Image formation apparatus

An image formation apparatus includes an image carrier, a first charging member which abuts on the image carrier and charges the image carrier, a second charging member which abuts on the image carrier and charges the image carrier, the second charging member having such resistance characteristics as being less in variation with environmental variation than the first charging member, a power supply apparatus which can apply a voltage to each of the first and second charging members, and a control device which sets a voltage to be applied to the first charging member by the power supply apparatus based on a first amount of current which flows from the power supply apparatus through the first charging member to the image carrier and a second amount of current which flows to the image carrier through the second charging member.

The entire disclosure of Japanese Patent Application No. 2017-091844 filed on May 2, 2017 is incorporated herein by reference in its entirety.

BACKGROUND

Technological Field

The present disclosure relates to an image formation apparatus and particularly to control of a charging apparatus.

Description of the Related Art

In general, an image formation apparatus (a printer, a copying machine, and a facsimile machine) making use of an electrophotographic process technique forms an electrostatic latent image by irradiating (exposing to light) a charged photoconductor with laser beams based on image data. Then, the electrostatic latent image is visualized by supplying toner from a development apparatus to the photoconductor on which the electrostatic latent image has been formed, and a toner image is thus formed. The toner image is directly or indirectly transferred to paper, and thereafter the toner image is fixed by heating and application of a pressure in a fixing nip. The toner image is thus formed on the paper.

In an image formation apparatus of this type, proper adjustment of a charge potential at which a charging apparatus charges a photoconductor has conventionally been demanded. The photoconductor, however, is not constant in film thickness. When the film thickness decreases, the charge potential varies and an image may be poor or a line may be thin.

Japanese Laid-Open Patent Publication No. 08-185017 has proposed a scheme of sensing a charge potential at a surface of a photoconductor, predicting production of a poor image, and setting a charge bias voltage.

SUMMARY

Though Japanese Laid-Open Patent Publication No. 08-185017 has proposed a scheme of calculating a charge potential based on an amount of current which flows to a charging roller as a scheme of sensing a charge potential of a photoconductor, resistance characteristics of the charging roller also vary with environmental variation.

Therefore, it has been difficult to accurately sense a charge potential and to set a proper charge bias voltage.

The present disclosure was made to solve the problem above and an object thereof is to provide an image formation apparatus which can set a proper charge bias voltage.

To achieve at least one of the abovementioned objects, according to an aspect of the present invention, an image formation apparatus reflecting one aspect of the present invention comprises an image carrier, a first charging member which abuts on the image carrier and charges the image carrier, a second charging member which abuts on the image carrier and charges the image carrier, the second charging member having such resistance characteristics as being less in variation with environmental variation than the first charging member, a power supply apparatus which can apply a voltage to each of the first and second charging members, and a control device which sets a voltage to be applied to the first charging member by the power supply apparatus based on a first amount of current which flows from the power supply apparatus through the first charging member to the image carrier and a second amount of current which flows to the image carrier through the second charging member.

Preferably, the control device calculates a resistance value of the first charging member based on subtraction of the first and second amounts of current and sets the voltage to be applied to the first charging member by the power supply apparatus based on a result of calculation.

Preferably, the control device sets a voltage resulting from addition of a voltage decrement caused by the first charging member based on the calculated resistance value to a prescribed voltage as the voltage to be applied to the first charging member.

Preferably, a switch which allows electrical connection of at least one of the first and second charging members to the power supply apparatus is further provided.

Preferably, the control device sets the voltage to be applied to the first charging member by the power supply apparatus based on the first amount of current which flows from the power supply apparatus through the first charging member to the image carrier and the second amount of current which flows to the image carrier through the second charging member during a period for stabilization of an image.

Preferably, the power supply apparatus applies an alternating-current (AC) or direct-current (DC) voltage to the first and second charging members.

Preferably, the second charging member includes at least any one of a metal member, a conductive guide member, and a brush.

Preferably, the metal member corresponds to a metal roller.

Preferably, a prescribed resistor connected between the power supply apparatus and the second charging member is further provided.

The foregoing and other objects, features, aspects and advantages of this invention will become more apparent from the following detailed description of the this invention when taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF EMBODIMENTS

Each embodiment will be described below with reference to the drawings. The same elements and components in the description below have the same reference characters allotted and their labels and functions are also the same. Therefore, detailed description thereof will not be repeated. Each embodiment and each modification described below may selectively be combined as appropriate.

