JP7124597B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

Japanese Patent Application Laid-Open No. 2002-200002 discloses an image forming apparatus that achieves both improvement in image quality of a low-print-rate image pattern and reduction in toner consumption. In the image forming apparatus, in order to improve the development performance, the developing bias used for development is developed at a first peak voltage that has the effect of causing the developer to fly in the direction from the developer carrier toward the image formation carrier. increase efficiency. In addition, the time ratio between the first peak voltage and the second peak voltage that causes the developer to fly in the opposite direction is changed so that the time average voltage becomes a constant value before and after the change in the first peak voltage.

Further, Japanese Patent Application Laid-Open No. 2002-200000 discloses that in an image forming apparatus using a two-component developer, it is possible to always form an image of a predetermined level or higher in accordance with the environment and time of a developing device that constitutes the image forming apparatus. An image forming apparatus is disclosed. The image forming apparatus includes a first printing rate storage section for storing an average document printing rate of a print job of a predetermined number of printed sheets, an area corresponding to the first printing rate storage section, and a development bias correction amount corresponding to the area. and a conversion table for storing the development bias in process control, when the area corresponding to the average document coverage rate in the predetermined number of printed sheets differs from the reference area, the conversion table is stored. is used to correct the development bias.

JP 2007-121747 A JP 2009-210786 A

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus that suppresses deterioration in image quality due to fluctuations in image density with a limited power supply capacity, as compared with the case where image quality is controlled only by the amplitude value of an AC voltage in a developing voltage. and

An image forming apparatus according to a first aspect includes an image carrier on which a latent image is formed, a developing device that transfers toner from a developing member facing the image carrier to the latent image to form a toner image, and a direct current. a developing power source for applying a development voltage constituted by a superimposed voltage obtained by superimposing an alternating voltage on a voltage between the image carrier and the developing member; a detection unit for detecting the image density of the toner image; and a control unit for controlling the developing power source so that the amplitude value of the AC voltage is decreased and the frequency is increased as the image density increases.

In the image forming apparatus of the second aspect, the controller controls the developing power supply so that the amplitude value of the AC voltage is increased and the frequency is decreased as the image density decreases.

In the image forming apparatus of the third aspect, the controller adjusts the amplitude value and the frequency so that the power of the development power source does not exceed a predetermined value.

In the image forming apparatus according to the fourth aspect, the control unit corrects the amplitude value of the AC voltage to decrease and the frequency to increase according to the elapsed time of use after the developer is replaced in the developing device. I do.

In the image forming apparatus according to the fifth aspect, the control section performs correction to decrease the amplitude value and increase the frequency of the AC voltage in accordance with the lapse of driving time of the image carrier.

The image forming apparatus of the sixth aspect further comprises a measurement unit that measures environmental conditions including at least one of temperature and humidity, and the control unit increases the amplitude value of the AC voltage as the temperature or humidity increases. is lowered and the frequency is raised.

In the image forming apparatus according to the seventh aspect, the controller increases the amplitude value of the AC voltage and decreases the frequency as the temperature or humidity decreases.

According to the first aspect, it is possible to suppress fogging accompanying an increase in image density with a limited power supply capacity, compared to the case where the image quality is controlled only by the amplitude value of the AC voltage in the developing voltage.

According to the second aspect, compared to the case where the image quality is controlled only by the amplitude value of the AC voltage in the developing voltage, it is possible to suppress the deterioration of developability due to the decrease in image density with a limited power supply capacity.

According to the third aspect, it is possible to suppress the deterioration of image quality due to the adjustment limit of the developing power source due to power shortage, compared to the case of adjusting the image quality without limiting the power.

According to the fourth aspect, fogging can be suppressed as compared with the case where the correction corresponding to the deterioration of the developer is not performed.

According to the fifth aspect, fogging can be suppressed as compared with the case where the correction is not performed according to the driving time of the image carrier.

According to the sixth aspect, it is possible to suppress fogging caused by an increase in temperature or humidity compared to the case where correction is not performed due to an increase in temperature or humidity.

