JP2021071517A - Image forming apparatus and control method - Google Patents

Abstract

To reduce the generation of image noise.SOLUTION: An image forming apparatus 100 has: an image carrier 10; a developing roller that supplies developer to the image carrier; a first power supply device 711 that applies voltage to the developing roller; a control unit 60 that determines the voltage of the image carrier 10 based on the voltage applied by the first power supply device 711; and a second power supply device 712 that applies a second voltage determined by the control unit 60 to the image carrier 10.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an image forming apparatus and a control method.

An image forming apparatus having a photoconductor on which a toner image is formed and a developing roller that supplies toner to the photoconductor is known. In such an image forming apparatus, toner (hereinafter, referred to as “fog toner”) may adhere to a portion of the photoconductor on which a toner image is not formed.

Generally, in an image forming apparatus having a photoconductor, filming, which is a phenomenon such as adhesion of an external additive to the photoconductor, may occur. Filming is a phenomenon in which an external additive adheres to a photoconductor. The image forming apparatus described in Patent Document 1 controls the amount of fog toner so that the amount of fog toner increases by controlling the charging potential of the photoconductor when a condition in which filming is likely to occur is satisfied. To do.

Japanese Unexamined Patent Publication No. 2006-72240

By the way, when the amount of the fog toner is excessively large, or when the amount of the fog toner is excessively small, image noise is generated on the photoconductor. In the image forming apparatus described in Patent Document 1, the amount of fog toner may be excessively large, and the amount of fog toner may be excessively small. Therefore, the image forming apparatus described in Patent Document 1 may have a problem that image noise is generated.

The present disclosure has been made to solve the above-mentioned problems, and an object in a certain aspect is to provide a technique for reducing the occurrence of image noise.

According to a certain aspect of the present disclosure, an image carrier in which an electrostatic latent image is developed by a developer, a developer carrier that supplies a developer to the image carrier, and a first that applies a voltage to the developer carrier. A power supply device, a control device that determines the voltage of the image carrier based on the voltage applied to the developer carrier, and a second power supply device that applies the voltage determined by the control device to the image carrier. An image forming apparatus comprising the above is provided.

In a certain aspect, an exposure device for exposing the image carrier is further provided, and the control device is based on the difference between the voltage applied to the developer carrier and the potential of the image carrier after exposure by the exposure device. Determine the voltage of the carrier.

In a certain aspect, a charging device for charging the developer negatively is further provided, and the control device is provided with a voltage applied to the developer carrier and an image carrier as the voltage applied to the developer carrier is smaller. The voltage of the image carrier is determined so that the difference from the potential in the region different from the region where the electrostatic latent image is developed becomes small.

In a certain aspect, a charging device for charging the developer negatively is further provided, and the control device increases the voltage applied to the developer carrier and the image carrier as the voltage applied to the developer carrier increases. The voltage of the image carrier is determined so that the difference from the potential in the region different from the region where the electrostatic latent image is developed becomes large.

In a certain aspect, a charging device for positively charging the developer is further provided, and the control device increases the voltage applied to the developer carrier and the image carrier as the voltage applied to the developer carrier decreases. The voltage of the image carrier is determined so that the difference from the potential in the region different from the region where the electrostatic latent image is developed becomes large.

In a certain aspect, a charging device for positively charging the developer is further provided, and the control device increases the voltage applied to the developer carrier and the image carrier as the voltage applied to the developer carrier increases. The voltage of the image carrier is determined so that the difference from the potential in the region different from the region where the electrostatic latent image is developed becomes small.

In a certain aspect, a charging device for charging the developer negatively is further provided, and the control device has a small difference between the voltage applied to the developer carrier and the potential of the image carrier after exposure by the exposure device. The voltage of the image carrier is determined so that the difference between the voltage applied to the developer carrier and the potential in a region different from the region where the electrostatic latent image of the image carrier is developed becomes smaller.

In a certain aspect, a charging device for charging the developer negatively is further provided, and the control device has a large difference between the voltage applied to the developer carrier and the potential of the image carrier after exposure by the exposure device. The voltage of the image carrier is determined so that the difference between the voltage applied to the developer carrier and the potential in a region different from the region where the electrostatic latent image of the image carrier is developed becomes larger.

In a certain aspect, a charging device for charging the developer positively is further provided, and the control device has a small difference between the voltage applied to the developer carrier and the potential of the image carrier after exposure by the exposure device. The voltage of the image carrier is determined so that the difference between the voltage applied to the developer carrier and the potential in a region different from the region where the electrostatic latent image of the image carrier is developed becomes larger.

In a certain aspect, a charging device for charging the developer positively is further provided, and the control device has a large difference between the voltage applied to the developer carrier and the potential of the image carrier after exposure by the exposure device. The voltage of the image carrier is determined so that the difference between the voltage applied to the developer carrier and the potential in a region different from the region where the electrostatic latent image of the image carrier is developed becomes smaller.

In one aspect, the control device determines the voltage of the image carrier based on at least one of the concentration of the developer on the developer carrier, the charge on the developer, and the linear velocity of the image forming apparatus.

According to another aspect of the present disclosure, a control method for controlling an image forming apparatus having an image carrier on which an electrostatic latent image is developed by a developer and a developer carrier for supplying the developer to the image carrier. Therefore, a control method including a step of determining the voltage of the image carrier based on the voltage applied to the developer carrier and a step of applying the determined voltage to the image carrier is provided. ..

According to the present disclosure, it is possible to reduce the occurrence of image noise.
The above and other objectives, features, aspects and advantages of the invention will become apparent from the following detailed description of the invention as understood in connection with the accompanying drawings.

It is a figure for demonstrating the whole structure of the image forming apparatus of this embodiment. It is a figure for demonstrating the internal structure of an image formation unit. It is a block diagram for demonstrating the main hardware configuration of the image forming apparatus of this embodiment. It is a figure for demonstrating an example of a stationary layer A. It is a figure for demonstrating the adherent toner. It is a figure for demonstrating the adherent toner. It is a figure for demonstrating the adherent toner. It is a figure for demonstrating the adherent toner. It is a figure for demonstrating the result of comparison between the image forming apparatus of a comparative example, and the image forming apparatus of this Embodiment. It is a figure for demonstrating the relationship between the development bias and the surface potential of the image carrier after charge. It is a figure for demonstrating an example of the method of calculating the development bias. It is a figure for demonstrating the functional configuration example of a control device. It is a flowchart which shows the processing of an image forming apparatus. It is a figure for demonstrating an example of the table group used in Embodiment 2. FIG. It is a figure for demonstrating the functional configuration example of the control apparatus of Embodiment 2. It is a flowchart which shows the process of the image forming apparatus 100 of Embodiment 2. It is a figure for demonstrating the relationship of the adhered toner amount, development bias, and toner density. It is a figure for demonstrating the relationship of the adhered toner amount, the development bias, and the toner charge amount. It is a figure for demonstrating the relationship between the amount of adhered toner, development bias, and linear velocity. This is a table used by the image forming apparatus of the sixth embodiment. This is a table used by the image forming apparatus of the seventh embodiment.

The image forming apparatus according to the present embodiment will be described below with reference to the drawings. When the number, quantity, etc. are referred to in the embodiments described below, the scope of the present embodiment is not necessarily limited to the number, quantity, etc., unless otherwise specified. The same parts and equivalent parts may be given the same reference number, and duplicate explanations may not be repeated. In addition, it is planned from the beginning to use the configurations in each embodiment in appropriate combinations.

<Embodiment 1>
[Configuration example of image forming apparatus]
FIG. 1 is a diagram for explaining the overall configuration of the image forming apparatus 100 as a color printer. Hereinafter, the image forming apparatus 100 as a color printer will be described, but the image forming apparatus 100 is not limited to the color printer. For example, the image forming apparatus 100 may be any of a monochrome printer, a copying machine, a facsimile, and a multi-function peripheral (MFP). Further, in the present embodiment, the toner may be referred to as a developer, and the toner and the carrier may be referred to as a developer (or a two-component developer). Further, the recording medium includes, for example, paper, a sheet, and the like. In addition, forming an image on a recording medium may be referred to as "printing".

The image forming apparatus 100 includes image forming units 1Y, 1M, 1C, 1K, an intermediate transfer belt 36, a primary transfer roller 31, a secondary transfer roller 33, a cassette 37, a driven roller 38, and a drive roller 39. A pickup roller 41, a timing roller 42, and a fixing device 43 are provided.

The image forming units 1Y, 1M, 1C, and 1K are arranged in order along the intermediate transfer belt 36. The image forming unit 1Y forms a yellow (Y) toner image. The image forming unit 1M forms a toner image of magenta (M). The image forming unit 1C forms a toner image of cyan (C). The image forming unit 1K forms a black (BK) toner image.

