JP2022069075A - Image forming apparatus - Google Patents

Abstract

To accurately obtain a surface potential of an image carrier and shorten the time required for obtaining the surface potential without using an expensive sensor such as a surface potential sensor.SOLUTION: An image forming apparatus 1 comprises: a developing device 64 that develops an electrostatic latent image formed on a photoreceptor drum 65 to form a toner image; an electrifying device 63 that electrifies the photoreceptor drum 65; a developing power supply 648 that applies a predetermined developing bias voltage to the developing device 64; and a calculation unit 647 that calculates a set value of an electrification bias according to the predetermined developing bias voltage based on a developing current flowing in the developing device 64. When the developing power supply 648 applies the predetermined developing bias voltage to the developing device 64, the electrifying device 63 sets a plurality of stages of electrification biases to be applied to the photoreceptor drum 65. A current measuring unit 646 measures a corresponding developing current for each of the plurality of stages of electrification biases.SELECTED DRAWING: Figure 2

Description

The present invention relates to an image forming apparatus.

In an electrophotographic image forming apparatus such as a copying machine or a printer, toner is adhered to an electrostatic latent image formed by exposing the surface of a uniformly charged photoconductor drum (image carrier) to form a toner image. The image forming process of developing the image is widely used. In order to obtain a high-quality image, it is required to perform development with a development bias provided with an appropriate potential difference with respect to the surface potential of the photoconductor drum.

Therefore, it is necessary to detect the actual surface potential of the photoconductor drum when forming an image, and conventionally, the surface potential of the photoconductor drum has been detected by using a surface potential sensor.

However, the surface potential sensor is expensive, and if scattered toner or the like adheres to the surface potential sensor, there is a problem that accurate measurement cannot be performed. Therefore, a technique for obtaining the surface potential of the photoconductor drum without using an expensive sensor such as a surface potential sensor has been proposed, and an example thereof is disclosed in Patent Document 1.

The electrophotographic apparatus of Patent Document 1 forms a pulsed electrostatic potential pattern on the photoconductor, applies a bias to the developing roller, and applies a current flowing from the photoconductor to the developing roller when developing the electrostatic potential pattern. The surface potential on the photoconductor is obtained by measurement. Specifically, the surface potential of the photoconductor is estimated by monitoring the current at the switching point of the pulsed electrostatic potential pattern. Thereby, the surface potential on the photoconductor can be obtained without using the surface potential sensor.

Japanese Patent Application Laid-Open No. 2003-295540

The problem is that the current monitored by the electrophotographic apparatus disclosed in Patent Document 1 is easily affected by aging of the photoconductor, the charging member, and the like, is unstable, and easily contains an error. As a result, there is concern that the accuracy of the surface potential on the photoconductor will decrease.

The present invention has been made in view of the above problems, and an object thereof is required to obtain the surface potential of the image carrier with high accuracy and to obtain the surface potential without using an expensive sensor such as a surface potential sensor. An object of the present invention is to provide an image forming apparatus capable of shortening the time.

The image forming apparatus according to the present invention includes an image carrier, a charging device, a developing device, a developing power source, a current measuring unit, and a calculating unit. An electrostatic latent image is formed on the surface of the image carrier. The charging device applies a charging bias to the image carrier to charge the image carrier. The developing device supplies toner to the image carrier and develops the electrostatic latent image formed on the image carrier to form a toner image. The developing power supply applies a predetermined development bias voltage to the developing apparatus. The current measuring unit measures the developing current flowing through the developing device. The calculation unit calculates the setting value of the charging bias according to the predetermined development bias voltage based on the development current measured by the current measurement unit. The charging device sets a plurality of stages of the charging bias applied to the image carrier when the developing power source applies a predetermined development bias voltage to the developing device. The current measuring unit measures the corresponding developing current for each of the plurality of stages of the charging bias.

According to the present invention, it is possible to obtain the surface potential of the image carrier with high accuracy and shorten the time required to obtain the surface potential without using an expensive sensor such as a surface potential sensor.

