JP2019032497A - Image forming apparatus - Google Patents

Abstract

To obtain an image forming apparatus in which a developing bias is precisely adjusted.SOLUTION: A linear velocity setting unit 41 sets, during normal printing, a relative transfer linear velocity of an intermediate transfer belt 5 to photoreceptor drums 1a to 1d to a normal linear velocity. A developing bias setting unit 42 causes the linear velocity setting unit 41, during adjustment, to set the transfer linear velocity to a predetermined adjustment linear velocity higher than the normal linear velocity and change the developing bias to a plurality of toner marks at the adjustment linear velocity, and specifies a target developing bias value to be a target toner density at the normal linear velocity from density measured values of the plurality of toner marks.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus.

  An image forming apparatus predicts a developing bias that becomes a target toner amount by using a toner mark formed with a developing bias lower than the target toner amount (see, for example, Patent Document 1).

  Another image forming apparatus specifies a developing bias that achieves a target toner density by lowering a linear velocity ratio between the photosensitive drum and the developing roller, and uses the developing bias as a target toner density during normal printing. (See, for example, Patent Document 2).

JP 2003-270873 A JP 2013-033293 A

  In general, in an electrophotographic image forming apparatus, a reflective optical sensor is used as a density sensor for density adjustment. The reflection type optical sensor has lower density detection accuracy for the high density toner mark than the low to intermediate density toner mark.

  When detecting the toner density using a reflective optical sensor, the toner density is determined by comparing the reflected light from the background of the image carrier when the toner mark is not formed with the reflected light from the toner mark. Many calculation methods are used.

  The high density toner mark covers the background of the image carrier thickly, but in the high density area, the change in sensor output is very small with respect to the density change of the high density toner mark, so the development bias must be set accurately. It is difficult.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus in which a developing bias is accurately adjusted.

  The image forming apparatus according to the present invention includes a photosensitive drum on which an electrostatic latent image is formed, a developing roller that holds toner to be attached to the electrostatic latent image, and the toner that is attached to the electrostatic latent image. An intermediate transfer belt to which a toner image formed in this manner is transferred, a linear speed setting unit that sets a relative linear velocity of the intermediate transfer belt with respect to the photosensitive drum to a normal linear speed during normal printing, A developing bias setting unit that sets a developing bias between the photosensitive drum and the developing roller to a target developing bias value that becomes a target toner density during normal printing, and a toner mark on the intermediate transfer belt during adjustment And a reflection type optical sensor for measuring the density. The developing bias setting unit causes the linear velocity setting unit to set the transfer linear velocity to a predetermined linear velocity that is higher than the normal linear velocity at the time of adjustment, and with respect to a plurality of toner marks at the adjusted linear velocity. The development bias is changed, and the target development bias value that becomes the target toner density at the normal linear velocity is specified from the density measurement values of the plurality of toner marks.

  According to the present invention, an image forming apparatus in which the developing bias is accurately adjusted can be obtained.

  These and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

FIG. 1 is a side view showing a mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing an example of the developing device 3a in FIG. FIG. 3 is a block diagram illustrating a configuration example of the controller 31 in the image forming apparatus illustrated in FIG. FIG. 4 is a diagram for explaining the correspondence between the actual toner density (reflection density) of the toner mark and the density measurement value (coverage M) for the toner mark. FIG. 5 is a diagram for explaining a change in the relationship between the developing bias and the reflection density of the toner mark with respect to a change in the transfer linear velocity. FIG. 6 is a view for explaining toner mark formation in the image forming apparatus shown in FIG.

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

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

  The image forming apparatus of this embodiment has a tandem color developing device. The color developing device includes photosensitive drums 1a to 1d, an exposure device 2, and developing devices 3a to 3d. The photoconductor drums 1a to 1d are four-color photoconductors of cyan, magenta, yellow, and black, and electrostatic latent images are formed on the photoconductor drums 1a to 1d. The exposure device 2 is a device that forms an electrostatic latent image by irradiating the photosensitive drums 1a to 1d with laser light. The exposure apparatus 2 includes a laser diode that is a light source of laser light and an optical element (lens, mirror, polygon mirror, etc.) that guides the laser light to the photosensitive drums 1a to 1d.

