JP2004117847A - Image forming device and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a high quality toner image in an image forming device of a wet development method. <P>SOLUTION: A CPU 113 executes a control program stored in a memory 116, thereby, increases development bias, forms a plurality of patch pictures, detects picture densities of the patch pictures respectively by a patch sensor 17, compares the picture densities and judges whether the picture densities are saturated or not. Then, the picture formation condition on which the picture density is substantially saturated is determined and is stored in the memory 116. When a print command signal is inputted from an external device via a main controller 100, a printing operation is performed under the image forming condition stored in the memory 116. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrophotographic image forming technique for a printer, a copying machine, a facsimile machine, and the like, and more particularly to an electrophotographic image forming technique using wet development as a developing method.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a charged photoconductor (image carrier) is exposed by an exposure unit to form an electrostatic latent image on the photoconductor, and toner is adhered to the photoconductor by a development unit to visualize the electrostatic latent image. 2. Description of the Related Art An electrophotographic image forming apparatus has been put to practical use in which a toner image is formed into a toner image, and the toner image is transferred to a transfer sheet to obtain a predetermined image. Here, as a developing method of the developing means, a wet developing method using a developing solution in which toner is dispersed in a liquid carrier is known. This wet development method has such advantages that a high-resolution image can be obtained because the particle diameter of the toner is as small as 0.1 to 2 μm, and a uniform image can be obtained because of high fluidity due to liquid. Therefore, various wet developing type image forming apparatuses have been proposed (for example, see Patent Document 1).
[0003]
This conventional image forming apparatus includes a developing roller (developing solution carrier) that transports a developing solution in which charged toner is dispersed in a liquid carrier to a developing position opposite to a photoreceptor while carrying the developing solution on the surface thereof. When the charged toner in the developer filling the gap between the photoconductor and the developing roller (developing gap) moves to the photoconductor, an electrostatic latent image on the photoconductor is visualized to form a toner image. It has become so.
[0004]
[Patent Document 1]
JP-A-7-209922 (
FIG. 1)
[0005]
[Problems to be solved by the invention]
By the way, the image density of the toner image formed as described above depends on the electric field applied to the charged toner at the developing position. This electric field is affected by changes in the developing bias, exposure energy, charging bias, etc., and the developing gap. In some cases, these changes affect the image density of the toner image, resulting in a decrease in image quality.
[0006]
The present invention has been made in view of the above problems, and has as its object to provide an image forming apparatus and a method capable of forming a high-quality toner image in a wet development type image forming apparatus.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to the present invention includes an image carrier configured to carry an electrostatic latent image on a surface thereof, and a developer in which a toner is dispersed in a liquid carrier. A developing solution carrier that is carried to a developing position opposite to the image carrier while carrying the toner, and a predetermined developing bias is applied to the developing solution carrier to cause a toner in the developing solution carried by the developing solution carrier. Is attached to the image carrier, the electrostatic latent image is visualized with toner to form a toner image, and an image density of the toner image as a patch image formed by the image forming means is detected. A plurality of patch images while changing the contrast potential, and responding to an increase in the contrast potential based on the image densities of the plurality of patch images detected by the density detecting means. Obtains an image forming condition the toner adhesion amount to the image bearing member is substantially saturated, is characterized by forming a normal toner image by the image forming condition.
[0008]
According to another aspect of the present invention, there is provided an image forming method, comprising: applying a predetermined developing bias to a developer carrier for carrying a developer in which a toner is dispersed in a liquid carrier; In a method of forming a toner image by adhering a toner in a developing solution carried on an image carrier and developing an electrostatic latent image on the image carrier with the toner to form a toner image, the contrast potential is changed. A step of forming a plurality of toner images as patch images, a step of detecting image densities of the plurality of patch images, and, based on the detection result, an amount of toner adhering to the image carrier with respect to an increase in contrast potential is substantially reduced. The method is characterized by comprising a step of obtaining an image forming condition that saturates and a step of forming a normal toner image under the image forming condition.
[0009]
According to these configurations, a plurality of patch images are formed while changing the contrast potential, the image densities of the plurality of patch images are detected, and based on the detection result, the toner on the image carrier against the increase in the contrast potential is detected. Image forming conditions under which the amount of adhesion is substantially saturated are obtained, and a normal toner image is formed under the image forming conditions. Here, “the image forming conditions under which the amount of toner adhering to the image carrier with respect to the increase in the contrast potential is substantially saturated” means that even if the contrast potential increases, the amount of toner that contributes to the visualization of the electrostatic latent image is almost zero. This means a condition that does not change, and includes, of course, a case where all the toner in the developer transported to the developing position by the developer carrier adheres to the image carrier. Depending on the characteristics of the carrier, there is also a case where even if the contrast potential increases, a predetermined ratio (for example, 90%) of the toner in the developing solution hardly changes in a state where the toner adheres to the image carrier. When a toner image is formed under such image forming conditions, the image density of the toner image hardly changes even if the image forming conditions and the size of the gap between the image carrier and the developer carrier slightly change. A quality toner image can be formed. Further, even when the image forming conditions change due to deterioration over time or the like, it is possible to always obtain the image forming conditions under which the amount of toner adhering to the image carrier with respect to the increase in the contrast potential is almost saturated. Can be formed.
[0010]
Further, when a solid image is used as the patch image and a high density image forming condition is obtained as the image forming condition, a high quality solid image can be formed.
[0011]
When a low-density image including a fine line or an isolated dot is used as the patch image and a low-density image forming condition is obtained as the image forming condition, the high-quality low-density image can be formed.
