JP2016218127A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of insufficient image density on a rear end side of an image with a high image area ratio.SOLUTION: In an image forming apparatus comprising: a photoreceptor 2K; a developing device including a developing roller 11K that develops an electrostatic latent image on the photoreceptor 2K with a toner on a surface thereof, and a regulation blade 12K that is in contact with the surface of the developing roller 11K to regulate the layer thickness of the toner on the surface; and a regulation power supply 154K that outputs a regulation bias to be applied to the regulation blade 12K, the regulation power supply 154K is configured to output, as a regulation bias, a bias composed of a superimposed voltage in which an AC voltage is superimposed on a DC voltage.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus.

  Conventionally, a toner carrier that develops a latent image on a latent image carrier with toner on its surface, a regulating member that abuts against the toner carrier and regulates the thickness of the toner layer on the surface, and a regulation against this An image forming apparatus having a bias applying unit is known.

  For example, the image forming apparatus described in Patent Document 1 applies a regulation bias composed of a DC voltage to a regulation blade that is a regulation member that contacts a developing roller that is a toner carrier. Then, the toner charge amount in the developing device is stabilized by changing the absolute value of the DC voltage of the regulation bias based on the result of detecting the toner adhesion amount of the test toner image. Thereby, it is said that a stable image density can be obtained over a long period of time.

  However, the present inventors have found that, in such a configuration, if the cumulative number of printed sheets is increased to, for example, several thousand sheets, the image density on the rear end side in an image with a high image area ratio tends to be insufficient. Found by experiment.

  In order to solve the above-described problems, the present invention provides a latent image carrier, a toner carrier that develops a latent image on the latent image carrier with toner on its surface, and a surface of the toner carrier. In the image forming apparatus including a developing unit that includes a regulating member that abuts and regulates the thickness of the toner layer on the surface, and a regulated power source that outputs a regulating bias to be applied to the regulating member, the regulating bias includes: The regulated power supply is configured to output a voltage composed of a superimposed voltage obtained by superimposing an AC voltage on a DC voltage.

  According to the present invention, there is an excellent effect that occurrence of insufficient image density on the rear end side in an image with a high image area ratio can be suppressed.

1 is a schematic configuration diagram showing a printer according to a reference form. FIG. 3 is an enlarged configuration diagram illustrating an image forming unit for K in the printer. FIG. 3 is a configuration diagram for explaining a bias application mode in an image forming unit for K of the printer. FIG. 3 is a block diagram illustrating a part of an electric circuit of the printer according to the embodiment. The schematic diagram which shows the relationship between an example of a virtual page, and a dot output rate. The schematic diagram for demonstrating the solid image output by a 3rd test print, and a virtual page. The graph which shows the relationship between each division of the same solid image, and dot output rate [%]. 14 is a graph showing a relationship between a peak-to-peak potential [V] of a regulation bias composed of a superimposed voltage in the printer according to a fourth specific example, a dot output rate, and a cumulative number of prints. The schematic diagram which shows an example of a virtual page. The schematic diagram for demonstrating the solid image output by a 4th test print, and a virtual page. FIG. 4 is a schematic diagram illustrating an example of a virtual page and an example of virtual page division in a printer according to a second detailed example.

Hereinafter, before describing an embodiment of an electrophotographic printer (hereinafter simply referred to as a printer) as an image forming apparatus to which the present invention is applied, a reference form to be referred to in understanding the printer according to the embodiment will be described. Such a printer will be described.
FIG. 1 is a schematic configuration diagram illustrating a printer according to a reference embodiment. In this figure, this printer includes four image forming units 1Y, 1M, 1C, and 1K for forming yellow, magenta, cyan, and black (hereinafter referred to as Y, M, C, and K) toner images. I have. These use Y, M, C, and K toners of different colors as the image forming material, but the other configurations are the same and are replaced when the lifetime is reached. The Y, M, C, and K toners are polyester polymer toners having an average particle diameter of 6.5 [μm]. This polyester polymerized toner is manufactured as follows. That is, first, 100 parts by weight of toner base particles and 2 parts by weight of hydrophobic silica and oil-containing silica RY50 silica manufactured by Nippon Aerosil Co., Ltd. are mixed to obtain a mixture. What was obtained by subjecting this mixture to a 20-liter Henschel mixer for 5 minutes under a condition of 40 [m / s] and then passing the mixture through a sieve having an opening of 75 [μm]. It is.

  Of the four image forming units 1Y, 1M, 1C, and 1K, taking the image forming unit 1K for forming a K toner image as an example, this is a latent image carrier and an image as shown in FIG. A drum-shaped photoconductor 2K as a carrier is provided. Also provided are a drum cleaning device 3K, a charge eliminating device, a charging device 4K, a developing device 5K, and the like. The image forming unit 1K, which is an image forming unit, can be attached to and detached from the printer body, so that consumable parts can be replaced at a time.

  The photoreceptor 2K is made of an organic photoreceptor having a diameter of 30 [mm]. The photosensitive member 2K is driven to rotate clockwise in the drawing at a process linear velocity of 140 [mm / s].

  The charging device 4K uniformly charges the surface of the photoreceptor 2K that is rotated clockwise in the drawing by the driving unit. The uniformly charged surface of the photosensitive member 2K is exposed and scanned by the laser beam L to carry an electrostatic latent image for K. The electrostatic latent image for K is developed into a Y toner image by the developing device 5K using K toner. Then, primary transfer is performed on an intermediate transfer belt 16 described later.

  The drum cleaning device 3K removes the transfer residual toner adhering to the surface of the photoreceptor 2K after the primary transfer process. The static eliminator neutralizes residual charges on the photoreceptor 2K after cleaning. By this charge removal, the surface of the photoreceptor 2K is initialized and prepared for the next image formation. Similarly, in the other color image forming units (1Y, 1M, 1C), (Y, M, C) toner images are formed on the photoreceptors (2Y, 2M, 2C), and an intermediate transfer belt 16 described later is formed. Intermediate transfer is performed on the top.

  The developing device 5K includes a vertically long hopper 6K that stores K toner and a developing unit 7K. In the hopper 6K, an agitator 8K that is rotationally driven by the driving means, an agitation paddle 9K that is rotationally driven by the driving means vertically below, and a toner supply roller 10K that is rotationally driven by the driving means in the vertical direction thereof. Etc. are arranged. The K toner in the hopper 6K moves toward the toner supply roller 10K by its own weight while being stirred by the rotational drive of the agitator 8K and the stirring paddle 9K. The toner supply roller 10K has a metal cored bar and a roller portion made of foamed resin or the like coated on the surface of the metal core roller 10K, while adhering K toner in the hopper portion 6K to the surface of the roller portion. Rotate.

  In the developing unit 7K of the developing device 5K, a developing roller 11K that rotates while contacting the photoreceptor 2K and the toner supply roller 10K, and a regulating blade 12K that makes the tip contact with the surface thereof are disposed.

  The developing roller 11K has a rotating shaft member and a conductive urethane rubber layer (rubber hardness 50 ° (JIS-A)) having a thickness of 4 [mm] fixed to the peripheral surface of the rotating shaft member and having a diameter of 16 [mm]. It consists of a roller and is driven to rotate at a linear speed of 200 [mm / s].

  The toner supply roller 10K is a roller having a diameter of 13 [mm] having a metal core and a roller portion made of conductive foamed urethane (cell diameter: 100 to 500 μm) coated on the surface thereof. Then, while the K toner in the hopper portion 6K is captured by the roller portion and rotated at a linear speed of 200 [mm / s], a contact portion of 4 to 5 [mm] is formed in the rotation direction. It is in contact with the developing roller 11K.

  The regulating blade 12K is made of a metal plate having a thickness of 0.1 [mm], and the tip thereof is bent at an angle of 14 [°].

  The K toner adhered to the toner supply roller 10K in the hopper 6K is supplied to the surface of the development roller 11K at the contact portion between the development roller 11K and the toner supply roller 10K. The developing roller 11K, which is a toner carrier, and the toner supply roller 10K, which is a toner supply body, are rotationally driven so that the surfaces of the developing roller 11K and the toner supply roller 10K are moved in opposite directions at the contact portions. The toner supply roller 10K moves its surface in the opposite direction to the developing roller 11K at the contact portion, thereby collecting K toner on the developing roller 11K or supplying new K toner to the developing roller 11K. To do.

  When the K toner supplied to the developing roller 11K passes through the contact portion between the developing roller 11K and the regulating blade 12K as the developing roller 11K rotates, frictional charging is promoted by friction with the regulating blade 12K. At the same time, the layer thickness on the roller surface is uniformly regulated. Then, the K toner after the layer thickness regulation adheres to the electrostatic latent image for K on the surface of the photosensitive member 2K in the developing region which is a contact portion between the developing roller 11K and the photosensitive member 2K. By this adhesion, the electrostatic latent image for K is developed into a K toner image.

  K toner that has not contributed to development adheres to the surface of the developing roller 11K after passing through the development area, but the amount of adhesion is not uniform, and there is unevenness corresponding to the electrostatic latent image. If new K toner is supplied as it is to the surface of the developing roller 11K in such a state, the unevenness of the toner adhesion amount remains, which causes uneven development density. Therefore, it is desirable to supply new K toner to the surface of the developing roller 11K after recovering K toner from the surface of the developing roller 11K after passing through the developing region. Therefore, as described above, the printer according to the reference embodiment employs a configuration in which the surface of the toner supply roller 10K is moved in the direction opposite to the developing roller 11K at the contact portion with the developing roller 11K. In such a configuration, K toner is scraped and collected from the surface of the developing roller 11K by the toner supply roller 10K in the vicinity of the entrance of the contact portion (position where the surface of the developing roller 11K enters the contact portion). Thereafter, K toner on the surface of the toner supply roller 10K can be supplied to the surface of the developing roller 11K in a region from the center of the contact portion to the vicinity of the exit.

