JP2021081658A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for suppressing the occurrence of image defects at an end portion of an image carrier. SOLUTION: The control has an image carrier whose surface is charged by a charging member, a developer carrier facing the image carrier, and a control unit for applying a development voltage to the developer carrier. In the unit, the relationship between the first absolute value of the surface potential of the image carrier charged by the charging member and the second absolute value of the developing voltage under predetermined conditions is the first absolute value < It is controlled so as to be the second absolute value. [Selection diagram] Fig. 4

Description

The present invention relates to an electrophotographic image forming apparatus.

In the conventional image forming apparatus, when the toner as a developer on the developer carrier is discarded, the image carrier whose surface is charged is exposed by the exposed portion according to the disposal pattern, and the toner is exposed on the exposed portion. Was attached and discarded (see, for example, Patent Document 1).

JP-A-2019-117219

However, in the conventional technique, there is a problem that image defects may occur from the end portion of the image carrier even if the toner is discarded. Specifically, there is a problem that after the conventional toner is discarded, the image defect at the end portion of the image carrier is caused earlier than the central portion by the time when the next toner is discarded.
An object of the present invention is to solve such a problem, and an object of the present invention is to suppress the occurrence of image defects at the ends of the image carrier.

Therefore, the present invention includes an image carrier whose surface is charged by a charging member, a developer carrier facing the image carrier, and a control unit that applies a developing voltage to the developer carrier. In the control unit, the relationship between the first absolute value of the surface potential of the image carrier charged by the charging member and the second absolute value of the developing voltage under predetermined conditions is the first absolute value. It is characterized in that it is controlled so that the value <the second absolute value.

The present invention in this manner has the effect of suppressing the occurrence of image defects at the edges of the image carrier.

Schematic side sectional view showing the configuration of the image forming apparatus in the Example Schematic side sectional view showing the configuration of the image forming unit in the embodiment. Explanatory drawing which shows the structure of the image formation unit in an Example A block diagram showing a control configuration of an image forming apparatus in an embodiment. Flowchart showing the flow of printing processing in the embodiment Flow chart showing the flow of toner disposal B processing in the embodiment Flow chart showing the flow of toner disposal A processing in the embodiment Explanatory drawing of development voltage in Example Explanatory drawing of toner image in Example Graph of developing voltage and surface potential of photosensitive drum in Examples Time chart of voltage application in Examples A flowchart showing the flow of the applied voltage determination process in the embodiment.

Hereinafter, examples of the image forming apparatus according to the present invention will be described with reference to the drawings.

FIG. 1 is a schematic side sectional view showing a configuration of an image forming apparatus in an embodiment.
In FIG. 1, the image forming apparatus 100 is a printing apparatus that forms an image using a developer by an electrophotographic method, and is a printer capable of color printing in this embodiment. The developer used in this example is a non-magnetic one-component negatively charged toner.

The image forming apparatus 100 has five color image forming units 10Y, 10M, 10C, 10K, and 10W of yellow (Y), magenta (M), cyan (C), black (K), and white (W). The image forming units 10Y, 10M, 10C, 10K, and 10W are detachable from the image forming apparatus 100.

The image forming units 10Y, 10M, 10C, 10K, and 10W are arranged in a row in this order. The image forming units 10Y, 10M, 10C, 10K, and 10W have the same configuration except for the toner contained therein. Therefore, it may be abbreviated as the image forming unit 10 below.

In this embodiment, the distance between adjacent image forming units 10 is referred to as "distance between image forming units" and is set to 80 mm.

The image forming apparatus 100 further cuts the roll paper holder 11 that mounts and holds the roll paper P that is the printing medium, the rewinder 12 that winds up the printed roll paper P, and the roll paper P at the end of printing of one page. It has a cutter 13. It is assumed that the roll paper P of this embodiment has a width of 105 mm in the main scanning direction.

The image forming apparatus 100 further superimposes a toner image as a developer image formed by the image forming units 10Y, 10M, 10C, 10K, and 10W on the lower part of the image forming units 10Y, 10M, 10C, 10K, and 10W. It is provided with an endless intermediate transfer belt 14 to be matched.

The intermediate transfer belt 14 as a transfer body transfers a toner image formed on each of the photosensitive drums of the image forming units 10Y, 10M, 10C, 10K, and 10W. The intermediate transfer belt 14 is sandwiched between the reverse bending roller 46 and the driven roller 48, and is rotated in the rotational direction indicated by the arrow in the figure by the rotational drive of the reverse bending roller 46.

The image forming apparatus 100 further displays a toner image on the opposite side of the image forming units 10Y, 10M, 10C, 10K, and 10W with the intermediate transfer belt 14 sandwiched between the image forming units 10Y, 10M, 10C, 10K, and 10W. The primary transfer rollers 15Y, 15M, 15C, 15K, and 15W to be transferred onto the 14 are provided, the backup roller 45 is provided inside the lower part of the intermediate transfer belt 14, and the intermediate transfer belt 14 is sandwiched between the lower parts of the backup roller 45. On the opposite side of the backup roller 45, a secondary transfer roller 16 for transferring the toner image formed on the intermediate transfer belt 14 onto the roll paper P is provided.

