JP2009251263A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device allowing a refresh process to function more effectively than a conventional image forming device by consuming toner in a developing device depending on diameter of particle efficiently. <P>SOLUTION: In this image forming device, an average print rate B is computed in a control part 90, and an amount of laser exposure of an exposing device 3 is increased when the number (n) of printed paper reaches the predetermined number A. Next, the control part 90 determines whether the average print rate B is less than the predetermined value PO (here, 5%) or not. If the average print rate is less than 5%, a solid pattern is formed as a toner discharge pattern T, and if the average print rate is above 5%, a dot pattern is formed. This image forming device performs refresh for discharging toner from a developing roller 25 on a predetermined toner discharge pattern formed on a photosensitive drum 1 by the exposing device 3. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using a photosensitive drum and a developing device, and more particularly to an image forming device provided with a refresh process for refreshing toner on a developing roller during non-image formation.

  In the conventional image forming apparatus, when the image formation is repeated, particularly when the printing rate on the image (the ratio of the printed area to the area where the image can be formed (paper area); the same applies hereinafter) is low. Since there is little toner used for development by flying from the developer carrier (development roller) to the electrostatic latent image carrier (photoreceptor drum), the toner particles in the developing device are hardly replaced, and the toner is excessively charged. In some cases, image density reduction and image fogging may occur. In particular, an image forming apparatus having a plurality of developing devices such as a color machine can handle images with a high printing rate such as photographs and graphic images to images with a low printing rate such as only characters and logo marks. It is necessary to increase the variation in the printing rate for each developing device.

  In such a case, a large amount of toner is ejected from the developing roller to the photosensitive drum side by printing a pattern having a high document coverage such as a solid (solid) pattern, and the toner is transferred to a recording medium to transfer the toner. However, if the solid pattern is left unprinted for a long time without being consumed, the toner particles are fixed on the surface of the developing roller due to the influence of humidity or the like without being consumed. And may not recover.

  Therefore, the toner surface has been improved so that the charge control ability of the toner is stabilized by optimizing the surface shape, material, or external additive of the toner. At present, it has not yet been surely prevented.

  In order to solve the above-described problems, various methods for forcibly discharging the toner on the developing roller have been proposed. For example, Patent Document 1 discloses that an AC bias is applied to the developing roller during non-image formation. A one-component development-type image forming apparatus that forcibly consumes toner on the developing roller by applying it in a superimposed manner is disclosed, and black portions and white portions such as line patterns and staggered patterns are alternately combined. In addition, there is also described a method of forcibly consuming by increasing the flying of toner having a large amount of reversely charged components by using a toner discharge pattern.

Further, in Patent Document 2, an average printing rate for a predetermined number of printed sheets is calculated based on an image area rate (printing rate) measured for each recording medium, and the average printing rate falls below a predetermined value. In addition, there has been proposed an image forming apparatus in which toner is forcibly consumed.
JP 2000-206770 A JP 2004-271898 A

  The degree of image density reduction and image fogging varies depending on the charged state of the toner on the developing roller. For example, when the image density decreases, the charged-up small-diameter toner increases. On the other hand, when image fogging is likely to occur, large-diameter toners with low charge and weak electrostatic adhesion are increasing. For this reason, in order to effectively suppress image density reduction and image fogging, it is desirable to optimize the particle size of the toner to be forcibly discharged accordingly, and to suppress variations in the toner particle size distribution in the developing device. However, in the methods of Patent Documents 1 and 2, when toner is forcibly consumed, the toner is averaged over the entire particle size distribution in the developing device, so that variation in the toner particle size distribution can be suppressed. There wasn't. Further, the toner having a particle diameter optimum for development is forcibly consumed, and the efficiency is poor.

  SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an image forming apparatus that makes the refreshing process function more effectively than the prior art by efficiently consuming the toner in the developing device for each particle size.

  In order to achieve the above object, the present invention provides an exposure apparatus for irradiating an image carrier with laser light to form an electrostatic latent image, and a toner which is disposed opposite to the image carrier and carries toner and supplies the toner to the image carrier. A developing device that develops an electrostatic latent image formed on the surface of the image carrier by the exposure device, and a toner supply member that supplies toner to the toner carrier. In an image forming apparatus capable of executing a refresh process for discharging toner from the toner carrier side to the image carrier side at the time of image formation, the laser exposure amount of the exposure device is larger than that at the time of image formation when the refresh process is executed. And a toner discharge pattern is formed on the image carrier.

  According to the present invention, in the image forming apparatus having the above-described configuration, a control unit that determines the toner ejection pattern based on an average print rate of a print image calculated for each predetermined number of prints is provided.

  According to the present invention, in the image forming apparatus configured as described above, the control unit forms a solid pattern as the toner ejection pattern when the average printing rate is less than a reference value P0.

  Further, according to the present invention, in the image forming apparatus having the above configuration, the control unit outputs an image having an average printing rate less than a reference value P0 and a printing rate P1 (> P0) or more during a predetermined number of printed sheets. If not, a solid pattern is formed as the toner discharge pattern.

  According to the present invention, in the image forming apparatus configured as described above, the control unit forms a dot pattern as the toner ejection pattern when the average printing rate is equal to or greater than a reference value P0.