The image forming units 1Y, 1M, 1C, and 1K each include an image carrier 10, a charging unit 11, an exposure unit 12, a developing unit 13, and a cleaning device 17, respectively. The image carrier 10 is typically a photoconductor whose image is developed by a developer. In other words, the image carrier 10 is typically a photoconductor that carries a toner image. The toner image may be called an electrostatic latent image. As an example, the image carrier 10 is a point typically a photoconductor drum. A photosensitive layer is formed on the surface of the photoconductor drum. The image carrier 10 rotates in the direction corresponding to the drive direction of the intermediate transfer belt 36 (the direction of the arrow in the image carrier 10 in FIG. 1).

In the color printing mode, the yellow (Y) toner image, the magenta (M) toner image, the cyan (C) toner image, and the black (BK) toner image are sequentially superimposed and transferred to the intermediate transfer belt 36. Toner. As a result, a color toner image is formed on the intermediate transfer belt 36. On the other hand, in the monochrome printing mode, the black (BK) toner image is transferred from the image carrier 10 (latent image carrier) to the intermediate transfer belt 36.

The intermediate transfer belt 36 is stretched on the driven roller 38 and the driving roller 39. The drive roller 39 is rotationally driven by, for example, a motor (not shown). The intermediate transfer belt 36 and the driven roller 38 rotate in conjunction with the drive roller 39. As a result, the toner image on the intermediate transfer belt 36 is transferred to the secondary transfer roller 33.

Paper S is housed in the cassette 37. The paper S is fed from the cassette 37 one by one to the secondary transfer roller 33 along the transport path 40 by the pickup roller 41 and the timing roller 42. The secondary transfer roller 33 applies a transfer voltage having a polarity opposite to that of the toner image to the paper S being conveyed. As a result, the toner image is attracted from the intermediate transfer belt 36 to the secondary transfer roller 33 and transferred to an appropriate position on the paper S.

The fixing device 43 pressurizes and heats the paper S passing through the fixing device 43. As a result, the toner image formed on the paper S is fixed on the paper S. After that, the paper S is discharged to the tray 48.

Further, the image forming apparatus 100 has a power supply device 72. The power supply device 72 includes a first power supply device 711 and a second power supply device 712. The first power supply device 711 applies a voltage to the developing roller 13d, which will be described later. It should be noted that "the first power supply device 711 applies a voltage to the developing roller 13d" is also referred to as "the first power supply device 711 charges the developing roller 13d". The voltage applied to the developing roller 13d is referred to as a "first voltage". Further, the development bias described later corresponds to the first voltage. The development bias may be the same value as the first voltage. Further, the development bias may be a value different from the first voltage. Therefore, the "development bias" may be referred to as the "first voltage". The second power supply device 712 applies a voltage to the image carrier 10. Further, the voltage applied to the image carrier 10 is referred to as a "second voltage".

Further, the image forming apparatus 100 has a control device 60 for controlling the image forming apparatus 100. The control device 60 and the power supply device 72 are described in the location shown in FIG. 1 for convenience, but are actually installed in other locations.

The IDC (Image Density Control) sensor 70 is arranged in the vicinity of the intermediate transfer belt 36 on the downstream side of the image forming unit 1K and on the upstream side of the drive roller 39 in the driving direction of the intermediate transfer belt 36. The IDC sensor 70 is arranged so as to face the image-carrying surface of the intermediate transfer belt 36.

The IDC sensor 70 measures the toner adhesion amount (toner density) of the patch images of each of the Y, M, C, and K colors formed on the intermediate transfer belt 36. The IDC sensor 70 is composed of, for example, a reflective optical sensor having a light emitting unit and a light receiving unit. The IDC sensor 70 irradiates the patch image formed on the intermediate transfer belt 36 with light from the light emitting unit, receives the reflected light at the light receiving unit, converts it into an electric signal, and outputs the light to the control device 60. The patch image has a predetermined gradation value (for example, gradation value 125). The control device 60 calculates the toner concentration based on the electric signal output from the IDC sensor 70.

[Internal configuration of image forming unit]
FIG. 2 is a diagram showing an example of the internal structure of the image forming units 1Y, 1M, 1C, and 1K. The internal structure of the image forming units 1Y, 1M, 1C, and 1K will be described with reference to FIG.

As shown in FIG. 2, each of the image forming units 1Y, 1M, 1C, and 1K includes a drum unit 15, an exposure unit 12, and a developing unit 13, respectively.

The drum unit 15 includes an image carrier 10, a charging unit 11, a cleaning device 17, and a support 19.

The support 19 supports each of the image carrier 10, the charging portion 11, and the cleaning device 17 to unitize each of these members.

The image carrier 10 includes a drum-shaped (cylindrical) substrate 10a made of aluminum or the like, and a photosensitive layer 10b formed on the outer peripheral surface of the substrate 10a. A toner image is formed on the outer peripheral surface of the image carrier 10.

The charging unit 11 is a roller that uniformly charges the peripheral surface of the image carrier 10 to a negative electrode. The charged portion 11 has a long shape along the rotation axis of the image carrier 10. The rotation axis of the charging unit 11 is parallel to the rotation axis of the image carrier 10.

The charged portion 11 includes a rigid columnar shaft made of metal (for example, stainless steel) and an elastic layer made of a conductive or semi-conductive elastic material formed on the peripheral surface of the shaft.

The cleaning device 17 is pressed against the image carrier 10. The cleaning device 17 recovers the toner by scraping off the toner remaining on the surface of the image carrier 10 after the toner image is transferred.

The exposure unit 12 irradiates the image carrier 10 with a laser beam in response to a control signal from the control device 60, and exposes the surface of the image carrier 10 according to the input image pattern. As a result, electric charges are generated by the charge generation layer of the photosensitive layer 10b in the exposed portion, and the absolute value of the surface potential (negative electrode property) of the exposed portion is the surface potential (negative electrode property) of the unexposed portion. It will be lower than the absolute value. In this way, an electrostatic latent image corresponding to the input image is formed on the image carrier 10.

In the present embodiment, the developing unit 13 develops an electrostatic latent image formed on the surface of the image carrier 10 with toner (using toner). That is, the developing unit 13 forms a toner image on the surface of the image carrier 10. The developing unit 13 includes a developing tank 13a, a pair of stirring screws 13b and 13c, a toner concentration sensor 73, and a developing roller 13d.

The developing tank 13a contains a two-component developer composed of toner and a carrier. The toner is non-magnetic. The carrier is formed of ferrite powder, iron powder, or the like. The developing tank 13a has two storage chambers 13e and 13f along the axial direction of the image carrier 10. The two storage chambers 13e and 13f communicate with each other at both ends. Stirring screws 13b and 13c are arranged in the storage chambers 13e and 13f, respectively. The stirring screws 13b and 13c are members that extend in the depth direction of the paper surface of FIG. By rotating the stirring screws 13b and 13c, the two-component developer stored in the storage chambers 13e and 13f is stirred in the process of circulating between the storage chamber 13e and the storage chamber 13f, and the toner and the carrier are mixed. At the same time, it is triboelectrically charged.

In the present embodiment, the resin particles constituting the toner and the resin coating the surface of the carrier so that the toner has a negative charge characteristic and the carrier has a positive charge characteristic due to the triboelectric charge between the toner and the carrier. The material is selected. Therefore, the toner is charged to the negative electrode property and the carrier is charged to the positive electrode property by being rubbed by stirring. Then, the negatively charged toner adheres to the periphery of the positively charged carrier. The developing tank 13a, the stirring screws 13b, 13c, and the accommodating chambers 13e, 13f correspond to the "charging device for charging the toner negatively" of the present disclosure. In the present embodiment, the toner is charged to the negative electrode by the charging device in principle, but there is an exception of the toner which is charged to the positive electrode which is the opposite of the negative electrode.

The developing roller 13d is a non-magnetic cylindrical member made of, for example, a stainless steel material. The developing roller 13d incorporates a magnet (not shown) having a plurality of magnetic poles, and is rotationally driven while maintaining a slight distance from the image carrier 10.

The two-component developer, that is, the carrier to which the toner is attached, which is conveyed in the axial direction of the stirring screw 13b in the storage chamber 13e, is attached to the peripheral surface of the developing roller 13d by the magnet built in the developing roller 13d.

The rotating developing roller 13d conveys the two-component developer adhering to the peripheral surface to a position (development region) facing the image carrier 10.

A voltage supplied from the first power supply device 711 (see FIG. 3) is applied to the developing roller 13d. For example, a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the developing roller 13d.

