JP7547929B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming device.

In electrophotographic image forming devices such as copiers and printers, an image formation process is widely used in which toner is attached to an electrostatic latent image formed by exposing the surface of a uniformly charged photosensitive drum (image carrier) to light, and then developed into a toner image. To obtain high-quality images, development is required using a development bias with an appropriate potential difference relative to the surface potential of the photosensitive drum.

For this reason, it is necessary to detect the actual surface potential of the photosensitive drum when forming an image, and conventionally, a surface potential sensor is used to detect the surface potential of the photosensitive drum.

However, surface potential sensors are expensive, and if scattered toner or the like adheres to them, they cannot be measured correctly. Therefore, technology has been proposed to obtain the surface potential of a photoconductor drum without using an expensive sensor such as a surface potential sensor, and one example of this is disclosed in Patent Document 1.

The electrophotographic device of Patent Document 1 forms a pulsed electrostatic potential pattern on the photoconductor, applies a bias to the developing roller, and measures the current flowing from the photoconductor to the developing roller when developing the electrostatic potential pattern to obtain the surface potential on the photoconductor. Specifically, the surface potential of the photoconductor is estimated by monitoring the current at the point where the pulsed electrostatic potential pattern switches. This makes it possible to obtain the surface potential on the photoconductor without using a surface potential sensor.

JP 2003-295540 A

The current monitored by the electrophotographic device disclosed in Patent Document 1 was unstable and prone to error, and was easily affected by changes over time in the photoconductor and charging member. This raised concerns that the accuracy of the surface potential on the photoconductor would decrease.

The present invention was made in consideration of the above problems, and its purpose is to provide an image forming apparatus that can obtain the surface potential of an image carrier with high precision without using expensive sensors such as surface potential sensors.

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 calculation unit. An electrostatic latent image is formed on the surface of the image carrier. The charging device charges 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 source applies a predetermined bias voltage to the developing device. The current measuring unit measures the developing current flowing through the developing device. The calculation unit calculates the surface potential of the image carrier based on the developing current measured by the current measuring unit. The current measuring unit measures the non-charged developing current flowing through the developing device in a non-charged state in which the charging device does not charge the image carrier. The current measuring unit measures the charged developing current flowing through the developing device in a charged state in which the charging device charges the image carrier. The calculation unit calculates the bias voltage when the charged developing current is equal to the non-charged developing current as the surface potential.

According to the present invention, it is possible to obtain the surface potential of the image carrier with high accuracy without using expensive sensors such as surface potential sensors.

FIG. 1 illustrates an example of a configuration of an image forming apparatus. FIG. 2 is a diagram showing an example of the configuration of a developing device 64. 13 is a diagram showing the development current measured by a current measuring unit 646. FIG. 13 is a diagram showing the development current measured by a current measuring unit 646. FIG. 13 is a diagram showing a non-charging development current measured by a current measuring unit 646. FIG. 13 is a diagram showing a charging and developing current measured by a current measuring unit 646. FIG. 13 is a diagram showing a charging and developing current measured by a current measuring unit 646. FIG. 1 is a graph showing the relationship between a development current and a bias voltage. The surface potential calculation process according to this embodiment will be described. This is a table showing the measured non-charged developing current and the measured charged developing current when four levels of bias voltage are applied to the developing roller 641 with a charging bias of 900 V in the image forming apparatus 1 of this embodiment. 9 is a graph showing the relationship between the bias voltage shown in FIG. 8 and the non-charging developing current and the charging developing current.

The following describes an embodiment of the present invention with reference to the drawings. Note that in the drawings, the same or corresponding parts are designated by the same reference symbols and will not be described repeatedly.

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

As shown in FIG. 1, the image forming device 1 includes an operation unit 2, a paper feed 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 discharge unit 9, and a control unit 10.

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

The paper feed unit 3 has a paper feed cassette 31 and a paper feed roller group 32. The paper feed cassette 31 can store multiple sheets of paper P. The paper feed roller group 32 feeds the paper P stored in the paper feed cassette 31 one sheet at a time to the transport unit 4. The paper P is an example of a recording medium.

The transport unit 4 includes rollers and guide members. 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, passing through the image forming unit 6 and the fixing unit 8.

