JP2021028701A - Image forming apparatus - Google Patents

Abstract

To obtain an image forming apparatus that prevents a reduction in image quality caused by a toner adhesion layer formed on a developing roller.SOLUTION: A control unit 51 executes light quantity calibration for adjusting the quantity of exposure light of exposure devices 2a to 2d within a predetermined range. A toner adhesion determination unit 52 determines that toner adhesion occurs on developing rollers when the quantity of exposure light is set to the lower limit of the predetermined range in the light quantity calibration and toner consumption in a predetermined period is equal to or more than a predetermined value. When the toner adhesion determination unit 52 determines that toner adhesion occurs on the developing rollers, the control unit 51 reduces the amount of toner adhered to photoreceptor drums 1a to 1d from the developing rollers.SELECTED DRAWING: Figure 4

Description

The present invention relates to an image forming apparatus.

In a certain image forming apparatus, the developing apparatus includes a developing roller and a magnetic roller, and a thin layer of toner is formed on the developing roller with toner in a two-component developer, and the developing roller shifts to an electrostatic latent image on a photoconductor drum. Toner is adhered, and the toner thin layer is peeled off and reformed between the papers during continuous printing to suppress afterimages on the developing roller during continuous printing (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2005-55839

On the other hand, as the number of prints increases, the toner on the developing roller may be deformed due to contact between the developing roller and the photoconductor drum and adhere to the surface of the developing roller to form a fixed layer. .. In particular, when a resin external additive is added to the toner, the external additive makes it easier for the toner to adhere to the surface of the developing roller.

When the toner fixing layer is formed on the developing roller in this way, the developing roller is easily charged, and the potential of the developing roller surface (that is, the surface of the toner fixing layer) becomes higher than the original development bias. , The image quality of the printed toner image deteriorates.

The present invention has been made in view of the above problems, and an object of the present invention is to obtain an image forming apparatus that suppresses image quality deterioration caused by a toner fixing layer formed on a developing roller.

The image forming apparatus according to the present invention includes a photoconductor drum, an exposure device that exposes the photoconductor drum to form an electrostatic latent image, and a developing roller that applies toner to the electrostatic latent image on the photoconductor drum. A developing device that forms a toner image by adhering, a control unit that executes light amount calibration for adjusting the exposure light amount of the exposure device within a predetermined range, and a lower limit value of the exposure light amount in the predetermined range in the light amount calibration. It is provided with a toner sticking determination unit for determining that toner sticking has occurred on the developing roller when the toner consumption amount in a predetermined period is set to or more than a predetermined value. Then, when the toner sticking determination unit determines that toner sticking has occurred on the developing roller, the control unit reduces the amount of toner adhering from the developing roller to the photoconductor drum.

According to the present invention, it is possible to obtain an image forming apparatus that suppresses image quality deterioration caused by a toner fixing layer formed on a developing roller.

The above or other object, feature and superiority of the present invention will be further clarified from the following detailed description with the accompanying drawings.

FIG. 1 is a side view showing a part of the mechanical internal configuration of the image forming apparatus according to the embodiment of the present invention. FIG. 2 is a diagram showing an example of various devices around the photoconductor drum 1a in FIG. FIG. 3 is a diagram showing an example of the configuration of the exposure device 2a in FIG. FIG. 4 is a block diagram showing a part of the electrical configuration of the image forming apparatus according to the embodiment of the present invention. FIG. 5 is a diagram illustrating a toner pattern used for light intensity calibration. FIG. 6 is a diagram illustrating a patch image in the toner pattern shown in FIG. FIG. 7 is a diagram illustrating light amount adjustment in light amount calibration.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a side view showing a part of the mechanical internal configuration of the image forming apparatus according to the embodiment of the present invention. The image forming apparatus shown in FIG. 1 is an apparatus having an electrophotographic printing function, such as a printer, a facsimile apparatus, a copying machine, and a multifunction device.

