JPH07111591B2 - Color image forming apparatus - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a color electrophotographic copying apparatus or a color recording apparatus having a computer output section.

2. Description of the Related Art Recently, the demand for color copying and printing has rapidly increased not only in special fields but also in the field of general office work, and improvement in color image quality has been demanded.

Conventionally, in a color image forming apparatus using an electrophotographic photosensitive member, that is, in an apparatus such as a color electrophotographic copying apparatus, a color laser beam printer, etc., an appropriate color balance and image density are obtained, and they are maintained constant. It was difficult. In the current color image forming apparatus, the biggest cause of such a problem is to achieve a color-balanced full-color image by superimposing three-color images of cyan, magenta, and yellow. It is necessary to strictly adjust the image characteristics, that is, the characteristics of image density, gamma, and fog, and it is difficult for general users to make such adjustments. Also, due to changes in the temperature and humidity environment of the photoconductor and the developer. It is difficult to keep the image density of each color stable for a long time due to characteristic changes, characteristic variations, characteristic deterioration, and the like.

Conventionally, as measures against the above problems, (1) JP-A-53-37025.
As disclosed in Japanese Patent Publication No. JP-A-2003-264, a method of detecting the surface potential of a latent image on a photoconductor and controlling image forming conditions of charging and exposure to converge the surface potential to a constant value (surface potential control method),
And (2) as described in JP-A-54-134646, the toner image density on the photoconductor is detected to charge, expose,
There is a method (toner image density control method) of controlling the image forming condition of development to converge the toner image density to a constant value.

Problems to be Solved by the Invention The first surface potential control method is based on the characteristics of the photoconductor, charging characteristics,
Alternatively, the surface potential can be easily and precisely controlled with respect to the change of the exposure amount, but there is a problem that the image density changes when the developing characteristic changes.

On the other hand, in the second toner image density control method, it is difficult to accurately detect the image density in the fog area or in the halftone near the bright part, and fog occurs in the image on the hard copy after control. Or, the reproducibility of halftone was likely to decrease. Frequent control such as image density control for each copy easily causes toner consumption, an increase in the load on the cleaning device, and an increase in toner scattering in the device. Further, as compared with the surface potential control method in which a potential sensor is provided near the corona discharger to detect the surface potential and control the corona discharge current, in image density control, an image density sensor is provided after the developing device to reduce the image density. Since the corona discharge current is detected and the corona discharge current is controlled, the distance from the detection position to the control position becomes long, and therefore the time required for the control becomes long, and frequent control is problematic.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a color image forming apparatus capable of efficiently obtaining a color image having proper and stable color balance and image density.

Means for Solving the Problems The above object is achieved by the image forming apparatus according to the present invention. The present invention is summarized as follows: in a color image forming apparatus for forming a color image with a plurality of toner images, condition setting means for setting an image forming condition corresponding to each toner from a reference pattern formed on an image carrier. A storage unit that stores the image forming conditions set by the condition setting unit, and image formation is performed with the image forming conditions stored in the storage unit within a predetermined time from the image formation under the conditions set from the reference pattern. The color image forming apparatus is characterized in that the image forming condition is set again from the reference pattern when the image is formed after a predetermined time has elapsed.

Further, according to the present invention, in a color image forming apparatus for forming a color image with a plurality of toner images, condition setting means for setting an image forming condition corresponding to each toner from a reference pattern formed on the image carrier. A storage unit for storing the image forming conditions set by the condition setting unit, the image forming unit storing the image forming conditions set from the reference pattern up to a predetermined number of image forming times. There is provided a color image forming apparatus characterized in that an image is formed under the condition, and when the image is formed after a predetermined number of times of image formation, the image forming condition is set again from the reference pattern.

Next, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

FIG. 1 illustrates a mode in which the image forming apparatus according to the present invention is embodied in a color laser beam printer. In this embodiment, the photosensitive drum 1 is rotatably arranged at the approximate center of the apparatus. The photosensitive drum 1 having, for example, an amorphous silicon photosensitive member on its surface layer is first uniformly exposed by the pre-exposure lamp 2 and then charged to a positive polarity by the corona discharger 3.

Next, the background portion of the image is scanned and exposed on the photosensitive drum 1 by the semiconductor laser beam I to form an electrostatic latent image. The laser beam I is generated when the semiconductor laser 41 is driven by the laser driver which receives the recording information signal in the laser scanner 4, and then the scanning optical system including the rotating polygon mirror 42, the f.theta. It is projected as spot light on the photosensitive drum via.