  Further, according to the present invention, in the image forming apparatus having the above-described configuration, the control unit outputs an image having an average printing rate of a reference value P0 or more and a printing rate of P2 (<P0) or more during a predetermined number of printed sheets. If not, a dot pattern is formed as the toner ejection pattern.

  According to the present invention, in the image forming apparatus having the above-described configuration, the dot pattern is formed by arranging one dot or a group of dots each having 2 to 6 dots on a side with an interval of 1 or more dots, and The print rate is less than 10%.

  According to the first configuration of the present invention, the refresh process is performed by utilizing the property that the change in the particle size of the toner that is preferentially consumed when the toner discharge pattern is formed is increased by increasing the laser exposure amount. Variations in the toner particle size distribution in the developing device can be effectively suppressed. Further, the duration of the refresh process and the toner consumption can be reduced.

  According to the second configuration of the present invention, in the image forming apparatus having the first configuration, the control unit determines the toner discharge pattern based on the average print rate of the print image calculated for each predetermined number of prints. By providing the above, it is possible to predict the toner particle size distribution fluctuation in the developing device from the average printing rate and automatically determine an appropriate toner discharge pattern.

  According to the third configuration of the present invention, in the image forming apparatus having the second configuration, when the average printing rate is less than the reference value P0, the solid pattern is formed as the toner ejection pattern, thereby reducing the low printing rate. When the image is continuously output and the proportion of the overcharged small-diameter toner increases, a solid pattern can be formed and the small-diameter toner can be discharged preferentially.

  According to the fourth configuration of the present invention, in the image forming apparatus having the second configuration, the average printing rate is less than the reference value P0, and the printing rate is P1 (> P0) or more during a predetermined number of printed sheets. When the image output is not performed, a solid pattern is formed as the toner discharge pattern, so that when the average printing rate is low, the overcharged small-diameter toner is preferentially discharged and the output of the high printing rate is suddenly output. In such a case, it is possible to reduce the waiting time of the user as much as possible by eliminating unnecessary refresh execution and to save the toner consumption.

  According to the fifth configuration of the present invention, in the image forming apparatus having any one of the second to fourth configurations, a dot pattern is formed as a toner ejection pattern when the average printing rate is equal to or greater than the reference value P0. Thus, when an image with a high printing rate is continuously output and the ratio of the low-charge large-diameter toner increases, a dot pattern can be formed to preferentially discharge the large-diameter toner.

  According to the sixth configuration of the present invention, in the image forming apparatus having any one of the second to fourth configurations, the average printing rate is equal to or more than the reference value P0, and the printing rate is within a predetermined number of printed sheets. When an image output of P2 (<P0) or more is not performed, a dot pattern is formed as a toner discharge pattern, so that when the average printing rate is high, low-charge large-diameter toner is discharged preferentially and suddenly When a low printing rate is output, wasteful refresh execution is eliminated, the waiting time of the user is minimized, and toner consumption can be saved.

  According to the seventh configuration of the present invention, in the image forming apparatus having the fifth or sixth configuration, a dot or a group of dots each having 2 to 6 dots on one side is spaced by 1 dot or more. By forming a dot pattern that is arranged in a matrix and has a printing rate of less than 10%, low-charge large-diameter toner can be efficiently ejected to the image carrier side.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a rotary developing type color image forming apparatus provided with the developing device of the present invention. In the image forming apparatus (here, a color printer) 100, when performing a copying operation, the photosensitive drum 1 that rotates counterclockwise in the drawing is uniformly charged by the charging unit 2 in the apparatus main body. Then, based on the original image data input to the image input unit (not shown) from a personal computer or the like, the exposure device 3 irradiates the photosensitive drum 1 with a laser beam, and the electrostatic latent image on the photosensitive drum 1. Is formed.

  The photosensitive drum 1 is formed, for example, by laminating a photosensitive layer on an aluminum drum, and the surface is charged by a charging unit 2. Then, an electrostatic latent image in which charging is attenuated is formed on the surface that has received the laser beam from the exposure apparatus 3. As the photosensitive material for forming the photosensitive layer, an amorphous silicon photoreceptor or an organic photoreceptor (OPC photoreceptor) is used. When positive OPC is used as the photosensitive layer, the generation of ozone or the like is small and charging is stable. In particular, the positive OPC having a single-layer structure has little change in photosensitive characteristics even when the film thickness changes after long-term use. Since the image quality is stable, it is preferably used in a system having a long life.

  The rotary type developing unit 4 that supplies toner onto the photosensitive drum 1 includes cartridge type yellow, magenta, cyan, and black developing devices 4a, 4b, 4c, and 4d in which a developing device and a toner container are integrated. By sequentially rotating the developing devices 4a to 4d to positions facing the photosensitive drum 1, toner is attached to the electrostatic latent image on the photosensitive drum 1 to form toner images of the respective colors. The Toner supply (toner installation) to the developing cartridges 4a to 4d is performed from the toner cartridge 5 through the supply pipe 5a.

  The intermediate transfer belt 6 onto which the toner image is transferred is wound around the intermediate transfer rollers 7a and 7b, the belt driving roller 9 and the driven roller 10, and while being in contact with the photosensitive drum 1, the driving means (not shown) rotates clockwise in the drawing. Rotate to. A sheet made of dielectric resin is used for the intermediate transfer belt 6, and a belt in which both ends thereof are overlapped and joined to form an endless shape, or a belt without a seam (seamless) is used.

