JP2009053396A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which shortens a period of time required to clean toner discharged forcibly from a developing roller, and exhibits the abrasion effect of the surface of a photoreceptor effectively. <P>SOLUTION: A toner-recovering destination is switched between a photoreceptor cleaning section (cleaning roller 8a and cleaning blade 8b) and a belt cleaning section (belt cleaning blade 15) according to the circumferential printing length L (a quantity of toner discharge) of a toner discharge pattern T formed on a photoreceptor drum 1 according to a print proportion during a refresh process or according to a toner characteristic such as a particle diameter or presence or absence of an abradant. <P>COPYRIGHT: (C)2009,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 toner carrier (developing 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. Image density reduction and 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 original printing ratio such as solid black, and the toner is transferred to a recording medium to consume the toner. However, if the solid black pattern is left unprinted for a long period of time, the toner particles are fixed to the surface of the developing roller due to the influence of humidity or the like without being consumed. Sometimes it doesn't 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 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 a DC bias when a non-image is formed on the developing roller. A one-component development type image forming apparatus that forcibly consumes toner on a developing roller by applying the superimposed toner is disclosed. Patent Document 2 proposes an image forming apparatus in which an image area ratio (average printing ratio) per unit driving time of the developing device is calculated and the forced consumption of toner is changed according to the image area ratio. Has been.
JP 2000-206770 A JP 2003-76079 A

  In an image forming apparatus capable of performing a forced discharge process (hereinafter referred to as a refresh process) of toner on a developing roller, the forced discharged toner is collected by a cleaning unit of a photosensitive member such as a cleaning roller or a cleaning blade. Used for polishing the body surface. However, in the methods of Patent Documents 1 and 2, no consideration is given to the collection of discharged toner. Therefore, it is necessary to increase the cleaning time when an amount of toner exceeding the recovery capability of the cleaning portion of the photosensitive member is forcibly discharged. In addition, in the case of a color machine, the color toner has a small amount of abrasive added to prevent color turbidity and has a spherical diameter. Therefore, the polishing performance is lower than that of an amorphous black toner, and the color toner passes through the cleaning blade and is exposed to light. It tends to remain on the body surface. For this reason, when only the spherical color toner having low polishing performance is forcibly discharged, the surface of the photoreceptor is not sufficiently polished, and toner cleaning failure occurs.

  SUMMARY OF THE INVENTION In view of the above problems, the present invention provides an image forming apparatus that controls the collection destination of toner forcedly discharged from a developing roller, thereby shortening the cleaning time and effectively functioning the polishing effect on the surface of the photoreceptor. For the purpose.

  In order to achieve the above object, the present invention has a toner carrier that is disposed opposite to an image carrier, carries toner and supplies the image carrier, and a toner image corresponding to an electrostatic latent image on the surface of the image carrier. And a transfer member onto which the toner image formed on the image carrier is transferred by the developing device, and discharges toner from the toner carrier side to the image carrier side during non-image formation. In the image forming apparatus capable of executing a refresh process, an image carrier cleaning device that collects toner on the image carrier and a transfer body cleaning device that collects toner on the transfer body are provided, and the refresh The collection destination of the toner discharge pattern discharged in the process is determined according to at least one of the continuous toner discharge amount and the toner characteristics, and the image carrier cleaning device and the transfer member cleaning device. It is characterized in that switching to the grayed device.

  In the image forming apparatus having the above-described configuration, the toner discharge amount in the refresh step is determined based on a difference between the print rate on the image and the reference print rate calculated over a predetermined number of prints. It is characterized by that.

  According to the present invention, in the image forming apparatus having the above-described configuration, a plurality of the developing devices are provided so as to face one image carrier, and the continuous discharge amount is a plurality of developments in which a refresh process is continuously performed. It is a total value of the amount of toner discharged from the apparatus.

  Further, according to the present invention, in the image forming apparatus having the above configuration, the toner discharged from each of the developing devices is either a spherical toner or an indeterminate toner, and a collection destination of a toner discharge pattern formed of the spherical toner is set as the collection destination. A transfer body cleaning device is used, and the image carrier cleaning device is used as a collection destination of a toner discharge pattern formed of irregular shaped toner.