[0012]
When a medium-density image including a white thin line or a white isolated dot is used as the patch image and a medium-density image forming condition is obtained as the image forming condition, a high-quality medium-density image is formed. be able to.
[0013]
Further, as the image forming conditions, an image forming condition that satisfies at least two of the following high-density image forming conditions, medium-density image forming conditions, and low-density image forming conditions may be obtained. Here, the high-density image forming condition is an image forming condition obtained by using a solid image as the patch image, and the medium-density image forming condition is a white thin line or a white isolated dot as the patch image. The low-density image forming condition is an image forming condition obtained by using a low-density image including a fine line or an isolated dot as the patch image.
[0014]
According to this configuration, it is possible to form at least two of a solid image, a medium-density image including white thin lines or isolated dots, and a low-density image including thin lines or isolated dots with high quality. .
[0015]
Further, when a developing solution having a γ saturation characteristic that the amount of toner adhered to the image carrier is substantially saturated with an increase in the contrast potential is used as the developing solution, the developing solution is applied to the image carrier with an increase in the contrast potential. Therefore, it is possible to reliably set an image forming condition in which the toner adhesion amount is substantially saturated, so that a high-quality toner image can be reliably formed. In this case, the toner concentration in the developer may be from about 5% by weight to about 40% by weight.
[0016]
Further, the density detecting means may detect an image density of a patch image formed on the image carrier. The image forming apparatus further includes a transfer unit that transfers the toner image formed on the image carrier to a transfer medium, wherein the density detection unit detects an image density of a patch image transferred from the image carrier to the transfer medium. You may make it.
[0017]
Generally, in an image forming apparatus, in order to adjust electrical control conditions of an image carrier, a developer carrier, and a transfer unit, a reference image having a predetermined pattern is formed and transferred to a transfer medium. Although the density is often detected, according to these configurations, the density detecting means for detecting the image density of the patch image for obtaining the toner density is replaced with the image density of the reference image for adjusting the electric control condition. It can also be used for detection, thereby suppressing an increase in the number of parts. Further, a patch image for obtaining an image forming condition can be made to function as a reference image, and efficient patch processing can be performed.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a diagram showing an internal configuration of a printer which is an embodiment of an image forming apparatus according to the present invention, and FIG. 2 is a block diagram showing an electrical configuration of the printer. This printer is a wet development type image forming apparatus that forms a monochromatic image using a developing solution containing black (K) toner. A print command signal including an image signal from an external device such as a host computer is transmitted to a main control unit. 100, the engine control unit 110 controls each part of the engine unit 1 in accordance with a control signal from the main control unit 100, and conveys the sheet from the sheet cassette 3 disposed at the lower portion of the apparatus main body 2. An image corresponding to the image signal is printed out on transfer paper, copy paper, and paper (hereinafter referred to as “transfer paper”) 4.
[0019]
The engine unit 1 includes a photoreceptor unit 10, an exposure unit 20, a developing unit 30, a transfer unit 40, and the like. Among these units, the photoconductor unit 10 includes a photoconductor 11, a charging unit 12, a charge removing unit 13, and a cleaning unit 14. The developing unit 30 includes a developing roller 31 and the like. Further, the transfer unit 40 includes an intermediate transfer roller 41 and the like.
[0020]
In the photoreceptor unit 10, the photoreceptor 11 is provided rotatably in an arrow direction 15 (clockwise direction in the figure) of FIG. Around the photoreceptor 11, a charging unit 12, a developing roller 31, an intermediate transfer roller 41, a charge removing unit 13, and a cleaning unit 14 are arranged along a rotation direction 15 thereof. A surface area between the charging unit 12 and the developing roller 31 is an irradiation area of the light beam 21 from the exposure unit 20. In the present embodiment, the charging unit 12 includes a charging roller, and a charging bias is applied from the charging bias generation unit 111 to uniformly charge the outer peripheral surface of the photoconductor 11 to a predetermined surface potential Vd (for example, Vd = DC + 600 V). And has a function as a charging unit.
[0021]
A light beam 21 formed by, for example, a laser is emitted from the exposure unit 20 toward the outer peripheral surface of the photoconductor 11 uniformly charged by the charging unit 12. The exposure unit 20 exposes the photoconductor 11 with the light beam 21 in accordance with a control command given from the exposure control unit 112, and forms an electrostatic latent image on the photoconductor 11 corresponding to an image signal. It has a function as an exposure unit. For example, when a print command signal including an image signal is provided from an external device such as a host computer to the CPU 101 of the main control unit 100 via the interface 102, the CPU 113 responds to a command from the CPU 101 of the main control unit 100 to cause the exposure control unit to execute. A control signal corresponding to the image signal is output to the device 112 at a predetermined timing. Then, a light beam 21 is emitted from the exposure unit 20 to the photoconductor 11 in response to a control command from the exposure control unit 112, and an electrostatic latent image corresponding to an image signal is formed on the photoconductor 11. When a patch image to be described later is formed as necessary, a control signal corresponding to a patch image signal of a predetermined pattern (for example, a solid image, a thin line image, or a thin white line image) is exposed from the CPU 113 to the exposure device. The electrostatic latent image is provided to the control unit 112 and is formed on the photoconductor 11 corresponding to the pattern. As described above, in this embodiment, the photoconductor 11 corresponds to the “image carrier” of the present invention.
