JP2016075812A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus with which it is possible to always optimize the discharge amount of toner when a forcible discharge of toner is executed in a development device.SOLUTION: The image forming apparatus comprises an image formation unit including a development device, and a control unit. When a concentration B of a patch image formed by the image forming unit is smaller than a threshold B1, the control unit calculates a reference printing rate Ps on the basis of at least two of parameters for a development device drive time, a patch image concentration, a toner concentration in the development device, and an absolute humidity. When the patch image concentration B is in the range B1 to B2 inclusive, the control unit calculates the reference printing rate Ps on the basis of a parameter for the drive time. Then, the control unit calculates the discharge amount of toner in this session of a refresh process by multiplying a difference between the calculated reference printing rate Ps and an average printing rate P in the printed number of sheets n from the previous session of the refresh process by the printed number of sheets n.SELECTED DRAWING: Figure 4

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 apparatus provided with a refresh process for refreshing toner on a toner carrier 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 (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. 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 having a high printing rate such as photographs and graphic images and images having 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 a solid, and the toner is transferred to a recording medium to consume 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 without being consumed by the effect of charge-up, etc. It 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 a method for inter-paper or non-printing according to the printing rate and the driving time of the developing device. An image forming apparatus that changes the discharge amount of toner that is forcibly discharged during printing is disclosed.

JP 2007-147780 A

  However, when the toner discharge amount is determined only by the printing rate and the driving time of the developing device as in Patent Document 1, the discharge amount is larger than the required amount depending on the use environment of the device, the developability of the toner, the toner concentration, and the like. It may become less or less. When the discharge amount is smaller than the necessary amount, a sufficient effect cannot be obtained. When the discharge amount is larger than the necessary amount, the running cost of the apparatus increases, which is a disadvantage for the user.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of always optimizing a toner discharge amount when forced toner discharge in a developing device is performed.

  In order to achieve the above object, a first configuration of the present invention includes an image forming unit, a control unit, a printed sheet count unit, a driving time measuring unit, an image density sensor, a toner density sensor, a humidity sensor, And an image forming apparatus. The image forming unit includes an image carrier on which an electrostatic latent image is formed, and a toner carrier that is disposed opposite to the image carrier and carries toner and supplies the toner to the image carrier. And a developing device that forms a toner image corresponding to the latent image. The control unit controls the amount of toner discharged from the toner carrier. The printed sheet count unit counts the number of printed sheets. The drive time measuring unit measures the drive time of the developing device. The image density sensor detects the patch image density of the patch image formed by the image forming unit. The toner concentration sensor detects the toner concentration in the two-component developer containing toner and magnetic carrier accommodated in the developing device. The humidity sensor detects the humidity inside the image forming apparatus. The image forming apparatus can execute a refresh process for discharging toner from the toner carrier side to the image carrier side during non-image formation. When the patch image density B detected by the image density sensor is smaller than the predetermined threshold value B1, the control unit includes parameters for absolute humidity calculated from the driving time, the patch image density, the toner density, and the detection result of the humidity sensor. Based on at least two, a reference print rate Ps, which is a required ejection amount per image, is calculated. Further, when the patch image density B is equal to or higher than B1 and equal to or lower than the threshold B2 (B1 <B2), the reference print rate Ps is calculated based on the parameter for the driving time. Then, the difference (Ps−P) between the calculated reference print rate Ps and the average print rate P in the number n of prints from the previous refresh step is multiplied by the number of prints n to obtain the toner discharge amount in the current refresh step. calculate.

  According to the first configuration of the present invention, a patch image is formed prior to the execution of the refresh process, and when the patch image density is smaller than the threshold value B1, the driving time of the developing device, the patch image density, the toner density, and the absolute humidity The reference print rate Ps is calculated based on at least two of the parameters. If the patch image density is not less than the threshold value B1 and not more than B2, the reference print rate Ps is calculated based on the drive time parameter of the developing device. Therefore, even if the development drive time is the same, the toner discharge amount can be changed according to the developability of the toner in the developing device and the usage environment. Therefore, the optimum toner is always used regardless of the usage conditions and usage environment of the image forming apparatus. The refresh process can be executed with the discharge amount.