When the electrostatic latent image forming portion reaches the position (development region) facing the developing roller 13d due to the rotation of the image carrier 10, toner (negatively charged) is transferred from the peripheral surface of the developing roller 13d from the carrier. It moves away to the image carrier 10. At this time, the carrier is attracted to the developing roller 13d by the magnetic force of the magnet built in the developing roller 13d, and does not move to the image carrier 10. In this way, the toner is transferred from the developing roller 13d to the image carrier 10, and the toner image corresponding to the electrostatic latent image is developed on the surface of the image carrier 10.

Further, the developing unit 13 has a regulating member 13h. The regulating member 13h is a member that adjusts (regulates) the amount of the two-component developer adhering to the developing roller 13d. Since the developing unit 13 has the regulating member 13h, the amount of the two-component developer adhering to the developing roller 13d can be set to an appropriate amount. In the present embodiment, a part of the developing tank 13a is a regulating member 13h.

The toner concentration sensor 73 detects the toner concentration of the two-component developer in the developing tank 13a. The toner concentration is also referred to as "Tc". The toner concentration sensor 73 typically includes a magnetic permeability sensor. The toner concentration sensor 73 measures the magnetic permeability of the processing region in the developing unit 13 where the toner is present. The carrier is mainly composed of iron, and when the magnetic permeability is high, it is assumed that the carrier is large, so that the Tc is low. On the other hand, when the magnetic permeability is low, it is assumed that the number of carriers is small, so that Tc is high. Further, the toner concentration sensor 73 converts the magnetic permeability detected by the magnetic permeability sensor into Tc. The conversion method may be, for example, a method using a predetermined formula. Further, the conversion method may be, for example, a method using a predetermined table. The conversion from magnetic permeability to Tc may be performed by the control device 60.

The toner concentration is typically obtained by dividing the weight of the toner by the weight of the toner plus the weight of the carrier. That is, the toner concentration is obtained by (toner weight) / (toner weight + carrier weight).

The cleaning device 17 includes a cleaning blade (hereinafter, referred to as “blade 18”). The cleaning device 17 holds the blade 18 so that one end 18A of the blade 18 comes into contact with the surface of the image carrier 10. The blade 18 removes the toner remaining on the surface of the image carrier 10 after the primary transfer.

Although the film thickness sensor 78 is shown by a broken line in FIG. 2 and FIG. 3 described later, the film thickness sensor 78 will be described in the embodiment described later.

[Hardware configuration of image forming apparatus]
An example of the hardware configuration of the image forming apparatus 100 will be described with reference to FIG. FIG. 3 is a block diagram showing a main hardware configuration of the image forming apparatus 100.

As shown in FIG. 3, the image forming apparatus 100 includes a power supply device 72, a CPU 55 (Central Processing Unit), an IDC sensor 70, a ROM 102 (Read Only Memory), a RAM 103 (Random Access Memory), and an operation panel. The 107 and the network interface 80 are included.

The CPU 55 executes the control program. The ROM 102 non-volatilely stores data including a control program executed by the CPU 55. The RAM 103 volatilely stores the data.

The operation panel 107 is composed of a display and a touch panel. The display and touch panel are stacked on top of each other. The operation panel 107 receives, for example, a command (for example, a print command, a scan command, etc.) from the user to the image forming apparatus 100. The image forming apparatus 100 receives a command from the user as a job.

The network interface 80 is connected to a network (not shown). The image forming apparatus 100 can communicate with an external device via the network interface 80. The external device includes, for example, a mobile communication terminal such as a smartphone, a server, and the like.

[About the stationary layer]
Next, the rest layer will be described. In the present embodiment, the dissociation of the toner of the image carrier 10 is improved, the wear of the blade 18 is suppressed, the torque is reduced by the contact between the blade 18 and the image carrier 10, and the image carrier 10 is moved by the charged portion 11. In order to suppress the discharge deterioration of the toner, a lubricant is externally added to the toner. Adhesive toner, residual toner, and toner and lubricant such as a toner patch are supplied to the blade 18.

FIG. 4 is a diagram showing an example of the stationary layer A. In the example of FIG. 4, it is the contact point B between the blade 18 and the image carrier 10. Further, the contact portion B is a portion where one end 18A of the blade 18 and the image carrier 10 are in contact with each other. In the example of FIG. 4, the rotation direction C of the image carrier 10 is clockwise. The stationary layer A is formed at the contact point B on the upstream side of the image carrier 10 in the rotation direction C.

Further, if the amount of the stationary layer A is too small, the toner on the image carrier 10 remains without being cleaned by the blade 18. As a result, streaky image noise is generated on the image carrier 10 due to the remaining toner. On the contrary, if the amount of the stationary layer A is too large, the amount of the lubricant on the image carrier 10 becomes excessive, and this lubricant adheres to the image carrier 10. As a result, the toner adheres to the adhered lubricant, and point-like image noise is generated on the image carrier 10. That is, it is preferable that an appropriate amount of stationary layer is formed on the image carrier 10.

Next, "residual toner" and the like will be described. The "residual toner" is toner that has not been transferred to the intermediate transfer belt 36 even though the primary transfer of the toner has been performed from the image carrier 10 to the intermediate transfer belt 36. A "toner patch" is a toner for image adjustment.

The “adhered toner” refers to toner that flies from the developing roller 13d to the image carrier 10 even though the image forming process has not been executed by the image forming apparatus 100. Adhesive toner is also called "fog toner". Adhesive toner includes a first adherent toner and a second adherent toner. The "first adherent toner" is a negatively charged toner. The "first adherent toner" is toner that adheres to the image carrier 10 by physically flying from the developing roller 13d to the image carrier 10. "Flying physically from the developing roller 13d to the image carrier 10" means, for example, "flying to the image carrier 10 by the centrifugal force from the rotating developing roller 13d". Further, the "second adherent toner" is charged in the opposite direction to the polarity (negative electrode property in the present embodiment) charged in the developing tank 13a, the stirring screws 13b and 13c, and the storage chambers 13e and 13f. Toner (positive electrode in this embodiment). The positively charged "second adhesive toner" is generally electrically adsorbed on the negatively charged developing roller 16d. However, the "second adherent toner" may fly to the image carrier 10 having a lower potential than the developing roller 16d.

FIG. 5 is a diagram for explaining that the second adhered toner adheres to the image carrier 10. The development bias in FIG. 5 is a bias charged in the development roller 13d. In the example of FIG. 5, the development bias is assumed to be −300 V. Further, it is assumed that the surface potential of the image carrier 10 on the surface of the image carrier 10 on which the toner image is not formed is −500 V. The “portion where the toner image is not formed” corresponds to the “region different from the region where the image of the image carrier is developed” of the present disclosure. Further, in FIG. 5, a positively charged toner 300A and a negatively charged toner 300B are shown. Further, the difference between the development bias and the surface potential of the image carrier 10 in the non-image forming portion is referred to as "potential difference ΔV". This potential difference ΔV is also called a “fog margin”. Further, the potential difference ΔV may be referred to as a second difference. Further, the "surface potential of the image carrier 10 in the portion where the toner image is not formed" and the "surface potential of the image carrier 10 charged by the charged portion 11" are the same or substantially the same.

The negatively charged toner 300B is electrically adsorbed on the developing roller 13d (= −300V) whose potential is lower than the surface potential (= −500V) of the image carrier 10. Therefore, the negatively charged toner 300B does not fly to the surface of the image carrier 10 from an electrical point of view. On the other hand, the positively charged toner 300A may electrically adhere to the developing roller 13d, but may also fly and adhere to the image carrier 10 having a lower potential than the developing roller 13d (= −300V). The positively charged toner 300A that electrically flies and adheres to the image carrier 10 becomes the adhered toner.

In order for the image forming apparatus 100 to continue forming an appropriate amount of the stationary layer A, it is effective to supply an appropriate amount of the adhered toner. This is because, as compared with the transfer residual toner supplied at the time of image formation and the toner patch supplied at the time of non-image formation, the adhered toner is supplied at the time of image formation and non-image formation.

The image forming apparatus 100 of the present embodiment executes an image stabilization process (hereinafter, simply referred to as “stabilization process”) at an arbitrary timing in order to keep the image density constant when printing is continued. To do. In the image stabilization process, the image forming apparatus 100 of the present embodiment selects an appropriate development bias according to the state of the developer and the image carrier 10.

On the other hand, in the image forming apparatus of the comparative example, the potential difference ΔV was not changed by executing the stabilization process. Therefore, in the image forming apparatus of the comparative example, when the development bias changes due to the stabilization process, the potential difference ΔV is the same, so that the amount of adhered toner changes.