It is a figure which shows an example of the structure of the image forming apparatus 1. It is a figure which shows an example of the structure of the developing apparatus 64. It is a figure which shows the development current measured by the current measuring part 646. It is a figure which shows the development current measured by the current measuring part 646. It is a graph which shows the correspondence relationship between the development current and the development bias voltage. It is a graph which shows the charging characteristic of the image forming apparatus 1. It is a graph which shows the relationship between a development current and a charge bias. It is a flowchart which shows the charge bias setting process which concerns on this embodiment. It is a table which shows the development current measured when the charge bias of 4 steps was applied to the photoconductor drum 65 in the image forming apparatus 1 which concerns on this Example. It is a graph which shows the relationship between the charge bias and the development current shown in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the figure, the same or corresponding parts are designated by the same reference numerals and the description is not repeated.

The configuration of the image forming apparatus 1 according to the embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing an example of the configuration of the image forming apparatus 1. The image forming apparatus 1 is, for example, a tandem color printer.

As shown in FIG. 1, the image forming apparatus 1 includes an operation unit 2, a paper feeding unit 3, a transport unit 4, a toner supply unit 5, an image forming unit 6, a transfer unit 7, a fixing unit 8, a fixing unit 9, and a control unit. A unit 10 is provided.

The operation unit 2 receives an instruction from the user. When the operation unit 2 receives an instruction from the user, the operation unit 2 transmits a signal indicating the instruction from the user to the control unit 10. The operation unit 2 includes a liquid crystal display 21 and a plurality of operation keys 22. The liquid crystal display 21 displays, for example, various processing results. The operation key 22 includes, for example, a numeric keypad and a start key. When an instruction indicating the execution of the image forming process is input, the operation unit 2 transmits a signal indicating the execution of the image forming process to the control unit 10. As a result, the image forming operation by the image forming apparatus 1 is started.

The paper feed unit 3 has a paper feed cassette 31 and a paper feed roller group 32. The paper cassette 31 can accommodate a plurality of sheets P. The paper feed roller group 32 feeds the paper P stored in the paper feed cassette 31 one by one to the transport unit 4. Paper P is an example of a recording medium.

The transport unit 4 includes a roller and a guide member. The transport unit 4 extends from the paper feed unit 3 to the discharge unit 9. The transport unit 4 transports the paper P from the paper feed unit 3 to the discharge unit 9 so as to pass through the image forming unit 6 and the fixing unit 8.

The toner supply unit 5 replenishes the image forming unit 6 with toner. The toner supply unit 5 includes a first mounting unit 51Y, a second mounting unit 51C, a third mounting unit 51M, and a fourth mounting unit 51K. The toner supply unit 5 is an example of a developer supply unit. Toner is an example of a developer.

The first toner container 52Y is mounted on the first mounting portion 51Y. Similarly, the second toner container 52C is mounted on the second mounting portion 51C, the third toner container 52M is mounted on the third mounting portion 51M, and the fourth toner container 52K is mounted on the fourth mounting portion 51K. The configurations of the first mounting portion 51Y to the fourth mounting portion 51K are the same except for the type of the toner container to be mounted. Therefore, the first mounting portion 51Y to the fourth mounting portion 51K may be collectively referred to as "mounting portion 51".

Toner is contained in the first toner container 52Y, the second toner container 52C, the third toner container 52M, and the fourth toner container 52K, respectively. In the present embodiment, the first toner container 52Y contains the yellow toner. Cyan toner is stored in the second toner container 52C. Magenta toner is housed in the third toner container 52M. Black toner is stored in the fourth toner container 52K.

The image forming unit 6 includes an exposure device 61, a first image forming unit 62Y, a second image forming unit 62C, a third image forming unit 62M, and a fourth image forming unit 62K.

Each of the first image forming unit 62Y to the fourth image forming unit 62K has a charging device 63, a developing device 64, and a photoconductor drum 65. The photoconductor drum 65 is an example of an image carrier.

The charging device 63 and the developing device 64 are arranged along the peripheral surface of the photoconductor drum 65. In the present embodiment, the photoconductor drum 65 rotates in the direction (clockwise) indicated by the arrow R1 in FIG.

The charging device 63 uniformly charges the photoconductor drum 65 to a predetermined polarity by electric discharge. In the present embodiment, the charging device 63 charges the photoconductor drum 65 to a positive polarity. The exposure apparatus 61 irradiates the charged photoconductor drum 65 with laser light. As a result, an electrostatic latent image is formed on the surface of the photoconductor drum 65.

The developing apparatus 64 develops an electrostatic latent image formed on the surface of the photoconductor drum 65 to form a toner image. In the developing device 64, toner is replenished from the toner replenishing unit 5. The developing device 64 supplies the toner replenished from the toner replenishing unit 5 to the surface of the photoconductor drum 65. As a result, a toner image is formed on the surface of the photoconductor drum 65.

