JP3584644B2 - Image forming device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine and a printer that visualizes an electrostatic latent image formed on an image carrier by attaching toner to the image.
[0002]
[Prior art]
Generally, a color copying machine as shown in FIG. 7 is known as this type of image forming apparatus. The illustrated color copier mainly includes a scanner unit 51 that reads a document image, an image processing unit 52 that performs processing such as gradation correction, color correction, and improvement in definition on image data output from the scanner unit 51, The image processing unit 52 includes a ROS (Raster Output Scanner) optical unit 53 that emits a laser beam in accordance with the image data processed by the image processing unit 52, and an image forming unit 54 that finally forms an image.
[0003]
In the image forming section 54, a charging device 56, an electrometer 57, a rotary developing device 58, a density sensor 59, a cleaner device 60, and a static elimination lamp 61 are sequentially provided around a drum-type photoreceptor 55 according to the rotation direction. ing. Further, in the rotary developing device 58, developing devices 58K, 58Y, 58M, and 58C are respectively incorporated corresponding to each color of K (black), Y (yellow), M (magenta), and C (cyan). Each of the developing devices 58K, 58Y, 58M, and 58C is provided with a toner dispensing device 62 that supplies toner of each color.
[0004]
In the image forming section 54, an image is formed using the well-known principle of xerography. That is, the surface of the rotating photoconductor 55 is uniformly positively charged by the charging device 56, and the first color electrostatic latent image is formed by the laser light from the ROS optical unit 53. The negatively charged black toner is attracted to the electrostatic latent image by the developing device 58 </ b> K of the first color (K) of the rotary developing device 58, so that the first color toner image is formed on the photoconductor 55. Formed. On the other hand, the paper (not shown) stored in the paper tray 63 is transported by the paper transport device 64 and wound around the transfer drum 65. Then, the toner image on the photoconductor 55 is transferred by the transfer corotron 66 onto the surface of the wound paper. At this time, the toner and electric charge remaining on the photoconductor 55 are removed by the cleaner device 60 and the charge removing lamp 61.
[0005]
Thereafter, in the same procedure as the above-mentioned first color (K), a total of four color toner images up to the second color (Y), the third color (M), and the fourth color (C) are transferred onto the paper on the transfer drum 65. Are sequentially transferred. When the transfer of the image of each color is completed, the sheet is separated from the transfer drum 65 by the separation corotron 67 at that stage, and further sent to the fixing device 68 to fix the image. Thus, a color copy image in which the images of the respective colors are superimposed is formed on the surface of the sheet. The charge removing corotron 69 provided around the transfer drum 65 is for removing excess charges on the paper and the transfer drum 65 after transferring the image of each color or after peeling off the paper.
[0006]
In the above-described color copying machine, in order to stabilize the image density in the image forming unit 54, image dots are counted, the amount of consumed toner is calculated from the counted value, and toner is supplied to the developing device. A function called "ICDC" and a "ADC" that forms a toner image (toner patch) for density detection on a photoreceptor, detects the density of the toner image with a density sensor, and compensates for excess or deficiency of toner in a developing device. There is known a concentration control method using a so-called ADC + ICDC which combines functions called “ADC + ICDC”. Further, in the image forming apparatus employing this density control method, when the image density detected by the density sensor is continuously detected to be lower than the target density, it is determined that the toner cartridge has run out of toner. Is displayed.
[0007]
Here, in the rotary developing device 58, as shown in FIG. 8, toner cartridges 70K, 70Y, 70M, and 70C are respectively tied and disposed with respect to the respective developing devices 58K, 58Y, 58M, and 58C. I have. To supply the toner in the toner cartridges 70K, 70Y, 70M, and 70C to the developing units 58K, 58Y, 58M, and 58C, a toner dispensing device as shown in FIG. 9A is incorporated for each color. . The illustrated toner dispensing device includes a transport auger 71 for dropping toner discharged from a toner cartridge 70 into a developing device, and the transport auger 71 is rotated by a dispense motor 72. The transport auger 71 has a cylindrical structure in which the internal space is spirally partitioned, and a toner intake port 71a corresponding to the toner outlet 70a of the toner cartridge 70 is provided at one end of the transport auger 71, and at the other end. Further, a toner supply port 71b for dropping toner into the developing device is provided on a peripheral surface opposite to the toner intake port 71a.
