodiment will be described in detail.

  The toner includes colored resin particles containing a binder resin, a colorant, and other additives as necessary, and colored particles to which an external additive such as colloidal silica fine powder is externally added. Yes. The toner is a negatively chargeable polyester resin, and the volume average particle size is preferably 4 μm or more and 10 μm or less. More preferably, it is 8 μm or less.

  Further, in recent toners, a toner having a low melting point or a toner having a low glass transition point Tg (for example, Tg ≦ 70 ° C.) is often used in order to improve the fixability. Further, in some cases, the toner contains a wax in order to improve the separability after fixing.

As the carrier, for example, surface-oxidized or non-oxidized iron, nickel, cobalt, manganese, chromium, rare earth and other metals and their alloys, or oxide ferrite can be preferably used. The method for producing the particles is not particularly limited. The carrier has a weight average particle diameter of 20 to 60 μm, preferably 30 to 50 μm, and a resistivity of 10 ⁷ Ωcm or more, preferably 10 ⁸ Ωcm or more. In this example, a 10 ⁸ Ωcm one was used.

  Incidentally, the volume average particle diameter of the toner used in this example was measured by the following apparatus and method. As a measuring device, an SD-2000 sheath flow electric resistance type particle size distribution measuring device (manufactured by Sysmex Corporation) was used. The measuring method is as follows.

  That is, 0.1 ml of surfactant, preferably alkylbenzene sulfonate, is added as a dispersant to 100 to 150 ml of 1% NaCl aqueous electrolytic solution prepared using primary sodium chloride, and 0.5 to 50 mg of a measurement sample is added. Add. The electrolytic aqueous solution in which the sample is suspended is subjected to dispersion treatment for about 1 to 3 minutes using an ultrasonic disperser, and particles having a size of 2 to 40 μm using an SD-2000 sheath flow electric resistance type particle size distribution measuring apparatus as a 100 μm aperture. The particle size distribution is measured to determine the volume average distribution. The volume average particle diameter is obtained from the volume average distribution thus obtained.

  For the carrier resistivity, a sandwich type cell having a measurement electrode area of 4 cm and an interelectrode spacing of 0.4 cm was used. Measurement was performed by applying an applied voltage E (V / cm) between the two electrodes to one electrode under a pressure of 1 kg and obtaining the carrier resistivity from the current flowing in the circuit.

<Control method of scattering toner discharge control mode>
Hereafter, a method for controlling the operation of the scattered toner discharge control mode, which is a characteristic part of the present invention, will be described in detail.

  Conventionally, when image formation with a low printing rate is continued, since the ratio of the toner transferred from the developing container 20 to the photosensitive drum 101 is small, the toner in the developing container 20 is stirred by the first and second screws 22a and 22b. Or, it is rubbed for a long time when passing through the regulating blade 25.

  As a result, the external additive of the toner is peeled off or the external additive is embedded in the toner surface, so that the exposure of the toner resin surface becomes remarkable. It has been found that the loss of the external additive from the toner surface in this way increases the binding between the toners and generates toner agglomerates.

  In this case, it has been found that not the printing rate but the attribute of the image described above changes, so that a significant difference is caused by the generation of toner aggregates.

  The agglomerates in the developing container 20 generated as described above receive a jumping up by the first screw 22a, are carried on the developing sleeve 24, and reach the developing area A with a higher probability than ordinary toner. As a result, the toner is ejected into the image forming apparatus as scattered toner.

  This is because the toner agglomerates generated as described above have a large volume (normally, the diameter of the toner is about 20 μm compared to about 6 μm). Therefore, since the mass is large, when it reaches the developing area A, it receives a strong centrifugal force due to the rotation of the developing sleeve, and is more likely to be scattered as compared with normal toner.

  Therefore, in this embodiment, the flag data of the character attribute is integrated, and the toner aggregates accumulated in the developing container 20 in a continuous case are selectively aggregated before the toner aggregates are scattered inside the apparatus main body 900A. The mass is discharged onto the photosensitive drum 101. Then, a scattering toner discharge control mode for collecting to the cleaner 109 of the photosensitive drum 101 is provided.

  Specifically, in this embodiment, a control bias for selectively discharging the above-mentioned toner aggregate to the photosensitive drum 101 is performed by applying a developing bias having a predetermined DC voltage to the developing sleeve 24.