  The developing devices 3a to 3d form toner images by attaching the toner in the toner cartridges to the electrostatic latent images on the photosensitive drums 1a to 1d. The photosensitive drum 1a and the developing device 3a develop magenta, the photosensitive drum 1b and the developing device 3b develop cyan, and the photosensitive drum 1c and the developing device 3c develop yellow. Then, black development is performed by the photosensitive drum 1d and the developing device 3d.

  The intermediate transfer belt 5 is an annular intermediate transfer member that contacts the photosensitive drums 1a to 1d and transfers the toner images on the photosensitive drums 1a to 1d. The intermediate transfer belt 5 is stretched around the driving roller 6a and the tension roller 6b, and rotates around in the direction from the contact position with the photosensitive drum 1a to the contact position with the photosensitive drum 1d by the driving force from the driving roller 6a. To go.

  The secondary transfer roller 7 brings the conveyed paper into contact with the intermediate transfer belt 5 and secondarily transfers the toner image on the intermediate transfer belt 5 to the paper. The sheet on which the toner image is secondarily transferred is conveyed to a fixing device (not shown), and the toner image is fixed on the sheet.

  The sensor 8 irradiates light to the intermediate transfer belt 5 at the time of adjustment, detects the reflected light (for example, regular reflection light and diffuse reflection light), and on the intermediate transfer belt 5 based on the detected amount of reflected light. This is a reflective optical sensor that measures the density of toner marks. In particular, when adjusting the toner density and gradation, the sensor 8 detects the density of the toner mark carried on the intermediate transfer belt 5.

  The primary transfer rollers 9 a to 9 d are respectively arranged to face the photosensitive drums 1 a to 1 d with the intermediate transfer belt 5 interposed therebetween, and the toner images on the photosensitive drums 1 a to 1 d are primarily transferred to the intermediate transfer belt 5. To do.

  FIG. 2 is a cross-sectional view showing an example of the developing device 3a in FIG. In FIG. 2, the developing device 3a is illustrated, but the developing devices 3b to 3d have the same configuration.

  As illustrated in FIG. 2, the developing device 3 a 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 via a supply port (not shown). In the housing 11, the two-component developer containing toner and carrier is stirred by the stirring screw 12. A magnetic material is used for the carrier.

  The magnetic roller 13 holds a two-component developer in a brush shape on its surface. The toner in the two-component developer moves to the developing roller 14 in accordance with a transport bias that is a voltage between the magnetic roller 13 and the developing roller 14.

  The developing roller 14 holds the toner transferred from the magnetic roller 13 as a thin toner layer on the surface thereof. In other words, the toner layer formed on the surface of the developing roller 14 that holds the toner to be attached to the electrostatic latent image on the photosensitive drum 1a is the voltage between the developing roller 14 and the photosensitive drum 1a. Is transferred to the photosensitive drum 1a by the developing bias.

  The photosensitive drum 1a is an image carrier on which an electrostatic latent image is formed by the exposure device 2. For example, an organic photoreceptor (OPC) drum is used for the photoreceptor drum 1a, and a touch-down developing type is used for the developing roller. The toner transferred from the developing roller 14 adheres to the electrostatic latent image on the photosensitive drum 1a.

  FIG. 3 is a block diagram illustrating a configuration example of the controller 31 in the image forming apparatus illustrated in FIG. Although the function of the controller 31 for the photosensitive drum 1a and the developing device 3a will be described here, the functions of the controller 31 for the other photosensitive drums 1b to 1d and the developing devices 3b to 3d are the same.

  The controller 31 electrically controls each part in the image forming apparatus. The controller 31 includes an ASIC (Application Specific Integrated Circuit), a microcomputer, and the like. The developing roller potential setting circuit 32 is a circuit that sets the potential of the developing roller 14 to a specified potential.