[0008]
In this toner dispensing device, the toner dropped by its own weight from the toner discharge port 70a of the toner cartridge 70 is taken into the transport auger 71 via the toner take-in port 71a. As shown in FIG. 9B, the toner thus taken in is sequentially sent in the axial direction (rightward in the figure) by the rotation of the transport auger 71 driven by the dispense motor 72, and is dropped from the toner supply port 71b. In rare cases, it is supplied to a developing device.
At this time, it is desirable that the amount of toner per unit time supplied from the toner dispensing device to the developing device (hereinafter, referred to as a dispensing rate) is a constant amount. , The dispense rate changes for each copy mode.
[0009]
FIG. 10 is a comparison diagram of the dispense rate depending on the copy mode.
In FIG. 10, the target value of the dispense rate is 240 mg / sec, and the dispense rate of the yellow toner with respect to this target value is displayed for each copy mode. As the copy mode, the first mode is a case where the full-color four-color mode is continuously processed, and the second mode is a case where the full-color four-color mode and the single-color (monochrome) mode are alternately repeated every ten copies. The third mode is a case where 20 sheets are copied in the single color (monochrome) mode and then one sheet is copied in the full-color four-color mode, and this is continuously and repeatedly processed.
As is clear from the figure, the dispense rate has reached the target value in the first mode, but the dispense rate is lower than the target value in both the second mode and the third mode. In particular, the dispense rate in the third mode is only about half of the target value.
[0010]
Here, when an image is formed in the copy mode in which the dispense rate is lower than the target value as in the second and third modes, the toner supply density to the developing device is insufficient and the density of the toner image gradually decreases. Therefore, it is detected that the density detected by the density sensor is continuously lower than the target density. In such a case, even though the toner is left in the toner cartridge, it is erroneously determined that "no toner". Therefore, even if the image processing is performed in the copy mode with the minimum dispensing rate, it is erroneously detected that the toner is present. The coefficient used in the ICDC control (hereinafter, referred to as an ICDC coefficient) is set in accordance with the minimum dispense rate so as to prevent the occurrence of the above.
The ICDC coefficient serves as a parameter for determining the toner supply operation time (ON time of the dispense motor) in the toner dispensing device. In the ICDC function, the amount of toner consumed is calculated by multiplying the image dot by the ICDC coefficient. Then, the toner supply operation time in the toner dispensing device is set according to the calculation result.
[0011]
When the ICDC coefficient is set in accordance with the minimum dispense rate as described above, when the toner is supplied at a normal dispense rate (for example, a dispense rate equivalent to a target value), a large amount of toner is supplied to the developing device. Is supplied, the image density gradually increases as the copying operation is repeated. Therefore, in the ADC control, the density of the toner image is detected by a density sensor, and when the detected density reaches a predetermined upper limit level UL as shown in FIG. 11, the toner supply to the developing device by the ICDC function is temporarily stopped. The control is suspended so that the image density does not exceed the upper and lower levels UL. Further, when the toner supply is interrupted, the image density gradually decreases due to the subsequent copying operation. Therefore, when the image density detected by the density sensor reaches a predetermined lower limit level DL, the developing device by the ICDC function is used. The toner supply to the printer is restarted, whereby the image density is controlled so as not to fall below the lower limit level DL.
The above is the operation principle of the density control method of ICDC + ADC, whereby the image density is within a predetermined allowable range (upper limit level) around the target density by the increase by the ICDC function and the correction (decrease) by the ADC function as shown in FIG. While the minute fluctuation is repeated between UL and the lower limit level DL), it is always maintained at an appropriate level.
[0012]
Here, conventionally, as shown in FIG. 12, a toner image (toner patch) for density detection is formed on a photoreceptor, and it is determined whether or not density detection means for detecting the density of the toner image is normal. It is determined (S1). If it is determined to be normal, density control by ICDC + ADC is performed. If it is determined to be abnormal, the density control is switched to ICDC function only (S2, S3). Further, when performing density control by ICDC + ADC for toner empty detection, it is determined whether or not the density of the toner image has become continuously lower than the previously measured density (S4). Display is performed (S5).
[0013]
[Problems to be solved by the invention]
However, in the above-described conventional image forming apparatus, the ICDC coefficient is set in accordance with the minimum dispense rate in order to prevent erroneous detection of the presence or absence of toner. When the toner is supplied to the developing device, the image density increases endlessly as the number of copies increases as shown in FIG. And fogging occurs.
