JP2021002007A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can execute, within a minimum required range, the acquisition of the advection coefficient and diffusion coefficient of developer by predicting variations in the advection coefficient and diffusion coefficient.SOLUTION: An image forming apparatus comprises: image carriers; developing devices; a toner supply device; a developing voltage power supply; a curent detection unit; and a control unit. The control unit determines the timing at which a toner consumption area inside a developer container where toner is consumed reaches a toner supply position of the developer container based on the advection and diffusion coefficient of the toner inside the developing container, and supplies toner to the toner consumption area by using the toner supply device. The control unit can execute an advection and diffusion measurement mode for measuring the advection and diffusion coefficient in a non-image formation period, and executes the advection and diffusion measurement mode when the amount of change in the amount of charge of toner in the developing devices, or the amount of change of a DC component of a developing curent flowing in the developer carriers when non-image forming parts of the image carriers face the developing rollers during image formation, is larger than a predetermined amount.SELECTED DRAWING: Figure 5

Description

The present invention relates to an image forming apparatus such as a copier, a printer, a facsimile, and a multifunction device thereof using an electrophotographic method, and particularly a two-component developing type developing device using a two-component developing agent composed of toner and a carrier. It relates to an image forming apparatus provided.

In the image forming apparatus, a latent image formed on an image carrier made of a photoconductor or the like is developed by a developing apparatus and visualized as a toner image. As one of such developing devices, a two-component developing method using a two-component developing agent is adopted. In this type of developing apparatus, a developing roller composed of a carrier and a toner is housed in a developing container, a developing roller for supplying the developing agent to an image carrier is arranged, and the developing agent inside the developing container is conveyed. A stirring and transporting member that supplies the developing roller while stirring is arranged.

In a two-component developing system, the developer deteriorates due to the influence of the number of printed sheets, environmental fluctuations, printing conditions, printing rate, and the like, and the amount of toner charged changes. As a result, there is a problem that problems such as a decrease or increase in image density, image fog, and toner scattering occur.

Therefore, by keeping the toner concentration in the developing container constant, it is possible to suppress the poor charging of the toner as much as possible. Specifically, new toner is replenished to the place where the toner is consumed to stabilize the toner concentration.

By the way, since the fluidity of the developer changes due to durable printing, it is necessary to measure the fluidity of the developer in order to reliably supply the toner to the portion where the toner is consumed. For example, in Patent Document 1, image formation in which toner is replenished by improving the prediction accuracy of a portion where toner is consumed by acquiring at least one of an advection coefficient (conveyance speed) and a diffusion coefficient of a developer in a developing apparatus. The device is disclosed.

JP-A-2009-205125

In order to obtain the advection coefficient and the diffusion coefficient as in Patent Document 1, the developer needs to circulate in the developing container for one or more rounds. Therefore, it takes time to obtain the advection coefficient and the diffusion coefficient. In addition, since it is necessary to replenish and consume toner when acquiring the advection coefficient and diffusion coefficient, it is necessary to return the toner concentration to the original state and stabilize it after acquiring the coefficient. As a result, there is a problem that the printing waiting time becomes long and the image forming efficiency decreases.

In view of the above problems, it is an object of the present invention to provide an image forming apparatus capable of acquiring the advection coefficient and the diffusion coefficient to the minimum necessary by predicting the fluctuation of the advection coefficient and the diffusion coefficient of the developer. And.

In order to achieve the above object, the first configuration of the present invention is an image forming apparatus including an image carrier, a developing apparatus, a toner replenishing apparatus, a developing voltage power supply, a current detecting unit, and a control unit. Is. A photosensitive layer is formed on the surface of the image carrier. The developing apparatus includes a developing container containing a developer containing a carrier and toner, a developing agent carrier that is arranged so as to face the image carrier and supports at least toner on the surface, and a developing agent in the developing container. A stirring and transporting member for stirring and transporting is provided, and toner is supplied to an electrostatic latent image formed on the image carrier to form a toner image. The toner replenishing device replenishes toner in the developing container. The developing voltage power supply applies a developing voltage obtained by superimposing an AC voltage on a DC voltage on the developing agent carrier. The current detection unit detects the DC component of the developing current that flows when the developing voltage is applied to the developer carrier. The control unit controls the developing device and the toner replenishing device. Based on the advection diffusion coefficient, which is at least one of the toner transfer coefficient and the diffusion coefficient inside the developing container, the control unit develops the toner consumption area inside the developing container where the toner is consumed by being supplied to the image carrier. The timing of reaching the toner replenishment position of the container is determined, and the toner replenishment device is used to replenish the toner in the toner consumption area. The control unit can execute a transfer diffusion measurement mode that measures the transfer diffusion coefficient during non-image formation, and the amount of change in the toner charge amount in the developing device or the non-image portion of the image carrier faces each other during image formation. When the amount of change in the DC component of the developing current flowing through the developer carrier is larger than a predetermined amount, the transfer diffusion measurement mode is executed.

According to the first configuration of the present invention, the amount of change in the amount of toner charged in the developing apparatus, or the direct current of the developing current flowing through the developing agent carrier when the non-image portions of the image carrier face each other during image formation. By executing the transfer diffusion measurement mode when the amount of change in the components is larger than a predetermined amount, the transfer diffusion measurement mode can be executed at an appropriate timing. Therefore, since the variation in the toner density in the developing apparatus due to the variation in the advection diffusion coefficient is suppressed, defects such as poor image density, image fog, and toner scattering can be effectively suppressed. In addition, it is possible to suppress an increase in printing waiting time and an increase in toner consumption and power consumption due to unnecessary execution of the advection-diffusion measurement mode.

Schematic cross-sectional view of the color printer 100 of the present invention Side sectional view of the developing device 3a mounted on the color printer 100 A plan sectional view showing a stirring part of the developing apparatus 3a. Block diagram showing an example of the control path of the color printer 100 A flowchart showing a control example of the advection-diffusion measurement mode in the color printer 100 according to the first embodiment of the present invention. A graph showing the transition of the toner concentration when the toner is replenished to the toner replenishing unit 20d of the developing device 3a and the developing device 3a is driven. The figure which shows the simulation result using the advection coefficient U and the diffusion coefficient D calculated from FIG. The figure which shows the relationship between the degree of deterioration of a developer and the diffusion coefficient The figure which shows the relationship between the cumulative number of prints and the diffusion coefficient A flowchart showing a control example of the advection-diffusion measurement mode in the color printer 100 according to the second embodiment of the present invention. The figure which shows the relationship between the direction of density change and the charge amount of toner when the frequency of the AC component of a developing voltage is increased. The figure which shows the prediction line predicted by the advection coefficient of 3 points measured in the 1st to 3rd advection diffusion measurement modes. The figure which shows the prediction line predicted by the advection coefficient of 4 points measured in the 1st to 4th advection diffusion measurement modes. A flowchart showing a control example of the advection-diffusion measurement mode in the color printer 100 according to the third embodiment of the present invention. In Example 1, when the convection-diffusion measurement mode of the first embodiment was executed and the toner concentration was changed (invention 1), the toner concentration and V0-Vdc were changed (invention 2), but not changed. A graph showing the transition of image fog when endurance printing is performed in the case (Comparative Example 1). In Example 2, when the convection-diffusion measurement mode of the second embodiment was executed and the toner concentration was changed (the present invention 3), and when the toner concentration and V0-Vdc were changed (the present invention 4), they were not changed. A graph showing the transition of image fog when endurance printing is performed in the case (Comparative Example 2). In Example 3, the convection-diffusion measurement mode of the third embodiment is executed, and durable printing is performed depending on whether the toner concentration and V0-Vdc are changed (5 of the present invention) or not (Comparative Example 3). Graph showing the transition of image fog at the time

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of the image forming apparatus of the present invention, and here shows a tandem color printer. In the main body of the color printer 100, four image forming portions Pa, Pb, Pc and Pd are arranged in order from the upstream side in the transport direction (right side in FIG. 1). These image forming units Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and are cyan, magenta, and yellow, respectively, depending on each step of charging, exposure, development, and transfer. And black images are formed in sequence.