Further, when the potential difference ΔV is the same, when the development bias is small, the amount of adhered toner is smaller than when the development bias is large. 5 and 6 are diagrams for explaining that when the potential difference ΔV is the same, the amount of adhered toner is smaller when the development bias is small than when the development bias is large. In both FIGS. 5 and 6, the potential difference ΔV is 200V, the development bias in FIG. 6 is −300V, and the development bias in FIG. 6 is −400V.

A development bias of −400 V as shown in FIG. 6 is a potential smaller than a development bias of −300 V as shown in FIG. Therefore, the positively charged toner 300A is electrically strongly adsorbed by the developing roller 13d to which the development bias of −400V is applied than to the developing roller 13d to which the development bias of −300V is applied. Therefore, when a development bias of −400 V is applied to the developing roller 13d, the positive charge flying to the image carrier 10 is higher than when a development bias of −300 V is applied to the developing roller 13d. The amount of toner 300A is reduced. In other words, when the potential difference ΔV is the same, when the development bias is small, the amount of adhered toner is smaller than when the development bias is large. Hereinafter, "the law that the amount of adhered toner is smaller when the development bias is small when the potential difference ΔV is the same than when the development bias is large" is referred to as "the first law".

Further, the larger the potential difference ΔV, the smaller the amount of adhered toner, and the smaller the potential difference ΔV, the larger the amount of adhered toner. 7 and 8 are diagrams for explaining that the larger the potential difference ΔV, the smaller the amount of adhered toner, and the smaller the potential difference ΔV, the larger the amount of adhered toner. In both FIGS. 7 and 8, the development bias is −300 V, the potential difference in FIG. 7 is 50 V, and the potential difference in FIG. 8 is 100 V. That is, the surface potential of the image carrier 10 of the non-image forming portion of FIG. 7 is −350V, and the surface potential of the image carrier 10 of the non-image forming portion of FIG. 8 is −400V.

The negatively charged toner flies to the image carrier 10 by the centrifugal force from the developing roller 13d. Here, when the surface potential of the image carrier 10 is −350 V, the repulsive force due to the negative polarities is weaker than when the surface potential of the image carrier 10 is −400 V. .. Therefore, as shown in FIGS. 7 and 8, when the surface potential of the image carrier 10 is −350 V, the image from the developing roller 13d is higher than when the surface potential of the image carrier 10 is −400 V. The amount of negatively charged toner 300B flying on the carrier 10 increases. In other words, the larger the potential difference ΔV, the smaller the amount of adhered toner (that is, the amount of the first adhered toner), and the smaller the potential difference ΔV, the larger the amount of adhered toner (that is, the amount of the first adhered toner). Hereinafter, "the larger the potential difference ΔV, the smaller the amount of adhered toner, and the smaller the potential difference ΔV, the larger the amount of adhered toner" is referred to as "the second law".

[Comparison between Comparative Example and This Embodiment]
Next, the result of comparison between the image forming apparatus of the comparative example and the image forming apparatus 100 of the present embodiment will be described. FIG. 9 is a diagram for explaining the result of comparison between the image forming apparatus of the comparative example and the image forming apparatus 100 of the present embodiment. In FIG. 9, the vertical axis represents the amount of adhered toner, and the horizontal axis represents the development bias. Further, the broken line in FIG. 9 indicates the image forming apparatus of the comparative example, and the solid line indicates the image forming apparatus of the present embodiment. Further, as shown in FIG. 9, in the present embodiment, an appropriate range of the amount of adhered toner is set. The appropriate range is the range of the lower limit value S1 to the upper limit value S2. When the image forming apparatus 100 continues the printing process in a state where the amount of adhered toner is less than the lower limit value S1 (that is, the amount of the stationary layer A is too small), streak-like image noise is generated on the image carrier 10. It ends up.

Further, when the image forming apparatus 100 continues the printing process in a state where the amount of adhered toner exceeds the upper limit value S2 (that is, the amount of the stationary layer A is too large), the amount of lubricant on the image carrier 10 becomes excessive. Therefore, this lubricant adheres to the image carrier 10, and point-like image noise is generated on the image carrier 10.

For example, in FIG. 9, when the development bias is large (for example, when the development bias is −200V), in the image forming apparatus of the comparative example, the amount of adhered toner exceeds the upper limit value S2 in the development bias (for example, when the development bias is −200V). See the first law). Therefore, when the development bias is large, the image forming apparatus 100 of the present embodiment increases the potential difference ΔV so that the amount of adhered toner belongs to an appropriate range based on the second law. As a result, the image forming apparatus 100 can reduce the amount of adhered toner. Therefore, the image forming apparatus 100 can form an appropriate amount of the stationary layer A.

Further, in FIG. 9, when the development bias is small (for example, when the development bias is −600V), in the image forming apparatus of the comparative example, the amount of adhered toner falls below the lower limit value S1 in the development bias (for example, when the development bias is −600V). See the first law). Therefore, when the development bias is small, the image forming apparatus 100 of the present embodiment reduces the potential difference ΔV so that the amount of adhered toner belongs to an appropriate range based on the second law. As a result, the image forming apparatus 100 can increase the amount of adhered toner. Therefore, the image forming apparatus 100 can form an appropriate amount of the stationary layer A.

[Relationship between development bias and surface potential of image carrier after charging]
Next, the relationship between the development bias and the surface potential of the image carrier after charging will be described. FIG. 10 is a diagram for explaining the relationship between the development bias and the surface potential of the image carrier after charging. The image forming apparatus 100 identifies the development bias in the stabilization process. In the example of FIG. 10, it is defined that the smaller the development bias, the smaller the potential difference ΔV, and the larger the development bias, the larger the potential difference ΔV.

In the example of FIG. 10, when the development bias is, for example, −100V, a potential difference of 110V ΔV is associated. Further, when the development bias is, for example, −600 V, a potential difference ΔV of 60 V is associated.

According to the description of FIG. 9 and the first rule, the intention of the provision of FIG. 10 is that when the development bias is small, the amount of adhered toner is smaller than when the development bias is large (the amount of the stationary layer A is smaller). ). Therefore, when the development bias is small, the amount of adhered toner is increased by reducing the potential difference ΔV based on the second law in order to increase the amount of the stationary layer A. On the other hand, when the development bias is large, the amount of adhered toner is reduced by increasing the potential difference ΔV based on the second law in order to reduce the amount of the stationary layer A. As a result, the image forming apparatus 100 can form an appropriate amount of the stationary layer A.

[Development bias calculation method]
Next, an example of the method for calculating the development bias of the present embodiment will be described. FIG. 11 is a diagram for explaining an example of a method for calculating the development bias. The control device 60 forms a patch of each color on the intermediate transfer belt 36 with each of a plurality of predetermined development biases. In the example of FIG. 11, it is assumed that the plurality of development biases are −200V, −300V, −400V, and −500V. Next, the IDC sensor 70 detects the density of the patch formed by each of the plurality of development biases. The control device 60 can create a first-order approximation line as shown by the broken line in FIG. The vertical axis of FIG. 11 shows the density of the image (for example, a patch) formed on the intermediate transfer belt 36, and the horizontal axis shows the development bias.

When the control device 60 executes the stabilization process, the control device 60 acquires the density of the image formed by the stabilization process. The execution condition of the stabilization process includes, for example, a first condition, a second condition, and the like. The first condition is that a predetermined timing is reached from when the power of the image forming apparatus 100 is switched from off to on until before the first printing is executed. The first condition may be, for example, a condition that the power supply of the image forming apparatus 100 is switched from off to on. The second condition is that the image forming apparatus 100 prints on a predetermined number of sheets of paper. The predetermined number of sheets is, for example, 500 sheets.

When the control device 60 executes the stabilization process, the control device 60 temporarily stores the image density in the printing process after the stabilization process is executed in a predetermined storage area. The predetermined storage area is, for example, RAM 103. The control device 60 acquires the image density from the RAM 103 when executing the stabilization process.

The control device 60 acquires the development bias corresponding to the density of the acquired image by referring to the linear approximation line created in advance. For example, in the example of FIG. 11, when the density of the image is "1.4", the control device 60 acquires −400 V as the development bias. In this way, the control device 60 acquires the development bias.

The control device 60 may generate a first-order approximation line of FIG. 11 each time the stabilization process is executed. Further, the control device 60 may generate a first-order approximation line at a predetermined timing and reuse the first-order approximation line in the stabilization process.

Further, the control device 60 may generate information corresponding to the first-order approximation line. The information corresponding to the first-order approximation line is, for example, a function. This function is a function that outputs the development bias when the density of the image is input. Further, the development bias may be obtained by another method without using the first-order approximation line and the function. For example, a development bias sensor may be provided so that the development bias sensor detects the development bias.