  FIG. 3 is a configuration diagram for explaining a bias application mode in the K image forming unit 1K. A developing bias output from a developing power supply 151K is applied to the developing roller 11K. The developing bias has the same polarity as the charging polarity of the K toner, and its absolute value (150 V in this example) is the absolute value of the background potential (550 V in this example) of the photosensitive member 2K and the electrostatic latent image potential. The value is between the absolute values (30 to 50 V in this example).

  A supply bias output from a supply power source 152K is applied to the toner supply roller 10K. The supply bias has the same polarity as the charging polarity of the K toner, and its absolute value is larger than the absolute value of the developing bias (for example, 350 V). For this reason, at the contact portion between the developing roller 11K and the toner supply roller 10K, an electrostatic force from the toner supply roller 10K side to the developing roller 11K side is applied to the K toner on the toner supply roller 10K. As a result, the K toner on the toner supply roller 10K is efficiently transferred to the developing roller 10K.

  A restriction bias output from the restriction power source 154K is applied to the restriction blade 12K. The regulation bias has the same polarity as the charging polarity of the K toner, and the absolute value thereof is larger than the absolute value of the developing bias (for example, 350 V). Therefore, the K toner that has entered the contact portion between the regulating blade 12K and the developing roller 11K is pressed toward the surface of the developing roller 11K, and frictional charging is promoted.

  Although the image forming unit for K has been described with reference to FIGS. 2 and 3, the surfaces of the photoreceptors 2Y, 2M, and 2C are also obtained in the same manner in the image forming units 1Y, 1M, and 1C for Y, M, and C. Y, M, and C toner images are formed.

  In FIG. 1, an optical writing unit 70 is disposed above the image forming units 1Y, 1M, 1C, and 1K in the vertical direction. The optical writing unit 70 serving as a latent image writing device emits light to the photoreceptors 2Y, 2M, 2C, and 2K in the image forming units 1Y, 1M, 1C, and 1K by laser light L emitted from a laser diode based on image information. Scan. Of the entire area on the surface of the uniformly charged photoreceptors 2Y, 2M, 2C, and 2K, the area irradiated with the laser light L attenuates the potential and carries an electrostatic latent image. For example, the potential of the background immediately after uniform charging is −550 [V], whereas the potential of the electrostatic latent image is attenuated to −30 to −50 [V]. In this way, electrostatic latent images for Y, M, C, and K are formed on the photoreceptors 2Y, 2M, 2C, and 2K. The optical writing unit 70 irradiates the photosensitive member through a plurality of optical lenses and mirrors while polarizing the laser light (L) emitted from the light source in the main scanning direction by a polygon mirror rotated by a polygon motor. To do. You may employ | adopt what performs optical writing by the LED light emitted from several LED of the LED array.

  Below the image forming units 1Y, 1M, 1C, and 1K, a transfer unit 15 that is endlessly moved counterclockwise in the drawing while an endless intermediate transfer belt 16 is stretched is disposed. In addition to the intermediate transfer belt 16, the transfer unit 15 that is a part of the transfer device includes a driven roller 17, a drive roller 18, four primary transfer rollers 19Y, 19M, 19C, and 19K. Further, it also has a secondary transfer roller 20, a belt cleaning device 21, a cleaning backup roller 22, and the like.

  The driven roller 17, the driving roller 18, the cleaning backup roller 22, and the four primary transfer rollers 19 </ b> Y, 19 </ b> M, 19 </ b> C, and 19 </ b> K are disposed inside the loop of the intermediate transfer belt 16. Among these, the cleaning backup roller 22 and the four primary transfer rollers 19Y, 19M, 19C, and 19K are in contact with the back surface of the intermediate transfer belt 16, but the winding angle of the belt with respect to the peripheral surface is very small. . For this reason, the intermediate transfer belt 16 is not substantially stretched. On the other hand, the driven roller 17 and the driving roller 18 stretch the intermediate transfer belt 16 while winding the intermediate transfer belt 16 around the circumferential surface at a winding angle of about 180 [°]. That is, the driven roller 17 and the driving roller 18 function as stretching rollers that stretch the intermediate transfer belt 16. The driving roller 18 is rotationally driven in the counterclockwise direction in the drawing by the driving means, thereby moving the intermediate transfer belt 16 endlessly in the same direction.

  The four primary transfer rollers 19Y, 19M, 19C, and 19K sandwich the intermediate transfer belt 16 that is moved endlessly in this manner between the photoreceptors 2Y, 2M, 2C, and 2K. By this sandwiching, primary transfer nips for Y, M, C, and K where the front surface of the intermediate transfer belt 16 and the photoreceptors 2Y, 2M, 2C, and 2K abut are formed. A primary transfer bias is applied to the primary transfer rollers 19Y, 19M, 19C, and 19K by a primary transfer bias power source, whereby the electrostatic latent images of the photoreceptors 2Y, 2M, 2C, and 2K and the primary transfer rollers are applied. A transfer electric field is formed between 19Y, M, C, and K. In place of the primary transfer rollers 19Y, 19M, 19C, and 19K, a transfer charger, a transfer brush, or the like may be employed.

  Examples of the belt substrate of the intermediate transfer belt 16 include polymer materials such as TPE (thermoplastic elastomer alloy), PC (polycarbonate), PI (polyimide), PAA (polyamide alloy), PVDF (polyvinylidene fluoride), and the like. Is possible. The belt substrate is the belt itself when the intermediate transfer belt 16 has a single-layer structure. In the case of a multilayer structure, the thickest layer is the belt substrate.

  When the Y toner formed on the surface of the photoconductor 2Y of the Y image forming unit 1Y enters the above-described primary transfer nip for Y as the photoconductor 2Y rotates, the photoconductor is exposed to light due to the transfer electric field and the nip pressure. Primary transfer is performed on the intermediate transfer belt 16 from the body 2Y. The intermediate transfer belt 16 on which the Y toner image is primarily transferred in this way passes over the primary transfer nips for M, C, and K along with the endless movement thereof, so that it is on the photoreceptors 2M, 2C, and 2K. The M, C, and K toner images are primarily transferred onto the Y toner image in a superimposed manner. A four-color toner image is formed on the intermediate transfer belt 16 by the primary transfer of the superposition.

  The drive roller 18 functions as a transfer lining roller that wraps a portion that forms a secondary transfer nip, which will be described later, on its peripheral surface in the entire circumferential region of the intermediate transfer belt 16 to form a belt curved portion. Yes. The secondary transfer roller 20 of the transfer unit 15 is in contact with the belt curved portion curved along the curvature of the driving roller 18 from the belt front surface side to form a secondary transfer nip. A secondary transfer bias is applied to one of the secondary transfer roller 20 and the driving roller 18 having the above configuration by a transfer bias power source. The other is grounded. As a result, a secondary transfer electric field is formed between the secondary transfer roller 20 and the driving roller 18.

  As the secondary transfer roller 20, a metal roller core bar covered with a conductive elastic layer made of a conductive and elastic material is used. Examples of the material for the conductive elastic layer include ion conductive materials (urethane + carbon dispersion, NBR, hydrin), and electronic conductive materials (EPDM).

  Below the transfer unit 15 in the vertical direction, a paper feed cassette 30 serving as a recording member storage unit that stores a plurality of recording papers P as recording members in a bundle of sheets slides relative to the housing of the printer. It is detachably arranged. In the paper feed cassette 30, a paper feed roller 30a is brought into contact with the top recording paper P of the paper bundle, and the recording paper is rotated by rotating it in a counterclockwise direction in the drawing at a predetermined timing. P is sent out toward the paper feed path 31.

  A registration roller pair 32 is disposed near the end of the paper feed path 31. The registration roller pair 32 is disposed obliquely above the end of the paper discharge cassette 30 on the paper discharge side. The recording paper P discharged from the paper feeding cassette 30 toward the side of the cassette in a substantially horizontal direction is largely turned at an angle of about 90 [°] immediately after being discharged, and enters the registration nip of the registration roller pair 32. Sent to. The registration roller pair 32 stops the rotation of both rollers as soon as the recording paper P delivered from the paper feed cassette 30 is sandwiched between the rollers. Then, rotation driving is restarted at a timing at which the sandwiched recording paper P can be synchronized with the four-color toner image on the intermediate transfer belt 16 in the above-described secondary transfer nip, and the recording paper P is directed to the secondary transfer nip. Send it out.

  The four-color toner image on the intermediate transfer belt 16 brought into intimate contact with the recording paper P at the secondary transfer nip is batch-transferred onto the recording paper P under the influence of the secondary transfer electric field and nip pressure, and the recording paper Combined with the white color of P, a full color toner image is obtained. The recording paper P having the full-color toner image formed on the surface in this way is separated from the secondary transfer roller 20 and the intermediate transfer belt 16 by curvature when passing through the secondary transfer nip. Then, it passes through a post-transfer conveyance path 33 and is sent to a fixing device 34 disposed above the secondary transfer nip.

  The transfer residual toner that has not been transferred to the recording paper P adheres to the intermediate transfer belt 16 after passing through the secondary transfer nip. This is cleaned from the belt surface by a belt cleaning device 21 in contact with the front surface of the intermediate transfer belt 16. The cleaning backup roller 22 disposed inside the loop of the intermediate transfer belt 16 backs up the cleaning of the belt by the belt cleaning device 21 from the inside of the loop.

  The fixing device 34 forms a fixing nip with a fixing roller 34a containing a heat source such as a halogen lamp and a pressure roller 34b that rotates while contacting the fixing roller 34a with a predetermined pressure. The recording paper P fed into the fixing device 34 is sandwiched between the fixing nips such that the unfixed toner image carrying surface is brought into close contact with the fixing roller 34a. Then, the toner in the toner image is softened by the influence of heating and pressurization, and the full color image is fixed.