  In the following, in this embodiment, first, it is shown that the generation rate of toner aggregates varies depending on the image area of a specific image, and the toner scattering level varies, and from there, the scattering toner discharge control mode is set according to the printing rate. Explain how to do this.

<Relationship between generation of toner agglomerates and toner scattering amount according to image printing rate>
As described above, when the ratio of toner transfer to the photosensitive drum 101 is small and the toner replenishment to the developing container 20 is small, toner deterioration proceeds and toner aggregates are generated. Therefore, the present inventors conducted the following experiment.

  That is, the developing device 104 is installed in a certain fixed environment (temperature 23 ° C./relative humidity 50%), the video count value of the toner is set to the same 5%, and the attribute flag for determining each color of YMCK is intentionally shaken. For this purpose, two types of images with different image area integration amounts (only character flags and only graphic flags) are subjected to continuous image formation on 10000 sheets on one side of A4 size paper, and the developing device in a state after continuous image formation is performed. The change in the amount of scattered toner was examined.

  Here, as a measurement of the amount of scattered toner, in the developing device 104, a plain paper for measurement is wound so as to cover the developing area A, and the developing sleeve 24, the first screw 22a, and the second screw 22b are kept at a certain time ( Spin for 1 minute. Then, the amount of toner scattered within that time and adhered to the plain paper for measurement was observed by an optical microscope and image analysis was performed.

  FIG. 10A is a graph showing the distribution of the toner scattering amount when only the character flag is used, and the graph showing the distribution of the toner scattering amount when only the graphic flag is used. The horizontal axis represents the toner particle diameter measured by image analysis, and the vertical axis represents the number of toners having the particle diameter. According to the graph of FIG. 10A, it can be read that the toner scattering amount of the image with only the character flag is larger than the toner scattering amount of the image with only the graphic flag. It can also be seen that the toner particle size distribution of the image with only the character flag is shifted to the larger particle size side than the toner particle size distribution of the image with only the graphic flag.

  That is, in the character flag, the toner particle size tends to be large and the aggregate is likely to be large. In particular, agglomerates of toner having a toner particle size of about 20 to 35 μm are unlikely to fly to the photosensitive drum 101, and it can be said that suppressing the scattering of toner agglomerates having such a toner particle size is effective in suppressing toner scattering. .

  When the experimenter actually observed the toner adhering to the plain paper for measuring the amount of scattering with an optical microscope, many agglomerated toners were observed. From this experimental result, it was found that as the number of character flags is larger than the graphic flag, toner aggregates are more likely to be generated, and further, the toner aggregates are more likely to be scattered by idling.

  The mechanism is considered as follows. It consists of 1 to 2 lines at 600 dpi and 1 to 3 lines in most office document characters. When the exposure spot diameter is about 80 μm larger than about one pixel, it is larger than one line of 600 dpi. Therefore, considering the distribution of spot diameters, the integrated light quantity is not a solid exposure but a halftone potential.

  In the particle size distribution, the development amount of finely pulverized toner smaller than the peak increases. This is because the fine powder toner has a larger triboelectric charge amount than the coarse powder toner, and the fine powder toner is considered to be easier to develop than the coarse powder toner and the agglomerated toner due to the strong mirror power. As a result, it is considered that fine powder toner hardly remains, but coarse powder toner and agglomerated toner are likely to accumulate.

  Therefore, in this embodiment, in order not to cause the deterioration of the scattering due to the toner agglomerates, the flag integrated amount corresponding to the amount of attribute flag data generated for the minimum image area determination is set as “toner scattering threshold flag integrated amount Vt”. Is defined. This is a value that can be calculated by experiments or the like.

  FIG. 10B is a table showing the toner scattering threshold flag integrated amount A for each color in the image forming apparatus. Note that the total number of pixels of the A3 image is 65659724 pixels in the case of the present embodiment in which the margin is 600 dpi and both ends are 5 mm. That is, when the determination is made for each pixel, the sum of all the attribute flags on the entire surface of A3 is 65659724. In order to simplify the arithmetic processing, the value of this pixel was normalized to 1023, and this value was set to A3, the maximum value for one sheet.