Photoreceptor drums 1a, 1b, 1c and 1d carrying visible images (toner images) of each color are arranged in these image forming portions Pa to Pd, respectively. Further, in FIG. 1, an intermediate transfer belt 8 rotating in the clockwise direction is provided adjacent to each image forming portion Pa to Pd.

When image data is input from a higher-level device such as a personal computer, first, the surfaces of the photoconductor drums 1a to 1d are uniformly charged by the charging devices 2a to 2d. Next, the exposure apparatus 5 irradiates light according to the image data to form an electrostatic latent image according to the image data on each of the photoconductor drums 1a to 1d. The developing devices 3a to 3d are filled with a predetermined amount of a two-component developer containing toners of each color of cyan, magenta, yellow and black, and the developing devices 3a to 3d put the developing agent on the photoconductor drums 1a to 1d. Toner is supplied and adheres electrostatically. As a result, a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure apparatus 5 is formed. When the toner in the developing devices 3a to 3d is consumed by the formation of the toner image, new toner is replenished from the toner containers 4a to 4d.

Then, an electric field is applied between the primary transfer rollers 6a to 6d and the photoconductor drums 1a to 1d at a predetermined transfer voltage by the primary transfer rollers 6a to 6d, and cyan, magenta, yellow and cyan, magenta, yellow and cyanide, magenta, yellow and The black toner image is primarily transferred onto the intermediate transfer belt 8. Toner and the like remaining on the surfaces of the photoconductor drums 1a to 1d after the primary transfer are removed by the cleaning devices 7a to 7d.

The transfer paper P on which the toner image is transferred is housed in a paper cassette 16 arranged at the lower part of the color printer 100. The transfer paper P is a nip portion (secondary transfer nip) of the secondary transfer roller 9 and the intermediate transfer belt 8 provided adjacent to the intermediate transfer belt 8 at a predetermined timing via the paper feed roller 12a and the resist roller pair 12b. It is transported to the department). The transfer paper P on which the toner image is secondarily transferred is conveyed to the fixing portion 13.

The transfer paper P conveyed to the fixing portion 13 is heated and pressurized by the fixing roller pair 13a to fix the toner image 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 discharged to the discharge tray 17 as it is (or after being distributed to the reversal transport path 18 by the branch portion 14 and the images are formed on both sides) by the discharge roller pair 15.

Further, the image density sensor 45 is arranged at a position facing the drive roller 11 with the intermediate transfer belt 8 interposed therebetween. As the image density sensor 45, an optical sensor including a light emitting element made of an LED or the like and a light receiving element made of a photodiode or the like is generally used. When measuring the amount of toner adhering to the intermediate transfer belt 8, when 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. It is incident on the light receiving element as light reflected by.

The reflected light from the toner and the belt surface includes specularly reflected light and diffusely reflected light. The specularly reflected light and the diffusely reflected light are separated by a polarization separation prism and then incident on separate light receiving elements. Each light receiving element photoelectrically converts the specularly reflected light and the diffusely reflected light received and outputs an output signal to the control unit 90 (see FIG. 4). Then, the toner amount is detected from the characteristic change of the output signals of the specularly reflected light and the diffusely reflected light, and the density correction (calibration) is performed for each color by adjusting the characteristic value of the developing voltage in comparison with a predetermined reference density. ) Is performed.

FIG. 2 is a side sectional view of the developing device 3a mounted on the image forming device 100. Note that FIG. 2 shows a state seen from the back side of the paper surface of FIG. 1, and the arrangement of each member in the developing apparatus 3a is reversed from that of FIG. Further, in the following description, the developing device 3a arranged in the image forming unit Pa of FIG. 1 is illustrated, but the configuration of the developing devices 3b to 3d arranged in the image forming units Pb to Pd is basically the same. Therefore, the description is omitted.

As shown in FIG. 2, the developing apparatus 3a includes a developing container 20 in which a two-component developing agent (hereinafter, also simply referred to as a developing agent) containing a magnetic carrier and toner is stored, and the developing container 20 is a partition wall. It is divided into a stirring transfer chamber 21 and a supply transfer chamber 22 by 20a. In the stirring transfer chamber 21 and the supply transport chamber 22, a stirring transfer screw 25 and a supply transfer screw 26 for mixing the toner supplied from the toner container 4a (see FIG. 1) with a magnetic carrier to stir and charge the toner, respectively. It is rotatably arranged.

Then, the developer is conveyed in the axial direction (direction perpendicular to the paper surface of FIG. 2) while being agitated by the stirring transfer screw 25 and the supply transfer screw 26, and the communication portions 20b and 20c formed at both ends of the partition wall 20a ( Both circulate between the stirring and transporting chamber 21 and the supply and transporting chamber 22 via (see FIG. 3). That is, a circulation path for the developer is formed in the developing container 20 by the stirring and transporting chamber 21, the supply and transporting chamber 22, and the communication portions 20b and 20c.

The developing container 20 extends diagonally upward to the right in FIG. 2, and a developing roller 31 is arranged diagonally upward to the right of the supply transport screw 26 in the developing container 20. Then, a part of the outer peripheral surface of the developing roller 31 is exposed from the opening 20d of the developing container 20 and faces the photoconductor drum 1a. The developing roller 31 rotates counterclockwise in FIG. The stirring transfer screw 25, the supply transfer screw 26, and the developing roller 31 rotate at a predetermined rotational speed by the driving force from the main motor 40 (see FIG. 4).

The developing roller 31 is composed of a cylindrical developing sleeve that rotates counterclockwise in FIG. 2 and a magnet (not shown) having a plurality of magnetic poles fixed in the developing sleeve. Although a developing sleeve having a knurled surface is used here, a developing sleeve having a large number of concave shapes (dimples) formed on the surface, a developing sleeve having a blasted surface, and a knurled or concave shape are used. It is also possible to use a knurled one or a plated one in addition to the formation of the above.

Further, a regulation blade 35 is attached to the developing container 20 along the longitudinal direction of the developing roller 31 (perpendicular to the paper surface of FIG. 2). A slight gap is formed between the tip of the regulation blade 35 and the surface of the developing roller 31.

A developing voltage power supply 53 (both see FIG. 4) is connected to the developing device 3a via a voltage control circuit 51. The developing voltage power supply 53 applies a developing voltage obtained by superimposing a DC voltage and an AC voltage on the developing roller 31. A developing agent is adhered (supported) to the surface of the developing roller 31 by the developing voltage and the magnetic force of the magnet in the developing roller 31 to form a magnetic brush.

In the stirring transfer chamber 21, a toner concentration sensor 27 is arranged so as to face the stirring transfer screw 25. The toner concentration sensor 27 detects the magnetic permeability of the developer in the developing container 20 and detects the toner concentration in the developing agent (the mixing ratio of toner to carriers in the developing agent; T / C). The control unit 90 transmits a control signal to the toner replenishment motor 41 (see FIG. 4 in each case), and is detected by the toner concentration sensor 27 so that the toner concentration of the developer in the developing container 20 becomes the reference toner concentration. Toner is replenished into the developing container 20 from the toner container 4a (see FIG. 1) via the toner replenishment port 20d (see FIG. 3) according to the toner concentration.

Next, the configuration of the stirring unit of the developing device 3a will be described in detail. FIG. 3 is a plan sectional view showing a stirring portion of the developing apparatus 3a. As described above, the developing container 20 is formed with a stirring transfer chamber 21, a supply transfer chamber 22, a partition wall 20a, an upstream communication portion 20b, and a downstream communication portion 20c, and a toner supply port. 20d and are formed. In the stirring transfer chamber 21, the left side of FIG. 3 is the upstream side, the right side of FIG. 3 is the downstream side, and in the supply transfer chamber 22, the right side of FIG. 3 is the upstream side and the left side of FIG. 3 is the downstream side. .. Therefore, the communication unit is referred to as an upstream side and a downstream side with reference to the supply / transport chamber 22.