An example in which a power supply apparatus is mounted on an image formation apparatus will be described in an embodiment below. Examples of the image formation apparatus include an MFP, a printer, a copying machine, or a facsimile machine.

[Internal Configuration of Image Formation Apparatus]

FIG. 1is a diagram showing one example of an internal structure of an image formation apparatus100based on an embodiment.

Image formation apparatus100on which a power supply apparatus50is mounted will be described with reference toFIG. 1.

FIG. 1shows image formation apparatus100as a color printer. Though image formation apparatus100as the color printer will be described below, image formation apparatus100is not limited to the color printer. For example, image formation apparatus100may be a multi-functional peripheral (MFP).

Image formation apparatus100has a monochrome printing mode in which an image is formed by using only black and a color printing mode in which an image is formed by using yellow, magenta, cyan, and black.

Image formation apparatus100includes image formation units1Y,1M,1C, and1K, an intermediate transfer belt30, a primary transfer roller31, a secondary transfer roller33, a cassette37, a driven roller38, a drive roller39, a timing roller40, a fixation apparatus43, and a power supply apparatus50.

Image formation units1Y,1M,1C, and1K are sequentially aligned along intermediate transfer belt30. Image formation unit1Y forms a toner image of yellow (Y) upon receiving supply of toner from a toner bottle15Y. Image formation unit1M forms a toner image of magenta (M) upon receiving supply of toner from a toner bottle15M. Image formation unit1C forms a toner image of cyan (C) upon receiving supply of toner from a toner bottle15C. Image formation unit1K forms a toner image of black (BK) upon receiving supply of toner from a toner bottle15K.

Image formation units1Y,1M,1C, and1K are arranged sequentially in a direction of rotation of intermediate transfer belt30along intermediate transfer belt30. Each of image formation units1Y,1M,1C, and1K includes a photoconductor10, a charging apparatus11, an exposure apparatus12, a development apparatus13, a deelectrifying apparatus16, and a cleaning apparatus17.

Charging apparatus11evenly charges a surface of photoconductor10. Exposure apparatus12irradiates photoconductor10with laser beams in response to a control signal from a main body control device51which will be described later and exposes the surface of photoconductor10in accordance with an input image pattern. An electrostatic latent image in accordance with an input image is thus formed on photoconductor10.

Development apparatus13applies a development bias to a development roller14while it rotates development roller14, to thereby attach toner onto a surface of development roller14. The toner is thus transferred from development roller14to photoconductor10and a toner image in accordance with the electrostatic latent image is developed on the surface of photoconductor10.

Photoconductor10and intermediate transfer belt30are in contact with each other at a portion where primary transfer roller31is provided. Primary transfer roller31is configured to be rotatable. A transfer voltage opposite in polarity to the toner image is applied to primary transfer roller31so that the toner image is transferred from photoconductor10to intermediate transfer belt30.

In the color printing mode, the toner image of yellow (Y), the toner image of magenta (M), the toner image of cyan (C), and the toner image of black (BK) are successively layered and transferred from photoconductor10to intermediate transfer belt30. The color toner image is thus formed on intermediate transfer belt30. In the monochrome printing mode, the toner image of black (BK) is transferred from photoconductor10to intermediate transfer belt30.

Intermediate transfer belt30is looped around driven roller38and drive roller39. Drive roller39is rotationally driven, for example, by a motor (not shown). Intermediate transfer belt30and driven roller38rotate in coordination with drive roller39. A toner image on intermediate transfer belt30is thus transported to secondary transfer roller33.

Deelectrifying apparatus16deelectrifies charged toner which adheres to the surface of photoconductor10. By deelectrifying charges of charged toner, recovery of toner by cleaning apparatus17which will be described later is facilitated.

Cleaning apparatus17is pressed against photoconductor10as being in contact therewith. Cleaning apparatus17recovers toner which remains on the surface of photoconductor10after transfer of the toner image.

