JPH09244472A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To output a stable image regardless of a difference in the material of a transfer material by providing an image forming condition setting means for setting the process parameter of an image forming means, in accordance with the kind of transfer material and the sticking quantity of a reference toner image measured by a measuring means. SOLUTION: A printer control part 30 obtains a measured value from an image sensor 26. A control panel 32 is connected to the printer control part, 30, to set/display various kinds of conditions. Before a normal image forming operation, the reference toner image 28 is formed in the nonimage region of a photoreceptor 10, with a normal image forming condition and detected by the image sensor 26, to adjust a developing bias, a surface potential, etc., in accordance with the detected value and stabilize an image. Therefore, the potentials of the developing bias and the surface of the photoreceptor are adjusted according to the transfer material used, to control the quantity of toner stuck onto the photoreceptor 10. Thus, an image having a desired density can be obtained regardless of the kind of transfer material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to image stabilization control of an image forming apparatus such as an electrophotographic printer.

[0002]

2. Description of the Related Art Most of the images created by an electrophotographic image forming apparatus are solid areas or halftone areas, and these images are output with the same input data in a color and a density that are determined with good reproducibility. Required to do so. However, due to changes in the photoconductor characteristics, development characteristics and charging characteristics in the electrophotographic process, the color and density change, and the stability of the image is impaired. Further, in a digital image forming apparatus, gradation is generally expressed by a combination of various halftone dots, lines, etc., and image fluctuations are caused by fluctuations in the printing area ratio for the same input data and fluctuations in the development amount per unit area. It occurs as a result. In order to respond to such image fluctuations, the development bias potential, photoconductor surface potential, laser exposure amount, etc. are adjusted by automatic density detection and automatic density control,
We are trying to stabilize the image.

[0003]

However, in an electrophotographic image forming apparatus, an image normally formed for plain paper is transferred to a transfer material having a different material, such as thick paper or OHP.
When an image is transferred onto a sheet, the electric field strength is reduced, which causes voids in characters and toner scattering. Further, in fixing an image on a thick paper or an OHP sheet, thermal efficiency is lowered and offset is applied. Also, OH
The image fixed on the P sheet has large light scattering at the edge of the dot, resulting in poor light transmission.

An object of the present invention is to provide an image forming apparatus which can output a stable image regardless of the difference in the material of the transfer material.

[0005]

An image forming apparatus according to the present invention is an image forming apparatus for forming an image on a transfer material by an electrophotographic process, and a transfer material setting means for identifying the transfer material and a pre-image forming operation. A measuring means for measuring the adhesion amount of the reference toner image formed on the photoconductor using a predetermined process parameter, the type of the transfer material set by the transfer material setting means, and the adhesion amount measured by the measuring means. Image forming condition setting means for setting process parameters of the image forming means so as to stabilize the toner adhesion amount on the photoconductor. As a result, the process parameters such as the developing bias potential and the photoconductor surface potential are adjusted according to the identified transfer material, and the target adhesion amount on the photoconductor can be obtained to stabilize the image. With a proper amount of adhesion on the transfer material, the thickness of the toner layer also becomes proper. In transfer, the decrease in electric field strength is also small. In fixing, the amount of transferred toner is also appropriate, so the decrease in thermal efficiency is small, and the transferred toner layer is also smoothed. Preferably, the image forming condition setting unit further includes a table that predetermines a mutual correspondence between process parameters for forming an equivalent toner image on the plurality of transfer materials. When a new transfer material is identified by the means, process parameters for the new transfer material corresponding to the process parameters set before the identification are set by referring to the table. Thereby, the setting can be simplified.

[0006]