The toner supply unit 5 supplies toner to the image forming unit 6. 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. The toner is an example of a developer.

The first toner container 52Y is attached to the first mounting section 51Y. Similarly, the second toner container 52C is attached to the second mounting section 51C, the third toner container 52M is attached to the third mounting section 51M, and the fourth toner container 52K is attached to the fourth mounting section 51K. The first mounting section 51Y to the fourth mounting section 51K are configured similarly except for the type of toner container that is attached. For this reason, the first mounting section 51Y to the fourth mounting section 51K may be collectively referred to as the "mounting section 51."

The first toner container 52Y, the second toner container 52C, the third toner container 52M, and the fourth toner container 52K each contain toner. In this embodiment, the first toner container 52Y contains yellow toner. The second toner container 52C contains cyan toner. The third toner container 52M contains magenta toner. The fourth toner container 52K contains black toner.

The image forming section 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 circumferential surface of the photosensitive drum 65. In this embodiment, the photosensitive drum 65 rotates in the direction indicated by the arrow R1 in FIG. 1 (clockwise).

The charging device 63 uniformly charges the photoconductor drum 65 to a predetermined polarity by discharging. In this embodiment, the charging device 63 charges the photoconductor drum 65 to a positive polarity. The exposure device 61 irradiates the charged photoconductor drum 65 with laser light. This forms an electrostatic latent image on the surface of the photoconductor drum 65.

The developing device 64 develops the electrostatic latent image formed on the surface of the photosensitive drum 65 to form a toner image. The developing device 64 receives toner from the toner supply unit 5. The developing device 64 supplies the toner supplied from the toner supply unit 5 to the surface of the photosensitive drum 65. As a result, a toner image is formed on the surface of the photosensitive drum 65.

In this embodiment, the developing device 64 of the first image forming unit 62Y is connected to the first mounting portion 51Y. Therefore, the developing device 64 of 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 of the first image forming unit 62Y.

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

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

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

The transfer unit 7 transfers each toner image formed on the surface of each photoconductor drum 65 of the first image forming unit 62Y to the fourth image forming unit 62K onto the paper P in a superimposed manner. In this embodiment, the transfer unit 7 transfers each toner image onto the paper P in a superimposed manner using a secondary transfer method. In more detail, 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 around four primary transfer rollers 71, a drive roller 73, and a driven roller 74. The intermediate transfer belt 72 is driven in response to the rotation of the drive roller 73. In FIG. 1, the intermediate transfer belt 72 rotates counterclockwise. The driven roller 74 is driven to rotate 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 facing the lower surface of the intermediate transfer belt 72 along the driving direction D of the lower surface of the intermediate transfer belt 72. In this embodiment, the first image forming unit 62Y to the fourth image forming unit 62K are arranged in this order from the upstream side to the downstream side of the driving direction D of the lower surface of the intermediate transfer belt 72.

Each primary transfer roller 71 is disposed opposite each photoconductor drum 65 via the intermediate transfer belt 72 and is pressed against each photoconductor drum 65. Therefore, the toner images formed on the surface of each photoconductor drum 65 are transferred sequentially to the intermediate transfer belt 72. In this embodiment, a yellow toner image, a cyan toner image, a magenta toner image, and a black toner image are transferred and stacked in this order onto the intermediate transfer belt 72. Hereinafter, the toner image in which a yellow toner image, a cyan toner image, a magenta toner image, and a black toner image are stacked may be referred to as a "laminated toner image."

The secondary transfer roller 75 is disposed opposite the drive roller 73 via the intermediate transfer belt 72. The secondary transfer roller 75 is pressed against the drive roller 73. This forms a transfer nip 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 this embodiment, the yellow toner image, cyan toner image, magenta toner image, and black toner image are transferred to the paper P in this order from top to bottom. The paper P to which the laminated toner image has been transferred is transported by the transport unit 4 toward the fixing unit 8.

The density sensor 76 is disposed facing the intermediate transfer belt 72 downstream of the first image forming unit 62Y to the fourth image forming unit 62K, and measures the density of the laminated toner image formed on the photoconductor drum 65. 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 unit 8 includes a heating member 81 and a pressure member 82. The heating member 81 and the pressure member 82 are arranged opposite each other to form a fixing nip. The paper P conveyed from the image forming unit 6 passes through the fixing nip and is pressurized while being heated at a predetermined fixing temperature. As a result, the laminated toner image is fixed to the paper P. The paper P is conveyed from the fixing unit 8 to the discharge unit 9 by the conveying unit 4.