The partition wall 20a extends in the longitudinal direction of the developing container 20 and partitions the stirring transfer chamber 21 and the supply transfer chamber 22 in parallel. The right end of the partition wall 20a in the longitudinal direction forms an upstream communication portion 20b together with the inner wall portion of the developing container 20. The left end portion of the partition wall 20a in the longitudinal direction forms a downstream communication portion 20c together with the inner wall portion of the developing container 20.

The toner replenishment port 20d is an opening for replenishing new toner contained in the toner container 4a (see FIG. 1) provided in the upper part of the developing container 20 into the developing container 20, and is upstream of the stirring and transporting chamber 21. It is arranged on the side (left side in FIG. 3).

The stirring transfer screw 25 has a rotating shaft 25b and a first spiral blade 25a that is integrally provided on the rotating shaft 25b and is formed spirally at a constant pitch in the axial direction of the rotating shaft 25b. Further, the first spiral blade 25a extends to both ends in the longitudinal direction of the stirring and transporting chamber 21, and is also provided to face the upstream side communication portion 20b and the downstream side communication portion 20c. The rotating shaft 25b is rotatably supported at both ends of the developing container 20 in the longitudinal direction.

The supply transport screw 26 is provided integrally with the rotary shaft 26b and the rotary shaft 26b, and faces the axial direction of the rotary shaft 26b at the same pitch as the first spiral blade 25a and in the opposite direction to the first spiral blade 25a (opposite phase). It has a second spiral blade 26a formed spirally by the blades. Further, the second spiral blade 26a has a length equal to or longer than the axial length of the developing roller 31, and is further extended to a position facing the upstream communication portion 20b. The rotating shaft 26b is arranged parallel to the rotating shaft 25b, and is rotatably supported at both ends in the longitudinal direction of the developing container 20.

In this way, the developer is stirred while circulating from the stirring and transporting chamber 21 to the upstream side communication portion 20b, the supply and transporting chamber 22, and the downstream side communication portion 20c, and the stirred developer is supplied to the developing roller 31. .. When the toner is consumed by the development, the toner is replenished from the toner replenishment port 20d into the stirring transfer chamber 21 by the toner replenishment motor 41 (see FIG. 4).

Next, the control path of the color printer 100 will be described. FIG. 4 is a block diagram showing an example of a control path used in the color printer 100 of the present embodiment. Since various controls are performed on each part of the device when the color printer 100 is used, the control path of the entire color printer 100 becomes complicated. Therefore, here, the part of the control path required for carrying out the present invention will be mainly described.

The control unit 90 includes a CPU (Central Processing Unit) 91 as a central processing unit, a ROM (Read Only Memory) 92 as a read-only storage unit, a RAM (Random Access Memory) 93 as a read / write storage unit, and a temporary storage unit. A plurality of (here, two) control signals are transmitted to each device in the temporary storage unit 94, the counter 95, and the color printer 100 for storing image data and the like, and input signals from the operation unit 80 are received. It has at least an I / F (interface) 96. Further, the control unit 90 can be arranged at an arbitrary location inside the main body of the color printer 100.

The ROM 92 contains data such as a control program for the color printer 100 and numerical values required for control that are not changed during use of the color printer 100. The RAM 93 stores necessary data generated during the control of the color printer 100, data temporarily required for the control of the color printer 100, and the like. The counter 95 integrates and counts the number of printed sheets.

Further, in the RAM 93 (or ROM 92), the advection diffusion coefficient measured in the advection diffusion measurement mode described later and the development current of the non-image portion used when determining the necessity of the advection diffusion measurement mode in the first embodiment are used. Threshold A1 of the fluctuation amount ΔA of the DC component of the above, the relationship between the concentration change when the frequency of the AC component of the development voltage is increased and the charge amount of the toner used when measuring the charge amount of the toner in the second embodiment ( (See FIG. 11) and the like are also stored.

Further, the control unit 90 transmits a control signal from the CPU 91 to each part and the device of the color printer 100 through the I / F 96. Further, a signal indicating the state and an input signal from each part and the device are transmitted to the CPU 91 through the I / F 96. The parts and devices controlled by the control unit 90 include, for example, the image forming units Pa to Pd, the exposure device 5, the primary transfer rollers 6a to 6d, the secondary transfer roller 9, the main motor 40, the toner replenishment motor 41, and the voltage control. Examples include the circuit 51 and the operation unit 80.

The image input unit 60 is a receiving unit that receives image data transmitted from a personal computer or the like to the color printer 100. The image signal input from the image input unit 60 is converted into a digital signal and then sent to the temporary storage unit 94.

The voltage control circuit 51 is connected to the charging voltage power supply 52, the developing voltage power supply 53, and the transfer voltage power supply 54, and operates each of these power supplies by the output signal from the control unit 90. In each of these power supplies, the charging voltage power supply 52 is connected to the charging devices 2a to 2d, the developing voltage power supply 53 is connected to the developing rollers 31 in the developing devices 3a to 3d, and the transfer voltage power supply 54 is connected to the developing voltage power supply 54 by the control signal from the voltage control circuit 51. A predetermined voltage is applied to each of the primary transfer rollers 6a to 6d and the secondary transfer roller 9.

The operation unit 80 is provided with a liquid crystal display unit 81 and a transmission / reception unit 82. The liquid crystal display unit 81 is designed to indicate the state of the color printer 100, the image formation status, and the number of printed copies. Various settings of the color printer 100 are performed from the printer driver of the personal computer. The transmission / reception unit 82 communicates with the outside using a telephone line or an Internet line.

The current detection unit 70 detects the DC component of the developing current that flows when the developing voltage is applied from the developing voltage power supply 53 to the developing roller 31.

The image forming apparatus 100 of the present invention executes an advection diffusion measurement mode for measuring at least one of the advection coefficient and the diffusion coefficient (hereinafter, abbreviated as the advection diffusion coefficient) of the developing agents in the developing devices 3a to 3d at the time of non-image formation. It is possible. The RAM 93 (or ROM 92) stores a program and data for calculating the advection-diffusion coefficient of the developer in the developing devices 3a to 3d, and the control unit 90 is based on the output value of the toner concentration sensor 27. The advection-diffusion coefficient is calculated, and the calculated timing at which the toner consumption region in the developing devices 3a to 3d reaches the toner supply port 20d is corrected using the calculated convection-diffusion coefficient.

Specifically, the relationship between the toner concentration C, the advection coefficient U, and the diffusion coefficient D is expressed by the following equation (1). In the formula (1), t represents the stirring time, and x represents the position in the developing devices 3a to 3d.

The advection-diffusion coefficient is roughly divided into (A) the advection-diffusion coefficient in the developer circulation path and (B) the advection-diffusion coefficient including the toner replenishment path. Next, a method of acquiring the advection-diffusion coefficient in the advection-diffusion measurement mode will be described.

(Toner replenishment type)
In the toner replenishment type, the developing devices 3a to 3d are driven to replenish a constant amount of toner. When the toner concentration in the developing devices 3a to 3d is monitored by the toner concentration sensor 27, the sensor output value changes (increases) according to the toner concentration when the toner-supplemented portion passes through the toner concentration sensor 27. When the developer circulates in the developing container 20 and the toner-supplemented portion passes through the toner concentration sensor 27 again, the sensor output value changes again. The time between the peaks of these two sensor output values shows the advection coefficient. The diffusion coefficient represents the degree of spread of the sensor output value with respect to the peak, and is represented by D in the above equation (1). Therefore, the diffusion coefficient can be obtained from the spread of the sensor output value at the time of the second sensor passage with respect to the sensor output value at the time of the first sensor passage.