In the present embodiment, the developing device 64 included in the first image forming unit 62Y is connected to the first mounting portion 51Y. Therefore, the developing apparatus 64 included in the first image forming unit 62Y is replenished with yellow toner. Therefore, a yellow toner image is formed on the surface of the photoconductor drum 65 included in the first image forming unit 62Y.

The developing device 64 included in the second image forming unit 62C is connected to the second mounting portion 51C. Therefore, cyan toner is replenished to the developing device 64 included in the second image forming unit 62C. Therefore, a cyan toner image is formed on the surface of the photoconductor drum 65 included in the second image forming unit 62C.

The developing device 64 included in the third image forming unit 62M is connected to the third mounting portion 51M. Therefore, the magenta toner is replenished to the developing device 64 included in the third image forming unit 62M. Therefore, a magenta toner image is formed on the surface of the photoconductor drum 65 included in the third image forming unit 62M.

The developing device 64 included in the fourth image forming unit 62K is connected to the fourth mounting portion 51K. Therefore, black toner is replenished to the developing device 64 included in the fourth image forming unit 62K. Therefore, a black toner image is formed on the surface of the photoconductor drum 65 included in the fourth image forming unit 62K.

The transfer unit 7 superimposes and transfers each toner image formed on the surface of each photoconductor drum 65 included in the first image forming unit 62Y to the fourth image forming unit 62K on the paper P. In the present embodiment, the transfer unit 7 superimposes and transfers each toner image on the paper P by a secondary transfer method. Specifically, the transfer unit 7 has four primary transfer rollers 71, an intermediate transfer belt 72, a drive roller 73, a driven roller 74, a secondary transfer roller 75, and a density sensor 76.

The intermediate transfer belt 72 is an endless belt stretched on four primary transfer rollers 71, a drive roller 73, and a driven roller 74. The intermediate transfer belt 72 is driven according to the rotation of the drive roller 73. In FIG. 1, the intermediate transfer belt 72 orbits counterclockwise. The driven roller 74 is rotationally driven in response to the drive of the intermediate transfer belt 72.

The first image forming unit 62Y to the fourth image forming unit 62K are arranged along the driving direction D of the lower surface of the intermediate transfer belt 72 so as to face the lower surface of the intermediate transfer belt 72. In the present embodiment, the first image forming unit 62Y to the fourth image forming unit 62K form the first image forming unit 62Y to the fourth image forming unit 62Y to the fourth image forming unit from the upstream side to the downstream side of the drive direction D of the lower surface of the intermediate transfer belt 72. Units 62K are arranged in this order.

Each primary transfer roller 71 is arranged facing each photoconductor drum 65 via an intermediate transfer belt 72, and is pressed toward each photoconductor drum 65. Therefore, the toner image formed on the surface of each photoconductor drum 65 is sequentially transferred to the intermediate transfer belt 72. In the present embodiment, the yellow toner image, the cyan toner image, the magenta toner image, and the black toner image are superimposed and transferred to the intermediate transfer belt 72 in this order. Hereinafter, a toner image in which a yellow toner image, a cyan toner image, a magenta toner image, and a black toner image are superimposed may be referred to as a “laminated toner image”.

The secondary transfer roller 75 is arranged to face the drive roller 73 via the intermediate transfer belt 72. The secondary transfer roller 75 is pressed toward the drive roller 73. As a result, a transfer nip is formed between the secondary transfer roller 75 and the drive roller 73. When the paper P passes through the transfer nip, the laminated toner image on the intermediate transfer belt 72 is transferred to the paper P. In the present embodiment, the yellow toner image, the cyan toner image, the magenta toner image, and the black toner image are transferred to the paper P in this order from the upper layer to the lower layer. The paper P on which the laminated toner image is transferred is conveyed toward the fixing portion 8 by the conveying portion 4.

The density sensor 76 is arranged on the downstream side of the first image forming unit 62Y to the fourth image forming unit 62K so as to face the intermediate transfer belt 72, and the density of the laminated toner image formed on the photoconductor drum 65. To measure. The density sensor 76 may measure the density of the laminated toner image on the intermediate transfer belt 72, or may measure the density of the toner image fixed on the paper P.

