JP4480066B2 - Image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a complex machine thereof, and in particular, an image forming apparatus that adjusts image forming conditions in order to maintain optimum image quality. It is about.

  Conventionally, in an image forming apparatus using an electrophotographic method, in order to stabilize the image quality in an output image, a development current during a development process is detected, and an image forming condition is controlled based on the detection result (process) Technology for controlling) is known.

  Specifically, for example, in Patent Document 1, a developing current that flows into the developing roller when a print check pattern is formed on the photosensitive drum in the developing process is detected, and the charging potential and the developing are determined based on the detection result. A technique for controlling the bias is disclosed. The purpose of this technique is to obtain a constant development characteristic even when film abrasion occurs on the photosensitive drum and the capacitance of the photosensitive drum changes.

  Patent Document 2 discloses a technique for detecting a developing current flowing through the developing roller and controlling the developing bias so that the detection result is constant. The purpose of this technique is to stabilize the developing electric field and make the image density constant even if the gap (developing gap) between the photosensitive drum and the developing roller in the developing region varies.

JP 2002-333745 A JP 7-271139 A

  In the conventional image forming apparatus described above, when the charge amount of the toner in the developing unit varies depending on the environment or varies with time, the toner adhesion amount of the toner image formed on the photosensitive drum varies, and the image of the output image There was a problem that the concentration was not stable or background stains were generated.

Details are as follows.
In a low-temperature and low-humidity environment, the charge amount per unit weight of toner (the charge amount per unit weight, hereinafter referred to as “Q / M” as appropriate) increases, and the toner adhesion amount on the photosensitive drum. Becomes smaller. In contrast, in a high-temperature and high-humidity environment, Q / M decreases and the toner adhesion amount on the photosensitive drum increases. Further, the deteriorated toner remaining in the developing portion over time has a lower Q / M than the fresh toner.

  Here, the developing current is a movement of electric charges caused by the toner carried on the developing roller moving on the photosensitive drum, and is determined by Q / M and the developing amount (toner adhesion amount). . In other words, the development current is the total amount of charge that moves in the development region during the development process (total charge amount), and is proportional to the product of Q / M and the toner adhesion amount per unit area. Therefore, even when the development current during the development process is detected and the image forming conditions are controlled based on the detection result when the Q / M is not stable as described above, the toner adhesion amount on the photosensitive drum is stable. Will not. Further, when Q / M decreases, background stains (a phenomenon in which toner adheres to a non-image portion where toner adhesion is not planned) are likely to occur.

  Therefore, in the technique of the above-mentioned patent document 1, the charging potential and the developing bias are controlled based on the developing current when the print check pattern is formed on the photosensitive drum in the developing process. For example, the toner adhesion amount on the photosensitive drum varies and the image density of the output image becomes unstable. Further, when the Q / M is lowered, background dirt is generated.

  Similarly, in the technique of Patent Document 2 described above, the development bias is controlled so that the development current is constant. However, when Q / M varies depending on the environment or the like, the toner adhesion amount on the photosensitive drum varies. As a result, the image density of the output image is not stable. Further, when the Q / M is lowered, background dirt is generated.

  The present invention has been made to solve the above-described problems. Even when the charge amount of the toner changes in the environment or changes with time, the variation in the toner adhesion amount on the photosensitive drum is small. Another object of the present invention is to provide an image forming apparatus in which the image density in the output image is stable and the background stain is not generated.