Since the toner replenishment type described above has a large variation in toner replenishment, it is preferable to calculate from the output value for two passages through the sensor from the viewpoint of accuracy. Further, in the toner replenishment type, both the (A) advection-diffusion coefficient in the developer circulation path and (B) the advection-diffusion coefficient including the toner replenishment path can be measured.

(Toner consumption type)
In the toner consumption type, the toner density is partially reduced by driving the developing devices 3a to 3d to develop the image pattern, and the reduced density portion is measured by the toner density sensor 27. In the toner consumption type as well, as in the toner replenishment type, it is desirable to calculate the advection diffusion coefficient from the sensor output values for two times when the density reduction portion passes through the toner concentration sensor 27, but in the case of the toner consumption type, it is desirable to calculate the advection diffusion coefficient. Since the timing of consumption can be grasped, it is possible to calculate with only one sensor output value.

In the toner consumption type, only (A) the advection-diffusion coefficient in the developer circulation path can be measured. When the influence of the toner replenishment route is almost nonexistent, the toner consumption type measurement is sufficient, but when the influence of the toner replenishment route is large, it is necessary to use the toner replenishment type. Further, in both the toner replenishment type and the toner consumption type, since the toner concentration in the developing devices 3a to 3d changes after the measurement of the advection diffusion coefficient, it is necessary to perform the operation of restoring the original state.

(Toner consumption / replenishment type)
In the toner consumption / replenishment type, the toner is replenished to the portion where the toner is consumed, and the fluctuation of the toner concentration in the replenishment portion is measured. The timing of toner replenishment is calculated using the already acquired advection-diffusion coefficient. If the toner replenishment timing and the replenishment amount match the toner consumption portion and the consumption amount, the toner concentration does not fluctuate when passing through the toner concentration sensor 27. If the toner replenishment timing and replenishment amount are deviated, the sensor output value in the deviated state is detected. The advection-diffusion coefficient can be calculated by analyzing the sensor output value in this deviated state. In the toner consumption type described above, since the transfer diffusion coefficient is calculated only by toner consumption, the transfer diffusion from the generation of the toner replenishment signal to the actual mixing of the toner with the developer is not taken into consideration. In the toner consumption / replenishment type, the convection-diffusion coefficient can be calculated using both the toner consumption and the toner replenishment, so that the calculation can be performed with higher accuracy.

Further, when the toner consumption / replenishment type is used, the toner is replenished in the vicinity of the portion where the toner concentration is lowered due to the image formation. Therefore, the influence of the toner concentration change due to toner consumption or toner replenishment is reduced, and the toner concentration becomes uniform in a short time. Therefore, the advection-diffusion measurement mode can be quickly terminated and the normal print mode can be returned. For both toner consumption and replenishment type, measurement accuracy can be improved by combining various toner consumption and replenishment such as "toner consumption-> toner replenishment-> toner consumption" and "toner small consumption-> toner replenishment-> toner large consumption". ..

As described above, in order to measure the convection-diffusion coefficient, it is necessary to circulate the developer in the developing devices 3a to 3d for one or more rounds, which requires time for measurement and requires toner replenishment and toner consumption for measurement. Therefore, it is necessary to stabilize the toner concentration after measuring the convection-diffusion coefficient. Therefore, if the advection-diffusion measurement mode is frequently executed, the image formation efficiency of the color printer 100 is lowered.

(First Embodiment)
In the color printer 100 according to the first embodiment of the present invention, the DC component of the developing current in the non-image portion at the time of image formation is detected, and the convection-diffusion measurement mode is based on the variation of the detected DC component of the developing current. It is decided that the necessity of execution is judged. The development current of the non-image portion in the present specification refers to the current flowing through the developing roller 31 when the non-image portion (margin portion) of the photoconductor drums 1a to 1d faces the developing roller 31 at the time of image formation. Say. This development current can be measured with an organic photoconductor, but it has been confirmed that the amorphous silicon photoconductor has a higher measurement sensitivity.

The advection-diffusion state of the developer changes with changes in the amount of toner charged. On the other hand, considering the developing current, as the toner charging amount increases, the toner transfer amount to the photoconductor drums 1a to 1d decreases, but the developing current increases because the charging amount per toner particle is high. When the amount of charge of the toner becomes low, the amount of movement of the toner increases, but the amount of charge per particle of the toner is low, and the toner moved to the surface of the developing roller 31 becomes a resistance layer, so that a more development current flows. It becomes difficult. Therefore, the change state of the toner charge amount can be estimated by measuring the DC component of the developing current.

That is, when the DC component of the developing current changes significantly, it is highly possible that the toner charge amount has changed significantly, and as a result, it is estimated that the advection-diffusion coefficient has changed. Therefore, the advection-diffusion coefficient can be effectively obtained by executing the advection-diffusion measurement mode at the timing when the DC component of the developing current changes significantly.

However, depending on the type of developer (thickness of the coat layer on the carrier surface and unevenness of the core shape), the carrier resistance may change abruptly, and the amount of developing current in the non-image area may change. Specifically, when the carrier has many irregularities and the coat layer is thin, the carrier resistance tends to decrease, and conversely, when the carrier has few irregularities and the coat layer is thick, the carrier resistance tends to increase due to toner adhesion. Therefore, it is necessary to confirm and understand the relationship between the change in the developing current of the non-image area and the change in the advection-diffusion coefficient in each developing agent system used in the color printer 100.

Furthermore, the short-term change in the convection-diffusion coefficient is confirmed by the change in the development current of the non-image area, and the long-term change in the convection-diffusion coefficient is confirmed by the convection-diffusion coefficient obtained by executing the convection-diffusion measurement mode. By changing the image formation conditions according to the convection-diffusion coefficient, it is possible to take appropriate measures according to the change in the fluidity of the developer.

For example, as the transfer diffusion coefficient becomes smaller, the mixing / stirring performance deteriorates, so that the toner concentration in the developing devices 3a to 3d is lowered, the development interval (between papers) is widened, and the stirring transfer screw 25 and the supply transfer screw 26 Measures such as increasing the rotation speed (rotation speed) and adjusting the developing voltage (increasing the potential difference V0-Vdc between the surface potential V0 of the photoconductor drums 1a to 1d and the DC component Vdc of the developing voltage) are assumed.

Of the above measures, changing the toner concentration in the developing devices 3a to 3d takes time from the completion of the change until the effect appears. Therefore, it is implemented as a measure against a long-term change in the advection diffusion coefficient and has immediate effect. Changes in the development interval, the rotation speed (rotation speed) of the stirring transfer screw 25 and the supply transfer screw 26, the development voltage, etc. are measures against short-term changes in the advection diffusion coefficient (changes in the development current in the non-image area). It is preferable to carry out.

Specifically, when the amount of toner charge is high and the image density is difficult to obtain, the target value of the toner concentration is determined by observing the transition of the advection diffusion coefficient over a long period of time, and then the change in the developing current of the non-image area is used. The procedure is to adjust the development interval, the rotation speed (rotation speed) of the stirring transfer screw 25 and the supply transfer screw 26, and the development voltage with reference to the result of the advection diffusion coefficient in a short period based on the above.

FIG. 5 is a flowchart showing a control example of the advection-diffusion measurement mode in the color printer 100 of the first embodiment. The procedure for executing the advection-diffusion measurement mode will be described in detail along the steps of FIG. 5 with reference to FIGS. 1 to 4 as necessary.

First, the current detection unit 70 detects the DC component of the development current of the non-image unit at the time of image formation (step S1). The development current of the non-image area may be detected every time the printing operation is performed, or when the power of the image forming apparatus 100 is turned on, when the image forming apparatus 100 is started up from the sleep (power saving) mode, when the number of printed sheets reaches a predetermined number, and the like. , It may be detected at a predetermined timing.

Next, the control unit 90 calculates the amount of fluctuation ΔA from the DC component of the development current of the non-image unit measured last time (step S2). Then, it is determined whether or not ΔA is larger than the predetermined value (threshold value) A1 (step S3). When ΔA is A1 or less (No in step S3), it is estimated that the change in the advection-diffusion coefficient is small, so the advection-diffusion coefficient is corrected without starting the advection-diffusion measurement mode (step S4).