  When the user inputs image formation start, a yellow toner image is formed on the photosensitive drum 1 at a predetermined timing. Then, the yellow toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 6 by the intermediate transfer rollers 7a and 7b to which a negative transfer bias (when positively charged toner is used) is applied (primary transfer). . Thereafter, the toner remaining on the surface of the photosensitive drum 1 is removed by the cleaning roller 8a and the cleaning blade 8b, and the developing unit 4 rotates by a predetermined amount (here, 90 °). Are formed on the photosensitive drum 1 and transferred onto the intermediate transfer belt 6.

  Thereafter, cyan and black toner images are transferred onto the intermediate transfer belt 6 from the photosensitive drum 1 by the same method as described above. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. A transfer roller 14 is pressed against the intermediate transfer belt 6 at a position facing the belt driving roller 9, and a belt cleaning blade 15 for removing residual toner on the surface of the intermediate transfer belt 6 is disposed downstream of the transfer roller 14. ing.

  The sheet P is conveyed from the sheet feeding mechanism 11 via the sheet feeding roller 12 and the registration roller pair 13 toward the intermediate transfer belt 6 on which the toner image is formed as described above, and sequentially onto the surface of the intermediate transfer belt 6. The formed full-color toner image is transferred onto the paper P at once by the transfer roller 14 to which a negative transfer bias is applied (secondary transfer). Then, the sheet on which the toner image is transferred is conveyed to the fixing device 16 and the toner image is fixed. The paper P that has passed through the fixing device 16 is discharged to a discharge tray 19 via a paper conveyance path 17 and a discharge roller pair 18.

  FIG. 2 is a side sectional view of the developing device of the present invention. In the following description, the configuration and operation of the developing device 4a opposite to the photosensitive drum 1 in FIG. 1 will be described. However, the configuration and operation of the developing devices 4b to 4d are basically the same and will not be described. To do.

  As shown in FIG. 2, the developing device 4 a is provided with a toner stirring unit 21 in which toner is stored and a toner supply unit 22 to which toner is supplied from the toner stirring unit 21 in a resin-made developing container 20. The toner stirring unit 21 and the toner supply unit 22 are partitioned by a boundary wall 23. A first opening 28 and a second opening 29 are formed in the boundary wall 23, and the second opening 29 is positioned above the first opening 28 in the drawing.

  In the toner agitation unit 21, an agitation paddle 24 in which an agitation blade such as a PET film is attached to a rotation shaft is rotatably supported in a counterclockwise direction in FIG. In the toner supply unit 22, the photosensitive drum 1 (see FIG. 1) that carries a latent image faces the developing roller 25 for developing the latent image, and a supply roller for supplying toner to the developing roller 25. 26, a metal regulating member 27 for regulating the toner layer thickness on the developing roller 25 and charging the toner is provided.

  The toner layer on the developing roller 25 is regulated in layer thickness by a regulating member 27 (for example, a SUS foil having a thickness of 0.08 mm and regulated pressure = 25 N / m) and is triboelectrically charged. 1 is used for development of an electrostatic latent image on 1. A seal member 30 (for example, a conductive high molecular weight PE film is used as a gap between the developing roller 25 and the developing container 20 on the side opposite to the regulating member 27 and is backed up with a urethane sponge so as to uniformly contact the developing roller 25. The seal member 30 prevents toner leakage.

  Further, since the developing roller 25 and the supply roller 26 rotate clockwise in FIG. 2, the second opening 29 is formed downstream of the first opening 28 in the rotation direction of the supply roller 26, and the second opening 29 is positioned above the upper end of the supply roller 26. The first opening 28 is positioned below the rotation axis of the stirring paddle 24.

  The developing process by the developing device 4 a will be described. The toner in the toner stirring unit 21 is sent to the toner supply unit 22 through the first opening 28 by the rotation of the stirring paddle 24. The toner sent to the toner supply unit 22 side is conveyed to the development roller 25 by the supply roller 26, is regulated to a thin layer by the regulating member 27 and is conveyed to the development nip portion, and the electrostatic latent image on the photosensitive drum 1 is converted. develop. The toner that is not used for development and remains on the developing roller 25 passes through the seal member 30, and then is peeled off by the supply roller 26 and returned to the toner supply unit 22.

  Of the toner conveyed by the supply roller 26, excess toner regulated by the regulating member 27 stays in the toner supply unit 22 together with new toner supplied (filled) from the first opening 28. When the amount of toner in the supply unit 22 increases, excess toner passes through the second opening 29 and returns to the toner stirring unit 21 from the toner supply unit 22 side, and the internal pressure of the toner supply unit 22 is reduced.

  Next, the control path of the image forming apparatus of the present invention will be described. FIG. 3 is a block diagram showing an example of a control path used in the image forming apparatus of the present invention. It should be noted that since various control of each part of the apparatus is performed when the image forming apparatus 100 is used, the control path of the entire image forming apparatus 100 becomes complicated. Therefore, here, a portion of the control path that is necessary for the implementation of the present invention will be mainly described.

  The control unit 90 includes a central processing unit (CPU) 91 as a central processing unit, a read only memory (ROM) 92 that is a read-only storage unit, a random access memory (RAM) 93 that is a read / write storage unit, A plurality of (two in this case) that transmit a control signal to each device in the temporary storage unit 94, the counter 95, and the image forming apparatus 100 for storing image data and the like, and receive an input signal from the operation unit 50. The I / F (interface) 96 is provided. Further, the control unit 90 can be arranged at an arbitrary location inside the apparatus main body.