According to a first aspect of the present invention, there is provided an image forming apparatus comprising: an image carrier on which an electrostatic latent image is formed; and a developer carrier that faces the image carrier and carries a developer. and parts, and a toner supply section for supplying toner to the developing unit, a cleaning unit for collecting the untransferred toner on the image carrier, voltage applying means for applying a developing bias to the developer carrier, the image Current detecting means for detecting a current output from the voltage applying means when a latent image formed on the carrier is developed to form a toner image; and the toner image formed on the image carrier. Adjusting means for adjusting at least one of a toner adhesion amount detecting means for detecting the toner adhesion amount , a charging potential on the image carrier, a latent image potential on the image carrier, and the developing bias. If, detection of the current sensing means Results and and a control unit for calculating the charge amount per unit weight of the toner image on the basis of the detection result of the toner adhesion amount detection means, said adjustment means, said charge amount calculated by the control unit Is smaller than a predetermined value, the background potential on the image carrier is adjusted to be large, and when the charge amount calculated by the control unit is larger than a predetermined value, Adjustment is made so that the development potential is increased, and adjustment is made so that the amount of toner replenished from the toner replenishment unit to the development unit decreases when the amount of charge calculated by the control unit is smaller than a predetermined threshold. Then, when the amount of charge calculated by the control unit is larger than a predetermined threshold, the amount of toner replenished from the toner replenishing unit to the developing unit is increased. And a first control unit that controls the charge amount to be within a predetermined range, and a case in which the charge amount is reduced and does not fall within the predetermined range even if the control by the first control unit is performed. And a second control means for controlling the adjusting means so that the background potential on the image carrier becomes small, and the toner in the developing unit is attached to the image carrier by the control by the second control means. Then, the adhered toner is collected by the cleaning unit .

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the second control unit controls the adjusting unit so that a ground potential on the image carrier is reduced. As a result, the toner in the developing unit adheres to the image carrier, and the toner replenishing unit is controlled so that toner is newly replenished to the developing unit.

An image forming apparatus according to a third aspect of the present invention is the image forming apparatus according to the first or second aspect , wherein the toner image is a patch pattern formed separately from the output image.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the toner image formed on the image carrier is transferred onto the transfer material or the second. The image forming apparatus includes a transfer unit that transfers the image onto a second image carrier, and the adjusting unit is configured to adjust a transfer bias supplied to the transfer unit.

An image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to any one of the first to fourth aspects, comprising a plurality of the developing sections.

An image forming apparatus according to a sixth aspect of the present invention is the image forming apparatus according to the fifth aspect, wherein the plurality of image carriers that respectively face the plurality of developing units, and the plurality of image carriers. And a plurality of transfer portions that transfer the toner images formed on the transfer material or the second image carrier.

  In the present invention, the charge amount of the toner related to the toner image formed during the development process is obtained and the image forming conditions are adjusted based on the obtained charge amount. In addition, it is possible to provide an image forming apparatus in which there is little variation in the toner adhesion amount on the photosensitive drum, the image density in the output image is stable, and problems such as background stains do not occur.

Embodiment 1 FIG.
Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is a main body of a color copying machine as an image forming apparatus, 2 is a writing unit that emits laser light based on image information, and 20Y, 20M, 20C, and 20BK are colors (yellow, magenta, cyan, and black). A process cartridge as an image forming unit corresponding to the above, 21 is a photosensitive drum as an image carrier housed in each of the process cartridges 20Y, 20M, 20C, and 20BK, 22 is a charging unit that charges the surface of the photosensitive drum 21, 23 is a developing unit that develops the electrostatic latent image formed on the photosensitive drum 21, 24 is a transfer bias roller as a transfer unit that transfers the toner image formed on the photosensitive drum 21 to the intermediate transfer belt 27, and Reference numeral 25 denotes a cleaning unit that collects untransferred toner on the photosensitive drum 21.

  Reference numeral 27 denotes an intermediate transfer belt as a second image carrier on which toner images of respective colors are transferred in an overlapping manner. Reference numeral 29 denotes a transfer portion that transfers the toner image formed on the intermediate transfer belt 27 to the transfer material P. The second transfer bias roller 30 is a transfer belt that conveys a transfer material P on which four color toner images are transferred, and 32Y, 32M, 32C, and 32BK are developments of the process cartridges 20Y, 20M, 20C, and 20BK. A toner replenishing unit for replenishing toner of each color to the unit 23; 61, a paper feeding unit for storing a transfer material P such as transfer paper; 66, a fixing unit for fixing an unfixed image on the transfer material P; 1 shows a scanner that optically reads a placed document.