Specifically, when the advection-diffusion coefficient is measured in the advection-diffusion measurement mode, the development current of the non-image portion (white background portion) is also measured. Then, it is compared with the convection-diffusion coefficient and the development current measured in the previous convection-diffusion measurement mode, and the amount of change (correction amount) of the convection-diffusion coefficient with respect to the amount of change in the development current is determined according to the comparison result. However, since there is no data on the advection-diffusion coefficient and the amount of change in the development current when the first advection-diffusion measurement mode is executed, the advection-diffusion coefficient is corrected according to the initial values stored in the RAM 93 (or ROM 92) in advance. From the second time onward, correction is performed based on the advection-diffusion coefficient and development current measured in the advection-diffusion measurement mode.

Next, the control unit 90 changes the first image formation condition based on the corrected advection-diffusion coefficient (step S5). The first image forming conditions to be changed include the development interval (between papers), the rotation speed (rotation speed) of the stirring transfer screw 25 and the supply transfer screw 26, the development voltage, and the like. As will be described later, since the fluidity of the developer decreases with time, the advection-diffusion coefficient also decreases with time. Therefore, in order to improve the mixing and stirring property of the developer, the development interval (between papers) is widened, the rotation speed (rotation speed) of the stirring transfer screw 25 and the supply transfer screw 26 is increased, or the development voltage is increased. .. After that, the process returns to step S1 and continues to detect the developing current of the non-image portion during image formation.

On the other hand, when ΔA is larger than A1 (Yes in step S3), it is estimated that the advection-diffusion coefficient has changed significantly. Therefore, the advection-diffusion measurement mode is started (step S6) and the advection-diffusion coefficient is measured (step S6). Step S7). The method for measuring the convection-diffusion coefficient may be any of the above-mentioned toner replenishment type, toner consumption type, and toner consumption / replenishment type, but the influence of the toner concentration change due to toner consumption or toner replenishment is small, and the convection-diffusion measurement mode is quickly set. A toner consumption / replenishment type that can be terminated in the above is preferable.

Next, an example of measuring the advection-diffusion coefficient will be described. As the conditions of the developing device 3a, a stirring transfer screw 25 and a supply transfer screw 26 in which a first spiral blade 25a having an outer diameter of 14 mm and a pitch of 30 mm, a second spiral blade 26a are formed on rotating shafts 25b and 26b having a diameter of 6 mm are used. , The rotation speed was 345 rpm. The amount of the developer contained in the developing container 20 was 180 g. Further, a two-component developer composed of a positively charged toner having an average particle diameter of 6.8 μm and a ferrite / resin coat carrier having an average particle diameter of 35 μm was used, and the toner concentration was set to 8%. The amount of toner replenished was 0.25 g. Then, a sensor for the stirring time when the upstream end (left end in FIG. 3) of the stirring transport chamber 21 is 0 [mm] and the center position of the toner concentration sensor 27 is 300 [mm] with respect to the transport direction of the developer. The transition of the output value was plotted.

FIG. 6 is a graph showing the transition of the toner concentration when toner is replenished from the toner replenishment port 20d of the developing device 3a and the developing device 3a is driven. When the measured value data shown in FIG. 6 is fitted (curve fitting) using the above equation (1), an advection coefficient U = 40 [mm / s] and a diffusion coefficient D = 250 [mm ² / s] are obtained. FIG. 7 shows the simulation results using the obtained advection coefficient U and diffusion coefficient D. The correlation coefficient of FIGS. 6 and 7 was 0.95.

Next, the relationship between the deterioration of the developer and the advection diffusion coefficient will be described. FIG. 8 is a diagram showing the relationship between the degree of deterioration of the developer and the diffusion coefficient. As shown in FIG. 8, as the developer deteriorates, the diffusion coefficient decreases. The reason for this is that as the developer deteriorates and the toner external additive is buried or removed, the adhesive force of the toner increases and the fluidity of the developer decreases. When the fluidity of the developer decreases, it becomes difficult for the developer to take in the replenishing toner, so that the diffusion coefficient decreases.

FIG. 9 is a diagram showing the relationship between the cumulative number of prints and the diffusion coefficient. As shown in FIG. 9, the diffusion coefficient decreases as the number of printed sheets increases. This is also a phenomenon caused by the fluidity of the developer, and as the number of printed sheets increases, the coating layer of the carrier peels off and becomes contaminated, so that the toner charge distribution becomes broad and the toner is electrostatically attached. Increases strength. As a result, the fluidity of the developer decreases. From the above, it can be seen that the diffusion coefficient decreases as the developer deteriorates or the number of printed sheets increases. Although the diffusion coefficient has been described here, the advection coefficient also shows the same tendency as the diffusion coefficient.

Returning to FIG. 5, the control unit 90 changes the second image formation condition based on the measured advection-diffusion coefficient (step S8). The second image forming condition to be changed includes a change in the toner density in the developing devices 3a to 3d. Specifically, in order to improve the mixing and stirring property of the developer, the toner concentration is lowered as the advection-diffusion coefficient becomes smaller. After that, the process returns to step S1 and continues to detect the developing current of the non-image portion during image formation.

According to this embodiment, the fluctuation of the convection-diffusion coefficient is estimated using the current value of the DC component of the development current of the non-image portion at the time of image formation, and the advection-diffusion is performed only when the fluctuation of the convection-diffusion coefficient is estimated to be large. By determining whether or not to execute the measurement mode, the advection-diffusion measurement mode can be executed at an appropriate timing. Therefore, since the variation in the toner density due to the variation in the advection diffusion coefficient is suppressed, defects such as poor image density, image fog, and toner scattering can be effectively suppressed.

Further, when the fluctuation amount of the DC component of the development current of the non-image portion is equal to or less than a predetermined value, it is estimated that the fluctuation of the convection-diffusion coefficient is small and only the correction of the convection-diffusion coefficient is performed. It is possible to suppress an increase in toner consumption and power consumption and a decrease in image formation efficiency due to the execution of the mode.

To acquire the fluctuation amount of the developing current, it is better to acquire the fluctuation amount from the reference value with reference to the current value at the end of the advection-diffusion measurement mode. The reason for this is that when the amount of fluctuation from the initial use of the developer is acquired, the effects of scraping of the coat layer on the carrier surface, selection of particle size, contamination of the developing roller, fluctuation of the developing gap, etc. are accumulated. ..

When the advection-diffusion coefficient is corrected without executing the advection-diffusion measurement mode, the development interval, the rotation speed (rotation speed) of the stirring transfer screw 25 and the supply transfer screw 26, the development voltage, etc. are changed. It is possible to deal with short-term changes in the advection-diffusion coefficient with immediate effect. On the other hand, when the advection-diffusion measurement mode is executed and the advection-diffusion coefficient is measured, effective measures can be taken against long-term changes in the advection-diffusion coefficient by changing the toner concentration in the developing devices 3a to 3d. It will be possible.

As shown in FIGS. 8 and 9, when the developer deteriorates, the advection-diffusion coefficient tends to decrease. Therefore, it is possible to predict the life of the developer by using the transition of the advection-diffusion coefficient over a long period of time. .. Specifically, each time the advection-diffusion measurement mode is executed, the measured advection-diffusion coefficient is stored in the RAM 93. Then, by arranging the stored advection-diffusion coefficients in chronological order, the change over time of the advection-diffusion coefficient is predicted. As a result, since the time when the advection-diffusion coefficient becomes smaller than the preset reference value is predicted, it is possible to give a notification prompting the replacement of the developer before the time when the advection-diffusion coefficient becomes smaller than the reference value. it can.