[0022]
The electrostatic latent image thus formed is visualized by toner supplied from the developing roller 31 of the developing unit 30. The developing unit 30 includes, in addition to the developing roller 31, a tank 33 that stores the developing solution 32, an application roller 34 that draws up the developing solution 32 stored in the tank 33 and applies the developing solution 32 to the developing roller 31, A regulating blade 35 for uniformly regulating the thickness of the layer, a cleaning blade 36 for removing the developing solution remaining on the developing roller 31 after supplying the toner to the photoreceptor 11, a toner density adjusting unit 37, and a memory 38 described later (FIG. 2) ). The developing roller 31 rotates at a peripheral speed equal to that of the photoconductor 11 in a direction (counterclockwise in FIG. 1) that follows the photoconductor 11. The application roller 34 rotates in the same direction as the developing roller 31 (counterclockwise in the figure) at a peripheral speed that is about twice as high.
[0023]
In the present embodiment, the developer 32 is a toner composed of a color pigment, an adhesive such as an epoxy resin that adheres the color pigment, a charge control agent that gives a predetermined charge to the toner, and a dispersant that uniformly disperses the color pigment. Are dispersed in a liquid carrier. In the present embodiment, for example, a silicone oil such as polydimethylsiloxane oil is used as a liquid carrier, and the toner concentration is 5 to 40% by weight, and a low-concentration developer (toner concentration of 1 to 2) often used in a wet development method is used. (% By weight). Note that the type of the liquid carrier is not limited to silicone oil, and the viscosity of the developer 32 is determined by the materials used for the liquid carrier and the toner used, the toner concentration, and the like. For example, the viscosity is set to 50 to 6000 mPa · s, which is higher than that of a low concentration developer.
[0024]
The toner concentration adjusting section 37 includes a supply tank 371 in which a developer having a higher toner concentration than the developer 32 stored in the tank 33 is stored and a supply tank 372 in which the liquid carrier is stored. When the toner supply pump 373 operates, the high-concentration developer is supplied from the supply tank 371 to the tank 33 to increase the toner concentration of the developer 32. On the other hand, when the carrier supply pump 374 operates, the liquid carrier is removed from the supply tank 372. 33, the toner concentration of the developer 32 decreases. The pumps 373 and 374 are driven by pump driving units 118 and 119. As described above, by controlling the operation of the pumps 373 and 374, the toner concentration of the developer 32 in the tank 33 is adjusted.
[0025]
In the developing unit 30 having such a configuration, the developer 32 stored in the tank 33 is pumped up by the application roller 34, and the thickness of the developer layer on the application roller 34 is uniformly regulated by the regulating blade 35. The developing solution 32 adheres to the surface of the developing roller 31 and is conveyed to the developing position 16 facing the photoconductor 11 as the developing roller 31 rotates. The toner is positively charged, for example, by the action of a charge control agent or the like. At the developing position 16, the toner moves from the developing roller 31 to the photoconductor 11 by the developing bias Vb applied from the developing bias generator 114 to the developing roller 31. Thus, the electrostatic latent image is visualized. The developing bias Vb is determined by an optimization process described later, and for example, about Vb = DC + 400 V is used. Thus, in this embodiment, the developing roller 31 corresponds to the “developer liquid carrier” of the present invention, and the developing bias generator 114 corresponds to the “image forming unit” of the present invention.
[0026]
The toner image formed on the photoconductor 11 as described above is conveyed to a primary transfer position 44 facing the intermediate transfer roller 41 as the photoconductor 11 rotates. The intermediate transfer roller 41 is rotated at a peripheral speed equal to that of the photoconductor 11 in a direction (counterclockwise in FIG. 1) that follows the photoconductor 11, and a primary transfer bias (for example, DC-400V Is applied, the toner image on the photoconductor 11 is primarily transferred to the intermediate transfer roller 41. Residual charges on the photoreceptor 11 after the primary transfer are removed by a charge removing unit 13 composed of an LED or the like, and a residual developing solution is removed by a cleaning unit 14.
[0027]
A secondary transfer roller 42 is disposed at an appropriate position of the intermediate transfer roller 41 (in FIG. 1, vertically below the intermediate transfer roller 41), and a primary transfer toner image primary-transferred to the intermediate transfer roller 41 is transferred to the intermediate transfer roller 41. With the rotation of 41, the sheet is conveyed to a secondary transfer position 45 facing the secondary transfer roller 42. On the other hand, the transfer paper 4 stored in the paper feed cassette 3 is transported to a secondary transfer position 45 by a transport drive unit (not shown) in synchronization with the transport of the primary transfer toner image. The secondary transfer roller 42 rotates at a peripheral speed equal to that of the intermediate transfer roller 41 in a direction (clockwise in FIG. 1) that follows the intermediate transfer roller 41. For example, when -100 μA is applied by constant current control, the toner image on the intermediate transfer roller 41 is secondarily transferred to the transfer paper 4. The residual developing solution on the intermediate transfer roller 41 after the secondary transfer is removed by the cleaning unit 43. The transfer paper 4 on which the toner image has been secondarily transferred is conveyed along a predetermined transfer paper conveyance path 5 (indicated by a dashed line in FIG. 1), and the fixing unit 6 fixes the toner image. Is discharged to a discharge tray provided in the printer.
[0028]
Further, between the developing roller 31 and the intermediate transfer roller 41 around the photoconductor 11, a patch sensor 17 composed of, for example, a reflection type optical sensor is disposed so as to face the photoconductor 11, and as will be described later, The density of the patch image formed on the image 11 is detected. An operation display panel 7 composed of, for example, a liquid crystal display and a touch panel is provided on the upper surface of the apparatus main body 2 to receive an operation instruction from a user and display predetermined information to notify the user. In this embodiment, the patch sensor 17 corresponds to the "density detecting means" of the present invention.