The image forming apparatus of this embodiment has a tandem type color developing apparatus. This color developing device includes photoconductor drums 1a to 1d, exposure devices 2a to 2d, and developing devices 3a to 3d for each color. The photoconductor drums 1a to 1d are four-color photoconductors of cyan, magenta, yellow, and black. The exposure devices 2a to 2d are devices that expose the photoconductor drums 1a to 1d to form an electrostatic latent image by irradiating the photoconductor drums 1a to 1d with a laser beam. The exposure devices 2a to 2d include a laser diode as a light source of laser light and an optical element (lens, mirror, polygon mirror, etc.) that guides the laser light to the photoconductor drums 1a to 1d, and are on the photoconductor drums 1a to 1d. Is irradiated with light to form an electrostatic latent image on the photoconductor drums 1a to 1d.

Toner containers filled with toners of four colors of cyan, magenta, yellow, and black are connected to the developing devices 3a to 3d. Development biases are applied to the developing devices 3a to 3d, respectively, and the toner supplied from the toner container is used for development based on the potential difference between the developing devices 3a to 3d and the photoconductor drums 1a to 1d. Toner is formed by adhering toner to the electrostatic latent images on the photoconductor drums 1a to 1d with a roller.

In this embodiment, a two-component developer is used and the toner is agitated with the carriers in the developing devices 3a-3d.

Magenta is developed by the photoconductor drum 1a, the exposure device 2a and the developing device 3a, cyan is developed by the photoconductor drum 1b, the exposure device 2b and the developing device 3b, and the photoconductor drum 1c and the developing device 2c are developed. And the developing device 3c develops yellow, and the photoconductor drum 1d, the exposure device 2d, and the developing device 3d develop black.

FIG. 2 is a diagram showing an example of various devices around the photoconductor drum 1a in FIG. Although various devices around the photoconductor drum 1a are shown in FIG. 2, the same configuration is also provided around the photoconductor drums 1b to 1d.

As shown in FIG. 2, in addition to the developing device 3a, a charging device 21 and a cleaning device 22 are provided around the photoconductor drum 1a. The charging device 21 charges the photoconductor drum 1a with a designated charging bias. In this embodiment, the charging device 21 includes a charging roller 21a that comes into contact with the photoconductor drum 1a, and the charging roller 21a charges the photoconductor drum 1a. The cleaning device 22 includes a cleaning blade 22a that comes into contact with the photoconductor drum 1a, and collects residual toner on the photoconductor drum 1a. Further, the primary transfer roller 23 is provided at a position facing the photoconductor drum 1a with the intermediate transfer belt 4 interposed therebetween.

The developing device 3a includes a housing 11, a stirring screw 12, a magnetic roller 13, and a developing roller 14.

A toner container (not shown) is connected to the developing device 3a, and toner is supplied from the toner container into the housing 11 through a supply port (not shown). Inside the housing 11, the stirring screw 12 stirs the two-component developer containing the toner and the carrier. A magnetic material is used for the carrier.

The magnetic roller 13 holds the two-component developer in a brush shape on its surface, and supplies the toner in the two-component developer to the developing roller 14. The toner of the two-component developer is transferred to the developing roller 14 according to the voltage difference between the magnetic roller 13 and the developing roller 14.

The developing roller 14 holds the toner transferred from the magnetic roller 13 on its surface as a thin toner layer. A development bias is applied to the developing roller 14, and the toner layer formed on the surface of the developing roller 14 is formed by the voltage of the photoconductor drum 1a with respect to the developing roller 14 (difference between the development bias and the surface potential of the photoconductor drum 1a). Transition to the photoconductor drum 1a. In this way, the developing roller 14 adheres the toner to the electrostatic latent image on the photoconductor drum 1a.

That is, the developing roller 14 holds the toner by the developing bias and attaches the toner to the electrostatic latent image.

Returning to FIG. 1, the intermediate transfer belt 4 is an image carrier that supports a toner image transferred from the photoconductor drums 1a to 1d, and is a non-terminal (that is, annular) intermediate transfer body. The intermediate transfer belt 4 is stretched on the drive roller 5 and orbits in the direction from the contact position with the photoconductor drum 1d to the contact position with the photoconductor drum 1a by the driving force from the drive roller 5.

That is, the toner image obtained by adhering the toner to the electrostatic latent image is primarily transferred to the intermediate transfer belt 4.

