JP2021086061A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can prevent a reduction in density of an image even when there is a difference between an output value from a toner concentration sensor and the concentration of toner in a developing device.SOLUTION: An image forming apparatus comprises image forming units, a fixing unit, a developing voltage power supply, an image density sensor, a fixing temperature sensor, and a control unit. The control unit defines the time to start image formation immediately after a first condition where the image forming apparatus is powered on and a temperature detected by the fixing temperature sensor is equal to or less than a predetermined temperature, or a second condition where the image forming apparatus is left standing for a predetermined time or longer from the end of immediately previous image formation is satisfied a reckoning start time, and calculates an active time Δt from a reckoning start time when the first condition or the second condition is satisfied next time to a final image formation time, and a development cumulative driving time Δtdev. When an active time development driving ratio Δtdev/Δt is equal to or more than a predetermined value, the image forming apparatus executes calibration when toner consumption reaches a predetermined amount.SELECTED DRAWING: Figure 6

Description

The present invention relates to an image forming apparatus such as a copier, a facsimile, a printer, etc., which is provided with a developing apparatus using a two-component developer composed of a magnetic carrier and a toner, and particularly, changes in the toner concentration in the developing agent in the developing apparatus. It concerns how to predict.

Conventionally, as a developing method using dry toner in an image forming apparatus using an electrophotographic process, a one-component developing method that does not use a carrier and a two-component developing agent that charges a non-magnetic toner using a magnetic carrier are used. A two-component developing method is known in which an electrostatic latent image on an image carrier (photoreceptor) is developed by a magnetic brush composed of toner and a carrier formed on a developing roller.

In a two-component developing system, the toner concentration in the developing device (the ratio of toner to carriers in the developing agent) is detected by a toner concentration sensor, and new toner is replenished by the amount of reduction due to printing or the like. However, if the output of the toner concentration sensor changes due to factors other than the fluctuation of the toner concentration, for example, the temperature, the toner concentration cannot be detected correctly, and the measured value of the toner concentration is the target toner concentration (reference) due to an unintended toner replenishment operation. It may increase more than the concentration).

In this case, the temperature inside the developing device drops due to leaving it for a long time after printing is completed, and the output of the toner concentration sensor returns to the original value, so that the toner is not replenished until the measured value of the toner concentration reaches the reference concentration. It will be printed. As a result, the amount of charge of the toner in the developing apparatus increases and the developability of the toner decreases, so that the image density may decrease sharply in the subsequent printing operation. As the above countermeasure, the increase / decrease in toner concentration can be mitigated by correcting the sensor output value according to the temperature, which is a variable factor of sensor output, but multiple sensors are required to improve the detection accuracy of toner concentration, which is costly. It leads to up.

As a method for alleviating a decrease in image density due to fluctuations in toner concentration, for example, Patent Document 1 describes between a toner image forming means for forming a toner image on an intermediate transfer belt and two toner images on an intermediate transfer belt. A test image forming means for forming a test image, a density detecting means for detecting the density of the test image, a difference calculating means for calculating the difference between a predetermined ideal value and the detected density, and a developing voltage according to the difference. An image forming apparatus capable of promptly correcting the density when the development characteristics change by providing an increasing / decreasing means for increasing / decreasing is disclosed.

Japanese Unexamined Patent Publication No. 2009-169057

In the method of Patent Document 1, a test image is printed between printings, an optimum value of the development voltage is set from the toner concentration, and then the test image is printed again during the next printing, and the optimum value of the development voltage is similarly printed. The optimum value of the development voltage is determined from the calculated values of the first and second development voltages. However, since the test image is output regardless of the output value of the toner concentration detecting means, for example, There is a problem that the output of the toner sensor is higher than the target value, and the test image is output even when it is not assumed that the density is clearly reduced by printing, and unnecessary toner is consumed. Further, when the distance between the image forming portions of each color of the image forming apparatus is short, it is necessary to take a long printing interval (between papers) in order to output the test image, and there is also a problem that the printing speed is lowered. It was.