[0029]
2, the main control unit 100 includes an image memory 103 for storing an image signal provided from an external device via an interface 102. The CPU 101 transmits a print command signal including the image signal from the external device. When received through the interface 102, the job data is converted into job data in a format suitable for the operation instruction of the engine unit 1, and is sent to the engine control unit 110. The memory 116 of the engine control unit 110 includes a ROM that stores a control program of the CPU 113 including preset fixed data, and a RAM that temporarily stores control data of the engine unit 1 and calculation results by the CPU 113. The CPU 113 stores in the memory 116 data relating to the image signal transmitted from the external device via the CPU 101.
[0030]
The memory 38 of the developing unit 30 stores data on the manufacturing lot of the developing unit 30, the use history, the characteristics of the built-in toner, the remaining amount of the developer 32, the toner concentration, and the like. The memory 38 is electrically connected to a communication unit 39, and the communication unit 39 is attached to, for example, the tank 33. When the developing unit 30 is mounted on the apparatus main body 2, the communication unit 39 is configured to be opposed to the communication unit 117 of the engine control unit 110 within a predetermined distance, for example, within 10 mm. Data can be transmitted and received in a non-contact state by wireless communication. As a result, the CPU 113 manages various kinds of information such as the management of consumables related to the developing unit 30. In this embodiment, data transmission / reception is performed in a non-contact manner using electromagnetic means such as wireless communication. However, for example, connectors are provided in the apparatus main body 2 and the developing unit 30, respectively. When the developing unit 30 is mounted, data transmission and reception may be performed mutually by mechanically fitting the two connectors. The memory 38 is preferably a non-volatile memory capable of storing data even when the power is off or the developing unit 30 is detached from the apparatus main body 2. Such a non-volatile memory is, for example, a flash memory or the like. An EEPROM, a ferroelectric memory, or the like can be used.
[0031]
FIG. 3 is an enlarged view of the developing nip portion, and FIG. 4 is a diagram illustrating a change in the amount of toner adhering to the photoconductor with respect to the contrast potential. As shown in FIG. 3, the distance D (development gap = thickness of the developer layer) between the photoconductor 11 and the developing roller 31 is a predetermined value in the range of 5 to 40 μm (for example, D = 7 μm in the present embodiment). It is regulated uniformly. Further, the developing nip distance L (the circumferential distance in which the developing solution layer is in contact with both the photoconductor 11 and the developing roller 31) is set to, for example, L = 5 mm in the present embodiment.
[0032]
Then, the developer 32 in which the toner 322 is dispersed in the liquid carrier 321 is conveyed to the developing position 16 while being carried on the surface of the developing roller 31. On the other hand, the photoconductor 11 is uniformly charged to the potential Vd by the charging unit 12, and the toner 322 adheres to a region where the charge is neutralized by being exposed by the light beam 21 of the exposure unit 20.
[0033]
As described above, in the present embodiment, the development gap D can be set small by using the developer 32 having a high toner concentration (for example, 5 to 40% by weight). Therefore, in the case of the low-concentration developer described above, the moving distance of the toner that moves by electrophoresis in the developer is reduced as compared with the case where a developing gap of 100 to 200 μm is required to increase the amount of toner. Development efficiency can be improved, and development can be performed at high speed.
[0034]
Further, since the developing gap D is set to be small, for example, when the contrast potential Vcont is increased by increasing the developing bias Vb, the generated electric field also sharply increases. Accordingly, as shown in FIG. The amount of toner adhering from the developing roller 31 to the photoconductor 11 sharply rises, and is substantially saturated at a certain potential (Vcont = Vt in the figure).
[0035]
As described above, since the toner adhesion amount is saturated in the range equal to or higher than the contrast potential Vt in FIG. 4A, the image density of the toner image formed in this range depends on the image density such as the developing bias, the charging bias, and the exposure energy. Even if the formation conditions fluctuate somewhat, it hardly changes. Therefore, as will be described later, this printer forms a toner image under image forming conditions included in this range. As a result, image quality deterioration due to insufficient density or uneven density is prevented.
[0036]
Here, “the toner adhesion amount is substantially saturated” means that even if the contrast potential Vcont increases, the toner amount contributing to the visualization of the electrostatic latent image hardly changes. In addition to the case where all the toner of the above developing solution adheres to the photoconductor 11, even if the contrast potential Vcont increases due to the characteristics of the apparatus (for example, the photoconductor unit 10 and the developing unit 30), the developing roller This includes a case where the toner of a predetermined ratio (for example, 90% or 95%) of the developer on the toner 31 is hardly changed in a state where the toner adheres to the photoconductor 11.
[0037]
On the other hand, when a developer having a low concentration (for example, 1 to 2% by weight) is used, it is necessary to set the developing gap D to be large (for example, D = 100 to 200 μm) in order to increase the toner amount. Even when the potential Vcont is increased, the generated electric field only increases slowly, and therefore, as shown in FIG. 4B of the comparative example, the amount of toner adhered from the developing roller 31 to the photoconductor 11 continues to increase gradually. Does not saturate.
[0038]
FIG. 5 is a diagram showing a surface potential profile of the photoconductor 11 when a solid image P1, a low-density image P2, and a medium-density image P3 are formed. FIG. 6 is a diagram showing a change in the developing bias Vb when each of the images P1 to P3 is formed. FIG. 6 is a diagram schematically showing a change in image density with respect to FIG. In FIG. 6, image forming conditions (charging bias, exposure energy, etc.) other than the developing bias Vb are fixed.
