JP6025672B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  In an electrophotographic image forming apparatus, the thickness of the toner layer on the developing roller is set to the target layer thickness by varying the transport bias, and the developing bias is varied to support the entire toner layer of the developing roller. The developing bias is set so that the developing bias can be transferred to the body (see, for example, Patent Document 1).

  In another apparatus, a toner bias formed with a developing bias lower than the target toner amount is used to predict a developing bias that becomes the target toner amount (see, for example, Patent Document 2).

JP 2005-308821 A JP 2003-270873 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.

  Since the high density toner mark covers the background of the image carrier thickly, in the high density area, the change in the sensor output is very small with respect to the density change of the high density toner mark. In the method, it is difficult to set the developing bias accurately.

  In particular, in the case of black toner, since the reflectance and transmittance of light at the toner mark are low, in the high density region, the change in the sensor output becomes smaller with respect to the density change of the high density toner mark, and the development bias is accurately set. It becomes difficult to set to.

  Further, the developing bias setting method described in Patent Document 2 described above is not a developing method in which the entire toner layer on the developing roller is transferred onto the image bearing member, but is developed with a toner amount that cancels the electric field due to the electrostatic latent image. The potential for setting is set.

  For example, in the case of using a photosensitive drum having a high relative dielectric constant such as an amorphous silicon photosensitive drum, in a developing bias region where all of the toner layer on the developing roller does not transfer onto the photosensitive drum, the toner with respect to the developing bias change Since the sensitivity of the development amount is high, the amount of toner used for development greatly fluctuates due to the gap fluctuation between the developing roller and the photosensitive drum. Therefore, for example, when using a photosensitive drum having a high relative dielectric constant, such as an amorphous silicon photosensitive drum, a developing method using all the toner layer on the developing roller for development is used, as described in Japanese Patent Application Laid-Open No. 2003-133260. It is preferable.

  In the case of a development method in which the entire toner layer on the development roller is used for development, it is difficult to set the development bias by the method described in Patent Document 2 because the development method is different.

  In the case of a developing method in which the entire toner layer on the developing roller is used for development, it is preferable to set the developing bias to a minimum value at which the entire toner layer on the developing roller can be shifted to development.

  However, as described above, since the resolution of the sensor for the high density region of toner is low, it is difficult to accurately specify the minimum developing bias. In other words, the minimum development bias is the minimum value of the potential at which all of the toner layer on the development roller can be shifted to development, so the density of the toner mark used to identify the development bias is high, and the sensor resolution is low. Therefore, it is difficult to accurately specify the minimum developing bias.

  Therefore, the minimum developing bias that can be developed by transferring all of the toner layer formed on the developing roller to the photosensitive drum with the conveyance bias lower than the normal printing condition is calculated, and based on the calculation result, the normal developing bias is calculated. A method is conceivable in which a minimum developing bias is predicted for the conveyance bias at the time of printing, and the developing bias is set based on the prediction result.

  However, when developing with a lower transport bias, only the toner necessary for canceling the electric field of the electrostatic latent image in the toner layer on the developing roller is transferred to the photosensitive drum, and the toner is transferred onto the developing roller. Since the amount of toner used at that time changes under the influence of the charge of the toner layer remaining on the developing roller, normal printing starts from the minimum developing bias for such a low transport bias. It is difficult to immediately predict the minimum development bias under conditions.

  The present invention has been made in view of the above problems, and image formation in which a developing bias is appropriately and accurately set in a developing method in which a toner layer formed on a developing roller is entirely transferred to a photosensitive drum and developed. The object is to obtain a device.