Paper S is set in cassette37. Paper S is sent from cassette37to secondary transfer roller33one by one along a transportation path41by timing roller40. Secondary transfer roller33applies a transfer voltage opposite in polarity to the toner image to transported paper S. The toner image is thus attracted from intermediate transfer belt30to secondary transfer roller33and the toner image on intermediate transfer belt30is transferred to paper S. Timing of transportation of paper S to secondary transfer roller33is adjusted by timing roller40in accordance with a position of the toner image on intermediate transfer belt30. Owing to timing roller40, the toner image on intermediate transfer belt30is transferred to an appropriate position on paper S.

Fixation apparatus43pressurizes and heats paper S which passes therethrough. The toner image formed on paper S is thus fixed onto paper S. Thereafter, paper S is ejected onto a tray48.

Power supply apparatus50supplies various necessary voltages, for example, to each apparatus in image formation apparatus100. Details of power supply apparatus50will be described later. In the present example, power supply apparatus50supplies a voltage of 24 V by way of example to an apparatus belonging to a drive system in image formation apparatus100. Power supply apparatus50supplies a voltage of 5 V by way of example to an apparatus belonging to a control system in image formation apparatus100.

[Hardware Configuration of Image Formation Apparatus]

FIG. 2is a block diagram showing a main hardware configuration of image formation apparatus100. One example of the hardware configuration of image formation apparatus100will be described with reference toFIG. 2.

As shown inFIG. 2, image formation apparatus100includes power supply apparatus50, main body control device51, a read only memory (ROM)102, a random access memory (RAM)103, a network interface104, an operation panel107, and a storage device130.

Main body control device51is implemented, for example, by at least one integrated circuit. The integrated circuit is implemented, for example, by at least one CPU, at least one DSP, at least one application specific integrated circuit (ASIC), at least one field programmable gate array (FPGA), or combination thereof.

Main body control device51controls both of power supply apparatus50and image formation apparatus100. Main body control device51is shared by power supply apparatus50and image formation apparatus100. Main body control device51may be configured separately from or integrally with power supply apparatus50. When main body control device51is configured separately from power supply apparatus50, power supply apparatus50is simplified in configuration.

Main body control device51selects any of a monochrome printing mode and a color printing mode in accordance with information input to operation panel107and controls power supply apparatus50and image formation apparatus100in accordance with the selected mode. Main body control device51outputs a selected mode identification signal indicating the selected mode to power supply apparatus50.

Main body control device51controls operations of image formation apparatus100by executing a control program for power supply apparatus50or image formation apparatus100.

Main body control device51reads a control program from storage device130to ROM102based on acceptance of an instruction to execute the control program. RAM103functions as a working memory and temporarily stores various types of data necessary for execution of the control program.

Main body control device51performs prescribed processing for power supply apparatus50based on an instruction to execute the control program. By way of example, main body control device51carries out control to switch from a normal mode to a power saving mode in response to an instruction to switch to the power saving mode given by a user through operation panel107.

An antenna (not shown) or the like is connected to network interface104. Image formation apparatus100exchanges data with external communication equipment through the antenna. External communication equipment includes, for example, a portable communication terminal such as a smartphone and a server. Image formation apparatus100may be configured to be able to download a control program from a server through the antenna.

Operation panel107is implemented by a display and a touch panel. The display and the touch panel are layered on each other and operation panel107accepts, for example, a printing operation or a scanning operation onto image formation apparatus100.

Storage device130is, for example, a storage medium such as a hard disk or an external storage device. Storage device130stores a control program for image formation apparatus100. A location where the control program is stored is not limited to storage device130, and the control program may be stored in a storage area of power supply apparatus50, a storage area of main body control device51(for example, a cache), ROM102, RAM103, or external equipment (for example, a server). The control program may be provided not as a program alone but as being incorporated as a part of any program. In this case, the control process according to the present embodiment is implemented in cooperation with any program. Even a program not including some modules as such does not depart from the gist of the control program according to the present embodiment. Some or all of functions provided by the control program may be implemented by dedicated hardware. Image formation apparatus100may be configured in such a form as what is called a cloud service in which at least one server implements some of the process of the control program.

FIG. 3is a diagram illustrating charging apparatus11based on the embodiment.

Power supply apparatus50is connected to charging apparatus11and supplies a charge bias voltage.