  The recording paper P discharged from the fixing device 34 passes through the post-fixing conveyance path 35 and then reaches the branch point between the paper discharge path 36 and the pre-reversal conveyance path 41. On the side of the post-fixing conveyance path 35, a switching claw 42 that is rotationally driven around a rotation shaft 42a is disposed. By the rotation, the vicinity of the end of the post-fixing conveyance path 35 is closed. Or open it. At the timing when the recording paper P is sent out from the fixing device 34, the switching claw 42 stops at the rotational position indicated by the solid line in the drawing, and the vicinity of the end of the post-fixing conveyance path 35 is opened. Therefore, the recording paper P enters the paper discharge path 36 from the conveyance path 35 after fixing, and is sandwiched between the rollers of the paper discharge roller pair 37.

  When the single-sided print mode is set by an input operation to an operation unit such as a numeric keypad or a control signal sent from a personal computer or the like, the recording paper P sandwiched between the paper discharge roller pair 37 remains as it is. It is discharged outside the machine. Then, it is stacked on the stack portion that is the upper surface of the upper cover 50 of the housing.

  On the other hand, when the duplex printing mode is set, the following operation is performed. That is, when the rear end side of the recording paper P conveyed in the paper discharge path 36 while being sandwiched between the pair of paper discharge rollers 37 passes through the post-fixing conveyance path 35, the switching claw 42 reaches the position of the one-dot chain line in the figure. By rotating, the vicinity of the end of the conveyance path 35 after fixing is closed. At substantially the same time, the paper discharge roller pair 37 starts to rotate in the reverse direction. Then, the recording paper P is conveyed while the rear end side is directed to the top, and enters the pre-reversal conveyance path 41.

  FIG. 1 shows a printer according to a reference embodiment from the front side. The front side in the direction perpendicular to the drawing is the front side of the printer, and the back side is the rear side. In the drawing of the printer according to the reference embodiment, the right side is the right side and the left side is the left side. The right end portion of the printer is a reversing unit 40 that can be opened and closed with respect to the housing body by rotating about a rotation shaft 40a. When the paper discharge roller pair 37 rotates in the reverse direction, the recording paper P enters the pre-reversal conveyance path 41 of the reversing unit 40 and is conveyed from the upper side to the lower side in the vertical direction. Then, after passing between the rollers of the pair of reverse conveying rollers 43, it enters the reverse conveying path 44 that is curved in a semicircular shape. Furthermore, while the upper and lower surfaces are reversed as the sheet is conveyed along the curved shape, the traveling direction from the upper side in the vertical direction to the lower side is also reversed, and conveyed from the lower side in the vertical direction toward the upper side. Is done. Thereafter, the toner enters the secondary transfer nip again through the above-described paper feed path 31. Then, after the full-color image is secondarily transferred collectively to the other surface, the post-transfer conveyance path 33, the fixing device 34, the post-fixation conveyance path 35, the paper discharge path 36, and the paper discharge roller pair 37 are sequentially passed. And discharged outside the machine.

  The reversing unit 40 has an external cover 45 and a rocking body 46. Specifically, the external cover 45 of the reversing unit 40 is supported so as to rotate about a rotation shaft 40a provided in the housing of the printer main body. By this rotation, the outer cover 45 opens and closes with respect to the housing together with the swinging body 46 held therein. As shown by the dotted line in the figure, when the outer cover 45 is opened together with the swinging body 46 therein, the paper feed path 31, the secondary transfer nip, the transfer formed between the reversing unit 40 and the printer main body side. The rear conveyance path 33, the fixing nip, the post-fixation conveyance path 35, and the paper discharge path 36 are vertically divided into two and exposed to the outside. Thereby, jammed paper in the paper feed path 31, the secondary transfer nip, the post-transfer conveyance path 33, the fixing nip, the post-fixation conveyance path 35, and the paper discharge path 36 can be easily removed.

  The swing body 46 is supported by the external cover 45 so as to rotate about a swing shaft provided in the external cover 45 in a state in which the external cover 45 is opened. When the swinging body 46 is opened with respect to the external cover 45 by this rotation, the pre-reversal transport path 41 and the reverse transport path 44 are vertically divided into two and exposed to the outside. As a result, the jammed paper in the pre-reversal conveyance path 41 and the reversal conveyance path 44 can be easily removed.

  The upper cover 50 of the printer housing is supported so as to be rotatable about a rotation shaft 51 as indicated by an arrow in the figure. The upper opening of the housing is greatly exposed to the outside. Thereby, the optical writing unit 71 is exposed.

  In the printer according to the reference embodiment, in order to simplify the configuration of the transfer unit 15 and reduce the size of the apparatus as much as possible, the intermediate transfer belt 16 is stretched by only two stretching rollers (17, 18). Yes. In such a configuration, either one (17, 18) functions as a driving roller. However, in the printer according to the reference embodiment, the tension roller that functions as a transfer backing roller functions as a driving roller. As a result, the transfer backing roller has multiple functions, but the transfer backing roller and the driving roller may be provided separately.

  In the printer according to the reference embodiment having the above-described configuration, if the cumulative number of prints increases to some extent, it tends to cause insufficient image density on the rear end side (hereinafter referred to as rear end blurring) in an image with a high image area ratio. was there. Therefore, the present inventors conducted intensive research on the cause of the failure and found the following. In other words, the image forming units 1Y, 1M, 1C, and 1K regard the time when the Y, M, C, and K toners in the developing devices 5Y, 5M, 5C, and 5K have been consumed as the end of the life, and make new ones. It is configured to be replaced. The lifetime is generally at the time when 15000 images having a general image area ratio are output.

  The inventors of the present invention performed the first test print using a print tester similar to the printer according to the reference embodiment. In this first test print, an A3 size paper is transported by a lateral transport in which the short side direction is aligned with the transport direction, and a test solid image (all solids) with a dot output rate = 100 [%] is printed to the A3 size. Was carried out continuously. Regarding the potential conditions, the developing bias = −150 [V], the photoreceptor background portion potential = −550 [V], the latent image potential = −30 to −50 [V], the supply bias = −350 or −400 [V]. Regulating bias = −350 or −400 [V]. The supply bias and the regulation bias were set to −350 [V] when the cumulative number of printed sheets was 1 to 5000 sheets, and −400 [V] when the accumulated number of printed sheets was 5001 to 6000 sheets.

For each 1000th print, the degree of occurrence of rear end side blurring of the test solid image was subjectively evaluated in two stages: no rear end side blurring (◯) and rear end side blurring (×). A similar test was performed on a test halftone image (all halftones) with a dot output rate of 50 [%]. The results are shown in Table 1 below.

  As shown in Table 1, in the case of all solid images (100%), the trailing edge side blur started to occur when the cumulative number of prints increased to 4000. In the case of a halftone image (50%), the trailing edge side blur started to occur when the cumulative number of prints increased to 5000.

  As a result of removing the developing roller from the printer tester and observing while repeating the same test print, it was found that the trailing edge side blur occurred as follows. That is, in the image forming units 1Y, 1M, 1C, and 1K, as the cumulative number of prints from the new state increases, the stirring and residence time of the Y, M, C, and K toners in the developing devices 5Y, 5M, 5C, and 5K Will increase. Then, the Y, M, C, and K toners are gradually deteriorated to lower their fluidity. As a result, a region upstream of the contact portion between the developing rollers 10Y, 10M, 10C, and 10K and the regulating blades 12Y, 12M, 12C, and 12K and in the vicinity of the contact portion (hereinafter referred to as “blade contact portion entrance vicinity”). In the “region”, toner stagnation begins to occur. The Y, M, C, and K toners are less likely to move toward the blade abutting portion, and are stagnant. This makes it difficult for Y, M, C, and K toners to adhere to the surfaces of the developing rollers 10Y, 10M, 10C, and 10K after passing through the contact portion. Then, when developing an image with a high image area ratio from the leading end side toward the trailing end side, the Y, M, C, and K toner adhesion amounts on the developing rollers 10Y, 10M, 10C, and 10K are gradually reduced. To go. As a result, it has been found that the rear end side blur is caused by the development failure due to the lack of toner in the image portion on the rear end side.

  In particular, as in the printer according to the reference embodiment, a toner containing oil-containing silica as an additive is used to obtain good toner cleaning properties and charge amount stability, and a large amount of toner is stored in the developing device. In the configuration, the rear end side blur of the image is likely to be caused. This is for the reason described below. That is, as the cumulative number of prints increases, the number of toner particles that have passed through the rubbing portion with the regulating blade many times and released the silicone oil of the oil-containing silica increases in the developing device. . This is because when the fluidity of the toner is reduced to a certain extent, the amount of toner in the developing process at the trailing edge of the image becomes insufficient when printing an image with a high image area ratio.

  In the first test print, when the cumulative number of prints increases to 4000, the trailing edge side blur occurs in all solid images, whereas the trailing edge side blur does not occur in all halftone images for the following reason. . That is, since the solid image consumes more toner per unit area, the amount of developing toner tends to be insufficient at the rear edge of the image.

Next, the printer according to the embodiment will be described. Unless otherwise specified below, the configuration of the printer according to the embodiment is the same as the reference embodiment.
The inventors of the present invention conducted intensive research on a method for reducing a toner stagnation phenomenon that starts to occur in the “blade contact portion entrance area” when the cumulative number of printed sheets increases to around 4000. As a result, when a regulation bias composed of a superimposed voltage obtained by superimposing an AC voltage on a DC voltage is used, the regulation blades 12Y, 12M, 12C, and 12K are slightly vibrated to contact the Y, M, C, and K toner blades. It was found that the flow to the club could be promoted.

  Therefore, in the printer according to the embodiment, the control bias that is applied to the control blades 12Y, 12M, 12C, and 12K is output from the control power source for Y, M, C, and K as a superimposed bias. Yes. In such a configuration, even if the fluidity of Y, M, C, and K toner in the developing device is reduced as the cumulative number of printed sheets increases, the regulating blades 12Y, 12M, 12C, The following effects are achieved by the fine vibration of 12K. In other words, a shortage of developer toner is suppressed by facilitating the flow of Y, M, C, and K toners to the blade contact portion in the “blade contact portion entrance region” by slight vibration, thereby suppressing toner stagnation. . As a result, it is possible to suppress the occurrence of blur on the rear end side of the image.

