JPH10319667A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a toner image from color slippage or position-shifting caused by a density deficiency of positioning patch serving as a positioning reference for respective patch pattern of plural colors for the density control. SOLUTION: Relating to this device the positioning patch YO is formed with a specific color (yellow for instance), that is detected by the density sensor and defined as the positioning reference. The density control is performed by defining this as the reference, forming the patch pattern for the density control of respective color (yellow, magenta and cyan), detecting these by the density sensor, and changing the image forming condition (such as bias) by controlling means based on the result thereof. When the residual toner of yellow is reduced, since the density of the positioning patch YO falls and the output of the density sensor does not reach the specified value, the reference value can not be precisely set, hence the color slippage and the position-shifting occurs on the color toner image. Accordingly, the positioning patch MO is formed by the color for which the output of the density sensor becomes beyond the specified value, excepting the yellow (yellow for instance). In such a manner, the reference position is precisely determined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a copying machine and a laser beam printer.

[0002]

2. Description of the Related Art An intermediate transfer member (for example, an intermediate transfer drum)
In a four-color full-color image forming apparatus using
Prior to image formation, for each color of yellow, magenta, cyan, and black, for example, 14 mm ×
Several types of density control toner images (hereinafter referred to as “patch patterns”) having a size of 16 mm are printed by changing the density. The density of the patch pattern is detected by a density sensor provided near the intermediate transfer member, and the density is measured. Among the measured densities, a value close to the target density or an average value of large and small values close to the target density is calculated, and feedback is provided to, for example, a developing bias or a drum potential so that the density becomes appropriate. . After the appropriate conditions for the print density are obtained in this way, a yellow toner image is formed on the photosensitive drum based on the image data signal, and this toner image is primarily transferred onto the intermediate transfer member. This primary transfer is also performed for the other three colors, that is, magenta, cyan, and black, and a four-color toner image is superimposed on the intermediate transfer member. Thereafter, the four color toner images are collectively secondary-transferred onto a transfer material such as paper by a secondary transfer roller. The toner image is fixed on the transfer material after the secondary transfer by a fixing device. On the other hand, the secondary transfer residual toner is removed from the intermediate transfer body after the secondary transfer by the cleaning device.

The above-described image density changes when the surface of the intermediate transfer member becomes dirty due to various conditions such as the environment in which the image forming apparatus is used, the number of prints, and the like, so that an original correct color tone cannot be obtained. Therefore, when the power is turned on, when the photosensitive drum is replaced, when the developing unit is replaced, after a predetermined number of sheets have been printed, when the environment changes, etc., a patch pattern for density detection is formed for each color on the intermediate transfer body to obtain the correct color tone. Then, the density is automatically detected by a density sensor, and the detection result is fed back to image forming conditions such as an exposure amount and a developing bias, and density control is performed to form an original color image.

In the above-described density sensor, first, the output value detected by the light emitting portion (emits a spot light having an infrared light wavelength of 950 nm) and the light receiving portion for the surface density of the intermediate transfer member is set to 2.0 V. Is done. According to this setting,
Pure white (Canon stock recommended color laser copy CLC paper 5
The output value in (overlapping) is 5.0V. When a patch pattern is printed on the intermediate transfer member with, for example, black toner, the output value decreases from 2.0 V as the toner density increases, and a value close to 0 V appears in solid black. In the case of the color toner, as the toner density increases, the amount of light reflected from the light emitting unit increases, and the output value of the light receiving unit becomes 5.
It approaches 0V.

[0005] As shown in FIG.
The patch pattern P is formed on the intermediate transfer drum 511 rotating in the direction, and is read by the density sensor 81. At this time, the position of the patch pattern P and the density control sensor 81
So that the read timing is synchronized, that is,
The irradiation light of the sensor light source of the density control sensor hits the center in the rotation direction of the patch pattern P, and the patch pattern of three colors (magenta, cyan, and yellow) is read so that the light reflected from the center can be read by the light receiving sensor. Prior to printing P, a toner image serving as a position reference (hereinafter referred to as a “positioning patch”, particularly a yellow one is referred to as a “patch Y0”) is printed with yellow toner and synchronized therewith. I have.