Embodiments of the present invention will be described below with reference to the accompanying drawings. (a) Configuration of Full Color Printer FIG. 1 shows a printer according to an embodiment of the present invention. A photoconductor 10 as an image carrier having a surface coated with an organic photoconductive material (OPC) is rotatably provided in the direction of arrow A. Further, around the photoconductor 10 along the rotation direction thereof, the charging brush 12, the laser exposure device 14, the developing device 16, the intermediate transfer member 18, and the cleaner unit 2 are sequentially arranged.
0 is arranged. In this copying machine, the photoconductor 10 is
It rotates in the direction of arrow A and is charged to a constant potential by the discharge of the charging brush 12. Then, the laser exposure device 14 irradiates the surface of the photoconductor 10 with a laser beam according to image information, and an electrostatic latent image is formed on the charged region. next,
The electrostatic latent image is conveyed to the developing unit, where toner is supplied from the developing device 16 and visualized as a toner image. In the case of a full color printer, the above process is sequentially repeated by the four types of developing devices 16 for yellow, magenta, cyan and black. The toner image visualized on the photoconductor 10 is conveyed to a transfer portion, where it is transferred to the intermediate transfer member 18 to which a voltage having a polarity opposite to that of the toner is applied. Four
The color toner images are overlaid on the intermediate transfer member 18 to form a multicolor image. The multi-colored toner image is the final transfer member.
It is electrostatically transferred to a transfer material by (not shown), carried to a fixing device (not shown), and fixed on the transfer material by the fixing device. Further, the toner remaining on the photoconductor 10 without being transferred by the intermediate transfer portion is collected by the cleaner unit 20. The charging power source 22 applies a voltage to the charging brush 12, and the developing bias power source 24 applies a developing bias potential to the developing device 16. In addition, the image sensor 26
Are provided to detect the density of the toner image 28 on the photoconductor. The printer control unit 30 controls the charging power source 22 and the developing bias power source 24. The printer control unit 30 also obtains a measurement value from the image sensor 26. The operation panel 32 is connected to the printer control unit 30 and sets and displays various conditions.

FIG. 2 shows the operation panel 32. In this printer, in addition to the normal mode using a normal transfer material,
An HP mode and a cardboard mode are provided. The normal mode is a mode in which a normal transfer material (plain paper) is used. The OHP mode is a mode in which OHP paper is used. The thick paper mode is a mode using thick paper. The user can specify the OHP mode or the thick paper mode by using the OHP key 40 or the thick paper key 42 provided on the operation panel. In the following description, the thick paper mode will not be described, but the same processing as in the OHP mode may be performed. The operation panel 30 is provided with a key 44 for designating a paper size, a key 46 for designating online, and a display device 48 for displaying various information.

(B) Electrophotographic process The density and gradation characteristics of the output image are the sensitivity characteristics of the photosensitive member, the developing characteristics and the charging potential V _o , the developing bias potential V _B , and the potential V _s after the attenuation of the electrostatic latent image. Determined by settings. In a full-color image forming apparatus, basically, it is required to stabilize an image so that the input image data always has the same color and density. Before discussing image stabilization, a brief overview of the electrophotographic process is provided. In FIG. 1, a negative charging voltage V _c is applied from a charging power source 22 to a charging brush 12 installed opposite to the photoconductor 10. The charge voltage V _c, the surface potential of the photosensitive member is charged to V _o. Since V _o is a value proportional to V _c , the surface potential V _o of the photoconductor can be controlled by the charging voltage V _c . When the photoconductor is exposed by laser exposure from the laser exposure device 14, the potential of the charged photoconductor 10 decreases, and the surface potential transits from V _o to the attenuation potential V _s of the electrostatic latent image. The maximum exposed surface potential is V _i . Also, the attenuation potential V
_s changes as the surface potential V _o changes even with the same exposure amount.

The developing device 16 includes a developing bias power source 24.
Is applied with the developing bias potential V _B. When the exposed electrostatic latent image on the photoconductor 10 reaches the developing position, the developing device 1 changes according to the values of the attenuation potential V _s and the developing bias potential V _B.
Toner negatively charged by being conveyed onto the developing roller 6 adheres onto the photoconductor 10. When the attenuation potential V _s becomes lower than the developing bias potential V _B , the latent image is developed with toner to form a toner image. The amount of adhered toner that is developed increases as the development potential difference ΔV = | V _B −V _s | increases.