1 is a schematic cross-sectional view illustrating an overall configuration of a color printer 100 that is an example of an image forming apparatus of the present invention. Sectional drawing of the developing device 3a used for the color printer 100 Block diagram showing the control path of the color printer 100 The flowchart which shows the execution procedure of the refresh process in the color printer 100

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to the present invention. Here, a tandem type color printer is shown. In the main body of the color printer 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  These image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c and 1d which carry visible images (toner images) of the respective colors, and are further illustrated by a driving means (not shown). 1, an intermediate transfer belt 8 that rotates in the clockwise direction is provided adjacent to each of the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1 a to 1 d are sequentially transferred onto the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1 a to 1 d, and then transferred onto the transfer paper at the secondary transfer roller 9. The image is transferred onto P at a time, and further fixed on the transfer paper P in the fixing unit 7 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d in the counterclockwise direction in FIG.

  In this embodiment, the photosensitive drums 1a to 1d are amorphous silicon (a-Si) photosensitive members, and an a-Si photoconductive layer is formed as a photosensitive layer on a conductive substrate (cylinder) such as aluminum. A surface protective layer made of an inorganic insulator or an inorganic semiconductor such as a-Si based SiC, SiN, SiO, SiON, or SiCN is laminated on the upper surface.

  The transfer paper P to which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the color printer 100 main body, and is conveyed to the secondary transfer roller 9 via the paper feed roller 12a and the registration roller pair 12b. A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a (seamless) belt having no seam is mainly used. A blade-shaped belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed downstream of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are charging devices 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure device 4 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning devices 5a, 5b, 5c and 5d are provided.

  When image data is input from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the charging devices 2a to 2d, and then light is irradiated by the exposure device 4 to each photosensitive member. Electrostatic latent images corresponding to image signals are formed on the drums 1a to 1d. Each of the developing devices 3a to 3d is filled with a predetermined amount of cyan, magenta, yellow, and black toner by a replenishing device (not shown). The toner is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and electrostatically attached to form a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure device 4. It is formed.

  After an electric field is applied to the intermediate transfer belt 8 at a predetermined transfer voltage, the cyan, magenta, yellow, and black toner images on the photosensitive drums 1a to 1d are transferred to the intermediate transfer belt 8 by the primary transfer rollers 6a to 6d. Transcribed above. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning devices 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched around a plurality of stretching rollers including an upstream conveying roller 10 and a downstream driving roller 11, and the rotation of the driving roller 11 by a driving motor (not shown) is performed. When the intermediate transfer belt 8 starts to rotate in the clockwise direction, the transfer paper P is conveyed from the registration roller pair 12b to the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and a full color image is formed. Transcribed. The transfer paper P onto which the toner image is transferred is conveyed to the fixing unit 7.

  The transfer paper P conveyed to the fixing unit 7 is heated and pressurized by the fixing roller pair 13 so that the toner image is fixed on the surface of the transfer paper P, and a predetermined full color image is formed. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portion 14 that branches in a plurality of directions. When an image is formed on only one side of the transfer paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller pair 15.

  On the other hand, when images are formed on both sides of the transfer paper P, a part of the transfer paper P that has passed through the fixing unit 7 is once protruded from the discharge roller pair 15 to the outside of the apparatus. Thereafter, the transfer paper P is redistributed to the registration roller pair 12b in a state where the image surface is reversed by rotating the discharge roller pair 15 in the reverse direction to be distributed to the paper conveyance path 18 by the branching section 14. Then, after the next image formed on the intermediate transfer belt 8 is transferred by the secondary transfer roller 9 to the surface of the transfer paper P where the image is not formed, and conveyed to the fixing unit 7 to fix the toner image. The paper is discharged to the discharge tray 17 through the discharge roller pair 15.

  Further, an image density sensor 40 is disposed at a position facing the driving roller 11 with the intermediate transfer belt 8 interposed therebetween. As the image density sensor 40, an optical sensor provided with a light emitting element composed of an LED or the like and a light receiving element composed of a photodiode or the like is generally used. When measuring the toner adhesion amount on the intermediate transfer belt 8, if the measurement light is irradiated from the light emitting element to each reference image formed on the intermediate transfer belt 8, the measurement light is reflected by the toner, and the belt surface. Is incident on the light receiving element as light reflected by the light.