In view of the above problems, the present invention provides an image forming apparatus capable of suppressing a decrease in image density even when there is a difference between the output value of the toner density sensor and the toner density in the developing apparatus. The purpose is.

In order to achieve the above object, the first configuration of the present invention includes an image forming unit, a fixing unit, a developing voltage power supply, an image density sensor, a fixing temperature sensor, a time measuring unit, and a control unit. It is an image forming apparatus provided. The image forming unit exposes an image carrier having a photosensitive layer formed on its surface, a charging device for charging the surface of the image carrier, and the surface of the image carrier charged by the charging device to produce an electrostatic latent image. It has an exposure device to be formed and a developing device. The developing apparatus includes a developing container that houses a two-component developing agent containing a carrier and a toner, a developing agent carrier that is rotatably supported in the developing container and supports the two-component developing agent on the surface, and two in the developing container. It has a toner concentration sensor that detects the toner concentration in the component developer, and develops an electrostatic latent image into a toner image using a developer carrier. The fixing unit fixes the toner image to the recording medium by heating and pressurizing the recording medium on which the toner image is formed by the image forming unit. The developing voltage power supply applies a developing voltage to the developer carrier. The image density sensor detects the image density of the toner image formed by the image forming unit. The fixing temperature sensor detects the temperature of the fixing portion. The control unit controls the image forming unit and the developing voltage power supply. The control unit can perform calibration for correcting the image density by adjusting the development voltage based on the detection result of the image density sensor. The control unit has a first condition in which the image forming apparatus is turned on and the detection temperature of the fixing temperature sensor is equal to or lower than a predetermined temperature, or a second condition in which the leaving time from the end of the immediately preceding image formation is equal to or longer than a predetermined time. When the condition is satisfied, the image formation start time immediately after the first condition or the second condition is satisfied is set as the calculation start time, and then from the calculation start time when the first condition or the second condition is satisfied to the final image formation time. The active time Δt and the cumulative development drive time Δtdev, which is the cumulative value of the drive time of the developing device within the active time, are calculated. When the active time development drive rate Δtdev / Δt obtained by dividing the cumulative development drive time Δtdev by the active time Δt is equal to or greater than a predetermined value, the control unit determines the toner consumption after satisfying the first condition or the second condition. Perform calibration when the threshold is reached.

According to the first configuration of the present invention, printing is performed frequently before the image forming apparatus is left for a long time, and the output value of the toner concentration sensor fluctuates due to a temperature rise, so that the toner concentration in the developing apparatus is changed. When is predicted to be higher than the reference density, calibration is performed at an appropriate time when the toner is consumed until the toner concentration in the developing device decreases. Therefore, it is possible to minimize the period during which the image forming apparatus is used in a state where the toner concentration in the developing apparatus fluctuates greatly. Further, since it is not necessary to correct the output value of the toner concentration sensor based on the temperature, the number of temperature sensors can be reduced. Further, it is possible to suppress an increase in toner consumption and a decrease in image formation efficiency due to execution of calibration at unnecessary timings.

Schematic diagram showing the overall configuration of the image forming apparatus 100 according to the embodiment of the present invention. Side sectional view of the developing apparatus 3a mounted on the image forming apparatus 100 of the present embodiment. Partial enlarged view around the image forming unit Pa including the control path of the image forming unit Pa The figure which shows the relationship between the active time Δt and the development drive time Δtdev A flowchart showing a calculation control example of the active time Δt and the development drive time Δtdev in the image forming apparatus 100 of the present embodiment. A flowchart showing a control example of the calibration routine in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the internal structure of the image forming apparatus 100 according to the embodiment of the present invention. In the main body of the image forming apparatus 100 (here, a color printer), four image forming portions Pa, Pb, Pc and Pd are arranged in order from the upstream side in the transport direction (left 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 sequentially.