According to the seventh aspect, it is possible to suppress deterioration of developability due to a decrease in temperature or humidity compared to the case where no correction is performed due to a decrease in temperature or humidity.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment; FIG. 2 is an enlarged view of an image forming section and a surrounding sheet conveying section of the image forming apparatus according to the embodiment; FIG. It is a block diagram which shows the hardware constitutions of a control system. 3 is a block diagram showing an example of the functional configuration of a CPU in the control device; FIG. FIG. 5 is a diagram showing the relationship between the amplitude value of AC voltage and the development rate; FIG. 4 is a diagram showing the relationship between the amplitude value of an AC voltage and the grade of fogging; FIG. 4 is a diagram showing the relationship between the frequency of AC voltage and the grade of fog; FIG. 5 is a diagram showing the relationship between the change over time of the developer and the grade of fogging. FIG. 4 is a diagram showing the relationship between the thickness of the charge transport layer and the grade of fogging in the photoreceptor drum. 4 is a flow chart showing the flow of adjustment processing according to the present embodiment. It is a flowchart which shows the flow of the 1st correction|amendment process in this embodiment. It is a flowchart which shows the flow of the 2nd correction|amendment process in this embodiment. It is a flowchart which shows the flow of the 3rd correction|amendment process in this embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, the image forming apparatus 10 of the present embodiment includes an image forming section 14, a sheet conveying section 16 for conveying a sheet 38, and a control device 50 for controlling the image forming section 14 in a housing 12. ing.

(Image forming section)
As shown in FIG. 2, the image forming section 14 includes a photosensitive drum 22, which is an example of an image carrier that rotates in the arrow A direction at a constant speed.

Around the photoreceptor drum 22, along the rotation direction of the photoreceptor drum 22 (clockwise direction indicated by arrow A in FIG. 2), there are devices such as a charging section 24, an exposure section 26, a developing section 28, and a transfer roll. 30, a cleaner 32 and an erase lamp 34 are arranged in this order. The developing section 28 is an example of a developing device.

A density sensor 66 is arranged downstream of the developing section 28 . A density sensor 66 detects the density of the toner image formed on the photosensitive drum 22 .

An LED printer head (LPH) is applied to the exposure unit 26 . Note that the exposure unit 26 is not limited to the LPH, and may be an optical scanning device that irradiates a rotating polygon mirror with laser and scans the reflected light.

After the surface of the photosensitive drum 22 is uniformly charged (charged with a predetermined surface potential of the photosensitive member) by the charging unit 24 , the photosensitive drum 22 is irradiated with a light beam by the exposure unit 26 to form a latent image on the photosensitive drum 22 . is formed. The photoreceptor drum 22 is a replaceable photoreceptor unit.

To the latent image formed on the photoreceptor drum 22 by the light beam, toner is supplied (transferred) by the difference voltage Vcln between the photoreceptor surface potential Vs and the developing voltage Vdev which is the developing bias applied to the developing unit 28 . be. That is, the developing section 28 transfers toner to the latent image to form a toner image on the photosensitive drum 22 . Note that the toner is negatively charged in the present embodiment.

The developing unit 28 also includes a developing roll 28A, which is an example of a developing member that faces the photosensitive drum 22 and is rotationally driven in the arrow B direction. The developing roll 28A is installed in a housing 28B containing an electrostatic charge image developer (not shown; hereinafter simply referred to as "developer") containing non-magnetic toner and magnetic carrier. The developer is contained in a developer cartridge (not shown), and a dispensing unit (not shown) is controlled by a CPU 51, which will be described later, to convey the developer contained in the developer cartridge into the housing 28B.

To the developing roll 28A, a superimposed voltage obtained by superimposing an alternating current component (AC) on a direct current component (DC) is applied from the developing power supply 20 as a developing voltage. Although the waveform of the AC component is a rectangular wave in this embodiment, it is not limited to this, and may be a triangular wave or a sine wave. Moreover, the frequency of the AC component is preferably in the range of 5 kHz or more and 20 kHz or less.

The power P required for the development power supply 20 can be expressed by the following equation 1, where Vpp is the amplitude value of the AC voltage and f is the frequency. _{C-- DEVE} is the electrostatic capacitance of the developing portion, and C-- _HV is the electrostatic capacitance for constant voltage control.

That is, if the amplitude value Vpp and the frequency f are variable, the power P, which is the power source capacity of the developing power source 20, is proportional to the square of the amplitude value Vpp in the AC voltage and proportional to the frequency f.