Charging apparatus11includes a charging roller110which abuts on photoconductor10, a charging roller111which is provided separately from charging roller110and abuts on photoconductor10, a switch circuit SW, and a current sensor SA.

Switch circuit SW switches a voltage supply path in response to an instruction from main body control device51. Specifically, switch circuit SW allows connection among power supply apparatus50, any one of charging rollers110and111, and power supply apparatus50in response to an instruction from main body control device51.

Charging roller111has such resistance characteristics as being less in variation with environmental variation than charging roller110. Specifically, a metal roller sufficiently lower in resistance value than charging roller110can be employed as charging roller111.

Current sensor SA senses a current which flows through a voltage supply path and outputs the current value to main body control device51.

Main body control device51controls a charge bias voltage to be output from power supply apparatus50based on the current sensed by current sensor SA.

Charging roller110evenly charges the surface of photoconductor10. Exposure apparatus12forms an electrostatic latent image on photoconductor10by emitting laser beams. Development apparatus13places toner in accordance with the electrostatic latent image. After an image is transferred to intermediate transfer belt30as a result of transfer by primary transfer roller31, a remaining potential on photoconductor10is removed by deelectrifying apparatus16and remaining toner is recovered by cleaning blade170.

FIG. 4is a diagram illustrating charging rollers110and111based on the embodiment.

As shown inFIG. 4, two charging rollers110and111for photoconductor10are arranged in a longitudinal direction and abuts on photoconductor10.

In the present example, charging rollers110and111for photoconductor10are viewed from above.

[Setting of Charge Bias Voltage]

Setting of a charge bias voltage will now be described.

Charging apparatus11applies a charge bias voltage resulting from superimposition of an AC voltage on a DC voltage such that the surface of photoconductor10is uniformly charged.

FIG. 5is a diagram illustrating a charge potential Vs of photoconductor10with respect to a peak-to-peak voltage value Vpp of an AC voltage Vac.

As shown inFIG. 5, so long as peak-to-peak voltage value Vpp is within a range from a charging start voltage value Vth to a voltage value 2×Vth twice as large as that, charge potential Vs is approximately in proportion to AC voltage Vac.

Charging start voltage value Vth is a voltage value at which charging of photoconductor10with a DC voltage Vdc is started, and it is determined by various characteristics of photoconductor10.

FIG. 5shows an example in which Vth is set to 800 V and 2×Vth is 1600 V.

Above 2×Vth, charge potential Vs is saturated and remains at an approximately constant charge potential Va0. Therefore, in order to make charge potential Vs uniform, a charge bias voltage resulting from superimposition of AC voltage Vac of which peak-to-peak voltage value Vpp exceeds 2×Vth should be applied to charging roller110.

Charge potential Va0at that time is dependent on DC voltage Vdc included in a charging voltage.

In the image formation apparatus, regardless of influence by an environment or manufacturing variation in resistance value of the charging roller, an amount of discharge of charging apparatus11should always be constant so that photoconductor10uniformly is charged without causing such problems as deterioration of photoconductor10or production of a poor image. Therefore, the image formation apparatus detects an AC current which flows from charging apparatus11through photoconductor10and makes adjustment based on a result of detection.

Specifically, values of AC currents which flow to charging roller110at the tune when a plurality of AC voltages Vac which are lower than 2×Vth and different in peak-to-peak voltage value Vpp from one another are successively applied while no paper is passing are measured with current sensor SA.

Similarly, values of AC currents at the time of application of a plurality of AC voltages Vac which are not lower than 2×Vth and are different in peak-to-peak voltage value Vpp from one another are also measured with current sensor SA.

FIG. 6is a diagram illustrating AC current values when a plurality of AC voltages Vac are applied.

In the present example, a region where peak-to-peak voltage value Vpp is lower than 2×Vth is defined as a forward discharge region where only transfer of charges from charging means to a photoconductor drum (that is, transfer of charges in a single direction) takes place.

A region equal to or higher than 2×Vth is defined as a back discharge region where bidirectional transfer of charges between photoconductor10and the charging apparatus alternately takes place.

As shown inFIG. 6, values of AC currents Iac1to Iac3which flow from charging apparatus11when AC voltages Vac1to Vac3in the forward discharge region are superimposed are obtained, and thereafter values of AC currents Iac1to Iac3are subjected to linear approximation to thereby obtain a characteristic line L1of the AC current values with respect to the AC voltages in the forward discharge region.