Photoreceptor drums (image carriers) 1a, 1b, 1c and 1d that support visible images (toner images) of each color are arranged on these image forming portions Pa to Pd, and further, a drive motor (FIG. An intermediate transfer belt (intermediate transfer body) 8 rotating in the counterclockwise direction in FIG. 1 is provided adjacent to each of the image forming portions Pa to Pd. The toner images formed on the photoconductor drums 1a to 1d are sequentially linearly transferred and superimposed on the intermediate transfer belt 8 that moves while abutting on the photoconductor drums 1a to 1d. After that, the toner image primaryly transferred onto the intermediate transfer belt 8 is secondarily transferred by the secondary transfer roller 9 onto the transfer paper P as an example of the recording medium. Further, the transfer paper P on which the toner image is secondarily transferred is discharged from the image forming apparatus 100 main body after the toner image is fixed in the fixing portion 13. The image forming process for each of the photoconductor drums 1a to 1d is executed while rotating the photoconductor drums 1a to 1d in the clockwise direction in FIG.

The transfer paper P on which the toner image is secondarily transferred is housed in a paper cassette 10 arranged in the lower part of the main body of the image forming apparatus 100. The transfer paper P is conveyed to the nip portion between the secondary transfer roller 9 and the drive roller 11 of the intermediate transfer belt 8 via the paper feed roller 12a and the resist roller pair 12b. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a seamless (seamless) belt is mainly used. Further, a blade-shaped belt cleaner 19 for removing toner and the like remaining on the surface of the intermediate transfer belt 8 is arranged on the downstream side of the secondary transfer roller 9.

Next, the image forming units Pa to Pd will be described. Around and below the rotatably arranged photoconductor drums 1a to 1d, charging devices 2a, 2b, 2c and 2d for charging the photoconductor drums 1a to 1d, and image information on each of the photoconductor drums 1a to 1d. The exposure apparatus 5 for exposing the above, the developing apparatus 3a, 3b, 3c and 3d for forming a toner image on the photoconductor drums 1a to 1d, and the developer (toner) remaining on the photoconductor drums 1a to 1d are removed. Cleaning devices 7a, 7b, 7c and 7d are provided.

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 corresponding to the image data on 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 cyan, magenta, yellow, and black, respectively. When the ratio of toner in the two-component developer filled in the developing devices 3a to 3d falls below the specified value due to the formation of the toner image described later, the toner containers 4a to 4d to the developing devices 3a to 3d are used. Toner is replenished. The toner in this developer is supplied onto the photoconductor drums 1a to 1d by the developing devices 3a to 3d 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.

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. These four-color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. After that, in preparation for the subsequent formation of a new electrostatic latent image, the 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 intermediate transfer belt 8 is hung on the driven roller 10 on the upstream side and the drive roller 11 on the downstream side. When the intermediate transfer belt 8 starts rotating counterclockwise with the rotation of the drive roller 11 by the drive motor (not shown), the transfer paper P is adjacent to the drive roller 11 at a predetermined timing from the resist roller pair 12b. It is conveyed to the nip portion (secondary transfer nip portion) with the secondary transfer roller 9 provided. When the transfer paper P passes through the secondary transfer nip portion, the full-color image on the intermediate transfer belt 8 is secondarily transferred onto the transfer paper P. 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 distributed in the transport direction by the branch portion 14 branched in a plurality of directions, and is sent to the double-sided transport path 18 and printed on both sides as it is (or after being sent to the double-sided transport path 18 and printed on both sides) by the discharge roller pair 15. It is discharged to the discharge tray 17.