  Further, according to the present invention, in the image forming apparatus configured as described above, the toner discharged from each of the developing devices is either a spherical toner or an indeterminate toner, and the total print length of the toner discharge pattern during the refresh process is When the total length is longer than the reference length, all the toner discharge patterns are collected by the image carrier cleaning device when the length is equal to or shorter than the reference length, and the toner discharge pattern formed with the irregular toner is included. A reference length toner discharge pattern is collected by the image carrier cleaning device, and the remaining toner discharge pattern is collected by the transfer member cleaning device.

  According to the present invention, in the image forming apparatus configured as described above, the printing length of the toner discharge pattern formed with the irregular toner is variable according to humidity.

  Further, according to the present invention, in the image forming apparatus having the above-described configuration, the spherical toner and the indefinite shape are contained in the toner collected by the image carrier cleaning device and the transfer body cleaning device when the refresh process is executed a predetermined number of times. It is characterized in that the toner is controlled to contain a predetermined ratio or more.

  According to the present invention, in the image forming apparatus configured as described above, the toner collected by the image carrier cleaning device and the transfer body cleaning device includes 5% or more of the spherical toner and the irregular toner, respectively. Yes.

  According to the present invention, in the image forming apparatus having the above-described configuration, the irregular toner is a black toner, the spherical toner is a color toner other than black, and the cumulative number of printed colors is a predetermined number in the refresh step. In this case, the control unit includes an averaging control for discharging a predetermined amount of black toner, and discharging a predetermined amount of color toner one color at a time when the cumulative number of monochrome prints reaches a predetermined number.

  According to the present invention, in the image forming apparatus having the above-described configuration, the refreshing step performs printing rate control for performing toner discharge based on a difference between a printing rate on the image calculated over a predetermined number of prints and a reference printing rate. When the averaging control is executed after the previous printing rate control, the toner discharge amount in the next printing rate control is determined by subtracting the toner discharge amount in the averaging control. It is characterized by doing.

  According to the first configuration of the present invention, the collection destination of the toner ejection pattern ejected in the refresh process is set as the image carrier cleaning device and the transfer body cleaning according to at least one of the continuous toner ejection amount and the toner characteristics. By switching to the apparatus, toner exceeding the recovery capability of the image carrier cleaning apparatus can be recovered by the transfer body cleaning apparatus, and the cleaning time can be shortened. In addition, by preferentially collecting the toner with externally added irregular shaped toner or abrasives with the image carrier cleaning device, the image carrier surface is prevented from being poorly cleaned, and at the same time the polishing effect is enhanced to improve the surface of the image carrier. The state can be stabilized.

  Further, according to the second configuration of the present invention, in the image forming apparatus having the first configuration, the toner discharge amount in the refreshing process is calculated based on the print rate on the image calculated over a predetermined number of prints and the reference print. By determining based on the difference from the rate, the amount of toner shortage consumed according to the actual printing rate is calculated and the toner discharge amount is determined. It can be.

  According to the third configuration of the present invention, in the image forming apparatus having the above first or second configuration, a color image forming apparatus in which a plurality of developing devices are provided facing one image carrier. Comparing the total amount of toner actually ejected onto the image carrier with the recovery capability of the image carrier cleaning device by adding the amount of toner ejected from a plurality of developing devices in which the refresh process is executed continuously can do.

  According to the fourth configuration of the present invention, in the image forming apparatus of the third configuration, when the toner discharged from each developing device is either a spherical toner or an irregular toner, the polishing effect is high. By collecting only the irregular shaped toner with the image carrier cleaning device, defective cleaning due to the remaining of the spherical toner on the surface of the image carrier is prevented, and the amount of toner collected by the image carrier cleaning device is suppressed to shorten the cleaning time. At the same time, the surface state of the image carrier can be maintained well.

  According to the fifth configuration of the invention, in the image forming apparatus having the third configuration, when the toner discharged from each developing device is either a spherical toner or an irregular toner, the irregular toner is removed. Since a certain amount of toner is supplied to the image carrier cleaning device, poor cleaning of the surface of the image carrier can be prevented, and the polishing performance can be stabilized. Further, since the spherical toner having high fluidity is also collected at the same time, the toner transportability by the recovery device that transports the waste toner from the image carrier cleaning device to the toner recovery container is improved.