  The reflected light from the toner and the belt surface includes regular reflection light and irregular reflection light. The specularly reflected light and irregularly reflected light are separated by the polarization separation prism and then incident on separate light receiving elements. Each light receiving element photoelectrically converts the received regular reflection light and irregular reflection light and outputs an output signal to the control unit 90 (see FIG. 3). Then, the toner correction is performed for each color by detecting the toner amount from the change in the characteristics of the output signals of the regular reflection light and the irregular reflection light, and adjusting the development bias characteristic value and the like in comparison with a predetermined reference density. .

  FIG. 2 is a side cross-sectional view showing the configuration of the developing device 3 a mounted on the color printer 100. Here, the developing device 3a disposed in the image forming unit Pa of FIG. 1 will be described, but the configuration of the developing devices 3b to 3d disposed in the image forming units Pb to Pd is basically the same, and thus described. Is omitted.

  As shown in FIG. 2, the developing device 3a includes a developing container 20 in which a two-component developer containing a magnetic carrier and toner (hereinafter also simply referred to as a developer) is stored. The first and second agitating chambers 20b and 20c are partitioned by the agitator 20a, and toner (positively charged toner) supplied from a toner container (not shown) is mixed with the carrier and agitated in the first and second agitating chambers 20b and 20c. The first stirring screw 21a and the second stirring screw 21b for charging are rotatably arranged.

  Then, the developer is agitated by the first agitating screw 21a and the second agitating screw 21b while being conveyed in the axial direction, and passes through the developer passages (not shown) formed at both ends of the partition wall 20a. It circulates between the second stirring chambers 20b and 20c. In the illustrated example, the developing container 20 extends obliquely upward to the left, and a magnetic roller 22 is disposed above the second stirring screw 21b in the developing container 20, and the developing is performed obliquely upward to the left of the magnetic roller 22. Rollers 23 are arranged opposite to each other. The developing roller 23 faces the photosensitive drum 1a on the opening side (left side in FIG. 3) of the developing container 20, and the magnetic roller 22 and the developing roller 23 rotate in the clockwise direction in the drawing.

  The developing container 20 is provided with a toner concentration sensor 27 facing the first agitating screw 21a. According to the toner concentration detected by the toner concentration sensor 27 (ratio of toner to carrier, T / C). Then, the toner is replenished from the replenishing device (not shown) into the developing container 20 through the toner replenishing port 20d.

  The magnetic roller 22 includes a non-magnetic rotating sleeve 22a and a fixed magnet body 22b having a plurality of magnetic poles enclosed in the rotating sleeve 22a. In the present embodiment, the magnetic poles of the fixed magnet body 22 b have a five-pole configuration including a main pole 35, a regulation pole (head cutting pole) 36, a transport pole 37, a separation pole 38, and a pumping pole 39. The magnetic roller 22 and the developing roller 23 face each other with a predetermined gap at the facing position (opposing position).

  Further, a spike cutting blade 25 is attached to the developing container 20 along the longitudinal direction of the magnetic roller 22 (direction perpendicular to the paper surface of FIG. 2), and the spike cutting blade 25 is rotated in the direction of rotation of the magnetic roller 22 (see FIG. 2 (clockwise direction) 2, it is positioned upstream of the position where the developing roller 23 and the magnetic roller 22 face each other. A slight gap (gap) is formed between the tip of the ear cutting blade 25 and the surface of the magnetic roller 22.

  The developing roller 23 includes a nonmagnetic developing sleeve 23a and a developing roller side magnetic pole 23b fixed in the developing sleeve 23a. The developing roller side magnetic pole 23b is different in polarity from the opposing magnetic pole (main pole) 35 of the fixed magnet body 22b.

  A developing bias power source 43 is connected to the developing roller 23 and the magnetic roller 22 via a bias control circuit 41 (see FIG. 3). Specifically, the developing roller 23 is connected to a first power source 43a including a DC power source and an AC power source, and the magnetic roller 22 is connected to a second power source 43b including a DC power source and an AC power source. As a result, a developing bias in which an AC voltage is superimposed on a DC voltage is applied to the developing roller 23, and a supply bias in which an AC voltage is superimposed on a DC voltage is applied to the magnetic roller 22.