The image density sensor 40 is arranged on the downstream side of the image forming unit Pd and at a position facing the intermediate transfer belt 8. As the image density sensor 40, 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 the light 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 main control unit 80 (see FIG. 3). Then, the amount of toner 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 of the present embodiment. In the following description, the developing devices 3a arranged in the image forming unit Pa of FIG. 1 will be illustrated, but the configurations of the developing devices 3b to 3d arranged in the image forming units Pb to Pd are 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 containing a magnetic carrier and toner (hereinafter, also simply referred to as a developing agent) is stored. The developing container 20 is divided into a stirring transport chamber 21 and a supply transport chamber 22 by a partition wall 20a. In the stirring transfer chamber 21 and the supply transport chamber 22, a stirring transfer screw 25a and a supply transfer screw 25b for mixing the toner supplied from the toner container 4a (see FIG. 1) with a magnetic carrier to stir and charge the toner are respectively provided. 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 25a and the supply transfer screw 25b, and passes through the developer (not shown) formed at both ends of the partition wall 20a. It circulates between the stirring and transporting chamber 21 and the supply and transporting chamber 22 via the path. That is, a circulation path for the developer is formed in the developing container 20 by the stirring transfer chamber 21, the supply transfer chamber 22, and the developer passage path.

The developing container 20 extends diagonally upward to the right in FIG. 2, and a developing roller 30 is arranged diagonally upward to the right of the supply transport screw 25b in the developing container 20. A part of the outer peripheral surface of the developing roller 30 is exposed from the opening 20b of the developing container 20 and faces the photoconductor drum 1a. The developing roller 30 rotates counterclockwise in FIG.

The developing roller 30 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 product or a plated product in addition to the formation of the knurled product.

Further, a regulation blade 27 is attached to the developing container 20 along the longitudinal direction of the developing roller 30 (the direction perpendicular to the paper surface of FIG. 2). A slight gap is formed between the tip of the regulating blade 27 and the surface of the developing roller 30.

A developing voltage composed of a DC voltage Vslv (DC) and an AC voltage Vslv (AC) is applied to the developing roller 30 by a high voltage generating circuit 43 (see FIG. 3).

In the stirring and transporting chamber 21, the toner concentration sensor 31 is arranged so as to face the stirring and transporting screw 25a. The toner concentration sensor 31 detects the ratio (T / C) of toner to carriers in the developing agent. For example, a magnetic permeability sensor that detects the magnetic permeability of the developing agent in the developing container 20 is used. When the magnetic permeability of the developer is detected by the toner concentration sensor 31, a voltage value corresponding to the detection result is output to the main control unit 80 (see FIG. 3) described later, and the main control unit 80 outputs the voltage value from the toner concentration sensor 31. The toner concentration is determined.

The sensor output value changes according to the toner concentration, and the higher the toner concentration, the higher the ratio of toner to the carrier, and the higher the ratio of non-magnetic toner, the lower the output value. On the other hand, as the toner concentration decreases, the ratio of toner to carriers decreases, and the ratio of carriers that conduct magnetism increases, resulting in an increase in output value. The main control unit 80 transmits a control signal to the toner replenishment motor (not shown) according to the determined toner concentration, and from the toner container 4a (see FIG. 1) to the stirring transfer chamber 21 via the toner replenishment port 20c. A predetermined amount of toner is replenished.

FIG. 3 is a partially enlarged view of the periphery of the image forming unit Pa including the control path of the image forming unit Pa. In the following description, the configuration and control path of the image forming unit Pa will be described, but the description will be omitted because the same applies to the configuration and control path of the image forming units Pb to Pd.

The developing roller 30 is connected to a high voltage generating circuit 43 that generates a vibration voltage in which a DC voltage and an AC voltage are superimposed. The high-voltage generation circuit 43 includes an AC constant-voltage power supply 43a and a DC constant-voltage power supply 43b. The AC constant voltage power supply 43a outputs a sinusoidal AC voltage generated from a low-voltage DC voltage pulse-modulated using a step-up transformer (not shown). The DC constant voltage power supply 43b outputs a DC voltage obtained by rectifying a sinusoidal AC voltage generated from a low-voltage DC voltage pulsed using a step-up transformer.

The high-voltage generation circuit 43 outputs a development voltage obtained by superimposing an AC voltage on a DC voltage from the AC constant voltage power supply 43a and the DC constant voltage power supply 43b at the time of image formation.