  Here, each of the process cartridges 20Y, 20M, 20C, and 20BK is obtained by integrating the photosensitive drum 21, the charging unit 22, the developing unit 23, and the cleaning unit 25, respectively. Then, image formation of each color (yellow, magenta, cyan, black) is performed on the photosensitive drum 21 in each of the process cartridges 20Y, 20M, 20C, and 20BK.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described.
Each of the four photosensitive drums 21 rotates counterclockwise in FIG. First, the surface of the photosensitive drum 21 is uniformly charged at a position facing the charging unit 22 (a charging process). Thereafter, the surface of the charged photosensitive drum 21 reaches the irradiation position of each laser beam.

  On the other hand, when a color original is placed on the original placement portion of the scanner 120, image information of the original is optically read by a reading portion (not shown). That is, the original is scanned with an illumination light source, and an original image is formed on a color CCD (not shown). The original image is photoelectrically converted by a color CCD to generate R, G, and B image signals. These image signals are transmitted to the writing unit 2. Thereafter, in the writing unit 2, laser light corresponding to the image signal is emitted from the light source corresponding to each color. The laser light is incident on the polygon mirror 3 and reflected, and then passes through the lenses 4 and 5. The laser light after passing through the lenses 4 and 5 passes through different optical paths for each color component of yellow, magenta, cyan, and black (this is an exposure process).

The yellow component laser light is reflected by the mirrors 6 to 8 and then irradiated to the surface of the photosensitive drum 21 of the first process cartridge 20Y from the right side of the drawing. At this time, the yellow component laser light is scanned in the rotation axis direction (main scanning direction) of the photosensitive drum 21 by the polygon mirror 3 that rotates at high speed. Thus, an electrostatic latent image of a yellow component is formed on the photosensitive drum 21 charged by the charging unit 22.
Similarly, the magenta component laser light is reflected by the mirrors 9 to 11 and then irradiated to the surface of the photosensitive drum 21 of the second process cartridge 20M from the right side of the paper, thereby forming an electrostatic latent image of the magenta component. The The cyan component laser light is reflected by the mirrors 12 to 14 and then irradiated to the surface of the photosensitive drum 12 of the third process cartridge 20C from the right side of the paper, thereby forming an electrostatic latent image of the cyan component. The black component laser light is reflected by the mirror 15 and then is irradiated onto the surface of the photosensitive drum 21 of the fourth process cartridge 20BK from the right side of the drawing to form a black component electrostatic latent image.

Thereafter, the surface of the photosensitive drum 21 on which the electrostatic latent images of the respective colors are formed further rotates and reaches a position facing the developing unit 23. Then, the toner of each color is supplied from the developing unit 23 onto the photosensitive drum 21, and the latent image on the photosensitive drum 21 is developed (this is a developing step).
Thereafter, the surface of the photosensitive drum 21 after the development process reaches a position facing the intermediate transfer belt 27. Here, the transfer bias roller 24 is installed at each facing position so as to contact the inner peripheral surface of the intermediate transfer belt 27. Then, the image of each color formed on the photosensitive drum 21 is sequentially transferred onto the intermediate transfer belt 27 at the position of the transfer bias roller 24 (first transfer step).

Then, the surface of the photosensitive drum 21 after the first transfer process reaches a position facing the cleaning unit 25. The untransferred toner remaining on the photosensitive drum 21 is collected by the cleaning unit 25 (this is a cleaning process).
Thereafter, the surface of the photosensitive drum 21 passes through a static elimination unit (not shown), and a series of image forming processes on the photosensitive drum 21 is completed.

On the other hand, the surface of the intermediate transfer belt 27 on which the images (toner images) of the respective colors on the photosensitive drum 21 are transferred in an overlapping manner travels in the direction of the arrow in the drawing and reaches the position of the second transfer bias roller 29. Then, the full-color image on the intermediate transfer belt 27 is secondarily transferred onto the transfer material P at the position of the second transfer bias roller 29 (secondary transfer process).
Thereafter, the surface of the intermediate transfer belt 27 reaches the position of an intermediate transfer belt cleaning unit (not shown). Then, the untransferred toner on the intermediate transfer belt 27 is collected by the intermediate transfer belt cleaning unit, and a series of transfer processes on the intermediate transfer belt 27 is completed.