The discharge section 9 has a pair of discharge rollers 91 and a discharge tray 93. The pair of discharge rollers 91 transports the paper P to the discharge tray 93 through a discharge opening 92. The discharge opening 92 is formed at the top of the image forming device 1.

The control unit 10 controls the operation of each unit of the image forming device 1. The control unit 10 includes a processor 11, a memory unit 12, and a prediction unit 13. The processor 11 includes, for example, a CPU (Central Processing Unit). The memory unit 12 includes a memory such as a semiconductor memory, and may also include a HDD (Hard Disk Drive). The memory unit 12 stores a control program. The processor 11 controls the operation of the image forming device 1 by executing the control program. The prediction unit 13 predicts the amount of toner that will move due to the fogging phenomenon described below.

Next, the configuration of the developing device 64 will be described in detail with reference to FIG. 2. FIG. 2 is a diagram showing an example of the configuration of the developing device 64. In detail, FIG. 2 shows the first developing device 64Y of the first image forming unit 62Y. In FIG. 2, the photosensitive drum 65 is illustrated by a two-dot chain line for ease of understanding. In this embodiment, the first developing device 64Y develops the electrostatic latent image formed on the surface of the photosensitive drum 65 by a two-component development 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 through the toner refill port 640h.

As shown in FIG. 2, the first developing device 64Y has a developing roller 641, a first stirring screw 643, a second stirring screw 644, and a blade 645 inside a developing container 640. In detail, the developing roller 641 is disposed opposite the second stirring screw 644. The blade 645 is disposed opposite 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 are connected to each other on the outside of both longitudinal ends of the partition wall 640c.

A first stirring screw 643 is disposed in the first stirring chamber 640a. A magnetic carrier is housed in the first stirring chamber 640a. Non-magnetic toner is supplied to the first stirring chamber 640a through the toner supply port 640h. In the example shown in FIG. 2, yellow toner is supplied to the first stirring chamber 640a.

A second stirring screw 644 is disposed in the second stirring chamber 640b. A magnetic carrier 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 consisting of the carrier and the yellow toner is formed. The two-component developer is an example of a developer, and may be referred to below simply as "developer".

The first stirring screw 643 and the second stirring screw 644 circulate and stir the developer between the first stirring chamber 640a and the second stirring chamber 640b. 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 rotating sleeve 641a and a magnet body 641b. The magnet body 641b is fixedly disposed inside the rotating sleeve 641a. The magnet body 641b includes multiple 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. 2. The developing roller 641 rotates to transport the magnetic brush to a position facing the blade 645. The blade 645 is positioned so that a gap is formed between the developing roller 641 and the blade 645. Therefore, the thickness of the magnetic brush is determined by the blade 645. The blade 645 is positioned upstream in the rotation direction of the magnetic roller 642 from 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. This causes the developer layer formed on the surface to be transported to a position facing the photoconductor drum 65, and the toner in the developer is attached to the photoconductor drum 65.

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

The current measurement unit 646 is connected, for example, between the development power supply 648 and the development roller 641. The development power supply 648 applies a predetermined bias voltage to the development roller 641 of the first development device 64Y. The current measurement unit 646 detects the development current flowing between the first development device 64Y, the photoconductor drum 65, and the development roller 641 in accordance with the bias voltage applied by the development power supply 648. The current measurement unit 646 is, for example, an ammeter, and measures the current value of the development current.

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

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

In this embodiment, when a user inputs an instruction to execute an image forming process to the image forming device 1, the control unit 10 controls the image forming unit 6 to start an image forming operation in each unit of the image forming device 1. Specifically, the control unit 10 controls the charging device 63, the first developing device 64Y, the developing power source 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. In more detail, when the charging device 63 applies a charging bias to the photoconductor drum 65, the surface of the photoconductor drum 65 is charged to a surface potential V0.