  According to the sixth configuration of the present invention, in the image forming apparatus having the fourth or fifth configuration, the printing length of the toner discharge pattern formed with the irregular toner is varied according to the humidity. The polishing effect at high humidity when the ionic substance is likely to adhere to the surface of the image carrier can be further enhanced.

  According to the seventh configuration of the present invention, in the image forming apparatus having any one of the fourth to sixth configurations, when the refresh process is executed a predetermined number of times, the image carrier cleaning device and the transfer body cleaning device are provided. By controlling so that the toner collected in the toner contains a spherical toner and an irregular toner in a predetermined ratio or more, the surface of the image carrier is prevented from being poorly cleaned, the polishing performance is stabilized, and the image carrier is provided. The toner conveying performance of the collecting device that conveys the waste toner from the cleaning device and the transfer member cleaning device to the toner collecting container can also be improved.

  According to the eighth configuration of the present invention, in the image forming apparatus having the seventh configuration, spherical toner and amorphous toner are each included in the toner collected by the image carrier cleaning device and the transfer body cleaning device. Therefore, the polishing performance of the image carrier and the transport performance of waste toner can be more suitably maintained.

  According to the ninth configuration of the invention, in the image forming apparatus having the seventh or eighth configuration, a predetermined amount of black toner, which is an amorphous toner, is printed when the cumulative number of color prints reaches a predetermined number. When it is seen in a predetermined cycle by incorporating averaging control into the refresh process that discharges a predetermined amount of color toner, which is a spherical toner, one time at a time when the cumulative number of printed monochrome sheets reaches a predetermined number The ratio of the spherical toner and the irregular toner collected by the image carrier cleaning device and the transfer member cleaning device can be easily averaged.

  According to the tenth configuration of the present invention, in the image forming apparatus having the ninth configuration, in the refresh process that combines the printing rate control and the averaging control, the averaging control is performed after the previous printing rate control is executed. Is performed, the toner discharge amount in the averaging control is subtracted to determine the toner discharge amount in the next printing rate control, thereby reducing unnecessary toner consumption and further averaging the ratio of each toner discharge amount. can do.

  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. The exposure unit 3 irradiates the photosensitive drum 1 with a laser beam based on the original image data input to an image input unit (not shown) from a personal computer or the like, 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 unit 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 used in the image forming apparatus 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 the description is omitted. 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, in addition to the reference print rate and the rotational speed of the photosensitive drum 1, which are used for calculating the number of printed sheets for determining whether or not the refresh process needs to be performed and the print length of the toner discharge pattern, the toner. A control program and the like for determining the collection destination of the discharge pattern 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. The parts and devices controlled by the control unit 90 include, for example, the photosensitive drum 1, the exposure unit 3, the developing unit 4 (developing devices 4a to 4d), the paper feeding mechanism 10, 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 sent 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 is a toner discharge length (printing length in the drum circumferential direction) obtained by multiplying the width H of the developing area of the developing roller 4a (see FIG. 2) and the toner discharge amount per image by the number of printed sheets. L is a rectangular shape with 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.

  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 printing length L varies depending on the printing rate.

  In the present invention, the toner collection destination is the photosensitive member cleaning unit (the cleaning roller 8a and the cleaning blade 8b) according to the print length L (toner discharge amount) of the toner discharge pattern T or the toner characteristics such as polishing performance and fluidity. By switching to the belt cleaning unit (belt cleaning blade 15), the cleaning performance of the photoconductor is stabilized and the surface condition of the photoconductor is stabilized as compared with the prior art by preventing toner cleaning failure and toner discharge exceeding the allowable amount. It was found that can be maintained well.

  For example, when a large amount of toner exceeding the cleaning performance of the cleaning roller 8a and the cleaning blade 8b is discharged, only the amount necessary for polishing the photosensitive member is collected by the cleaning roller 8a and the cleaning blade 8b out of the total discharge amount, By transferring the remainder onto the intermediate transfer belt 6 and collecting it with the belt cleaning blade 15, the cleaning time of the photosensitive drum 1 can be shortened and the polishing effect can be maintained.

  In a color image forming apparatus 100 having a plurality of developing devices 4a to 4d for one photosensitive drum 1 as shown in FIG. 1, spherical toner is generally used for yellow, magenta, and cyan color toners. An irregular toner is used as the black toner. Spherical toner easily passes through the cleaning blade 8b and remains on the surface of the photoreceptor, and has low polishing performance. In addition, it is difficult to add an abrasive to the color toner to ensure color transmission, so that the polishing performance is excellent. By collecting the black toner preferentially by the cleaning roller 8a and the cleaning blade 8b, it is possible to prevent the photoconductor drum 1 from being poorly cleaned and to obtain a sufficient polishing effect.