[Example of functional configuration of control device]
Next, a functional configuration example of the control device 60 will be described. FIG. 12 is a diagram for explaining a functional configuration example of the control device 60. The control device 60 has functions of a calculation unit 602, a determination unit 604, a control unit 608, and a table storage unit 606. The table of FIG. 10 is stored in the table storage unit 606.

The control device 60 acquires the image density E. The control device 60 acquires the image density E from the predetermined storage area (for example, RAM 103) described above. The acquired image density E is input to the calculation unit 602.

The calculation unit 602 calculates the development bias using the image density E. The calculation unit 602 calculates the development bias using, for example, the first-order approximation line described with reference to FIG. The calculated development bias is input to the determination unit 604. The determination unit 604 identifies the surface potential of the image carrier 10 after charging with reference to the table described with reference to FIG. 10 (the table stored in the table storage unit 606). In the example of FIG. 10, when the development bias is, for example, −200 V, the surface potential of the image carrier after charging is determined as −300 V.

Here, the "voltage applied by the second power supply device 712 to the image carrier 10" and the "surface potential of the image carrier 10 after charging" may be different. Therefore, the designer of the image forming apparatus 100 or the like calculates in advance the difference X between the "voltage applied to the image carrier 10 by the second power supply device 712" and the "surface potential of the image carrier 10 after charging". It is preferable to keep it. Then, the determination unit 604 applies a voltage in which the difference X is added to the "surface potential of the image carrier 10 after charging" determined by the determination unit 604, "the second power supply device 712 applies the image carrier 10 to the image carrier 10." Determined as "voltage to be used". The “voltage applied to the image carrier 10 by the second power supply device 712” determined by the determination unit 604 is output to the control unit 608.

The control unit 608 transmits a control signal including "a voltage applied to the image carrier 10 by the second power supply device 712" to the second power supply device 712. Upon receiving the control signal, the second power supply device 712 applies the image carrier 10 at the voltage included in the control signal. As a result, the control device 60 can set the surface potential of the image carrier 10 after charging to an appropriate potential. Therefore, as a result, the control device 60 can set the amount of adhered toner to an appropriate amount. Therefore, the control device 60 can form an appropriate amount of stationary layer A.

[Processing flow of image forming apparatus]
FIG. 13 is a flowchart showing the processing of the image forming apparatus 100. In step S2, the control device 60 of the image forming device 100 acquires a print job. Here, the print job is a job based on a print instruction. The print command is input by the user from the operation panel 107.

Next, in step S4, the control device 60 determines whether or not to execute the stabilization process. In step S4, when it is determined that the execution condition of the above-mentioned stabilization process is satisfied, the control device 60 determines YES and proceeds to step S6. Further, in step S4, when the control device 60 determines that the execution condition of the above-mentioned stabilization process is not satisfied, it determines NO and proceeds to step S10.

Next, in step S6, the calculation unit 602 (see FIG. 12) calculates the development bias based on the image density E. Next, in step S8, the determination unit 604 determines the "surface potential of the image carrier 10 after charging" based on the development bias with reference to the table (see FIG. 10). The control unit 608 determines an applied voltage (surface potential of the image carrier 10) such that the surface potential of the image carrier 10 becomes the determined “surface potential of the image carrier 10 after charging”. In step S8, the control unit 608 transmits a control signal including the determined applied voltage to the second power supply device 712.

Next, in step S10, the control device 60 prints one image specified in the print job on the paper. Further, even when NO is determined in step S4, in step S10, the control device 60 prints one image specified in the print job on the paper.

Here, in step S10 after the flow of YES, step S6, and step S8 in step S4, the image carrier 10 is charged with the charging potential determined by step S8 (that is, in the control device 60). The image forming apparatus 100 executes the printing process (with the controlled second voltage applied to the image carrier 10). On the other hand, in step S10 after the determination of NO in step S4, the image carrier 10 is charged with a charging potential (for example, the default charging potential) that does not reflect the processing of steps S6 and S8. The image forming apparatus 100 executes a printing process.

After the end of step S10, in step S12, the control device 60 determines whether or not the print job is completed. In step S12, the control device 60 determines whether or not the printing of the number of sheets specified in the print job has been completed. When the control device 60 determines that the print job has been completed (printing of all the number of sheets specified in the print job has been completed) (YES in step S12), the process ends. On the other hand, if the control device 60 determines that the print job has not been completed (printing of all the number of sheets specified in the print job has not been completed) (NO in step S12), the process proceeds to step S4. Return.

[Brief Summary]
(1) The determination unit 604 of the control device 60 of the present embodiment is based on the first voltage (development bias in the present embodiment) applied to the developing roller 13d, and the second voltage (in the present embodiment). , The surface potential of the image carrier 10) is determined. Typically, the controller 60 determines the second voltage with reference to the table of FIG. The control device 60 charges the image carrier 10 with the determined second voltage. Therefore, the control device 60 controls the surface potential of the image carrier 10 based on the first law and the second law. Therefore, the image forming apparatus 100 can set the amount of the adhered toner to an appropriate amount, and as a result, can form an appropriate amount of the stationary layer A. As a result, the image forming apparatus 100 can reduce the occurrence of image noise.

(2) Further, the image forming apparatus 100 of the present embodiment charges the toner negatively. Further, in the table of FIG. 10 used by the control device 60 of the present embodiment, the smaller the first voltage (that is, the development bias), the more the first voltage and the region where the toner image of the image carrier 10 is developed. It is specified that the second difference (that is, the potential difference ΔV) from the potentials in the different regions becomes small. According to the first rule described above, the smaller the first voltage, the smaller the amount of adhered toner (see also FIG. 9). In order to increase the amount of adhered toner that has decreased, the amount of adhered toner can be increased by reducing the potential difference ΔV based on the second law. Therefore, the image forming apparatus 100 of the present embodiment can set the amount of adhered toner to an appropriate amount, and as a result, can form an appropriate amount of the stationary layer A.

(3) Further, the table of FIG. 10 used by the control device 60 of the present embodiment is defined so that the larger the first voltage, the larger the potential difference ΔV. According to the first rule described above, the larger the first voltage, the larger the amount of adhered toner (see also FIG. 9). In order to reduce the increased amount of adhered toner, the amount of adhered toner can be reduced by increasing the potential difference ΔV based on the second law. Therefore, the image forming apparatus 100 of the present embodiment can set the amount of adhered toner to an appropriate amount, and as a result, can form an appropriate amount of the stationary layer A.

<Embodiment 2>
In the first embodiment, the control device 60 has been described as controlling the second voltage based on the first voltage applied by the first power supply device 711. In the second embodiment, the control device 60 is based on the difference between the first voltage (that is, development bias) applied by the first power supply device 711 and the potential after exposure of the image carrier 10 by the exposure unit 12. , Control the second voltage. The "difference between the first voltage applied by the first power supply device 711 and the potential of the image carrier 10 after exposure by the exposure unit 12" is also referred to as "first difference".

Generally, the larger the difference between the development bias and the surface charge of the image carrier 10 after exposure by the exposure unit 12, the more toner is used for image formation. Here, the surface potential of the image carrier 10 after exposure by the exposure unit 12 is the surface potential of the portion of the image carrier 10 where the toner image is not formed (that is, the electrostatic latent image of the image carrier 10). The potential in a region different from the region being developed). When more toner is used for image formation, more toner does not move from the surface of the image carrier 10 to the intermediate transfer belt 36 (that is, the toner remaining on the image carrier 10). Therefore, the amount of toner supplied to the stationary layer A formed on the blade 18 increases. In this case, the image forming apparatus 100 needs to reduce the amount of adhered toner. Therefore, the image forming apparatus 100 increases the potential difference ΔV and reduces the amount of adhered toner.

Conversely, the smaller the difference between the development bias and the surface charge of the image carrier 10 after exposure by the exposure unit 12, the less toner is used for image formation. When less toner is used for image formation, less toner does not transfer from the surface of the image carrier 10 to the intermediate transfer belt 36 (that is, less toner remains on the image carrier 10). In this case, the image forming apparatus 100 needs to increase the amount of adhered toner. Therefore, the image forming apparatus 100 reduces the potential difference ΔV and increases the amount of adhered toner.

As described above, the larger the "difference between the development bias and the surface potential of the image carrier 10 after exposure by the exposure unit 12," the larger the amount of adhered toner, and "the development bias and after exposure by the exposure unit 12". The smaller the "difference from the surface potential of the image carrier 10", the smaller the amount of adhered toner "is called the" third law ".