The latent image on the photosensitive drum formed as described above is then developed by the developing device 5. The developing device 5 is composed of developing devices 51, 52, 53, and 54 having yellow, magenta, cyan, and black toners (negative polarity), and developing devices of a color designated according to the type of color of recorded information are used. Development is performed by sequentially rotating to the developing position.

On the other hand, the transfer paper P in the selected cassette 6 is fed into the machine by the paper feed roller 7, and the leading end of the transfer paper is gripped by the gripper 81 of the transfer drum 8. As the transfer drum 8 rotates, the transfer paper P is conveyed to the transfer unit while being wound around the mesh screen stretched around the cylinder cutout of the transfer drum.

In the transfer section, the transfer corona discharger 83 charges the back surface of the transfer paper through the opening of the mesh screen and also charges the back surface of the mesh screen to transfer the toner image on the photosensitive drum 1 to the transfer paper. At the same time, the transfer paper is electrostatically adsorbed on the surface of the mesh screen.

After the toner images sequentially formed on the photosensitive drum 1 are aligned and multi-transferred for four colors on the transfer paper P on the transfer drum 8, the gripper 81 is released and the separation claw 84 is operated. Separate the transfer paper.

Next, the transfer paper P is heated by the conveyor belt 9 to a heating roller fixing device.
The transferred toner image is guided to 10 and heated and fixed to obtain a full-color image.

The toner on the photosensitive drum 1 that has not been transferred is the cleaner 11
Collected by.

By the way, when the image is formed by the above procedure, the following steps are performed. In order to detect the density of the developed image (toner image) on the photosensitive drum, an image density sensor 12 is provided immediately after the developing position and close to the surface of the photosensitive drum 1. The electrostatic latent image pattern for detecting the image density is formed in the image forming area on the drum 1 at a predetermined timing by the pattern generator PT, so that the image density sensor 12 is located at a position corresponding to the detecting pattern in the drum axial direction. It is provided in.

The image density sensor 12 is an integrated light source that illuminates the surface of the photosensitive drum and an optical sensor that receives the reflected light. For example, a small tungsten lamp is used as the light source and visible light is absorbed immediately before the light receiving portion as the optical sensor. A silicon photodiode provided with a filter having a near infrared light transmission characteristic (for example, SC-74 filter manufactured by Fuji Photo Film) is used. Thus, by detecting the image density with near-infrared light, a color toner having a high reflectance for near-infrared light and an amorphous silicon having a high absorptivity (low reflectance) for near-infrared light The toner image density can be measured by utilizing the characteristics of the photosensitive drum. That is, regardless of the color of the toner, the toner image density is detected by utilizing the phenomenon that the reflected light intensity of the near infrared light by the toner increases when the amount of toner adhered is large. If used, this phenomenon can be utilized).

Further, a potential sensor 13 for detecting the surface potential of the latent image pattern for image density detection is provided immediately after the exposure section, in proximity to the drum surface, and in the axial direction at a position corresponding to the image density sensor 12. .

FIG. 2 is a block diagram for explaining one embodiment of the image density control circuit of the apparatus shown in FIG. Only the essential parts of the photosensitive drum and its periphery are shown.

In this embodiment, a photo disk and a photo interrupter (not shown) for detecting the rotation angle of the photosensitive drum 1.
As a result, a drum clock pulse corresponding to the drum rotation angle is output. This clock pulse is counted by the main sequence controller 107 of the device, and the controller 107
In this way, a timing signal for measuring the surface potential or the density of the developed image (toner image) and a timing signal for switching the high voltage, the developing bias voltage, the laser beam intensity, etc. are supplied to the image density controlling microcomputer 109.

The toner image density detected by the image density sensor 12 is measured by the image density measuring circuit 111, converted into a digital signal by the A / D converter 113, and then supplied to the computer 109.
Similarly, the drum surface potential detected by the surface potential sensor 13 is measured by the surface potential measuring circuit 115, and the A / D converter 11
After being converted into a digital signal in 7, it is supplied to the computer 109. The computer 109 calculates according to a control formula so that the toner image density D converges to the density target value Do of each color toner which is selected and set in advance by the switch board 119. Also, the computer 109 calculates according to a control formula so that the dark surface potential Vd converges to the surface potential target value Vdo of each color toner stored during the image density control process described later.