Also, a magnetic brush formed on the surface of the developing roll 28A is brought into contact with the photosensitive drum 22, and a developing voltage, which is a superimposed voltage, is applied. As a result, the toner adhering to the carrier, that is, the toner held on the developing roll 28A is supplied to the photoreceptor drum 22, and the latent image formed on the surface of the photoreceptor drum 22 is developed as a toner image.

The developing roll 28A is selected according to the type of developer, and for example, a magnet roll having a plurality of magnetic poles can be used. A magnetic permeable sensor 68 is provided at the bottom of the housing 28B. The magnetic permeability sensor 68 is a sensor that detects the toner density of the developer by detecting the magnetic permeability of the developer composed of non-magnetic toner and magnetic carrier.

The developing section 28 including the developing power source 20 is electrically connected to, for example, a control device 50 provided in the image forming apparatus 10, and is controlled by the control device 50 to apply a developing voltage to the developing roll 28A. . The developing roll 28A holds, for example, the developer accommodated in the housing 28B on its surface, and supplies the toner contained in the developer from the developing section 28 to the surface of the photosensitive drum 22. As shown in FIG. Note that the carrier is returned to the developing section 28 while being held by the developing roll 28A.

On the other hand, the toner image on the photosensitive drum 22 is transferred by the transfer roll 30 onto a sheet of paper 38 as a recording medium. Hereinafter, the area where the toner image is transferred may be referred to as "transfer portion TR".

After the transfer at the transfer section TR, the toner remaining on the photosensitive drum 22 is removed by the cleaner 32, neutralized by the erase lamp 34, charged again by the charging section 24, and the same image forming process is performed. It can be repeated.

On the other hand, the paper 38 onto which the toner image has been transferred by the transfer section TR is conveyed to a fixing section 40 having a pressure roller 40A and a heating roller 40B, and is subjected to a fixing process. As a result, the toner image is fixed and a desired image is formed on the paper 38 . The paper 38 on which the image is formed is discharged out of the apparatus.

(Paper transport system)
As shown in FIG. 1, the image forming apparatus 10 is equipped with a plurality of feeding devices 82 for feeding the sheets 38 to the image forming section 14 .

The supply device 82 has different storage containers 84 for storing paper 38 of different types, such as plain paper and thick paper. Each storage container 84 can be pulled out from the housing 12 of the image forming apparatus 10 , and the sheets 38 are loaded (replenished) while the storage container 84 is pulled out from the image forming apparatus 10 .

The supply device 82 has a transport roll 86 that takes out the uppermost sheet of paper 38 stored in the storage container 84 and transports the taken out sheet of paper 38 toward the image forming section 14 .

As shown in FIGS. 1 and 2, the image forming apparatus 10 is provided with a sheet conveying section 16 for conveying the sheet 38 . The paper transport section 16 has a main transport path 88 , a reverse transport path 90 and a sub transport path 91 .

The main transport path 88 is used to transport the paper 38 supplied from any of the supply devices 82 to the image forming section 14 and discharge the paper 38 on which an image is formed to the outside of the image forming apparatus 10 .

Along the main transport path 88, from the upstream side in the direction in which the paper 38 is transported, the transport roll 86, the registration roll 92, the transfer roll 30, and the fixing section 40 (the pressure roller 40A and the heat roller 40B). , and a discharge roll 94 are arranged.

For example, the registration rolls 92 are temporarily stopped while holding the leading edge of the paper 38 conveyed from the supply device 82 side, and the paper 38 is moved so as to coincide with the timing when the toner image is transferred to the transfer portion TR. toward the transfer roll 30.

The discharge roll 94 discharges the paper 38 on which the toner has been fixed by the fixing section 40 to the outside of the image forming apparatus 10 .

The reversing conveying path 90 is a conveying path used for reversing the sheet 38 having the toner image fixed on one side thereof and supplying the sheet 38 toward the image forming section 14 again.

For example, a pair of reversing transport rolls 96 are appropriately arranged along the reversing transport path 90 . In the reversing conveyance path 90, the paper 38 is supplied from the rear end side by rotating the discharge roll 94 in the reverse direction with the rear end of the paper 38 sandwiched by the discharge roll 94, and the supplied paper 38 is reversed. It is conveyed to a position upstream of the registration roll 92 by the conveying rolls 96 , 96 .