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

The exposure device 61, under the control of the control unit 10, irradiates the photoconductor drum 65, which has been charged to a surface potential V0 by the charging device 63, with laser light. This forms an electrostatic latent image on the surface of the photoconductor drum 65.

When an electrostatic latent image is formed on the surface of the photoconductor drum 65, the first developing device 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 development current. In FIG. 3A, the development current Id1 is the sum of the current that flows when the toner in the magnetic brush formed on the development roller 641 moves to the development roller 641 and the current Ia1 that flows from the photoconductor drum 65 through the magnetic brush formed on the development roller 641.

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

In this way, the direction of the development current measured by the current measurement unit 646 is reversed when the DC component of the bias voltage is greater than the surface potential V0 and when the DC component of the bias voltage is less than the surface potential V0.

In addition, when the DC component of the bias voltage is equal to the surface potential V0, the development field strength is zero, and the magnitude of the development current is zero. From this, it is possible to predict that the DC component of the bias voltage when the magnitude of the development current is zero is the surface potential V0. As a result, when developing an electrostatic latent image, a bias voltage with an appropriate potential difference can be applied to the development roller 641, making it possible to form a higher quality image.

However, in the image forming device 1, even when the development electric field strength is zero, a development current may be observed due to toner with a low charge amount, which has a weak electrostatic binding force, adhering to the photoconductor drum 65 and moving (fogging phenomenon).

In contrast, in this embodiment, the surface potential of the photosensitive drum 65 is predicted taking into account the development current caused by such fogging phenomena.

Specifically, in this embodiment, the surface potential of the photoconductor drum 65 is calculated based on the current that flows when the toner moves from the development roller 641 to the photoconductor drum 65 when the development electric field strength is zero.

Next, the current used as a reference (non-charged developing current) will be described with reference to FIG. 4. FIG. 4 is a diagram showing the non-charged developing current measured by the current measuring unit 646. The non-charged developing current is the current that flows through the first developing device 64Y in an uncharged state in which the charging device 63 is not charging the photoconductor drum 65.

Specifically, the charging device 63 does not apply a charging bias (0 [V]) to the photoconductor drum 65. The development power supply 648 applies a bias voltage with a DC component of 0 [V] to the development roller 641.

At this time, the current measuring unit 646 measures the non-charged development current Id0, which is the sum of the current Ia0 that flows when the toner moves to the photoconductor drum 65 and the current that flows to the photoconductor drum 65 through the magnetic brush formed on the development roller 641.

Next, the image forming device 1 measures the current value of the charging development current flowing through the first developing device 64Y in a charged state in which the charging device 63 has charged the photosensitive drum 65, and predicts the surface potential based on the measured value of the charging development current and the measured value of the non-charging development current.

Specifically, the calculation unit 647 acquires the measured values of the charging development current and the non-charging development current measured by the current measurement unit 646, and calculates the surface potential based on each measured value.

Next, the measurement of the charging development current will be described with reference to Figures 5A and 5B. Figures 5A and 5B are diagrams showing the charging development current measured by the current measurement unit 646.

The charging device 63 applies a charging bias to the photoconductor drum 65 to charge the surface of the photoconductor drum 65 to a surface potential V0 (Figures 5A and 5B).

The development power supply 648 applies multiple levels of bias voltage to the first development device 64Y. The current measurement unit 646 measures the corresponding charging development current for each of the multiple levels of bias voltage.

For example, the development power supply 648 applies a bias voltage Vdc3 to the development roller 641 such that a charging development current Id3 larger than the non-charging development current Id0 flows. At this time, the current measurement unit 646 measures the current value of the charging development current Id3. The calculation unit 647 acquires the bias voltage Vdc3 applied by the development power supply 648 and the current value of the charging development current Id3 measured by the current measurement unit 646 (FIG. 5A).

In addition, the development power supply 648 applies a bias voltage Vdc4 to the development roller 641 such that a charging development current Id4 smaller than the non-charging development current Id0 flows. At this time, the current measurement unit 646 measures the current value of the charging development current Id4. The calculation unit 647 acquires the bias voltage Vdc4 applied by the development power supply 648 and the current value of the charging development current Id4 measured by the current measurement unit 646 (FIG. 5B).