Similarly, a characteristic line L2of values of AC currents with respect to AC voltages in the back discharge region is also obtained.

An intersection between characteristic lines L1and L2is determined as a value of an AC voltage Vaci to be superimposed in a printing process.

A process of such a type is performed, for example, in control for stabilizing an image during warm-up, forced replenishment with toner, or adjustment of a toner to carrier ratio (TCR).

FIG. 7is a diagram illustrating relation between peak-to-peak voltage value Vpp and an α value based on the embodiment.

InFIG. 7, an α value (μm/100 k rotations) represents an amount of abrasion of a photoconductor layer of photoconductor10per one hundred thousand rotations. Three regions are shown by way of example. Specifically, a stable region, a photoconductor wear region, and a poor image region are shown. In the present example, a peak-to-peak voltage value Vppt defined as a target value is within the stable region.

When a voltage higher than peak-to-peak voltage value Vppt is applied and the peak-to-peak voltage value enters the photoconductor wear region, a degree of wear of photoconductor10increases.

On the other hand, when a voltage lower than peak-to-peak voltage value Vppt is applied and the peak-to-peak voltage value enters the poor image region, a poor image is produced.

Therefore, the peak-to-peak voltage value should be maintained in the stable region.

Resistance characteristics of charging roller110, however, also vary due to manufacturing variation or environmental variation. Therefore, due to variation in resistance characteristics, a value for the peak-to-peak voltage actually applied to photoconductor10may be set to be lower than peak-to-peak voltage value Vppt defined as the target value.

Specifically, due to a voltage drop in charging roller110, a peak-to-peak voltage value Vppr may be applied to photoconductor10.

The voltage drop significantly varies with environmental variation. Therefore, unless a peak-to-peak voltage is corrected, a poor image may be produced.

When a relatively high peak-to-peak voltage is set, a degree of wear of photoconductor10also increases.

In the present embodiment, a voltage drop in charging roller110is accurately detected so that a proper charge bias voltage is set.

Specifically, charging roller111different from charging roller110is provided, a current which flows to each of them is detected to calculate a voltage drop, and a charge bias voltage is set.

InFIG. 3, switch circuit SW sets a path through which a prescribed charge bias voltage is supplied from power supply apparatus50to charging roller110in response to an instruction from main body control device51. In this case, in the present example, a current I2flows to charging roller110. Switch circuit SW sets a path through which a prescribed charge bias voltage is supplied from power supply apparatus50to charging roller111in response to an instruction from main body control device51. In this case, in the present example, a current I1flows to charging roller111.

Currents I1and I2are detected by current sensor SA.

Main body control device51can calculate a resistance value Rx of charging roller110based on a prescribed charge bias voltage V/(I1−I2). Though a resistance value of charging roller111is not included in calculation assuming that the resistance value of charging roller111is sufficiently smaller than a resistance value of charging roller110, the resistance value of charging roller111may be included in calculation.

Then, the voltage drop in charging roller110can be calculated based on the calculated resistance value of charging roller110and current I2.

Therefore, main body control device51can set, in consideration of the voltage drop in charging roller110from target value Vppt, a charge bias voltage resulting from addition of that voltage decrement.

Specifically, main body control device51sets the charge bias voltage based on target value Vppt+current I2×calculated resistance value Rx of charging roller110. Main body control device51instructs power supply apparatus50to output the charge bias voltage.

A proper charge bias voltage in the stable region is thus set so that production of a poor image is suppressed and wear of photoconductor10can also be suppressed. Timing to replace photoconductor10can thus be set to be within a proper period and photoconductor10can have a longer lifetime.

A prescribed charge bias voltage V in the present example in calculation of a resistance value of charging roller110may be the same as or different from a voltage used in a printing process. An AC voltage or a DC voltage may be applied.

The charge bias voltage can be set in control for stabilizing an image during warm-up, forced replenishment with toner, or adjustment of a toner to carrier ratio (TCR) as described above.

FIG. 8is a diagram illustrating a charging apparatus11# based on a first modification of the embodiment.

Charging apparatus11# includes a movable conductive member120instead of charging roller111.