The signal of the above calculation result is supplied to the D / A converter 123 via the bus line 121 and converted into an analog signal. The analog-converted signal is supplied to the power supply control circuit 125, which controls the high-voltage power supply 127 to control the discharge current Ip of the corona discharger 3. Similarly, an analog signal is supplied to the power supply control circuit 129 to control the power supply 131 to control the developing bias voltage Vdev applied to the developing device 5.

3 to 5 are flowcharts showing the control operation of the image forming apparatus according to the present invention.

Referring to FIG. 3, when the operation start button is pressed in the image forming apparatus according to the present invention, the timer count memory used for the purpose described later is reset. Next, prior to the image forming operation, control of charging conditions and developing bias conditions for forming target values is performed for each color (condition control), and subsequently, charging and developing bias control for image formation of each color are performed (image forming). Control), and then the image forming work is performed. When the image forming work is completed, the timer starts counting for the purpose described later.

Next, the condition control will be described in more detail. When the operation start button is pressed, first, the image density control is started. As can be understood from FIG. 4, whether the image forming work (copy work in this embodiment) currently being performed in steps 1 and 2 is in continuous copying, and how many hours have elapsed after the timer count was started. Is determined. 1
In the case of the first copy, negative determination is made in step 2, and when the target dark portion potential Vdo is not set in step 3, charging and developing bias condition control operations for each color are performed.

In performing such a condition control operation, the discharge current Ip of the corona discharger 3 having an initial value preset for each color is output, and the photosensitive drum is charged. Then, the drum surface is scanned and exposed by the laser beam based on the signal from the pattern generator to form a latent image pattern for image density detection (step 4). The surface potential Vd of the latent image pattern (dark portion) and the light portion potential Vl of the exposure area (corona discharge current is given under the same conditions as the dark portion) adjacent to the latent image pattern.
Is detected by the potential sensor 13 (step 5). A developing bias voltage Vd applied to the developing device when the latent image pattern is developed by adding a predetermined voltage to the detected light portion potential Vl.
ev is required (step 6).

The latent image pattern is developed with one color of each color toner, for example, a yellow toner to form an image density detection pattern. The image density Dd of the image density detection pattern is detected by the sensor 12 (step 8), and the detected density Dd and the target density Ddo are compared (step 9). Where | Dd−Dd
Determine whether o | is within the tolerance C ₁ . If negative determination, control formula for corona discharge current Ip ΔIp = αΔDd (α is a constant)
Control (step 10). Then, the process returns to step 4, and the steps from step 4 to step 10 are repeated. | Dd
-Ddo | tolerances C proceeds to step 11 if a positive determination is made in ₁ in the now step 9, the surface potential in the affirmative decision and summer were detected concentrations Dd control process after the surface potential Vd of the corresponding latent image pattern on The control target value Vdo is stored in the computer 109. The above steps are performed for each color, the conditions (target dark area potential) Vdo for all colors are set, and the condition control operation is completed (step 12).

When the above condition control operation is completed, the image forming apparatus shifts to the image formation control operation. Referring to FIG. 5, a corona discharge current Ip having a preset initial value for each color is output and the photosensitive drum is charged (step 13). Next, the dark potential Vd on the photosensitive drum is detected by the surface potential sensor 13 (step 14), and the detected potential Vd and the target potential Vdo are compared (step 15). Here, it is determined whether or not | Vd−Vdo | is within the allowable error C ₂ . If a negative determination is made, in step 16, the corona discharge current Ip is controlled according to the control equation ΔIp = βΔVd (β is a constant). Then, the process returns to step 13 and the steps 13 to 16 are repeated.

If | Vd−Vdo | falls within the allowable error C ₂ and a positive determination is made in step, the process proceeds to step 17. At this time, the corona discharge current Ip that gives the detection potential Vd that is determined to be affirmative is stored in the computer 109 and output as the corona discharge current at the time of making a hard copy later.

Then, under the output of the corona discharge current Ip, the operation exposure by the laser beam is performed based on the signal of the pattern generator (step 17), and the bright portion potential Vl is detected (step 18). Further, in step 18, a predetermined potential is added to the bright portion potential Vl to generate a developing bias voltage during hard copy formation.
Vdev is sought and stored in computer 109 along with the above Ip.

The above steps are performed for each color, the charging and developing bias conditions for image formation of all colors are set, and the image forming control operation is completed. When the image forming control operation is completed,
The image forming apparatus carries out an image forming operation, and is then reset (steps 19 to 22).