  The amount of character flags is accumulated for each sheet. Specifically, if five character flags 224 are continuously generated, the flag integrated amount becomes 1120. Of course, these integrated values may already use compression means for various calculation values. For this reason, it can be said that when five character flags 224 are continuously generated and the flag integrated amount becomes 1120, the pixel value 1023 is exceeded.

<Control method of scattering toner discharge control mode>
Next, a control method and operating conditions of the scattered toner discharge control mode will be described. First, as a premise, the control concept of the scattered toner discharge control mode is the same for each color. Accordingly, in some cases, descriptions of colors are omitted in the following flowcharts and the like, but it should be noted that in this case, common control is performed for each color. In this embodiment, as an easy-to-understand example, an image in which the printing rate per sheet is Y = 5%, M = 5%, C = 5%, K = 1% with respect to each color of YMCK (hereinafter “black”). Let us consider a case where images are continuously formed on A4 size paper (referred to as “Low Duty Image Chart 1”).

  FIG. 11 is a flowchart showing the scattered toner discharge control by the CPU 800. When image formation starts, the image area determination unit (see FIG. 2B) of the CPU 800 generates an attribute flag for each color character (S1). The flag to be generated is determined by the method described above.

  The CPU 800 adds the attribute flag V to the integrated value X obtained by integrating the toner scattering flag since the toner aggregation occurs and the toner scattering due to the aggregation proceeds if there is a character attribute flag (S2). Here, the integrated value X is an index representing the current state of toner scattering due to the toner aggregate, and is an integrated value of the addition flag.

  The CPU 800 calculates a difference (A−X) between the threshold value A, which is a threshold value of a flag for executing the scattering toner discharge, and the integrated value X calculated and updated every time the image is formed (S3). The threshold value A is a predetermined value that can be arbitrarily set. The smaller the threshold value A, the more frequently the scattered toner discharge control operation is executed for continuous image formation with the same flag integrated amount. The threshold A is set to 112000 here. For example, there is a tendency that the threshold A can be set larger as the capacity of the developer held inside the developing container 20 is larger. The CPU 800 determines whether the difference (A−X) between the integrated value X and the threshold A is positive or negative (S4).

  When the difference (A−X) is positive (that is, when the integrated value X is less than the threshold value A), the CPU 800 generates toner agglomerates so that the scattered toner must be discharged immediately. Is determined not to proceed, and image formation is subsequently executed (S6). When the difference (A−X) is negative (that is, when the integrated value X is larger than the threshold value A), the CPU 800 generates toner agglomerates so that the scattered toner must be discharged immediately. It is determined that the process is in progress, the image formation is interrupted, and the scattered toner is discharged (S5). The CPU 800 resets the integrated value X to 0 after the scattered toner ejection operation in S5 (S7).

  FIG. 12 is a flowchart showing the scattered toner discharge control by the CPU 800. The flowchart of FIG. 12 shows a process after the image forming operation of S5 is stopped.

  When the integrated value integrated by the attribute flag integrating unit 1006 reaches a predetermined integrated amount, the CPU 800 as the “controller” does the following when the non-image part of the photosensitive drum 101 faces the developing sleeve 24. That is, the CPU 800 applies a discharge control mode in which the application unit 150 applies only a DC voltage to the developing sleeve 24 and discharges toner that does not form an image on the recording material P from the developing sleeve 24 to the photosensitive drum 101. Control to execute. This will be described in detail below. When the difference (A−X) is a negative value, the CPU 800 interrupts image formation and executes a scattered toner discharge operation.

  The CPU 800 applies a transfer bias having a polarity opposite to that during normal image formation (that is, a transfer bias having the same polarity as that of the toner image on the photosensitive drum 101) to the primary transfer bias (S101).

  The CPU 800 converts the electrostatic image on the surface of the photosensitive drum 101 for discharging scattered toner into a halftone image instead of a solid image. Then, the CPU 800 discharges the toner amount corresponding to the video count equivalent to the threshold value A for executing the scattering toner discharge to the photosensitive drum 101 (S102). Further, the CPU 800 needs to set the developing bias to be applied to the developing sleeve 24 to a DC voltage during the scattered toner discharging operation.