Switch circuit SW connects power supply apparatus50, any one of charging roller110and conductive member120, and power supply apparatus50in response to an instruction from main body control device51.

Conductive member120is movably provided and provided to be able to be in/out of contact with photoconductor10.

In the present example as well, a voltage drop in charging roller110is accurately detected so that a proper charge bias voltage is set.

Specifically, switch circuit SW sets a path through which a prescribed charge bias voltage is supplied from power supply apparatus50to charging roller110in response to an instruction from main body control device51. In this case, in the present example, current I2flows to charging roller110. Switch circuit SW sets a path through which a prescribed charge bias voltage is supplied from power supply apparatus50to conductive member120in response to an instruction from main body control device51. In this case, in the present example, current I1flows to conductive member120.

Currents I1and I2are detected by current sensor SA.

A resistance value of charging roller110can be calculated based on prescribed charge bias voltage V/(I1−I2).

Then, the voltage drop in charging roller110can be calculated based on the calculated resistance value of charging roller110and current I2.

Therefore, in consideration of the voltage drop in charging roller110from target value Vppt, a charge bias voltage resulting from addition of that voltage decrement can be set.

Specifically, main body control device51sets the charge bias voltage based on target value Vppt+current I2×the calculated resistance value of charging roller110. Main body control device51instructs power supply apparatus50to output the charge bias voltage.

A proper charge bias voltage in the stable region is thus set so that production of a poor image is suppressed and wear of photoconductor10can also be suppressed.

Prescribed charge bias voltage V in the present example in calculation of a resistance value of charging roller110may be the same as or different from a voltage used in a printing process. An AC voltage or a DC voltage may be applied.

By providing movable conductive member120not steadily in contact with photoconductor10, wear of photoconductor10can be suppressed. Without being limited to charging roller111and conductive member120, a metal brush or a conductive guide member can also be employed.

FIG. 9is a diagram illustrating a charging apparatus11A based on a second modification of the embodiment.

Charging apparatus11A in which a resistor112is connected in series in a voltage supply path for charging roller111is shown. According to the configuration, an amount of current which flows through the voltage supply path can be decreased.

Switch circuit SW connects power supply apparatus50, any one of charging rollers110and111, and power supply apparatus50in response to an instruction from main body control device51.

In the present example as well, a voltage drop in charging roller110is accurately detected so that a proper charge bias voltage is set.

Specifically, switch circuit SW sets a path through which a prescribed charge bias voltage is supplied from power supply apparatus50to charging roller110in response to an instruction from main body control device51. In this case, in the present example, current I2flows to charging roller110. Switch circuit SW sets a path through which a prescribed charge bias voltage is supplied from power supply apparatus50to charging roller111in response to an instruction from main body control device51. In this case, in the present example, a current I3flows to charging roller111.

Currents I2and I3are detected by current sensor SA.

Photoconductor10has a resistance value Rp and resistor112has a resistance value Ry. An example in which a resistance value of charging roller111is not included in calculation assuming that it is sufficiently lower than that of resistor112will be described.

Resistance value Rp of photoconductor10is calculated as [V−(I3×Ry)]/I3.

Resistance value Rx of charging roller110is thus calculated as [V−(I2×Rp)]/I2.

Then, the voltage drop in charging roller110can be calculated based on the calculated resistance value of charging roller110and current I2.

Therefore, in consideration of the voltage drop in charging roller110from target value Vppt, a charge bias voltage resulting from addition of that voltage decrement can be set.

Specifically, main body control device51sets the charge bias voltage based on target value Vppt+current I2×calculated resistance value Rx of charging roller110. Main body control device51instructs power supply apparatus50to output the charge bias voltage.

A proper charge bias voltage in the stable region is thus set so that production of a poor image is suppressed and wear of photoconductor10can also be suppressed.

Prescribed charge bias voltage V in the present example in calculation of a resistance value of charging roller110may be the same as or different from a voltage used in a printing process. An AC voltage or a DC voltage may be applied.

In the present example, power consumption can be reduced by decreasing an amount of current which flows through the path for supply of a voltage to charging roller111by providing resistor112.

Though an example in which a power supply apparatus is mainly used in an image formation apparatus has been described in the present example, a scheme can generally be used also for other applications without being particularly limited to the image formation apparatus.