The diffusion coefficient D [mm2 / s] in durability is expressed by the following formula (2). In the formula (2), Dm represents the saturation diffusion coefficient, D0 represents the initial diffusion coefficient, α represents a proportionality constant, and t represents the number of printed sheets. By fitting using the equation (2), the change of the diffusion coefficient D with time can be predicted with very high accuracy.
D = Dm- (Dm-D0) exp (-αt) ... (2)

A predetermined value is used for Dm, but if D is smaller than Dm during endurance printing, D at that time may be set to Dm. Further, similarly to the diffusion coefficient D, the change of the advection coefficient U with time can be predicted by using the equation (2).

As a result, it is possible to notify the appropriate replacement time of the developer before the life of the developer is reached, and effectively suppress the occurrence of image density defect, image fog, and toner scattering due to deterioration of the developer. be able to. In addition, predictive maintenance of the image forming apparatus 100 can be reliably performed, and the monitoring burden and maintenance cost by the service person can be reduced. As a method of notifying the serviceman, for example, the transmission / reception unit 82 sends a notification prompting the serviceman's communication terminal to replace the developer as a CBM (Condition Based Maintenance) alert.

(Second Embodiment)
In the color printer 100 according to the second embodiment of the present invention, the toner charge amount is measured, and the necessity of executing the convection-diffusion measurement mode is determined based on the measured toner charge amount. Since the convection-diffusion state of the developer changes according to the change in the toner charge amount, the convection-diffusion coefficient can be effectively obtained by executing the convection-diffusion measurement mode at the timing when the toner charge amount changes significantly.

FIG. 10 is a flowchart showing a control example of the advection-diffusion measurement mode in the color printer 100 of the second embodiment. The procedure for executing the advection-diffusion measurement mode will be described in detail along the steps of FIG. 10 with reference to FIGS. 1 to 4 as necessary.

In FIG. 10, the color printer 100 is set to the normal print mode, and the control unit 90 determines whether or not a print command has been received (step S1). When a print command is received (Yes in step S1), printing is executed by a normal image forming operation (step S2). If the print command is not transmitted (No in step S1), it is determined whether or not it is the timing for measuring the toner charge amount (step S3).

If it is not the timing for measuring the toner charge amount (No in step S3), the process returns to step S1 and the process shifts to the standby state of the print command. When it is the timing to measure the toner charge amount (Yes in step S3), the toner charge amount is measured (step S4). The toner charge measurement timing is set, for example, when the color printer 100 is turned on, when the color printer 100 is started up from the sleep (power saving) mode, or when the number of prints from the previous toner charge measurement reaches a predetermined number. Will be done.

As a method for measuring the amount of toner charged, first, the photoconductor drums 1a to 1d are charged to a predetermined surface potential by the charging devices 2a to 2d. Next, two electrostatic latent images having the same measurement pattern are formed by exposure from the exposure apparatus 5. Then, toner is supplied from the developing devices 3a to 3d to the formed electrostatic latent image to develop the toner image. At this time, the frequency of the AC component of the developing voltage applied to the developing roller 30 is switched to two levels of f1 [Hz] and f2 [Hz] to form two types of measurement patterns on the photoconductor drums 1a to 1d. Next, a predetermined primary transfer voltage is applied to the primary transfer rollers 6a to 6d to transfer the measurement pattern onto the intermediate transfer belt 8, and the density of each transferred measurement pattern is detected by the image density sensor 45.

FIG. 11 is a diagram showing the relationship between the direction of change in toner concentration (image density) and the amount of charge of toner when the frequency of the AC component of the developing voltage is increased. From FIG. 11, it can be estimated that the toner charge amount is low when the concentration change when the frequency is increased is increasing (+), and the toner charge amount is high when the concentration change is decreasing. Therefore, the density difference between the two types of measurement patterns can be calculated, and the toner charge amount Q / M can be estimated using the relationship between the concentration change shown in FIG. 11 and the toner charge amount.

The method for measuring the amount of toner charge is not limited to the method described above. For example, when a plurality of measurement patterns having different image densities (printing rates) are formed, the difference in the amount of development (difference in density) of each measurement pattern and the measurement pattern are formed. A method of measuring the amount of toner charge based on the relationship with the difference in the flowing development current, and the formation of the frequency and measurement pattern when an electrostatic latent image of the same measurement pattern is developed by changing the frequency of the AC component of the development voltage. It is also possible to use a method of measuring the toner charge amount based on the relationship with the difference in the developing current that sometimes flows.

Next, the control unit 90 calculates the fluctuation amount ΔQ from the toner charge amount measured last time (step S5). Then, it is determined whether or not ΔQ is larger than the predetermined value (threshold value) Q1 (step S6). When ΔQ is Q1 or less (No in step S6), it is estimated that the change in the advection-diffusion coefficient is small, so the advection-diffusion coefficient is corrected without starting the advection-diffusion measurement mode (step S7). The method of correcting the advection-diffusion coefficient is the same as that of the first embodiment.

Next, the control unit 90 changes the first image formation condition based on the corrected advection-diffusion coefficient (step S8). The first image forming conditions to be changed include the development interval (between papers), the rotation speed (rotation speed) of the stirring transfer screw 25 and the supply transfer screw 26, the development voltage, and the like, as in the first embodiment. After that, the process returns to step S1 and the standby state of the print command is continued.

On the other hand, when ΔQ is larger than Q1 (Yes in step S6), it is estimated that the advection-diffusion coefficient has changed significantly. Therefore, the advection-diffusion measurement mode is started (step S9) and the advection-diffusion coefficient is measured (step S9). Step S10). The method for measuring the advection-diffusion coefficient is the same as that in the first embodiment.

The control unit 90 changes the second image formation condition based on the measured advection-diffusion coefficient (step S11). The second image forming condition to be changed includes a change in the toner concentration in the developing devices 3a to 3d as in the first embodiment. After that, the process returns to step S1 and the standby state of the print command is continued.

According to the present embodiment, the fluctuation of the convection-diffusion coefficient is estimated based on the amount of charge of the toner, and it is determined whether or not the advection-diffusion measurement mode is executed only when the fluctuation of the convection-diffusion coefficient is estimated to be large. , The advection-diffusion measurement mode can be executed at an appropriate timing. Therefore, since the variation in the toner density due to the variation in the advection diffusion coefficient is suppressed, defects such as poor image density, image fog, and toner scattering can be effectively suppressed.

When the fluctuation amount of the toner charge amount is less than a predetermined value, it is estimated that the fluctuation of the advection-diffusion coefficient is small and only the transfer diffusion coefficient is corrected. Therefore, the toner consumed by executing the unnecessary advection-diffusion measurement mode. It is possible to suppress an increase in power consumption and a decrease in image formation efficiency.

On the other hand, in the present embodiment, since it is necessary to measure the toner charge amount at the time of non-image formation, the image formation efficiency is lower than that of the first embodiment which is determined by using the developing current of the non-image portion at the time of image formation. ..

Here, in the present embodiment, since the convection-diffusion measurement mode is executed only when the fluctuation amount of the toner charge amount is larger than the predetermined value, the number of times the transfer diffusion coefficient is measured is smaller than the number of times the toner charge amount is measured.

Since it is necessary to replenish and consume toner for the measurement of the convection-diffusion coefficient, it takes a long time to measure and it involves consumption of toner other than printing. Therefore, it is preferable to reduce the number of times as much as possible. On the other hand, in the measurement of the toner charge amount, it is necessary to form a reference image, but the toner consumption amount is overwhelmingly smaller than that in the case of measuring the convection-diffusion coefficient, and the measurement time can be shortened. Therefore, it is possible to accurately determine whether or not the advection-diffusion measurement mode is to be executed by using the measured value of the toner charge amount while suppressing the consumption of toner and the decrease in image formation efficiency as much as possible.

(Third Embodiment)
In the color printer 100 according to the third embodiment of the present invention, by arranging the convection-diffusion coefficients measured in the already executed convection-diffusion measurement mode in chronological order, the transition of the convection-diffusion coefficient in the future is predicted and the convection-diffusion is performed. The predicted value of the diffusion coefficient is compared with the measured value, and the prediction formula is modified according to the result.