  The controller 31 includes a linear velocity setting unit 41, a development bias setting unit 42, a toner density specifying unit 43, and a bias setting value storage unit 44.

  The linear velocity setting unit 41 sets the relative linear velocity of the intermediate transfer belt 5 relative to the photosensitive drum 1a to the normal linear velocity during normal printing.

  For example, the linear velocity setting unit 41 controls the linear velocity of the intermediate transfer belt 5 by controlling the driving roller 6a and the like, and thereby the relative linear velocity of the intermediate transfer belt 5 with respect to the photosensitive drum 1a (that is, A linear speed difference or a linear speed ratio between the photosensitive drum 1a and the intermediate transfer belt 5 is set. The linear velocity setting unit 41 controls the linear velocity of the photosensitive drum 1 a and the linear velocity of the developing roller 14 while maintaining the linear velocity ratio between the photosensitive drum 1 a and the developing roller 14, and thereby the photosensitive member. The relative linear velocity of the intermediate transfer belt 5 with respect to the drum 1a may be set.

  The developing bias setting unit 42 uses the developing roller potential setting circuit 32 to set a developing bias (here, a DC bias) between the photosensitive drum 1 a and the developing roller 14. The toner density specifying unit 43 specifies the density of the toner mark on the intermediate transfer belt 5 based on the output of the sensor 8. The bias set value storage unit 44 is a nonvolatile storage device that stores a target development bias value during normal printing. During normal printing, the development bias setting unit 42 sets the development bias to a target development bias value that is a target toner density.

  FIG. 4 is a diagram for explaining the correspondence between the actual toner density (reflection density) of the toner mark and the density measurement value (coverage M) for the toner mark.

  As the density measurement value, for example, a coverage M based on the following equation is used.

  M = 1-{(R-Rd)-(D-Dd)} / {(Rg-Rd)-(Dg-Dd)}

  Here, Rd is the dark potential of the regular reflection light receiving element of the sensor 8, Dd is the dark potential of the diffuse reflection light receiving element of the sensor 8, and Rg is an image carrier detected by the regular reflection light receiving element ( That is, it is a detection voltage of regular reflection light from the background of the intermediate transfer belt 5, and Dg is the diffuse reflection light from the image carrier (that is, the background of the intermediate transfer belt 5) detected by the diffuse reflection light receiving element. R is a detection voltage, R is a detection voltage of regular reflection light from the toner mark detected by the regular reflection light receiving element, and D is a detection voltage of diffuse reflection light from the toner mark detected by the diffuse reflection light receiving element. It is.

  As shown in FIG. 4, the coverage M based on the output of the sensor 8 is saturated when the actual toner density of the toner mark is increased, and it is difficult to measure an accurate density.

  FIG. 5 is a diagram for explaining a change in the relationship between the developing bias and the reflection density of the toner mark with respect to a change in the transfer linear velocity.

  At the time of adjustment (that is, calibration of density characteristics and gradation characteristics), the developing bias setting unit 42 causes the linear speed setting unit 41 to set the transfer linear speed to a predetermined adjustment linear speed higher than the normal linear speed, and perform adjustment. Development biases for a plurality of toner marks are changed at a linear speed, and a target development bias value that becomes a target toner density at a normal linear speed is specified from density measurement values of the plurality of toner marks.

  At the time of adjustment, the transfer linear velocity is set to an adjustment linear velocity higher than the normal linear velocity, so that the toner mark layer thickness is reduced, and the toner concentration at the adjustment linear velocity corresponding to the target toner concentration at the normal linear velocity. (Hereinafter referred to as “adjusted target toner density”) falls within the non-saturated region.

  Specifically, at the time of adjustment, the development bias setting unit 42 obtains the development bias value that becomes the adjustment target toner density from the density measurement values of the plurality of toner marks, and the target development bias that becomes the target toner density at the normal linear velocity. Identifies as a value. In other words, as shown in FIG. 5, for example, when the target toner density during normal printing is 1.4 in reflection density, the target toner density during adjustment is 0.8 in reflection density. The adjustment linear velocity is determined based on the ratio between the adjustment target toner concentration and the target toner concentration during normal printing and the normal linear velocity.