The sub-transport path 91 is a transport path for supplying the image forming section 14 with paper 38 different from the paper 38 accommodated in the supply device 82 . The paper 38 is supplied to the sub-conveyance path 91 from the left side of the image forming apparatus 10 in FIG. A transport roller 99 is provided in the sub-transport path 91 . The transport roll 99 transports the paper 38 supplied to the sub-transport path 91 toward the image forming section 14 .

(Other configurations)
In addition, a control device 50 , a communication section 60 , a temperature sensor 62 and a humidity sensor 64 are provided inside the housing 12 .

The communication unit 60 is connected to a network such as the Internet, LAN, or WAN, and can communicate with an external PC or the like via the network.

A temperature sensor 62 measures the temperature inside the housing 12 . Also, the humidity sensor 64 measures the humidity inside the housing 12 .

(control system)
First, the hardware configuration of the control system of the image forming apparatus 10 will be described with reference to FIG.

As shown in FIG. 3, the control device 50 of the image forming apparatus 10 is composed of, for example, a computer. The control device 50 includes a CPU (Central Processing Unit) 51 , a ROM (Read Only Memory) 52 , a RAM (Random Access Memory) 53 , a nonvolatile memory 57 and an input/output interface (I/O) 55 . A CPU 51 , ROM 52 , RAM 53 , nonvolatile memory 57 and I/O 55 are connected via a bus 56 .

The CPU 51 is a central processing unit that executes various programs and controls each section. That is, the CPU 51 reads a program from the ROM 52 or the nonvolatile memory 57 and executes the program using the RAM 53 as a work area. In this embodiment, an execution program for executing various processes is stored in the nonvolatile memory 57 . The CPU 51 functions as the detection unit 70, the measurement unit 72, and the control unit 74 shown in FIG. 4 by executing the execution program.

The ROM 52 stores various programs and various data. The RAM 53 temporarily stores programs or data as a work area.

The non-volatile memory 57 is an example of a storage device in which stored information is maintained even when power supply is interrupted. For example, a semiconductor memory is used, but a hard disk may be used.

The I/O 55 is connected to the image forming section 14 , the conveying motor group 80 , the communication section 60 , the temperature sensor 62 , the humidity sensor 64 , the density sensor 66 and the magnetic permeability sensor 68 . Here, the image forming section 14 includes a developing power source 20 for applying a developing voltage. Further, the transport motor group 80 includes motors for driving transport rolls 86, registration rolls 92, discharge rolls 94, reversing transport rolls 96, and the like.

FIG. 4 is a block diagram showing an example of the functional configuration of the CPU 51. As shown in FIG. As shown in FIG. 4 , the CPU 51 has a detection section 70 , a measurement section 72 and a control section 74 . Each functional configuration is realized by the CPU 51 reading an execution program stored in the nonvolatile memory 57 and executing it.

The detection unit 70 has a function of detecting the image density of the toner image. Specifically, the detection unit 70 calculates the image density from the image data received by the communication unit 60 .

The measurement unit 72 has a function of measuring environmental conditions inside the housing 12 related to temperature and humidity. The measurement unit 72 measures temperature based on the signal from the temperature sensor 62 and measures humidity based on the signal from the humidity sensor 64 .

The control section 74 has a function of controlling each function of the image forming section 14 . Further, the control unit 74 of the present embodiment controls the development power source 20 to change the amplitude value Vpp and the frequency f of the AC voltage.

(Relationship between AC voltage and image quality)
First, there are relationships (A) and (B) below between the density of an image formed on the paper 38 (hereinafter simply referred to as "image density") and the image quality.
(A) Continuous printing at a high image density lowers the toner charge amount. As a result, fogging occurs in which toner is discharged to the blank portion other than the latent image. Fog becomes worse as the image density increases.
(B) Continuous printing at a low image density increases the toner charge amount. Along with this, the developability of the toner deteriorates. Developability deteriorates as image density decreases.

On the other hand, it is known from the experimental results shown in FIGS. ing.
(1) As shown in FIG. 5, the developability is improved by increasing the amplitude value Vpp of the AC voltage. Note that the development rate in FIG. 5 corresponds to the transfer rate of toner from the development roll 28A to the photosensitive drum 22. As shown in FIG.
(2) As shown in FIG. 6, if the amplitude value Vpp of the AC voltage is increased, the fog is slightly worsened. The grade (G) in FIG. 6 is an evaluation index determined for each degree of fog in the standard limit sample for fog (limit sample manufactured by Fuji Xerox Co., Ltd.), and the higher the grade, the worse the fog. indicates that Based on the above (1), when the amplitude value Vpp is increased, the effect of improving developability is greater than the deterioration of fog.
(3) As shown in FIG. 7, fog is improved by increasing the frequency f of the AC voltage.
(4) As shown in FIG. 8, the more the developer (carrier) is (deteriorated), the more the toner charge amount is decreased, so that the fogging is worsened.
(5) As shown in FIG. 9, the thinner the charge transport layer (CTL) of the photosensitive drum 22, the worse the fog.
(6) Generally, it is known that the higher the temperature and humidity, the lower the charge amount of the toner and the worse the fogging.

Based on the above problems (A) and (B) and the relationships (1) to (6), the CPU 51 of the present embodiment sets the power P of the development power supply 20 to a predetermined value (for example, the power supply of the development power supply 20 The amplitude value Vpp and the frequency f were changed within the range of the capacity (maximum power). As a result, deterioration of image quality, that is, occurrence of fogging and deterioration of developability can be suppressed. Note that the CPU 51 may change the amplitude value Vpp and the frequency f while monitoring the upper limit value of the power P, or may change the amplitude value Vpp and the frequency f by referring to a table in which preset values are defined. good too.

(action)
Control of the developing power source 20 by the CPU 51 will be described below with reference to flow charts of FIGS. 10 to 13. FIG.

FIG. 10 is a flowchart relating to adjustment processing of the amplitude value Vpp and the frequency f with respect to the image density.

In step S100, the CPU 51 sets initial values for the amplitude value Vpp and the frequency f at the start of the print job. Note that when the first to third correction processes, which will be described later, are being executed, the values after correction are set. Then, the process proceeds to the next step S101.

In step S101, the CPU 51 sets a predetermined standard value for image density. Then, the process proceeds to the next step S102.

In step S<b>102 , the CPU 51 calculates image density from the image data received by the communication section 60 . Then, the process proceeds to the next step S103.

In step S103, the CPU 51 determines whether the image density is increasing, that is, whether the image density calculated in step S102 is higher than the currently set image density. When the CPU 51 determines that the calculated image density is higher (has increased) than the currently set image density, the process proceeds to the next step S104. On the other hand, when the CPU 51 determines that the calculated image density is not higher than the currently set image density (not increased), ie, is equal to or less than the currently set image density, the process proceeds to step S105.

In step S104, the CPU 51 adjusts the amplitude value Vpp from the current value to decrease and the frequency f from the current value to increase. Then, the process proceeds to step S107.

In step S105, the CPU 51 determines whether the image density has decreased, that is, whether the image density calculated in step S102 is lower than the currently set image density. When the CPU 51 determines that the calculated image density is lower (has decreased) than the currently set image density, the process proceeds to the next step S106. On the other hand, when the CPU 51 determines that the calculated image density is not lower than the currently set image density (not decreased), ie, the same as the currently set image density, the process proceeds to step S107. That is, when the image density does not change, the CPU 51 maintains the amplitude value Vpp and the frequency f.

In step S106, the CPU 51 increases the amplitude value Vpp from the current value and adjusts the frequency f to decrease from the current value. Then, the process proceeds to the next step S107.

In step S107, the CPU 51 determines whether the print job has ended. When the CPU 51 determines that the print job has ended, it ends the adjustment process. On the other hand, when the CPU 51 determines that the print job has not ended, the process returns to step S102.

FIG. 11 is a flowchart relating to the first correction process for changing the amplitude value Vpp and the frequency f with respect to the elapsed time after the developer is replaced in the developing section 28 .

In step S200, the CPU 51 obtains the elapsed time since the developing unit 28 was replenished with new developer. That is, the developer is replaced in the developing section 28, and the usage time of the newly replenished developer is acquired. The usage time in this embodiment is the accumulated value of the driving time of the developing unit 28 after the developer is replaced. Then, the process proceeds to the next step S201.