[0006]

However, the amount of toner used for each color is not uniform among users. For example, for a user who frequently uses yellow, yellow toner is consumed more than toners of other colors. Therefore, the density of the patch Y0 may not be sufficiently obtained. In this case, the patch Y0 may not be detected by the density sensor 81, and the following problem occurs. Since the writing position of the image is different depending on the color, even if the image is output with two or more colors superimposed, the color is shifted to each color and the image quality is degraded. The leading edge position of writing starts to shift greatly in one transfer material,
There is a case where the margin is too large or the writing part is missing due to a mismatch with the paper feed timing.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a color image forming apparatus capable of preventing a color shift and a positional shift of a leading end of an image.

[0008]

According to the first aspect of the present invention, there is provided an image carrier having a movable image forming surface on which toner images of a plurality of colors are sequentially superimposed, and each color image on the image carrier. Density detecting means for detecting the density of a density-detecting patch pattern formed of the toner, and control means for adjusting the density of the toner image by changing image forming conditions based on the output of the density detecting means. In the image forming apparatus, the density detecting means is formed in a predetermined color on the image carrier prior to forming the patch pattern of each color, in order to improve the printing position accuracy and reading accuracy of the patch pattern of each color. The control unit adjusts the position of the patch pattern based on the output of the density detection unit, and reads the position of the patch pattern. If the output from the density detection unit does not reach a certain value when the positioning patch of the predetermined color is detected, the color of the toner forming the positioning patch is changed to another color capable of outputting a certain value or more, It is characterized by the following.

According to a second aspect of the present invention, the density detecting means receives the light reflected by the toner image on the image carrier, out of the spot light. A reflection type optical sensor having a light receiving section;
It is characterized by the following.

According to a third aspect of the present invention, the width of the patch pattern of the positioning patch in the moving direction of the image forming surface is set substantially equal to the spot diameter of the spot light, and the movement of the image forming surface is controlled. Accordingly, a position at which the reflected light of the spot light that scans the positioning patch has a peak value is set as a reference position.

[Operation] The main operation (operation corresponding to claim 1) based on the above configuration is as follows. When the density of the positioning patch for the position reference of the predetermined color is detected by the density detecting means, if the density is low and the output from the density detecting means does not reach a certain value, the color of the toner forming the positioning patch is changed to By changing the color to another color capable of outputting a certain value or more, when the changed position patch is detected by the density detecting means, a value equal to or more than a certain value is output. Based on this position patch, the density control of each color is performed. And the printing position accuracy and reading accuracy of the patch pattern can be maintained satisfactorily.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> FIG. 1 schematically shows a schematic configuration of a color image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 1 is a four-color full-color laser beam printer. The “image carrier” in claims 1 to 3 of the present invention corresponds to the intermediate transfer drum 51 in FIG.

A laser beam printer (hereinafter, referred to as “image forming apparatus”) shown in FIG. 1 includes an electrophotographic drum-type photosensitive member (hereinafter, referred to as “photosensitive drum”) 1.

The photosensitive drum 1 is constituted by providing a photosensitive layer of OPC (organic optical semiconductor) or the like on the outer peripheral surface of a metal drum base, and the surface is an image forming surface on which a toner image is formed. The photosensitive drum 1 is driven to rotate in a direction indicated by an arrow R1 by a driving unit (not shown). Around the photosensitive drum 1, a charging unit 2, an exposing unit 3, a developing unit 4, a transferring unit 5, a cleaning unit 6, and the like are arranged substantially in order along the rotation direction.

The transfer means 2 has a charging roller (charging member) 21 arranged in contact with the surface of the photosensitive drum 1 and a charging bias power supply (not shown) for applying a charging bias thereto. Polarity, uniformly charged to a predetermined potential.

The exposure means 3 has a laser oscillator, a polygon mirror (both not shown) and the like, irradiates the surface of the photosensitive drum 1 with light based on image information, and forms an electrostatic latent image on the surface of the photosensitive drum.