  As described above, the first stirring screw 21a and the second stirring screw 21b circulate in the developing container 20 while the developer is being stirred to charge the toner, and the second stirring screw 21b causes the developer to move to the magnetic roller 22. Be transported. Since the regulation pole 36 of the fixed magnet body 22 b faces the ear cutting blade 25, a nonmagnetic material or a magnetic body having a polarity different from that of the regulation pole 36 is used as the ear cutting blade 25. A magnetic field is generated in a direction attracting the gap with the sleeve 22a.

  Due to this magnetic field, a magnetic brush is formed between the ear cutting blade 25 and the rotating sleeve 22a. When the magnetic brush on the magnetic roller 22 is regulated by the cutting blade 25 and then moved to a position facing the developing roller 23, the magnetic field attracted by the main pole 35 of the fixed magnet body 22b and the developing roller side magnetic pole 23b. Therefore, the magnetic brush contacts the surface of the developing roller 23. Then, a toner thin layer is formed on the developing roller 23 by a potential difference ΔV between Vmag (DC) applied to the magnetic roller 22 and Vslv (DC) applied to the developing roller 23 and a magnetic field.

  The thickness of the toner layer on the developing roller 23 varies depending on the resistance of the developer and the rotational speed difference between the magnetic roller 22 and the developing roller 23, but can be controlled by ΔV. When ΔV is increased, the toner layer on the developing roller 23 is thickened, and when ΔV is decreased, the toner layer is thinned. The range of ΔV at the time of development is generally about 100V to 350V.

  Next, the control path of the color printer 100 of the present invention will be described. FIG. 3 is a block diagram illustrating an example of a control path used in the color printer 100. In addition, since various controls of each part of the apparatus are performed when the color printer 100 is used, the control path of the entire color printer 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 bias control circuit 41 is connected to the charging bias power source 42, the developing bias power source 43, and the transfer bias power source 44, and operates each of these power sources in accordance with an output signal from the control unit 90. In accordance with a control signal from the control circuit 41, the charging bias power source 42 is applied to the charging rollers in the charging devices 2a to 2d, the developing bias power source 43 is applied to the magnetic roller 22 and the developing roller 23 in the developing devices 3a to 3d, and the transfer bias power source 44 is supplied. Applies a predetermined bias to the primary transfer rollers 6a to 6d and the secondary transfer roller 9, respectively.

  The in-machine temperature / humidity sensor 45 detects the temperature and humidity inside the color printer 100. The detection result is transmitted to the control unit 90 via an I / F 96 described later. The in-machine temperature / humidity sensor 45 is controlled by the control unit 90 and can measure temperature / humidity unless the main power supply is turned off. For example, temperature / humidity information can be collected periodically every minute, and temperature / humidity information can also be collected by setting conditions such as at the start of printing.

  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 (in this case, 2) control signals are transmitted to the temporary storage unit 94, counter 95, timer 97, and each device in the color printer 100 for storing image data and the like, and input signals from the operation unit 50 are received. At least one I / F (interface) 96. Further, the control unit 90 can be arranged at an arbitrary location inside the apparatus main body.

  The ROM 92 stores a program for controlling the color printer 100, numerical values necessary for control, and the like that are not changed during use of the color printer 100. In the RAM 93, necessary data generated during the control of the color printer 100, such as measurement data of the toner density sensor 27, the image density sensor 40, or the in-machine temperature / humidity sensor 45, and temporarily necessary for the control of the color printer 100 are stored. And the like are stored.

  In addition, the ROM 92 (or RAM 93) includes developing devices 3a to 3d used for determining whether or not the refresh process is necessary or determining the toner discharge amount, as will be described later, in addition to the reference number of printed sheets for determining the execution timing of the refresh process. The accumulated drive time, the patch image density, the toner density in the developing devices 3a to 3d, the parameter value of absolute humidity, and the like are also stored. The counter 95 adds up the number of printed sheets and counts it. The timer 97 measures the cumulative driving time of each part of the apparatus. Note that the number of printed sheets or the driving time may be stored in the RAM 93, for example, without providing the counter 95 and the timer 97 separately.

  The control unit 90 transmits a control signal from the CPU 91 to the respective units and devices in the color printer 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. For example, the image forming units Pa to Pd, the exposure device 4, the fixing unit 7, the intermediate transfer belt 8, the secondary transfer roller 9, the toner density sensor 27, and the image density sensor 40 are the parts and devices controlled by the control unit 90. , Bias control circuit 41, in-machine temperature / humidity sensor 45, operation unit 50, and the like.