The secondary transfer roller 6 brings the conveyed paper into contact with the intermediate transfer belt 4 and secondarily transfers the toner image on the intermediate transfer belt 4 to the paper. The paper on which the toner image is transferred is conveyed to the fixing device 9, and the toner image is fixed on the paper.

The roller 7 has a cleaning brush, and the cleaning brush is brought into contact with the intermediate transfer belt 4 to remove the toner remaining on the intermediate transfer belt 4 after the secondary transfer of the toner image to the paper. A cleaning blade may be used instead of the roller 7 having the cleaning brush.

The sensor 8 is a reflective optical sensor that detects toner on the intermediate transfer belt 4. In order to detect the toner concentration in calibration, the intermediate transfer belt 4 is irradiated with light and the reflected light is detected. In the calibration, the sensor 8 irradiates a predetermined area through which the test toner pattern formed on the intermediate transfer belt 4 passes, detects the reflected light of the light, and outputs an electric signal according to the detected light amount. Output.

FIG. 3 is a diagram showing an example of the configuration of the exposure device 2a in FIG. The exposure devices 2b to 2d corresponding to the photoconductor drums 1b to 1d have the same configuration as the exposure devices 2a shown in FIG.

In FIG. 3, the laser diode 31 is a light source that emits a laser beam for exposure. The optical system 32 is a group of various lenses arranged between the laser diode 31 and the polygon mirror 33 and / or between the polygon mirror 33 and the photoconductor drum 1a and the PD sensor 34. An fθ lens or the like is used for the optical system 32. Further, the optical system 32 includes a mirror 32a parallel to the scanning direction of the laser beam.

Further, the polygon mirror 33 is an element having an axis perpendicular to the axis of the photoconductor drum 1a, having a polygonal cross section perpendicular to the axis, and having a side surface thereof as a mirror. The polygon mirror 33 rotates about its axis and scans the laser beam emitted from the laser diode 31 along the axial direction (main scanning direction) of the photoconductor drum 1a. This laser beam is reflected by the mirror 32a and is incident on the photoconductor drum 1a.

The polygon motor unit 33a rotates the polygon mirror 33 according to a control signal from the driver circuit 35.

Further, the PD sensor 34 is a sensor that receives a laser beam scanned by the polygon mirror 33 at a predetermined position in order to generate a main scanning synchronization signal. When light is incident, the PD sensor 34 induces an output voltage according to the amount of light. The PD sensor 34 is arranged at a predetermined position on the line on which the light is scanned, detects the timing at which the spot of light passes through that position, and outputs a pulse formed at that timing as a main scanning synchronization signal.

The driver circuit 35 controls the laser diode 31 according to the exposure light amount set value specified from the controller 43 described later, causes the laser diode 31 to emit a laser beam, and controls the polygon motor unit 33a to control the polygon mirror 33. Rotate at a predetermined number of revolutions. The driver circuit 35 controls the laser diode 31 so that it is exposed by the laser beam in a pattern corresponding to the image to be formed in synchronization with the main scanning synchronization signal.

FIG. 4 is a block diagram showing a part of the electrical configuration of the image forming apparatus according to the embodiment of the present invention. As shown in FIG. 4, the image forming apparatus further includes a bias circuit 41, a storage device 42, and a controller 43.

The bias circuit 41 applies a development bias to the developing rollers 14 of the developing devices 3a to 3d, and applies a bias to the magnetic rollers 13 of the developing devices 3a to 3d, respectively.

The storage device 42 is a rewritable non-volatile storage device, and includes process set values (surface voltage set values of photoconductor drums 1a to 1d, exposure light amount set values of exposure devices 2a to 2d, and developing devices 3a to 3d. Bias setting value, etc.) is stored, and toner consumption data is stored.

The toner consumption data indicates a value corresponding to the toner consumption from the previous light amount calibration (measured value of toner consumption, average printing rate with a predetermined number of prints, etc.).

The controller 43 is, for example, a processing circuit including a computer operated by a control program, an ASIC (Application Specific Integrated Circuit), and the like, and operates as a control unit 51 and a toner sticking determination unit 52.