In step S201, the CPU 51 determines whether or not the developer has been replaced. When the CPU 51 determines that the developer has been replaced, the process proceeds to the next step S202. On the other hand, when the CPU 51 determines that the developer has not been replaced, the process proceeds to step S203.

In step S202, the CPU 51 sets initial values for the amplitude value Vpp and the frequency f. Then, the first correction process ends.

In step S203, the CPU 51 determines whether or not a predetermined time has elapsed since the developer was replaced in the developing section 28 and the new developer has been used. When the CPU 51 determines that the usage time of the developer has passed the predetermined time, the process proceeds to the next step S204. Note that when the usage time of the developer has passed the "predetermined time", the usage time for which the next correction is scheduled is set in the "predetermined time". On the other hand, when the CPU 51 determines that the usage time of the developer has not passed the predetermined time, it ends the first correction process. That is, in this case, the CPU 51 maintains the values of the amplitude value Vpp and the frequency f.

In step S204, the CPU 51 adjusts to decrease the amplitude value Vpp from the current value and to increase the frequency f from the current value. Then, the first correction process ends.

FIG. 12 is a flowchart relating to the second correction process for changing the amplitude value Vpp and the frequency f with respect to the driving time of the photoreceptor unit.

In step S250, the CPU 51 obtains the driving time after the start of use of the photosensitive unit. Then, the process proceeds to the next step S251.

In step S251, the CPU 51 determines whether or not the photosensitive unit has been replaced. When the CPU 51 determines that the photoreceptor unit has been replaced, the process proceeds to the next step S252. On the other hand, when the CPU 51 determines that the photosensitive unit has not been replaced, the process proceeds to step S253.

In step S252, the CPU 51 sets initial values for the amplitude value Vpp and the frequency f. Then, the second correction processing ends.

In step S253, the CPU 51 determines whether or not the driving time of the photoreceptor unit has passed a predetermined time. When the CPU 51 determines that the driving time of the photoreceptor unit has passed the predetermined time, the process proceeds to the next step S254. Note that when the driving time of the photoreceptor unit has passed the "predetermined time", the driving time scheduled to be corrected next is set in the "predetermined time". On the other hand, when the CPU 51 determines that the driving time of the photoreceptor unit has not passed the predetermined time, it ends the second correction process. That is, in this case, the CPU 51 maintains the values of the amplitude value Vpp and the frequency f.

In step S254, the CPU 51 adjusts the amplitude value Vpp from the current value to decrease and the frequency f from the current value to increase. Then, the second correction processing ends.

FIG. 13 is a flowchart relating to the third correction process for changing the amplitude value Vpp and frequency f with respect to the temperature and humidity inside the housing 12 .

In step S<b>300 , the CPU 51 measures the temperature inside the housing 12 with the temperature sensor 62 and measures the humidity inside the housing 12 with the humidity sensor 64 . Then, the process proceeds to the next step S301.

In step S301, the CPU 51 determines whether the temperature and humidity measured in step S300 are higher than those measured last time (for example, when the power is turned on), in other words, whether it is hot and humid. When the CPU 51 determines that the measured temperature and humidity are higher than the previously measured temperature and humidity, the process proceeds to the next step S302. On the other hand, when the CPU 51 determines that the measured temperature and humidity are not greater than the previously measured temperature and humidity, ie, are equal to or less than the previous temperature and humidity, the process proceeds to step S303.

In step S302, the CPU 51 adjusts the amplitude value Vpp to decrease from the current value and the frequency f to increase from the current value. Then, the third correction process ends.

In step S303, the CPU 51 determines whether the temperature and humidity measured in step S300 are lower than those measured last time (for example, when the power is turned on), in other words, whether the temperature and humidity are low and low. When the CPU 51 determines that the measured temperature and humidity are lower than the previously measured temperature and humidity, the process proceeds to the next step S304. On the other hand, when the CPU 51 determines that the measured temperature and humidity are not lower than the previously measured temperature and humidity, that is, are the same as the previous temperature and humidity, it ends the third correction process. That is, when the temperature and humidity do not change, the CPU 51 maintains the amplitude value Vpp and the frequency f.