Next, the calculation of the surface potential will be described with reference to FIG. 6. FIG. 6 is a graph showing the correspondence between the development current and the bias voltage. In FIG. 6, the vertical axis shows the development current, and the horizontal axis shows the bias voltage.

Based on the acquired bias voltage Vdc3 and charge development current Id3, and the bias voltage Vdc4 and charge development current Id4, the calculation unit 647 calculates the bias voltage at which a charge development current equal to the non-charge development current Id0 measured by the current measurement unit 646 flows as the surface potential V0.

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

The control unit 10 may determine the bias voltage Vdc to be applied to the developing roller 641 based on a surface potential calculated by a method other than the calculation by the calculation unit 647. For example, when forming images on multiple sheets of paper P, the control unit 10 determines the bias voltage Vdc based on the surface potential V0 calculated by the calculation unit 647 when forming an image on the first sheet of paper P, and determines the bias voltage Vdc based on a predetermined surface potential or a surface potential predicted by another method when forming images on the second or subsequent sheets of paper P.

In this embodiment, the exposure device 61 does not irradiate the photoconductor drum 65 with laser light when the current measurement unit 646 measures the uncharged development current and the charged development current. In this way, by performing the measurement of the uncharged development current and the charged development current using the non-exposed area of the photoconductor drum 65, the white area where toner does not fly much is used even when the fogging phenomenon occurs, so the development current mainly includes the current due to the movement of carriers. Therefore, the surface potential of the photoconductor drum 65 can be measured with high accuracy.

In this embodiment, the configuration of the developing device 64 possessed by each of the first image forming unit 62Y to the fourth image forming unit 62K is substantially the same except for the type of toner supplied from the toner supply section 5. Therefore, the description of the configuration of the second developing device 64C to the fourth developing device 64K possessed by the second image forming unit 62C to the fourth image forming unit 62K will be omitted.

(Prediction of toner amount moved due to fogging phenomenon)
In this embodiment, the more the amount of toner that moves due to the fogging phenomenon, the larger the non-charged developing current becomes and the further away it is from zero, so if the DC component of the bias voltage when the magnitude of the developing current becomes zero is predicted as the surface potential (FIGS. 3A and 3B), the difference between the actual surface potential becomes large. In addition, frequent measurement of the non-charged developing current reduces productivity.

The prediction unit 13 predicts the amount of toner that moves due to the fogging phenomenon. For example, since the fogging phenomenon is likely to occur when the density of the toner image is high, the prediction unit 13 predicts that the amount of toner that moves is large when the density of the toner image measured by the density sensor 76 is high. In addition, the prediction unit 13 may predict whether the amount of toner that moves is large or small based on multiple parameters other than the density of the toner image, such as the charge amount of the toner, the advection-diffusion coefficient of the developer, the frequency of the AC component of the bias voltage, and the carrier resistance value that indicates the difficulty of the carrier current that flows when the carrier that does not contain toner flows from the photoconductor drum 65 to the development roller 641.

For example, when the prediction unit 13 predicts that the amount of toner moving is greater than a predetermined threshold, the control unit 10 controls the charging device 63, the first developing device 64Y, and the developing power source 648 to calculate the surface potential based on the non-charging developing current.

On the other hand, when the prediction unit 13 predicts that the amount of toner moving is less than a predetermined threshold, the control unit 10 controls the charging device 63, the first developing device 64Y, and the developing power source 648 so as not to calculate the surface potential, or controls the charging device 63, the first developing device 64Y, and the developing power source 648 so as to calculate the surface potential with the non-charged developing current set to 0 [A]. Also, in this embodiment, when the amount of toner moving due to the fogging phenomenon is small, the magnitude of the non-charged developing current may be set to zero, and the calculation of the surface potential shown in Figures 3A and 3B may be performed.

In this embodiment, for example, if the calculated surface potential differs from the previously calculated surface potential by a predetermined reference value or more, the calculation unit 647 determines that the newly calculated surface potential is a measurement error. In this case, the calculation unit 647 may recalculate the surface potential, or may use the previously calculated surface potential as the calculation result.

In addition, in this embodiment, by storing the surface potential calculated by the calculation unit 647, it becomes possible to observe changes in the surface potential of the photosensitive drum 65, and to predict deterioration of the charging device 63, the photosensitive drum 65, etc.