[0014]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem. An object of the present invention is to reduce fog caused by an abnormal increase in density even when the density control is performed only by the ICDC function due to the occurrence of an abnormality in the density detection means. It is an object of the present invention to provide an image forming apparatus capable of preventing the image formation.
[0015]
[Means for Solving the Problems]
According to the image forming apparatus of the present invention, a developing device that develops an electrostatic latent image formed on an image carrier into a toner image, a toner supply unit that supplies toner to the developing device, and an image on which an image is formed Toner amount control means for controlling the amount of toner supplied from the toner supply means to the developing device by driving the toner supply means in accordance with the consumed toner amount obtained by multiplying the number of dots by the coefficient; Density detecting means for detecting the density of the toner image developed by the developing device, and correcting means for correcting the amount of toner supplied to the developing device by the toner amount controlling means based on the density of the toner image detected by the density detecting means If, when the abnormality detecting means for detecting whether an abnormality has occurred in the concentration detection means, which by the abnormality detecting means abnormalities concentration detection means is detected, the toner supply amount by correcting means The correction operation is stopped, and the coefficient by which the number of image dots is multiplied is changed from the first coefficient to a second coefficient smaller than the first coefficient, thereby controlling the toner supply amount by the toner amount control unit. And a control means for executing the control.
[0016]
In the image forming apparatus having the above configuration, when any abnormality occurs in the density detecting unit, the abnormality detecting unit detects the occurrence of the abnormality, and in response, the control unit changes the driving condition of the toner supply unit. As a result, the amount of toner supplied to the developing device is corrected so as to be smaller by a predetermined amount than when the density detecting means is normal. Even when the density control is performed only by using the density control, the image density does not endlessly increase.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Note that the basic configuration of the image forming apparatus to which the present invention is applied is the same as that shown in FIGS. 7 to 9, and a description thereof will be omitted.
FIG. 1 is a block diagram showing an embodiment of the image forming apparatus according to the present invention.
In FIG. 1, a density detection value by a density detection unit, a detection signal (abnormality presence / absence signal) by an abnormality detection unit 3, and a count value of image dots by a dot counter 4 are input to a control unit 1 as a control unit. It has become so. Further, the control unit 1 outputs control signals to the ADC function unit 5 and the ICDC function unit 6, respectively, and the toner dispensing device 7 as a toner supply unit is driven and controlled based on the control signals. ing. Further, a memory 8 is connected to the control unit 1, and an ICDC coefficient used by the ICDC function unit 6 is stored in the memory 8. Here, two types (first and second) of ICDC coefficients (described later) are stored in advance in the memory 8 according to different dispensing rates, and the ICDC function unit 6 is operated using either of the ICDC coefficients. Whether or not to perform the selection is selected by the control unit 1 based on the detection signal from the abnormality detection unit 3.
[0018]
The density detecting means 2 forms a toner image (toner patch) for density detection on a photoreceptor or a transfer body, and detects the density of the toner image with a density sensor. The reflection type optical sensor shown in FIG. In the configuration of the illustrated density sensor 10, a light emitting element 12 composed of a light emitting diode (LED) and a light receiving element 13 composed of a phototransistor are incorporated in a sensor main body 11 having a housing structure. Then, with respect to the image carrier 14 formed of a photoconductor or a transfer body, the image carrier 14 is opposed to the lower ground of the image carrier 14 so that the reflected light of the light emitted from the light emitting element 12 is received by the light receiving element 13. It is arranged.
[0019]
In the density control by the ADC function unit 5 using the density detection unit 2, for example, a reference potential portion (patch) is formed in a non-image area of a photoconductor serving as an image carrier, and the reference potential portion is applied to a toner image by a developing device. And the density sensor 2 detects the reflectance of the toner image area. Further, the reflectance (Vp) of the toner image area detected by the density sensor 2 is compared with the reflectance (Vc) of the ground surface on the photoconductor detected in advance by the density sensor 2, and the toner image area reflectance relative to the actual reflectance of the lower ground is compared. Based on the difference between the reflectance ratio (Vp / Vc) and the target reflectance ratio, the toner supply to the developing device by the ICDC function unit 6 is corrected and controlled.
[0020]
The abnormality detection unit 3 detects whether or not an abnormality has occurred in the density detection unit 2. For example, when the reflectance (Vc) of the lower surface of the image carrier on the ground is not equal to the reference value, or when the density sensor 10 If the amplifier gain value is not equal to the reference value, the output of the potential sensor in the image forming unit is abnormal, or the setup fails, for example, an abnormality such that the density detection unit 2 cannot accurately detect the density. When this occurs, a detection signal to that effect is output to the control unit 1.