[0039]
When the photoconductor 11 charged to a uniform potential Vd (for example, Vd = DC + 600 V in the present embodiment) by the charging unit 12 is partially exposed by the light beam 21, the charge of the portion is neutralized and the surface of the photoconductor 11 is neutralized. An electrostatic latent image is formed on the surface of the photoreceptor 11 in the solid image P1, and the surface potential profile of the photoreceptor 11 is substantially equal to the residual potential Vr determined by the characteristics of the photoreceptor 11. The well type is reduced to V1. On the other hand, in the low-density image (in the present embodiment, for example, a fine line image) P2, the exposed area is narrow, so that the surface potential Vs has a sharp dip-shaped profile, and decreases only to the potential V2 (> V1). Conversely, in the medium-density image (in this embodiment, for example, a thin white line image) P3, the non-exposed area sandwiched between the areas to be exposed is narrow, so that the surface potential Vs of the white part increases only to the potential V3, It does not return to the potential Vd. Note that the images P2 and P3 in FIG. 5 show an example of only one line, but the same applies to a case of a plurality of lines spaced apart from each other.
[0040]
Then, when the electrostatic latent image having such a surface potential profile is conveyed to the developing position 16 facing the developing roller 31 carrying the toner (FIG. 3), the toner in the developing solution 32 at the developing position 16 322 adheres to any one of the developing roller 31 and the photosensitive member 11 according to the DC potential of each part. At this time, as the potential difference between the developing bias Vb and the surface potential Vs of the photoconductor 11, that is, the contrast potential Vcont is larger, the movement of the toner from the developing roller 31 to the photoconductor 11 is promoted. Therefore, the potential difference, that is, the contrast potential Vcont is larger. As the amount of toner attached to the photoconductor 11 increases, the image density also increases, and as described above, the image density substantially saturates at a certain potential.
[0041]
Here, the formation of the solid image P1 will be described first. As shown in FIG. 6, when the developing bias Vb is increased from 0, when Vb> V1, the contrast potential Vcont becomes positive and the image density starts to increase. Then, from the time when a sufficient contrast potential Vcont is obtained (Vb = V4> V1 in FIG. 6), even if the developing bias Vb is increased, the image density does not increase but becomes constant, and is substantially saturated.
[0042]
Subsequently, formation of the low-density image P2 will be described. When the developing bias Vb is increased from 0, when Vb> V2, the contrast potential Vcont becomes positive and the image density starts to increase. Then, from the time when a sufficient contrast potential Vcont is obtained (Vb = V5> V2 in FIG. 6), even if the developing bias Vb is increased, the image density does not increase but becomes constant, and is substantially saturated.
[0043]
Next, formation of the medium density image P3 will be described. When the developing bias Vb is increased from 0, when Vb> V1, the contrast potential Vcont becomes positive and the image density starts to increase. Then, from the time when a sufficient contrast potential Vcont is obtained (Vb = V4> V1 in FIG. 6), even if the developing bias Vb is increased, the image density does not increase but becomes constant, and is substantially saturated. When the developing bias Vb is further increased and Vb> V3, the toner also adheres to the white portion, so that the image density increases. When the developing bias Vb becomes sufficiently higher than the potential V3, the image density becomes the same level as that of the solid image and is almost saturated. In this embodiment, the saturation start potential of the medium-density image P3 and that of the solid image P1 match, but they may not match depending on the type of toner and the device configuration.
[0044]
From the above, the following can be understood. That is,
{Circle around (1)} When the developing bias Vb is set to a predetermined value that satisfies V4 <Vb, the solid image P1 can be formed favorably.
{Circle around (2)} When the developing bias Vb is set to a predetermined value satisfying V5 <Vb, a solid image P1 can be favorably formed in addition to the low-density image P2.
(3) When the developing bias Vb is set to a predetermined value that satisfies V4 <Vb <V3, a solid image P1 can be favorably formed in addition to the medium density image P3.
(4) When the developing bias Vb is set to a predetermined value that satisfies V5 <Vb <V3, the solid image P1, the low-density image P2, and the medium-density image P3 can be formed satisfactorily.
[0045]
Therefore, this printer forms a plurality of patch images for patch images corresponding to the solid image P1, the low-density image P2, and the medium-density P3 while changing the contrast potential, and detects the image densities. Is performed at an appropriate timing such as when the power is turned on or when the number of printed sheets reaches a predetermined number. Hereinafter, an example of each patch image will be described, and then the operation of the present embodiment will be described in detail.
[0046]
FIG. 7 is a diagram illustrating an example of a low-density patch image Q2 corresponding to the low-density image P2, and FIG. 8 is a diagram illustrating an example of a medium-density patch image Q3 corresponding to the medium-density image P3. In the present embodiment, the low-density patch image Q2 is a thin line image including one dot line group of 1 on and 10 off, as shown in FIG. The number of the on-dot line group may be two or more, but is preferably 1 in order to obtain image forming conditions for reliably forming a fine line image. Further, the number of off-dot line groups is not limited to ten, and may be any number enough to separate adjacent dot line groups, for example, three or more. In FIG. 7, a thin line image is used, but an image composed of isolated dots may be used instead.
[0047]
Further, in the present embodiment, the medium density patch image Q3 is a white thin line image composed of a group of white dots of 10 ON and 1 OFF as shown in FIG. The number of the white dot line groups may be two or more, but is preferably 1 in order to obtain image forming conditions for reliably forming a white fine line image. Also, the number of on-dot line groups is not limited to 10, and may be any number, such as 3 or more, at which adjacent white dot line groups are sufficiently separated. Although FIG. 8 shows a thin white line image, an image composed of white isolated dots may be used instead.