An image forming apparatus according to the present invention includes a magnetic roller that holds a two-component developer including toner and a carrier, a developing roller that holds toner transferred from the magnetic roller, and a photosensitive drum on which an electrostatic latent image is formed. A linear speed ratio setting unit that sets a linear speed ratio that is a ratio of a linear speed of the outer peripheral surface of the developing roller and a linear speed of the outer peripheral surface of the photosensitive drum, and the photosensitive drum and the developing roller. A developing bias setting unit for setting a developing bias therebetween, and a conveying bias setting unit for setting a conveying bias between the magnetic roller and the developing roller. The developing bias setting unit sets the developing bias to a target developing bias value that causes all of the toner layer on the developing roller to transfer to the photosensitive drum during normal printing, and the transport bias setting unit performs normal printing. At times, the transport bias is set to a target transport bias value. In the adjustment, the linear speed ratio setting unit sets the linear speed ratio to be lower than the linear speed ratio in the normal printing, and the development bias setting unit and / or the transport bias setting unit At the time of adjustment, the development bias and / or the transport bias for a plurality of toner marks are changed, and the target development bias value and / or the target at the time of normal printing are determined from the density measurement values of the plurality of toner marks. Determine the transport bias value. The developing bias setting unit specifies a minimum developing bias value for transferring all the toner layers on the developing roller to the photosensitive drum from the density measurement values of the plurality of toner marks during the adjustment, and specifies the specified The minimum development bias value is set as the target development bias value during the normal printing. In the adjustment, the conveyance bias setting unit changes the linear velocity ratio in the normal printing and the line in the adjustment from the measured density values of the plurality of toner marks to the target toner density in the normal printing. A transport bias value corresponding to the toner density multiplied by the ratio with the speed ratio is specified, and the specified transport bias value is set as the target transport bias value during the normal printing. In the adjustment, the linear speed ratio setting unit sets the linear speed ratio to be lower than the linear speed ratio during the normal printing, and the linear speed of the outer peripheral surface of the magnetic roller and the outer periphery of the developing roller. The ratio with the surface linear velocity is the same as the value during normal printing.

  According to the present invention, the developing bias in the developing method in which the entire toner layer formed on the developing roller is transferred to the photosensitive drum and developed is set appropriately and accurately.

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 a controller in the image forming apparatus illustrated in FIG. FIG. 4 is a diagram for explaining the relationship between the toner transfer amount to the photosensitive drum and the minimum developing bias. FIG. 5 is a diagram illustrating the correspondence between the toner mark density and the sensor output for the toner mark. FIG. 6 is a view for explaining toner mark formation in the image forming apparatus shown in FIG. FIG. 7 is a diagram illustrating the specification of the target transport bias value. FIG. 8 is a diagram for explaining identification of the target development bias value.

  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 rollers 3a to 3d. The photoconductor drums 1a to 1d are four-color photoconductors of cyan, magenta, yellow, and black. 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 6 and circulates 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 6.

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

  The sensor 8 irradiates the intermediate transfer belt 5 with light and detects the reflected light. In particular, the sensor 8 detects the density of the toner mark on the intermediate transfer belt 5 during adjustment. The sensor 8 is a reflective optical sensor that measures the density of toner marks for adjustment.

  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. The toner layer formed on the surface of the developing roller 14 is transferred to the photosensitive drum 1a by a developing bias that is a voltage between the developing roller 14 and the photosensitive drum 1a.

  The photosensitive drum 1a is an image carrier on which an electrostatic latent image is formed by the exposure device 2. For the photosensitive drum 1a, a photosensitive drum having a high relative dielectric constant such as an amorphous silicon photosensitive drum is used.

  FIG. 3 is a block diagram illustrating a configuration example of a controller 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 magnetic roller potential setting circuit 33 is a circuit that sets the potential of the magnetic roller 13 to a specified potential.

  The controller 31 includes a linear velocity ratio setting unit 41, a development bias setting unit 42, a transport bias setting unit 43, a toner density specifying unit 44, and a bias setting value storage unit 45.