FIG. 14 is an example of a table group used in this embodiment. The table group of the present embodiment includes a table (a plurality of tables) specified for each type of development bias. In the example of FIG. 14, a table when the development bias is −100 V, a table when the development bias is −400 V, and a table when the development bias is −600 V are described. However, in reality, the image forming apparatus 100 has 11 types of development bias = -100V, -150V, -200V, -250V, -300V, -350V, -400V, -450V, -500V, -550V, and -600V. The development bias of each table is stored.

In the table of development bias = −400V in FIG. 14, the larger the “difference between the development bias and the surface potential of the image carrier 10 after exposure by the exposure unit 12,” that is, according to the third law, the adhered toner. It is specified that the larger the amount, the larger the potential difference ΔV. In the following, the difference between the development bias and the surface charge of the image carrier 10 after exposure by the exposure unit 12 is also referred to as a “second difference”. According to the second law, when the potential difference ΔV is large, the amount of adhered toner decreases. Therefore, even when the "difference between the development bias and the surface potential of the image carrier 10 after exposure by the exposure unit 12" is large, that is, even when the amount of adhered toner is large, the potential difference ΔV is large. By doing so, the amount of adhered toner can be reduced.

On the other hand, the smaller the "difference between the development bias and the surface potential of the image carrier 10 after exposure by the exposure unit 12," that is, the smaller the amount of adhered toner, the smaller the potential difference ΔV. It is stipulated in. According to the second law, when the potential difference ΔV is small, the amount of adhered toner increases. Therefore, even when the "difference between the development bias and the surface potential of the image carrier 10 after exposure by the exposure unit 12" is small, that is, even when the amount of adhered toner is small, the potential difference ΔV is small. By doing so, the amount of adhered toner can be increased.

Also, in the table with development bias = -100V and the table with development bias = -600V, the smaller the "difference between the development bias and the surface potential of the image carrier 10 after exposure by the exposure unit 12," the smaller the potential difference ΔV. It is specified that the potential difference ΔV becomes larger as the difference becomes smaller and the difference becomes larger. As for other development bias tables, the smaller the "difference between the development bias and the surface potential of the image carrier 10 after exposure by the exposure unit 12", the smaller the potential difference ΔV, and the larger this difference, the smaller the potential difference ΔV. Is specified to be large.

Further, as in the table of development bias = -100V, the table of development bias = -400V, and the table of development bias = -600V, it is stipulated that the smaller the development bias, the smaller the potential difference ΔV. It is specified that the larger the value is, the larger the potential difference ΔV is. The significance of this provision is the same as that described in FIG.

FIG. 15 is a diagram showing a functional configuration example of the control device 60A included in the image forming device of the present embodiment. As shown in FIG. 15, the control device 60A has functions of a calculation unit 602, an acquisition unit 650, a difference calculation unit 652, a determination unit 604, a table storage unit 606, and a control unit 608. The table storage unit 606 stores the table group described with reference to FIG. Further, as shown in FIGS. 2 and 3, the image forming apparatus 100 of the present embodiment has a film thickness sensor 78 shown by a broken line. The film thickness sensor 78 detects the film thickness of the photosensitive layer 10b of the image carrier 10. The image forming apparatus of the present embodiment uses the film thickness sensor 78 in order to obtain the surface potential of the image carrier after exposure. However, the image forming apparatus of the present embodiment may obtain the surface potential of the image carrier after exposure by another method.

The acquisition unit 650 acquires the film thickness of the photosensitive layer 10b of the image carrier 10. When the acquisition unit 650 acquires the film thickness of the photosensitive layer 10b, the acquisition unit 650 obtains the surface potential of the image carrier 10 after exposure based on the film thickness. For example, the acquisition unit 650 holds a table in which the “thickness” and the “surface potential of the image carrier 10 after exposure” are associated with each other, and by referring to the table, the “image carrier 10 after exposure 10” is used. "Surface potential" is calculated.

The difference calculation unit 652 calculates the difference between the “development bias calculated by the calculation unit 602” and the “surface potential of the image carrier 10 after exposure specified by the acquisition unit 650”. This difference is the "difference between the development bias and the image carrier 10 after exposure" described with reference to FIG.

The determination unit 604 specifies a table corresponding to the development bias calculated by the calculation unit 602 from the table group. The determination unit 604 specifies, for example, a table with a development bias = -100V when the development bias calculated by the calculation unit 602 is -100V. Then, the determination unit 604 refers to the specified table and refers to the “surface of the image carrier 10 after charging” corresponding to the “difference between the development bias and the image carrier 10 after exposure” calculated by the difference calculation unit 652. Identify the "potential". In the example of FIG. 14, when the development bias is −400 V and the “difference between the development bias and the surface potential of the image carrier 10 after exposure” is 240 V, “the surface of the image carrier 10 after charging”. The "potential" is specified as -480V.

FIG. 16 is a flowchart showing the processing of the image forming apparatus 100 of the present embodiment. After the development bias is calculated in step S6, in step S102, the determination unit 604 identifies a table corresponding to the calculated development bias.

Next, in step S104, when the acquisition unit 650 acquires the film thickness of the photosensitive layer 10b, the acquisition unit 650 identifies the surface potential of the image carrier 10 after charging based on the film thickness. Next, in step S106, the difference calculation unit 652 calculates the difference between the “development bias calculated by the calculation unit 602” and the “surface potential of the image carrier 10 after exposure specified by the acquisition unit 650”. To do.

Next, in step S108, the determination unit 604 refers to the specified table and refers to the “image after charging” corresponding to the “difference between the development bias and the image carrier 10 after exposure” calculated by the difference calculation unit 652. The "surface potential of the carrier 10" is specified.

[Brief Summary]
(1) As described in FIG. 14 and the like, the determination unit 604 of the control device 60A of the present embodiment has the first voltage (that is, the development bias) and the surface of the image carrier 10 after being exposed by the exposure unit 12. The second voltage is determined based on the difference from the potential. Therefore, the control device 60A of the present embodiment can determine the second voltage based not only on the first law and the second law but also on the third law.

(2) Further, in the table of FIG. 14 used by the control device 60A of the present embodiment, the smaller the first difference is, the more the first voltage is different from the region where the toner image of the image carrier 10 is developed. It is specified that the difference from the potential (that is, the potential difference ΔV) becomes small. According to the third law described above, the smaller the first difference, the smaller the amount of adhered toner. In order to increase the amount of adhered toner that has decreased, the amount of adhered toner can be increased by increasing the potential difference ΔV based on the second law. Therefore, the image forming apparatus 100 of the present embodiment can set the amount of adhered toner to an appropriate amount, and as a result, can form an appropriate amount of the stationary layer A.

(3) Further, in the table of FIG. 14 used by the control device 60A of the present embodiment, the larger the first difference is, the more the first voltage is different from the region where the toner image of the image carrier 10 is developed. It is specified that the difference from the potential (that is, the potential difference ΔV) becomes large. According to the third law described above, the larger the first difference, the larger the amount of adhered toner. In order to reduce the increased amount of adhered toner, the amount of adhered toner can be reduced by reducing the potential difference ΔV based on the second law. Therefore, the image forming apparatus 100 of the present embodiment can set the amount of adhered toner to an appropriate amount, and as a result, can form an appropriate amount of the stationary layer A.

(4) Further, in the image forming apparatus of the first embodiment, the first voltage, that is, the second voltage is controlled based on one parameter. Further, in the image forming apparatus of the second embodiment, the second voltage is controlled based on the "first voltage" and the "potential after the exposure of the image carrier 10 by the exposure unit 12", that is, two parameters. Therefore, since the image forming apparatus of the second embodiment uses a larger number of parameters than the image forming apparatus of the first embodiment, the accuracy of controlling the second voltage can be improved. Further, the image forming apparatus of the first embodiment can reduce the amount of calculation as compared with the image forming apparatus of the second embodiment.

<Embodiment 3>
The image forming apparatus 100 of the third embodiment controls the second voltage by using parameters other than the development bias. In the present embodiment, the parameters other than the development bias are the toner concentration in the charging device (developing tank 13a, stirring screws 13b, 13c, and accommodating chambers 13e, 13f).

First, the toner concentration will be described. FIG. 17 is a diagram for explaining the relationship between the amount of adhered toner, the development bias, and the toner concentration. In FIG. 17, the solid line is a diagram showing a case where the toner concentration is high. The broken line is a diagram showing the case where the toner concentration is normal (when the toner concentration is normal). The alternate long and short dash line is a diagram showing a case where the toner concentration is low. The toner concentration is detected by the toner concentration sensor 73 (see FIG. 2).