Here, the transfer material P at the position of the second transfer bias roller 29 is transported from the paper feeding unit 61 via the transport guide 63, the registration roller 64, and the like.
Specifically, the transfer paper P fed by the paper feed roller 62 from the paper feed unit 61 that stores the transfer material P is guided to the registration roller 64 after passing through the conveyance guide 63. The material P to be transferred that has reached the registration roller 64 is conveyed toward the position of the second transfer bias roller 29 in synchronization with the toner image on the intermediate transfer belt 27.

Thereafter, the transfer material P onto which the full color image has been transferred is guided to the fixing unit 66 by the transfer belt 30. In the fixing unit 66, the color image is fixed on the transfer material P at the nip between the heating roller 67 and the pressure roller 68.
Then, the transfer material P after the fixing process is discharged as an output image outside the apparatus main body 1 by the paper discharge roller 69, and a series of image forming processes is completed.

Next, the image forming unit of the image forming apparatus will be described in detail with reference to FIGS. FIG. 2 is a cross-sectional view showing the image forming unit, and FIG. 3 is a cross-sectional view taken along the line AA showing the developing unit 23.
The four image forming units installed in the apparatus main body 1 have substantially the same structure except that the color of the toner T to be stored is different. Therefore, the alphabets (Y, M, C) of the reference numerals in the process cartridge and the toner replenishing unit are used. , BK).

As shown in FIG. 2, the process cartridge 20 mainly includes a photosensitive drum 21 as an image carrier, a charging unit 22, a developing unit 23, and a cleaning unit 25, which are integrally stored in a case 26. ing.
The developing unit 23 mainly includes a developing roller 23a as a developer carrying member facing the photosensitive drum 21, a first conveying screw 23b facing the developing roller 23a, and a first conveying screw 23b via a partition member 23e. A second conveying screw 23c facing each other and a doctor blade 23d as a regulating member facing the developing roller 23a are configured. In the developing unit 23, a two-component developer composed of carrier C and toner T is accommodated. The developing roller 23a includes a magnet that is fixed inside and forms a magnetic field on the circumferential surface of the roller, and a sleeve that rotates around the magnet. A predetermined developing gap is provided between the developing roller 23 a and the photosensitive drum 21.

The above-described image forming process will be described in more detail with a focus on the developing process.
The developing roller 23a rotates in the direction of the arrow in FIG. As shown in FIG. 3, the developers T and C in the developing unit 23 are driven by the rotational drive of the first transport screw 23b and the second transport screw 23c disposed so as to interpose the partition member 23e therebetween. It circulates in the longitudinal direction while being agitated and mixed with the toner T replenished from the replenishing section 32 through the toner replenishing port 26a (circulation in the direction of the arrow in FIG. 3). The toner T that is frictionally charged and adsorbed on the carrier C is supplied to the developing roller 23a together with the carrier C by the first conveying screw 23b, and the developers T and C are carried on the developing roller 23a.

Thereafter, the developers T and C carried on the developing roller 23a are adjusted to an appropriate amount at the position of the doctor blade 23d, and then reach a position facing the photosensitive drum 21 (developing area). At the opposite position, the toner T in the developer adheres to the electrostatic latent image formed on the surface of the photosensitive drum 21. Specifically, the toner T is latently developed by an electric field (development electric field) formed by a potential difference (development potential) between the latent image potential of the image portion irradiated with the laser beam L and the development bias applied to the development roller 23a. Adhere to the image.
Thereafter, most of the toner T adhering to the photosensitive drum 21 is transferred onto the intermediate transfer belt 27. Then, the toner T remaining on the photosensitive drum 21 is collected in the cleaning unit 25 by the cleaning blade 25a and the cleaning roller 25b that are in contact with the photosensitive drum 21.

  Here, the toner supply unit 32 provided in the apparatus main body includes a replaceable toner bottle 33, and a bottle holding unit 34 that holds and rotates the toner bottle 33 and supplies fresh toner T to the developing unit 23. And is composed of. The toner bottle 33 stores toner T (which is one of yellow, magenta, cyan, and black).

  The toner T in the toner bottle 33 is appropriately supplied into the developing unit 23 from the toner supply port 26a as the toner T in the developing unit 23 is consumed. The toner replenishing port 26a is provided at one end in the longitudinal direction (the vertical direction in FIG. 3) of the second transport screw 23c and above the second transport screw 23c.