The intermediate transfer belt 14 accommodates a belt cleaning member 43 that scrapes off the toner remaining on the intermediate transfer belt 14 after transfer by the secondary transfer roller 16 from the intermediate transfer belt 14, and a toner scraped off by the belt cleaning member 43. A belt waste toner accommodating portion 44 is provided.
Further, a sensor 60 for detecting the amount of toner on the intermediate transfer belt 14 is provided on the intermediate transfer belt 14.

The sensor 60 as a reading unit is an optical sensor that optically reads the toner image transferred on the intermediate transfer belt 14 and detects the amount (concentration) of the toner in the toner image.
The image forming apparatus 100 further includes a heating roller 17 and a pressure roller 18 for fixing the toner image transferred to the roll paper P to the roll paper P by heating and pressurizing.

In this embodiment, an example including an image forming unit 10Y, 10M, 10C, 10K, and 10W using five color toners of yellow, magenta, cyan, black, and white is described, but six or more. The image forming unit 10 may be provided, or four or less image forming units 10 may be provided.

FIG. 2 is a schematic cross-sectional view of the image forming unit 10.

The image forming unit 10 has a cylindrical photosensitive drum (image carrier) 19 on which an electrostatic latent image is formed on the surface. The photosensitive drum 19 rotates in one direction (here, counterclockwise indicated by an arrow in the figure) by a motor driving force obtained from a drive motor control unit 40 described later.

A charging roller (charging member) 20, an exposure head (exposure means) 21, and a developing roller (developer carrier) 22 are arranged around the photosensitive drum 19 as an image carrier.
The photosensitive drum 19 is a rotating body that rotates about a rotation axis, and the surface is uniformly charged by the charging roller 20 and selectively exposed by the exposure head 21 to form an electrostatic latent image. is there.

The charging roller 20 as a charging member is subjected to a predetermined bias voltage (hereinafter, simply referred to as “bias”) from the charging roller power supply 33, which will be described later, and is driven to rotate as the photosensitive drum 19 rotates. The surface of the drum is uniformly charged.
The charging cleaning roller 56 is arranged in contact with the charging roller 20. The charging cleaning roller 56 rotates in a driven rotation or with a peripheral speed difference as the charging roller 20 rotates, and scrapes off the toner and the toner external agent adhering to the charging roller 20.

The exposure head 21 as an exposure means has an LED (Light Emitting Diode), which is a plurality of light emitting elements arranged in the main scanning direction (the direction of the rotation axis of the photosensitive drum 19), and a rod lens array, and responds to image data. By forming an image of the light of the light emitting element that emits light on the photosensitive drum 19 by a rod lens array, the surface of the photosensitive drum 19 charged by the charging roller 20 is exposed to form an electrostatic latent image.

In the photosensitive drum 19, the exposure region exposed by the exposure head 21 and the region outside the exposure region are charged by the charging roller 20 in the rotation axis direction.

The developing roller 22 as the developing agent carrier is rotatably arranged so as to face the photosensitive drum 19. The developing roller 22 is given a predetermined bias from the developing roller power supply 34 described later, rotates in the same direction as the photosensitive drum 19 at the contact portion with the photosensitive drum 19, and has an electrostatic latent shape formed on the surface of the photosensitive drum 19. Toner is attached to the image for development.

Further, a supply roller (developer supply member) 23 and a developing blade (developer regulation member) 24 are arranged adjacent to the developing roller 22.
The supply roller 23 is given a predetermined bias from the power supply 35 for the supply roller, which will be described later, and rotates in the opposite direction of the developing roller 22 at the contact portion with the developing roller 22 to supply toner to the surface of the developing roller 22.

The developing blade 24 is arranged so as to be pressed against the surface of the developing roller 22, and the thickness of the developer layer (toner layer) is regulated by this pressing force to form a thin toner layer on the developing roller 22. A predetermined bias is applied to the developing blade 24 from the power supply 35 for the supply roller, which will be described later.
In the image forming unit 10, a portion (a portion including a developing roller 22, a supply roller 23, and a developing blade 24) that contributes to the development of an electrostatic latent image is referred to as a “development device”.

When the image forming unit 10 is incorporated into the image forming apparatus 100, the photosensitive drum 19 comes into contact with the intermediate transfer belt 14, and the primary transfer roller 15 is arranged on the opposite side of the photosensitive drum 19 with the intermediate transfer belt 14 interposed therebetween. To.
The primary transfer roller 15 is subjected to a predetermined bias from the transfer roller power supply 32 described later, and transfers the toner image formed on the surface of the photosensitive drum 19 to the intermediate transfer belt 14.

A cleaning member 25 is provided on the downstream side of the photosensitive drum 19 in the rotation direction.
The cleaning member 25 is in contact with the photosensitive drum 19, and removes the toner remaining on the surface of the photosensitive drum 19 after transfer.
A waste toner transport member 50 is provided directly below the cleaning member 25.

The waste toner transport member 50 transports the toner removed from the photosensitive drum 19 by the cleaning member 25 toward the waste toner chamber 54 that houses the waste toner, as will be described later.
On the downstream side of the cleaning member 25 in the rotation direction of the photosensitive drum 19, an antistatic light 26 that removes the residual charge of the drum without contacting the drum is arranged.