(C) Image Stabilization Control Using Detection of Reference Toner Image In the electrophotographic process, the developing characteristics and the photoreceptor characteristics change mainly depending on the use environment and the degree of durability, so that the image can be reproduced with good reproducibility. In order to stabilize, it is necessary to compensate for these characteristic fluctuations in advance. Therefore, before the normal image forming operation, a reference toner image 28 is formed in the non-image area of the photoconductor under the standard image forming condition, the reference toner image 28 is detected by the image sensor 26, and development is performed according to the detected value. The bias V _B , the surface potential V _o, etc. are adjusted to stabilize the image. In this stabilization control, when the amount of adhesion on the photoconductor is changed, it suffices to adjust the developing bias potential V _B , but since the area ratio of the dots is changed at this time, the gradation of the color is It will change. Therefore, the photoreceptor surface potential V
_o must be adjusted accordingly. The feature of the stabilization control of the present embodiment is that the developing bias potential V _B and the photoconductor surface potential V _o are adjusted according to the transfer material to be used to control the toner adhesion amount on the photoconductor, as described below. It is to be. This makes it possible to obtain an image having a desired density regardless of the type of transfer material.

In this full-color printer, gradation is represented by a variation of halftone dot structure. Therefore, one of the factors of the variation in color and density that hinders the stability of the image is the variation in the printing area ratio due to the variation in the dot size forming the halftone image. As the print area ratio increases, the image density increases. The other cause of variation is a variation in the height direction, which is a variation in the amount of toner developed in the dots forming the halftone image. Even if the dot size is the same, the larger the amount of developed toner, the darker the image. The change in the amount of toner developed in the dot occurs in synchronization with the change in the development amount of the solid image. Therefore, in order to stabilize the image and express gradation with good reproducibility, a stable image can be obtained by detecting a two-dimensional change such as a change in the print area ratio and a three-dimensional change such as a change in the development amount. Have to control.

FIG. 3 shows the construction of an image sensor 26 for detecting two different factors, that is, the area ratio of a halftone image and the development amount of a solid image. The image sensor 26 includes an LED 260 that emits a reference toner image 28 and two photo sensors 262 and 2 that detect reflected light from the reference toner image.
64. The first photo sensor 262 is an LED
It is installed at a position symmetrical to the normal line of 260 and the photoconductor 10 and used for detecting the area ratio of halftone dots. In addition, the second photo sensor 264 has the LED 26 with respect to the normal line of the photoconductor surface.
It is installed on the side of 0 and used for detecting the development amount of a solid image. 4 and 5 schematically show the reference toner images 280 and 282 detected by the image sensor 26. The first reference toner image 280 is a reference halftone dot image formed of halftone halftone dots of a predetermined size, and the second reference toner image 282 is a reference solid image of a predetermined size.

First, the detection of the area ratio of the halftone dot image using the first photo sensor 262 will be described. Before a normal image forming operation, a reference halftone dot image 280 (FIG. 4) composed of halftone halftone density (for example, half the maximum density) halftone dots is formed on the surface of the non-image area of the photoconductor 10 by a predetermined standard operation. Created by developing under image conditions. When the reference halftone dot image 280 passes through the image sensor 26, the LED 2 in the image sensor
60 is turned on, and the amount of reflected light from the reference halftone dot image 280 is
The photo sensor 262 installed at a position symmetrical to the LED 260 with respect to the normal line of the photoconductor 10 detects it. LED26
Light incident from 0 is hardly scattered on the surface of the photoconductor on which toner is not attached, and most of it is specularly reflected.
However, the light is scattered on the surface of the toner, and the light in the specular reflection direction is reduced. That is, most of the amount of light detected by the photo sensor 262 installed at a position symmetrical to the LED 260 with respect to the normal line of the photoconductor 10 is from the photoconductor surface of the reference halftone dot image 280 on which the toner does not adhere. It is specularly reflected light. Therefore, when the dot size of the reference halftone dot image 280 changes due to the characteristic change of the electrophotographic process,
Since the area of the exposed surface of the photoconductor that does not adhere to the toner changes and the amount of light reflected from the LED 260 also changes, the change in dot size can be detected by the photosensor 262.

On the other hand, regarding the detection of the development amount of a solid image,
A fully exposed reference solid image 282 (FIG. 5) is formed on the surface of the photoconductor under predetermined image forming conditions, and the amount of developed toner is measured by the second photosensor 262. The first photosensor 262 used for detecting the area ratio of the halftone image cannot be used for detecting the development amount of the solid image. The second photo sensor 264 is installed at a position closer to the LED 260 inside the angle formed by the LED 260 and the photoconductor normal. This allows
In the second photosensor 264, only the scattered light having a correlation with the adhesion amount is detected without the specular reflection component of the reflected light from the LED 260 entering, and the development amount of the solid image can be detected.