Here, the consumption of the toner T in the developing unit 23 is indirectly detected by a reflection type photosensor 28 serving as a toner adhesion amount detecting unit facing the photosensitive drum 21. Specifically, first, a patch pattern (a rectangular pattern of about 30 mm square and a solid toner image) is formed on the photosensitive drum 21 through the above-described charging process, exposure process, and development process. Light is emitted from the light emitting element (LED) of the photosensor 28 toward the patch pattern. The light reflected by the patch pattern is received by the light receiving element (photodiode) of the photosensor 28. At this time, information related to the magnitude of the amount of light received by the light receiving element (the magnitude of the output voltage) is transmitted to the control unit 40, and the control unit 40 uses the toner adhesion amount (mg / cm ²⁾ in the patch pattern. ). If it is determined that the toner adhesion amount is small, it is assumed that the toner T in the developing unit 23 is consumed at a high level, and fresh toner is supplied from the toner replenishing unit 32 to the developing unit 23 based on a command from the control unit 40. Replenish. On the other hand, when it is determined that the toner adhesion amount is large, it is assumed that the consumption of the toner T in the developing unit 23 is small, and toner supply to the developing unit 23 is suspended or reduced.

Further, the developing power source 41 as a voltage applying unit that applies a developing bias to the developing roller 23a can vary the magnitude of the developing bias to be applied by a control unit 40 as an adjusting unit. The developing bias may be a DC voltage, an AC voltage, or both.
Further, the developing power supply 41 is provided with a current detection means having a resistor connected in the power supply circuit. Then, the voltage applied across the resistor is detected to detect the current output from the developing power supply 41. Information on the output current (developing current) detected by the current detecting means of the developing power supply 41 is transmitted to the control unit 40.

In addition, the charging power source 42 that applies a charging voltage to the charging unit 22 (charging roller) can vary the magnitude of the charging voltage applied by a control unit 40 as an adjusting unit. Thereby, the charging potential formed on the photosensitive drum 21 in the charging process is adjusted.
Further, the writing unit 2 that irradiates the exposure light L onto the photosensitive drum 21 can vary the exposure amount of the exposure light L by the control unit 40 as an adjusting unit. Thereby, the latent image potential formed on the photosensitive drum 21 in the exposure process is adjusted.
The control unit 40 is configured to be able to adjust all of the image forming conditions related to the image forming process such as the transfer voltage related to the transfer process, in addition to the above-described developing bias, charging potential, and latent image potential.

Next, characteristic control in the first embodiment will be described.
In the first embodiment, the image forming condition is adjusted based on the detection result of the current detection unit and the detection result of the photosensor 28. Specific control is as follows.

  First, apart from the image formation of the output image, a patch pattern is formed on the photosensitive drum 21 through the above-described charging process, exposure process, and development process. At this time, in the developing process of the patch pattern, that is, in the process of moving the toner T on the developing roller 23a toward the latent image of the patch pattern, the developing current flowing through the developing roller 23a is detected by the current detection unit of the developing power supply 41. Detected.

For example, assume that a change in development current with respect to time (development time) as shown in FIG. 4 is detected during the development process. At this time, the integrated value of the development current fluctuation with respect to the development time (the hatched area in FIG. 4) is the total charge amount Q related to the toner T moving through the development gap during the development process. Therefore, the charge amount (Q / A) per unit area related to the development of the patch pattern is (total charge amount Q during the development step) / (area of the patch pattern).
Thus, based on the developing current detected by the current detection means, the calculation unit of the control unit 40 determines the charge amount (Q / A) per unit area.

Thereafter, the patch pattern as a toner image formed on the photosensitive drum 21 reaches a position facing the photosensor 28 as the toner adhesion amount detection means, and the photosensor 28 detects the toner adhesion amount.
Specifically, an output voltage corresponding to the amount of light reflected from the patch pattern received by the light receiving element of the photosensor 28 is transmitted to the control unit 40. Information related to the toner adhesion amount (M) corresponding to the output voltage of the photosensor 28 and information related to the area (A) of the patch pattern are held in advance in the calculation unit of the control unit 40. Based on the output value transmitted from the photosensor 28, the calculation unit of the control unit 40 determines the toner adhesion amount (M / A) per unit area on the photosensitive drum 21.