Next, the control system of the image forming apparatus 100 will be described with reference to FIG. The image forming apparatus 100 is provided with a main control unit 80 composed of a CPU or the like. The main control unit 80 is connected to a storage unit 70 including a ROM, a RAM, or the like. The main control unit 80 is based on the control program and control data stored in the storage unit 70, and each part of the image forming apparatus 100 (charging apparatus 2a to 2d, exposure apparatus 5, developing apparatus 3a to 3d, primary transfer roller 6a to 6d, cleaning devices 7a to 7d, fixing unit 13, high voltage generation circuit 43, voltage control unit 45, etc.) are controlled.

The fixing temperature sensor 44 detects the temperature of the fixing roller pair 13a of the fixing portion 13. The voltage control unit 45 controls the high voltage generation circuit 43. The voltage control unit 45 may be composed of a control program stored in the storage unit 70. The time measurement unit 47 measures the time required for calculating the active time Δt and the cumulative development drive time Δtdev, which will be described later.

A liquid crystal display unit 90 and a transmission / reception unit 91 are connected to the main control unit 80. The liquid crystal display unit 90 functions as a touch panel for the user to make various settings of the image forming apparatus 100, and displays the state of the image forming apparatus 100, the image forming status, the number of prints, and the like. The transmission / reception unit 91 communicates with the outside using a telephone line or an Internet line.

By the way, there is a problem that the output value of the toner density sensor 31 fluctuates depending on the usage environment of the image forming apparatus 100, and the toner density in the developing agents in the developing devices 3a to 3d greatly deviates from the reference density. Specifically, when a magnetic permeability sensor is used as the toner concentration sensor 31, the sensitivity decreases as the sensor temperature rises. That is, since the output value does not decrease even if the toner is supplied, the toner concentration in the developing devices 3a to 3d becomes higher than the reference concentration due to the excessive toner supply.

When the image forming apparatus 100 is left for a long time and the sensor temperature decreases and the output value returns to normal, printing is performed without replenishing the toner until the toner concentration in the developing apparatus 3a to 3d decreases to the reference density. .. As a result, the amount of charge of the toner in the developing apparatus increases and the developability of the toner decreases. If printing is performed in this state, the image density may drop sharply in the printing of several sheets immediately after.

Therefore, in the present invention, when printing is performed immediately after the detection temperature of the fixing temperature sensor 44 is equal to or lower than a certain temperature (when the first condition is satisfied) when the power of the image forming apparatus 100 is turned on (when the power is turned on). Alternatively, the calculation starts from the time of printing immediately after the image forming apparatus 100 is left for a predetermined time (when the second condition is satisfied) from the final printing, and then starts when the first condition or the second condition is satisfied. The difference between the time and the final printing time (hereinafter referred to as the active time) is calculated, and the cumulative value of the drive times of the developing devices 3a to 3d within the active time (hereinafter referred to as the cumulative development drive time) is divided by the active time. (Hereinafter, referred to as active time development drive rate) is calculated. Then, when the active time development drive rate is equal to or higher than a certain value, calibration is executed when a certain amount of toner is consumed.

Even when the power of the image forming apparatus 100 is turned on, if the elapsed time from the immediately preceding power off is short, it is considered that the previous active time is continued, and the calculation of the next active time is not started. That is, even when the power is turned on, in order to eliminate the case where the elapsed time from the immediately preceding power off is short, the condition that "the detection temperature of the fixing temperature sensor 44 is below a certain temperature" is required in the first condition. Become.

FIG. 4 is a diagram showing the relationship between the active time Δt and the cumulative development drive time Δtdev. As shown in FIG. 4, a print command is input in a state where the detection temperature of the fixing temperature sensor 44 mounted on the fixing unit 13 is equal to or lower than a predetermined temperature (first condition) when the power is turned on, or an image is obtained from the final printing. When a print command is input while the forming apparatus 100 is left for a predetermined time (second condition), that time is set as the start time (= tstart1). Then, the measurement of the development drive time (= tdev) is started from the calculation start time.