  The adjustment target toner density is a density in a region where the density measurement value of the sensor 8 with respect to the actual toner density is not saturated. For this reason, in this embodiment, the adjustment linear velocity is set so that the adjustment target toner density is any value in the range of 0.4 to 0.8 in terms of reflection density. For example, the adjustment linear speed is set so that the density of the plurality of toner marks falls within a range from 0.4 to 0.8.

  When the reflection density is less than 0.4, the measured density is easily affected by the background state of the intermediate transfer belt 5, and when the reflection density exceeds 0.8, the toner density during normal printing is saturated. Therefore, it is preferable that the adjustment linear velocity is set so that the reflection density becomes any value in the range from 0.4 to 0.8.

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

  FIG. 6 is a view for explaining toner mark formation in the image forming apparatus shown in FIG.

  In the adjustment, the controller 31 rotates the intermediate transfer belt 5 twice. First, in the first round, the toner concentration specifying unit 43 detects the output of the sensor 8 by the reflected light from the background at the positions where the toner marks are formed in the second and third rounds. Next, in the second round, the development bias is adjusted with the transfer linear velocity set to the adjustment linear velocity.

  In the development bias adjustment at the adjustment linear velocity in the second round, the linear velocity setting unit 41 sets the transfer linear velocity to an adjustment linear velocity higher than the normal linear velocity during normal printing.

  Then, the developing bias setting unit 42 changes the developing bias for the plurality of toner marks for adjustment, acquires the density measurement values (coverage ratio M) of the plurality of toner marks by the toner density specifying unit 43, and uses the sensor 8. From the measured density values (coverage ratio M) of the plurality of toner marks, the development bias value that is the adjusted target toner density is determined as the target development bias value.

  Specifically, the controller 31 controls the exposure device 2 while changing the development bias for each toner mark by the development bias setting unit 42 to generate an electrostatic latent image corresponding to a plurality of toner marks on the photosensitive drum 1a. ˜1d. As a result, the electrostatic latent image is developed with a toner amount corresponding to the developing bias, and the toner images formed by the development are transferred from the photosensitive drums 1 a to 1 d to the intermediate transfer belt 5. The toner density specifying unit 43 detects the output of the sensor 8 due to the reflected light from the formed toner mark, and based on the difference between the output value of the first round sensor 8 and the output value of the second round sensor 8, The density measurement value of each toner mark in the second round is specified.

  The development bias setting unit 42 specifies a development bias value that becomes an adjustment target toner density by linear interpolation or the like from density measurement values of a plurality of toner marks corresponding to a plurality of development bias values, and sets the bias as the target development bias value. Store in the value storage unit 44.

  Then, during normal printing (that is, when printing an original image), the development bias setting unit 42 reads out the target development bias value and sets the development bias to the target development bias value. Then, the controller 31 controls the exposure device 2 under the condition of the developing bias to form an electrostatic latent image of the original image, develop the toner image on the photosensitive drums 1a to 1d, and the intermediate transfer belt 5. The primary transfer of the toner image to the toner, the secondary transfer of the toner image to the printing paper, and the fixing of the toner image are executed.

  As described above, according to the above-described embodiment, the linear speed setting unit 41 sets the relative transfer linear speed of the intermediate transfer belt 5 with respect to the photosensitive drums 1a to 1d to the normal linear speed during normal printing. . The development bias setting unit 42 causes the linear speed setting unit 41 to set the transfer linear speed to a predetermined adjustment linear speed higher than the normal linear speed during adjustment, and changes the development bias for a plurality of toner marks at the adjustment linear speed. The target development bias value that is the target toner density at the normal linear velocity is specified from the density measurement values of the plurality of toner marks.