Next, a printer according to an example in which a more characteristic configuration is added to the printer according to the embodiment will be described. Unless otherwise specified below, the configuration of the printer according to the example is the same as that of the embodiment.
FIG. 4 is a block diagram illustrating a part of the electric circuit of the printer according to the embodiment. In the figure, only some of the various devices electrically connected to the main control unit 100 are shown. The main control unit 100 includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), a nonvolatile memory, and the like, and controls driving of various devices in the entire printer and arithmetic processing. Is.

  In the printer according to the embodiment, a device that is electrically connected to the main control unit 100 via the I / O interface 101 includes a print server circuit 104, an image data processing unit 105, and a LAN (Local Area Network). Examples include port 102. In addition, the USB port 103, the writing control unit 107, the unit replacement detector 109, the optical writing unit 70, the power control units 153Y, 153M, 153C, and 153K for each color are also connected to the main control unit via the I / O interface 101. 100.

  The power controller (153Y, M, C, K) for each color controls the output of each power source for each color based on the signal sent from the main controller 100. Specifically, the output value of the development bias from the development power supply (151Y, M, C, K) is controlled, or the output value of the supply bias from the supply power supply (152Y, M, C, K) is controlled. The output value of the regulation bias from the regulation power supply (154Y, M, C, K) is controlled.

  The LAN port 102 can acquire image data of an image to be output by communicating with a personal computer or a scanner via an external local area network. Further, the USB port 103 can acquire image data of an image to be output by communicating with an external personal computer via a USB cable.

  Image data input from the personal computer to the LAN port 102 via the local area network is input to the image data processing unit 105 via the print server circuit 104. The color image data input from the personal computer to the USB port 103 is input to the image data processing unit 105 as it is.

  The image data processing unit 105 separates the received color image data into R (red), G (green), and B (blue) color separation image data, and then separates them into four colors Y, M, C, and K. Convert to color separation image data. Then, the obtained color separation image data of Y, M, C, and K is transmitted to the writing control unit 107. The writing control unit 107 controls the driving of the optical writing unit 70 based on the Y, M, C, and K color-separated image data received from the image data processing unit 105, and the photoreceptors 2Y, M, C, Each K is optically scanned. Further, a page synchronization signal for synchronizing each page is transmitted to the main control unit 100 and the power control units (153Y, M, C, K) for each color. The main control unit 100 controls the delivery of the recording paper P from the paper feed cassette 30 and the registration roller pair 32 based on the page synchronization signal. The power control units (153Y, M, C, K) for each color control output values of various biases based on the page synchronization signal.

  The image data processing unit 105 calculates the dot output rate for each of the Y, M, C, and K toner images, and transmits the result to the power control units 153Y, 153M, 153C, and 153K for Y, M, C, and K. . The power control units 153Y, 153M, 153C, and 153K are for Y, M, C, and K based on the Y, M, C, and K dot output rates and the synchronization signal sent from the optical writing unit 70. The output value of various biases is controlled.

  The unit replacement detector 109 acquires the ID numbers of the image forming units 1Y, 1M, 1C, and 1K by wireless communication with IC tags mounted on the image forming units 1Y, 1M, 1C, and 1K. Then, for each of the image forming units 1Y, 1M, 1C, and 1K, it can be detected that the exchange has been performed based on the change in the ID number. When the exchange is detected, a unit exchange signal corresponding to the same color as the image forming unit is transmitted to the main control unit 100. When the main control unit 100 receives the unit replacement signal, the main control unit 100 resets the cumulative value of the cumulative number of prints to zero for the color corresponding to the unit replacement signal.

  Further, the main control unit 100 can bring the intermediate transfer belt 16 into and out of contact with the three photoconductors 2Y, 2C, and 2M by changing the stretching posture of the intermediate transfer belt 16. If the received image data is color image data, the color transfer operation is started after the intermediate transfer belt 16 is brought into contact with the photosensitive members 2Y, 2M, 2C, and 2K of the respective colors. At this time, each of the image forming units 1Y, 1M, 1C, and 1K for each color is operated. On the other hand, when the received image data is monochrome image data, the monochrome transfer operation is started after the intermediate transfer belt 16 is separated from the three photoconductors 2Y, 2M, and 2C. At this time, only the image forming unit 1K for K among the colors is operated. As a result, during monochrome printing, the operations of the image forming units 1Y, 1M, and 1C unnecessary for image formation are stopped, and unnecessary deterioration of the Y, M, and C toners in the developing devices 5Y, 5M, and 5C is avoided. Yes.

  Further, every time a print job is performed on one sheet of recording paper P, the main control unit 100 performs cumulative printing only for K for monochrome printing and Y, M, C, and K for each color printing. Count up the accumulated number of sheets by one. And the result is transmitted to a corresponding power supply control part (153Y, M, C, K).

  As shown in Table 1 above, even if all solid images having the maximum dot output rate are printed using only a DC voltage as the regulation bias, if the cumulative number of prints is about 3000, the back of the image It can be seen that no end-side scraping occurs. In other words, if the cumulative number of printed sheets is about 3000 sheets, the rear end side blur of the image is not generated even if the DC bias voltage or the superimposed voltage is used as the regulation bias. is there. On the other hand, the present inventors have found through experiments that when a bias voltage composed of a superimposed voltage is used, the regulating blades 12Y, 12M, 12C, and 12K are caused to vibrate slightly by the AC component to generate noise. It was. Therefore, for the period until the cumulative number of printed sheets increases to some extent, it is desirable to use a DC bias voltage as the regulation bias.

  Further, it is desirable that the end of the period varies depending on the dot output rate of the output image. For example, in the example of Table 1, when the cumulative number of prints reaches 4000, the trailing edge side blur occurs in all solid images with a dot output rate of 100%, whereas all halftones with a dot output rate of 50%. No trailing edge blur occurs in the image. Therefore, it is desirable to set the end to 3999 for all solid images, but it is desirable to delay the end for all halftone images.

  Therefore, the power control units 153Y, 153M, 153C, and 153K for Y, M, C, and K have a case where the dot output rate sent from the image data processing unit 105 is equal to or less than a predetermined switching reference value, The type of regulation bias is switched between cases where this is not the case. Specifically, when the dot output rate is equal to or less than a predetermined switching reference value, a regulation bias including only a DC voltage is output from the regulation power supplies 154Y, 154M, 154C, and 154K. On the other hand, when the dot output rate is not equal to or less than the switching reference value, the regulation bias including the superimposed voltage is output from the regulation power supplies 154Y, 154M, 154C, and 154K.

  In such a configuration, when the dot output rate is relatively low and there is a low possibility of occurrence of trailing edge side blurring, a regulation bias consisting only of a DC voltage is used. Thereby, it is possible to reduce the frequency of generating noise due to the slight vibration of the regulating blade due to the use of the regulating bias composed of the superimposed voltage.

  Further, the power control units 153Y, 153M, 153C, and 153K for Y, M, C, and K decrease the switching reference value according to the increase in the cumulative number of prints of Y, M, C, and K, respectively. Perform the process. Specifically, when the cumulative number of printed sheets is within a range of 1 to 3000, 100 [%] is used as the switching reference value. When the cumulative number of prints is within the range of 3001 to 4000, 50 [%] is used as the switching reference value. When the cumulative number of prints is in the range of 4001 to 10000, 40 [%] is used as the switching reference value. When the cumulative number of prints is 10001 or more, 30 [%] is used as the switching reference value.

  In such a configuration, the regulation bias can be switched from the superimposed voltage only to the superimposed voltage at an appropriate timing according to the combination of the cumulative number of prints and the dot output rate.

  The inventors improved the above-described print tester to have the same configuration as the printer according to the example. Then, a second test print was performed using this print tester. Also in this second test print, a test solid image (full solid) with a dot output rate = 100 [%] is printed in the A3 size while A3 size paper is conveyed by lateral conveyance in which the short side direction is aligned with the conveyance direction. The operation was carried out continuously. Regarding the potential conditions, the developing bias = −150 [V], the photoreceptor background portion potential = −550 [V], the latent image potential = −30 to −50 [V], and the supply bias = −350 [V]. As for the regulation bias, when the dot output rate is lower than the switching reference value, only the DC voltage of −350 [V] is used, while the dot output rate is equal to or higher than the switching reference value. In some cases, a superposed voltage was used. As the superimposed voltage, a DC voltage of −150 [V] and a sine AC voltage with a peak-to-peak potential of 1000 [V] and a frequency of 1 [kHz] are used. The number of continuous prints was 6000. A similar test was performed for all halftone images with a dot output rate of 50%. The results are shown in Table 2 below.

  As shown in Table 2, when the cumulative number of prints increases from 3000 to 13001, the dot output rate switching reference value is changed from 100 [%] to 50 [%]. As a result, when all solid images are output, the dot output rate (= 100%) exceeds the switching reference value (= 50%). Will be changed. As a result, the trailing edge side blur of all the solid images can be effectively suppressed even under the condition of the cumulative number of printed sheets of 3001 sheets in which the trailing edge side blurring of all the solid images occurs under the condition of the regulation bias consisting of only the DC voltage. is made of. On the other hand, when all halftone images are output, the dot output rate (= 50%) is equal to or less than the switching reference value (= 50%), so that only the DC voltage is used as the regulation bias. Used. As a result, it is possible to avoid the generation of noise due to the use of the regulation bias composed of the superimposed voltage without causing the rear end side blur of the all halftone image.

  When the cumulative number of printed sheets increases to 4001, the dot output rate switching reference value is changed from 50 [%] to 40 [%]. Thereby, even when all halftone images are output, since the dot output rate (= 50%) exceeds the switching reference value (= 40%), the regulation bias is composed only of DC voltage, It is changed to one consisting of superposition voltage. As a result, the trailing edge side blur of all the halftone images is effectively suppressed even under the condition of the cumulative number of printed sheets of 4001 sheets in which the trailing edge side blurring of all the halftone images is generated under the condition of the regulation bias consisting of only the DC voltage. Is able to.