The fixing portion 8 includes a heating member 81 and a pressurizing member 82. The heating member 81 and the pressurizing member 82 are arranged so as to face each other and form a fixing nip. The paper P conveyed from the image forming unit 6 is pressurized while being heated at a predetermined fixing temperature by passing through the fixing nip. As a result, the laminated toner image is fixed on the paper P. The paper P is conveyed from the fixing unit 8 to the discharging unit 9 by the conveying unit 4.

The discharge unit 9 has a discharge roller pair 91 and a discharge tray 93. The discharge roller pair 91 conveys the paper P to the discharge tray 93 via the discharge port 92. The discharge port 92 is formed on the upper part of the image forming apparatus 1.

The control unit 10 controls the operation of each unit included in the image forming apparatus 1. The control unit 10 includes a processor 11 and a storage unit 12. The processor 11 includes, for example, a CPU (Central Processing Unit). The storage unit 12 includes a memory such as a semiconductor memory, and may include an HDD (Hard Disk Drive). The storage unit 12 stores the control program. The processor 11 controls the operation of the image forming apparatus 1 by executing a control program.

Next, the configuration of the developing apparatus 64 will be described in detail with reference to FIG. FIG. 2 is a diagram showing an example of the configuration of the developing device 64. Specifically, FIG. 2 shows a first developing device 64Y included in the first image forming unit 62Y. In FIG. 2, the photoconductor drum 65 is shown by a two-dot chain line for easy understanding. In the present embodiment, the first developing apparatus 64Y develops an electrostatic latent image formed on the surface of the photoconductor drum 65 by a two-component developing method. As already described with reference to FIG. 1, the developing container 640 of the first developing device 64Y is connected to the first toner container 52Y. Therefore, yellow toner is replenished to the developing container 640 of the first developing device 64Y via the toner replenishing port 640h.

As shown in FIG. 2, the first developing apparatus 64Y has a developing roller 641, a first stirring screw 643, a second stirring screw 644, and a blade 645 inside the developing container 640. Specifically, the developing roller 641 is arranged to face the second stirring screw 644. The blade 645 is arranged to face the developing roller 641.

The developing container 640 is divided into a first stirring chamber 640a and a second stirring chamber 640b by a partition wall 640c. The partition wall 640c extends in the axial direction of the developing roller 641. The first stirring chamber 640a and the second stirring chamber 640b communicate with each other at both ends in the longitudinal direction of the partition wall 640c.

A first stirring screw 643 is arranged in the first stirring chamber 640a. A magnetic carrier is housed in the first stirring chamber 640a. Non-magnetic toner is replenished to the first stirring chamber 640a via the toner replenishment port 640h. In the example shown in FIG. 2, the first stirring chamber 640a is replenished with yellow toner.

A second stirring screw 644 is arranged in the second stirring chamber 640b. The carrier of the magnetic material is housed in the second stirring chamber 640b.

The yellow toner is stirred by the first stirring screw 643 and the second stirring screw 644 and mixed with the carrier. As a result, a two-component developer composed of a carrier and yellow toner is formed. Since the two-component developer is an example of a developer, it may be abbreviated as "developer" below.

The first stirring screw 643 and the second stirring screw 644 circulate the developer between the first stirring chamber 640a and the second stirring chamber 640b to stir. As a result, the toner is charged to a predetermined polarity. In this embodiment, the toner is charged to a positive polarity.

The developing roller 641 is composed of a non-magnetic rotary sleeve 641a and a magnet body 641b. The magnet body 641b is fixedly arranged inside the rotary sleeve 641a. The magnet body 641b includes a plurality of magnetic poles. The developer is attracted to the developing roller 641 by the magnetic force of the magnet body 641b. As a result, a magnetic brush is formed on the surface of the developing roller 641.

In this embodiment, the developing roller 641 rotates in the direction indicated by the arrow R2 (counterclockwise) in FIG. The developing roller 641 rotates to convey the magnetic brush to a position facing the blade 645. The blade 645 is arranged so as to form a gap with the developing roller 641. Therefore, the thickness of the magnetic brush is defined by the blade 645. The blade 645 is arranged on the upstream side in the rotational direction of the magnetic roller 642 with respect to the position where the developing roller 641 and the photoconductor drum 65 face each other.

A predetermined voltage is applied to the developing roller 641. As a result, the developer layer formed on the surface is conveyed to a position facing the photoconductor drum 65, and the toner in the developer is adhered to the photoconductor drum 65.