Furthermore, the control unit 40 uses the charge amount per unit area (Q / A) based on the developing current value and the toner adhesion amount (M / A) per unit area based on the reflected light amount to charge per unit weight. The quantity Q / M is determined. Here, Q / M is obtained by the following equation.
Q / M = (Q / A) / (M / A)

Thereafter, the image forming conditions in the image forming unit are adjusted based on the Q / M calculated by the control unit 40.
Specifically, when Q / M is smaller than a predetermined value, the development is performed so that the background potential (the potential difference between the charging potential and the developing bias) on the photosensitive drum 21 is larger than the normal value. Adjust at least one of bias and charging potential. As a result, the force for attracting the toner to the non-image area is weakened, so that even if the Q / M of the toner is lowered due to environmental fluctuations or the like, the background stain is less likely to occur.

  On the other hand, when Q / M is larger than a predetermined value, the developing potential on the photosensitive drum 21 (the potential difference between the latent image potential and the developing bias) is larger than the normal value. At least one of the developing bias and the latent image potential is adjusted. As a result, the force for attracting the toner to the image portion is increased, so that even if the Q / M of the toner increases due to environmental fluctuations or the like, the toner adhesion amount is stable, and the image density is less likely to decrease.

Here, in addition to the above-described control, the image forming apparatus according to the first embodiment includes a control unit that keeps Q / M within a predetermined range. Specific control for keeping Q / M constant is as follows.
The first control means adjusts the amount of toner replenished from the toner replenishing unit 32 to the developing unit 23 based on the Q / M calculated by the control unit 40. Specifically, when Q / M is smaller than a predetermined threshold, the toner replenishing amount from the toner replenishing unit 32 is set to be smaller than the normal toner replenishing amount. That is, when Q / M is small, control is performed so that the toner density of the developer in the developing unit 23 (the ratio of the toner T in the developer, which is referred to as TC) is small. Adjust to be larger. Thereby, the fall of Q / M is restrict | limited and it becomes difficult to generate | occur | produce background dirt. Furthermore, toner scattering due to a decrease in electrostatic attraction between the toner T and the carrier C as Q / M decreases is also reduced.

On the other hand, when Q / M is larger than a predetermined threshold, the toner supply amount from the toner supply unit 32 is set to be larger than the normal toner supply amount. That is, when Q / M is large, control is performed so that the toner density of the developer increases, and adjustment is made so that Q / M decreases. As a result, the increase in Q / M is restricted and carrier adhesion on the photosensitive drum 21 is less likely to occur.
Here, in the carrier adhesion, the charged state of the carrier is weakened by the toner having a high Q / M, and the carrier is in the vicinity of the toner image edge portion (the boundary portion between the image portion and the non-image portion) on the photosensitive drum 21. It is a phenomenon that adheres. When carrier adhesion occurs, white spots corresponding to the output image are generated.

Further, the second control means discharges the deteriorated toner remaining in the developing unit 23 over a long period of time based on the Q / M calculated by the control unit 40 and supplies fresh toner instead. is there.
Specifically, if the above-described image forming condition control or toner replenishment amount control is performed, if the Q / M does not return to the predetermined value within a predetermined toner density (TC) range, the background is temporarily removed. Adjust the imaging conditions to reduce the potential. As a result, the deteriorated toner having a low Q / M adheres as background dirt on the photosensitive drum 21 and is positively discharged from the developing unit 23. By supplying fresh toner instead of the discharged deteriorated toner in the developing unit 23, the charge distribution of the toner in the developing unit 23 is almost restored to the initial state. The second control unit described above is performed separately from the normal image formation of the output image.

  As described above, in the image forming apparatus configured as in the first embodiment, the charge amount Q / M of the toner T related to the toner image (patch pattern) formed during the development process is obtained and The image forming conditions are adjusted based on Q / M. Further, the charge amount Q / M of the toner T is controlled so as to be within a predetermined range. As a result, even when the charge amount Q / M of the toner T varies with the environment or changes over time, the variation in the toner adhesion amount on the photosensitive drum 21 is small, and the image density in the output image is stable. Problems such as background contamination, toner scattering, and carrier adhesion can be suppressed.