  As described above, the second test print proved the operational effect of the printer according to the example.

  When applying a regulation vice consisting only of DC voltage to the regulation blade (12Y, M, C, K), the toner is excellent while suppressing the shortage of toner supply to the developing roller (11Y, M, C, K). In order to triboelectrically charge, the DC voltage needs to be as follows. That is, it is necessary to make the absolute value larger than the absolute value of the developing bias. Therefore, in the printer according to the embodiment, as the DC voltage of the regulation bias including only the DC voltage, a voltage whose absolute value (350V) is larger than the absolute value (150V) of the developing bias is adopted.

  On the other hand, when an AC voltage having a relatively large amplitude is applied to the regulating blade (12Y, M, C, K), the blade fine voltage can be reduced without making the absolute value of the regulating blade DC voltage larger than the absolute value of the developing bias. The toner can be frictionally charged favorably by the vibration. Therefore, the printer according to the embodiment employs a DC bias absolute value (150 V) smaller than the DC bias absolute value of the regulation bias consisting only of the DC voltage as the regulation bias consisting of the superimposed voltage. . In this case, when an AC voltage having a sine wave such as a sine wave or a rectangular wave having a duty of 50 [%] is used, the discharge at the blade contact portion is performed. The occurrence of reverse charging of the toner due to the toner can be suppressed. If the absolute value of the DC voltage of the regulation bias consisting of the superimposed voltage is relatively large, the potential difference between the peak value of the regulation bias and the development bias is made larger than the discharge start voltage, and the blade-roller This is because it becomes easier to generate the discharge.

  Further, when an alternating voltage having a large amplitude is applied to the regulating blade (12Y, M, C, K), the flow of toner to the blade contact portion is promoted by the fine blade vibration. As a result, the thickness of the toner thin layer on the developing roller (11Y, M, C, K) may be made larger than intended and the image density may be excessively increased. However, the absolute value of the DC component in the regulation bias composed of the superimposed voltage is made smaller than the absolute value of the DC component of the regulation bias composed only of the DC voltage, so that the electrostatic force directed from the blade to the roller is further reduced. It is possible to suppress an increase in the thickness of the material. Thereby, the occurrence of excessive image density can be suppressed.

  The action of promoting the flow of toner to the blade contact portion in the “blade contact portion entrance vicinity region” by applying a superimposed voltage to the regulating blade (12Y, M, C, K) is mainly performed by the fine blades. This is probably due to vibration and toner vibration. As the fine vibration of the blade is normalized more efficiently, the toner flow can be more efficiently promoted. As in the printer according to the embodiment, when the restriction blade (12Y, M, C, K) is made of a metal, a desired strength can be obtained with a thinner thickness than when a non-metal is used. Thus, it becomes possible to normalize the fine vibration of the blade more satisfactorily. Thereby, the toner flow can be more efficiently promoted. Examples of the metal include stainless steel, phosphor bronze, and aluminum.

Next, specific examples in which a more characteristic configuration is added to the printer according to the embodiment will be described. Unless otherwise specified below, the configuration of the printer according to each specific example is the same as that in the embodiment.
[First example]
As described above, when an AC voltage having a large amplitude is applied to the regulating blade (12Y, M, C, K), the thickness of the toner thin layer on the developing roller (11Y, M, C, K) is more than intended. If it is increased, the image density may be excessively increased. Therefore, in the printer according to the first specific example, when the restriction bias composed of the superimposed voltage is used, the power supply control is performed so that the absolute value of the developing bias is made smaller than when the restriction bias composed of only the DC voltage is used. The units 153Y, 153M, 153C, and 153K are configured. In such a configuration, when a regulation bias composed of a superposed voltage is used, it is possible to suppress the occurrence of excessive image density by making the development potential smaller by reducing the absolute value of the development bias. In the first specific example, when the regulation bias composed of the superimposed voltage is used, the developing bias is set to −100 [V].

  The action of accelerating the flow of toner to the blade contact portion in the “blade contact portion entrance region” obtained by the regulation bias composed of the superimposed voltage is based on the fact that the peak-to-peak potential of the AC voltage is the development bias and the latent image of the photoreceptor. When the potential difference is less than 10 times the potential difference, it is difficult to obtain. On the other hand, the printer according to the first specific example employs an AC voltage having a peak-to-peak potential of 1000 [V]. Further, since the developing bias = −100 [V] and the latent image potential = −30 to −50 [V], the potential difference between them is 70 to 50 [V]. Since the peak-to-peak potential is 10 times or more of the potential difference, the above-described action can be reliably obtained.

  The power supply control units 153Y, 153M, 153C, and 153K are configured to perform control to increase the absolute value of the DC voltage of the supply bias as the dot output rate of the output image increases. In this configuration, the absolute value of the supply bias is increased from the toner supply roller (10Y, M, C, K) to the developing roller (11Y, M) as the dot output rate increases and the trailing edge side blur tends to occur. , C, K). As a result, the occurrence of the trailing edge side blur of the image can also be suppressed by suppressing the occurrence of the insufficient amount of the developing toner.

[Second example]
The rear end blur of the image is caused by a shortage of the developing toner amount on the downstream side (rear end side) of the image in the moving direction of the photoreceptor surface, and is easily generated. Is better correlated with the dot output rate for each section, which will be described below, than the dot output rate for the entire image area. That is, the dot output rate for each section obtained by partitioning a virtual page representing an output image into a plurality of sections in a direction orthogonal to the surface movement direction of the photoreceptor. For example, it is assumed that a solid image covering the entire area is formed only in one of the plurality of sections. In this case, the dot output rate of the entire virtual page is not so large. For example, if the number of sections is 10, the dot output rate in the entire virtual page is 10 [%], which is a relatively low value. However, in one section where a solid image is output, toner is consumed in a concentrated manner, so that the trailing edge side blur occurs in the solid image under the condition that the cumulative number of prints has increased to some extent. If attention is paid to only one section where a solid image is output, the dot output rate is a maximum value of 100 [%], which correlates well with the ease of occurrence of trailing edge blurring.

  Therefore, in the printer according to the second specific example, the image data processing unit 105 is configured to perform the following processing. That is, for each color, a virtual page expressing an output image is divided into a plurality of directions in a direction orthogonal to the surface movement direction of the photoreceptor (2Y, M, C, K), and the dot output rate of each section is calculated. This is a process of transmitting the calculation results of these sections to the power control unit (153Y, M, C, K). Further, the power control units 153Y, 153M, 153C, and 153K for the respective colors are configured so as to perform the following processing. That is, the maximum dot output rate among the respective dot output rates in the plurality of sections sent from the image data processing unit 105 is specified. When the maximum dot output rate is equal to or less than the switching reference value, a regulation bias consisting of only a DC voltage, and when it is not equal to or less than, a regulation bias consisting of a superimposed voltage is used as a regulation power source (154Y, M, C, This is a process of outputting from (K).

  In such a configuration, even when the image portion is concentrated in only some of the plurality of sections and the dot output rate of the entire virtual page does not exceed the switching reference value, the control bias includes the superimposed voltage. Appropriate selection can be made to suppress the occurrence of blur at the rear end of the image.

[Third example]
The ease with which the trailing edge of the image is generated correlates better with the dot output rate for each section, which will be described below, than with the dot output rate of the entire image area. That is, the dot output rate for each section obtained by dividing the virtual page representing the output image into a plurality of sections in the direction of surface movement of the photoreceptor.

  In the printer according to the third specific example, the image data processing unit 105 is configured to perform the following processing. That is, for each color, a virtual page representing an output image is divided into a plurality of sections in the surface movement direction of the photoconductor (2Y, M, C, K), and the dot output rate of each section is calculated. This is a process of transmitting the result to the power control unit (153Y, M, C, K).

  FIG. 5 is a schematic diagram illustrating a relationship between an example of a virtual page and a dot output rate. The direction of arrow A in the figure shows the surface movement direction of the photoreceptor. The image data processing unit 105 calculates the dot output rate for each of Y, M, C, and K as follows. That is, first, as indicated by a dotted line in the figure, the virtual page is divided into a plurality of sections in the direction of arrow A (= the direction extending in the paper transport direction along the surface of the recording paper). The virtual page is a virtual area having the same posture as the paper surface when the recording paper P that is the output target of the image is in the same posture as the transport posture in the apparatus. For example, when an image is formed on A4 size paper that is transported vertically, the virtual page is a virtual region that has the same posture as the A4 size paper surface whose longitudinal direction is along the transport direction. In the illustrated example, the virtual page is divided into 16 sections at equal intervals along the surface movement direction of the photoreceptor, but the number of divisions is not limited to 16.

  When the image data processing unit 105 divides the virtual page into a plurality of sections, it calculates a dot output rate (total number of output dots in the section / total number of pixels in the section) in each section. Then, the calculation results are transmitted to the power control unit (153Y, M, C, K).

  The power control units 153Y, 153M, 153C, and 153K for the respective colors, for a plurality of sections sent from the image data processing unit 105, only the DC voltage when the dot output rate in the section is equal to or less than the switching reference value. To use a regulatory bias consisting of On the other hand, when the dot output rate in the section is not equal to or less than the switching reference value, it is determined to use the regulation bias including the superimposed voltage. Then, based on the page synchronization signal sent from the writing control unit 107 during the print job, the development start timing of each section is calculated. As for the development start timing, the tip of the region corresponding to the aforementioned section of the entire area in the surface movement direction of the photoreceptors 2Y, 2M, 2C, and 2K enters the contact portion with the developing rollers 11Y, 11M, 11C, and 11K. It is timing. The power supply control units 153Y, 153M, 153C, and 153K carry out the following processing for each section when a timing earlier than the development start timing by a predetermined time has arrived. That is, this is a process for making the regulation bias output from the regulation power supplies 154Y, 154M, 154C, and 154K the same as that previously determined for the section.

  In such a configuration, it is possible to suppress the occurrence of vibration due to the minute vibrations of the regulating blades 12Y, 12M, 12C, and 12K by using a superposed voltage as a regulating bias only during a development period for developing an image. it can.