  The operation unit 50 is provided with a liquid crystal display unit 51 and LEDs 52 that indicate various states, and displays the state of the color printer 100 and displays the image forming status and the number of copies to be printed. Various settings of the color printer 100 are performed from a printer driver of a personal computer.

  In addition, the operation unit 50 includes a start button for instructing the user to start image formation, a stop / clear button used for stopping image formation, and various settings of the color printer 100 when making the default settings. A reset button or the like to be used is provided.

  The color printer 100 of the present invention is used when the image forming apparatus is not transferred to a sheet, for example, when the image forming apparatus is started from a power-off state or a sleep (power saving) mode to a copy start state, or when a predetermined number of prints are performed. The refreshing process for discharging the toner on the developing roller 23 in the developing devices 3a to 3d to the photosensitive drums 1a to 1d can be executed.

  By periodically executing this refresh step, the overcharged (charged up) toner existing on the developing roller 23 is forcibly discharged toward the photosensitive drums 1a to 1d. Replacement of particles is promoted. Therefore, even when images with a low printing rate are continuously printed, it is possible to suppress image density reduction and image fogging due to overcharged toner.

  Next, a method for calculating the toner discharge amount during execution of the refresh process will be described. In the conventional calculation method, the toner discharge amount is determined based on the cumulative number n of prints after the previous refresh step and the driving time A of the developing device. Specifically, assuming that the number of printed sheets until the next refresh process is executed after the previous refresh process is executed, the control unit 90 performs the process for each image based on the digital signal in the temporary storage unit 94. A printing rate pn is calculated, and an integrated printing rate Σpn obtained by adding the printing rate pn is calculated.

  Then, the integrated printing rate Σpn is divided by the number of printed sheets n counted by the counter 95 to calculate an average printing rate P (%) per number of printed sheets n. Since the printing rate difference Ps−P between the average printing rate P and the reference printing rate (the printing rate threshold that requires refreshing) Ps (%) is the required discharge amount (shortage of consumption) per image, Multiplying this by the number n of prints (Ps−P) × n (%) becomes the toner discharge amount when the refresh process is executed.

  In general, the longer the driving time of the developing devices 3a to 3d is, the more the toner in the developing devices 3a to 3d is deteriorated, and the developability is lowered. Therefore, the reference depends on the driving time A of the developing devices 3a to 3d. The printing rate Ps is determined. For example, assuming that the number n of printed sheets is 200 and the reference print ratio Ps is 2%, when the average print ratio P is 2%, (2-1.5) × 200 = 100 (%) of toner is ejected. To do. As described above, the toner discharge amount is calculated for each of the developing devices 3a to 3d, and the refresh process is executed.

  However, in the conventional method as described above, even when the developability of the toner varies depending on the toner density in the developing devices 3a to 3d, the usage environment of the color printer 100, and the like, the number of printed sheets n and the developing devices 3a to 3d. If the 3d drive time A is the same, the toner discharge amount is the same. For this reason, there are cases where excessive toner is ejected even though the toner developability is high, or sufficient toner is not ejected even though the toner developability is low.

  Therefore, in the present invention, when the number of printed sheets n that serves as a trigger for executing the refresh process is reached, a patch image is formed, the patch image density is measured, and a toner ejection amount calculation procedure is performed according to the measurement result of the patch image density. Is going to change.

  When the measured patch image density exceeds a predetermined threshold value (high density), it is considered that the toner in the developing devices 3a to 3d has not deteriorated and developability is maintained. Therefore, the toner on the developing roller 23 is not forcibly discharged.

  When the measured patch image density is near a predetermined threshold (normal), it is considered that the toner in the developing devices 3a to 3d has a normal deterioration level. Therefore, the reference print rate Ps is determined according to the driving time A of the developing devices 3a to 3d, and the print rate difference Ps−P between the average print rate P per the print number n and the reference print rate Ps is multiplied by the print number n. Further, the toner discharge amount is calculated by (Ps−P) × n (%), and the toner is discharged by the calculated discharge amount.