Embodiment 2. FIG.
5 and 6, the second embodiment of the present invention will be described in detail.
FIG. 5 is a cross-sectional view showing an image forming unit in the second embodiment, and corresponds to FIG. 2 in the first embodiment. The second embodiment is different from the first embodiment in that the transfer bias is also adjusted by the adjusting means.

  Referring to FIG. 5, a transfer bias roller 24 as a transfer portion for transferring a toner image (image) on the photosensitive drum 21 onto an intermediate transfer belt 27 as a second image carrier, and the intermediate transfer belt 27. A transfer bias is supplied from a transfer power supply 43 to the second transfer bias roller 29 as a transfer portion for further transferring the toner image to the transfer material P. A transfer power supply 43 that supplies a transfer bias (transfer current and transfer voltage) to the transfer bias roller 24 and the second transfer bias roller 29 is variable by a control unit 40 as an adjusting unit. it can. Thereby, the transfer bias in the first transfer process and the secondary transfer process described in FIGS. 1 and 2 of the first embodiment is adjusted.

  Here, the transfer bias roller 24 and the second transfer bias roller 29 are formed by forming an elastic layer made of NBR, EPDM, urethane, silicon or the like on a metal core such as stainless steel.

Also in the second embodiment, as in the first embodiment, the charge amount Q / M of the toner T related to the toner image (patch pattern) formed during the development process is obtained, and the Q / M is obtained. Adjust the imaging conditions based on this.
At this time, the image forming conditions to be adjusted are supplied to the transfer bias roller 24 and the second transfer bias roller 29 in addition to the image forming conditions (charge potential, latent image potential, development bias) adjusted in the first embodiment. Transfer bias.

FIG. 6 is a graph showing the relationship between the transfer bias current and the transfer rate in the transfer units 24 and 29. In FIG. 6, the horizontal axis indicates the transfer bias supplied from the transfer power source 43, and the vertical axis indicates the transfer rate. Here, the transfer rate is a ratio at which the toner image on the intermediate transfer belt 27 or the photosensitive drum 21 is transferred onto the transfer material P or the intermediate transfer belt 27. A solid line R1 indicates a change in transfer rate when the charge amount Q / M of the toner T is high, and a solid line R2 indicates a change in transfer rate when the charge amount Q / M of the toner T is low.
As shown in FIG. 6, the optimum transfer bias size that maximizes the transfer rate varies depending on the charge amount Q / M of the toner T.

  The control unit 40 of the apparatus main body 1 holds information related to the optimum transfer bias according to the charge amount Q / M of the toner T. Then, based on the charge amount Q / M of the toner T calculated from the detection results detected by the current detection means 41 and the photosensor 28, each transfer unit is set so that the transfer rate in the transfer units 24 and 29 is maximized. The transfer bias supplied to 24 and 29 is optimized.

  Specifically, when Q / M is high, the transfer bias is set high. On the other hand, when Q / M is low, the transfer bias is set low. As a result, even when the Q / M of the toner fluctuates due to environmental fluctuations, TC fluctuations, etc., it is possible to always maintain the optimum transferability. Therefore, as the transferability is stabilized, the image density in the output image is also stabilized, the toner adhesion amount on the photosensitive drum 21 or the intermediate transfer belt 27 is also stabilized, and the toner yield is improved. The maintenance cycle of the intermediate transfer cleaning unit can also be extended.

  Here, the image forming apparatus according to the second embodiment is a tandem type color image forming apparatus, and corresponds to the four photosensitive drums 21 corresponding to the four color image forming processes, and the four facing each other. A developing unit 20 and four transfer bias rollers 24 are provided. The above-described adjustment control is performed individually for all these image forming processes. As a result, even when the optimum image forming condition differs for each color, the image forming condition can be adjusted in accordance with the variation in the charge amount Q / M of the toner T.

  As described above, in the image forming apparatus configured as in the second embodiment, a high transfer rate is maintained even when the charge amount Q / M of the toner T changes in the environment or changes over time. In addition, the variation in the toner adhesion amount on the photosensitive drum 21 is small, the image density in the output image is stable, and problems such as background contamination, toner scattering, and carrier adhesion can be suppressed.