  Further, the power supply control unit (153Y, M, C, K) outputs the development bias (151Y, M, C, K) when the regulation bias including the superimposed voltage is output from the regulation power supply (154Y, M, C, K). The developing bias output from is controlled as follows. That is, the absolute value of the developing bias is made smaller than when a regulation bias consisting of only a DC voltage is output. In such a configuration, by using a superposed voltage as the regulation bias, the image density is excessively increased due to promoting the flow of toner to the blade contact portion in the “blade contact portion entrance vicinity region”. Can be suppressed.

  The inventors improved the above-described print tester to have the same configuration as that of the printer according to the third specific example. And the 3rd test print was implemented using the printing test machine. In this third test print, the solid image shown in FIG. 6 was continuously printed. This is a solid image on a triangle whose area increases as the position becomes upstream in the direction of arrow A (= surface movement direction of the photoconductor) in the figure, and is output on A3 size paper that is conveyed vertically. The dotted line in the figure shows the boundary of the above-mentioned section. A margin of 10 mm is taken at the front and rear ends of the virtual page, and the sections are divided at equal intervals on the inside. The section width W was set to the same value as the circumferential length of the developing rollers 11Y, 11M, 11C, and 11K. The power control units 153Y, 153M, 153C, and 153K are controlled to switch the regulation bias and the development bias for each section. Continuous printing of solid images (6000 sheets) as shown in the figure was performed under conditions A, B, and C described later. And about the output solid image, the generation | occurrence | production degree of the rear end side blurring and the deterioration degree of background dirt were evaluated. The degree of deterioration of background dirt will be described later.

  Under condition A, the regulation bias based on the dot output rate was not repeated, and the regulation bias consisting only of the DC voltage was continuously output from the regulation power source (154Y, M, C, K) regardless of the dot output rate. The DC voltage of the regulation bias was set to −350 [V] from the first to the 5000th printed sheets, and −400 [V] from the 5001st sheet.

  In condition B, as in the second test print, based on the comparison between the dot output rate and the switching reference value for the entire page, whether the regulation bias is made of only a DC voltage or the superimposed voltage is used. It was made to decide. The relationship between the cumulative number of prints and the switching reference value was the same as that shown in Table 2. Note that, when the regulation bias composed of the superimposed voltage is output, the absolute value of the developing bias is made smaller than that in the case of the DC voltage unlike the second test print. The value was determined according to a predetermined algorithm.

  In condition C, as in the case of the printer according to the third specific example, when developing each section, a regulation bias is determined in advance based on a comparison between the dot output rate in the section and the switching reference value. Output from the regulated power supply. The relationship between the cumulative number of prints and the switching reference value was the same as that shown in Table 2. Similarly to condition B, the absolute value of the developing bias is made smaller than that in the case of the DC voltage when the regulation bias composed of the superimposed voltage is output.

  FIG. 7 is a graph showing the relationship between each section of the solid image output by the third test print and the dot output rate [%]. From the relationship between the cumulative number of prints and the switching reference value in Table 2 and the graph of FIG. 7, it can be seen that under the condition C, the following regulation bias control is performed. In other words, from the first sheet to the 3000th sheet, all the sections are developed under a condition using a regulation bias including only a DC voltage. From the 3001st sheet to the 4000th sheet, the development from the first section to the sixth section is performed under the condition using the regulation bias consisting only of the DC voltage, and the other sections are developed under the condition using the regulation bias consisting of the superimposed voltage. . Further, from the 4001st sheet to the 6000th sheet, development is performed under a condition using a regulation bias including only a DC voltage from the first section to the fifth section, and development is performed under a condition using a regulation bias including a superimposed voltage in the other sections. Is done.

The results of the third test print are shown in Table 3 below.

  In Table 3, the background stain is a phenomenon in which toner adheres to the background portion (non-image portion) of the photoconductor, and is easily generated according to the background potential that is a potential difference between the background portion potential and the development bias. It becomes difficult to occur. When the background potential is constant, the background potential changes in accordance with the development bias, and the background potential increases as the development bias decreases. Therefore, in the condition B and the condition C in which the development bias is changed according to the regulation bias, the background potential is further increased when the absolute value of the development bias is decreased as the regulation bias including the superimposed voltage is output. If the toner is normally negatively (negatively) charged, if the background potential increases, the background stains are less likely to occur. However, in the case where positively charged toner is included due to low charging ability, or in the case of toner having low electrical resistance, conversely, if the background potential increases, the background stains are more likely to occur. There is. For example, in the case of a toner having a low electrical resistance, a positive charge is injected from the developing roller into the toner in the developing area in the background portion, and the polarity of the toner is reversed (positively charged). Since the test print uses toner with such properties, scumming is more likely to occur when outputting a regulation bias consisting of a superimposed voltage than when a regulation bias consisting only of a DC voltage is output. Become.

  The degree of background contamination in Table 3 indicates how many times the standard is the degree of background contamination in condition B and condition C, based on the level of background contamination in condition A.

  Under the condition A in which the regulation bias composed of the superimposed voltage is not used, when the cumulative number of printed sheets exceeds 4000, the trailing edge side blur of the image starts to occur. On the other hand, according to the comparison result between the dot output rate and the switching reference value, 6000 test solid images are output under the condition B and the condition C where the regulation bias is switched between only the DC voltage and the superimposed voltage. However, the trailing edge side blur of the image was not generated.

  Comparing the deterioration degree of the background dirt with the condition B and the condition C, the degree of the background dirt can be lowered under the condition C. This is for the reason explained below. That is, in the condition B, when a regulation bias composed of a superposed voltage is output, a large background potential is applied to the non-image portion of the entire page, so that background stain is generated in the non-image portion of the entire page. Make it easier. On the other hand, in the condition C, when developing a section where the dot output rate is relatively low and the ratio of the non-image part is high among the plurality of sections, a regulation bias consisting of only a DC voltage is used. It is hard to generate dirt. When developing a section where the dot output rate is relatively high and the ratio of the image part is high, it is easy to generate a background stain because the regulation bias composed of the superimposed bias is used, but the ratio of the non-image part is low. , The dirt on the page is inconspicuous. As a result, the condition C can reduce the degree of soiling.

[Fourth example]
As already described, as the cumulative number of printed sheets increases, the fluidity of the toner deteriorates and the trailing edge side of the image is liable to occur. Further, if the toner has the same poor fluidity, the amount of toner consumption increases as the dot output rate of the image increases, and the trailing edge side blur tends to occur.

  Therefore, in the printer according to the fourth specific example, as the cumulative number of printed sheets increases or the dot output rate increases, the processing for increasing the peak-to-peak potential of the AC component of the regulation bias is performed. The power supply control unit (153Y, M, C, K) is configured. In such a configuration, as the toner tends to stagnate in the “region near the blade contact portion entrance”, a larger blade fine vibration is generated by an increase in the peak-to-peak potential, so that the toner is directed toward the blade contact portion. Promote the flow more. As a result, the occurrence of blurring on the rear end side of the image can be suppressed more reliably.

  In addition, as the peak-to-peak potential is increased, reverse charge is easily injected into the toner due to discharge at the blade contact portion, thereby easily causing scumming. Therefore, when the cumulative number of printed sheets and the dot output rate are relatively low, it is desirable to keep the peak-to-peak potential at a relatively small value.

  FIG. 8 is a graph showing the relationship between the peak-to-peak potential [V] of the regulation bias composed of the superimposed voltage in the printer according to the fourth specific example, the dot output rate, and the cumulative number of prints. Until the cumulative number of prints reaches 3000, even if the dot output rate is 100 [%], the rear end side blur of the image does not occur, and a regulation bias consisting only of DC voltage is used. In the figure, the peak-to-peak potential is indicated as 0 [V]. When the cumulative number of prints reaches 3001 or more, a regulation bias composed of a superimposed voltage is used depending on the dot output rate. At this time, when the cumulative number of printed sheets is in the range of 3001 to 4000 and the dot output rate exceeds 50 [%], the peak-to-peak potential = 1.0 [kV] as the alternating current component of the regulation bias Is output. Further, when the cumulative number of printed sheets is 4001 to 10,000 and the dot output rate exceeds 40 [%] and is 75 [%] or less, peak-to-peak potential = 1.25 [as the alternating current component of the regulation bias. kV] is output. Further, when the cumulative number of printed sheets is 4001 to 10,000 and the dot output rate exceeds 75 [%], the output of the peak-to-peak potential = 1.5 [kV] is output as the AC component of the regulation bias. The Further, when the cumulative number of printed sheets is 10001 or more and the dot output rate is more than 30 [%] and 50 [%] or less, the peak-to-peak potential = 1.5 [kV] as the alternating current component of the regulation bias. ] Is output. Further, when the cumulative number of printed sheets is 10001 or more and the dot output rate exceeds 50 [%], a peak-to-peak potential = 2.0 [kV] is output as the AC component of the regulation bias. .

  Although the frequency of the AC component is 1 [kHz] regardless of the peak-to-peak potential, the frequency may be increased as the peak-to-peak potential increases. Further, the configuration of the fourth specific example may be applied to a configuration in which the regulation bias is switched for each of a plurality of sections on the virtual page, such as the printer according to the second specific example or the printer according to the third specific example.

[First detailed example]
Next, a first detailed example in which a more characteristic configuration is added to the printer according to the second specific example will be described. Unless otherwise specified, the configuration of the printer according to the first detailed example is the same as that of the second specific example.

  FIG. 9 is a schematic diagram illustrating an example of a virtual page. The direction of arrow A in the figure shows the surface movement direction of the photoreceptor. The image data processing unit 105 calculates the dot output rate for each of Y, M, C, and K as follows. That is, first, as indicated by the dotted line in the figure, a plurality of sections are set by dividing a virtual page into a plurality of directions in a direction orthogonal to the direction of arrow A (= a direction orthogonal to the paper transport direction along the surface of the recording paper). To do. The virtual page is a virtual area having the same posture as the paper surface when the recording paper P that is the output target of the image is in the same posture as the transport posture in the apparatus. For example, when an image is formed on A4 size paper that is transported vertically, the virtual page is a virtual region that has the same posture as the A4 size paper surface whose longitudinal direction is along the transport direction. Such virtual pages are divided into a plurality of sections. The width of the partition is preferably 4 [mm] for the following reason. That is, when developing a vertical band solid image having a width of 4 mm or less, the area (vertical band development area) for developing the vertical band solid image on the surface of the developing roller (11Y, M, C, K) is developed. The toner in the left and right areas can easily flow. Further, when the vertical belt development area after development enters the toner supply roller (10Y, M, C, K), the toner in the left and right areas of the toner supply roller is easily supplied to the vertical belt development area. As a result, the rear end side blur is less likely to occur in the vertical band solid image having a width of 4 mm or less. If the width of the section is larger than 4 [mm], the dot output rate of the section is calculated to be relatively low in spite of the vertical band solid section when the image includes the vertical band solid section. There is a fear. Therefore, the width of the section is preferably 4 [mm].

When the image data processing unit 105 divides the virtual page into a plurality of sections, the dot output rate in each section (Δx ₁ , Δx ₂ ... Δx _n ) (total number of output dots in the section / total number of pixels in the section). Is calculated. And among these calculation results (η ₁ , η ₂ ... Η _n ), the maximum value is defined as the maximum dot output rate η _max, and among the plurality of sections, the section corresponding to the maximum dot output rate η _max The following processing is performed for a certain “maximum output section”. That is, when the number of output dots is accumulated from the downstream end (the front end of the page) toward the upstream end in the direction of movement of the photoreceptor surface (direction of arrow A) on the virtual page, the accumulated result is 1 [%] of the total number of output dots. The first position y ₁ is specified, and the area from the downstream end to the first position y ₁ is defined as a first area Δy ₁ . In addition, when the number of output dots is accumulated from the upstream end (the rear end of the page) in the direction of movement of the photoreceptor surface on the virtual page toward the downstream end, the second position y ₂ where the accumulated result is 1 [%] of the total number of output dots. identify, the region up to the second position y ₂ and the third region △ y ₃ from the upstream end. Further, the first position y ₁ of the space between the second position y ₂ and the second region △ y _2. Since the dot output rate is particularly high in the second area y ₂ in the entire “maximum output section”, the dot output rate is recalculated only in the second area Δy ₂ in the section (output dots in the second area). Total number / total number of pixels in the second area), and the result is the corrected maximum dot output rate η _max ′. Even in the “maximum output section”, the maximum dot output rate η _max becomes a relatively low value when the solid image portion is concentrated only in a part of the area of the photosensitive member surface movement direction. The corrected maximum dot output rate η _max ′ becomes a relatively high value. The image data processing unit 105 individually calculates the corrected maximum dot output rate η _max ′ for each color of Y, M, C, and K. Then, the obtained information about the corrected maximum dot output rate η _max ′, the first position y ₁ , and the second position y ₂ is transmitted to the power supply control unit (153Y, M, C, K).

When the corrected maximum dot output rate η _max ′ sent from the image data processing unit 105 is equal to or less than the switching reference value, the power supply control units 153Y, 153M, 153C, and 153K It is decided to use what consists of. On the other hand, when it is not equal to or less than the switching reference value, it is determined to use a superposed voltage as the regulation bias. In such a configuration, even in the following case, it is possible to appropriately select a restriction bias composed of a superimposed voltage and suppress the occurrence of blurring on the rear end side of the image. That is, this is a case where the solid image portion is concentrated on a part of the photosensitive member surface moving direction in the “maximum output section” and the maximum dot output rate η _max does not exceed the switching reference value.

In addition to determining whether or not the corrected maximum dot output rate η _max ′ is equal to or smaller than the switching reference value, whether or not the distance between the first position y ₁ and the second position y ₂ is equal to or greater than a threshold value. It is also possible to determine whether to use a superimposed voltage or a DC voltage. In this case, it is possible to more appropriately select the restriction bias composed of the superimposed voltage and more reliably suppress the occurrence of the trailing edge side blur of the image.

The power control units 153Y, 153M, 153C, and 153K calculate the second region development start timing and the second region development end timing based on the page synchronization signal sent from the writing control unit 107 during the print job. . The second area development start timing is such that the tip of the area corresponding to the second area Δy ₂ of the entire area in the surface movement direction of the photoreceptors 2Y, 2M, 2C, and 2K is the same as the developing rollers 11Y, 11M, 11C, and 11K. This is the timing for entering the contact portion. The second area development end timing is a timing at which the rear end of the area corresponding to the second area Δy ₂ comes out of the contact portion. When the power supply control units 153Y, 153M, 153C, and 153K have decided to use the regulation bias composed of the superimposed voltage, the regulation bias is applied when a timing earlier than the second area development start timing arrives by a predetermined time. Switch from DC voltage to superimposed voltage. Thereafter, when a timing earlier than the second region development end timing by a predetermined time arrives, the regulation bias is switched from the superimposed voltage to the DC voltage.

  In such a configuration, the generation of noise due to minute vibrations of the regulation blades 12Y, 12M, 12C, and 12K is further suppressed by using the superimposed bias voltage as the regulation bias only when necessary within the development period for developing the image. Can do.

  Instead of referring to the second area development end timing, the second area rear end development start timing may be referred to. The second region rear end development start timing is a timing at which the rear end of the second region enters the contact portion with the developing rollers 11Y, 11M, 11C, and 11K. Further, the regulation bias may be switched at the second area development start timing, the second area development end timing, and the second area rear end development start timing.

[Second detailed example]
Next, a second detailed example in which a more characteristic configuration is added to the printer according to the third specific example will be described. Unless otherwise specified, the configuration of the printer according to the second detailed example is the same as that of the printer according to the third specific example.

  In the printer according to the third specific example described above, it is assumed that the regulation bias is switched while the image portion is being developed. Then, uneven rotation of the developing roller (11Y, M, C, K) and uneven toner supply amount to the developing roller may occur, causing streaky image density unevenness extending in the roller axis direction. There is.

  Therefore, in the printer according to the second detailed example, the virtual pages for each of the colors Y, M, C, and K are not divided at equal intervals in the photosensitive member surface movement direction, but are divided as follows. The image data processing unit 105 is configured. That is, as shown in FIG. 11, the image is divided into a section with an image portion where an image portion exists and a section without an image portion where an image portion does not exist in the photosensitive member surface movement direction (arrow A direction). More specifically, first, it is determined whether or not the first pixel line of the virtual page includes a dot output pixel. The pixel line is a pixel line having a width of one pixel including a plurality of pixels arranged over the entire page in the main scanning direction. The first pixel line is the first pixel line existing at the top of the page. The image data processing unit 105 determines that the first pixel line includes a dot output pixel when there is at least one dot output pixel among the plurality of pixels, and there is no dot output pixel. In this case, it is determined that the dot output pixel is not included. The same determination is performed for all the pixel lines. Then, in the photosensitive body surface moving direction, an area where pixel lines not including dot output pixels are continuous is defined as a section without an image portion, while an area where pixel lines including dot output pixels are continuous is an image portion. It is a parcel. After the virtual page is partitioned in this way, next, the dot output rate is calculated for each section with an image portion, or the section leading end position and the section rear end position for each section with an image portion are respectively calculated. Or to identify. Then, the information of the dot output rate, the partition leading edge position, and the partition trailing edge position in each section with image portion is transmitted to the power supply control unit (153Y, M, C, K).

  The power supply control units 153Y, 153M, 153C, and 153K are DC voltages when the dot output rate in the sections is equal to or less than the switching reference value for a plurality of sections with image sections sent from the image data processing section 105. Decide to use a regulatory bias consisting only of On the other hand, when the dot output rate in the section is not equal to or less than the switching reference value, it is determined to use the regulation bias including the superimposed voltage. In the print job, the development start timing and the development end are determined based on the page synchronization signal sent from the writing control unit 107, the front end position of the section, and the rear end position of the section for each section having the image portion. Know the timing. The regulation bias is changed to the one consisting only of the DC voltage at a timing earlier than the development end timing by a predetermined time from the development start timing.

  In such a configuration, since the regulation bias is not switched during development of the image portion, it is possible to avoid occurrence of streak-like image density unevenness due to switching of the regulation bias.

What was demonstrated above is an example, and there exists an effect peculiar for every following aspect.
[Aspect A]
Aspect A includes a latent image carrier (for example, photoconductors 2Y, 2M, 2C, and 2K) and a toner carrier (for example, developing roller 11Y, 11) that develops the latent image on the latent image carrier with toner on its surface. M, C, K) and developing means (for example, 5Y) including a regulating member (for example, regulating blades 12Y, 12M, 12C, 12K) that contacts the surface of the toner carrier and regulates the thickness of the toner layer on the surface. , M, C, K) and an image forming apparatus (for example, a printer) including a regulation power source (for example, regulation power source 154Y, M, C, K) that outputs a regulation bias to be applied to the regulation member. The regulated power supply is configured to output a bias composed of a superimposed voltage obtained by superimposing an AC voltage on a DC voltage.

  In such a configuration, the regulating member is slightly vibrated by the alternating current component of the superimposed voltage by applying the regulating bias composed of the superimposed voltage to the regulating member. This slight vibration urges the flow of toner toward the contact portion in the vicinity of the contact portion entrance upstream of the contact portion between the toner carrier and the regulating member toward the contact portion. Toner is supplied without any delay. As a result, the stagnation of the toner in the region near the entrance of the abutting portion causes the toner supply amount to the toner carrier to become insufficient when developing the rear end side of the image having a high image area ratio. Can be suppressed.