[0048]
As the solid patch image Q1 corresponding to the solid image P1, for example, as shown in FIG. 5, a solid image similar to the solid image P1 may be used.
[0049]
9 is a flowchart showing an image forming condition optimization processing routine, FIG. 10 is a flowchart showing a solid patch processing subroutine of FIG. 9, FIG. 11 is a flowchart showing a low density patch processing subroutine of FIG. 9, and FIGS. 10 is a flowchart illustrating a middle density patch processing subroutine in FIG. 9. A control program for optimizing the image forming conditions is stored in the memory 116 of the engine control unit 110. Then, the following optimization processing is executed by the CPU 113 controlling each unit of the apparatus according to the control program.
[0050]
In the image forming condition optimizing process, first, a solid patch process is performed (# 10 in FIG. 9). In the solid patch processing, as shown in FIG. 10, the developing bias Vb is set to a predetermined value (for example, V1 in FIG. 6) (# 20), and a solid patch image Q1 is formed (# 22). In this embodiment, image forming conditions (charging bias, exposure energy, etc.) other than the developing bias Vb are fixed. Therefore, the contrast potential Vcont can be arbitrarily set by changing the developing bias Vb. Then, at a timing when the solid patch image Q1 moves to a position facing the patch sensor 17 with the rotation of the photoconductor 11, a detection signal output from the patch sensor 17 is fetched, and a solid patch is generated based on the signal. The density of the image Q1 is obtained and stored in the memory 116 (# 24).
[0051]
Next, the contrast potential Vcont is increased by increasing the developing bias Vb by a predetermined width (# 26). Then, the solid patch image Q1 is formed under the image forming conditions (# 28), and the density is obtained based on the detection signal output from the patch sensor 17 and stored in the memory 116 in the same manner as in step # 24 described above ( # 30). Further, the density of the previously formed solid patch image Q1 and the density of the previously formed solid patch image Q1 are compared, and for example, whether or not the amount of change in the density is saturated or not is smaller than a predetermined width. It is determined whether or not the density is saturated (# 32). If the density is saturated (YES in # 32), the process proceeds to # 34. If the density is not saturated (NO in # 32), the process returns to # 26 and The steps are repeated. In # 32, for example, when the change amount of the density becomes equal to or less than 1/10 of the change amount of the initial density (for example, the inclined portion of the line of the solid image P1 in FIG. 6), it is determined that the density is saturated. You may do so.
[0052]
Then, in # 34, the developing bias Vb at the time of saturation (for example, V4 in FIG. 6) is stored in the memory 116, the process returns to FIG. 9, and then the low density patch process is performed (# 12 in FIG. 9). In this low-density patch processing, as shown in FIG. 11, the developing bias Vb is set to a predetermined value (for example, V2 in FIG. 6) (# 40), and a low-density patch image Q2 is formed (# 42). ). The operations of # 44 to # 52 are executed in the same procedure as the solid patch processing of FIG. 10 except for the step (# 48) of forming the low-density patch image Q2, and the low-density patch image is saturated until the image density is saturated. Formation of Q2 and concentration detection are performed.
[0053]
Then, in # 54, the developing bias Vb at the time of saturation (for example, V5 in FIG. 6) is stored in the memory 116, and the process returns to FIG. 9, and then the medium density patch processing is performed (# 14 in FIG. 9). In the medium density patch processing, as shown in FIG. 12, the developing bias Vb is set to a predetermined value (for example, V1 in FIG. 6) (# 60), and a medium density patch image Q3 is formed (# 62). ). The operations of # 64 to # 72 are executed in the same procedure as the solid patch processing of FIG. 10 except for the step (# 68) of forming the medium density patch image Q3, and the medium density patch image is processed until the image density is saturated. Formation of Q3 and concentration detection are performed.
[0054]
Then, in # 74, the developing bias Vb at the time of saturation (for example, V4 in FIG. 6) is stored in the memory 116. The subsequent steps # 76 to # 80 in FIG. 13 are performed in exactly the same manner as steps # 66 to # 70 in FIG. Then, in # 82, the density of the medium-density patch image Q3 formed immediately before and the density of the medium-density patch image Q3 formed immediately before are compared, and for example, whether or not the amount of change in density exceeds a predetermined width is determined. Then, it is determined whether the image density has started increasing again, and if the image density has not started increasing (NO in # 82), the process returns to # 76 and the above procedure is repeated.
[0055]
Then, when the image density of the middle density patch image Q3 starts to increase again (YES in # 82), the developing bias Vb (for example, V3 in FIG. 6) at the time of the increase is stored in the memory 116, and the process returns to FIG. Next, the optimum value of the developing bias Vb is determined and stored in the memory 116 (# 16 in FIG. 9). As the optimum value of the developing bias Vb, for example, in the example of FIG. 6, a predetermined value that satisfies V5 <Vb <V3 is set. The image forming conditions thus determined may be written in the memory (developing unit mounting memory) 38 of the developing unit 30. Then, the image forming conditions in the memory 38 may be written into the memory 116 at an appropriate timing, for example, when the developing unit 30 is attached to the apparatus main body 2.