  When the measured patch image density is less than a predetermined threshold (low density), it is considered that the toner in the developing devices 3a to 3d is more deteriorated than usual. Therefore, in addition to the driving time A of the developing devices 3a to 3d, parameters for the toner discharge amount (reference printing rate Ps) are set for the patch image density B, the toner density C in the developing devices 3a to 3d, and the absolute humidity D. To do. Then, the set printing parameters Ps are determined by adding the set parameters, and the toner discharge amount is calculated based on the determined reference printing rate Ps. Table 1 shows an example of parameter settings for the development drive time A, patch image density B, toner density C, and absolute humidity D.

  Regarding the development drive time A, as described above, the mechanical stress applied to the toner increases or the external additive peels off as the drive time of the developing devices 3a to 3d becomes longer. As a result, the toner is easily charged up, and the deterioration of the toner is promoted. Therefore, the parameter value is set to increase as the development drive time A becomes longer.

  Regarding the patch image density B, it is considered that the toner developability decreases as the image density decreases. Therefore, the parameter value is set to increase as the patch image density B (ID, image density) decreases.

  As for the toner density C, the lower the toner density in the developing devices 3a to 3d (the higher the ratio of the carrier to the toner), the more the toner charge is promoted, and the toner deterioration is accelerated. Therefore, the parameter value is set to increase as the toner density C decreases.

  Regarding the absolute humidity D, generally, the charged state of the developer (toner) depends on the absolute humidity D, and the lower the absolute humidity D, the higher the charge amount of the toner. Therefore, the parameter value is set to increase as the absolute humidity D decreases.

  FIG. 4 is a flowchart showing the execution procedure of the refresh process in the present invention. The execution procedure of the refresh process will be described along the steps of FIG. 4 while referring to FIGS. 1 to 3 and Table 1 as necessary. In the following control example, a procedure in which the refresh process is executed for one of the developing devices 3a to 3d will be described, but the same procedure is executed for the other three developing devices. Further, after execution of the refresh process, normally, the reference print number n1 until the next refresh process is executed is set to 200 sheets (reference sheet number), and control is performed so as to calculate the toner discharge amount (reference print rate Ps) every 200 sheets. Yes.

  First, when an image forming process command is transmitted by the operation of the operation panel 50 or a personal computer by the user, printing is started, and the number of printed sheets n is counted by the counter 95 (step S1). On the other hand, the development drive time A of the developing devices 3a to 3d is measured by the timer 97, and the measurement of the toner density C by the toner density sensor 27 and the measurement of the absolute humidity D by the in-machine temperature / humidity sensor 45 are executed in parallel (step). S2). The measurement result is transmitted to the control unit 90 and stored in the RAM 93.

  The controller 90 determines whether or not the number of printed sheets n has reached the reference number of printed sheets n1 (step S3). Until the number of printed sheets n reaches the reference number of printed sheets n1, the process returns to step S1, and the counting of the number of printed sheets n, the measurement of the development driving time A, the measurement of the toner density C, and the measurement of the absolute humidity D are continued. When the number n of printed sheets reaches the reference number of printed sheets, a patch image (solid image) of each color is formed on the intermediate transfer belt 8 (step S4). Then, the patch image density B is measured using the image density sensor 40 (step S5).

  The controller 90 determines whether or not the measured patch image density B is B1 ≦ B ≦ B2 (B1 <B2) (step S6). If the image density B is not less than the threshold value B1 and not more than B2 (YES in step S6), the reference print rate Ps is determined based on the number of printed sheets n, the development drive time A, and the image density B (step S7).

  For example, when B1 = 1.0 and B2 = 1.2, when the development drive time A is 2.5 [sec] and the image density B is 1.1, the development drive time A and the image density B are shown in Table 1. The parameter values for are respectively 0.4 and 0.6, and the reference print rate Ps is 1.0 (%), which is the sum of the parameter values (0.4 + 0.6).

  If the patch image density B is not B1 ≦ B ≦ B2 (NO in step S6), it is determined whether or not B <B1 (step S8). If the image density B is smaller than the threshold value B1 (YES in step S8), the reference print rate Ps is determined by adding the parameters of the toner density C and the absolute humidity D to the number n of printed sheets, the development drive time A, and the image density B. Determine (step S9).

