JPS61254961A - Color image forming device - Google Patents

Abstract

PURPOSE:To obtain a color image which has proper and stable color balance and density by setting image formation condition on the basis of target condition signals of respective colors set by using a reference density pattern formed on an image carrier. CONSTITUTION:A sensor 12 which detects development density on a photosensitive drum 1 and a sensor 13 which detects the surface potential of a latent image pattern are provided, and the detected density of the sensor 12 is measured by a circuit 111 and converted 113 into a digital signal, which is supplied to a computer 109. The detected potential of the sensor 13, on the other hand, is measured by a circuit 115 and converted 117 into a digital signal, which is supplied to the computer 109, so that the computer 109 performs arithmetic while converging the toner image density to a previously set command. Consequently, the frequency of density control regarding development characteristics which vary for a long period is decreased and that on photosensitive body characteristics which vary for a short period is increased to perform precise and efficient density control, thus obtaining a copy which has proper and stable color balance and image density.

Description

[Detailed description of the invention]

11 The present invention relates to a color image forming apparatus such as a color electrophotographic copying apparatus or a color recording apparatus of a computer output section.

[Kurachi Ushiken]Recently, the demand for color copying and printing has increased rapidly, not only in special fields but also in general managing fields, and improvements in color image quality are desired. Conventionally, in color image forming apparatuses using electrophotographic photoreceptors, such as color electrophotographic copying apparatuses and color laser beam printers, it has been necessary to obtain appropriate color balance and image density, and to maintain them constant. It was difficult. The biggest cause of this problem is that in current color image forming devices, a full-color image with good color balance cannot be achieved by overlapping three-color images of cyan, magenta, and yellow, so the image characteristics of each color are In other words, it is necessary to precisely adjust the characteristics of image density, gamma, and fog, and such adjustment work is difficult for general users, and the characteristics change due to changes in the temperature and humidity environment of the photoreceptor and developer. It is difficult to maintain the image density of each color in a stable state for a long time due to variations in color, deterioration of characteristics, etc. Conventionally, as a countermeasure for the above problem, (1) Unexamined Japanese Patent Publication No. 53-37
As described in Publication No. 025, a method in which the surface potential of a latent image on a photoreceptor is detected and the image forming conditions of charging and exposure are controlled to converge the surface potential to a constant value (surface potential control method) , and (2) as described in Japanese Patent Application Laid-Open No. 54-134646, the toner image density on the photoreceptor is detected and the image forming conditions of charging, exposure, and development are controlled to keep the toner image density constant. There is a method (toner image density control method) of converging to a value. , I will do it,
The first surface potential control method is based on the characteristics of the photoreceptor,
Although it is possible to easily and precisely control the surface potential with respect to changes in charging characteristics or exposure amount, there is a problem in that image density fluctuates if there is a change in development characteristics. On the other hand, with the second toner image density control method, it is difficult to accurately detect image density in foggy areas or in halftones near bright areas, and fogging may occur on the image on the hard copy after control. Alternatively, the reproducibility of intermediate tones was likely to deteriorate. In addition, frequent control, such as image density control for each copy, tends to cause toner consumption, an increased burden on the cleaning device, and an increase in toner scattering within the device. Furthermore, compared to the surface potential control method described above in which a potential sensor is installed near the corona discharger to detect the surface potential and control the corona discharge current, image density control uses an image density sensor installed after the developer to control the image density. Since the corona discharge current is detected and controlled, the distance from the detection position to the control position becomes long, and therefore the time required for control becomes long, which poses a problem if the control is performed frequently. Accordingly, an object of the present invention is to provide a color image forming apparatus that can efficiently obtain color images having appropriate and stable color balance and image density. (b) The above object is achieved by an image forming apparatus according to the present invention.To summarize, the present invention provides a color image forming apparatus that forms a color image using a plurality of toner images. a condition control means for setting a condition target value for each color using the reference density pattern obtained by the image formation control means; and an image formation control means for setting an image formation condition for each color based on a condition target signal from the condition control means; Color image formation characterized in that when forming the color image a plurality of times within a predetermined period or consecutively, the image formation control means uses a condition signal from the condition control means determined previously. It is a device. Further, according to the present invention, in a color image forming apparatus that forms a color image using a plurality of toner images, a condition control means sets a condition target value for each color using a reference density pattern formed on an image carrier. and an image forming control means for setting image forming conditions for each color based on a condition target signal from the condition control means, and when forming the color image after a predetermined period has elapsed, the condition control means is used again. setting target condition values for each color using a reference density pattern formed on the image carrier, and setting image forming conditions for each color by the image forming control means based on a target condition signal from the condition control means. A color image forming apparatus is provided which is characterized by the following features. Next, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings. FIG. 1 illustrates an embodiment of an image forming apparatus according to the present invention as a color laser beam printer. In this embodiment, the photosensitive drum l is rotatably arranged approximately in the center of the apparatus. The photosensitive drum l having, for example, an amorphous silicon photoreceptor on its surface layer is first uniformly exposed by a pre-exposure lamp 2, and then exposed to light. It is charged to positive polarity by the corona discharger 3. Next, the background portion of the image on the photosensitive drum 1 is scanned and exposed by the semiconductor laser beam I, and an electrostatic latent image is formed. The laser beam I is transmitted to a semiconductor laser 41 by a laser scanner 4.