The static elimination light 26 is composed of, for example, an LED.
The image forming unit 10 includes an unused toner chamber 47 for accommodating unused toner, a waste toner chamber 54, and a partition member 52.

The partition member 52 is an LDPE (low density polyethylene) film having a thickness of 0.1 to 0.4 mm. The partition member 52 is installed between the unused toner chamber 47 and the waste toner chamber 54, and the end portion of the partition member 52 is fixed to the housing so that the unused toner and the waste toner are not mixed.

In the waste toner chamber 54, a waste toner transport member 51 for transporting the waste toner to the waste toner chamber 54 is installed.

A toner hopper 59 is installed below the unused toner chamber 47, and a replenishment port 58 is installed between the unused toner chamber 47 and the toner hopper 59. The toner hopper 59 primarily stores the toner replenished from the replenishment port 58.
In the image forming apparatus 100 of the present embodiment, toner is adhered to the surface of the photosensitive drum 19 charged to a predetermined surface potential by the developing roller 22 to which a predetermined bias is applied, and the toner is transferred from the photosensitive drum 19 by the cleaning member 25. Toner is discarded.

FIG. 3 is an explanatory view showing the configuration of the image forming unit in the embodiment, and is a perspective view of the image forming unit 10 shown in FIG.
In FIG. 3, a waste toner transfer drive member is installed at one end of the waste toner transfer member 51, and the other end of the waste toner transfer member 51 is installed inside the side plate 53 and extends to the vicinity of the waste toner transfer member 50. ing.

The waste toner removed from the photosensitive drum 19 by the cleaning member 25 shown in FIG. 2 is conveyed by the waste toner transfer member 50 toward the waste toner chamber 54.

FIG. 4 is a block diagram showing a control configuration of the image forming apparatus in the embodiment.

In FIG. 4, the image forming apparatus 100 receives print data including image data from a print control unit 27 that controls various controls and an external device such as a PC (personal computer), and outputs head emission command data to the exposure head 21. The image data conversion unit 28 to be generated, the drum rotation speed measurement unit 29 for measuring the rotation speed of the photosensitive drum 19, and the head light emission number measurement unit 30 for measuring the light emission number of the light emitting element corresponding to the image data of the exposure head 21. , A print data monitoring unit 31 that monitors page transitions of print data received from an external device, a transfer roller power supply 32 that applies a predetermined voltage to the primary transfer roller 15 and the secondary transfer roller 16, and a charging roller. A charging roller power supply 33 that applies a predetermined voltage to 20, a developing roller power supply 34 that applies a predetermined voltage to the developing roller 22, and a supply roller that applies a predetermined voltage to the supply roller 23 and the developing blade 24. The operation of the power supply 35, the head drive control unit 36 that drives the light emission of the exposure head 21, the static elimination light power supply 37 that applies a predetermined voltage to emit the static elimination light 26, and the heating roller 17 and the pressurizing roller 18. The fixing control unit 38 that controls the data, the transfer motor control unit 39 that controls the operation of the roll paper feeder 11 and the reminder 12, the intermediate transfer belt 14, the secondary transfer roller 16, the photosensitive drum 19, and the reverse bending roller 46. It is composed of a drive motor control unit 40 that controls the data, a cutter control unit 41 that controls the operation of the cutter 13, a calculation unit 42 that performs various calculations, and a storage unit 57 such as a memory.

Hereinafter, description will be made with reference to FIGS. 1 and 2.

The print control unit 27 as a control unit controls the operation of the entire image forming apparatus 100 by a control means such as a CPU (Central Processing Unit) based on a control program (software) stored in the storage unit 57.
Further, the print control unit 27 is connected to the sensor 60, and the toner amount (toner image density) of the toner image formed on the intermediate transfer belt 14 based on the reading value of the sensor 60 and the information stored in advance in the storage unit 57. ) Is detected.

Further, the print control unit 27 applies a development voltage to the developing roller 22 and discards the toner that discharges the toner carried by the developing roller 22 to the photosensitive drum 19.
The drum rotation speed measuring unit 29 measures the drum count E and the disposal drum count J for each image forming unit 10. The drum count E and the disposal drum count J are measured values of the rotation speed (printing distance) of the photosensitive drum 19. Hereinafter, the drum counts E of all the image forming units 10 are collectively referred to as a drum count E *, and the drum counts J are collectively referred to as a drum count J *.

The head emission number measuring unit 30 measures the dot count F for each image forming unit 10. The dot count F is the number of dots lit when the exposure head 21 forms dots. Hereinafter, the dot count F of all the image forming units 10 is also collectively referred to as a dot count F *.

The calculation unit 42 calculates the cumulative discard dot count I for each image forming unit 10 from the drum count E and the dot count F for each image forming unit 10. The cumulative waste dot count I is a value used when it is determined whether or not to execute the operation process of the toner waste B. The cumulative discard dot count I is calculated by adding the print discard dot count Ip required for printing the current one job to the current cumulative discard dot count I each time one job is printed. Cumulative discard dot count I is updated. In the following, the cumulative discard dot count I of all the image forming units 10 is collectively referred to as the cumulative discard dot count I *, and the current print discard dot count Ip of all the image forming units 10 is collectively referred to as the current print discard dot count Ip *. Also called.