[0056]
FIG. 14 is a flowchart showing a print processing routine. When a print command signal is input from an external device via the main control unit 100, first, a predetermined charging bias and exposure energy are set as image forming conditions, and an image forming condition optimizing process ( The developing bias Vb obtained in FIG. 9 and stored in the memory 116 is set (# 90). Then, a printing operation is performed under the set image forming conditions (# 92). As described above, since the printing operation is performed under the image forming conditions determined by the optimization processing, high quality image formation can be performed for the solid image P1, the low density image P2, and the medium density image P3.
[0057]
As described above, according to the present embodiment, a plurality of solid patch images Q1 are formed while changing the contrast potential, the respective image densities are detected by the patch sensor 17, and the increase in the contrast potential is applied to the photosensitive member 11. Since a high-density image forming condition in which the amount of adhered toner is substantially saturated is determined and a toner image is formed under the high-density image forming condition, a high-density image can be formed with high quality. Further, even when the state of the apparatus changes due to deterioration over time or the like, the above-described high-density image forming conditions can always be obtained.
[0058]
Further, according to the present embodiment, a plurality of low-density patch images Q2 are formed while changing the contrast potential, the respective image densities are detected by the patch sensor 17, and the toner on the photoconductor 11 with respect to the increase in the contrast potential is detected. A low-density image forming condition in which the amount of adhesion is almost saturated is determined, and a toner image is formed under the low-density image forming condition. Therefore, a low-density image including fine lines or isolated dots can be formed with high quality. it can. Further, even when the state of the apparatus changes due to aging, the low-density image forming condition can always be obtained.
[0059]
Further, according to the present embodiment, a plurality of medium-density patch images Q3 are formed while changing the contrast potential, and the respective image densities are detected. Since a medium density image forming condition that saturates is obtained and a toner image is formed under the medium density image forming condition, a medium density image including white fine lines or white isolated dots can be formed with high quality. it can. In addition, even when the state of the apparatus changes due to deterioration over time or the like, the above-described medium-density image forming conditions can be always obtained.
[0060]
Note that the present invention is not limited to the above embodiment, and various changes can be made to the above described one without departing from the gist thereof. For example, the following modified embodiments (1) to ( 6) can be adopted.
[0061]
(1) Although the solid patch image Q1, the low-density patch image Q2, and the medium-density patch image Q3 are used as the patch images in the above embodiment, the present invention is not limited to this. For example, only the solid patch image Q1 may be used. According to this aspect, the above-described high-density image forming condition can be obtained, and a high-density image can be formed with high quality by forming a toner image under the high-density image forming condition.
[0062]
Alternatively, for example, only the low-density patch image Q2 may be used as the patch image. According to this aspect, the low-density image forming conditions can be obtained, and a low-density image including fine lines or isolated dots can be formed with high quality by forming a toner image under the low-density image forming conditions. Can be.
[0063]
Further, for example, only the medium density patch image Q3 may be used as the patch image. According to this aspect, the medium density image forming condition can be obtained. By forming a toner image under the medium density image forming condition, a medium density image including a white thin line or a white isolated dot can be obtained with high quality. Can be formed.
[0064]
As the patch image, for example, any two of the solid patch image Q1, the low-density patch image Q2, and the medium-density patch image Q3 may be used. In particular, when an image forming condition that satisfies both the low-density image forming condition and the medium-density image forming condition is obtained by using two of the low-density patch image Q2 and the medium-density patch image Q3, the image forming condition is as shown in FIG. As shown, the high-density image forming condition is also satisfied, so that a high-density image can be easily formed with high quality without using the solid patch image Q1.
[0065]
(2) In the above embodiment, a charging bias by the charging unit 12, a developing bias applied to the developing roller 31, a primary transfer bias applied to the intermediate transfer roller 41, and a secondary transfer bias applied to the secondary transfer roller 42. In order to adjust the electrical control conditions such as, for example, a reference image of a predetermined pattern (for example, a solid image) is formed, the image density of the reference image is detected by the patch sensor 17, and the above-described electrical control is performed according to the detection result. The target control condition may be adjusted. According to this embodiment, the patch sensor 17 for detecting the image densities of the patch images Q1 to Q3 can also be used for detecting the image density of the reference image for adjusting the electric control conditions, and the increase in the number of parts can be suppressed. . Further, all or any of the patch images Q1 to Q3 for obtaining the image forming conditions may be made to function as the reference image. As a result, efficient patch processing can be performed.
[0066]
(3) In the above embodiment, the image density of the patch image formed on the photoconductor 11 is detected, but the density detection position is not limited to this. For example, the image density of the patch image primarily transferred from the photoconductor 11 to the intermediate transfer roller 41 may be detected. In this case, a patch sensor may be disposed facing the intermediate transfer roller 41 between the primary transfer position 44 and the secondary transfer position 45. In this embodiment, the intermediate transfer roller 41 corresponds to the “transfer medium” of the present invention, and the transfer bias generator 115 corresponds to the “transfer unit” of the present invention. Further, the configuration may be such that the patch image is transferred to the transfer paper 4 and the image density of the patch image is detected.
[0067]
Further, for example, a dedicated member (for example, a patch transfer roller) for transferring a patch image is disposed in contact with the photoconductor 11 or the intermediate transfer roller 41, and a transfer bias is applied to the dedicated member to transfer the image to the dedicated member. The image density of the applied patch image may be detected. In this case, the patch sensor may be arranged to face the dedicated member. In this embodiment, the dedicated member corresponds to the “transfer medium” of the present invention, and the unit that applies the transfer bias to the dedicated member corresponds to the “transfer unit” of the present invention.