  The ROM 92 stores a control program for the image forming apparatus 100, data necessary for control, and the like that are not changed during use of the image forming apparatus 100. The RAM 93 stores necessary data generated during the control of the image forming apparatus 100, data temporarily required for controlling the image forming apparatus 100, and the like. In addition, the ROM 92 (or RAM 93) stores the print length of the toner discharge pattern in addition to the reference print rate used when determining the number of prints and the toner discharge pattern for determining whether or not the refresh process needs to be executed (described later). The outer peripheral lengths of the developing roller 25 and the supply roller 26 for calculation, linear speed ratio data for the photosensitive drum 1, and the like are also stored. The counter 95 adds up the number of printed sheets and counts it. Note that the number of times may be stored in the RAM 93, for example, without providing the counter 95 separately.

  In addition, the control unit 90 transmits a control signal from the CPU 91 to the respective units and apparatuses in the image forming apparatus 100 through the I / F 96. In addition, a signal indicating the state and an input signal are transmitted from each part or device to the CPU 91 through the I / F 96. As each part and device controlled by the control unit 90, for example, the photosensitive drum 1, the exposure device 3, the development unit 4 (development devices 4a to 4d), the paper feed mechanism 11, the fixing device 16, the image input unit 40, and the operation Part 50 and the like.

  When the image forming apparatus 100 is a printer as shown in FIG. 1, the image input unit 40 is a receiving unit that receives image data transmitted from a personal computer or the like. When the image forming apparatus 100 is a copying machine, Scanning optical system equipped with a scanner lamp that illuminates the document during copying and a mirror that changes the optical path of the reflected light from the document, a condensing lens that focuses the reflected light from the document and forms an image It is an image reading unit composed of a CCD or the like that converts image light into an electrical signal. The image signal input from the image input unit 40 is converted into a digital signal and then transmitted to the temporary storage unit 94.

  The operation unit 50 is provided with a liquid crystal display unit 51, LEDs 52 indicating various states, and a numeric keypad 53, and the user operates the operation unit 50 to input instructions, thereby making various settings of the image forming apparatus 100. And execute various functions such as image formation. The liquid crystal display unit 51 displays the state of the image forming apparatus 100, displays the image forming status and the number of copies, and can be used as a touch panel to perform various settings such as functions such as double-sided printing and black-and-white reversal, magnification setting, and density setting. It has become. The numeric keypad 53 is used for setting the number of copies to be printed and for inputting the other party's FAX number when the image forming apparatus 100 also has a FAX function.

  In addition, the operation unit 50 includes a start button for instructing the user to start image formation, a stop / clear button used when the image formation is stopped, and various settings of the image forming apparatus 100 in a default state. A reset button or the like is provided for use.

  When the image forming apparatus of the present invention is not transferred to a recording medium, for example, when the image forming apparatus is started up from a power-off state or a sleep (power saving) mode to a copy start state, or a predetermined number of prints are performed. Sometimes, a refreshing process for discharging the toner on the developing roller 25 in the developing devices 4a to 4d to the photosensitive drum 1 side can be executed.

  An actual toner discharge pattern is shown in FIG. The toner discharge pattern T has a rectangular shape having a predetermined toner discharge width H and a toner discharge length (printing length in the drum circumferential direction) L as two sides. In addition, when separation claws (not shown) for preventing the paper from adhering to the drum surface are provided at a plurality of positions in the longitudinal direction of the photosensitive drum 1, a toner discharge pattern is provided so that the toner does not adhere to the separation claws. A white portion is provided in a portion facing the separation claw of T. Further, the toner discharge width H is set to be approximately equal to the width of the developing area of the developing roller 25 (see FIG. 2).

  By the way, when a low printing rate image is continuously printed, the proportion of small-diameter toner increases in the developing device, and when a high printing rate image is continuously printed, the proportion of large-diameter toner increases. Are known. This is because, although large-diameter toner has a larger charge amount per particle than small-diameter toner, the electrostatic charge per unit weight is smaller than that of small-diameter toner. However, the larger diameter toner becomes weaker. Therefore, in the image with a low printing rate, the large-diameter toner having a weak adhesion to the developing roller is preferentially developed, and the proportion of the small-diameter toner to be developed increases as an image with a high printing rate is formed.

  In the conventional refresh process, the print rate is calculated every predetermined time (predetermined number of sheets), and the duration of the refresh process, that is, the print length L of the toner ejection pattern T is determined by comparing with the reference print rate. However, the particle size of the discharged toner has not been considered.

  In the present invention, when the refresh process is executed, the laser exposure amount is increased, and the solid pattern is developed on the photosensitive drum, whereby the small-diameter residual toner in the developing device can be selectively and forcibly consumed. It has been found that by developing a low dot pattern, the large diameter residual toner can be selectively and forcibly consumed.

  5 and 6 show a case where a laser exposure amount of the exposure apparatus 3 is set to 0.22 mW at the time of normal image formation and a dot pattern (printed with one dot) with a printing rate of 6% is formed and a solid pattern is formed. 6 is a graph comparing the toner particle size distribution and the distribution center particle size in the toner image with the toner particle size distribution and distribution center particle size in the developing device. The toner particle size distribution was measured using a particle size distribution measuring device (Multisizer III manufactured by Beckman Coulter, Inc., aperture diameter 100 μm).

  As is apparent from FIG. 5, the toner particle size distribution in the toner image is slightly different between the dot pattern (shown by the broken line in FIG. 5) and the solid pattern (shown by the solid line in FIG. 5) at the exposure amount during normal image formation. However, there was no significant change compared to the toner particle size distribution in the developing device (indicated by a bold line in FIG. 5). Further, as apparent from FIG. 6, the distribution center particle size is 6.16 μm for the toner in the developing device, whereas it is 6.39 μm for the dot pattern and 6.02 μm for the solid pattern, which is approximately ± 0.2 μm. It was in range.

  7 and 8 are graphs comparing the toner particle size distribution and distribution center particle size with the toner particle size distribution and distribution center particle size in the developing device when the laser exposure amount of the exposure device 3 is set to 0.7 mW. . 7 and 8, when the exposure amount is increased, the toner particle size distribution in the toner image is shifted in the small diameter direction (left direction in FIG. 7) in the solid pattern (indicated by the solid line in FIG. 7), and the distribution center particle size is increased. Was 5.92 μm, which was about 0.3 μm smaller than the toner in the developing device. On the other hand, in the dot pattern (indicated by a broken line in FIG. 7), the toner particle size distribution in the toner image is shifted in the large diameter direction (right direction in FIG. 7), and the distribution center particle size is 6.66 μm. Compared to about 0.5 μm.

  The reason for this is considered as follows. That is, when the laser exposure amount is increased, the electrostatic latent image formed on the photosensitive drum is deepened (that is, the potential difference between the electrostatic latent image and the other portions is increased), and the allowable charge amount is increased. When a low printing rate pattern (dot pattern) is formed in this state, toner having a larger diameter than the average particle diameter having a small amount of adhesion to the developing roller is developed with higher priority. On the other hand, when a high printing rate pattern (solid pattern) is formed, the residual charge after developing the large-diameter toner increases due to the increase in the allowable charge amount, and the consumption amount of the small-diameter toner increases accordingly. .

  Therefore, it is possible to effectively suppress variations in the toner particle size distribution in the developing device using this property. That is, after continuously forming an image with a low printing rate, the ratio of the overcharged small-diameter toner in the developing device is increased, so that the exposure amount is increased when the refresh process is performed, and the toner ejection pattern T By using a solid pattern, small-diameter toner can be discharged preferentially. On the contrary, after continuously forming an image with a high printing rate, the ratio of the large-diameter toner having a low charge amount in the developing device is increased. By using the ejection pattern T as a dot pattern, the large diameter toner can be discharged preferentially. Further, since toner having a desired particle size is discharged preferentially, the toner discharge amount (refresh duration time) in the refresh process can be suppressed. Accordingly, the waiting time of the user can be shortened and the running cost of the image forming apparatus can be reduced.

  If each dot constituting the dot pattern is too large, the interval between dots is too narrow, or if the printing rate is too high, it becomes close to a solid pattern and large-diameter toner cannot be discharged preferentially. . Therefore, as a dot pattern, as shown in FIGS. 9A to 9C, one dot or a group of dots each having 2 to 6 dots on one side is arranged in a matrix at intervals of 1 dot or more. Thus, a pattern having a printing rate of less than 10% is preferable.

  FIG. 10 is a flowchart showing a first control example of the refresh process executed in the image forming apparatus of the present invention. The execution procedure of the refresh process will be described with reference to FIGS. Here, the procedure for executing the refresh process for one of the developing devices 4a to 4d will be described, but the same procedure is performed for the other three developing devices.

  First, when the image forming process is started by the user operating the operation panel 50 or a personal computer, the counter 95 counts the number of printed sheets n (step S1). The control unit 90 calculates a printing rate bn for each image based on the digital signal in the temporary storage unit 94, and further calculates an integrated printing rate Σbn obtained by integrating the printing rate bn. Next, it is determined whether or not the number n of printed sheets has reached the predetermined number A (step S2). When n = A, the control unit 90 calculates the average printing rate B by Σbn / A (step S3). Further, the laser exposure amount of the exposure apparatus 3 is increased (step S4).

  Next, the control unit 90 determines whether or not the average printing rate B is less than a predetermined value P0 (here, 5%) (step S5). If it is less than 5%, a solid pattern is formed as the toner ejection pattern T (step S6), and if it is 5% or more, a dot pattern is formed (step S7). Then, a refreshing process for discharging the toner from the developing roller 25 onto a predetermined toner discharge pattern formed on the photosensitive drum 1 by the exposure device 3 is executed (step S8). Thereafter, the count number n of the counter 95 is reset to 0 (step S9), and the process returns to step S1 again.

  According to the first control example shown in FIG. 10, the toner discharge pattern T of a solid pattern or a dot pattern is formed based on the average printing rate until the refresh process is executed. The toner particle size distribution can be predicted, and an appropriate toner ejection pattern corresponding to the toner particle size distribution can be automatically determined to execute the refresh process. The printing length L (see FIG. 4) of the toner discharge pattern T may be set to a predetermined length in advance, or may be varied according to the average printing rate B. Although the predetermined value P0 is 5% here, it may be set as appropriate according to the specifications of the image forming apparatus and the developing apparatus, the image forming conditions, and the environmental conditions such as toner to be used and temperature and humidity.

  In the first control example, the refresh process is executed by forming a solid pattern when the average printing rate is less than 5% and forming a dot pattern when the average printing rate is 5% or more. Alternatively, the control may be performed such that the solid pattern is formed and the refresh process is executed only when the ratio is less than 5%, or the dot pattern is formed and the refresh process is executed only when the average printing rate is 5% or more.

  Further, when the printing length L of the toner discharge pattern T is the same, the amount of toner discharged differs between the solid pattern and the dot pattern. Therefore, in order to make the toner discharge amount equal between the solid pattern and the dot pattern, it is necessary to make the printing length L (refresh duration) of the dot pattern longer than that of the solid pattern.

  FIG. 11 is a flowchart showing a second control example of the refresh process executed in the image forming apparatus of the present invention. In the second control example, the average printing rate B calculated in step S3 is less than the predetermined value P0 (5%) (YES in step S4), and the printing rate is the predetermined value P1 (during printing of the predetermined number A). > P0 (25% in this case) Only when there is no more output (NO in step S5), the laser exposure amount is increased (step S6) to form a solid toner discharge pattern (step S7), and the refresh process Is executed (step S8).

  According to the second control example, even if the average printing rate of the predetermined number A is less than 5%, the small diameter toner is consumed when the high printing rate output is 25% or more. Therefore, the refresh process is not executed. As a result, when the average printing rate is low, overcharged small-diameter toner is discharged to effectively suppress image fogging and density reduction, and when suddenly high printing rate is output, wasteful refresh is executed. The waiting time of the user can be shortened as much as possible and toner consumption can be saved. The predetermined value P1 may be set as appropriate similarly to P0.

  FIG. 12 is a flowchart showing a third control example of the refresh process executed in the image forming apparatus of the present invention. In the third control example, the average printing rate B calculated in step S3 is less than 5% (YES in step S4), and the printing rate is equal to or higher than the predetermined value P1 (25%) during printing of the predetermined number A. Only when there is no output (NO in step S5), the laser exposure amount is increased (step S6), a solid pattern toner ejection pattern is formed (step S7), and a refresh process is executed (step S8).

  Further, when the average printing rate B is 5% or more (NO in step S4) and there is no output with the printing rate equal to or lower than the predetermined value P2 (<P0, here 3%) during printing of the predetermined number A ( Only in step S8 NO, the laser exposure amount is increased (step S9), a toner discharge pattern of a dot pattern is formed (step S10), and a refresh process is executed (step S11).

  According to the third control example, even if the average printing rate of the predetermined number A is less than 5%, the small diameter toner is consumed when the high printing rate output is 25% or more. Even if the average printing rate is 5% or more, if there is an output with a low printing rate of 3% or less, the large diameter toner is consumed, so the refresh process is not executed. This preferentially eliminates overcharged small-diameter toner and low-charged large-diameter toner according to the average printing rate to improve the toner particle size distribution variation in the developing device and eliminate unnecessary refresh execution. The waiting time of the user can be shortened as much as possible, and the toner consumption can be saved. The predetermined value P2 may be set as appropriate similarly to P0 and P1.

  Note that either step S5 or step S8 in FIG. 12 may be deleted, and the refresh process may be executed whenever the average printing rate is less than 5% or more than 5%.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above embodiment, the average printing rate is calculated by the control unit 90, but an arithmetic unit that calculates the average printing rate may be provided separately from the control unit 90. In the present invention, only a rotary development type color printer has been described as an example. However, an analog monochrome copying machine, a tandem color copying machine, an analog monochrome copying machine, a facsimile machine, a laser printer, etc. Of course, the present invention can be applied to various image forming apparatuses equipped with a developing device including a developing roller and a supply roller.

  When continuous printing was performed using the image forming apparatus of the present invention shown in FIG. 1, the relationship between the laser exposure amount during execution of the refresh process and the toner particle size distribution in the developing device was investigated. The test conditions were: drum surface potential (bright potential) of 350 V, laser exposure during image formation of 0.22 mW, developing roller peripheral speed 1.5 times that of the photosensitive drum (600 mm / second), and supply roller circumference. The speed was 900 mm / second, the rotational speed of the photosensitive drum was 150 mm / second, the gap between the drum and the developing roller was 250 mm, and the gap between the developing roller and the supply roller was 350 μm.

  A bias in which an AC component Vpp1 (1.6 kV, frequency 2.7 kHz, duty ratio 70%) is superimposed on the DC component Vdc1 (300 V) is applied to the developing roller, and a DC component Vdc2 (400 V) is applied to the supply roller. A bias superimposed with an alternating current component Vpp2 (2.8 kV, frequency 2.7 kHz, duty ratio 70%) having the same period and opposite phase as Vpp1 was applied. Further, a two-component developer having a toner average particle diameter of 6.5 μm, a carrier average particle diameter of 35 μm, and a saturation magnetization of 65 eum / g was used. The saturation magnetization was measured using a vibrating sample magnetometer VSM-P7 (manufactured by Toei Kogyo Co., Ltd.) with a magnetic field of 79.6 kA / m (1 kOe).

  Then, a test image having a printing rate of 1% was continuously printed, an average printing rate was calculated every 50 sheets printed, and a refreshing process for forcibly discharging toner in a solid pattern during non-image formation was executed. The present invention 1 is a case where the exposure amount is increased to 0.7 mW and the toner is forcibly discharged for 3 seconds, and the case where the exposure amount is 0.22 mW and the toner is forcibly discharged for 3 seconds is Comparative Example 1, and the toner is discharged for 10 seconds. As a comparative example 2, the case of forced discharge was compared with the initial particle size distribution in the developing device after printing a predetermined number of sheets. The toner particle size distribution was measured with an aperture diameter of 100 μm (measurement range of 2.6 to 60 μm) using a particle size distribution measuring device (Multisizer III manufactured by Beckman Coulter, Inc.). The results are shown in Table 1.

  As shown in Table 1, in the present invention 1 in which the toner was discharged for 3 seconds at an exposure amount of 0.7 mW, the toner particle size distribution in the developing device was maintained at the initial particle size distribution even after printing 10,000 sheets. . On the other hand, in Comparative Example 1 in which the toner was discharged for 3 seconds at an exposure amount of 0.22 mW, a change was observed in the particle size distribution when 1,000 sheets were printed. In Comparative Example 2 in which the toner was discharged for 10 seconds at an exposure amount of 0.22 mW, the initial particle size distribution was maintained until the printing time of 5,000 sheets, but fluctuation was observed at the printing time of 6,000 sheets. . Further, since the forced discharge time is set to 10 seconds, the amount of toner consumption increases.

  Using the image forming apparatus of Example 1, 500 test images with a printing rate of 1% were printed continuously under the same test conditions, and the exposure amount was increased to 0.7 mW for every 50 sheets to form a solid pattern for 3 seconds. The present invention 2 is the case where the refreshing process is executed, and the comparative example 3 is the case where the refreshing process is not executed. The initial particle size distribution and the distribution center particle size are defined as the toner particle size distribution and the distribution center particle size in the developing device. Compared. The results are shown in FIGS.

  As apparent from FIGS. 13 and 14, in the second aspect of the present invention in which the solid pattern is formed at an exposure amount of 0.7 mW every 50 sheets printed, the toner particle size distribution in the developing device (shown by a solid line in FIG. 13) is the initial value. There was no significant change compared to the toner particle size distribution (shown in bold in FIG. 13). The distribution center particle size was also 6.26 μm, which was only 0.1 μm higher than the initial particle size of 6.16 μm. On the other hand, in Comparative Example 3 in which the refresh process was not executed, the toner particle size distribution in the developing device (indicated by a broken line in FIG. 13) was shifted in the smaller diameter direction compared to the initial toner particle size distribution. The distribution center particle size was 5.9 μm, which was 0.26 μm smaller than the initial particle size of 6.16 μm.

  Using the image forming apparatus of Example 1, 500 test images having a printing rate of 100% (solid image) were continuously printed under the same test conditions, and the exposure amount was increased to 0.7 mW for 3 seconds every 50 sheets printed. When the refresh process for forming a dot pattern of one dot (laser dot diameter 60 μm) is executed, the present invention 3 is used, and the case where the refresh process is not executed is Comparative Example 4, and the toner particle size distribution and distribution center in the developing device The particle size was compared to the initial particle size distribution and the distribution center particle size. The results are shown in FIGS.

  As apparent from FIGS. 15 and 16, in the second aspect of the present invention in which the dot pattern is formed at an exposure amount of 0.7 mW every 50 sheets printed, the toner particle size distribution in the developing device (shown by a solid line in FIG. 15) is the initial value. There was no significant change compared to the toner particle size distribution (shown in bold in FIG. 15). The distribution center particle size was 6.32 μm, which was only 0.16 μm higher than the initial particle size of 6.16 μm. On the other hand, in Comparative Example 4 in which the refresh process was not executed, the toner particle size distribution in the developing device (indicated by a broken line in FIG. 15) was shifted in the larger diameter direction compared to the initial toner particle size distribution. The distribution center particle size was also 6.56 μm, which was 0.4 μm larger than the initial particle size of 6.16 μm.

  Based on the above results, the toner particle size distribution in the developing device is longer when the refresh process is executed with the exposure amount higher than that during image formation, compared to when the refresh process is executed with the exposure amount during image formation. It was confirmed that the toner consumption was stable over time. In addition, when a low printing rate image is output continuously, a solid pattern is formed, and when a high printing rate image is output continuously, a dot pattern is formed so that the toner particle size distribution in the developing device It was confirmed that the variation in the thickness can be effectively suppressed. Although not shown here, the same result can be obtained even when the second and third control examples in which the refresh process is not executed when the printing rate is greater than or equal to a predetermined value or less than the predetermined value are output. It has been confirmed.

  The present invention relates to an exposure apparatus that forms an electrostatic latent image by irradiating an image carrier with laser light, a toner carrier that is disposed opposite to the image carrier and carries toner and supplies the toner to the image carrier, and the toner carrier. And a developing device that develops an electrostatic latent image formed on the surface of the image carrier by the exposure device, and from the toner carrier side to the image carrier side during non-image formation In an image forming apparatus capable of executing a refresh process for discharging toner to the image forming apparatus, when executing the refresh process, the laser exposure amount of the exposure apparatus is increased as compared with the image formation to form a toner discharge pattern on the image carrier.