The control unit 51 controls the photoconductor drums 1a to 1d, the exposure devices 2a to 2d, the developing devices 3a to 3d, the charging device 21, the bias circuit 41, and the like to form an electrostatic latent image of an image to be printed. Develops, transfers and fixes the toner image corresponding to the latent image, and feeds and ejects the printing paper.

Further, the control unit 51 executes various calibrations at a predetermined timing (for each predetermined number of prints, timing specified by the user, etc.). In particular, the control unit 51 executes a light amount calibration for adjusting the exposure light amount of the exposure devices 2a to 2d.

In the light amount calibration, the control unit 51 adjusts the exposure light amount of the exposure devices 2a to 2d within a predetermined range.

FIG. 5 is a diagram illustrating a toner pattern used for light intensity calibration. FIG. 6 is a diagram illustrating a patch image in the toner pattern shown in FIG. FIG. 7 is a diagram illustrating light amount adjustment in light amount calibration.

For example, the control unit 51 uses the exposure devices 2a to 2d to form an electrostatic latent image of the toner pattern used for the light amount calibration on the photoconductor drums 1a to 1d, and uses the developing devices 3a to 3d. Then, a patch image corresponding to the electrostatic latent image is formed, the primary transfer is performed to the intermediate transfer belt 4, the color toner concentration of each patch image is measured by the sensor 8, and the color toner concentration is a predetermined target value. The amount of exposure light is adjusted so as to be.

For example, as shown in FIG. 5, a plurality of n sets of toner patterns 61 to 6n for light intensity calibration as shown in FIG. 5 are formed with different exposure light intensity set values. Each toner pattern 6i (i = 1, ..., N) has patch images 6iK, 6iM, 6iC, 6iY corresponding to a plurality of toner colors. Each patch image 6iK, 6iM, 6iC, 6iY is formed so as to have a density of a predetermined halftone level. For example, as shown in FIG. 6, each patch image 6iK, 6iM, 6iC, 6iY has dots at a predetermined ratio (1/4 in FIG. 6) of the two-dimensional pixel positions. Each patch image 6iK, 6iM, 6iC, 6iY is a two-dimensional arrangement of unit patterns 71. Then, the exposure light amount setting value of each toner pattern 6i is set so that the dot density (density) differs between the toner patterns 6i. In FIG. 6, the maximum exposure light amount setting value represented by 4 bits is 15 (0xF).

Then, for example, as shown in FIG. 7, when the same number of measurement results as the toner patterns 61 to 6n (the pair of the exposure light amount set value and the color toner density 81, 82, 83) are obtained, based on the measurement results, The control unit 51 specifies an exposure light amount set value corresponding to the density target value. For example, by extrapolating or interpolating based on the measurement result, the exposure light amount setting value corresponding to the density target value is specified, or the characteristic straight line is specified by the least squares method based on the measurement result, and the characteristic straight line is specified. The exposure light amount setting value corresponding to the density target value is specified based on the above. At that time, when the specified exposure light amount set value is less than the lower limit value of the predetermined range, the control unit 51 clamps the exposure light amount set value to the lower limit value, and the specified exposure light amount set value is within the predetermined range. When the upper limit value of is exceeded, the control unit 51 clamps the exposure light amount set value to the upper limit value.

Here, when the toner adheres to the developing roller 14 as described above, the surface potential of the developing roller 14 becomes higher than the original potential, so that the measured color toner concentration becomes high. Therefore, as the toner sticking to the developing roller 14 progresses, the exposure light amount setting value corresponding to the density target value approaches the lower limit value, and when the toner sticking to the developing roller 14 reaches a predetermined degree, the density target value is reached. The corresponding exposure light amount setting value is clamped to the lower limit value.

In the toner sticking determination unit 52, the exposure light amount is set to the lower limit value of the predetermined range in the light amount calibration, and the light amount calibration from the previous light amount calibration to the current light amount calibration during a predetermined period (for example, the period in which the latest predetermined number of prints are printed). When the toner consumption amount (such as the period until the test) is equal to or higher than a predetermined value, it is determined that the toner is stuck on the developing roller 14. When the control unit 51 determines that the toner sticking has occurred on the developing roller 14 by the toner sticking determination unit 52, the control unit 51 reduces the amount of toner adhering from the developing roller to the photoconductor drums 1a to 1d as described later. ..