After the power is turned off, the power is turned on again, and the print command is input in a state where the output value of the fixing temperature sensor 44 is equal to or lower than the predetermined temperature (first condition), or the print command is left for a predetermined time or longer after the final printing. When the print command is input in this state (second condition), the active time Δt1 obtained by subtracting the calculation start time tstart1 from the print end time tend1 at the time of the previous final printing is calculated. At the same time, the cumulative development drive time Δtdev (= Σtdev) within the active time Δt is calculated. Further, the above procedure is repeated with the time when the next print command is input while satisfying the first condition or the second condition as the start time (= tstart2) of the next active time Δt2.

FIG. 5 is a flowchart showing a calculation control example of the active time Δt and the development drive time Δtdev in the image forming apparatus 100 of the present embodiment. The procedure for calculating the active time Δt and the cumulative development drive time Δtdev will be described with reference to FIGS. 1 to 4.

First, a state in which the image forming apparatus 100 is turned on and the detection temperature of the fixing temperature sensor 44 is equal to or lower than a predetermined temperature (first condition), or the leaving time of the image forming apparatus 100 from the final printing time to the current time. When the state (second condition) of the predetermined time or longer is satisfied (step S1), it is determined whether or not the print command has been received by the main control unit 80 (step S2). When the print command is received (Yes in step S2), it is determined whether or not it is the first print after satisfying the first condition or the second condition (step S3).

In the case of the first printing (Yes in step S3), the current time t at the start of printing is set to the starting time (tstart) of the active time (step S4), and the printing operation is executed (step S5). If it is not the first print (No in step S3), the print operation is executed without setting the start time (tstart) of the active time (step S5). In either case, the development drive time (tdev) in the printing operation is calculated after the printing is executed (step S6).

After that, the main control unit 80 again determines whether or not either the first condition or the second condition is satisfied (step S7). If the first condition and the second condition are not satisfied (No in step S7), the process returns to step S2 and the standby state of the print command is continued.

When either the first condition or the second condition is satisfied (Yes in step S7), the current time t at the end of printing immediately before is set as the start time (tend) of the active time (step S8). Then, the active time (Δt) obtained by subtracting the calculation start time (tstart) from the calculation end time (tend) set in step S4 is calculated (step S9). Further, the cumulative development drive time (Δtdev) obtained by accumulating and adding the development drive time (tdev) calculated in step S6 is calculated (step S10). Then, the calibration routine is performed based on the calculated active time (Δt) and the cumulative development drive time (Δtdev) (step S11). The calibration routine will be described later.

After that, Δt and Δtdev are reset (step S12), the process returns to step S2, the next active time (Δt) is started, and the calculation of the cumulative development drive time (Δtdev) is started (steps S2 to S12).

FIG. 6 is a flowchart showing a control example of the calibration routine in FIG. The procedure for executing the calibration will be described along the steps of FIG. 6 with reference to FIGS. 1 to 5 as necessary. The calibration routine shown in FIG. 6 is, for example, when the power of the image forming apparatus 100 is turned on, when returning from the power saving (sleep) mode, when the cumulative number of prints from the previous calibration reaches a predetermined number, and the like. It is performed separately from the normal calibration that is automatically performed.

First, the main control unit 80 determines whether or not the active time development drive rate (Δtdev / Δt) is equal to or greater than the threshold value X (step S1). When Δtdev / Δt ≧ X (Yes in step S1), the integrated print rate W1 is calculated and stored in the storage unit 70 (step S2). The integrated printing rate in this control example is the integrated printing rate from the start of use of the image forming apparatus 100.

After that, the main control unit 80 shifts to a standby state for determining whether or not a print command has been received (step S3). When a print command is received (Yes in step S3), printing is executed by a normal image forming operation (step S4), and the current integrated print rate W is calculated (step S5). Then, it is determined whether or not the difference W1-W between the integrated print rate W1 and the current integrated print rate W is equal to or greater than the threshold value Y (step S6).