  As a result, since the target development bias value is specified in the non-saturated region during adjustment, the development bias during normal printing is accurately adjusted.

  Various changes and modifications to the above-described embodiment will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing its intended advantages. That is, such changes and modifications are intended to be included within the scope of the claims.

  For example, in the above embodiment, a sensor for measuring at least one of the environmental temperature and the environmental humidity is provided in the image forming apparatus, and the linear velocity setting unit 41 responds to at least one of the environmental temperature and the environmental humidity measured by the sensor. Thus, the above-described transfer linear velocity may be changed.

  For example, in a Dutchdown development system that uses an organic photoconductor drum, the toner density changes greatly with changes in the development bias, resulting in variations in the distance between the developing roller and the photoconductor drum, unevenness in the surface potential of the photoconductor drum, etc. As a result, the contrast potential tends to fluctuate, and the development bias may not be adjusted accurately.

  As described above, since the characteristics of the toner density with respect to the development bias vary due to environmental changes, it is preferable to adjust the development bias in order to obtain an appropriate toner density according to the environment. In particular, in a high-temperature and high-humidity environment, the photosensitive drums 1a to 1d are weakly charged, so that the toner density characteristic with respect to the developing bias (that is, the toner density change with respect to the developing bias change) becomes steep. Therefore, when the transfer linear velocity is changed as described above, the transfer linear velocity is increased as the environmental temperature is higher or the environmental humidity is higher. As a result, since the above-described characteristics become gentle, the developing bias corresponding to the target toner density is specified more accurately.

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

1a to 1d Photosensitive drum 5 Intermediate transfer belt 8 Sensor (an example of a reflective optical sensor)
14 Developing roller 41 Linear speed setting section 42 Developing bias setting section

Claims (6)

A photosensitive drum on which an electrostatic latent image is formed;
A developing roller for holding toner to adhere to the electrostatic latent image;
An intermediate transfer belt to which a toner image formed by attaching the toner to the electrostatic latent image is transferred;
A linear velocity setting unit that sets a relative linear velocity of the intermediate transfer belt with respect to the photosensitive drum to a normal linear velocity during normal printing;
A developing bias setting unit that sets a developing bias between the photosensitive drum and the developing roller to a target developing bias value that becomes a target toner density during the normal printing;
A reflective optical sensor for measuring the density of the toner mark on the intermediate transfer belt at the time of adjustment,
The developing bias setting unit causes the linear velocity setting unit to set the transfer linear velocity to a predetermined linear velocity that is higher than the normal linear velocity at the time of adjustment, and the development for a plurality of toner marks at the adjusted linear velocity. Changing the bias and specifying the target development bias value that becomes the target toner density at the normal linear velocity from the density measurement values of the plurality of toner marks;
An image forming apparatus. The development bias setting unit determines a development bias value that is an adjustment target toner density corresponding to the target toner density from the density measurement values of the plurality of toner marks during adjustment, and sets the target toner density at the normal linear velocity. Specified as the target development bias value,
The target toner density at the adjustment linear velocity is set to a density of an area where the density measurement value with respect to the actual toner density of the reflective optical sensor is not saturated.
The image forming apparatus according to claim 1.   3. The image formation according to claim 2, wherein the adjustment linear velocity is set so that the adjustment target toner density is any value in a range of 0.4 to 0.8 in terms of reflection density. apparatus.   4. The linear speed setting unit controls a linear speed of the intermediate transfer belt to set a relative transfer linear speed of the intermediate transfer belt with respect to the photosensitive drum. The image forming apparatus according to claim 1.   The linear velocity setting unit controls a linear velocity of the photosensitive drum and a linear velocity of a developing roller to set a relative linear velocity of the intermediate transfer belt with respect to the photosensitive drum. The image forming apparatus according to any one of claims 1 to 3. A sensor for measuring at least one of environmental temperature and environmental humidity;
The linear velocity setting section adjusts the transfer linear velocity in accordance with at least one of environmental temperature and environmental humidity measured by the sensor;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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