  The collection destination is switched by controlling the transfer bias applied to the temporary transfer rollers 7 a and 7 b facing the photosensitive drum 1 via the intermediate transfer belt 6. For example, when the discharged toner is sent to the cleaning roller 8a and the cleaning blade 8b, a bias having a reverse polarity (same polarity as the toner) is applied to the temporary transfer rollers 7a and 7b. Conversely, when collecting with the belt cleaning blade 15, a bias having the same polarity as in normal printing (opposite polarity with toner) is applied.

  Next, the toner discharge pattern collection control will be described in detail with reference to FIGS. For example, the diameters of the developing roller 25 and the supply roller 26 are 14 mm and 13 mm, respectively, the linear speed ratio S1 of the developing roller 25 to the photosensitive drum 1 is 1.1 times, and the linear speed ratio S2 of the supply roller 26 to the developing roller 25 is 1. .2 times. Further, the linear velocity of the photosensitive drum 1 is set to 150 mm / second.

  First, a method for calculating the printing length L of the toner discharge pattern T will be described. Assuming that the number of printed sheets for executing the refresh process is A, 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. calculate.

  Then, the integrated printing rate Σbn is divided by the number of printed sheets A counted by the counter 95 to calculate an average printing rate B (%) per printed sheet A. Since the printing rate difference C−B between the average printing rate B and the reference printing rate (threshold of printing rate that requires refreshing) C (%) is a necessary discharge amount (shortage of consumption) per image, Multiplying this by the number of printed sheets A (C−B) × A (%) becomes the toner discharge amount when the refresh process is executed. Note that the number of printed sheets A and the reference print rate C (%) can be set as appropriate according to the usage status of the user, the characteristics of the toner of each color, and the like.

  The printing length L of the toner discharge pattern T is calculated by L = L0 × (C−B) × A / 100, where L0 is the circumferential length of the image size that is the reference (100%) for calculating the printing rate. The

  For example, assuming that the number of printed sheets A is 10 and the reference printing rate C is 5%, when the average printing rate B is 2%, the toner ejection pattern T for (5-2 = 3)% × 10 sheets is obtained. Print. This is because when an A4 size image (width 210 mm × circumferential length 297 mm) is used as a reference (100%) for calculating the printing rate, L = 297 (= L0) × (5-2) × 10/100 = 89. 1 mm, which corresponds to a toner ejection pattern T with L = 89.1 mm. Since the rotational speed of the photosensitive drum 1 is 150 mm / second, it is sufficient to discharge the toner for 89.1 / 150 = 0.594 seconds. As described above, the printing length L of the toner discharge pattern T is calculated for each of the developing devices 4a to 4d, and the refresh process is executed.

  Next, an actual collection destination switching control example will be described in detail. A first control example is shown in Table 1.

* In the table, BC indicates a belt cleaning unit, and DC indicates a drum cleaning unit.

  In the control shown in Table 1, when a yellow (Y) and magenta (M) toner discharge pattern T, which is a spherical toner, is discharged, a transfer bias (opposite polarity with respect to the toner) is applied during normal printing to perform intermediate transfer. After the transfer onto the belt 6, the belt is collected by the belt cleaning blade 15. Further, when the black toner discharge pattern T, which is an irregular toner, is discharged, the transfer bias is reversed (same polarity as the toner) during normal printing, and the toner is collected by the cleaning roller 8a and the cleaning blade 8b.

  By this control, even when the total discharge amount of the toner exceeds the recovery capability of the cleaning roller 8a and the cleaning blade 8b, the color toner is recovered from the intermediate transfer belt 6, and therefore the toner recovery time on the photosensitive drum 1 (Cleaning time) can be shortened. Further, since the cleaning roller 8a and the cleaning blade 8b collect only the black toner necessary for polishing the drum surface, the polishing effect is improved and the cleaning failure on the photosensitive drum 1 due to the remaining color toner does not occur.

  Further, in order to enhance the polishing effect of the photosensitive drum 1 at high humidity (for example, 70% RH or more), the black toner discharge amount may be increased. Such control is shown in Table 2 as a second control example.

  In the control shown in Table 2, by increasing the black (K) reference printing rate from 3% to 5%, the difference in printing rate from the reference printing rate is large even if the average printing rate is 0% as in Table 1. Thus, the printing length of the black toner discharge pattern T is increased. Accordingly, the amount of black toner supplied to the cleaning roller 8a and the cleaning blade 8b increases, and the drum polishing effect can be enhanced as compared with the control in Table 1.

  Ordinarily, the toner is collected on the photosensitive drum 1, and when the total toner discharge amount exceeds a predetermined value, the excess amount may be transferred onto the intermediate transfer belt 6 and collected. Such control is shown in Table 3 as a third control example.

  In the control shown in Table 3, the print lengths of yellow (Y), magenta (M), cyan (C), and black (K) are calculated and added together to obtain the total print length in advance. If the total print length exceeds the reference length, the latter half of the total print length including black toner is collected on the photosensitive drum 1, and the remaining first half is placed on the intermediate transfer belt 6. Transfer to and collect.

  For example, when the reference length is 300 mm, the print lengths of black, cyan, and magenta are 89.1 mm, 59.4 mm, and 118.8 mm, respectively, in the example of Table 3, and therefore yellow that can be collected on the photosensitive drum 1. The printing length is 300− (59.4 + 89.1 + 118.8) = 32.7 mm. Since the actual printing length of yellow is 118.8 mm, the printing length transferred onto the intermediate transfer belt 6 is 118.8−32.7 = 86.1 mm.

  That is, until a yellow toner discharge pattern is discharged by 86.1 mm, a transfer bias at the time of normal printing is applied and transferred onto the intermediate transfer belt 6, and thereafter a transfer bias of reverse polarity is applied to change the toner collection destination. Switch to the cleaning roller 8a and the cleaning blade 8b. Accordingly, a certain amount of toner including black toner is supplied to the cleaning roller 8a and the cleaning blade 8b, and the polishing performance can be stabilized. Further, since the spherical color toner having high fluidity is also collected at the same time, the toner transportability by a recovery device such as a recovery spiral for transporting the waste toner from the cleaning roller 8a and the cleaning blade 8b to the toner recovery container is improved. As in the second control, the polishing effect of the photosensitive drum 1 can be enhanced by increasing the black reference print rate and increasing the black toner discharge amount at high humidity.

  Incidentally, even if the first to third controls (print rate control) for determining the toner discharge amount based on the print rate difference between the reference print rate and the average print rate as described above are performed, for example, the black print rate If the high toner state continues for a long period of time, the discharge amount of the irregular toner decreases.If the high color printing rate continues for a long period of time, the discharge amount of the spherical toner decreases. The ratio of the discharge amount of the regular toner is biased, and the polishing effect of the photosensitive drum 1 and the transport performance of the collected waste toner cannot be maintained. For example, when the ratio of black toner (indeterminate toner) in the total toner discharge amount within a predetermined period is less than 5%, it is difficult to maintain the surface state of the photosensitive drum 1. Further, if the ratio of the color toner (spherical toner) in the total discharge amount is less than 5%, it becomes difficult to maintain the waste toner conveyance performance.

  Therefore, in addition to the first to third controls, the black toner is forcibly discharged when the cumulative number of printed colors reaches the predetermined number A1, and the color when the cumulative number of monochrome printed sheets reaches the predetermined number A2. It is preferable to execute the averaging control for forcibly discharging the toner.

  For example, assuming that A1 is 16 sheets and A2 is 64 sheets, black toner is ejected by a predetermined amount (for example, an A4 size image with a printing rate of 25%) when the cumulative number of printed colors reaches 16. Further, when the cumulative number of monochrome printed sheets reaches 64, yellow toner is ejected by a predetermined amount (for example, an A4 size image with a printing rate of 25%), and thereafter every time the cumulative number of printed sheets reaches 64, magenta. , Cyan, yellow,..., One color at a time. The toner discharge amount for an A4 size image having a printing rate of 25% may be formed by forming a toner discharge pattern corresponding to 1/4 of an A4 size solid image (printing rate 100%).

  In the averaging control, the transfer bias applied to the temporary transfer rollers 7a and 7b is set to 0, and the discharged toner adheres substantially evenly to the photosensitive drum 1 side and the intermediate transfer belt 6 side by physical force. To do. Therefore, about 1/2 of the toner is collected on the photosensitive drum 1 and the intermediate transfer belt 6. Accordingly, toner containing a predetermined amount of irregular black toner and spherical color toner is also supplied to the belt cleaning blade 15, so that the transportability of waste toner from the belt cleaning blade 15 to the toner collection container is improved. Further, the toner adhered to the intermediate transfer belt 6 can be used for refreshing the belt surface.

  By executing this averaging control in combination with the first to third controls, the ratio of the discharge amount of each toner is substantially averaged when viewed in a relatively long cycle of 50 sheets and 100 sheets. The surface polishing effect and the waste toner conveyance performance can be stabilized. Since the execution cycle of the averaging control may be longer than that of the first to third controls, the predetermined number of sheets A1 and A2 is set to a value larger than the number of printed sheets A on which the first to third controls are executed. The

  In addition, when the averaging control is executed and the toner is discharged during the counting of the number of printed sheets A in the printing rate control (first to third controls), the discharging in the averaging control is performed in the printing rate control executed immediately after. The printing length of the toner discharge pattern is determined by subtracting the amount. Thereby, wasteful toner consumption can be suppressed and the ratio of the discharge amounts of the respective toners can be further averaged.

  FIG. 5 is a flowchart showing an 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. FIG. 5 shows control in which averaging control is combined with the third control shown in Table 3.

  First, when the image forming process is started by the operation of the operation panel 50 or a personal computer by the user, the counter 95 counts the number n of printed sheets, the accumulated number of printed sheets nc, and the accumulated number of printed sheets nm of monochrome (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). Control in the case of n = A will be described later.

  Next, it is determined whether or not the cumulative number of printed sheets nc has reached the predetermined number A1 (step S3). When nc = A1, black (K) toner is ejected by a predetermined amount (here, the printing length L0) (step S4). Then, nc is reset to 0 (step S5), and the process returns to step S1 again. If nc ≠ A1 in step S3, it is subsequently determined whether or not the monochrome accumulated print number nm has reached the predetermined number A2 (step S6). When nm = A2, yellow (Y) toner is ejected by a predetermined amount (here, the printing length L0) (step S7). Thereafter, when nm = A2 again, magenta (M) and cyan (C) toners are sequentially ejected for the print length L0. Then, nm is reset to 0 (step S8), and the process returns to step S1 again. If nm ≠ A2 in step S6, the process returns to step S1 without performing toner discharge.

  If n = A in step S2, the control unit 90 calculates the average printing rate B by Σbn / A (step S10). Next, the toner discharge amount (CB) × A (%) is calculated by multiplying the printing rate difference C−B between the average printing rate B and the reference printing rate C (%) by the number A of printed sheets, and further the printing rate. The print length Lnow of the toner ejection pattern T is calculated based on the circumferential length L0 of the image size that is the calculation reference (100%) (step S11). Then, it is determined whether toner discharge (step S4 or S7) has been performed during the A sheet count (step S12). If toner discharge has not been performed, the print length Lnow calculated in step S11 is actually used. Printing length L (step S13). On the other hand, when toner is ejected, the actual print length L is obtained by subtracting the print length L0 ejected in step S4 or S7 from the print length Lnow (step S14).

  Then, the toner discharge pattern T having the printing length L calculated in step S13 or S14 is discharged onto the photosensitive drum 1 to execute a refresh process (step S15). At the same time, a total print length ΣL obtained by adding the print lengths L of the toner discharge patterns T of the respective colors is calculated (step S16), and it is determined whether or not ΣL exceeds a predetermined length L1 (for example, 300 mm) ( Step S17).

  If ΣL> L1, first, a transfer bias during normal printing is applied, and the toner ejection pattern for the first half ΣL-L1 is transferred onto the intermediate transfer belt 6 and collected on the belt (step S18). During the toner discharge, the transfer bias is reversed and the latter half L1 toner discharge pattern including the black toner discharge pattern is collected on the photosensitive drum 1 (step S19). On the other hand, if ΣL ≦ L1 in step S17, a reverse transfer bias is applied from the beginning, and all toner ejection patterns are collected on the photosensitive drum 1 (step S20). Thereafter, the number n of prints is reset to 0 (step S21), and the process returns to step S1 again.

  In the case where the first control shown in Table 1 and the second control shown in Table 2 and the averaging control are combined, the process of assigning the collection destination of the toner discharge pattern (Steps S17 to S20) is performed as the toner. If the distribution is changed according to the particle shape, the same explanation can be made using the flowchart of FIG. Further, instead of the toner particle shape, the collection destination may be distributed according to the amount of abrasive in the external additive and the fluidity of the toner.

  In addition, the printing length L may be determined using a toner discharge amount setting table in which a plurality of toner discharge modes that define the toner discharge amount discharged from the developing roller 25 for each printing rate level when the refresh process is executed are stored. it can.

  An example of the toner discharge amount setting table is shown in FIG. In FIG. 6, the average printing rate B is assigned to each row of the toner discharge amount setting table from 1% to 5% at 1% intervals, and each column is assigned 6 levels of toner discharge modes from 0 to 5. . In each toner discharge mode, the toner discharge amount per printed sheet corresponding to the print rate level is defined by the print length (mm). In mode 0, toner discharge is not performed regardless of the average print rate, and the toner discharge amount at each print rate level is set to increase stepwise up to mode 5. In each mode, the toner discharge amount is set to decrease as the average printing rate increases. When the average printing rate is 5% or more, toner discharge is not performed in any mode. The toner discharge mode may be set manually or may be automatically set according to the temperature and humidity inside the apparatus.

  When the average printing rate B is calculated by the control unit 90, the calculated average printing rate B and the toner discharge amount (printing length per printed sheet) at the position where the row and the column corresponding to the setting mode intersect are determined. Is done. The toner discharge amount Lnow is calculated by multiplying the toner discharge amount thus obtained by the number of printed sheets A after the previous refresh step.

  For example, when the calculated average printing rate B is 1.5% and the setting mode is MODE 4, the printing length per printed sheet at the position where the row of 1 ≦ B <2 and the mode 4 column intersect. 4.0 mm is selected. Here, if the number of printed sheets A is 10, the toner discharge amount Lnow is 4.0 × 10 = 40 mm. When toner is discharged by averaging control on the A sheet, the actual print length L is determined by subtracting L0 from Lnow.

  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.

  In a monochrome or tandem type color image forming apparatus, only one type of toner is ejected to the photosensitive drum, so that the collection destination is not sorted according to the characteristics of the toner. By sorting the collection destinations according to the toner collection capability, the cleaning time can be shortened while maintaining the surface state of the drum.

  The present invention includes a developing device that has a toner carrier that is disposed opposite to an image carrier, carries toner, and supplies the toner to the image carrier, and forms a toner image corresponding to the electrostatic latent image on the surface of the image carrier; An image forming apparatus capable of executing a refreshing process for discharging toner from the toner carrier side to the image carrier side during non-image formation, and a transfer body onto which the toner image formed on the image carrier by the developing device is transferred The image carrier cleaning device for collecting the toner on the image carrier and the transfer member cleaning device for collecting the toner on the transfer body are provided, and the collection destination of the toner ejection pattern ejected in the refresh process is provided. The image carrier cleaning device and the transfer member cleaning device are switched according to at least one of the continuous toner discharge amount and the toner characteristics.

  Accordingly, it is possible to provide an image forming apparatus capable of reducing the cleaning time by recovering toner exceeding the recovery capability of the image carrier cleaning apparatus by the transfer body cleaning apparatus. In addition, by preferentially collecting toner with externally added irregular shaped toner or abrasives with an image carrier cleaning device, it prevents cleaning defects due to remaining spherical toner and improves the polishing effect to improve the surface of the image carrier. The state can be stabilized.

  Further, in a color image forming apparatus provided with a plurality of developing devices facing one image carrier, collection is easy when toner discharged from each developing device is either spherical toner or irregular toner. In this case, only the irregularly shaped toner having a high polishing effect is collected by the image carrier cleaning device, so that the amount of toner collected by the image carrier cleaning device is reduced to shorten the cleaning time and prevent the image carrier from being poorly cleaned. The state can be maintained well.

  In addition, since a toner discharge pattern having a reference length including a toner discharge pattern formed of irregular shaped toner is collected by the image carrier cleaning device, spherical toner having high fluidity is also collected at the same time. Therefore, the toner transportability by the recovery device that transports the waste toner from the toner to the toner recovery container is also improved.