In the light quantity calibration, the control unit 51 controls the charging device 21, the developing devices 3a to 3d, and the like according to the determination result of whether or not the toner sticking has occurred on the developing roller 14 by the toner sticking determination unit. , Change the process setting value as described later.

For example, when the toner sticking determination unit 52 determines that toner sticking has occurred on the developing roller 14, the control unit 51 controls the charging device 21 as follows. That is, in the charging device 21, the surface potentials of the photoconductor drums 1a to 1d are the surface potentials of the photoconductor drums 1a to 1d when the toner sticking determination unit 52 determines that toner sticking does not occur on the developing roller. The photoconductor drums 1a to 1d are charged so as to be higher. As a result, the surface potentials of the photoconductor drums 1a to 1d are increased so as to offset the increase in the potential difference between the photoconductor drums 1a to 1d and the developing roller 14 due to toner sticking, and the surface potential of the photoconductor drums 1a to 1d is increased during toner development due to toner sticking. Toner excess is suppressed.

For example, when the toner sticking determination unit 52 determines that toner sticking has occurred on the developing roller 14, the control unit 51 controls the bias circuit 41 as follows. That is, the bias circuit 41 develops with the magnetic roller 13 when the potential difference between the magnetic roller 13 and the developing roller 14 is determined by the toner sticking determination unit 52 that no toner sticking has occurred on the developing roller 14. Bias is applied to the developing roller 14 and the magnetic roller 13 so as to be lower than the potential difference between the roller 14 and the roller 14. As a result, the amount of toner transferred from the magnetic roller 13 to the developing roller 14 is reduced, so that the amount of toner transferred from the developing roller 14 to the photoconductor drums 1a to 1d is also reduced, and the toner excess during toner development due to toner sticking is also reduced. Is suppressed.

For example, when the toner sticking determination unit 52 determines that toner sticking has occurred on the developing roller 14, the control unit 51 controls the developing devices 3a to 3d as follows. That is, in the developing devices 3a to 3d, when the toner carrier ratio in the developing devices 3a to 3d is determined by the toner sticking determination unit 52 that no toner sticking has occurred on the developing roller 14, the developing devices 3a to 3d It is controlled to be lower than the toner carrier ratio in. For example, the stirring time of the developer in the developing devices 3a to 3d is adjusted so that the toner carrier ratio becomes such. As a result, the amount of toner transferred from the magnetic roller 13 to the developing roller 14 is reduced, so that the amount of toner transferred from the developing roller 14 to the photoconductor drums 1a to 1d is also reduced, and the toner excess during toner development due to toner sticking is also reduced. Is suppressed.

Next, the operation of the image forming apparatus will be described.

Each time the control unit 51 executes printing, the control unit 51 specifies a value corresponding to the toner consumption such as the toner consumption and the printing rate in printing, and obtains the toner consumption data based on the toner consumption and the printing rate. It is updated and the toner consumption data is reset every time the light amount is calibrated.

When the predetermined timing of the light quantity calibration comes, the control unit 51 executes the light quantity calibration.

In the light amount calibration, after the control unit 51 completes the adjustment of the exposure light amount set value, the toner sticking determination unit 52 determines whether or not the adjusted exposure light amount set value has reached the lower limit value of the predetermined range, and adjusts. When the subsequent exposure light amount setting value becomes the lower limit value of the predetermined range, it is determined based on the toner consumption amount data whether or not the toner consumption amount in the predetermined period is equal to or more than the predetermined value. Then, when the toner consumption amount from the previous light amount calibration is equal to or more than a predetermined value, the toner sticking determination unit 52 determines that the exposure light amount set value is the lower limit value of the predetermined range due to the toner sticking. Judgment (that is, it is determined that toner sticking has occurred on the developing roller 14). For example, when the average printing rate in the latest predetermined number of prints is equal to or higher than a predetermined value (for example, any of 10% to 30%), it is determined that toner is stuck on the developing roller 14.