Next, the image stabilization control will be described with reference to the sensitometry diagram. FIG. 6 is a sensitometry diagram showing changes in the image when the developing bias potential V _B is changed. The sensitometry chart shows the exposure amount distribution of the latent image, the photoconductor characteristics, the development characteristics and the output image density distribution.
The exposure amount, the surface potential V _s , the output image density (ID) and the position are represented as a function. Now, when the developing bias potential V _B is increased from V _B1 to V _B2 (I → II in the developing characteristics), the saturation value V _i of the decay potential of the photoconductor 10 and the developing bias potential V _B
Difference (developing voltage) becomes larger (photoreceptor characteristics),
The solid image development amount can be increased (output image density distribution). In addition, the potential at which the development is started also rises, and the development is performed up to the bottom of the latent image (exposure amount distribution of the latent image).
The size of the dots can also be increased. FIG.
Is a sensitometry showing a change in the image (III → IV) when the photoreceptor surface potential V _o is changed instead of the developing bias potential V _B. The surface potential V _{o of the} photoconductor is changed from V _o1 to V _o2.
If the value is lowered to (photoreceptor characteristics), the exposure amount required to reach the potential at which development starts is reduced, so development is performed up to the bottom of the latent image and the dot size increases (latent image Exposure distribution). On the other hand, since the saturation value V _i of the attenuation potential does not change so much as the surface potential V _o changes (photoreceptor characteristic and developing characteristic), the development amount of the solid image does not change (density distribution of output image). Also, the laser exposure apparatus 1
The same change can be obtained by increasing the light amount of 4. From the above, in order to obtain the image of the desired density,
Reference halftone dot image 28 detected by the image sensor 28
Depending on the density level of 0 and the reference solid image 282, the development amount of the solid image adjusts the development bias potential V _B , and the halftone dot area ratio is the photoreceptor surface potential V _o , the development bias potential V _B or laser exposure. Adjust the amount. In this full-color printer, the control of the image density, dot area ratio adjusts the surface potential of the photosensitive member V _o.

Tables 1 to 4 are tables used by the printer control unit 30 in image stabilization control. Tables 1 and 2 are used when the transfer material identification signal is in the normal mode. Table 1 is a table of the developing bias potential set value V _B and the photoconductor surface potential reference value that are selected according to the density level of the reference solid image, and Table 2 is set according to the density level of the reference halftone dot image. it is a table of the photosensitive member surface potential V _o to be. Tables 3 and 4 are used when the transfer material identification signal is in the OHP mode. Table 3 shows the developing bias potential setting value V _B selected according to the density level of the reference solid image.
Table 4 is a table of photoreceptor surface potential reference values, and Table 4 is a table of photoreceptor surface potential V _o set according to the density level of the reference halftone dot image. In Table 1 and Table 3, the developing bias potential V _B and the surface potential reference value are determined corresponding to the amount of development of the reference solid image detected by the image sensor 26. Further, in Tables 2 and 4, the surface potential adjustment value is set corresponding to the change in the density of the reference halftone dot image created based on this surface potential reference value, and the surface potential V _o is set.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

[Table 3]

[0020]

[Table 4]

FIG. 8 is a flow chart for setting electrophotographic process parameters in the image stabilization control of the printer controller 30. First, a transfer material identification signal is detected in order to identify what the transfer material is (step S10). This is set by the key 40 on the operation panel 32 (FIG. 2). Next, a predetermined developing bias potential V _B and a photosensitive member surface potential V _o are set, a reference solid image is printed on the non-image area of the photosensitive member, and the density is detected by the image sensor 26 (step S12). Determine which density level the developed amount is. According to the result, the developing bias potential V _B is determined using Table 1 (normal mode) or Table 3 (OHP mode). Tables 1 and 3 are tables of the developing bias potential set value V _B and the photoconductor surface potential reference value that are selected according to the density level of the reference solid image in the normal mode and the OHP mode, respectively. Further, the developing bias potential V _B is set to this determined value (step S
14), a reference halftone dot image is formed at a predetermined photoconductor surface potential V _o set according to the level of the developing bias potential V _B , and the image sensor 2 detects the density of the image.
6 is performed (step S16), and the density level of the reference halftone dot image is determined. Then, according to the result in Table 2 (normal mode) or Table 4 to determine the surface potential of the photosensitive member V _o with (OHP mode) (step S1
8). Tables 2 and 4 are tables of the photoreceptor surface potential V _o set according to the density level of the reference halftone dot image in the normal mode and the OHP mode, respectively. The electrophotographic process parameter setting described above is performed for each color (cyan, magenta, yellow, and black). The setting operation is performed each time a new transfer material identification signal is received (that is, each time the transfer material is changed). After that, the image forming operation is performed based on the set electrophotographic process parameters.