The developing device 4 includes a fixedly disposed black (Bk) developing device 4Bk and three movable developing devices mounted on the rotary 4A, ie, yellow (Y) and magenta (M). ), Developing device 4 for cyan (C)
Y, 4M, and 4C. The three movable developing units are arranged at developing positions where the developing units for developing the electrostatic latent image on the photosensitive drum 1 are opposed to the photosensitive drum 1 by the rotation of the rotary 4A. Note that, in the figure, the yellow developing device 4Y is arranged at the developing position. The developing means 4 develops a toner image by attaching toner to the electrostatic latent image on the photosensitive drum 1 by these developing devices.

The transfer means 5 includes an intermediate transfer drum (image carrier) 51 formed in a cylindrical shape. The intermediate transfer drum 51 is grounded and driven to rotate in the direction of arrow R5. A primary transfer bias is applied to the intermediate transfer drum 51 by a primary transfer bias power supply 52, whereby the toner image on the photosensitive drum 1 is transferred to the intermediate transfer drum 51.
The primary transfer is performed.

The cleaning means 6 has a cleaning blade (not shown) arranged in contact with the surface of the photosensitive drum 1 and removes the primary transfer residual toner remaining on the photosensitive drum 1 without being primarily transferred to the intermediate transfer drum 51.

Below the intermediate transfer drum 51, there is provided a secondary transfer belt 55 stretched over a secondary transfer roller 53 and a driving roller 54. A secondary transfer bias is applied to the secondary transfer roller 53 from a secondary transfer bias power supply (not shown), whereby the transfer material S such as paper fed through the registration roller 71 is applied to the intermediate transfer drum 53. 51
The upper four toner images are collectively secondary-transferred. The transfer material S after the secondary transfer of the toner image is heated and pressed by the fixing device 72 to fix the toner image on the surface. On the other hand, the secondary transfer residual toner remaining on the surface of the intermediate transfer drum 51 after the secondary transfer without being transferred to the transfer material S is removed by the cleaning device 56. The cleaning device 5
Reference numeral 6 denotes a secondary transfer residual toner charged on the intermediate transfer drum 51 to the opposite polarity, and the secondary transfer residual toner charged to the opposite polarity is used to transfer the toner image on the photosensitive drum 1 to the intermediate transfer drum 51. Simultaneously with the primary transfer upward, the toner image is transferred from the intermediate transfer drum 51 to the photosensitive drum 1 and removed by the above-described cleaning means 6.

Further, a density sensor 81 for density control is provided so as to face the surface of the intermediate transfer drum 51. The density sensor 81 includes a light emitting unit and a light receiving unit (both not shown), and emits spot light from the light emitting unit to a patch pattern formed on the surface of the intermediate transfer drum 51, and receives the reflected light. The light is received by the unit, and the density is detected based on the amount of light at this time. Density sensor 81
Is connected to the control device 82, and the control device 82
Based on the output of the density sensor 81, image forming conditions such as the exposure amount of the exposure unit 3 and the developing bias of the developing unit 4 are changed to control the image density to be appropriate.

In the above-described image forming apparatus, first, the photosensitive drum 1 is rotated in the direction of arrow R1, and the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity and a predetermined potential by the charging roller 21. Next, exposure based on the yellow image information is performed by the exposure unit 3 to form an electrostatic latent image on the photosensitive drum 1 for yellow. By rotating the rotary 4A, the yellow developing unit 4Y is arranged at the developing position, and toner is adhered to the electrostatic latent image on the photosensitive drum 1 to develop as a yellow toner image. This toner image is primarily transferred onto the intermediate transfer drum 51 by applying a primary transfer bias to the intermediate transfer drum 51 by a primary transfer bias power supply 52. Photosensitive drum 1 after primary transfer of toner image
After the primary transfer residual toner is removed by the cleaning unit 6, the toner is used for forming a toner image of the next color.