  This is because, according to experiments, it has been found that toner agglomerates generated by image formation differ in how they are developed on the photosensitive drum 101 depending on the type of developing bias applied to the developing sleeve. That is, the scattered toner is more likely to fly to the photosensitive drum 101 more efficiently when the DC voltage alone is used than when the AC voltage is mixed.

  FIG. 13 shows a photoconductor obtained by developing a developer that has a durability of 10,000 sheets at a printing rate of 1% with only a character attribute flag, in the case of normal AC + DC bias and in the case of DC bias for controlling the ejection of scattered toner. 3 is a graph of toner particle size distribution developed on a drum 101.

  As shown in FIG. 13, when an electrostatic image shallower than normal image formation is developed only by DC bias (a halftone image is formed), an electrostatic image shallower than normal image formation by AC + DC bias is formed. Comparison was made with the case of developing (forming a halftone image). In this case, when the image was formed only with the DC bias, the toner aggregates of 20 μm to 35 μm were more easily scattered than when the image was formed with the AC + DC bias.

  From this, it was found that toner aggregates of 20 μm to 35 μm can be selectively developed when an electrostatic image shallower than normal image formation is developed with a DC bias (DC voltage). Accordingly, it is preferable that the developing bias during the operation of ejecting the scattered toner is a DC voltage, unlike normal image formation.

  Here, the description returns to FIG. The toner discharged onto the photosensitive drum 101 is collected by the cleaner 109 of the photosensitive drum 101 without being transferred to the intermediate transfer belt 121 because the primary transfer bias has the same polarity as the toner (S103). The CPU 800 resets the integrated value X to 0 (S104). The CPU 800 returns the primary transfer bias to the positive polarity bias during normal image formation (S105). The CPU 800 completes the scattered toner discharge operation and returns to the normal image forming operation.

  FIG. 14 is a control block diagram before and after the CPU 800. An attribute flag integrating unit 1006 as “integrating means” shown in FIG. 14 integrates attribute flags. Information on the result of video counting by the attribute flag integrating unit 1006 is transmitted to the CPU 800. As described above with reference to FIGS. 11 and 12, the CPU 800 controls the ejection of the scattered toner by the scattered toner ejection control 1008. Then, the image forming unit 1009 executes image formation. As described above, in this embodiment, in the scattered toner discharge control mode, a DC voltage different from that during normal image formation is applied to the developing sleeve in order to selectively discharge the toner agglomerates that cause the scattering. The amount of scattering can be suppressed by the above operation.

  FIG. 15 is a table of coefficients to be multiplied when the integrated amount according to the second embodiment is weighted for each attribute. In the second embodiment, not only character flags but also graphic flags and halftone dots are accumulated, and scattered toner is discharged and controlled. In the first embodiment, scattered toner is discharged only by integrating character attribute flags. And it was different from the control. In the second embodiment, in consideration of the difference in the occurrence rate of the toner aggregate due to the attribute, a coefficient to be multiplied when weighting the integrated amount for each attribute is provided. In this case, the attribute flag integration unit 1006 that is an “accumulation unit” weights each character, graphic, and halftone attribute, and integrates the amount corresponding to the pixel amount to which the predetermined attribute is assigned.

  As a result, it is possible to execute appropriate scattering toner discharge considering not only the character attribute flag but also the integrated amount of the graphic attribute flag and the halftone dot attribute flag. Descriptions of block diagrams and descriptions common to the first embodiment are omitted.

  In this embodiment, the integrated value X is managed for each attribute. The integrated value of the character attribute is X1, the integrated value of the graphic attribute is X2, and the integrated value of the halftone dot attribute is X3. The toner scattering threshold flag integrated amount A is set to the same color 11200 as in the first embodiment.

  The coefficient multiplied by the integrated value of the character attribute flag is double the coefficient multiplied by the graphic or halftone attribute flag. In other words, the specific frequency of the toner discharge operation means that when only the character attribute flag is used, the frequency becomes twice as large as when the graphic and halftone attribute flags are mixed. Here, the scattered toner discharge coefficient F of the graphic and the halftone is the same. However, characters with a size larger than a predetermined size, such as 20 points, and less than a predetermined size, such as 30 points, are used as graphic attributes. It is also possible to set the toner discharge coefficient F larger than that.

  FIG. 16 is a flowchart showing toner discharge control. As a flow, S1000 to S1003 are related to character attribute flags, S1004 to S1007 are related to graphic attribute flags, and S1008 to S1011 are related to graphic attribute flags. Each flow is common to S1 to S3 of the first embodiment.

  That is, the CPU 800 calculates the character attribute flag V1 (S1000). The CPU 800 multiplies the attribute flag V1 by the scattered toner ejection coefficient F1 to create a new attribute flag V1 (S1001). The CPU 800 calculates X1 + V1 by adding the integrated value X1 and the attribute flag V1 (S1002). The CPU 800 calculates (A−X1) from the integrated value X1 and the threshold A (S1003).

  The CPU 800 calculates a graphic attribute flag V2 (S1004). The CPU 800 multiplies the attribute flag V2 by the scattered toner ejection coefficient F2 to create a new attribute flag V2 (S1005). The CPU 800 calculates X2 + V2 by adding the integrated value X2 and the attribute flag V2 (S1006). The CPU 800 calculates (A−X2) from the integrated value X2 and the threshold A (S1007).

  The CPU 800 calculates a halftone dot attribute flag V1 (S1008). The CPU 800 multiplies the attribute flag V3 by the scattering toner discharge coefficient F3 to create a new attribute flag V3 (S1009). The CPU 800 adds the integrated value X3 and the attribute flag V3 to calculate X3 + V3 (S1010). The CPU 800 calculates (A−X3) from the integrated value X3 and the threshold A (S1011).

  The CPU 800 adds the integrated values X1, X2, and X3, and determines whether the difference from A is positive or negative (S1012). S1013 to S1015 are common to S5 to S7 of the first embodiment. That is, when (A− (X1 + X2 + X3)) is positive, the CPU 800 continues to accumulate the accumulated value X without performing the operation of discharging scattered toner (S1013). On the other hand, if (A− (X1 + X2 + X3)) is negative, the CPU 800 stops image formation and executes an ejection operation (S1014). Then, the CPU 800 ends the scattered toner discharge operation and resets the integrated value X to 0 (S1015).

  As described above, in this embodiment according to the present invention, it is possible to realize more appropriate toner ejection control by having a coefficient to be multiplied by each attribute flag. Needless to say, the present invention can be carried out in combination with the conventionally known concept and method of toner discharge control according to the image duty.

  According to the configuration of the above embodiment, the agglomerated toner is selectively consumed with an inexpensive configuration, and the scattering of the toner is satisfactorily prevented. As described above, in the first embodiment, the attribute flag is a character flag. However, as in the second embodiment, the attribute flag is any two or more of a character flag, a graphic flag, and a halftone flag, and the CPU 800 weights each of the character flag, the graphic flag, and the halftone flag. But it ’s okay.

24 Development sleeve (developer carrier)
101 Photosensitive drum (image carrier)
103X exposure equipment (exposure means)
104 Developing Device 300 Intermediate Image Processing Unit (Generation Unit)
800 CPU (controller)
900 Image forming apparatus 1006 Attribute flag integration unit (integration unit)

Claims (5)

An image carrier;
Exposure means for exposing the surface of the image carrier to form an electrostatic image;
A developing device that includes a developer carrying member carrying the developer, and that develops the electrostatic image on the surface of the image carrier with the developer;
An integration unit that integrates an amount corresponding to a pixel amount to which a predetermined attribute is given among attributes of an image given to each pixel;
A controller that controls to execute an ejection control mode in which toner that is not image-formed on a recording material is transferred from the developing device to the image carrier when the integrated value integrated by the integrating unit reaches a predetermined integrated amount;
An image forming apparatus comprising:   The discharge control mode is a mode in which only a DC voltage is applied to the developer carrying member to discharge toner from the developer carrying member to the image carrying member. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the predetermined attribute is a character-only attribute.   The image forming apparatus according to claim 1, wherein the predetermined attribute is any two or more of a character attribute, a graphic attribute, and a halftone dot attribute. The predetermined attribute is any two or more of a character attribute, a graphic attribute, and a halftone dot attribute,
The image forming apparatus according to claim 1, wherein the accumulating unit weights each attribute of a character, a graphic, and a halftone dot.

Images