For example, when B = 0.9 (<1.0), the development drive time A is 2.5 [sec], the toner density C is 10 [%], and the absolute humidity D is 4 [g / m ³ ]. From Table 1, the parameter values for development drive time A, image density B, toner density C, and absolute humidity D are 0.4, 0.9, 0.4, and 0.5, respectively, and the reference printing rate Ps is the parameter. The total value (0.4 + 0.9 + 0.4 + 0.5) is 2.2 (%).

  Then, the average printing rate P per number of printed sheets n is calculated by dividing the integrated printing rate Σpn obtained by integrating the printing rate pn for each image by the number of printed sheets n counted by the counter 95, and the average printing rate P is the reference. It is determined whether or not it is smaller than the printing rate Ps (step S10). If P <Ps, toner discharge is executed with (Ps−P) × n (%) obtained by multiplying the print rate difference Ps−P by the number of printed sheets n (%) (step S11).

  On the other hand, if B <B1 is not satisfied in step S8 (B> B2), it is determined that the toner has not deteriorated, and the toner is not discharged (step S12). If P ≧ Ps in step S10, the toner consumption in actual printing is equal to or greater than the toner consumption necessary for refreshing, and thus no toner is discharged (step S12). Thereafter, the count number n of the counter 95 is reset to 0 (step S13), and the process returns to step S1 again.

  According to the above control, since a patch image is formed prior to the execution of the refresh process and toner is not discharged when the patch image density is higher than a predetermined threshold value, wasteful toner consumption can be suppressed. . Further, when the patch image density is near the threshold, the reference printing rate Ps is calculated based on the development drive time and patch image density parameters, and when the patch image density is lower than the threshold, the development drive time, the patch image density, Since the reference print rate Ps is calculated based on the parameters of toner density and absolute humidity, the toner discharge amount is changed according to the developability of the toner in the developing devices 3a to 3d and the usage environment even if the development drive time is the same. it can. Therefore, the refresh process can always be executed with an optimal toner discharge amount regardless of the use conditions and use environment of the color printer 100.

  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 control example, when the image density B is within a predetermined threshold range (B1 ≦ B ≦ B2), the reference print rate Ps is determined based on the development drive time A and the image density B. The reference print rate Ps may be determined based only on the development drive time A.

  In the above control example, when the image density B is smaller than the predetermined threshold (B <B1), the reference print rate Ps is set using the parameters of the development drive time A, the image density B, the toner density C, and the absolute humidity D. For example, the reference print rate Ps may be calculated using any two or three of the parameters of the development drive time A, the image density B, the toner density C, and the absolute humidity D, for example.

  Further, the present invention is not limited to the developing device including the magnetic roller 22 carrying the two-component developer and the developing roller 23 carrying only the toner as shown in FIG. The present invention can be applied in exactly the same manner to a two-component developing system that develops an electrostatic latent image on a photosensitive drum using a magnetic brush formed on a roller 23.

  Further, in the present invention, only the tandem color printer 100 as shown in FIG. 1 has been described as an example, but a two-component developer such as a monochrome printer, a monochrome and color copier, a digital multifunction machine, a facsimile, a laser printer, or the like. Needless to say, the present invention can be applied to various image forming apparatuses equipped with a developing device using the above. Hereinafter, the effects of the present invention will be described more specifically with reference to examples.

  In the color printer 100 of the present invention shown in FIG. 1, the relationship between the toner discharge amount determination method and the image density when the refresh process is executed was investigated. In the test method, the calculation method of the reference printing rate Ps is changed according to the patch image density B by the control shown in the flowchart of FIG. 4 and the reference printing rate Ps is calculated using the parameters shown in Table 1 ( The density reduction of the solid image of the present invention 1 to 11) was evaluated. Further, the density reduction of the solid image when the reference printing rate Ps is constant (2%) (comparative example) was also evaluated. Note that the reference number n of prints, which is the interval of the refresh process, was 200. The results are shown in Table 2.

In Table 2, “ordinary” driving time A corresponds to 2 to 3 seconds in Table 1. The patch density B corresponding to “dark” corresponds to an ID of 1.2 or more, “normal” corresponds to 1.0 to 1.2, and “light” corresponds to 1.0 or less. Further, “high” toner density C corresponds to a T / C of 11% or more, “normal” corresponds to a T / C of 9 to 11%, and “high” corresponds to a T / C of 9% or less. The absolute humidity D is "high" is 10 g / m ³ or more, "normal" is 5 to 10 g / m ^3, "low" corresponds to less 5 g / m ^3.

  For example, in the invention 3 of Table 2, the driving time A is “normal”, the patch density B is “light”, the toner density C is “high”, and the absolute humidity D is “high”. The parameter is 0.4, the parameter of the patch density B is 0.6, the parameter of the toner density C is 0.2, the parameter of the absolute humidity D is 0.1, and the reference printing rate Ps = (0.4 + 0.6 + 0.2 + 0) .1) = 1.6 (%).

  The image density was evaluated by visual observation, and a case where a sufficient density was obtained was indicated as ◯, a case where a slight decrease in density was observed, and a case where a significant decrease in density was observed as x.

  As apparent from Table 2, in the present invention in which the calculation method of the reference printing rate Ps is changed according to the patch image density B, the reference printing rate Ps = 0% when the patch density is high (Invention 1), and the toner Although no discharge was performed, no decrease in image density was observed. On the other hand, in the comparative example, the reference printing rate Ps = 2.0%, so unnecessary toner discharge is performed.

  Similarly, in the present inventions 2 to 4 and 6, since the reference printing rate Ps is lower than that of the comparative example, the toner discharge amount can be reduced without causing a decrease in image density. On the other hand, in the present inventions 8, 10, and 11, the reference printing rate Ps is set higher than that in the comparative example, and the reduction in image density generated in the comparative example can be improved.

  The present invention can be used in an image forming apparatus including a refresh process for refreshing toner on a toner carrier during non-image formation. By utilizing the present invention, it is possible to provide an image forming apparatus capable of always optimizing the toner discharge amount when the forced discharge of the toner on the toner carrier is executed.

1a to 1d Photosensitive drum (image carrier)
3a to 3d Developing device 26 Magnetic roller 23 Developing roller (toner carrier)
27 Toner density sensor 40 Image density sensor 45 In-machine temperature / humidity sensor (humidity sensor)
90 control unit 91 CPU
92 ROM
93 RAM
94 Temporary storage section 95 Counter (Number of printed sheets count section)
97 Timer (Driving time measurement unit)
100 color printer

Claims (5)

An image carrier on which an electrostatic latent image is formed;
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;
An image forming unit including:
A controller for controlling the amount of toner discharged from 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 during non-image formation,
A print count section for counting the number of prints;
A driving time measuring unit for measuring the driving time of the developing device;
An image density sensor for detecting a patch image density of a patch image formed by the image forming unit;
A toner concentration sensor for detecting a toner concentration in a two-component developer containing toner and a magnetic carrier contained in the developing device;
A humidity sensor that detects the humidity inside the image forming apparatus;
Is provided,
When the patch image density B detected by the image density sensor is smaller than a predetermined threshold B1, the control unit is calculated from the drive time, the patch image density, the toner density, and the detection result of the humidity sensor. Based on at least two parameters for absolute humidity, a reference print rate Ps, which is a required discharge amount per image, is calculated,
When the patch image density B is equal to or higher than B1 and equal to or lower than a threshold B2 (B1 <B2), the reference print rate Ps is calculated based on a parameter for the driving time;
The difference (Ps−P) between the calculated reference print rate Ps and the average print rate P in the number n of prints from the previous refresh step is multiplied by the number n of prints to obtain the toner discharge amount in the current refresh step. An image forming apparatus characterized by calculating.   The image forming apparatus according to claim 1, wherein the controller does not perform toner discharge when the patch image density B is larger than a threshold value B2.   When the patch image density B is smaller than a predetermined threshold B1, the control unit calculates the reference print rate Ps based on four parameters for the driving time, the patch image density, the toner density, and the absolute humidity. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The parameter values for the driving time, the patch image density, the toner density, and the absolute humidity are such that the longer the driving time, the lower the patch image density, and the lower the toner density, the lower the absolute humidity. The image forming apparatus according to claim 3, wherein the reference print rate Ps is calculated by adding the parameter values together.   2. The control unit according to claim 1, wherein when the patch image density B is not less than B1 and not more than B2, the control unit calculates the reference print rate Ps based on parameters for the drive time and the patch image density. The image forming apparatus according to claim 4.

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