When the toner sticking determination unit 52 determines that toner sticking has occurred on the developing roller 14, the control unit 51 determines the process set value (charging bias of the photoconductor drums 1a to 1d) as described above. The bias of the developing roller 14 and the magnetic roller 13, the toner carrier ratio, etc.) are changed and set. In the subsequent printing, the printing is executed with the set value, and the amount of toner adhered from the developing roller 14 to the photoconductor drums 1a to 1d is reduced corresponding to the increase due to the sticking of the toner.

As described above, according to the above embodiment, the control unit 51 executes the light amount calibration for adjusting the exposure light amount of the exposure devices 2a to 2d within a predetermined range. Then, when the exposure light amount is set to the lower limit value of the predetermined range in the light amount calibration and the toner consumption amount in the predetermined period is equal to or more than the predetermined value, the toner sticking determination unit 52 causes toner sticking on the developing roller 14. Judged as Then, when the toner sticking determination unit 52 determines that toner sticking has occurred on the developing roller 14, the control unit 51 reduces the amount of toner adhering from the developing roller 14 to the photoconductor drums 1a to 1d.

As a result, even if toner sticking occurs, the amount of toner sticking from the developing roller 14 to the photoconductor drums 1a to 1d becomes appropriate, and deterioration of image quality due to toner sticking formed on the developing roller 14 is suppressed. ..

It should be noted that various changes and modifications to the above-described embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without leaving the intent and scope of the subject and without diminishing the intended benefits. That is, it is intended that such changes and amendments are included in the claims.

For example, in the above embodiment, the developing devices 3a to 3d are developing devices for two-component developing agents, but may be developing devices for one-component developing agents.

The present invention is applicable to, for example, an electrophotographic image forming apparatus.

1a to 1d Photoreceptor drum 2a to 2d Exposure device 3a to 3d Developing device 13 Magnetic roller 14 Developing roller 21 Charging device 41 Bias circuit 51 Control unit 52 Toner sticking judgment unit

Claims (4)

Photoreceptor drum and
An exposure device that exposes the photoconductor drum to form an electrostatic latent image,
A developing device that forms a toner image by adhering toner to the electrostatic latent image on the photoconductor drum with a developing roller.
A control unit that executes light intensity calibration that adjusts the exposure light intensity of the exposure device within a predetermined range, and
When the exposure light amount is set to the lower limit value of the predetermined range and the toner consumption amount in the predetermined period is equal to or more than the predetermined value in the light amount calibration, it is determined that toner is stuck on the developing roller. Equipped with a sticking judgment unit
When the control unit determines that toner sticking has occurred on the developing roller by the toner sticking determination unit, the control unit reduces the amount of toner adhering from the developing roller to the photoconductor drum.
An image forming apparatus characterized by. A charging device for charging the photoconductor drum is further provided.
When the toner sticking determination unit determines that toner sticking has occurred on the developing roller, (a) the control unit controls the charging device to transfer the toner from the developing roller to the photoconductor drum. The amount of toner adhered is reduced, and (b) the charging device determines that the surface potential of the photoconductor drum does not cause toner sticking on the developing roller by the toner sticking determination unit. Charging the photoconductor drum so that it is higher than the surface potential of the body drum.
The image forming apparatus according to claim 1. The developing apparatus includes a magnetic roller that supplies toner to the developing roller, and a bias circuit that applies a bias to the developing roller and the magnetic roller, respectively.
When the toner sticking determination unit determines that toner sticking has occurred on the developing roller, (a) the control unit controls the bias circuit to transfer the developing roller to the photoconductor drum. The amount of toner adhered is reduced, and (b) the bias circuit determines that the potential difference between the magnetic roller and the developing roller is such that the toner sticking determination unit does not cause toner sticking on the developing roller. Applying a bias to the developing roller and the magnetic roller, respectively, so as to be lower than the potential difference between the magnetic roller and the developing roller in the case of
The image forming apparatus according to claim 1. When the control unit determines that toner sticking has occurred on the developing roller by the toner sticking determination unit, the toner carrier ratio in the developing device is determined by the toner sticking determination unit on the developing roller. The feature is that the toner carrier ratio in the developing apparatus is set by controlling the developing apparatus so that the toner carrier ratio in the developing apparatus is lower than the toner carrier ratio in the developing apparatus when it is determined that toner sticking has not occurred. The image forming apparatus according to claim 1.

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