[0021]
The dot counter 4 counts the number of image dots actually formed in the image forming operation.
In the density control by the ICDC function unit 6 using the dot counter 4, as shown in FIG. 3, image dots in one copy are counted by the dot counter 4 (S11), and an ICDC coefficient is added to the counted number of dots. By multiplying, the consumed toner amount in one copy is obtained (S12, S13). Then, a drive signal corresponding to the obtained consumed toner amount is given to the toner dispensing device 7, thereby controlling the amount of toner supplied from the toner dispensing device 7 to the developing device.
[0022]
FIG. 4 is a diagram showing the correspondence between the ICDC coefficients and the addresses in the memory 8 described above.
As shown in the figure, the memory 8 stores ICDC coefficients corresponding to each color of black (K), yellow (Y), magenta (M), and cyan (C) with a first ICDC coefficient and a second ICDC coefficient. And stored at different addresses.
Among them, the first ICDC coefficients (ICDC-K-1, ICDC-Y-1, ICDC-M-1, and ICDC-C-1) stored at the addresses 7210 to 7213 are the minimum values in the toner dispensing device 7. This is set according to the dispense rate.
On the other hand, the second ICDC coefficients (ICDC-K-2, ICDC-Y-2, ICDC-M-2, ICDC-C-2) stored in the addresses 7214 to 7217 are obtained by the toner dispensing device 7. Are set in accordance with the normal dispensing rate (for example, the dispensing rate target value in FIG. 10).
[0023]
Due to the difference in the reference dispense rate, the second ICDC coefficient is set to a smaller value for the first ICDC coefficient. Therefore, even when the number of image dots counted by the dot counter 4 is the same, the consumed toner amount calculated using the first ICDC coefficient is the same as the consumed toner amount calculated using the second ICDC coefficient. Therefore, the toner supply operation time of the toner dispensing device 7 is set longer accordingly.
The driving condition (toner supply operation time corresponding to the ICDC coefficient in the present embodiment) of the toner dispensing device 7 changed by the control unit 1 in response to the occurrence of the abnormality of the density detecting unit 2 is determined by the target dispensing rate. Even if toner supply is performed, it is sufficient that the setting is made so that abnormal increase (fog) of image density does not occur.
[0024]
Subsequently, a processing procedure by the control unit 1 will be described with reference to FIG.
First, it is determined whether or not an abnormality has occurred in the density detecting means 2 based on the detection signal from the abnormality detecting section 3 (S20). If it is determined that the density detecting means 2 is normal, the first ICDC coefficient among the first and second ICDC coefficients stored in the memory 8 is set in accordance with the minimum dispense rate. Is called from the memory 8 and the called first ICDC coefficient is given to the ICDC function unit 6 to be used (S21). Further, the ADC function unit 5 and the ICDC function unit 6 are respectively operated to execute the density control by ADC + ICDC (S22), and the toner empty detection processing is performed based on the density information obtained via the density detection unit 2 (S23). ). Note that the toner empty detection process here is the same as the process steps enclosed by the broken line in FIG.
[0025]
Thus, at the time of the actual copying operation, the ICDC function unit 6 multiplies the count value of the image dots by the dot counter 4 by the first ICDC coefficient, and according to the toner consumption amount calculated by this, the toner dispensing device 7 To the drive signal. In response to this, the toner dispensing device 7 performs the toner supply operation (the rotation operation of the transport auger) for a predetermined time (hereinafter, the first time) corresponding to the first ICDC coefficient. A corresponding amount of toner is supplied to the developing device. At this time, since the first ICDC coefficient used in the ICDC function unit 6 is set in accordance with the minimum dispense rate, the image density gradually increases as the copy operation is repeated. Therefore, the ADC function unit 7 monitors the density of the toner image (toner patch) obtained via the density detection unit 2 and interrupts or restarts the toner supply operation of the toner dispensing device 7 by the ICDC function unit 6. By doing so, the toner supply amount to the developing device is corrected.