FIG. 9 shows the developing bias potential V _B and the photoreceptor surface potential V _o using the offset tables (Tables 5 and 6).
7 shows a flow of the printer control unit 30 for determining the. Here, Table 5 is an offset table of the development bias potential V _B in the normal mode and the OHP mode, and Table 6 is
Photosensitive member surface potential V _o in the normal mode and the OHP mode
Is an offset table of. In this variation,
At startup, the flow of FIG. 8 is performed once to determine the developing bias potential V _B and the photoconductor surface potential V _o . Then, using the two tables of Table 5 (development bias potential V _B ) and Table 6 (photoconductor surface potential V _o ), for example, in the OHP mode, the development bias potential V _B and the photoreceptor surface potential V _o are , _Is determined based on the developing bias potential V _B and the photoreceptor surface potential V _o in the normal mode. Conversely, in the normal mode, the developing bias potential V _B and the photoreceptor surface potential V _o are
It is determined based on the development bias potential V _B and the photoconductor surface potential V _o in the OHP mode. That is, using this flow, every time a new transfer material identification signal is received (that is, each time the transfer material changes) (step S100), a new transfer material corresponding to the transfer material is displayed by the offset table (Table 5 and Table 6). Development bias potential V _B and photoreceptor surface potential V _o
Is uniquely determined (step S102). In this setting, since a simple offset table is used, there is some error from an appropriate value. However, there is an advantage that the trouble of performing the setting operation in FIG. 8 again can be saved.

[0023]

[Table 5]

[0024]

[Table 6]

Although the transfer material is manually selected on the operation panel 32 in the above-described embodiment, a transfer material having a different material from a normal transfer material may be automatically identified. Since the OHP sheet is transparent, the OHP sheet can be detected by optically detecting that the transfer material is transparent with an optical sensor. Further, the thick paper can be detected by measuring the thickness of the transfer material. For example, when the thickness measurement value exceeds the reference value, it may be determined as thick paper.

[0026]

According to the present invention, a transfer material having a different material from a normal transfer material, such as a thick paper or an OHP sheet, can be used.
Eliminates missing characters and toner scatter. Also,
The OHP sheet can output a stable image having good image transparency.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a main part of a printer.

FIG. 2 is a plan view of an operation panel.

FIG. 3 is a front view of the image sensor.

FIG. 4 is a diagram schematically showing a toner image of a reference halftone dot image.

FIG. 5 is a diagram schematically showing a toner image of a reference solid image.

FIG. 6 is a sensitometry diagram showing a change in an image when the developing bias potential V _B is changed.

FIG. 7 is a sensitometry diagram showing a change in image when the surface potential V _{o of the} photoconductor is changed.

FIG. 8 is a first flowchart of image stabilization control.

FIG. 9 is a second flowchart of image stabilization control.

[Explanation of symbols]

10 photoconductor, 12 charging brush, 16 developing device, 26 image sensor, 30 printer control unit, 32 operation panel, 40 OHP key.

Claims (2)

[Claims] 1. An image forming apparatus for forming an image on a transfer material by an electrophotographic process, wherein a transfer material setting means for identifying the transfer material and a predetermined process parameter before the image forming operation are used to form on the photoconductor. The toner adhesion amount on the photoconductor is stabilized according to the measuring means for measuring the adhered amount of the reference toner image, and the transfer material type set by the transfer material setting means and the adhered amount measured by the measuring means. And an image forming condition setting means for setting process parameters of the image forming means so as to be changed. 2. The image forming condition setting means further comprises a table in which correspondences between process parameters for forming the same toner image on a plurality of transfer materials are predetermined. When a new transfer material is identified by the material setting means, the process parameter for the new transfer material corresponding to the process parameter set before the identification is set by referring to the table. The image forming apparatus according to claim 2.