  It should be noted that the present invention is not limited to the above-described embodiment, and it is obvious that the embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the embodiment. In addition, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiment, and can be set to a number, position, shape, and the like that are suitable for implementing the present invention.

1 is a configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a side cross-sectional view showing an image forming unit in the image forming apparatus of FIG. 1. It is sectional drawing which shows the AA cross section of the image development part in the image formation part of FIG. It is a graph which shows the development current detected at the time of a development process. It is side surface sectional drawing which shows the image formation part in Embodiment 2 of this invention. It is a graph which shows the relationship between a transfer bias and a transfer rate.

Explanation of symbols

1 image forming apparatus body (apparatus body), 2 writing unit,
20, 20Y, 20M, 20C, 20BK Process cartridge (imaging part),
21 photosensitive drum (image carrier), 22 charging unit,
23 developing section, 23a developing roller (developer carrier),
23b 1st conveyance screw, 23c 2nd conveyance screw,
23d doctor blade, 23e partition member,
24 transfer bias roller (transfer section), 25 cleaning section,
27 Intermediate transfer belt (second image carrier),
28 Photosensor (toner adhesion amount detection means),
29 Second transfer bias roller (transfer section),
32, 32Y, 32M, 32C, 32BK toner supply unit, 40 control unit,
41 Development power supply (voltage application means, current detection means), 42 Charging power supply,
43 Transfer power supply.

Claims (6)

An image carrier on which an electrostatic latent image is formed;
A developing unit provided with the developer carrying member for carrying a developer as well as opposed to the image bearing member,
A toner replenishing unit for replenishing toner to the developing unit;
A cleaning unit for collecting untransferred toner on the image carrier;
Voltage applying means for applying a developing bias to the developer carrying member;
Current detection means for detecting a current output from the voltage application means when developing a latent image formed on the image carrier to form a toner image;
Toner adhesion amount detection means for detecting the toner adhesion amount of the toner image formed on the image carrier;
Adjusting means for adjusting at least one of a charging potential on the image carrier, a latent image potential on the image carrier, and the developing bias ;
A control unit that calculates a charge amount per unit weight of the toner image based on a detection result of the current detection unit and a detection result of the toner adhesion amount detection unit ;
With
The adjusting unit adjusts the background potential on the image carrier to be large when the charge amount calculated by the control unit is smaller than a predetermined value, and the charge amount calculated by the control unit. Is adjusted so that the development potential on the image carrier increases when
When the charge amount calculated by the control unit is smaller than a predetermined threshold, the amount of toner supplied from the toner replenishing unit to the developing unit is adjusted to be small and calculated by the control unit. When the charge amount is larger than a predetermined threshold value, the amount of toner replenished from the toner replenishing unit to the developing unit is adjusted to be controlled so that the charge amount falls within a predetermined range. First control means;
A second control unit configured to control the adjustment unit to reduce a background potential on the image carrier when the charge amount decreases and does not fall within the predetermined range even when the control by the first control unit is performed; Control means;
Further comprising
An image forming apparatus , wherein the toner in the developing unit is attached to the image carrier under the control of the second control unit, and the attached toner is collected by the cleaning unit . The second control unit controls the adjusting unit so as to reduce the background potential on the image carrier, thereby causing the toner in the developing unit to adhere to the image carrier and newly adding toner to the developing unit. The image forming apparatus according to claim 1, wherein the toner replenishing unit is controlled to replenish the toner. The image forming apparatus according to claim 1, wherein the toner image is a patch pattern formed separately from an output image. A transfer unit that transfers a toner image formed on the image carrier onto a transfer material or a second image carrier;
The image forming apparatus according to claim 1, wherein the adjusting unit is configured to adjust a transfer bias supplied to the transfer unit. The image forming apparatus according to claim 1, further comprising a plurality of the developing units. A plurality of the image carriers respectively facing the plurality of developing sections;
6. The apparatus according to claim 5, further comprising: a plurality of transfer units that transfer toner images respectively formed on the plurality of image carriers onto a transfer material or a second image carrier. Image forming apparatus.

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