[Aspect B]
Aspect B is that in Aspect A, the restriction power supply is configured to output by switching between the superposed voltage and the direct current voltage as the restriction bias, and the dot output of the output image A calculation means for calculating a rate (for example, the image data processing unit 105), and when the calculation result by the calculation means is a relatively high value, the regulation power source that outputs the regulation bias composed of a superimposed voltage is output. And a control means (for example, power supply control units 153Y, 153, M, C, and K) that outputs the regulation bias consisting only of a DC voltage from the regulation power supply when the calculation result by the means is not a relatively high value. To do. In such a configuration, it is possible to suppress the generation of noise due to applying a regulation bias composed of a superimposed voltage to the regulation member at an unnecessary timing.

[Aspect C]
Aspect C provides an accumulation means (for example, main control unit 100) that accumulates the accumulated operation time or a predetermined parameter correlated with the accumulated operation time in aspect B, and as the accumulation result by the accumulation means increases, The control unit is configured to change a determination reference value for determining whether or not the calculation result by the calculation unit is a relatively high value to a smaller value. With such a configuration, it is possible to suppress the occurrence of noise by using the regulation bias composed of the superimposed voltage only when developing an image that is highly likely to cause the trailing edge blur regardless of the degree of deterioration of the toner fluidity. .

[Aspect D]
Aspect D is characterized in that, in aspect B or C, the absolute value of the DC voltage in the regulation bias consisting of a superimposed voltage is made smaller than the absolute value of the DC voltage in the regulation bias consisting only of a DC voltage. It is. With such a configuration, it is possible to suppress the occurrence of excessive image density when using a regulation bias composed of a superimposed voltage.

[Aspect E]
Aspect E is any one of aspects B to D, and includes a developing power source (for example, developing power sources 151Y, 151M, 151C, and 150K) that outputs a developing bias to be applied to the toner carrier, and a superimposed voltage. The absolute value of the DC voltage of the developing bias is made smaller when outputting the restriction bias consisting of DC from the restriction power supply than when outputting the restriction bias consisting only of DC voltage from the restriction power supply. It is what. Even in such a configuration, it is possible to suppress the occurrence of excessive image density when the regulation bias including the superimposed voltage is used.

[Aspect F]
Aspect F is any one of aspects B to E, comprising a developing power source that outputs a developing bias to be applied to the toner carrier, and a peak-to-peak voltage of the superimposed voltage is a DC voltage of the developing bias. It is at least 10 times the potential difference from the potential of the latent image, and the regulating member is made of metal. With such a configuration, it is possible to reliably suppress the occurrence of blurring on the rear end side of the image by using the restricting member having the superimposed voltage. Furthermore, the toner flow can be more reliably promoted by the fine vibration of the regulating member than when a regulating member made of non-metal is used.

[Aspect G]
A mode G includes a power source (for example, a power source 152Y, M, C, K) that outputs a supply bias to be applied to the toner supply body in any one of modes B to F, and the dot output rate. The control means is configured to increase the absolute value of the DC voltage of the supply bias output from the supply power source as the value becomes higher. In such a configuration, the increase in the supply bias from the toner supply body to the toner carrying body due to the increase in supply bias can suppress the occurrence of image trailing edge blurring.

[Aspect H]
In aspect H, in any one of aspects B to G, a virtual page expressing an output image is partitioned into a plurality of directions in a direction orthogonal to the surface movement direction of the latent image carrier, and a dot output rate in each section is calculated. Then, based on the maximum dot output rate among the calculation results, it is determined whether the regulation bias output from the regulation power source is made of only a DC voltage or a superposed voltage. A combination of the calculation means and the control means is configured. In such a configuration, as compared with the case where the type of the regulation bias is determined based on the dot output rate of the entire page, the sorting between the image that may cause the trailing edge blur of the image and the image that is not so is more accurate. It can be carried out.

[Aspect I]
In the aspect I, when it is determined in the aspect H that the superimposed bias is used as the restriction bias, the latent image carrier is provided for the maximum output section having the highest dot output rate among the plurality of sections. When the number of output dots is accumulated from the page downstream end in the surface movement direction toward the page upstream end side, development of dots at the first position where the accumulated result is a predetermined ratio of the total number of output pixels in the maximum output section is performed. After switching the regulation bias from the DC voltage to the superimposed voltage based on the start timing, when the number of output dots is accumulated from the page upstream end to the page downstream end side, the accumulated result is all output dots in the maximum output section. The regulation bias is changed from the superimposed voltage to the DC voltage based on the timing of starting or ending the development of the dots at the second position that is a predetermined ratio of the number. Ri changing manner, it is characterized in that constitutes the control means. With such a configuration, it is possible to further reduce the occurrence of noise due to applying a regulation bias composed of a superimposed voltage to the regulation member at an unnecessary timing.

[Aspect J]
Aspect J is any one of Aspects B to G, with respect to a virtual page representing an output image, an image portion having an image portion in the surface movement direction of the latent image carrier and an image portion having no image portion. The calculation means is configured to calculate the dot output rate of each section having an image portion separately from the section having no image portion, and when developing each section having the image portion, the section having the image portion When the dot output is relatively high, the regulation bias consisting of a superimposed voltage is output from the regulation power supply, whereas when the dot output is not relatively high, the regulation bias consisting only of a DC voltage is output from the regulation power supply. The control means is configured so as to output from the above. With such a configuration, it is possible to reduce the generation of noise due to applying a regulation bias composed of a superimposed voltage to the regulation member at an unnecessary timing.

2Y, M, C, K: photoconductor (latent image carrier)
11Y, M, C, K: developing roller (toner carrier)
10Y, M, C, K: Toner supply roller (toner supply body)
12Y, M, C, K: regulating blade (regulating member)
5Y, M, C, K: Developing device (developing means)
154Y, M, C, K: Regulated power supply 153Y, M, C, K: Power supply control unit (control means)
100: Main control unit (integrating means)
105: Image data processing unit (calculation means)
151Y, M, C, K: Development power supply 152Y, M, C, K: Power supply

JP 2001-265110 A

Claims (10)

A latent image carrier;
Development comprising a toner carrier that develops a latent image on the latent image carrier with toner on its surface, and a regulating member that contacts the surface of the toner carrier and regulates the thickness of the toner layer on the surface Means,
In an image forming apparatus comprising: a regulated power source that outputs a regulating bias to be applied to the regulating member;
2. The image forming apparatus according to claim 1, wherein the regulation power source is configured to output a regulation bias including a superimposed voltage obtained by superimposing an AC voltage on a DC voltage. The image forming apparatus according to claim 1.
As the regulation bias, the regulation power supply is configured so as to switch and output the one composed of the superimposed voltage and the one composed only of the DC voltage,
And calculating means for calculating the dot output rate of the output image, and outputting the restriction bias composed of the superimposed voltage from the restriction power supply when the calculation result by the calculation means is a relatively high value, An image forming apparatus comprising: a control unit configured to output the regulation bias including only a DC voltage from the regulation power supply when the calculation result obtained by the calculation is not a relatively high value. The image forming apparatus according to claim 2.
Accumulating means for accumulating the cumulative operation time or a predetermined parameter correlated with the cumulative operation time is provided, and the calculation result by the calculation means is relatively high as the integration result by the integration means increases. An image forming apparatus characterized in that the control means is configured to change a determination reference value for determining whether or not to a smaller value. The image forming apparatus according to claim 2 or 3,
An image forming apparatus, characterized in that an absolute value of a DC voltage in the regulation bias composed of a superimposed voltage is made smaller than an absolute value of the DC voltage in the regulation bias composed only of a DC voltage. The image forming apparatus according to claim 2, wherein:
A development power source that outputs a development bias for application to the toner carrier;
In addition, when the regulation bias consisting of the superimposed voltage is output from the regulation power supply, the absolute value of the DC voltage of the developing bias is made smaller than when the regulation bias consisting only of the DC voltage is outputted from the regulation power supply. An image forming apparatus. The image forming apparatus according to any one of claims 2 to 5,
A development power source that outputs a development bias for application to the toner carrier;
The peak-to-peak voltage of the superimposed voltage is at least 10 times the potential difference between the DC voltage of the developing bias and the potential of the latent image;
The image forming apparatus is characterized in that the regulating member is made of metal. The image forming apparatus according to any one of claims 2 to 6,
A power supply for outputting a supply bias to be applied to the toner supply body is provided;
The image forming apparatus is characterized in that the control means is configured to increase the absolute value of the DC voltage of the supply bias output from the supply power source as the dot output rate increases. The image forming apparatus according to any one of claims 2 to 7,
A virtual page representing the output image is divided into a plurality of sections in a direction orthogonal to the surface movement direction of the latent image carrier, and a dot output rate in each section is calculated. Based on the maximum dot output rate among the calculation results Thus, the combination of the calculation means and the control means is configured so as to determine whether the regulation bias output from the regulation power source is composed of only a DC voltage or a superimposed voltage. An image forming apparatus. The image forming apparatus according to claim 8.
When it is determined to use a superimposed bias voltage as the regulation bias, the page downstream end in the surface movement direction of the latent image carrier for the maximum output section having the highest dot output rate among the plurality of sections. When the number of output dots is accumulated from the page toward the upstream end of the page, the accumulated result is a predetermined ratio of the total number of output pixels in the maximum output section. After the bias is switched from the DC voltage to the superimposed voltage, when the number of output dots is accumulated from the page upstream end to the page downstream end side, the accumulation result becomes a predetermined ratio of the total output dots in the maximum output section. The control so that the regulation bias is switched from the superimposed voltage to the DC voltage based on the timing of starting or ending the development of the dot at the position. An image forming apparatus characterized by being configured the stage. The image forming apparatus according to any one of claims 2 to 7,
The virtual page representing the output image is divided into a section with an image portion where an image portion exists and a section without an image portion where there is no image portion in the direction of surface movement of the latent image carrier, and there is an individual image portion. Configuring the calculating means to calculate the dot output rate of the section;
When developing each of the sections with image portions, if the dot output of the section with image portions has a relatively high value, the control bias is output from the control power supply while the control bias is output. An image forming apparatus, wherein the control means is configured to output from the regulated power supply the regulation bias consisting only of a DC voltage when the value is not a particularly high value.

Images