  As a result, an image forming apparatus that suppresses variations in the toner particle size distribution in the developing device by executing the refresh process to prevent problems such as image fog and density reduction, and can also reduce toner consumption in the refresh process. be able to.

  In addition, a control unit is provided for determining a toner discharge pattern based on an average print rate of a print image calculated for each predetermined number of printed sheets. When the average print rate is low, a solid pattern is formed, and when the average print rate is high Since a dot pattern is formed, overcharged small-diameter toner or low-charged large-diameter toner can be discharged preferentially to maintain the toner particle size distribution balance in the developing device appropriately.

  Also, the refresh process should not be executed when an image with a high printing rate is output midway even when the average printing rate is low, or when an image with a low printing rate is output midway even when the average printing rate is high. By doing so, it is possible to eliminate unnecessary refresh execution, shorten the waiting time of the user as much as possible, and save toner consumption.

FIG. 1 is a schematic cross-sectional view showing an overall configuration of an image forming apparatus of the present invention. These are sectional views of a developing device used in the image forming apparatus of the present invention. FIG. 3 is a block diagram showing a control path of the image forming apparatus of the present invention. FIG. 4 is a diagram illustrating an example of a toner discharge pattern used in the present invention. In the developing device, the toner particle size distribution in the toner image in the case where the laser exposure amount is set to 0.22 mW and the dot pattern (printing with 1 dot) with a printing rate of 6% is formed and the solid pattern is formed. 6 is a graph compared with a toner particle size distribution. The laser exposure amount is set to 0.22 mW, and the distribution center particle size in the toner image in the case where a dot pattern (printing with 1 dot) with a printing rate of 6% and a solid pattern is formed is determined in the developing device. It is the graph compared with the distribution center particle size. In the developing device, the toner particle size distribution in the toner image when the laser exposure amount is set to 0.7 mW and a dot pattern (printing with 1 dot) with a printing rate of 6% is formed and when a solid pattern is formed. 6 is a graph compared with a toner particle size distribution. The laser exposure amount is set to 0.7 mW, and the distribution center particle size in the toner image in the case of forming a dot pattern (printing with one dot) with a printing rate of 6% and in the case of forming a solid pattern in the developing device It is the graph compared with the distribution center particle size. These are figures which show the example of a dot pattern. These are the flowcharts which show the 1st control example of the refresh process in the image forming apparatus of this invention. These are flowcharts showing a second control example of the refresh process in the image forming apparatus of the present invention. These are flowcharts showing a third control example of the refresh process in the image forming apparatus of the present invention. These are graphs in Example 2 in which the particle size distribution of the toner in the developing device in the present invention 2 and Comparative Example 3 is compared with the initial particle size distribution. These are graphs in Example 2 in which the distribution center particle size of the toner in the developing devices of the present invention 2 and Comparative Example 3 is compared with the initial distribution center particle size. These are graphs in Example 3 in which the particle size distribution of the toner in the developing device of the present invention 3 and Comparative Example 4 is compared with the initial particle size distribution. These are graphs in Example 3 in which the distribution center particle size of the toner in the developing devices of the present invention 3 and Comparative Example 4 is compared with the initial distribution center particle size.

Explanation of symbols

1 Photosensitive drum (image carrier)
DESCRIPTION OF SYMBOLS 3 Exposure apparatus 4 Developing unit 4a-4d Developing apparatus 25 Developing roller 26 Supply roller 90 Control part (control means)
91 CPU
92 ROM
93 RAM
94 Temporary storage unit 95 Counter 100 Image forming apparatus T Toner discharge pattern L (Toner discharge pattern) circumferential print length

Claims (7)

An exposure device that irradiates the image carrier with laser light to form an electrostatic latent image; and
A toner carrier that is disposed opposite to the image carrier and carries the toner and supplies the toner to the image carrier; and a toner supply member that supplies the toner to the toner carrier, and the image carrier is configured by the exposure device. A developing device for developing the electrostatic latent image formed on the surface,
In an image forming apparatus capable of executing a refresh process for discharging toner from the toner carrier side to the image carrier side during non-image formation,
An image forming apparatus, wherein when performing a refreshing step, a toner discharge pattern is formed on the image carrier by increasing a laser exposure amount of the exposure apparatus as compared with that during image formation.   The image forming apparatus according to claim 1, further comprising a control unit that determines the toner discharge pattern based on an average print rate of a print image calculated for each predetermined number of printed sheets.   The image forming apparatus according to claim 2, wherein the control unit forms a solid pattern as the toner ejection pattern when the average printing rate is less than a reference value P0.   The control unit forms a solid pattern as the toner ejection pattern when the average printing rate is less than the reference value P0 and the image output of the printing rate P1 (> P0) or more is not performed during a predetermined number of prints. The image forming apparatus according to claim 2.   5. The image forming apparatus according to claim 2, wherein the control unit forms a dot pattern as the toner ejection pattern when the average printing rate is equal to or greater than a reference value P <b> 0.   The control unit forms a dot pattern as the toner ejection pattern when the average printing rate is equal to or higher than the reference value P0 and image output equal to or higher than the printing rate P2 (<P0) is not performed during a predetermined number of printed sheets. The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus.   The dot pattern is formed by arranging one dot or a group of dots each having 2 dots or more and 6 dots or less in a matrix with an interval of 1 dot or more, and the printing rate is less than 10%. The image forming apparatus according to claim 5.