FIG. 12 is a diagram showing a prediction line predicted by the advection coefficients of three points measured in the first to third advection diffusion measurement modes, and FIG. 12 is a diagram measured in the first to fourth advection diffusion measurement modes. It is a figure which shows the prediction line predicted by the advection coefficient of 4 points. The prediction line of FIG. 13 is slightly modified from the prediction line of FIG. While modifying the prediction line (prediction formula) in this way, the advection-diffusion measurement mode is executed at the timing when the advection-diffusion coefficient does not change significantly.

FIG. 14 is a flowchart showing a control example of the advection-diffusion measurement mode in the color printer 100 of the third embodiment. The procedure for executing the advection-diffusion measurement mode will be described in detail along the steps of FIG. 14 with reference to FIGS. 1 to 4 as necessary.

In FIG. 14, the color printer 100 is set to the normal print mode, and the control unit 90 determines whether or not a print command has been received (step S1). When a print command is received (Yes in step S1), printing is executed by a normal image forming operation (step S2). If the print command is not transmitted (No in step S1), the predicted value k of the advection-diffusion coefficient is calculated using the prediction formula (step S3). Before the execution of the first advection-diffusion measurement mode, the prediction value k is calculated using the prediction formula stored in the RAM 93 (or ROM 92) in advance, and the prediction formula is sequentially corrected as the new measurement value is acquired. ..

Next, the control unit 90 determines whether or not the amount of change in the predicted value k from the previous advection-diffusion measurement mode has reached a predetermined number of prints expected to be equal to or greater than a predetermined value (step S4). Before the execution of the first advection-diffusion measurement mode, the determination is made using the number of printed sheets in which the amount of change of the predicted value k from the default value stored in the RAM 93 (or ROM 92) in advance is expected to be equal to or more than a predetermined value.

If the predetermined number of prints has not been reached (No in step S4), the process returns to step S1 without starting the advection-diffusion measurement mode, and the state shifts to the standby state of the print command. When the predetermined number of prints has been reached (Yes in step S4), the advection-diffusion measurement mode is started (step S5), and the measured value k1 of the advection-diffusion coefficient is measured (step S6). The method for measuring the advection-diffusion coefficient is the same as that in the first embodiment.

Next, the control unit 90 calculates the difference | k1-k | = Δk between the measured value k1 and the predicted value k (step S7), and determines whether or not Δk is smaller than the predetermined value (threshold value) K (step). S8). When Δk ≧ K (No in step S8), it is determined whether or not the comparison between Δk and the threshold value K is the first time (step S9), and when it is the first time (Yes in step S9) k1. Returning to step S6 in consideration of the possibility of erroneous measurement of k1, remeasurement of k1 is performed.

When the comparison between Δk and the threshold value K is the second time (No in step S9), the prediction formula is corrected based on the actually measured value k1 measured in step S6 (step S10). Then, the image formation conditions are changed based on the actually measured value k1 (step S11). The image formation conditions to be changed include changes in the toner concentration in the developing devices 3a to 3d, the development interval, the rotation speed (rotation speed) of the stirring transfer screw 25 and the supply transfer screw 26, and V0-Vdc. After that, the process returns to step S1 and the standby state of the print command is continued.

According to this embodiment, by arranging the convection-diffusion coefficients measured in the convection-diffusion measurement mode in chronological order, the future transition of the convection-diffusion coefficient is predicted, and only when it is estimated that the fluctuation of the convection-diffusion coefficient is large. By determining whether or not to execute the convection-diffusion measurement mode, the convection-diffusion measurement mode can be executed at an appropriate timing. Therefore, since the variation in the toner density due to the variation in the advection diffusion coefficient is suppressed, defects such as poor image density, image fog, and toner scattering can be effectively suppressed. In addition, since the execution timing of the convection-diffusion measurement mode can be determined without measuring the DC component of the developing current and the charge amount of the toner, it is possible to effectively suppress an increase in toner consumption and power consumption and a decrease in image formation efficiency. it can.

Others The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in each of the above embodiments, the transmission / reception unit 82 is used to directly notify the serviceman that the life of the developer is near, but for example, by displaying a notification prompting the replacement of the developer on the liquid crystal display unit 81. , The user may be notified that the developer is nearing the end of its life.

Further, the present invention is not limited to the tandem type color printer shown in FIG. 1, and various image forming apparatus using a two-component developing method such as a digital or analog type monochrome copier, a monochrome printer, a color copier, and a facsimile. It is applicable to. Hereinafter, the effects of the present invention will be described in more detail with reference to Examples.

The advection-diffusion measurement mode of the first embodiment was executed, and a verification test was conducted on the effect of suppressing image fog when the image formation conditions were changed based on the measured advection-diffusion coefficient. The conditions of the developing devices 3a to 3d were the same as in the measurement example of the advection-diffusion coefficient.

As a test method, the advection diffusion measurement mode is executed when the fluctuation amount of the DC component of the development current in the non-image area becomes 0.03 μA, and the toner concentration in the developing devices 3a to 3d is increased according to the decrease in the advection diffusion coefficient. (Invention 1), the difference between the surface potential V0 of the photoconductor drums 1a to 1d and the DC component Vdc of the developing voltage is V0-Vdc according to the decrease in the advection diffusion coefficient in addition to the decrease in the toner concentration. When the size was increased (2 in the present invention) and when the image conditions were not changed (Comparative Example 1), 600 k sheets of durable printing were performed to evaluate the occurrence of image fog.

The advection-diffusion measurement mode was executed when the number of printed sheets reached 69 k, 165 k, and 366 k. The evaluation of image fog is a sensory evaluation (visual). If image fog is not recognized, rank 5 is recognized, if image fog is recognized but not bothered at all, rank 4, and if image fog is recognized but not bothered. Rank 3, image fog was recognized and anxious was ranked 2, and image fog was recognized and unacceptable was ranked 1. The results are shown in FIG.

As is clear from FIG. 15, in the present invention 1 (data series of × in FIG. 15) in which the toner concentration is reduced according to the decrease in the convection-diffusion coefficient, the image fog after endurance printing of 600 k sheets is rank 3. , The image fog was not a concern. Further, in the present invention 2 (data series of ○ in FIG. 15) in which V0-Vdc is increased in addition to the decrease in toner concentration, the image fog after endurance printing of 600 k sheets is rank 3.5, and the image fog is completely present. I don't care ~ It was a level I didn't care about.

On the other hand, in Comparative Example 1 (data series of ● in FIG. 15) in which the image formation conditions were not changed, the image fog after endurance printing of 600 k sheets was rank 1.5, and the image fog was anxious. ~ It was an unacceptable level.

The advection-diffusion measurement mode of the second embodiment was executed, and a verification test was conducted on the effect of suppressing image fog when the image formation conditions were changed based on the measured advection-diffusion coefficient.

As a test method, the advection diffusion measurement mode was executed when the amount of change in the toner charge amount became 2.5 μC / g, and the toner concentration in the developing devices 3a to 3d was decreased according to the decrease in the advection diffusion coefficient. In the case (3 of the present invention), in addition to the decrease in toner concentration, the difference V0-Vdc between the surface potential V0 of the photoconductor drums 1a to 1d and the DC component Vdc of the development voltage is increased in accordance with the decrease in the advection diffusion coefficient. (4) of the present invention and when the image conditions were not changed (Comparative Example 2), endurance printing of 600 k sheets was performed to evaluate the occurrence of image fog.

The toner charge amount was measured every 30 k, and the advection-diffusion measurement mode was executed when the number of printed sheets reached 90 k, 180 k, and 390 k. The conditions of the developing devices 3a to 3d and the evaluation criteria for image fog were the same as in Example 1. The results are shown in FIG.

As is clear from FIG. 16, in the present invention 3 (+ data series in FIG. 16) in which the toner concentration is reduced according to the decrease in the convection-diffusion coefficient, the image fog after endurance printing of 600 k sheets is rank 3. , The image fog was not a concern. Further, in the present invention 4 (data series of ○ in FIG. 16) in which V0-Vdc is increased in addition to the decrease in toner concentration, the image fog after endurance printing of 600 k sheets is rank 3.5, and the image fog is completely present. I don't care ~ It was a level I didn't care about.

On the other hand, in Comparative Example 2 (data series of ● in FIG. 16) in which the image formation conditions were not changed, the image fog after endurance printing of 600 k sheets was rank 1.5, and the image fog was anxious. ~ It was an unacceptable level.

The advection-diffusion measurement mode of the third embodiment was executed, and a verification test was conducted on the effect of suppressing image fog when the image formation conditions were changed based on the measured advection-diffusion coefficient.

As a test method, the advection-diffusion measurement mode is executed when the amount of change in the advection coefficient is 5 or more (or the amount of change in the diffusion coefficient is 30 or more), and in the developing devices 3a to 3d according to the decrease in the advection-diffusion coefficient. When the toner concentration of the photoconductor drums 1a to 1d is lowered and the difference V0-Vdc between the surface potential V0 of the photoconductor drums 1a to 1d and the DC component Vdc of the developing voltage is increased (the present invention 5), the image conditions are not changed. In this case (Comparative Example 3), 600 k sheets of durable printing were performed to evaluate the occurrence of image fog.

The advection-diffusion measurement mode was executed when the number of printed sheets reached 0 k, 30 k, 60 k, and 90 k, and thereafter, the execution timing was determined according to an approximate formula. Actually, the advection-diffusion measurement mode was executed with 125 k sheets, 238 k sheets, 395 k sheets, and 600 k sheets. The conditions of the developing devices 3a to 3d and the evaluation criteria for image fog were the same as in Examples 1 and 2. The results are shown in FIG.

As is clear from FIG. 17, in the present invention 5 (+ data series in FIG. 17) in which the toner concentration is decreased and V0-Vdc is increased in accordance with the decrease in the convection-diffusion coefficient, the image after endurance printing of 600 k sheets is performed. The fog was rank 3.5, and the image fog was at a level that did not bother me at all.

On the other hand, in Comparative Example 3 (data series of ● in FIG. 17) in which the image formation conditions were not changed, the image fog after endurance printing of 600 k sheets was rank 1.5, and the image fog was anxious. ~ It was an unacceptable level.

From the results of Examples 1 to 3, the advection-diffusion measurement mode is executed at a predetermined timing, and the image formation conditions are changed according to the decrease in the advection-diffusion coefficient, whereby the occurrence of image fog is effective for a long period of time. It was confirmed that it can be suppressed. Further, it was confirmed that the occurrence of image fog can be suppressed more effectively by increasing V0-Vdc in addition to lowering the toner concentration.

The present invention can be used in a developing apparatus using a two-component developer composed of toner and a carrier and an image forming apparatus including the same. By utilizing the present invention, it is possible to accurately predict fluctuations in the advection coefficient and the diffusion coefficient of the developer, and it is possible to provide an image forming apparatus capable of executing the advection diffusion measurement mode to the minimum necessary.

1a-1d Photoreceptor drum (image carrier)
3a to 3d developing device 20 developing container 20d toner supply port 25 stirring transfer screw (stirring transfer member)
26 Supply transfer screw (stirring transfer member)
27 Toner concentration sensor 31 Developing roller (developer carrier)
41 Toner replenishment motor (toner replenishment device)
51 Voltage control circuit 53 Development voltage power supply 70 Current detection unit 81 Liquid crystal display unit (notification device)
82 Transmitter / receiver (notification device)
90 Control unit 92 ROM (storage unit)
93 RAM (storage unit)
95 Counter 100 color printer (image forming device)

Claims (12)

An image carrier having a photosensitive layer formed on its surface,
A developing container containing a developing agent containing a carrier and toner,
A developer carrier that is arranged so as to face the image carrier and that at least supports the toner on the surface.
A stirring and transporting member that stirs and transports the developer in the developing container, and
A developing device that supplies the toner to an electrostatic latent image formed on the image carrier to form a toner image.
A toner replenishing device that replenishes the toner in the developing container,
A developing voltage power supply that applies a developing voltage obtained by superimposing an AC voltage on a DC voltage on the developing agent carrier.
A current detector that detects the DC component of the developing current that flows when the developing voltage is applied to the developer carrier, and
A control unit that controls the developing device and the toner replenishing device,
With
The control unit is inside the developing container where the toner is consumed by being supplied to the image carrier based on the transfer diffusion coefficient which is at least one of the transfer coefficient and the diffusion coefficient of the toner inside the developing container. In an image forming apparatus that determines the timing at which the toner consuming region of the developing container reaches the toner replenishing position of the developing container and replenishes the toner to the toner consuming region using the toner replenishing device.
The control unit can execute an advection-diffusion measurement mode that measures the advection-diffusion coefficient during non-image formation.
The amount of change in the amount of toner charged in the developing device, or the amount of change in the DC component of the developing current flowing through the developing agent carrier when the non-image parts of the image carrier face each other during image formation is a predetermined amount. An image forming apparatus, characterized in that the transfer diffusion measurement mode is executed when it is larger than. The image forming apparatus according to claim 1, wherein the control unit changes image forming conditions based on a change in the advection-diffusion coefficient. The image forming apparatus according to claim 2, wherein the control unit changes the toner concentration in the developer in the developing container when the convection-diffusion measurement mode is executed. When the change amount of the toner charge amount or the change amount of the DC component of the development current is within a predetermined amount, the control unit does not execute the convection-diffusion measurement mode and is currently using the convection-diffusion. The image forming apparatus according to claim 2 or 3, wherein the coefficient is corrected. When the convection-diffusion coefficient is corrected, the control unit supplies the toner to the electrostatic latent image formed on the image carrier to form the toner image, the rotation speed of the stirring and transporting member, and the said. The image forming apparatus according to claim 4, wherein at least one of the developing voltages is changed. In the convection-diffusion measurement mode, the convection-diffusion coefficient is measured by both replenishing the toner in the developing container and consuming the toner in the developing container by supplying the toner to the image carrier. The image forming apparatus according to any one of claims 1 to 5. The control unit replenishes the toner at a timing when the toner consumption region reaches the toner replenishment position, which is determined based on the advection-diffusion coefficient, and executes the advection-diffusion measurement mode. Item 6. The image forming apparatus according to Item 6. A storage unit for storing the advection-diffusion coefficient is provided.
The control unit creates a prediction formula for the convection-diffusion coefficient based on the time transition data of the convection-diffusion coefficient stored in the storage unit, and the predicted value of the convection-diffusion coefficient predicted from the prediction formula and The image forming apparatus according to any one of claims 1 to 7, wherein the prediction formula is corrected by comparing with the measured value measured by the convection-diffusion measurement mode. 8. The control unit executes the advection-diffusion measurement mode when the amount of change in the predicted value from the previous advection-diffusion measurement mode reaches a number of prints expected to be equal to or greater than a predetermined value. The image forming apparatus according to. The control unit re-executes the transfer diffusion measurement mode when the difference between the predicted value and the measured value is larger than a predetermined value, and when the comparison between the predicted value and the measured value is the first time, 2 The image forming apparatus according to claim 8 or 9, wherein when it is the second time, the prediction formula is corrected and the image forming conditions are changed. 8. The control unit determines that the developer has reached the end of its life when the advection-diffusion coefficient predicted based on the prediction formula becomes smaller than a preset reference value. The image forming apparatus according to any one of claims 10. A notification device capable of notifying the life of the developer predicted based on the advection-diffusion coefficient is provided.
The image according to claim 11, wherein the control unit uses the notification device to give a notification prompting the replacement of the developer before the time when the advection-diffusion coefficient becomes smaller than the reference value. Forming device.

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