is generated by being driven by a laser driver that receives a recording information signal, and is then projected as a spot light onto the photosensitive drum via a scanning optical system consisting of a rotating polygon @42, an f.0 lens 43, and a mirror 44. . The latent image formed on the photosensitive drum 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 the developing devices of the designated colors sequentially develop the colors according to the color type of the recorded information. The image is then rotated and developed. 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 edge of the transfer paper is gripped by the gripper 81 of the transfer drum 8. Transfer paper P is transferred to transfer drum 8
As the image rotates, the image is conveyed to the transfer section while being wrapped around a mesh screen stretched across the cylinder notch of the transfer drum. In the transfer section, a 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 attracted to the surface of the mesh screen. After the four colors of toner images sequentially formed on the photosensitive drum l are aligned and multi-transferred to the transfer paper P on the transfer drum 8, the gripper 81 is released and the separation claw 84 is activated. Separate the transfer paper. Next, the transfer paper P is guided to a heating roller fixing device 10 by a conveyor belt 9, and the transferred toner image is heated and fixed to obtain a full color image. The toner on the photosensitive drum l that has not been transferred is removed by cleaner 1.
Collected by 1. By the way, when an image is formed in step E, the following steps are performed. An electrostatic latent image pattern for 0 image density detection in which an image density sensor 12 is provided immediately after the development position and close to the surface of the photosensitive drum l to detect the density of the developed image (toner image) on the photosensitive drum. is formed within the image forming area on the drum l at a predetermined timing by the pattern generator FT, and therefore the image density sensor 12 is provided at a position corresponding to the detection pattern in the drum axis direction. The image density sensor 12 is an integrated device that includes a light source that illuminates the surface of the photosensitive drum and an optical sensor that receives the reflected light.For example, the light source is a small tungsten lamp, and the optical sensor is a visible light absorbing sensor immediately before the light receiving section. A filter with near-infrared light transmission characteristics (for example, 5C-7 manufactured by Fuji Photo Film)
A silicon photodiode equipped with 4 filters is used. By detecting image density using near-infrared light in this way, we can develop color toner that has a high reflectance to near-infrared light and amorphous silicon photosensitive material that has a high absorption rate (low reflectance) to near-infrared light. The toner image density can be measured using the characteristics of the drum. In other words, toner image density is detected by utilizing the phenomenon that the intensity of near-infrared light reflected by the toner increases when the amount of toner adhered is large, regardless of the color of the toner. This phenomenon can be exploited if Further, a potential sensor 13 for detecting the surface potential of the latent image pattern for image density detection is provided close to the drum surface immediately after the exposure section, and in the axial direction, the potential sensor 13 detects the surface potential of the latent image pattern.
It is located at a position that corresponds to FIG. 2 is a block diagram illustrating one embodiment of the image density control circuit of the apparatus shown in FIG. Only the main parts of the photosensitive drum and its surroundings are shown. In this embodiment, a chopper disk and a photointerrupter (not shown) detect the rotation angle of the photosensitive drum l.
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 apparatus, and the controller 107 controls the microcomputer 1 for image density control.
A timing signal for measuring the surface potential or the density of a developed image (toner image), and a timing signal for switching high voltage current, developing bias voltage, laser beam intensity, etc. are supplied to 09. The toner image density detected by the image density sensor 12 is measured by an image density measurement circuit 111, and the toner image density is measured by an image density measurement circuit 111.
after being converted into a digital signal. The data is supplied to the computer 109. Similarly, the drum surface potential detected by the surface potential sensor 13 is measured by a surface potential measuring circuit 115, converted into a digital signal by an A/D converter 117, and then supplied to the computer 109. The computer 109 determines the toner image density based on the target density of each color toner, which is selected and set in advance on the switch board 119. Calculate according to the control formula to converge to . Further, the computer 109 calculates according to a control formula so that the dark area surface potential Vd converges to a surface potential target value Vdo of each color toner stored during an image density control process to be described later. The signal resulting from the above calculation is passed through the path line 121 to the D/
The signal is supplied to the A converter 123 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, which controls the power supply 131 to control the developing bias voltage Vdev applied to the developing device 5. 3 to 5 are flowcharts showing control operations of the image forming apparatus according to the present invention. Referring to FIG. 3, 1. 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 below is reset. Charging conditions for formation and development bias conditions are controlled for each color (
condition control). Subsequently, charging and developing bias control for image formation of each color is performed (image formation control), and after the zero image formation operation is completed, a timer starts counting for the purpose described later. Next, when the 0 operation start button, which will explain the condition control in more detail, is pressed, first, image density control starts. As can be understood from FIG. 4, steps 1 and 2 determine whether or not the image forming work (copying work in this embodiment) currently being performed is continuous copying, and how many hours have passed since the timer count started. It is determined whether 1
In the case of the second copy, a negative determination is made in step 2, and if the target dark potential Vdo is not set in step 3, charging and developing bias condition control operations for each color are performed.
will be carried out. In performing such a condition control operation, the discharge current IP of the corona discharger 3 having a preset initial value for each color is output, and the laser beam is activated based on the signal of the zero-order pattern generator for charging the photosensitive drum. The drum surface is scanned and exposed to form a latent image pattern for image density detection (step 4).The surface potential Vd of this latent image pattern (dark area) is