The storage unit 57 stores the cumulative discard dot count I *. Further, in the storage unit 57, a disposal standard printing duty H, which is a printing duty that serves as an implementation standard for toner disposal B, is recorded, and is set to 5 [%] in this embodiment.

The print duty is the ratio of the area of the image actually formed on the paper to the area when the solid image is formed in the image-forming region. In other words, the print duty is the ratio of the count value of the dots when actually printed when the state when the dots are formed on the entire surface of the area within the predetermined area in the print medium is 100 [%]. The print rate. For example, when the dot count when printing on a certain paper is dc and the dot count when the entire surface is exposed on the same paper is dc, the print duty is calculated by dc / dca × 100 [%]. Note that this printing duty calculation formula is an example, and the printing duty may be calculated by another calculation formula.

Here, when printing with a printing duty lower than the disposal standard printing duty H continues and the toner is hardly consumed by printing, the toner in the toner hopper 59 continues to be stirred in the toner hopper 59 and the developing roller 22 The toner adhering to the toner is continuously rubbed by the supply roller 23, the developing blade 24, and the photosensitive drum 19.

In this case, the toner on the developing roller 22 tends to be triboelectrically charged to increase the potential, and if the potential becomes too high, the image formed on the roll paper P will be stained or the like.
In addition, the toner is damaged if it is continuously rubbed, and the contained external additive is separated from the surface of the toner.
In that case, the image forming unit 10 cannot normally charge the toner, causing stains, fog, blurring, and the like on the image, increasing the risk of deterioration of image quality.

Therefore, in the image forming apparatus 100, it becomes necessary to discard the deteriorated toner that causes these.

Further, in the image forming unit 10, the deteriorated toner tends to be easily accumulated at the left and right ends (both ends in the rotation axis direction of the photosensitive drum 19). While the accumulated amount of deteriorated toner is small, the image is not affected because it is outside the image area, but as the amount of accumulated deteriorated toner increases and the accumulated amount progresses into the image area, the left and right edges of the image area become dirty and fogged. , Blurring, etc. are likely to occur.

When toner is discarded using the toner disposal LED light emission pattern, it is difficult to dispose of the deteriorated toner accumulated at the left and right ends because it is outside the light emitting region. Since the deteriorated toner accumulated at the left and right ends cannot be completely discarded, it is necessary to shorten the interval until the next toner disposal or increase the amount of toner to be discarded at one time.

Therefore, the print control unit 27 of the image forming apparatus 100 has a first absolute value of the surface potential of the photosensitive drum 19 charged by the charging roller 20 and a second developing voltage applied to the developing roller 22 under predetermined conditions. The toner is discarded by controlling so that the relationship with the absolute value of is equal to the first absolute value <the second absolute value.

The operation of the above-described configuration will be described.

The printing process performed by the image forming apparatus will be described with reference to FIGS. 1, 2, and 4 according to the steps represented by S in the flowchart of the flowchart showing the flow of the printing process in the embodiment of FIG.

The image forming apparatus 100 of this embodiment has two types of toner disposal treatments, that is, the toner disposal treatment of toner disposal A performed before printing and the toner disposal treatment of toner disposal B performed after printing. Then, the toner disposal process is carried out by the printing process described below.

When the print data monitoring unit 31 of the image forming apparatus 100 receives the print data and the image data conversion unit 28 converts the image data included in the print data into light emission data (head light emission command data), the print control unit 27 receives the print data. The print process is started by reading the print process program from the storage unit 57 and executing it.

S101: The print control unit 27 determines whether or not the measured disposal drum count J is the threshold value of 500 or less, and if it is determined that the disposal drum count J is the threshold value of 500 or less, the toner disposal process of the toner disposal A is performed. It is determined that it is not necessary to perform the process yet, and the process is shifted to S103. On the other hand, if it is determined that the discard drum count J is not less than or equal to the threshold value of 500, that is, it exceeds the threshold value, it is determined that the toner disposal process of toner waste A needs to be performed. The process is transferred to S102.

S102: The print control unit 27 performs the toner disposal process of the toner disposal A, and shifts the process to S103. The details of the toner disposal process of the toner disposal A will be described later.

In this embodiment, the print control unit 27 performs the toner disposal process of toner disposal A after receiving the print data as a print instruction and before performing the printing operation based on the print data.
In this way, the print control unit 27 performs the toner disposal process of the toner disposal A under predetermined conditions.

S103: The print control unit 27 reads the stored cumulative discard dot count I * from the storage unit 57.

S104: The print control unit 27 starts the measurement of the drum count E * by the drum rotation speed measuring unit 29, and stores the drum count E * at that time in the storage unit 57 as the starting drum count E1 *.

The start drum count E1 * collectively indicates the start drum count E1 of all the image forming units 10.

S105: The print control unit 27 starts the measurement of the dot count F * by the head emission number measuring unit 30, and stores the drum count F * at that time in the storage unit 57 as the start dot count F1 *.