The above-described series of operations are performed for the other three colors, that is, cyan, magenta, and black, and the toner images of four colors are superimposed on the intermediate transfer drum 51. The toner images of the four colors are collectively and secondarily transferred onto the transfer material S by applying a secondary transfer bias to the secondary transfer roller 53, and then fixed on the transfer material S by the fixing device 72. You. The secondary transfer residual toner on the intermediate transfer drum 51 is charged to the opposite polarity by the cleaning device 56, transferred to the photosensitive drum 1, and then removed by the cleaning device 56. Thus, a four-color full-color image is formed.

In the image forming apparatus having the configuration and operation described above, when the power of the image forming apparatus main body is turned on,
The cleaning operation of the intermediate transfer drum 51 and the photosensitive drum 1 is performed. Thereafter, prior to printing the above-described patch pattern on the intermediate transfer drum 51, a position reference using yellow toner is performed to align the density sensor 81 shown in FIG. 2 with the patch pattern P on the intermediate transfer drum 51. The patch Y0 (printing patch) is printed. The patch Y0 is equal to or slightly smaller in the sub-scanning direction (the rotation direction of the intermediate transfer drum 51; the vertical direction in FIG. 3) than the spot diameter at which the light emitting portion of the density sensor 81 irradiates the surface of the intermediate transfer drum 51. Printing is performed at a small width of 6 mm, and printing is performed at 16 mm, which is sufficiently larger than the spot diameter in the main scanning direction (horizontal direction in FIG. 3).

The lower part of FIG. 3 shows the output value (sensor output value) V of the light receiving portion with respect to the moving distance of the patch Y0 on the intermediate transfer drum 51. The peak of the sensor output value indicates 4.0 V when the center of the spot substantially coincides with the center of the patch Y0 in the sub-scanning direction.

The patch pattern P of each color is formed using the position indicating the peak value of 4.0 V as a reference position, and an image is formed. That is, after the reference is determined, a patch pattern of 14 mm in the sub-scanning direction and 16 mm in the main scanning direction is printed by sequentially changing the developing bias in eight steps with magenta toner. The density of the patch pattern at this time is read by the density sensor 81, and an appropriate magenta developing bias is obtained from a target sensor output value. Hereinafter, an appropriate developing bias is similarly obtained for other colors.

Thereafter, when a print command is input from, for example, a host computer (not shown), an electrostatic latent image corresponding to each color is sequentially formed on the photosensitive drum 1, and magenta, cyan, yellow, and black are sequentially arranged. , And are sequentially developed with the previously adjusted developing bias. After these toner images are sequentially primary-transferred to the intermediate transfer drum 51 in sequence, the toner images are collectively transferred onto a transfer material S supplied from a paper feed cassette (not shown) via a registration roller 71 by a secondary transfer roller 53 or the like. Then, the toner image is secondary-transferred and then fixed by the fixing device 72.

In the first embodiment, a patch Y0 serving as a position reference for density control is formed by yellow toner by the above-described method. However, when the consumption of yellow toner is large and the sensor output cannot be sufficiently obtained when the patch Y0 is printed, as shown in FIG. 4, when the maximum output of the patch Y0 becomes 2.5 V or less, When the contrast becomes 0.5 V or less with respect to the output 2.0 V of the base of the transfer drum 51, a magenta patch M0 is formed instead of the yellow patch Y0, and the patch pattern P of each color is formed based on the magenta patch M0. Print and perform density control. As a result, even if the positioning is difficult with the yellow toner, the positioning can be performed with other colors, and a clear image can be obtained.

<Embodiment 2> When the output of the patch Y0 with the yellow toner cannot be sufficiently obtained and the command from the host computer is a single color other than yellow (for example, black), the density sensor is used. The patch Bk0 is printed with black toner in order to align the 81 with the patch pattern P on the intermediate transfer drum 51. That is, when the command from the host computer is a single color, a positioning patch corresponding to the color is printed. In the case of the second embodiment, it is a black patch Bk0, and its size is 6 mm × 14 mm, as in the first embodiment. In the case of the patch Bk0, as shown in FIG. 5, the peak value is about 0.7V with respect to 2.0V of the base of the intermediate transfer drum 51. As described above, in the case of a single color, by using the positioning patch Bk0 and the patch pattern P that match the color used by the user, efficient toner consumption can be performed, and an appropriate image can be obtained.