In step S304, the CPU 51 increases the amplitude value Vpp from the current value and adjusts the frequency f to decrease from the current value. Then, the third correction process ends.

(Summary of embodiments)
The image forming apparatus 10 of the present embodiment suppresses deterioration of image quality due to changes in image density, consumable parts conditions, and changes in the image forming environment by changing the characteristics of the AC voltage that constitutes the developing voltage. Specifically, the CPU 51 as a control unit controls the developing power supply 20, adjusts the amplitude value Vpp and the frequency f of the AC voltage according to changes in the image density, and adjusts the state of consumable parts and changes in the image forming environment. Accordingly, the amplitude value Vpp and frequency f of the AC voltage are corrected. In the present embodiment, the amplitude value Vpp and frequency f are corrected according to changes in the state of consumable parts and the image forming environment, and then the amplitude value Vpp and frequency f are adjusted according to changes in image density.

In both cases of this adjustment and correction, the CPU 51 increases the frequency f when the amplitude value Vpp is decreased, and decreases the frequency f when the amplitude value Vpp is increased. As shown in Equation 1 above, the power P in the developing power source 20 is proportional to the square of the amplitude value Vpp of the AC voltage and proportional to the frequency f. Therefore, in this embodiment, by always controlling the amplitude value Vpp and the frequency f in opposite directions, it is possible to suppress an increase in the power P compared to the case where the image quality is controlled only by the amplitude value Vpp of the AC voltage. .

In this embodiment, when the toner charge amount decreases with continuous printing at a high image density and there is a risk of fogging, the CPU 51 reduces the amplitude value Vpp and the frequency f make adjustments to increase As a result, the present embodiment can suppress fogging accompanying an increase in image density with a limited power supply capacity, compared to the case where image quality is controlled only by the amplitude value Vpp of the AC voltage.

Further, in the present embodiment, when the toner charge amount increases with continuous printing at a low image density and there is a risk that the developability may deteriorate, the CPU 51 increases the amplitude value Vpp and increases the frequency Vpp compared to the case of high image density. Adjust to lower f. As a result, the present embodiment can suppress the deterioration of developability due to the decrease in image density with a limited power supply capacity, compared to the case where the image quality is controlled only by the amplitude value Vpp of the AC voltage.

In particular, in the present embodiment, the CPU 51 may adjust the amplitude value Vpp and the frequency f by setting a predetermined value, ie, an upper limit, for the power P. As a result, compared with the case where the image quality is adjusted without limiting the power, it is possible to suppress the deterioration of the image quality due to the adjustment limit of the developing power supply 20 due to the power shortage. According to this embodiment, the capacity of the power supply can be effectively used, and the cost of the development power supply 20 can be suppressed. It should be noted that even if one of the amplitude value Vpp and the frequency f is preferentially changed based on the selection by the user, the toner density of the developer, the charge amount, the image density of the preceding and following images, etc., among the power supply capacities. good.

Further, when the CPU 51 adjusts the amplitude value Vpp and the frequency f of the AC voltage, the adjustment may be made when the image density calculated from the image data exceeds a predetermined threshold, or the calculated image density increases or decreases. You can adjust it from time to time. Furthermore, the CPU 51 of this embodiment adjusts the amplitude value Vpp and the frequency f based on the image density calculated from the image data, but the present invention is not limited to this. For example, the density sensor 66 may detect the toner image formed on the photosensitive drum 22 and the CPU 51 may analyze the image density to adjust the amplitude value Vpp and the frequency f.

Further, in this embodiment, in order to suppress the occurrence of fogging due to a decrease in the amount of charge due to deterioration of the developer, the CPU 51 sets the amplitude value according to the elapsed time after the developer is replaced with new developer in the developing unit 28. Correction is performed to lower Vpp and raise the frequency f. Accordingly, in this embodiment, fogging can be suppressed as compared with the case where correction is not performed according to the deterioration of the developer. On the other hand, when the developing unit 28 is replenished with new developer by replacing the developer, the CPU 51 resets the amplitude value Vpp and the frequency f to initial values.