And the bright area potential Vl of the exposed area adjacent to the latent image pattern (the corona discharge current is given under the same conditions as the dark area) is detected by the potential sensor 13 (step 6).
A developing bias voltage Vdev to be applied to the developing device when developing the latent image pattern is determined by adding a predetermined voltage to the detected bright area potential Vl (step 6). The latent image pattern is developed with one color of toner, for example, yellow toner, to form an image density detection pattern. In step 8), the image density Dd of the image density detection pattern is detected by the sensor 12.
and target concentration Dd. (step 9), where 1Dd-Ddol
It is determined whether or not is within the allowable error CI. If the judgment is negative, the corona discharge current Ip is controlled by the formula Δ■p=α
Control according to ΔDd (α is a constant) (step 10)
, and then returns to step 4 and repeats the steps from step 4 to step IO. If 1Dd-Ddol is within the tolerance C1 and an affirmative determination is made in step 9, step 1
1, the surface potential Vd of the latent image pattern corresponding to the detected density Dd for which an affirmative determination has been made is stored in the computer 109 as a control target value Vdo of the surface potential in a subsequent control step. The above steps are performed for each color, and the gold condition (target dark potential) Vdo is set, and the condition control operation is completed (step 12). When the above condition control operation is completed, the image forming apparatus shifts to an image formation control operation. Referring to FIG. 5, in block 221, a corona discharge current IP of a preset initial value is output for each color, and the photosensitive drum is charged (step 13). 13, the detected potential Vd is compared with the target potential Vdo (step 15).
), here it is determined whether 1Vd-VdOl is within the tolerance C2. If the determination is negative, the corona discharge current Ip is controlled in accordance with the control formula ΔIP=βΔVd (β is a constant) in step 16. Then, the process returns to step 13 and the steps 13 to 16 are repeated. If 1Vd-Vdol is within the allowable error Cz and an affirmative determination is made in the step, the process proceeds to step 17. At this time, the corona discharge current I that gives the detected potential Vd for which the affirmative determination is made is
P is stored in the computer 109 and output as a corona discharge current when a hard copy is made later. Next, under the output of the corona discharge current Ip, operation exposure with a laser beam is performed based on the signal from the pattern generator (step 17), and the bright area potential Vl is detected (step 18). In step 18, a predetermined potential is added to the bright area potential Vl to obtain a developing bias voltage Vdev for forming a hard copy, which is stored in the computer 109 together with the above-mentioned Ip. The above steps are performed for each color, charging and developing bias conditions for image formation of all colors are set, and the image formation control operation is completed. When the image formation control operation is completed, 5
The image forming apparatus performs an image forming operation and is then reset (steps 19 to 22). Returning to FIG. 4, the case of continuous copying will be explained. If an affirmative determination is made in step 1 and a memory of the target dark potential Vdo exists, the above conditional control operation is not necessary and the process immediately proceeds to the image formation control operation shown in FIG. If there is no memory of the potential Vdo, the condition control operation described above is performed, and then the process proceeds to the image control operation. Furthermore, according to another feature of the invention, a step 2 is provided in the condition control operation. In other words, when a copy operation is performed after the image forming apparatus starts operating, that is, after a predetermined time (T) has elapsed after the timer count starts, even if the conditional target dark potential Vdo (step 3) is stored in memory, The point is that the configuration is such that the condition control 1 effect for the target value is performed again. As can be understood from the above explanation, according to the characteristics of the present invention, the control interval for one image density control is such that the change in the development characteristics of the toner (image density characteristics relative to the surface potential) changes to the latent image characteristics of the photoreceptor (the change in exposure amount). Changes in surface potential characteristics (with respect to logarithm) and charging,
Since changes occur over a longer period of time than changes in exposure conditions, the first step is to negotiate and control the changes before making a hard copy (steps 1 to 12).
) and image formation control (steps 13 to 18), and thereafter, if a predetermined time T has elapsed since the previous copy was made, for example, when making the next copy after 10 minutes, the vehicle is turned off. Image formation control process (step 1)
3 to step 18), and when creating the next copy after a predetermined time T has elapsed since the previous copy was created, for example 2 hours or more, the condition control (step 1) is performed in advance.
~Step 12) and image formation control (Step 13~Step 18) are performed. As another example, instead of a predetermined time, T can be the number of copies. First, condition control (step 1 to step 12) and image formation control (step 13 to step 18) are performed before making l\-tocobee, and after that, after making 100 copies, the image is Only the formation control (steps 13 to 18) is performed, and after making 1000 copies, condition control (steps 1 to 12) and image formation control (steps 13 to 18) are performed before making the next copy. conduct. As explained above, in the color image forming apparatus of the present invention, the number of times of image density control related to the development characteristics that fluctuate over a relatively long period of time is reduced, and the exposure sensitivity that fluctuates over a relatively short period of time is reduced. By increasing the number of image density controls related to physical characteristics, charging, and exposure characteristics, it is possible to achieve highly accurate and efficient image density control, and to obtain hard copies with appropriate and stable color balance and image density. It will be done. The embodiments of the present invention have been described above with reference to a color laser beam printer using a background scanning method in which a laser beam is applied to the background part of an image and toner is deposited on the last exposed part by regular development. It goes without saying that this method can be applied to a color laser beam printer using an image scanning method in which toner is attached to an exposed area exposed to a laser beam by reversal development, and furthermore, it can be applied to an Anapro color electrophotographic copying device. .