  The linear speed ratio setting unit 41 sets the linear speed ratio S / D by controlling the rotational speeds of the photosensitive drum 1a, the developing roller 14, and the like. The linear velocity ratio S / D is a ratio between the linear velocity S of the outer peripheral surface of the developing roller 14 and the linear velocity D of the outer peripheral surface of the photosensitive drum. The developing bias setting unit 42 uses the developing roller potential setting circuit 32 to set a developing bias between the photosensitive drum 1 a and the developing roller 14. The transport bias setting unit 43 uses the magnetic roller potential setting circuit 33 to set the transport bias between the magnetic roller 13 and the developing roller 14. The toner density specifying unit 44 specifies the density of the toner mark on the intermediate transfer belt 5 based on the output of the sensor 8. The bias setting value storage unit 45 is a non-volatile storage device that stores a target developing bias value and a target transport bias value during normal printing.

  The development bias setting unit 42 sets the development bias to a target development bias value during normal printing. The target developing bias value is a minimum developing bias value necessary for transferring all the toner layers on the developing roller 14 to the photosensitive drum 1a.

  Further, the transport bias setting unit 43 sets the transport bias to the target transport bias value during normal printing.

  At the time of adjustment, the linear speed ratio setting unit 41 sets the linear speed ratio S / D lower than the linear speed ratio S / D during normal printing, and the development bias setting unit 42 and / or the transport bias setting unit 43 The development bias and / or the transport bias for the plurality of toner marks are changed, and the target development bias value and / or the target transport bias value during normal printing are determined from the density measurement values of the plurality of toner marks by the sensor 8.

  In this embodiment, at the time of adjustment, the development speed setting unit 42 is set in a state where the linear speed ratio setting unit 41 sets the linear speed ratio S / D lower than the linear speed ratio S / D during normal printing. The conveyance bias setting unit 43 changes the development bias and the conveyance bias for the plurality of toner marks, and determines the target development bias value and the target conveyance bias value during normal printing from the density measurement values of the plurality of toner marks by the sensor 8. To decide.

  Specifically, the development bias setting unit 42 specifies a minimum development bias value for transferring all the toner layers on the development roller 14 to the photosensitive drum 1a from the density measurement values of the plurality of toner marks described above during adjustment. The specified minimum development bias value is set as the target development bias value during normal printing.

  More specifically, the conveyance bias setting unit 43 adjusts the linear velocity ratio S / D during normal printing and the target toner density during normal printing from the density measurement values of a plurality of toner marks during adjustment. The conveyance bias value corresponding to the toner density multiplied by the ratio with the linear velocity ratio S / D at the time is specified, and the specified conveyance bias value is set as the target conveyance bias value at the time of normal printing.

  Note that the linear speed ratio S / D at the time of adjustment is set so that the toner density of the plurality of toner marks is the density of an area where the output value of the sensor 8 with respect to the toner density is not saturated.

  The linear speed ratio setting unit 41 controls the rotational speed of the magnetic roller 13 and the like during adjustment, and sets the linear speed ratio S / D to be lower than the linear speed ratio during normal printing. The ratio of the linear velocity of the outer peripheral surface 13 to the linear velocity of the outer peripheral surface of the developing roller 14 is the same as the value at the time of normal printing.

  FIG. 4 is a diagram for explaining the relationship between the toner transfer amount to the photosensitive drum and the minimum developing bias. In order to grasp the characteristics of fluctuations in the amount of toner used for development (hereinafter referred to as “development toner amount”) with respect to the development bias when the linear speed ratio S / D is changed, the developing roller 14 and the photosensitive drum Electric field analysis during As a result, as shown in FIG. 4, the minimum value of the developing bias (that is, the minimum developing bias value) in the region where the developing toner amount is saturated is substantially constant regardless of the linear speed ratio S / D. I understood.

  FIG. 5 is a diagram for explaining the correspondence between the toner mark density (that is, the layer thickness) and the sensor output for the toner mark. As shown in FIG. 5, the output of the sensor 8 saturates as the toner mark density increases, making it difficult to measure the correct density.

  Therefore, in this embodiment, at the time of adjustment, the linear speed ratio S / D is set to be lower than the linear speed ratio S / D at the time of normal printing so that the non-saturated region of the sensor 8 (the output value with respect to the toner density is A low density toner mark is formed in a non-saturated region), and the target development bias value and the target transport bias value are determined using the low density toner mark.