When the toner concentration in the charging device is high, it means that the amount of toner in the charging device is large. In this case, as shown in FIG. 17, the amount of adhered toner increases. Therefore, in the image forming apparatus of the present embodiment, when the toner concentration in the charging apparatus is higher than a predetermined threshold value, the amount of adhered toner is reduced by increasing the potential difference ΔV. For example, when the idea of the third embodiment is applied to the image forming apparatus of the first embodiment, the control device of the present embodiment is the potential difference calculated by the image forming apparatus of the first embodiment. Correct ΔV. This correction is, for example, a correction so that the amount of adhered toner belongs to an appropriate range (see the downward arrow attached to the solid line in FIG. 17). This correction is, for example, a correction in which the potential difference ΔV calculated by the image forming apparatus of the first embodiment is multiplied by a value larger than 1.

On the other hand, when the toner concentration in the charging device is low, it means that the amount of toner in the charging device is small. In this case, as shown in FIG. 17, the amount of adhered toner is reduced. Therefore, in the image forming apparatus of the present embodiment, when the toner concentration in the charging apparatus is lower than a predetermined threshold value, the amount of adhered toner is increased by reducing the potential difference ΔV. For example, when the idea of the third embodiment is applied to the image forming apparatus of the first embodiment, the control device of the present embodiment is the potential difference calculated by the image forming apparatus of the first embodiment. Correct ΔV. This correction is, for example, a correction so that the amount of adhered toner belongs to an appropriate range (see the downward arrow attached to the alternate long and short dash line in FIG. 17). This correction is, for example, a correction in which the potential difference ΔV calculated by the image forming apparatus of the first embodiment is multiplied by a value smaller than 1.

Further, the idea of the third embodiment can be applied not only to the image forming apparatus of the first embodiment but also to the image forming apparatus of the second embodiment.

According to the image forming apparatus of the present embodiment, not only the first voltage but also the toner concentration in the charging apparatus is used to control the second voltage. Therefore, the accuracy of controlling the second voltage can be improved as compared with the first and second embodiments.

<Embodiment 4>
The image forming apparatus 100 of the fourth embodiment controls the second voltage by using parameters other than the development bias. In this embodiment, the parameter other than the development bias is the amount of charge of the toner.

First, the toner charge amount will be described. The toner charging amount is the amount of electricity charged to the toner in the charging device (developing tank 13a, stirring screws 13b, 13c, and accommodating chambers 13e, 13f). FIG. 18 is a diagram for explaining the relationship between the amount of adhered toner, the development bias, and the amount of toner charge. In FIG. 18, the solid line is a diagram showing a case where the toner charge amount is high. The broken line is a diagram showing a case where the toner charge amount is normal (when the toner charge amount is normal). The alternate long and short dash line is a diagram showing a case where the toner charge amount is low. The toner charge amount is detected by, for example, a toner charge amount sensor (not shown in particular).

When the toner charge amount is high, the charge amount of the positively charged toner 300A, which has the opposite polarity to the polarity that the charging device charges the toner, also becomes high. Therefore, the electrically attractive force between the positively charged toner 300A having a high charge amount and the image carrier 10 becomes high. In this case, as shown in FIG. 18, the amount of adhered toner (the amount to which the positively charged toner 300A adheres) increases. Therefore, in the image forming apparatus of the present embodiment, when the amount of toner charged in the charging device is higher than a predetermined threshold value, the amount of adhered toner is reduced by increasing the potential difference ΔV. For example, when the idea of the fourth embodiment is applied to the image forming apparatus of the first embodiment, the control device of the present embodiment is the potential difference calculated by the image forming apparatus of the first embodiment. Correct ΔV. This correction is, for example, a correction so that the amount of adhered toner belongs to an appropriate range (see the downward arrow attached to the solid line in FIG. 18). This correction is, for example, a correction in which the potential difference ΔV calculated by the image forming apparatus of the first embodiment is multiplied by a value larger than 1.

On the other hand, when the toner charge amount is low, the charge amount of the positively charged toner 300A, which has the opposite polarity to the polarity charged by the charging device to the toner, is also low. Therefore, the electrical attraction between the positively charged toner 300A having a low charge amount and the image carrier 10 becomes low. In this case, as shown in FIG. 18, the amount of adhered toner (the amount to which the positively charged toner 300A adheres) becomes small. Therefore, in the image forming apparatus of the present embodiment, when the amount of toner charged in the charging device is lower than a predetermined threshold value, the amount of adhered toner is increased by reducing the potential difference ΔV. For example, when the idea of the fourth embodiment is applied to the image forming apparatus of the first embodiment, the control device of the present embodiment is the potential difference calculated by the image forming apparatus of the first embodiment. Correct ΔV. This correction is, for example, a correction so that the amount of adhered toner belongs to an appropriate range (see the downward arrow attached to the alternate long and short dash line in FIG. 18). This correction is, for example, a correction in which the potential difference ΔV calculated by the image forming apparatus of the first embodiment is multiplied by a value smaller than 1.

Further, the idea of the fourth embodiment can be applied not only to the image forming apparatus of the first embodiment but also to the image forming apparatus of the second embodiment.

According to the image forming apparatus of the present embodiment, the second voltage is controlled by using not only the first voltage but also the amount of toner charged in the charging apparatus. Therefore, the accuracy of controlling the second voltage can be improved as compared with the first and second embodiments.

<Embodiment 5>
The image forming apparatus 100 of the fifth embodiment controls the second voltage by using parameters other than the development bias. In the present embodiment, the parameters other than the development bias may include the linear velocity of the image forming apparatus 100. The linear velocity of the image forming apparatus 100 means, for example, the rate of image forming per unit time. More specifically, the linear velocity of the image forming apparatus 100 is, for example, the number of sheets of paper for which an image is formed per unit time.

First, the linear velocity will be described. FIG. 19 is a diagram for explaining the relationship between the amount of adhered toner, the development bias, and the linear velocity. In FIG. 19, the solid line is a diagram showing a case where the line speed is high. The broken line is a diagram showing the case where the linear velocity is normal (when the linear velocity is normal). The alternate long and short dash line is a diagram showing a case where the linear velocity is slow. Further, in the image forming apparatus of the present embodiment, a linear velocity is set by, for example, a user or a serviceman, and the set linear velocity is stored in a predetermined storage area. The image forming apparatus of this embodiment acquires a linear velocity from the predetermined storage area.

The case where the linear speed of the image forming apparatus is high is, for example, the case where the rotation speed of the developing roller 13d is high, so that the toner adhering to the developing roller 13d receives a strong centrifugal force from the developing roller 13d. When the toner adhering to the developing roller 13d receives a strong centrifugal force from the developing roller 13d, in this case, as shown in FIG. 19, the amount of adhered toner increases. Therefore, in the image forming apparatus of the present embodiment, when the linear velocity of the image forming apparatus is faster than a predetermined threshold value, the amount of adhered toner is reduced by increasing the potential difference ΔV. For example, when the idea of the fifth embodiment is applied to the image forming apparatus of the first embodiment, the control device of the present embodiment is the potential difference calculated by the image forming apparatus of the first embodiment. Correct ΔV. This correction is, for example, a correction so that the amount of adhered toner belongs to an appropriate range (see the downward arrow attached to the solid line in FIG. 19). This correction is, for example, a correction in which the potential difference ΔV calculated by the image forming apparatus of the first embodiment is multiplied by a value larger than 1.

On the other hand, when the linear speed of the image forming apparatus is slow, for example, the rotation speed of the developing roller 13d is slow, so that the toner adhering to the developing roller 13d receives a weak centrifugal force from the developing roller 13d. Become. Even if the toner adhering to the developing roller 13d receives a weak centrifugal force from the developing roller 13d, the toner adhering to the developing roller 13d flies to the image carrier 10 based on this weak centrifugal force. The amount is small. Therefore, when the linear velocity of the image forming apparatus is slow, the amount of adhered toner decreases as shown in FIG. Therefore, in the image forming apparatus of the present embodiment, when the linear velocity of the image forming apparatus is slower than a predetermined threshold value, the amount of adhered toner is increased by reducing the potential difference ΔV. For example, when the idea of the fifth embodiment is applied to the image forming apparatus of the first embodiment, the control device of the present embodiment is the potential difference calculated by the image forming apparatus of the first embodiment. Correct ΔV. This correction is, for example, a correction so that the amount of adhered toner belongs to an appropriate range (see the downward arrow attached to the alternate long and short dash line in FIG. 19). This correction is, for example, a correction in which the potential difference ΔV calculated by the image forming apparatus of the first embodiment is multiplied by a value smaller than 1.

Further, the idea of the fifth embodiment can be applied not only to the image forming apparatus of the first embodiment but also to the image forming apparatus of the second embodiment.