If W1-W <Y (No in step S6), the process returns to step S3 and the standby state of the print command is continued. If W1-W ≧ Y (Yes in step S6), calibration is executed (step S7). Specifically, a plurality of patch images (density correction patterns) having different densities are formed for each of the magenta, cyan, yellow, and black colors. Then, the density of the patch image transferred on the intermediate transfer belt 8 is detected by the image density sensor 40, and the development voltage is adjusted using the detection result.

If Δtdev / Δt <X in step S1 (No in step S1), it means that the developing devices 3a to 3d were not driven so much within the active time, so calibration was performed from the memory of the integrated printing rate W1. The process ends without performing the procedure (steps S2 to S7) up to the execution of the operation.

According to the above control, when the active time development drive rate Δtdev / Δt is equal to or greater than the threshold value X, the integrated print rate W1 at the time of performing calibration is stored in the storage unit 70. Then, when the difference W1-W from the integrated print rate W due to the subsequent printing operation becomes equal to or greater than the threshold value Y, calibration is executed.

As a result, the image forming apparatus 100 is printed with high frequency before being left for a long time, the output value of the toner density sensor 31 fluctuates due to the temperature rise, and the toner concentration in the developing apparatus 3a to 3d becomes the reference density. On the other hand, when it is predicted that the toner is high, the calibration is executed at an appropriate timing when the toner in the developing devices 3a to 3d is consumed in a predetermined amount. Therefore, it is possible to minimize the period during which the image forming apparatus 100 is used in a state where the toner concentration in the developing apparatus 3a to 3d fluctuates greatly. Further, since it is not necessary to correct the output value of the toner concentration sensor 31 based on the temperature, the number of temperature sensors can be reduced.

Further, when the active time development drive rate Δtdev / Δt is smaller than the threshold value X, the calibration is executed only when the normal calibration execution condition is satisfied, so that the toner consumed by executing the calibration at an unnecessary timing is consumed. It is possible to suppress an increase and a decrease in image formation efficiency (increase in printing waiting time).

In the control example shown in FIG. 6, the integrated print rate is calculated as the integrated print rates W1 and W from the start of use of the image forming apparatus 100. For example, W1 and W are set to Δtdev / Δt ≧ X. It may be the integrated printing rate from a certain point before the satisfaction. Further, the integrated printing rate only for the printing operation after satisfying Δtdev / Δt ≧ X may be calculated separately. That is, the calibration may be executed when the integrated printing rate by the printing operation after satisfying Δtdev / Δt ≧ X reaches a constant printing rate (toner consumption).

Further, the necessity of performing the calibration is determined based on the difference W1-W between the integrated print rate W1 after satisfying Δtdev / Δt ≧ X and the current integrated print rate W, but the toner consumption is determined. As long as it is a representative value, it is not limited to the integrated printing rate. For example, the necessity of performing calibration is determined based on the increase in the output value of the toner density sensor 31, the total number of prints after satisfying Δtdev / Δt ≧ X, and the total drive time of the developing devices 3a to 3d. You can also do it.

Others The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, the image forming apparatus 100 provided with the two-component developing type developing devices 3a to 3d provided with the developing roller (developing agent carrier) 30 carrying the two-component developing agent has been described, but the present invention has been described. Is not limited to this. A developer carrier such as a magnetic roller is further provided between the supply transport screw 25b and the developing roller 30, and after the developer is supplied from the supply transport screw 25b to the magnetic roller, only toner is supplied from the magnetic roller to the developing roller 30. It can be applied in exactly the same way to an image forming apparatus provided with a developing apparatus.

Further, the present invention is not limited to the color printer as shown in FIG. 1, and various image forming devices including a two-component developing type developing device such as a monochrome printer, a monochrome copying machine, a digital multifunction device, a color copying machine, and a facsimile are provided. Applicable to devices.

The present invention can be used in an image forming apparatus including a developing apparatus using a two-component developer. By utilizing the present invention, it is possible to provide an image forming apparatus capable of suppressing a decrease in image density even when there is a difference between the output value of the toner density sensor and the toner density in the developing apparatus.