Specifically, the first developing device 64Y further includes a current measuring unit 646, a calculating unit 647, and a developing power supply 648.

The current measuring unit 646 is connected, for example, between the developing power supply 648 and the developing roller 641. The developing power supply 648 applies a predetermined development bias voltage to the developing roller 641 of the first developing apparatus 64Y. The current measuring unit 646 detects the developing current flowing between the first developing apparatus 64Y and the photoconductor drum 65 and the developing roller 641 according to the developing bias voltage applied by the developing power source 648. The current measuring unit 646 includes, for example, an ammeter and measures the current value of the developing current.

Next, the developing current flowing through the first developing apparatus 64Y will be described with reference to FIGS. 3A and 3B. 3A and 3B are diagrams showing the developing current measured by the current measuring unit 646.

For example, the current measuring unit 646 measures the current value of the developing current while the first developing device 64Y develops the electrostatic latent image formed on the surface of the photoconductor drum 65.

In the present embodiment, when an instruction indicating the execution of the image forming process by the user is input to the image forming apparatus 1, the control unit 10 causes the image forming unit 6 to start the image forming operation in each portion included in the image forming apparatus 1. To control. Specifically, the control unit 10 controls the charging device 63, the first developing device 64Y, the developing power supply 648, and the exposure device 61.

The charging device 63 charges the surface of the photoconductor drum 65 to a predetermined charging potential (surface potential V0) under the control of the control unit 10. Specifically, when the charging device 63 applies the charging bias V1 to the photoconductor drum 65, the surface of the photoconductor drum 65 is charged to the surface potential V0.

The developing power supply 648 applies a developing bias voltage to the developing roller 641 under the control of the control unit 10. The development bias voltage includes a DC component and an AC component. FIG. 3A shows a case where a development bias voltage having a DC component magnitude (Vdc1) smaller than the surface potential V0 is applied to the developing roller 641. The development bias voltage does not have to include an AC component.

The exposure device 61 irradiates the photoconductor drum 65 charged with the surface potential V0 by the charging device 63 with laser light under the control of the control unit 10. As a result, an electrostatic latent image is formed on the surface of the photoconductor drum 65.

When the electrostatic latent image is formed on the surface of the photoconductor drum 65, the first developing apparatus 64Y develops the electrostatic latent image formed on the surface of the photoconductor drum 65 under the control of the control unit 10.

At this time, the current measuring unit 646 measures the current value of the developing current. In FIG. 3A, the developing current Id1 flows from the photoconductor drum 65 through the current flowing when the toner in the magnetic brush formed on the developing roller 641 moves to the developing roller 641 and the magnetic brush formed on the developing roller 641. This is the combined current with the current Ia1.

On the other hand, FIG. 3B shows a case where a development bias voltage having a DC component magnitude (Vdc2) larger than the surface potential V0 is applied to the developing roller 641. In FIG. 3B, the development current Id2 is a combination of the current Ia2 that flows when the toner is developed on the photoconductor drum 65 and the current that flows to the photoconductor drum 65 through the magnetic brush formed on the developing roller 641. ..

As described above, the direction of the development current measured by the current measuring unit 646 is opposite to that when the DC component of the development bias voltage is larger than the surface potential V0 and when the DC component of the development bias voltage is smaller than the surface potential V0. Become.

When the DC component of the development bias voltage is equal to the surface potential V0, the development electric field strength becomes zero and the magnitude of the development current indicates zero. From this, it can be predicted that the DC component of the development bias voltage when the magnitude of the development current becomes zero is the surface potential V0.

Next, the calculation of the surface potential will be described with reference to FIGS. 3 and 4. FIG. 4 is a graph showing the correspondence between the development current and the development bias voltage. In FIG. 4, the vertical axis shows the developing current and the horizontal axis shows the developing bias voltage.

For example, the developing power supply 648 applies a developing bias voltage Vdc1 to the developing roller 641. At this time, the current measuring unit 646 measures the current value of the developing current Id1. The calculation unit 647 acquires the development bias voltage Vdc1 applied by the development power supply 648 and the current value of the development current Id1 measured by the current measurement unit 646 (FIG. 3A).