  Note that the lower the linear speed ratio S / D, the lower the linear velocity of the developing roller 14, and the smaller the amount of toner transferred from the developing roller 14 to the photosensitive drum 1a.

  However, the lower the linear velocity ratio S / D, the longer the toner particles stay in the region where the electric field strength due to the electrostatic latent image is high, and the toner particles that are relatively difficult to fly to the photosensitive drum 1a also fly. The bias value is detected slightly lower. For this reason, a value obtained by adding a predetermined margin to the minimum developing bias value when the low-density toner mark is used may be used as the target developing bias value during normal printing.

  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. FIG. 7 is a diagram illustrating the specification of the target transport bias value. FIG. 8 is a diagram for explaining identification of the target development bias value.

  In the adjustment, the controller 31 rotates the intermediate transfer belt 5 three times.

  First, in the first round, the toner concentration specifying unit 44 detects the output of the sensor 8 due to 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, adjustment of the transport bias (that is, setting of the target transport bias value during normal printing) is executed.

  In the adjustment of the conveyance bias, the linear speed ratio setting unit 41 sets the linear speed ratio S / D lower than the linear speed ratio S / D during normal printing. For example, when the linear speed ratio S / D during normal printing is 1.6, the linear speed ratio setting unit 41 sets the linear speed ratio S / D to 1.0 in the adjustment of the conveyance bias.

  Then, the transport bias setting unit 43 changes the transport bias with respect to the plurality of toner marks for adjustment, and determines the target transport bias value during normal printing from the density measurement values of the plurality of toner marks by the sensor 8.

  Specifically, the transport bias setting unit 43 changes the transport bias for each toner mark, and the controller 31 controls the exposure device 2 to display electrostatic latent images 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 conveyance 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 44 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 of each toner mark in the second round is specified.

  Then, as shown in FIG. 7, the conveyance bias setting unit 43 calculates the linear speed ratio during adjustment and normal printing from the density measurement values of the plurality of toner marks corresponding to the plurality of conveyance bias values with respect to the target toner amount. A transport bias value that is a value obtained by multiplying the ratio with the linear velocity ratio of the hour (that is, a toner amount that is lower than the target toner amount by that ratio) is specified by interpolation, and the specified transport bias value is determined as the target transport bias. Let it be the value Vt.

  Next, in the third round, adjustment of the developing bias (that is, setting of the target developing bias value during normal printing) is executed.

  In the adjustment of the developing bias, the linear speed ratio setting unit 41 sets the linear speed ratio S / D lower than the linear speed ratio S / D during normal printing. For example, when the linear speed ratio S / D during normal printing is 1.6, the linear speed ratio setting unit 41 sets the linear speed ratio S / D to 1.0 in the adjustment of the developing bias.

  Then, the development bias setting unit 42 changes the development bias for the plurality of toner marks for adjustment, and determines the target development bias value during normal printing from the density measurement values of the plurality of toner marks by the sensor 8.

  Specifically, while the developing bias setting unit 42 changes the developing bias for each toner mark, the controller 31 controls the exposure device 2 to display the electrostatic latent images corresponding to the 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 44 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 third round sensor 8, The density of each toner mark on the third round is specified.

Then, as shown in FIG. 8, the development bias setting unit 42 specifies and specifies the minimum development bias value at which the density measurement value is saturated from the density measurement values of the plurality of toner marks corresponding to the plurality of development bias values. The development bias value is a target development bias value Vd.

  The development bias setting unit 42 and the conveyance bias setting unit 43 store the target development bias value Vd and the target conveyance bias value Vt in the bias setting value storage unit 45.