Note that the CPU 51 of this embodiment corrects the amplitude value Vpp and the frequency f according to the elapsed time after the developing unit 28 is replenished with new developer, but the present invention is not limited to this. For example, the CPU 51 may estimate the toner concentration of the developer from the magnetic permeability detected by the magnetic permeability sensor 68, and the CPU 51 may correct the amplitude value Vpp and the frequency f according to changes in the toner concentration.

Further, in the present embodiment, in order to suppress the occurrence of fogging due to a decrease in the toner charge amount due to a decrease in the thickness of the charge transport layer (CTL) of the photoreceptor drum 22, after the photoreceptor unit is replaced, As the drive time elapses, the CPU 51 performs correction to decrease the amplitude value Vpp and increase the frequency f. Accordingly, in this embodiment, fogging can be suppressed as compared with the case where the correction is not performed according to the passage of the drive time of the photoreceptor drum 22 . On the other hand, when a new photoconductor unit is installed in the developing section 28 by replacing the photoconductor unit, the CPU 51 resets the amplitude value Vpp and the frequency f to initial values.

Although the CPU 51 of this embodiment corrects the amplitude value Vpp and the frequency f according to the driving time after the photosensitive unit is replaced, the present invention is not limited to this. For example, a surface potential sensor (not shown) may be provided adjacent to the photosensitive drum 22, and the CPU 51 may correct the amplitude value Vpp and the frequency f based on the actually measured charge amount.

Further, in the present embodiment, when the toner charge amount decreases with an increase in temperature or humidity and there is a risk of fogging, the CPU 51 lowers the amplitude value Vpp and reduces the frequency f compared to when the temperature or humidity is low. Correction to raise. As a result, the present embodiment can suppress fogging as compared to the case where no correction is performed due to an increase in temperature or humidity.

Furthermore, in the present embodiment, when the toner charge amount increases with a decrease in temperature or humidity, and there is a risk of deteriorating developability, the CPU 51 increases the amplitude value Vpp and increases the frequency f is corrected by lowering the As a result, the present embodiment can suppress deterioration of developability compared to the case where no correction is performed due to a decrease in temperature or humidity.

When changing the amplitude value Vpp and the frequency f, the CPU 51 may change the amplitude value Vpp and the frequency f continuously or stepwise.

Although the image forming apparatus 10 for monochrome printing including one image forming unit 14 has been described in the present embodiment, the image forming apparatus is not limited to this, and may be an image forming apparatus for color printing including a plurality of image forming units. .

REFERENCE SIGNS LIST 10 image forming apparatus 20 power supply for development 22 photoreceptor drum (an example of an image carrier)
28 development section (an example of a development device)
28A development roll (an example of a development member)
70 detection unit 72 measurement unit 74 control unit

Claims (7)

an image carrier on which a latent image is formed;
a developing device that transfers toner from a developing member facing the image carrier to the latent image to form a toner image;
a development power source that applies a development voltage composed of a superimposed voltage obtained by superimposing an AC voltage on a DC voltage between the image carrier and the developing member;
a detection unit that detects the image density of the toner image;
a control unit for controlling the power source for development so that the amplitude value of the AC voltage is decreased and the frequency is increased as the image density increases;
image forming apparatus. The control unit
2. The image forming apparatus according to claim 1, wherein the developing power supply is controlled so that the amplitude value of the AC voltage is increased and the frequency is decreased as the image density decreases. The control unit
3. The image forming apparatus according to claim 2, wherein said amplitude value and said frequency are adjusted so that the power of said developing power supply does not exceed a predetermined value. The control unit
4. The method according to any one of claims 1 to 3, wherein the amplitude value of the AC voltage is decreased and the frequency is increased according to the elapsed time of use after the developer is replaced in the developing device. Image forming device. The control unit
5. The image forming apparatus according to any one of claims 1 to 4, wherein correction is performed to decrease the amplitude value and increase the frequency of the AC voltage in accordance with the lapse of driving time of the image carrier. Further comprising a measurement unit that measures environmental conditions including at least one of temperature and humidity,
The control unit
6. The image forming apparatus according to claim 1, wherein as the temperature or humidity increases, the amplitude value of the AC voltage is decreased and the frequency is increased. The control unit
7. The image forming apparatus according to claim 6, wherein as the temperature or humidity decreases, the amplitude value of the AC voltage is increased and the frequency is decreased.

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