In addition, in this embodiment, the non-exposed area not irradiated with laser light is used to measure the non-charged development current and the charged development current, and the surface potential is calculated. However, this is not limited to the above, and the non-charged development current and the charged development current may be measured using the exposed area after irradiation with laser light by the exposure device 61, and the surface potential may be calculated.

Next, the surface potential calculation process according to this embodiment will be described with reference to FIG. 7. FIG. 7 is a flowchart showing the surface potential calculation process according to this embodiment.

When the prediction unit 13 predicts that the amount of toner moving due to the fogging phenomenon is greater than a predetermined threshold (step S11), the current measurement unit 646 measures the non-charged development current Id0 (step S12).

The current measurement unit 646 measures the charging development current Id3 that flows when a bias voltage Vdc3 that causes a charging development current Id3 larger than the non-charging development current Id0 to flow is applied to the developing roller 641 (step S13).

The current measurement unit 646 measures the charging development current Id4 that flows when a bias voltage Vdc4 that causes a charging development current Id4 that is greater than the non-charging development current Id0 to flow is applied to the developing roller 641 (step S14).

Based on the charging development current Id3 and the bias voltage Vdc4 measured by the current measurement unit 646, the calculation unit 647 calculates a bias voltage that causes a charging development current equal to the non-charging development current Id0 measured by the current measurement unit 646 to flow (step S15).

The order of steps S13 and S14 may be reversed.

In this embodiment, the non-charged developing current Id0 is the current that flows when the photoconductor drum 65 is in an uncharged state and the DC component of the bias voltage applied by the developing power source 648 to the developing roller 641 is 0 [V], but this is not limited to this.

Normally, as the DC component of the bias voltage increases, the development current increases. Also, when the development electric field strength is small and weaker than the adhesive force between the toner and the magnetic brush, the amount of change in development current (ΔId) relative to the amount of change in development electric field strength is small. On the other hand, when the development electric field strength becomes stronger than the adhesive force between the toner and the magnetic brush, the toner moves more actively and ΔId increases rapidly.

If ΔId is small, the calculation error of the surface potential will be large, so in order to calculate the surface potential with high accuracy, it is preferable that ΔId is large.

The development power supply 648 applies a bias voltage Vdc0 (measurement bias voltage) containing a DC component such that ΔId is equal to or greater than a predetermined value to the development roller 641 when the photoconductor drum 65 is in an uncharged state. The current measurement unit 646 measures the uncharged development current Id01 that flows while the measurement bias voltage is being applied.

The calculation unit 647 uses the above method to calculate the bias voltage Vdc5 at which a charging development current equal to the non-charging development current Id01 flows. The calculation unit 647 calculates the bias voltage obtained by subtracting the bias voltage Vdc0 from the bias voltage Vdc5 as the surface potential V0.

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

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

The experimental conditions for the multifunction printer were as follows:
Photoconductor drum 65: Positively charged organic photoconductor drum (OPC: Organic Photo Conductor)
Film thickness of photoconductor drum 65: 32 μm
Charging device 63: charging roller core metal outer diameter 6 mm, rubber thickness 3 mm, rubber resistance 6.0 Log Ω
Charging bias: DC only Blade 645: SUS430, magnetic Blade 645 thickness: 1.5 mm
Surface shape of the developing roller 641: knurled + blasted Outer diameter of the developing roller 641: 20 mm
Developing roller 641 recesses: 80 rows in the circumferential direction Circumferential speed of developing roller 641/circumferential speed of photosensitive drum 65: 1.8
Distance between the developing roller 641 and the photosensitive drum 65: 0.30 mm
Bias voltage AC component: Vpp 1200V, duty 50%, square wave, 8kHz
Toner: Particle diameter 6.8 μm, positively charged Carrier: Particle diameter 38 μm, ferrite Resin-coated carrier Toner concentration: 6%
Print speed: 55 sheets/min

Next, the surface potential calculated in the image forming device 1 according to this embodiment will be described with reference to Figures 8 and 9.

Figure 8 is a table showing the measured non-charged development current and the measured charged development current when four levels of bias voltage are applied to the developing roller 641 with a charging bias of 900 V in the image forming apparatus 1 according to this embodiment.