<Embodiment 3> When the output of the positioning patches of each of the colors magenta, cyan and yellow is not sufficiently obtained, the positioning patches may be formed by overlapping two or more colors. For example, as shown in FIG.
Even when the voltage is 5 V or less, a sensor output close to 3 V can be obtained by overlapping magenta and cyan. In the third embodiment, a positioning patch is formed by overlapping color toners. In this case, an appropriate image quality can be obtained for an image formed only with black toner.

The present invention can be widely applied not only to the color image forming apparatus shown in FIG. 1, but also to other general color image forming apparatuses. For example, even if the same intermediate transfer member as described above is used, a belt-shaped intermediate transfer belt is used instead of the above-mentioned intermediate transfer drum 5, or a transfer material is wound around the surface of the transfer drum, A toner image of a plurality of colors is sequentially formed on the transfer material, and these toner images are sequentially transferred to the transfer material on the transfer drum described above. be able to.

[0033]

As described above, according to the present invention,
When the toner amount of the toner of a predetermined color forming the positioning patch decreases and the output of the density detecting unit becomes insufficient, the output of the density detecting unit is formed by forming the positioning patch with toner of another color. The reference position can be detected with high accuracy by setting the value to a certain value or more, so that the printing position accuracy and the reading accuracy of the patch pattern of a plurality of colors formed based on the reference position can be maintained with high accuracy. It is possible to form a clear color image without any shift or position shift.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus according to the present invention.

FIG. 2 is a diagram illustrating a positional relationship among an intermediate transfer drum, a density sensor, a Y0 patch, and a patch pattern.

FIG. 3 is a diagram showing a relationship between a position of a spot light in a sub-scanning direction and a sensor output in a Y0 patch.

FIG. 4 is a diagram illustrating a relationship between a position of a spot light in a sub-scanning direction and a sensor output in a Y0 patch and an M0 patch.

FIG. 5 is a diagram illustrating a relationship between a position of a spot light in a sub-scanning direction and a sensor output in a Bk patch.

FIG. 6 is a diagram illustrating a relationship between a position of a spot light in a sub-scanning direction and a sensor output in a two-color superimposed patch.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum 2 charging means 3 exposure means 4 developing means 4Bk black developing device 4C cyan developing device 4M magenta developing device 4Y yellow developing device 5 transfer means 6 cleaning means 51 image carrier (intermediate transfer drum) 81 density detection Means (density sensor) 82 Control means Bk0 Black positioning patch M0 Magenta positioning patch Y0 Yellow positioning patch P Density detection patch pattern S Transfer material

Claims (3)

[Claims] An image carrier having a movable image forming surface on which a plurality of color toner images are sequentially superimposed, and a patch pattern for density detection formed on the image carrier with toner of each color. An image forming apparatus comprising: a density detecting unit configured to detect a density; and a control unit configured to change an image forming condition based on an output of the density detecting unit to adjust the density of the toner image. In order to improve the printing position accuracy and reading accuracy of the patch pattern of each color, read the position of a positioning patch for position reference formed in a predetermined color on the image carrier prior to forming the patch pattern of each color, The control means adjusts the position of the patch pattern based on the output of the density detection means, and adjusts the position of the patch pattern when the density detection means detects the positioning patch of the predetermined color. If the output from the concentration detecting means does not reach a constant value,
A color image forming apparatus, wherein the color of the toner forming the positioning patch is changed to another color capable of outputting a certain value or more. 2. A reflection type wherein said density detecting means has a light projecting unit for irradiating a spot light, and a light receiving unit for receiving, of said spot light, light reflected by a toner image on said image carrier. The color image forming apparatus according to claim 1, wherein the color image forming apparatus is an optical sensor. 3. A width of a patch pattern of the positioning patch in a moving direction of the image forming surface is set to be substantially the same as a spot diameter of the spot light, and the width of the patch on the positioning patch is moved with the movement of the image forming surface. 3. The color image forming apparatus according to claim 2, wherein a position at which the reflected light of the spot light for scanning the image reaches a peak value is set as a reference position.