Returning to FIG. 4, the case of continuous copying will be described. If the affirmative judgment is made in Step 1 and the memory of the target dark portion potential Vdo exists, the above condition control operation is not necessary and the process immediately proceeds to the image formation control operation shown in FIG.
On the other hand, when there is no memory for the target dark area potential Vdo, the above condition control operation is performed, and then the image control operation is performed.

Furthermore, according to another feature of the invention, step 2 is provided for the conditional control operation. That is, when the image forming apparatus starts the operation, that is, when the copy operation is performed after the lapse of the predetermined time (T) after the start of the timer count, even if the condition target dark portion potential Vdo (step 3) is stored, The point is that the condition control operation for the target value is performed again.

As can be understood from the above description, according to the feature of the present invention, the control interval of the image density control is such that the change of the developing characteristic of the toner (image density characteristic with respect to the surface potential) is the latent image characteristic (exposure amount Since it occurs in a longer period than changes in surface potential characteristics with respect to logarithm, changes in charging, and exposure conditions, first condition control (step 1 to step 1) is performed before hard copy creation.
2) and image forming control (steps 13 to 18) are performed, and thereafter, when the next copy is made within a predetermined time T after the previous copy is made, for example, when the next copy is made after about 10 minutes. Only the image forming control process (steps 13 to 18) is performed in advance, and when a predetermined time T has passed after the previous copy was made, for example, two hours or more have passed, the condition for making the next copy must be met in advance. Control (steps 1 to 12) and image forming control (steps 13 to 18) are performed.

As another example, the count T may be the number of copies instead of the predetermined time. First, the condition control (step 1 to step 12) and the image formation control (step 13 to step 18) are performed before the hard copy is made, and thereafter 100
After making one copy, only the image formation control (step 13 to step 18) is performed before making another copy, and after making 1000 copies, the condition control (step 1 to step 1) is made before making another copy. Step 12) and image formation control (steps 13 to 18) are performed.

As described above, in the color image forming apparatus of the present invention, the number of times of image density control relating to the developing characteristics that fluctuates over a relatively long period is reduced, and the photosensitive member that fluctuates over a relatively short period of time is reduced. By increasing the number of times of image density control relating to the characteristics, charging and exposure characteristics, it is possible to control the image density with high accuracy and efficiency, and obtain a hard copy having proper and stable color balance and image density.

The embodiment of the present invention has been described in the color laser beam printer by the back ground scanning method in which the laser beam is applied to the background portion of the image and the toner is attached to the final exposure portion by regular development. It may be applied to a color laser beam printer by an image scanning method in which toner is attached to the exposed portion to which a laser beam is applied by reverse development. Of course, it may be applied to an analog type color electrophotographic copying apparatus.

[Brief description of drawings]

FIG. 1 is an apparatus configuration diagram showing an embodiment of a color image forming apparatus embodying the present invention. FIG. 2 is a block diagram of the image density control circuit in the apparatus of FIG. FIG. 3 is a flow chart showing the operation of FIG. FIG. 4 is a flow chart of condition control. FIG. 5 is a flowchart of image control. 1: Photosensitive drum 3: Corona discharger 4: Laser scanner 5: Development device 8: Transfer drum 12: Image density sensor 13: Potential sensor 107: Sequence controller 109: Microcomputer for image density control 111: Image density measurement circuit 115: Surface Potential measuring circuit

Claims (2)

[Claims] 1. In a color image forming apparatus for forming a color image with a plurality of toner images, condition setting means for setting an image forming condition corresponding to each toner from a reference pattern formed on an image carrier, and the condition setting means. A storage unit for storing the image forming condition set by the setting unit, and the image forming is performed under the image forming condition stored in the storing unit within a predetermined time from the image formation under the condition set from the reference pattern. A color image forming apparatus, wherein the image forming condition is set again from the reference pattern when the image is formed after a predetermined time has elapsed. 2. A color image forming apparatus for forming a color image with a plurality of toner images, and condition setting means for setting an image forming condition corresponding to each toner from a reference pattern formed on an image carrier, and the condition setting means. A storage unit for storing the image forming conditions set by the setting unit, and the image is formed under the image forming conditions stored in the storage unit from the image formation under the set conditions to the predetermined number of image formations based on the reference pattern. A color image forming apparatus characterized in that image forming conditions are set again from a reference pattern when forming an image after a predetermined number of times of image formation.