  Further, when the refresh process is performed a predetermined number of times, the toner collected by the image carrier cleaning device and the transfer body cleaning device includes a spherical toner and an irregular toner at a predetermined ratio or more, respectively. In addition, the cleaning performance and the polishing performance of the image forming apparatus are stabilized, and the toner conveying performance of the collecting device that conveys the waste toner from the image carrier cleaning device and the transfer member cleaning device to the toner collecting container is improved.

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. These are the flowcharts which show an example of the execution procedure of the refresh process in the image forming apparatus of this invention. FIG. 4 is a diagram showing an example of a toner discharge amount setting table used in the present invention.

Explanation of symbols

1 Photosensitive drum (image carrier)
4 Developing unit 4a to 4d Developing device 6 Intermediate transfer belt (transfer body)
8a Cleaning roller (image carrier cleaning device)
8b Cleaning blade (image carrier cleaning device)
15 Belt cleaning blade (transfer body cleaning device)
25 Developing roller (toner carrier)
26 Supply roller 90 Control unit 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 (10)

A developing device that has a toner carrier that is disposed opposite to the image carrier and carries toner and supplies the toner to the image carrier, and forms a toner image corresponding to the electrostatic latent image on the surface of the image carrier;
A transfer body onto which a toner image formed on the image carrier by the developing device is transferred;
With
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 carrier cleaning device for collecting toner on the image carrier, and a transfer member cleaning device for collecting toner on the transfer body,
The collection destination of the toner ejection pattern ejected in the refresh process is switched between the image carrier cleaning device and the transfer body cleaning device according to at least one of a continuous toner ejection amount and toner characteristics. Image forming apparatus.   2. The image formation according to claim 1, wherein the toner discharge amount in the refresh step is determined based on a difference between a print rate on the image calculated over a predetermined number of prints and a reference print rate. apparatus.   A plurality of the developing devices are provided to face one image carrier, and the continuous discharge amount is a total value of toner amounts discharged from the plurality of developing devices in which the refresh process is continuously executed. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The toner discharged from each of the developing devices is either spherical toner or irregular toner, and the transfer destination cleaning device is a collection destination of the toner discharge pattern formed of spherical toner, and is formed with irregular toner. 4. The image forming apparatus according to claim 3, wherein a collection destination of the toner discharge pattern is the image carrier cleaning device.   The toner discharged from each of the developing devices is either a spherical toner or an irregular toner. When the total print length of the toner discharge pattern during the refresh process is equal to or less than a reference length, all the toner discharge patterns are displayed. When the total print length exceeds the reference length, the image carrier cleaning device collects a reference length toner discharge pattern including a toner discharge pattern formed of an irregular toner with the image carrier cleaning device. The image forming apparatus according to claim 3, wherein the image forming apparatus collects and the remaining toner discharge pattern is collected by the transfer body cleaning device.   6. The image forming apparatus according to claim 4, wherein a printing length of the toner discharge pattern formed of the irregular toner is variable according to humidity.   When the refresh process is executed a predetermined number of times, control is performed so that the toner collected by the image carrier cleaning device and the transfer member cleaning device includes the spherical toner and the irregular toner in a predetermined ratio or more. The image forming apparatus according to claim 4, wherein the image forming apparatus is an image forming apparatus.   8. The image forming apparatus according to claim 7, wherein the toner collected by the image carrier cleaning device and the transfer body cleaning device includes 5% or more of the spherical toner and the irregular toner, respectively.   The irregular toner is a black toner, the spherical toner is a color toner other than black, and the refreshing step discharges a predetermined amount of black toner when the cumulative number of color prints reaches a predetermined number. 9. The image forming apparatus according to claim 7, further comprising an averaging control that discharges a predetermined amount of color toner one by one in order when the number of printed sheets reaches a predetermined number.   The refresh step is a combination of printing rate control for performing toner ejection based on the difference between the printing rate on the image calculated over a predetermined number of printed sheets and the reference printing rate, and the averaging control. 10. The image according to claim 9, wherein when the averaging control is executed after executing the printing rate control, the toner discharging amount in the next printing rate control is determined by subtracting the toner discharging amount in the averaging control. Forming equipment.