Figure 9 is a graph showing the relationship between the bias voltage shown in Figure 8 and the non-charged developing current and the charged developing current. In Figure 9, the vertical axis shows the developing current, and the horizontal axis shows the bias voltage.

In this embodiment, the measured non-charged developing current is 1.10 μA. When the bias voltage is 180 V, the developing current (charged developing current) is 0.57 μA. When the bias voltage is 200 V, the developing current (charged developing current) is 0.68 μA. When the bias voltage is 220 V, the developing current (charged developing current) is 1.00 μA. When the bias voltage is 240 V, the developing current (charged developing current) is 1.60 μA.

As shown in FIG. 9, in the image forming device 1 of this embodiment, the surface potential is calculated to be 223 [V].

In this embodiment, the difference in the applied bias voltages is a maximum of 60 V, but it is not limited to this and may be a maximum of 100 V. However, it is preferable that the difference in the applied bias voltages is about 50 V.

In addition, in this embodiment, the photoconductor drum 65 is a positively charged organic photoconductor drum, but this is not limited to this and may be an amorphous silicon drum. When an amorphous silicon drum is used for the photoconductor drum 65, the dielectric constant of the photosensitive layer is higher than that of a positively charged organic photoconductor drum, making it easier for current to flow and reducing the carrier resistance value, resulting in higher measurement accuracy.

In addition, in this embodiment, a two-component developer is used, but this is not limiting, and a one-component developer may also be used.

The above describes an embodiment of the present invention 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 forms without departing from the gist of the present invention. The drawings are mainly schematic, showing each component, for ease of understanding, and the thickness, length, number, etc. of each component shown in the drawings may differ from the actual ones due to the convenience of creating the drawings. In addition, the materials, shapes, dimensions, etc. of each component shown in the above embodiment are merely examples and are not particularly limited, and various modifications are possible without substantially departing from the effects of the present invention.

This invention can be used in the field of image forming devices.

1: Image forming apparatus 13: Prediction unit 63: Charging device 64: Developing device 65: Photoconductor drum 641: Developing roller 646: Current measurement unit 647: Calculation unit 648: Development power supply Id0: Non-charged developing current Id1, Id2: Developing current Id3, Id4: Charged developing current V0: Surface potential Vdc: Bias voltage Vdc3, Vdc4: Bias voltage

Claims (7)

an image carrier on whose surface an electrostatic latent image is formed;
a charging device for charging the image carrier;
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 development power source for applying a predetermined bias voltage to the developing device;
a current measuring unit for measuring a development current flowing through the developing device;
a calculation unit that calculates a surface potential of the image carrier based on the development current measured by the current measurement unit,
the current measuring unit measures a non -charging developing current flowing through the developing device when a DC component of the bias voltage is a predetermined voltage in a non-charging state in which the charging device does not charge the image carrier,
the current measuring unit measures a charging/developing current flowing through the developing device in a charged state in which the charging device charges the image carrier,
The calculation unit calculates, as the surface potential, a difference between the bias voltage and the voltage when the charging development current is equal to the non-charging development current. the developing power supply applies a plurality of stages of the bias voltage to the developing device;
the current measuring unit measures the charging and developing current corresponding to each of the bias voltages;
The image forming apparatus according to claim 1 , wherein the calculation section calculates the surface potential based on each of the charging and developing currents. The image forming apparatus according to claim 1 or 2, wherein the developing power supply applies the bias voltage such that the charging developing current flows larger than the non-charging developing current, and the bias voltage such that the charging developing current flows smaller than the non-charging developing current. The image forming apparatus according to any one of claims 1 to 3, wherein the calculation unit calculates the surface potential before the image forming apparatus performs an image forming process for forming an image on a recording medium. The image forming apparatus according to any one of claims 1 to 4, wherein the current measuring unit measures the development current of the image carrier in a non-exposed state. The image forming apparatus further includes a prediction unit for predicting an amount of toner moving due to a fogging phenomenon,
6. The image forming apparatus according to claim 1, wherein the calculation section calculates the surface potential based on the non-charged developing current when the prediction section predicts that the toner amount is greater than a predetermined threshold value. The image forming apparatus according to claim 1 , wherein the voltage is 0 V.

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