[0068]
(4) In the above-described embodiment, the image forming condition in which the toner adhesion amount is saturated by detecting the image density of the patch image while increasing the developing bias Vb is obtained. However, the present invention is not limited to this. The maximum value of the developing bias Vb that can be applied may be obtained based on the characteristics of the apparatus described above, and a plurality of patch images may be formed while decreasing the developing bias Vb by a predetermined width from this maximum value.
[0069]
(5) In the above embodiment, the contrast potential Vcont is changed by changing the developing bias Vb. However, the present invention is not limited to this. Vcont may be changed. In this case, the charging bias generation unit 111 is controlled to change the charging potential Vd of the photoconductor 11 by the charging unit 12, or the exposure control unit 112 is controlled to change the light amount of the light beam 21 from the exposure unit 20. You can do it.
[0070]
(6) In the above embodiment, a printer that prints an image given from an external device such as a host computer on transfer paper has been described. However, the present invention is not limited to this, and a copier, a facsimile machine, or the like may be used. The present invention can be applied to general electrophotographic image forming apparatuses. In the above-described embodiment, the present invention is applied to a monochrome image forming apparatus. However, the present invention is not limited to this, and the present invention can be applied to a color image forming apparatus. .
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an internal configuration of a printer according to an embodiment of the invention.
FIG. 2 is a block diagram showing an electrical configuration of the printer.
FIG. 3 is an enlarged view of a developing nip portion.
FIG. 4 is a view for explaining a change in toner adhesion amount with respect to a contrast potential.
FIG. 5 is a diagram showing a surface potential profile of a photoconductor.
FIG. 6 is a diagram schematically illustrating a change in image density with respect to a change in a developing bias.
FIG. 7 is a diagram illustrating an example of a low-density patch image.
FIG. 8 is a diagram illustrating an example of a medium density patch image.
FIG. 9 is a flowchart of an image forming condition optimization processing routine;
FIG. 10 is a flowchart of a solid patch processing subroutine of FIG. 9;
FIG. 11 is a flowchart of a low-density patch processing subroutine of FIG. 9;
FIG. 12 is a flowchart of a middle-density patch processing subroutine in FIG. 9;
FIG. 13 is a flowchart of a middle-density patch processing subroutine in FIG. 9;
FIG. 14 is a flowchart illustrating a print processing routine.
DESCRIPTION OF SYMBOLS 4 ... Transfer paper (transfer medium), 11 ... Photoconductor (image carrier), 17 ... Patch sensor (density detecting means), 31 ... Development roller (developer carrier), 116 ... Memory (storage) 41) Intermediate transfer roller (transfer medium), 113 CPU, 114 developing bias generator (image forming unit), 115 transfer bias generator (transfer unit)

Claims (10)

An image carrier configured to carry an electrostatic latent image on its surface,
A developer carrier in which a developer in which a toner is dispersed in a liquid carrier is transported to a development position opposed to the image carrier while being carried on the surface thereof;
Applying a predetermined developing bias to the developer carrier, causing the toner in the developer carried on the developer carrier to adhere to the image carrier, and visualizing the electrostatic latent image with toner. Image forming means for forming a toner image;
Density detecting means for detecting the image density of a toner image as a patch image formed by the image forming means,
Forming multiple patch images while changing the contrast potential,
Determining image forming conditions under which the amount of toner adhered to the image carrier with respect to an increase in contrast potential is substantially saturated, based on the image densities of the plurality of patch images detected by the density detecting means;
An image forming apparatus which forms a normal toner image under the image forming conditions. The image forming apparatus according to claim 1, wherein a high-density image forming condition is obtained as the image forming condition using a solid image as the patch image. The image forming apparatus according to claim 1, wherein a low-density image including a fine line or an isolated dot is used as the patch image, and a low-density image forming condition is obtained as the image forming condition. 2. The image forming apparatus according to claim 1, wherein a medium density image forming condition including a white fine line or a white isolated dot is used as the patch image, and a medium density image forming condition is obtained as the image forming condition. 2. The image forming apparatus according to claim 1, wherein the image forming conditions satisfying at least two of the following high density image forming conditions, medium density image forming conditions, and low density image forming conditions are obtained. .
The high-density image forming condition is an image forming condition obtained by using a solid image as the patch image,
The medium-density image forming condition is an image forming condition obtained by using a medium-density image including a white thin line or a white isolated dot as the patch image,
The low-density image forming condition is an image forming condition determined using a low-density image including a fine line or an isolated dot as the patch image. The image forming apparatus according to claim 1, wherein a developer having a γ-saturation characteristic that an amount of toner adhered to the image carrier is substantially saturated with an increase in contrast potential is used as the developer. . The image forming apparatus according to claim 6, wherein the toner concentration in the developer is about 5% by weight to about 40% by weight. The image forming apparatus according to claim 1, wherein the density detecting unit detects an image density of a patch image formed on the image carrier. The image forming apparatus further includes a transfer unit that transfers the toner image formed on the image carrier to a transfer medium,
The image forming apparatus according to claim 1, wherein the density detecting unit detects an image density of a patch image transferred from the image carrier to the transfer medium. A predetermined developing bias is applied to a developer carrier that carries a developer in which a toner is dispersed in a liquid carrier, and the toner in the developer carried on the developer carrier adheres to the image carrier, and the image In an image forming method for forming a toner image by visualizing an electrostatic latent image on a carrier with toner,
Forming a plurality of toner images as patch images while changing the contrast potential;
Detecting image densities of the plurality of patch images;
A step of obtaining an image forming condition under which the amount of toner adhered to the image carrier with respect to an increase in contrast potential is substantially saturated, based on the detection result;
Forming a normal toner image under the image forming conditions.

Images