  During normal printing (that is, when printing an original image), the development bias setting unit 42 and the conveyance bias setting unit 43 read the target development bias value Vd and the target conveyance bias value Vt, and develop the development bias into the target development. The bias value Vd is set, and the transport bias is set to the target transport bias value Vt. Then, the controller 31 controls the exposure device 2 under the conditions of the development bias and the transport bias to form an electrostatic latent image of the original image, and develops the toner image on the photosensitive drums 1a to 1d, and the intermediate The primary transfer of the toner image to the transfer belt 5, 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 embodiment, at the time of adjustment, the linear speed ratio setting unit 41 sets the linear speed ratio between the developing roller 14 and the photosensitive drum 1a to the linear speed ratio during normal printing. The development bias setting unit 42 and / or the conveyance bias setting unit 43 are set to be low, and the development bias and / or the conveyance bias for the plurality of toner marks are changed, and the density measurement values of the plurality of toner marks are used during normal printing. The target development bias value and / or the target transport bias value is determined.

  As a result, the developing bias in the developing method in which all the toner layer formed on the developing roller 14 is transferred to the photosensitive drum 1a and developed without being affected by the characteristics of the sensor 8 is set appropriately and accurately.

  The above-described embodiments are preferred examples of the present invention, but the present invention is not limited to these, and various modifications and changes can be made without departing from the scope of the present invention. is there.

  For example, in the above embodiment, one of the target transport bias value and the target development bias value may be determined by another method.

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

1a to 1d Photosensitive drum 8 sensor (an example of a reflective optical sensor)
13 Magnetic roller 14 Developing roller 41 Linear speed ratio setting section 42 Developing bias setting section 43 Conveyance bias setting section

Claims (3)

A magnetic roller holding a two-component developer including toner and carrier;
A developing roller for holding toner transferred from the magnetic roller;
A photosensitive drum on which an electrostatic latent image is formed;
A linear speed ratio setting unit that sets a linear speed ratio that is a ratio of the linear speed of the outer peripheral surface of the developing roller and the linear speed of the outer peripheral surface of the photosensitive drum;
A developing bias setting unit for setting a developing bias between the photosensitive drum and the developing roller;
A transport bias setting unit for setting a transport bias between the magnetic roller and the developing roller;
The development bias setting unit sets the development bias to a target development bias value that causes the entire toner layer on the development roller to transfer to the photosensitive drum during normal printing,
The transport bias setting unit sets the transport bias to a target transport bias value during normal printing,
The linear speed ratio setting unit sets the linear speed ratio to be lower than the linear speed ratio at the time of normal printing during adjustment.
The development bias setting unit and / or the transport bias setting unit may change the development bias and / or the transport bias with respect to a plurality of toner marks at the time of the adjustment, and from the density measurement values of the plurality of toner marks, Determining the target development bias value and / or the target transport bias value in the normal printing ;
The developing bias setting unit specifies a minimum developing bias value for transferring all the toner layers on the developing roller to the photosensitive drum from the density measurement values of the plurality of toner marks during the adjustment, and specifies the specified The minimum development bias value is set as the target development bias value in the normal printing,
In the adjustment, the conveyance bias setting unit changes the linear velocity ratio in the normal printing and the line in the adjustment from the measured density values of the plurality of toner marks to the target toner density in the normal printing. A transport bias value corresponding to the toner density multiplied by the ratio with the speed ratio is specified, and the specified transport bias value is set as the target transport bias value at the time of normal printing,
In the adjustment, the linear speed ratio setting unit sets the linear speed ratio to be lower than the linear speed ratio during the normal printing, and the linear speed of the outer peripheral surface of the magnetic roller and the outer periphery of the developing roller. The ratio of the surface linear velocity to the same value as in the normal printing,
An image forming apparatus. A reflection type optical sensor for measuring the density of the plurality of toner marks;
The development bias setting unit and / or the transport bias setting unit changes the development bias and / or the transport bias with respect to a plurality of toner marks during the adjustment, and the plurality of toner marks by the reflective optical sensor are changed. Determining the target development bias value and / or the target transport bias value in the normal printing from the density measurement value of
The image forming apparatus according to claim 1 Symbol mounting characterized. 4. The image forming apparatus according to claim 3 , wherein the toner density of the plurality of toner marks is a density of an area in which an output value with respect to the toner density of the reflective optical sensor is not saturated.

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