Further, the developing power supply 648 applies the developing bias voltage Vdc2 to the developing roller 641. At this time, the current measuring unit 646 measures the current value of the developing current Id2. The calculation unit 647 acquires the development bias voltage Vdc2 applied by the development power supply 648 and the current value of the development current Id2 measured by the current measurement unit 646 (FIG. 3B).

The calculation unit 647 calculates the development bias voltage at which the development current does not flow as the surface potential V0 based on the acquired development bias voltage Vdc1 and development current Id1 and the development bias voltage Vdc2 and development current Id2.

In the present embodiment, the configurations of the developing apparatus 64 included in each of the first image forming unit 62Y to the fourth image forming unit 62K differ only in the type of toner supplied from the toner supply unit 5, and the other configurations are omitted. The same is true. Therefore, the description of the configuration of the second developing device 64C to the fourth developing device 64K included in the second image forming unit 62C to the fourth image forming unit 62K will be omitted.

For example, the control unit 10 determines the development bias voltage Vdc applied to the development roller 641 by the development power supply 648 based on the surface potential V0 calculated by the calculation unit 647.

As a result, when developing an electrostatic latent image, a development bias voltage provided with an appropriate potential difference can be applied to the developing roller 641, and a higher quality image can be formed.

In such calculation of the surface potential, for example, the image forming unit 6 is controlled so that the control unit 10 starts the image forming operation after an instruction indicating the execution of the image forming process is input to the image forming apparatus 1 by the user. It is done before.

By calculating the surface potential corresponding to a plurality of charging biases by using the above method, the correspondence relationship (charging characteristics) between the charging bias and the surface potential can be obtained.

Next, the charging characteristics of the image forming apparatus 1 in the present embodiment will be described with reference to FIGS. 3A to 5. FIG. 5 is a graph showing the charging characteristics of the image forming apparatus 1. In FIG. 5, the vertical axis shows the surface potential and the horizontal axis shows the charging bias.

For example, the charging device 63 applies the charging biases V1A, V1B, and V1C to the photoconductor drum 65 instead of the charging bias V1, and the calculation unit 647 calculates the surface potential for each charging bias. When this is done, the surface potentials V0A, V0B, and V0C are calculated.

Based on the charging characteristics calculated in this way, the control unit 10 sets the charging bias applied by the charging device 63 during the image forming process. For example, when the surface of the photoconductor drum 65 is charged to the surface potential V0X, the control unit 10 sets the charging bias applied by the charging device 63 to the charging bias V1X. By calculating the charging characteristics in this way, it is possible to set the surface potential to be set at the time of image formation.

However, in the above method, in order to obtain the charging characteristics, it is necessary to apply a developing bias voltage to the developing roller 641 in a plurality of steps for each of a plurality of charging biases to measure the developing current, and set the desired surface potential. It takes time.

On the other hand, in the present embodiment, the required time is shortened by using the following method.

In the present embodiment, it is assumed that the surface potential to be set at the time of image formation is the surface potential V0X. For example, when an instruction indicating execution of the image forming process is input to the image forming apparatus 1 by the user, the control unit 10 applies a developing bias voltage VdcX having the same magnitude as the surface potential V0X to the developing roller 641. Controls 648. Further, the control unit 10 controls the calculation unit 647 to calculate the set value of the charge bias according to the development bias voltage VdcX.

For example, the control unit 10 controls the charging device 63 so as to apply a charging bias V1A to the photoconductor drum 65 to charge the surface of the photoconductor drum 65 to the surface potential V0A. At this time, the current measuring unit 646 measures the developing current IdA. The control unit 10 determines, for example, the charging bias V1A to be applied so that the surface potential V0A is smaller than the surface potential V0X.

The calculation unit 647 acquires the current value of the development current IdA measured by the current measurement unit 646. Further, the calculation unit 647 acquires the charging bias V1A applied by the charging device 63.

Next, the control unit 10 controls the charging device 63 so as to apply a charging bias V1B to the photoconductor drum 65 to charge the surface of the photoconductor drum 65 to the surface potential V0B. At this time, the current measuring unit 646 measures the developing current IdB. The control unit 10 determines, for example, the charging bias V1B to be applied so that the surface potential V0B becomes larger than the surface potential V0X.

The calculation unit 647 acquires the current value of the development current IdB measured by the current measurement unit 646. Further, the calculation unit 647 acquires the charging bias V1B applied by the charging device 63.