According to the image forming apparatus of the present embodiment, the second voltage is controlled by using not only the first voltage but also the linear velocity of the image forming apparatus 100. Therefore, the accuracy of controlling the second voltage can be improved as compared with the first and second embodiments.

Further, the parameters other than the development bias may include at least one of the density of the toner in the developing roller 13d, the amount of charge of the toner, and the linear velocity of the image forming apparatus.

<Embodiment 6>
In the first embodiment, the charging device has been described as charging the toner negatively. In this embodiment, the charging device described in the first embodiment charges the toner positively. In the present embodiment, the toner may be charged to the negative electrode property opposite to the positive electrode property by the charging device.

FIG. 20 is a table used by the image forming apparatus of this embodiment. The determination unit 604 of the first embodiment has been described as using the table of FIG. However, the determination unit 604 of this embodiment uses the table shown in FIG.

In FIG. 20, the smaller the first voltage, the larger the second difference (that is, the potential difference ΔV) between the first voltage and the potential in the region different from the region where the toner image of the image carrier 10 is developed. It is stipulated. Therefore, in the control device of the sixth embodiment, the smaller the first voltage, the larger the second difference between the first voltage and the potential in the region different from the region where the toner image of the image carrier 10 is developed. As such, the second voltage is controlled.

Further, in FIG. 20, it is defined that the larger the first voltage is, the smaller the second difference between the first voltage and the potential in the region different from the region where the toner image of the image carrier 10 is developed becomes smaller. .. Therefore, in the control device of the sixth embodiment, the larger the first voltage, the smaller the second difference between the first voltage and the potential in the region different from the region where the toner image of the image carrier 10 is developed. As such, the second voltage is controlled.

The image forming apparatus of the present embodiment has the same effect as the image forming apparatus of the first embodiment.
<Embodiment 7>
In the second embodiment, the charging device has been described as charging the toner negatively. In this embodiment, the charging device described in the second embodiment charges the toner positively. In the present embodiment, the toner is charged to the positive electrode by the charging device in principle, but there is an exception of the toner which is charged to the negative electrode which is the opposite of the positive electrode.

FIG. 21 is a table used by the image forming apparatus of this embodiment. The determination unit 604 of the second embodiment has been described as using the table of FIG. However, the determination unit 604 of this embodiment uses the table shown in FIG.

In FIG. 21, it is defined that the smaller the first difference, the larger the second difference between the first voltage and the potential in the region different from the region where the toner image of the image carrier 10 is developed. Therefore, the control device of the seventh embodiment sets the second voltage so that the second difference between the first voltage and the potential in the region different from the region where the toner image of the image carrier 10 is developed becomes large. Control.

Further, in FIG. 21, it is defined that the larger the first difference is, the smaller the second difference between the first voltage and the potential in the region different from the region where the toner image of the image carrier 10 is developed becomes smaller. .. Therefore, in the control device of the seventh embodiment, the larger the first difference, the smaller the second difference between the first voltage and the potential in the region different from the region where the toner image of the image carrier 10 is developed. As such, the second voltage is controlled. Further, in the example of FIG. 21, it is defined that the larger the development bias, the smaller the second difference, and the smaller the development bias, the larger the second difference.

Further, at least a part of the matters described in the third to fifth embodiments may be applied to the image forming apparatus of the sixth embodiment and the image forming apparatus of the seventh embodiment.

The image forming apparatus of the present embodiment has the same effect as the image forming apparatus of the first embodiment.
In addition, it should be considered that each embodiment disclosed this time is an example in all respects and is not restrictive. The scope of the present invention is shown not by the above description but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims. In addition, the inventions described in the embodiments and the modifications are intended to be implemented, either alone or in combination, wherever possible.

10 image carrier, 10a substrate, 10b photosensitive layer, 11 charged part, 12 exposed part, 13 developing part, 13a developing tank, 13b, 13c stirring screw, 13d developing roller, 13e, 13f storage chamber, 13h regulating member, 15 drum unit , 17 Cleaning device, 18 blades, 19 supports, 20A external device, 31 primary transfer roller, 33 secondary transfer roller, 36 intermediate transfer belt, 37 cassette, 38 driven roller, 39 drive roller, 40 transfer path, 41 pickup roller , 42 Timing Roller, 43 Fixing Device, 48 Tray, 60, 60A Control Device, 72 Power Supply Device, 73 Toner Concentration Sensor, 78 Thickness Sensor, 80 Network Interface, 100 Image Forming Device, 102 ROM, 103 RAM, 107 Operation Panel , 300A positively charged toner, 300B negatively charged toner, 602 calculation unit, 604 determination unit, 606 table storage unit, 608 control unit, 650 acquisition unit, 652 difference calculation unit, 711 first power supply device, 712 second power supply device.

Claims (12)

An image carrier on which an electrostatic latent image is developed by a developer, and
A developer carrier that supplies the developer to the image carrier, and
A first power supply device that applies a voltage to the developer carrier,
A control device that determines the voltage of the image carrier based on the voltage applied to the developer carrier.
An image forming apparatus including a second power supply device that applies a voltage determined by the control device to the image carrier. An exposure apparatus for exposing the image carrier is further provided.
The control device determines the voltage of the image carrier based on the difference between the voltage applied to the developer carrier and the potential of the image carrier after exposure by the exposure device. The image forming apparatus according to. A charging device for charging the developer negatively is further provided.
In the control device, as the voltage applied to the developer carrier is smaller, the voltage applied to the developer carrier is different from the region where the electrostatic latent image of the image carrier is developed. The image forming apparatus according to claim 1, wherein the voltage of the image carrier is determined so that the difference from the potential of the image carrier is small. A charging device for charging the developer negatively is further provided.
In the control device, as the voltage applied to the developer carrier is larger, the voltage applied to the developer carrier is different from the region where the electrostatic latent image of the image carrier is developed. The image forming apparatus according to claim 1, wherein the voltage of the image carrier is determined so that the difference from the potential of the image carrier becomes large. A charging device for positively charging the developer is further provided.
In the control device, as the voltage applied to the developer carrier is smaller, the voltage applied to the developer carrier is different from the region where the electrostatic latent image of the image carrier is developed. The image forming apparatus according to claim 1, wherein the voltage of the image carrier is determined so that the difference from the potential of the image carrier becomes large. A charging device for positively charging the developer is further provided.
In the control device, as the voltage applied to the developer carrier is larger, the voltage applied to the developer carrier is different from the region where the electrostatic latent image of the image carrier is developed. The image forming apparatus according to claim 1, wherein the voltage of the image carrier is determined so that the difference from the potential of the image carrier is small. A charging device for charging the developer negatively is further provided.
In the control device, the smaller the difference between the voltage applied to the developer carrier and the potential of the image carrier after exposure by the exposure device, the smaller the difference between the voltage applied to the developer carrier and the image. The image forming apparatus according to claim 2, wherein the voltage of the image carrier is determined so that the difference from the potential of the region different from the region where the electrostatic latent image of the carrier is developed is small. A charging device for charging the developer negatively is further provided.
In the control device, the larger the difference between the voltage applied to the developer carrier and the potential of the image carrier after exposure by the exposure device, the greater the difference between the voltage applied to the developer carrier and the image. The image forming apparatus according to claim 2, wherein the voltage of the image carrier is determined so that the difference from the potential of the region different from the region where the electrostatic latent image of the carrier is developed is large. A charging device for positively charging the developer is further provided.
In the control device, the smaller the difference between the voltage applied to the developer carrier and the potential of the image carrier after exposure by the exposure device, the smaller the difference between the voltage applied to the developer carrier and the image. The image forming apparatus according to claim 2, wherein the voltage of the image carrier is determined so that the difference from the potential of the region different from the region where the electrostatic latent image of the carrier is developed is large. A charging device for positively charging the developer is further provided.
In the control device, the larger the difference between the voltage applied to the developer carrier and the potential of the image carrier after exposure by the exposure device, the greater the difference between the voltage applied to the developer carrier and the image. The image forming apparatus according to claim 2, wherein the voltage of the image carrier is determined so that the difference from the potential of the region different from the region where the electrostatic latent image of the carrier is developed is small. The control device determines the voltage of the image carrier based on at least one of the concentration of the developer in the developer carrier, the charge amount of the developer, and the linear velocity of the image forming apparatus. The image forming apparatus according to any one of claims 1 to 10. A control method for controlling an image forming apparatus having an image carrier on which an electrostatic latent image is developed by a developer and a developer carrier for supplying the developer to the image carrier.
A step of determining the voltage of the image carrier based on the voltage applied to the developer carrier, and
A control method comprising a step of applying a determined voltage to the image carrier.

Images