[0026]
On the other hand, if it is determined in step S20 that an abnormality has occurred in the density detecting means 2, the second ICDC coefficient set in accordance with the normal dispense rate is called from the memory 8, and the called second ICDC coefficient is called. The ICDC coefficient of 2 is given to the ICDC function unit 6 to be used (S24). Further, an operation stop command is given to the ADC function unit 5 to execute the density control only by the ICDC function unit 6 (S25).
[0027]
At this time, since the second ICDC coefficient used in the ICDC function unit 6 is set in accordance with the normal dispensing rate as described above, when the density detection unit 2 is normal (the first ICDC coefficient is The amount of consumed toner per the same number of dots is smaller than in the case of using the same, and accordingly, the toner supply operation time in the dispensing device 7 is also changed to the second time shorter than the first time. You. As a result, the amount of toner supplied to the developing device is reduced. Therefore, even when the density control is performed only by the ICDC function unit 6 due to the occurrence of an abnormality in the density detection unit 2, the image density may endlessly increase as in the related art. Disappears.
[0028]
Incidentally, when the second ICDC coefficient is set in accordance with the normal dispensing rate, if the copying operation is continuously repeated under the condition (copy mode) that the actual dispensing rate is always lower than the normal dispensing rate, FIG. As shown in FIG. 2, there is a concern that the image density may decrease with an increase in the number of copies. However, in a general copy usage situation, that is, in a situation where each operator randomly selects and uses a desired copy mode, ICDC is used. Even when the second ICDC coefficient is used in the function unit 6, the decrease in the image density is considered to change extremely slowly. Further, the process of changing the driving conditions by the control unit 1 is only a short-term provisional measure until a serviceman repairs the device when an abnormality occurs in the density detecting means 2, so that a decrease in image density becomes a problem during that time. Is considered to be none. Further, even if the image density is significantly reduced, the problem in the copy processing is smaller than that in the conventional case where fog is generated due to the increase in density.
[0029]
In the above-described embodiment, as the driving condition of the toner dispensing device 7 as the toner supply unit, the ICDC coefficient which is a parameter for determining the toner supply operation time is changed, but the present invention is not limited to this. Instead, for example, the rotation speed of the toner dispensing motor may be changed.
[0030]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, when the abnormality detecting unit detects the abnormality of the density detecting unit, the supply of the toner to the developing device is compared with when the density detecting unit is normal. The driving condition of the toner supply unit is changed by the control unit so that the amount is reduced by a predetermined amount. Without ascending. As a result, the occurrence of fog due to an abnormal increase in image density can be prevented, so that the image density can be stabilized when an abnormality occurs.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a configuration diagram of a density sensor in a density detection unit.
FIG. 3 is a diagram illustrating the principle of concentration control by ICDC.
FIG. 4 is a diagram showing the correspondence between ICDC coefficients and addresses.
FIG. 5 is a flowchart showing a processing procedure according to the present invention.
FIG. 6 is a diagram illustrating a transition of an image density in the embodiment.
FIG. 7 is a basic configuration diagram of a color copying machine.
FIG. 8 is a schematic configuration diagram of a rotary developing device.
FIG. 9 is a schematic configuration diagram of a toner dispensing device.
FIG. 10 is a comparison diagram of a dispense rate.
FIG. 11 is a diagram showing transition of image density by ADC + ICDC.
FIG. 12 is a flowchart showing a conventional processing procedure.
FIG. 13 is a diagram showing a change in image density in the related art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Control part 2 Concentration detection means 3 Abnormality detection part 5 ADC function part 6 ICDC function part 7 Toner dispensing device 8 Memory

Claims (1)

A developing device for developing the electrostatic latent image formed on the image carrier into a toner image,
Toner supply means for supplying toner to the developing device;
The amount of toner supplied from the toner supply unit to the developing unit is controlled by driving the toner supply unit according to the consumed toner amount obtained by multiplying the number of image dots formed by the image by a coefficient. Means for controlling the amount of toner
Density detection means for detecting the density of the toner image developed by the developing device,
Correction means for correcting the amount of toner supplied to the developing device by the toner amount control means based on the density of the toner image detected by the density detection means;
Abnormality detection means for detecting whether an abnormality has occurred in the concentration detection means,
When an abnormality of the density detecting unit is detected by the abnormality detecting unit, the correction operation of the toner supply amount by the correcting unit is stopped, and a coefficient to be multiplied by the number of image dots is calculated from a first coefficient. An image forming apparatus comprising: a control unit that controls the toner supply amount by the toner amount control unit by changing to a second coefficient smaller than the first coefficient .

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