[Brief explanation of the drawing]

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 an image density control circuit in the apparatus of FIG. 1. FIG. 3 is a flowchart showing the operation of FIG. 2. FIG. 4 is a flowchart of condition control. FIG. 5 is a flowchart of image control. 1: Photosensitive drum 3: Corona discharger 4: Laser scanner 5: Developing device 8: Transfer drum 12-image density sensor 13: Potential sensor 107: Sequence controller 109: Image density control microcomputer 111: Image density measurement circuit 115: Surface potential measurement circuit Figure 5

Claims (1)

[Claims] 1) In a color image forming apparatus that forms a color image using a plurality of toner images, a condition control means that sets a condition target value for each color using a reference density pattern formed on an image carrier. and an image formation control means for setting image formation conditions for each color based on a condition target signal from the condition control means, and when forming the color image within a predetermined period or a plurality of times in succession, the image formation control means A color image forming apparatus characterized in that the formation control means uses a condition signal from the condition control means determined previously. 2) In a color image forming apparatus that forms a color image using a plurality of toner images, a condition control means sets a condition target value for each color using a reference density pattern formed on an image carrier, and the condition control means and an image forming control means for setting image forming conditions for each color based on condition target signals from the image forming apparatus. A condition target value for each color is set using a reference density pattern formed in the image formation control means, and image formation conditions for each color are set by the image formation control means based on a condition target signal from the condition control means. A color image forming apparatus characterized by: