JPH0854784A - Digital color image forming device - Google Patents

Abstract

PURPOSE:To provide a digital color image forming device in which an improvement in color and density stability is made by an accurate adjustment while increase in design cost due to the adjustment is minimized. CONSTITUTION:Based on data on the density of a color patch image detected by a detection sensor 9, a control part 8 reads a control coefficient from a memory 21. The amount of toner to be attached is accurately controlled according to a change in detection density data, in order to set the rotating speed of each of developing sleeves 3a-3d so that a color image having a prescribed density is obtained. The increase in design cost caused by the adjustment is minimized and, at the same time, the color and density stability can be improved by the accurate, satisfactory responsive adjustment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital color image forming apparatus utilizing an electrophotographic process such as a copying machine and a printer, and more particularly, to controlling the amount of toner adhered to an image carrier to stabilize the color and density. It is related to the technology to improve.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses of digital type and reversal development have been put to practical use, for example, color electrophotographic copying machines and color recording apparatuses forming an output section of personal computers, facsimiles and the like are known. In such an image forming apparatus, it is necessary to perform adjustment work in order to obtain a recorded image with good reproducibility even during continuous operation, but this adjustment work is complicated and complicated. Had. In order to solve this problem, an image density control technique using a patch detection method is currently used.

In the color patch detection system, the primary color, Y
ellow (Y), Magenta (M), Cyan
(C), Black (Bk) and secondary colors, Red, Gr
In order to ensure the color stability of all een and blue, it is necessary to detect the patch density pattern for each color. The technique disclosed in Japanese Patent Laid-Open No. 63-113568 is also an example of this patch detection method, in which a gradation density pattern for each color is formed on a photoconductor and the pattern density is measured by a detection sensor. The correction amount is obtained in step (1), and the exposure amount of the laser beam or the like is variably controlled based on the correction amount to perform the density adjustment processing.

In addition to the above-mentioned exposure amount control, a technique for controlling a charge amount and a developing bias is also disclosed.

[0005]

However, in the case of measuring the gradation density pattern for each color as described above, there are many kinds and quantity of measurement data, and the program relating to the adjustment processing becomes complicated or prepared. There is a new problem that the correction data increases and the design cost becomes too large.

The present invention has been made in view of such conventional problems, and provides a digital color image forming apparatus capable of improving the stability of colors and densities while suppressing an increase in design cost related to adjustment processing as much as possible. The purpose is to provide.

[0007]

Therefore, the present invention solves the above-mentioned problems of the prior art, in which the optical detecting means detects the density data value for each color of the color patch image to obtain the image. In a digital color image forming apparatus of reversal development for controlling the formation conditions of, the color patch image forming means for forming a color patch image according to the reference density data previously stored in the apparatus on the image carrier, and the developing sleeve. A sleeve rotating means for rotating the speed in a variable speed, and a control coefficient for controlling the rotation speed of the developing sleeve in the direction of making the density closer to the reference density for the density data value of the color patch image are stored as a data table. A control coefficient storage means, and a control coefficient is read from the control coefficient storage means based on the concentration data value detected by the detection means. A sleeve rotating speed control means for feedback controlling the serial sleeve rotating means, it is an equipped configuration.

Here, the digital color image forming apparatus may be an image forming apparatus for reversal development. The sleeve rotation speed control means multiplies the control coefficient based on the detected density data value of the color patch image formed by the color patch image forming means by the rotation speed of the sleeve rotation means to perform feedback control of the sleeve rotation means. It can be configured to.

Further, the sleeve rotation speed control means is
It is also possible to adopt a configuration in which the control coefficient based on the detected density data value of the color patch image formed by the color patch image forming means is added to the rotational speed of the sleeve rotating means to perform feedback control of the sleeve rotating means. Further, in the color patch image forming means, the upper limit is a point at which the detected density data value of the detection means has a fluctuation tendency, and the lower limit is a point at which the detected density data value of the detection means tends to be saturated. Alternatively, the reference density data may be set such that a color patch image having a constant density is formed.

[0010]

Therefore, according to the digital color image forming apparatus of the present invention, the sleeve rotation speed control means controls from the control coefficient storage means based on the density data value of the color patch image detected by the optical detection means. Since the coefficient is read out and the rotation speed of the developing sleeve is feedback-controlled in a variable speed, the toner adhesion amount is accurately controlled according to the fluctuation of the detected density data value, and the increase in design cost related to the adjustment process is suppressed as much as possible. , The stability of color and density can be improved.

Further, in the case where the sleeve rotation speed control means is adapted to multiply the control coefficient based on the detected density data value of the color patch image by the rotation speed of the sleeve rotation means, the rotation speed of the sleeve is changed. The responsiveness at the time of control can be speeded up. Further, the sleeve rotation speed control means may add the control coefficient based on the detected density data value of the color patch image to the rotation speed of the sleeve rotation means.

Further, the color patch image forming means is
A color patch image having a constant density is formed in a region where the upper limit is a point at which the detected density data value of the detection unit has a fluctuation tendency and the lower limit is a point at which the detected density data value of the detection unit has a saturation tendency. In the case of setting the reference density data as described above, the detection means does not detect the color patch image in the unstable detection area, and therefore the accurate adjustment processing can be performed.

[0013]

EXAMPLE An example of the present invention will be described below. FIG.
FIG. 2 is a schematic control block diagram of the digital color image forming apparatus in this embodiment. The operation of the normal image recording mode will be described with reference to FIG.

A charging device 2, a developing device 3, a transfer roller 4, a charge eliminating brush 5 and a cleaning portion 6 are provided so as to face the photoconductor 1 as an image bearing member which rotates in the direction of the arrow. When the photosensitive member 1 charged by the charger 2 is irradiated with laser light corresponding to an image from an unillustrated exposing portion, toner adheres to the irradiated portion of the surface of the photosensitive member 1 by the developing device 3 to electrostatically discharge. The latent image is visualized. The developing device 3 has four developing sleeves 3a, 3 for each of the primary colors Y, M, C, Bk.
b, 3c, 3d and a developing sleeve drive motor (not shown) as a sleeve rotating means, and a developing sleeve 3a, to which a direct current (DC) bias is applied when forming an image of a specific color, By superimposing an alternating current (AC) bias on a specific developing sleeve among 3b, 3c and 3d,
The toner particles on the rotating developing sleeve are excited by the developing sleeve drive motor and adhere to the photoconductor 1 to form a specific color image. Development sleeve 3 for secondary colors
A desired color can be formed by combining a, 3b, 3c, and 3d.

When the toner image formed on the photoconductor 1 by the developing device 3 reaches the transfer position of the transfer roller 4, the recording paper (not shown) whose timing is controlled is also conveyed to the transfer position, and the recording paper is transferred. A transfer bias having a polarity opposite to that of the toner is applied from the back surface, the toner image on the photoconductor 1 is transferred to the surface of the recording paper by the action of electrostatic attraction, and the charge removal brush 5 removes the unnecessary potential.

When a color image is formed, the charging, exposing and developing steps are carried out for the Y color, and the series of steps are repeated for the M, C and Bk colors in sequence, and the transfer step is finally carried out at the end. The recording paper is separated from the photoconductor 1 by a known separation means such as a separation claw or curvature separation, and is thermally fixed by a fixing device (not shown) and discharged from the apparatus. Then, the cleaning unit 6 cleans the residual toner on the photoconductor 1 to prepare for the next recording.

Next, the operation of the automatic image adjustment by the characteristic color patch image of the present invention will be described in detail with reference to the drawings. The color patch image data is stored in advance in the memory 7, and the control unit 8 sequentially reads the color patch image data of each color from the memory 7 in the image adjustment mode,
By outputting the color patch image data to the exposure section, the charged photoconductor 1 is exposed, and the electrostatic latent image is visualized by the developing device 3. In this way, the charger 2,
The exposure unit, the developing unit 3, the memory 7, and the control unit 8 have a function as a color patch image forming unit. Here, the control unit 8 sets the rotation speed of the developing sleeve to 1 in the image recording mode.
Since the control is performed so as to reduce to / 3, the toner adhesion amount of the color patch image on the photoconductor 1 is also reduced to 1/3.
The reason for this will be described later.

On the other hand, the detection sensors 9 provided between the charge removal brush 5 and the cleaning section 6 are 40 ° to the virtual perpendicular line (dotted line) of the photoconductor 1 as shown in the schematic structure of FIG. It is composed of a pair of photodiodes (LEDs) and phototransistors (PtTrs) installed at an angle, and receives reflected light according to the amount of toner forming a color patch image.

FIG. 3 shows the color patch image detection circuit 10 of the LED and PtTr. A current based on the voltage V _LED and the resistance 11 flows through the _LED, and emits a constant amount of light. On the other hand, PtTr obtains a current value proportional to the amount of received light, and when a variable voltage determined by the ratio of the resistance 12 and the resistance 13 is input to the OP amplifier 16, it is amplified and output at the amplification rate determined by the resistance 14 and the resistance 15. A voltage (detection signal) is obtained.

Therefore, as can be seen from FIG. 4 which shows the relationship between the detection signal and the toner adhesion amount, when the toner is not adhered on the photoconductor 1, the received light amount of PtTr is the maximum, so that the detection signal of the color patch image detection circuit is detected. Also becomes maximum, and the detection signal value decreases as the toner adhesion amount increases until the toner covers the photoconductor 1. However, in the area where the toner is low, the PtTr
Since the amount of received light of 1 varies, the detection signal indicates the upper limit of the stable region, and thereafter, the fluctuation tendency becomes large. Further, since the amount of received light of PtTr does not change even if the toner adhesion amount increases after the toner covers the photoconductor 1, the detection signal reaches the lower limit and becomes saturated. Such a fluctuation region and a saturation region are unstable regions, and a stable output voltage with respect to the toner adhesion amount cannot be obtained.

The toner adhesion amount at the upper limit of the detection signal was 0.1 mg / cm ² , and the toner adhesion amount at the lower limit was 0.6 mg / cm ² , as a result of the measurement. The control unit 8 as the sleeve rotation speed control unit is composed of a CPU or the like with a ROM in which a control program is stored, and is controlled from the memory 21 as the control coefficient storage unit according to the detection signal from the color patch image detection circuit 10. By reading the coefficient and controlling the rotation speed of the development sleeve drive motor, the rotation speed of the development sleeve is set to be changeable.

Generally, the toner adhesion amount is too large or, conversely, small.
It is not possible to ensure the stability of color even if it is too much.
Therefore, the standard toner adhesion amount is specified and deviation from the standard value is generated.
It is necessary to control the amount of adhered toner so that the toner does not twist. Obedience
Therefore, the standard toner adhesion amount of the color patch image is also printed.
0.6 mg / cm as the reference toner adhesion amount for the printed image ²
Set the reference toner adhesion amount in the unstable area where it should be
Since accurate adjustment processing cannot be performed,
Is the reference toner adhesion amount of the print image, which is 0.6.
mg / cm²1/3 of 0.2 mg / cm²Color
It is defined as the reference toner adhesion amount of the touch image. Soshi
The detected density of the color patch image is 0.2 mg / cm²
By measuring how much it is increasing or decreasing,
The standard toner adhesion amount of the
It is to be reproduced.

For example, if the detected toner adhesion amount of the color patch image is (0.2-0.02) mg / cm ² , the reference toner adhesion amount of the print image is (0.6-0.06).
mg / cm ² (Because there is a triple relationship between the color patch image adhesion amount and the reference toner adhesion amount of the print image, the error is 3
Double. ) Is expected, and adjustment processing is performed so that the toner adhesion amount in the image recording mode is set to 0.6 mg / cm ² .

As described above, since the color patch image data is set in the memory 7 constituted by the ROM or the like so that the density of the color patch image is formed in the stable region, the measured density of the color patch image is low. It fluctuates because of the concentration,
Because of the high density, there is no difference from the measured value, and a stable color patch image can be obtained, so that accurate adjustment processing can be performed.

FIG. 5 is a diagram showing the relationship between the toner adhesion amount and the developing sleeve rotation speed. As can be seen from the figure, the present invention controls the toner adhesion amount by paying attention to the fact that the relationship between the toner adhesion amount and the developing sleeve rotation speed is in a substantially proportional relationship. The reference toner adhesion amount can be easily obtained.

[0026]

[Table 1]

A data table as shown in Table 1 is previously stored in the memory 21 composed of a ROM or the like,
When the data of the detection signal is input, the control coefficient is output as the data. The control unit 8 reads the control coefficient according to the control program and performs the following multiplication operation. V _{sleeve (i + 1)} = V _{sleeve (i)} × control coefficient (1) Here, V _{sleeve (i)} is the rotation speed of the developing sleeve at the time of measurement, and V _{sleeve (i + 1)} is a correction value. The developing sleeve rotation speed after that is shown. As a result, the developing sleeve drive motor is changed and controlled, and the rotation speed of the developing sleeve is set to V _{sleeve (i + 1)} .

Further, instead of the above equation (1), addition operation of the following equation can be performed. V _{sleeve (i + 1)} = V _{sleeve (i)} + control coefficient (2) In this case, the control coefficient is set in the data table shown in Table 2 instead of Table 1.

[0029]

[Table 2]

However, although there is no difference in the calculation processing time between the formula (1) and the formula (2), when the control unit 8 controls the rotation speed of the developing sleeve, the latter is constant because of the control program. Since the rotation speed is controlled to be increased / decreased at every minute rotation step, it takes time to complete the density correction, but in the former case, the rotation speed set by V _{sleeve (i + 1)} is controlled at once as it is. Therefore, it is preferable in terms of the response of the density correction. Therefore, when the latter case is used, the image adjustment may be performed more frequently than in the former case in order to shorten the transient state of the adjustment process.

Next, a flow chart of the image adjustment processing is shown in FIG. Although not shown, the following image adjustment mode is executed when a predetermined number of images are recorded in the normal image recording mode. First, in S1, the control unit 8 inputs the image forming pattern data of the color patch image from the memory 7 and reduces the number of rotations of the developing sleeve to 1/3 as described above to set each of Y, M, C and Bk to 1
One color patch image is formed, the detection sensor 9 reads the color patch image, and the color patch image detection circuit 1
0 outputs a detection signal according to the density data of the color patch image.

Next, in S2, according to the data table as set in Table 1 or Table 2, multiplication operation or addition operation is performed using the control coefficient, and the developing sleeve rotation speed V is obtained.
_{The sleeve (i + 1)} is calculated and feedback control is performed to change the rotation speed of the developing sleeve. In S3, the number of recording sheets is counted while returning to the image recording mode and performing normal recording. The above shows the control program of the CPU, which can be adjusted by software. Since the number of recorded sheets differs depending on the calculation form used and control accuracy, it is preferable to set the number of sheets according to the target control level of the apparatus.

As described above, since the number of color patches is one for each color, the responsivity and controllability are better than the image density control by the conventional patch detection method, and the design cost related to the adjustment processing is increased as much as possible. Can be deterred.

[0034]

[Table 3]

Table 3 shows the result of the actual shooting test of each characteristic in the image adjustment processing. Here, 100 sheets in the initial state and 100 sheets in the 100,000 printed state are recorded.
When three sheets were randomly extracted from the recorded sheets and evaluated, the effect of the image adjustment in Examples 1 and 2 was remarkable, and particularly under the condition that the image adjustment is performed once every 5 times of the normal recording. It was found that, as compared with Example 2, Example 1 can obtain excellent results in terms of responsiveness of image adjustment.

[0036]

As described above, according to the digital color image forming apparatus having the above-described structure, the sleeve rotation speed control means controls from the control coefficient storage means based on the density data value of the color patch image detected by the detection means. Since the coefficient is read out and the rotation speed of the developing sleeve is feedback-controlled in a variable speed, the toner adhesion amount is accurately controlled according to the fluctuation of the detected density data value, and the increase in design cost related to the adjustment process is suppressed as much as possible. In addition, it is possible to improve the stability of color and density. Further, in the sleeve rotation speed control means, the control coefficient based on the detected density data value of the color patch image is multiplied by the rotation speed of the sleeve rotation means. It is possible to speed up the responsiveness when changing and controlling the rotational speed of the sleeve.

Further, the sleeve rotation speed control means may add the control coefficient based on the detected density data value of the color patch image to the rotation speed of the sleeve rotation means. Further, in the color patch image forming means, the upper limit is a point at which the detected density data value of the detection means has a fluctuation tendency, and the lower limit is a point at which the detected density data value of the detection means tends to be saturated. In addition, in the case of setting the reference density data such that a color patch image having a constant density is formed, since the detection means does not detect the color patch image in the unstable detection area, accurate adjustment processing can be performed. it can.

[Brief description of drawings]

FIG. 1 is a schematic control block diagram of a digital color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a detection sensor according to an embodiment of the present invention.

FIG. 3 is a color patch image detection circuit diagram according to an embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between a detection signal and a toner adhesion amount according to an embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between a toner adhesion amount and a developing sleeve rotation speed in one embodiment of the present invention.

FIG. 6 is a flowchart of image adjustment processing according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 3 Developing device 7,21 Memory 8 Control part 9 Detection sensor 10 Color patch image detection circuit

Claims (5)

[Claims] 1. A digital color image forming apparatus for controlling an image forming condition by detecting a density data value for each color of a color patch image by an optical detecting means, wherein a reference density stored in advance in the apparatus. Color patch image forming means for forming a color patch image according to the data on the image carrier; sleeve rotating means for rotating the developing sleeve at a variable speed; and the density for the density data value of the color patch image. From the control coefficient storage means based on the density data value detected by the detection means, a control coefficient storage means for storing a control coefficient for controlling the rotation speed of the developing sleeve in the direction of approaching the reference density as a data table. Sleeve rotation speed control means for reading out a control coefficient and performing feedback control of the sleeve rotation means. Digital color image forming apparatus characterized by. 2. The digital color image forming apparatus according to claim 1, wherein the digital color image forming apparatus is a reversal developing image forming apparatus. 3. The sleeve rotation speed control means multiplies the control coefficient based on the detected density data value of the color patch image formed by the color patch image forming means by the rotation speed of the sleeve rotation means to perform the calculation. The digital color image forming apparatus according to claim 1, wherein the rotating means is feedback-controlled. 4. The sleeve rotation speed control means adds the control coefficient based on the detected density data value of the color patch image formed by the color patch image forming means with the rotation speed of the sleeve rotation means to perform the arithmetic operation. The digital color image forming apparatus according to claim 1, wherein the rotating means is feedback-controlled. 5. The color patch image forming means has an upper limit as a point at which the detected density data value of the detection means tends to change, and a lower limit as a point at which the detected density data value of the detection means tends to saturate. 5. The digital color image forming apparatus according to claim 1, wherein reference density data for forming a color patch image having a constant density is set in the area.