Next, with reference to FIGS. 3A to 6, the relationship between the developed currents IdA and IdB and the calculated charging biases V1A and V1B will be described. FIG. 6 is a graph showing the relationship between the developing current and the charging bias. In FIG. 6, the vertical axis shows the developing current and the horizontal axis shows the charging bias.

The calculation unit 647 calculates the charging bias V1X when the developing current stops flowing, based on the acquired charging bias V1A and the developing current IdA, and the charging bias V1B and the developing current Idb.

In this way, by fixing the development bias voltage and changing the charge bias to calculate the charge bias V1X when the development current stops flowing, the calculation of the charge characteristics is omitted and the desired surface potential is set. Time can be shortened.

In the present embodiment, two charging biases V1A and V1B are used to calculate the charging bias V1X, but the present invention is not limited to this, and three or more charging biases may be used. As the number of charge biases used increases, the accuracy of the calculated charge bias V1X increases, but the required time also increases.

Further, since the charging characteristics of the photoconductor drum 65 change depending on the usage environment, film thickness, transfer bias, roller resistance of the charging device 63, etc., if the setting value and number of charging biases are set according to the charging characteristics, the charging bias V1X Can be calculated with high accuracy.

Next, the charge bias setting process according to the present embodiment will be described with reference to FIG. 7. FIG. 7 is a flowchart showing the charge bias setting process according to the present embodiment.

First, when an instruction indicating the execution of the image forming process by the user is input to the image forming apparatus 1 (step S11), the control unit 10 applies a developing bias voltage VdcX having the same magnitude as the desired surface potential V0X to the developing roller 641. The developing power supply 648 is controlled so as to be applied to (step S12).

The control unit 10 controls the charging device 63 so as to set a predetermined charging bias and apply it to the photoconductor drum 65 (step S13). The current measuring unit 646 measures the developing current (step S14).

The control unit 10 determines whether or not the charging bias V1X can be calculated when the developing current stops flowing (step S15). When the development current sufficient for the calculation of the charge bias V1X by the calculation unit 647 is not measured (No in step S15), the control unit 10 applies a different charge bias to the photoconductor drum 65. 63 is controlled (step S13).

On the other hand, the control unit 10 controls the calculation unit 647 to calculate the charge bias V1X when a development current sufficient for the calculation unit 647 to calculate the charge bias V1X is measured (Yes in step S15). (Step S16).

The control unit 10 sets the charge bias V1X calculated by the calculation unit 647 (step S17), and executes the image formation process (step S18).

In the present embodiment, for example, when the calculated charge bias V1X differs from the previous calculation result by a predetermined reference value or more, the calculation unit 647 determines that the charge bias V1X is a measurement error. In this case, the calculation unit 647 may recalculate the charge bias V1X, or may use the previous calculation result as the charge bias V1X.

Further, in the present embodiment, the calculation unit 647 is configured to calculate the charging bias when the developing current stops flowing, but the present invention is not limited to this, and the developing current flowing when the surface of the photoconductor drum 65 is not charged. You may calculate the charge bias when the development current of the same magnitude as the above flows.

In the present embodiment, the calculation of the surface potential is not limited to before the execution of the image forming process, but may be performed after or during the execution of the image forming process. Further, for example, according to an instruction input from the user, only the surface potential may be calculated without executing the image forming process.

Next, the present invention will be specifically described based on examples, but the present invention is not limited to the following examples.

In the embodiment of the present invention, a multifunction device was used as the image forming apparatus 1. The multifunction device was a modified TASKalfa2550Ci (Kyocera Document Solutions Co., Ltd.).

The experimental conditions of the multifunction device were as follows.
・ Photoreceptor drum 65: Amorphous silicon (a—Si) drum ・ Film thickness of photoconductor drum 65: 20 μm
-Charging device 63: Outer diameter of the core metal of the charging roller 6 mm, rubber wall thickness 3 mm, rubber resistance 6.0 LogΩ
-Charging bias: DC and AC, Vpp1000V, frequency 3kHz
-Blade 645: SUS430, magnetic blade 645 thickness: 1.5 mm
・ Surface shape of developing roller 641: knurling + blasting ・ Outer diameter of developing roller 641: 20 mm
・ Recessed portions of the developing roller 641: 80 rows in the circumferential direction ・ Peripheral speed of the developing roller 641 / peripheral speed of the photoconductor drum 65: 1.8
Distance between the developing roller 641 and the photoconductor drum 65: 0.30 mm
-AC component of development bias voltage: Vpp1200V, duty50%, square wave, 8kHz
-Toner: Particle diameter 6.8 μm, Positive chargeability-Carrier: Particle diameter 38 μm, Ferrite-Resin coat carrier-Toner concentration: 6%
・ Print speed: 55 sheets / minute ・ DC component setting of development bias voltage: 250V

Next, the surface potential calculated in the image forming apparatus 1 according to the present embodiment will be described with reference to FIGS. 8 and 9.

FIG. 8 is a table showing the development currents measured when a four-step charging bias is applied to the photoconductor drum 65 in the image forming apparatus 1 according to the present embodiment.

FIG. 9 is a graph showing the relationship between the charging bias shown in FIG. 8 and the developing current. In FIG. 7, the vertical axis shows the developing current and the horizontal axis shows the charging bias.

In this embodiment, when a charging bias of 280 [V] is applied, the measured development current is 1.8 [μA]. When a charging bias of 320 [V] is applied, the measured development current is 0.5 [μA]. When a charging bias of 360 [V] is applied, the measured development current is −0.4 [μA]. When a charging bias of 400 [V] is applied, the measured development current is −1.26 [μA].

As shown in FIG. 9, in the image forming apparatus 1 according to the present embodiment, the charging bias when the developing current stops flowing is calculated as 347 [V].

Further, in this embodiment, the photoconductor drum 65 is an amorphous silicon drum, but the present invention is not limited to this, and a positively charged organic photoconductor drum may be used. When an amorphous silicon drum is used for the photoconductor drum 65, the dielectric constant of the photosensitive layer is higher than that of the positively charged organic photoconductor drum, current easily flows, and the carrier resistance value is small, so that the measurement accuracy is high. Become.

Further, in this embodiment, the two-component developer is used, but the present invention is not limited to this, and a one-component developer may be used.

The embodiments of the present invention have been described above with reference to the drawings (FIGS. 1 to 9). However, the present invention is not limited to the above embodiment, and can be implemented in various embodiments without departing from the gist thereof. The drawings are schematically shown mainly for each component for easy understanding, and the thickness, length, number, etc. of each of the illustrated components are different from the actual ones for the convenience of drawing creation. .. Further, the material, shape, dimensions, etc. of each component shown in the above embodiment are merely examples, and are not particularly limited, and various changes can be made without substantially deviating from the effects of the present invention. be.

The present invention can be used in the field of image forming apparatus.

1: Image forming device 10: Control unit 63: Charging device 64: Developing device 65: Photoconductor drum 641: Developing roller 646: Current measuring unit 647: Calculation unit 648: Developing power supply Id1, Id2, IdA, IdB: Developing current V0 , V0A, V0B, V0X: Surface potential V1, V1A, V1B, V1X: Charging bias Vdc, Vdc1, Vdc2, VdcX: Development bias voltage

Claims (4)

An image carrier on which an electrostatic latent image is formed on the surface,
A charging device that applies a charging bias to the image carrier to charge the image carrier, and
A developing device that supplies toner to the image carrier and develops the electrostatic latent image formed on the image carrier to form a toner image.
A developing power supply that applies a predetermined development bias voltage to the developing device, and
A current measuring unit that measures the developing current flowing through the developing device,
A calculation unit for calculating a set value of the charging bias according to the predetermined development bias voltage based on the development current measured by the current measurement unit is provided.
The charging device sets the charging bias in a plurality of stages to be applied to the image carrier when the developing power supply applies a predetermined development bias voltage to the developing device.
The current measuring unit is an image forming apparatus that measures the corresponding developing current for each of the plurality of stages of the charging bias. The image forming apparatus according to claim 1, wherein the calculation unit calculates a set value of the charge bias when the development current stops flowing, based on the development current corresponding to each charge bias. The current measuring unit measures the uncharged developing current flowing through the developing device in an uncharged state in which the charging device does not charge the image carrier.
The calculation unit according to claim 1 or 2, wherein the calculation unit calculates the charge bias when the development current equal to the uncharged development current flows based on the development current corresponding to each charge bias. Image forming device. The plurality of stages of the charging bias are such that the surface potential of the image carrier is larger than the predetermined development bias voltage, and the surface potential of the image carrier is smaller than the predetermined development bias voltage. The image forming apparatus according to any one of claims 1 to 3, comprising the charging bias as described above.

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