Pa to Pd Image forming parts 1a to 1d Photoreceptor drum (image carrier)
2a to 2d Charging device 3a to 3d Developing device 5 Exposure device 8 Intermediate transfer belt 20 Developing container 21 1st stirring screw 22 2nd stirring screw 30 Developing roller (developer carrier)
31 Toner density sensor 40 Image density sensor 43 High-voltage generation circuit (development voltage power supply)
44 Fixation temperature sensor 47 Time measurement unit 70 Storage unit 80 Main control unit 100 Image forming device

Claims (7)

An image carrier with a photosensitive layer formed on its surface,
A charging device that charges the surface of the image carrier,
An exposure device that exposes the surface of the image carrier charged by the charging device to form an electrostatic latent image, and an exposure device.
A developing container containing a two-component developer containing a carrier and a toner, a developer carrier rotatably supported in the developing container and carrying the two-component developer on the surface, and the two in the developing container. A developing apparatus having a toner concentration sensor for detecting the toner concentration in the component developer and developing the electrostatic latent image into a toner image using the developer carrier.
Image forming part having
A fixing unit for fixing the toner image to the recording medium by heating and pressurizing the recording medium on which the toner image is formed by the image forming unit.
A developing voltage power source that applies a developing voltage to the developer carrier,
An image density sensor that detects the image density of the toner image formed by the image forming unit, and an image density sensor.
A fixing temperature sensor that detects the temperature of the fixing part and
The image forming unit, the control unit that controls the developing voltage power supply, and
In an image forming apparatus equipped with
The control unit can execute calibration for correcting the image density by adjusting the development voltage based on the detection result of the image density sensor.
The control unit is in the first condition when the image forming apparatus is turned on and the detection temperature of the fixing temperature sensor is equal to or lower than a predetermined temperature, or when the leaving time from the end of the immediately preceding image forming is equal to or longer than a predetermined time. When a certain second condition is satisfied, the image formation start time immediately after the first condition or the second condition is satisfied is set as the calculation start time, and then the calculation when the first condition or the second condition is satisfied. The active time Δt from the start time to the final image formation time and the development cumulative drive time Δtdev which is the cumulative value of the drive time of the developing device within the active time are calculated.
When the active time development drive rate Δtdev / Δt obtained by dividing the cumulative development drive time Δtdev by the active time Δt is equal to or greater than a predetermined value, the toner consumption after satisfying the first condition or the second condition is predetermined. An image forming apparatus characterized in that calibration is performed when a threshold is reached. When the Δtdev / Δt is equal to or greater than a predetermined value, the control unit determines whether or not the toner consumption has reached the threshold value based on the integrated printing rate after satisfying the first condition or the second condition. The image forming apparatus according to claim 1, wherein the image forming apparatus is characterized in that. When the Δtdev / Δt is equal to or greater than a predetermined value, the control unit reaches the threshold value based on the output value of the toner concentration sensor after satisfying the first condition or the second condition. The image forming apparatus according to claim 1, wherein it is determined whether or not the image has been formed. When the Δtdev / Δt is equal to or greater than a predetermined value, the control unit reaches the threshold value based on the integrated number of prints by image formation after satisfying the first condition or the second condition. The image forming apparatus according to claim 1, wherein it is determined whether or not the image is formed. When the Δtdev / Δt is equal to or greater than a predetermined value, the control unit determines the toner consumption amount based on the integrated drive time of the developing device by image formation after satisfying the first condition or the second condition. The image forming apparatus according to claim 1, wherein it is determined whether or not a threshold value has been reached. When the Δtdev / Δt is smaller than the predetermined value, the control unit reaches the predetermined number of integrated prints after the previous calibration is executed, when the power of the image forming apparatus is turned on, when returning from the power saving mode, and so on. The image forming apparatus according to any one of claims 1 to 5, wherein the calibration is performed when at least one of the conditions of time is satisfied. The image forming apparatus according to any one of claims 1 to 6, wherein the toner concentration sensor is a magnetic permeability sensor that detects the magnetic permeability of the two-component developer.

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