The start dot count F1 * collectively indicates the start dot count F1 of all the image forming units 10.

S106: The print control unit 27 brings the secondary transfer roller 16 into contact with the intermediate transfer belt 14 by the drive motor control unit 40.

S107: The print control unit 27 monitors whether or not the printing of one job is completed, and if it is determined that the printing of one job is completed, the process shifts to S108 and the printing of one job is not completed. If it is determined, the monitoring of whether or not the printing of one job is completed is continued.

Here, one job is a job of print data (for example, print data of one page) printed on the roll paper P from the cutting position on the upstream side in the transport direction to the cutting position on the downstream side in the transport direction.

While the print control unit 27 is performing the printing operation of one job, the drum rotation speed measurement unit 29 measures the drum count E and the discard drum count J for each image forming unit 10, and the head emission number measurement unit 30. Measures the dot count F for each image forming unit 10.

S108: When the print control unit 27 finishes printing one job, the drum rotation speed measuring unit 29 finishes measuring the drum count E * and the discard drum count J *, and when the drum count E * at this time is finished. The drum count E2 * is stored in the storage unit 57, and the discard drum count J * is stored in the storage unit 57.

The end-time drum count E2 * collectively indicates the end-time drum count E2 of all the image forming units 10.

S109: The print control unit 27 ends the measurement of the dot count F * by the head emission number measuring unit 30, and stores the dot count F * at this time in the storage unit 57 as the end dot count F2 *.

The end-time dot count F2 * collectively indicates the end-time dot count F2 of all the image forming units 10.

S110: The print control unit 27 performs the print duty in consideration of the print duty from the start drum count E1 *, the start dot count F1 *, the end drum count E2 *, and the end dot count F2 * in one job this time. The printing waste dot count Ip *, which is the waste dot count, is calculated by the calculation unit 42.

The current print discard dot count Ip * indicates the current print discard dot count Ip of all the image forming units 10.

S111: The print control unit 27 updates the cumulative discard dot count I * by adding the print discard dot count Ip * calculated in S110 to the current cumulative discard dot count I * by the calculation unit 42.

S112: When the cumulative discard dot count I * is larger than the predetermined cumulative discard dot count upper limit value, the print control unit 27 sets the cumulative discard dot count upper limit value in the cumulative discard dot count I *, while the predetermined cumulative discard. If it is smaller than the lower limit of the dot count, set the lower limit of the cumulative discard dot count in the cumulative discard dot count I *.

S113: The print control unit 27 determines whether or not the calculated cumulative discard dot count I of all the image forming units 10 is 0 or less, and the cumulative discard dot count I of all the image forming units 10 is 0 or less. If it is determined that there is, the process of the toner disposal operation B does not need to be performed yet, and the process is shifted to S115. On the other hand, if it is determined that the cumulative disposal dot count I of any of the image forming units 10 is larger than 0, the toner disposal operation B is performed. Since it is necessary to perform the process, the process is transferred to S114.

S114: The print control unit 27 performs the toner disposal process of the toner disposal B, and shifts the process to S116. The details of the toner disposal process of the toner disposal B will be described later.

S115: The print control unit 27 separates the secondary transfer roller 16 from the intermediate transfer belt 14 by the drive motor control unit 40, and shifts the process to S116.

S116: The print control unit 27 stores the updated cumulative discard dot count I * in the storage unit 57.

S117: The print control unit 27 determines whether or not the job still exists, returns the process to S101 if it determines that the job exists, and ends this process if it determines that the job does not exist.

Next, the toner disposal B process performed by the print control unit will be described with reference to FIGS. 1, 2, and 4 according to the steps represented by S in the flowchart of the flowchart showing the flow of the toner disposal B process in the embodiment of FIG. To do. The toner disposal B treatment is a treatment performed in S114 of FIG.

S201: The print control unit 27 separates the secondary transfer roller 16 from the intermediate transfer belt 14 by the drive motor control unit 40. As a result, the image forming apparatus 100 prevents the toner disposal pattern of the toner discarded on the intermediate transfer belt 14 from being transferred to the secondary transfer roller 16 and the roll paper P from being back-stained by the discarded toner at the next printing. To do.

S202: The print control unit 27 uses the exposure head 21 to form the toner disposal LED light emitting pattern (toner image TB shown in FIG. 9) in all the image forming units 10 having a positive cumulative discard dot count I *. The photosensitive drum 19 is exposed by simultaneously emitting light (LED light emission pattern), and then developed with toner to discard the toner.

S203: The print control unit 27 reduces the total waste dot count I from the total waste dot count I in the image forming unit 10 that emits light from the toner disposal LED light emission pattern, thereby causing the cumulative waste dot count. Update I and end this process.

Next, the toner disposal A process performed by the print control unit will be described with reference to FIGS. 1, 2, and 4 according to the steps represented by S in the flowchart of the flowchart showing the flow of the toner disposal A process in the embodiment of FIG. To do. The toner disposal A treatment is a treatment performed in S102 of FIG.

S301: The print control unit 27 biases the charging roller 20 to the charging roller 20 and the developing roller 22 with respect to the charging roller power supply 33 and the developing roller power supply 34 based on the applied voltage determined in the applied voltage determination process described later. An instruction is given to apply the bias V (A2). The charging roller power supply 33 applies a bias V (A1) to the charging roller 20, and the developing roller power supply 34 applies a bias V (A2) to the developing roller 22.

Further, the head drive control unit 36 disposes of toner according to the instruction of the print control unit 27 without performing exposure by the exposure head 21.
Here, the charging roller power supply 33 and the developing roller power supply 34 satisfy | V (A1) | << V (A2) |.

That is, the developing roller power supply 34 applies the absolute value (second absolute value) of the bias V (A2) applied to the developing roller 22 to the bias V (A1) applied by the charging roller power supply 33 to the charging roller 20. Make it larger than the absolute value (third absolute value).

Therefore, in the charging roller 20, the charging voltage of the absolute value (third absolute value) of the bias V (A1) smaller than the absolute value (second absolute value) of the bias V (A2) applied to the developing roller 22 is It is applied to charge the photosensitive drum to the surface potential of the first absolute value.

FIG. 8 shows the magnitude relationship between the absolute value (second absolute value) of the bias V (A2) applied to the developing roller 22 at this time and the absolute value (first absolute value) of the surface potential of the photosensitive drum. It is shown that the absolute value of the surface potential of the photosensitive drum (first absolute value) <absolute value of bias V (A2) (second absolute value).

Here, the toner image formed by the toner waste A treatment will be described with reference to the explanatory diagram of the toner image in the embodiment of FIG.

FIG. 9 shows the toner image TB on the intermediate transfer belt 14 when the toner is discarded in the toner disposal LED light emission pattern of the toner disposal B treatment, and | V (A1) | <| V (A2) in the toner disposal A treatment. It is a figure which compared with the toner image TA on the intermediate transfer belt 14 when the toner was discarded by |.

As shown in FIG. 9, the toner image TB in the case of toner disposal in the toner disposal LED emission pattern can dispose of toner only up to the exposure area LER, but | V (A1) | << V (A2). ) | When the toner image TA is formed and the toner is discarded, the toner up to the left and right ends (the ends in the rotation axis direction of the photosensitive drum 19) where the deteriorated toner of the NE outside the exposure area including the exposure area LER is likely to accumulate. Can be discarded.

Here, the exposure region LER is a region corresponding to the exposure region of the photosensitive drum 19 exposed by the exposure head 21 in the rotation axis direction of the photosensitive drum 19. Further, the NE outside the exposure region is a region corresponding to the outside of the exposure region of the photosensitive drum 19 exposed by the exposure head 21 in the rotation axis direction of the photosensitive drum 19.

The relationship of | V (A1): bias applied to the charging roller 20 | <| V (A2): bias applied to the developing roller 22 | is most preferable, but | surface potential of the photosensitive drum | << | developing roller 22 If the applied bias to | can be satisfied, the | applied bias to the charging roller 20 | ≧ | applied bias to the developing roller 22 | may be satisfied.

For example, FIG. 10 is a graph of the developing voltage and the surface potential of the photosensitive drum in the examples, and shows the relationship between the bias applied to the charging roller 20 and the surface potential of the photosensitive drum. As shown in FIG. 10, even if the voltage applied to the charging roller 20 is −600 V (−0.6 kV) and the applied bias to the developing roller 22 is −400 V, the surface potential of the photosensitive drum is about −80 V. , | There is no problem because the surface potential of the photosensitive drum | <| the bias applied to the developing roller 22 | is satisfied.

S302: According to the instruction of the print control unit 27, the charging roller power supply 33 and the developing roller power supply 34 return the applied bias to the charging roller 20 and the applied bias to the developing roller 22 to the original applied bias.

11A and 11B are time charts of voltage application in Examples, FIG. 11A shows a time chart of application bias to the charging roller 20, and FIG. 11B shows a time chart of application bias to the developing roller 22. Shown.

In FIG. 11, the bias application time T to the charging roller 20 and the bias application time T to the developing roller 22 are the same time T, and the toner is discarded only during that time T. This time T may be changed depending on conditions such as color and environment.

S303: The print control unit 27 resets the discard drum count J of the storage unit 57 to “0” and ends this process.

Next, the applied voltage determination process performed by the print control unit will be described with reference to FIGS. 1, 2, and 4 according to the steps represented by S in the flowchart of the flowchart showing the flow of the applied voltage determination process in the embodiment of FIG. To do. The applied voltage determination process is a process for determining the bias V (A1) applied to the charging roller 20 and the bias V (A2) applied to the developing roller 22, and is performed when a predetermined condition is satisfied. ..

The predetermined conditions are when the installation environment of the image forming apparatus 100 changes, when the toner density is corrected, and the like. For example, when the print control unit 27 detects that the temperature / humidity sensor has changed from a low temperature / low humidity environment (temperature 10 ° C., humidity 20%) to a high temperature / high humidity environment (temperature 28 ° C., humidity 80%), the image forming apparatus 100 Judge that the installation environment has changed. Further, the print control unit 27 corrects the toner density when the drum count E exceeds the threshold value.

S401: The print control unit 27 applies the reference bias V (A3) stored in the storage unit 57 in advance to the charging roller 20 by the charging roller power supply 33, and stores the reference bias V (A3) in the storage unit 57 in advance. (A4) is applied to the developing roller 22 by the developing roller power supply 34 to form a toner pattern on the intermediate transfer belt 14. However, | V (A3) | << V (A4) |.

S402: The print control unit 27 reads the toner pattern (toner image) on the intermediate transfer belt 14 with the sensor 60, and calculates the toner amount from the read value. The print control unit 27 stores information on the relationship between the read value of the sensor 60 and the toner amount in the storage unit 57 in advance, and derives the toner amount based on the information.

S403: The print control unit 27 calculates the toner amount of the difference between the toner amount on the derived intermediate transfer belt 14 and the target toner amount. The target toner amount is stored in the storage unit 57 in advance.

S404: The print control unit 27 uses the amount of change in the amount of toner with respect to the amount of change stored in the storage unit 57 in advance (| applied bias to the developing roller 22 |-| applied bias to the charging roller 20 |). Then, the amount of change (difference) of (| applied bias to the developing roller 22 |-| applied bias to the charging roller 20 |) with respect to the difference toner amount obtained in S403 is calculated.

In this embodiment, the larger the difference toner amount obtained in S403, the larger the amount of change (difference) in (| applied bias to the developing roller 22 |-| applied bias to the charging roller 20 |).
As described above, the print control unit 27 has an absolute value (second absolute value) of the bias V (A2) applied to the developing roller 22 based on the toner amount of the toner image and a bias V (second absolute value) applied to the charging roller 20. The absolute value (third absolute value) of A1) is determined.

S405: In the print control unit 27, the bias applied to the charging roller 20 is fixed (V (A3) remains), and the absolute amount of the bias applied to the developing roller 22 is the target amount of toner to be discarded. Calculate and change the value (second absolute value).

The print control unit 27 sets the bias applied to the charging roller 20 at this time to V (A1) (= V (A3)) and the bias applied to the developing roller 22 to V (A2), and ends this process.

Here, when the toner amount of the toner image on the intermediate transfer belt 14 derived in S402 is larger than the target target toner amount (target amount), the print control unit 27 reduces the amount of toner to be discarded (| The amount of change (difference) in V (A1) |-| V (A2) |) is reduced.

On the other hand, when the toner amount of the toner image on the intermediate transfer belt 14 derived in S402 is smaller than the target target toner amount (target amount), the print control unit 27 increases the amount of toner to be discarded (| V). Increase the amount of change (difference) in (A1) |-| V (A2) |).

Therefore, when the toner amount of the toner image on the intermediate transfer belt 14 derived in S402 is less than the target target toner amount, the print control unit 27 of (| V (A1) |-| V (A2) |) V (A1) and V (A2) are determined so that the amount of change (difference) is larger than when the amount of toner in the toner image on the intermediate transfer belt 14 derived in S402 is larger than the target amount of target toner. To do.

That is, when the amount of toner in the toner image on the intermediate transfer belt 14 is less than the target amount, the print control unit 27 sets the absolute value (second absolute value) of the bias V (A2) applied to the developing roller 22 and the charging roller. The difference from the absolute value (third absolute value) of the bias V (A1) applied to 20 is applied to the developing roller 22 when the amount of toner in the toner image on the intermediate transfer belt 14 is larger than the target amount. It is made larger than the difference between the absolute value (second absolute value) of (A2) and the absolute value (third absolute value) of the bias V (A1) applied to the charging roller 20.

As described above, in this embodiment, the bias V (A1) applied to the charging roller 20 and the bias V (A2) applied to the developing roller 22 in the case of toner disposal A are determined, depending on the environment and aging. It is possible to control the amount of toner that is discarded even if the conditions change.

Therefore, as compared with the case where the toner is discarded by the LED emission pattern for toner disposal, the toner outside the exposure region of the photosensitive drum can also be discarded. Since the deteriorated toner tends to be accumulated at both ends in the longitudinal direction of the image forming unit 10, the accumulated deteriorated toner can be efficiently discarded.

Therefore, image deterioration (deterioration of graininess, deterioration of residual power blurring, deterioration of fog, dirt, etc.) from both ends in the longitudinal direction of the photosensitive drum, which has been a problem, is less likely to occur, and image defects occur at the ends of the photosensitive drum. Can be suppressed.

Further, it is not necessary to increase the number of times of toner disposal and the amount of toner to be discarded at one time.
In this embodiment, the bias applied to the charging roller 20 is fixed and the bias applied to the developing roller 22 is changed, but the bias applied to the charging roller 20 may be changed.

Further, the desired amount of toner may be changed depending on the color, environment, and the like.
Further, the method for determining the application bias to the developing roller 22 and the application bias to the charging roller 20 in this embodiment is an example, and may be determined by another method.

Further, in this embodiment, the development bias and the charging bias to which only the DC voltage is applied are shown, but the present invention is not limited to this, and the AC voltage is superimposed on the DC voltage, and the application bias to the charging roller 20 and the charging bias The bias applied to the developing roller 22 may be an AC voltage + a DC voltage. In this case, paying attention to the voltage value of the component of the DC voltage, the surface potential of the photosensitive drum | << | the bias applied to the developing roller 22 | is set in the DC component.

In the method of discarding toner A, it is possible to efficiently discard the deteriorated toner accumulated at the left and right ends outside the exposed area, but there is a possibility that excess toner in the exposed area is discarded. Therefore, it is better to combine with the method of toner disposal B, which controls the amount of toner to be discarded according to the amount of toner used, instead of always discarding by the method of toner disposal A.

In this embodiment, the timing at which the toner disposal A is performed is defined by the drum count, but other conditions such as changes in the environment and changes over time may be used.

Further, although the toner disposal A is performed before printing and the toner disposal B is performed after printing, the order may be changed, and both the toner disposal A and the toner disposal B may be performed before or after printing. good.

When the toner disposal A is performed before printing, the potential remaining on the surface of the photosensitive drum 19 immediately after printing affects the absolute surface potential of the photosensitive drum 19 due to the charging roller 20, as compared with the case where the toner is discarded after printing. It is possible to suppress an event in which the value cannot be set to a desired potential when the toner is discarded, and the toner can be reliably discarded.

As described above, in this embodiment, the effect of suppressing the occurrence of image defects at the end of the photosensitive drum can be obtained.

Further, it is possible to obtain the effect that it is not necessary to increase the number of times of toner disposal and the amount of toner to be discarded at one time.
In this embodiment, the image forming apparatus has been described as an intermediate transfer type printer for printing roll paper, but the present invention is not limited to this, and a printer for printing cut paper or a direct transfer type printer may be used. Further, the printer is not limited to the LED printer, and may be a laser beam printer.
Further, the image forming apparatus is not limited to a printer, and may be a copying machine, a facsimile apparatus, a multifunction device (MFP), or the like.

10, 10Y, 10M, 10C, 10K, 10W Image forming unit 14 Intermediate transfer belt 15Y, 15M, 15C, 15K, 15W Primary transfer roller 16 Secondary transfer roller 17 Heating roller 18 Pressurizing roller 19 Photosensitive drum 20 Charging roller 21 Exposure head 22 Development roller 23 Supply roller 24 Development blade 27 Print control unit 28 Image data conversion unit 29 Drum rotation speed measurement unit 30 Head light emission measurement unit 31 Print data monitoring unit 32 Transfer roller power supply 33 Charging roller power supply 34 Development roller Power supply for power supply 35 Power supply for supply roller 36 Head drive control unit 37 Power supply for static elimination light 38 Fixation control unit 39 Conveyor motor control unit 40 Drive motor control unit 41 Cutter control unit 42 Calculation unit 57 Storage unit 60 Sensor 100 Image forming device

Claims (9)

An image carrier whose surface is charged by a charging member and
A developer carrier facing the image carrier and
A control unit that applies a developing voltage to the developer carrier,
Have,
Under predetermined conditions, the control unit determines the relationship between the first absolute value of the surface potential of the image carrier charged by the charging member and the second absolute value of the developing voltage.
An image forming apparatus characterized in that the first absolute value is controlled to be less than the second absolute value. In the image forming apparatus according to claim 1,
The charging member is
An image forming apparatus, characterized in that a charging voltage having a third absolute value smaller than the second absolute value of the developing voltage is applied to charge the image carrier to the surface potential. In the image forming apparatus according to claim 2,
The control unit measures the rotation speed of the image carrier and determines the number of rotations.
The predetermined condition is an image forming apparatus characterized in that the rotation speed exceeds a threshold value. In the image forming apparatus according to claim 3,
The image forming apparatus is characterized in that the predetermined condition is a condition after receiving a printing instruction and before performing a printing operation based on the printing instruction. In the image forming apparatus according to any one of claims 2 to 4.
A transfer body to which the developer image formed on the image carrier is transferred, and
A reading unit that detects the amount of developing agent in the developing agent image transferred to the transfer body, and
Have,
The control unit is an image forming apparatus that determines the second absolute value and the third absolute value based on the amount of the developer in the developer image. In the image forming apparatus according to claim 5,
The control unit
When the amount of the developer in the developer image is less than the target amount, the difference between the second absolute value and the third absolute value is obtained, and when the amount of the developer in the developer image is larger than the target amount, the first An image forming apparatus characterized in that the difference between the absolute value of 2 and the third absolute value is made larger. In the image forming apparatus according to claim 6,
The control unit is an image forming apparatus characterized in that the third absolute value is fixed and the second absolute value is changed. In the image forming apparatus according to any one of claims 1 to 7.
The control unit is an image forming apparatus characterized in that a developing voltage is applied to the developer carrier and the developer carried by the developer carrier is discharged to the image carrier. In the image forming apparatus according to any one of claims 1 to 8.
It has an exposure means for exposing an image carrier whose surface is charged by the charging member.
The image carrier is a rotating body that rotates about a rotation axis, and an exposure region exposed by the exposure means and a region outside the exposure region in the direction of the rotation axis are charged by the charging member.
The control unit is an image forming apparatus characterized in that the developer is discharged without exposing the image carrier by the exposure means.

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