JP2000039762A - Concentration control device and method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To be able to respond to a change in sensitivity of a density sensor. SOLUTION: Measurement is performed by a density sensor 113, and an irradiation light amount of the density sensor 113 and an output shift level of an output voltage (measurement result) from the density sensor 113 are variably set so that the measurement result falls within an allowable range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a density control apparatus and method for an electrophotographic color image forming apparatus.

[0002]

2. Description of the Related Art The structure of a conventional multicolor image forming apparatus and its operation will be described below with reference to FIG.

In FIG. 1, latent images formed for each color by an optical unit 101 on an image carrier 100 are Y (yellow), M (magenta), and M (magenta) supplied from respective color developing units Dy, Dm, Dc, and Dk. C (cyan), K (black)
The transfer belt 10 is developed and visualized by each color toner.
The image is transferred a plurality of times on the outer periphery of the image forming apparatus 2 to form a multicolor image. Here, a high voltage is applied to the transfer belt 102 to transfer the toner onto the transfer belt 102. Next, the recording paper 1 supplied from the paper supply unit 103 or the paper supply toner 104 is used.
05 is conveyed by a paper conveyance path, and a multicolor image is retransferred from the transfer belt 102.

After that, the recording paper 105 is transported by the transport rollers 10.
6 and is fixed by the fixing unit 107, and is discharged to the discharge tray unit 108 or the discharge unit 109.
Here, each color developing device has a rotation support shaft at both ends thereof, each of which is rotatably held on the developing device mechanism 110, and each developing device is rotated for selecting a developing device. You.
Reference numeral 111 denotes a cleaning unit for cleaning toner on the transfer belt 102; 112, a waste toner unit for holding waste toner from the image carrier 100; and 113, a density sensor.

In the above configuration, as shown in FIG. 2, a toner image (hereinafter referred to as a patch) 20 formed on the image carrier 100 is disposed in a direction perpendicular to the surface of the image carrier 100. Light is emitted from the light emitting element 1 included in the density sensor 113, the reflected light is detected by the light receiving element 2, and a difference from a predetermined detection level is corrected as a change amount corresponding to a developing bias. In order to stabilize the image density.

Here, an example of the content related to the density control will be described. The density control includes a development bias control for obtaining a development bias value that is the maximum value of the toner density, and a halftone for controlling the intermediate density by changing the image data while fixing the development bias value determined by the development bias control. There are two types of density control. Here, the description of the developing bias control will be described.

FIG. 3 is a block diagram showing a configuration relating to the developing bias control. In FIG. 3, reference numeral 3 denotes an A / D converter, which converts an analog detection signal from the density sensor (light receiving element) 113 into a digital signal. Reference numeral 4 denotes a data comparing unit, which determines whether or not the output value of the density sensor on the surface base of the image carrier is within a predetermined value. 5 is LE
A D light quantity setting unit that varies the LED light quantity to secure an output range in the case of several types of patch measurement.

[0008] Data storage means 6 complements the detected data. Reference numeral 7 denotes a density calculator which converts the measured sensor output value of the patch into a density value. Reference numeral 8 denotes a density-development bias comparison unit which determines the density value converted by the density calculation unit 7 and the value of the development bias value corresponding to the density value.

Reference numeral 9 denotes a developing bias control unit, which outputs a high voltage output unit 10 so as to output the determined value of the developing bias.
Give an order to The high voltage output unit 10 is a developing bias control unit 1
The output specified from 1 is applied to the developing device. Reference numeral 50 denotes a CPU in a DC controller (not shown) installed in the image forming apparatus main body. Each of the blocks 3 to 9 in the CPU 50 may be a DC controller or a concentration sensor 1 depending on the configuration.
13 in some cases.

FIG. 4 is a flowchart showing the operation of the developing bias control. In FIG. 4, the base measurement of the image carrier is performed in S101. The process proceeds to S102, and if the read value of the base of the image carrier indicates a predetermined value, the process proceeds to S104. If there is a change in the reading value of the base of the image carrier due to contamination of the density sensor 113 or deterioration over time, the output calibration of the density sensor is performed in S103.

The output calibration of the density sensor is performed by A in FIG.
This is performed by each block of the / D converter 3, the data comparison means 4, the LED light quantity setting unit 5, and the data storage means 6.
In S104, the density of the base surface at the position where the patch on the image carrier is to be printed is measured. In step S105, the patch density is measured. Here, by measuring the density of the base in S104, the density of the patch from the base can be measured in contrast. After the reading value of the density sensor 113 is converted into a density value in S106, S107
Proceed to. How to determine the optimum developing bias value in S107 will be described below.

FIG. 5 shows an example of a measurement patch. 20-a
Has the lowest concentration and 20-e has the highest concentration. This concentration is schematically represented by hatching. Note that the number of patches is not limited to this example, and varies depending on the size of the diameter of the image carrier, the time required for density control, and the like. Patches 20-a, 20-b, 20-c, 20- shown in FIG.
FIG. 6 shows the relationship between the density values obtained by the density sensors 113 of d and 20-e and the developing bias value during patch formation.

In FIG. 6, when a target density value to be obtained from among the measured densities of five patches exists between any two points, an optimum phenomenon bias for the target density is obtained by linear interpolation of the two points. Can be.

FIG. 7 shows a case where all the measured patches do not reach the target density. In this case, linear interpolation is performed on the two patches having the density closest to the target density, and an optimum developing bias value for the target density is predicted.

FIG. 8 shows a case where all the measured patches do not reach the target density, and a peak of the density value is found between 20-b to 20-d. In this case, the value of the developing bias of the patch having the density closest to the target density (the patch that reaches the peak of the density value) is the value of the optimum developing bias.

After the optimum developing bias indicating the maximum density is determined by the developing bias control, the halftone density control is performed. Also in the case of the halftone density control, a plurality of patches are printed on the image carrier, and the patch density is measured by the density sensor 113 as in the case of the development bias control. FIG. 9 shows the relationship between the image data of the intermediate length density control patch and the density value.
In the image data-density characteristic curve shown in FIG. 9, the rise of the density near the center of the image data is remarkable.
As shown by 0, a process of deriving a halftone correction curve by calculation and linearly correcting the characteristic curve is performed. As a result, the reproduction accuracy of the intermediate density at which the color reproducibility of the image changes greatly can be improved.

[0017]

However, in the conventional image carrier measurement at the time of toner image density control, the output voltage (referred to as reference voltage v0) when the image carrier is irradiated with light is determined by using a color image forming apparatus. There has been an inconsistency that the surface of the image carrier is shaved due to the durability and the light sensitivity to light is increased due to the material characteristics of the image carrier. Also, the density sensor becomes dirty due to toner contamination inside the image forming apparatus,
As a result, there is a problem that light sensitivity is deteriorated.

Accordingly, it is an object of the present invention to provide a density control device and method capable of coping with a change in light sensitivity.

[0019]

In order to achieve the above object, a first aspect of the present invention is to irradiate a toner image formed on an image carrier by an electrophotographic process with light by a density sensor. A density controller that measures the density of the toner image by receiving the reflected light in the density sensor and photoelectrically converts the density, and controls image forming conditions based on the measurement result; Determining means for determining whether or not is within an allowable range; and if the determination is negative, outputting the amount of light emitted from the density sensor and the photoelectric conversion result of the density sensor so as to fall within the allowable range. Control means for correcting the sensitivity of the density sensor by variably setting the voltage shift level.

According to a second aspect of the present invention, in the density control device according to the first aspect, the sensitivity correction of the density sensor by the determination unit and the control unit is performed immediately before image measurement for controlling the image forming condition. It is characterized by performing.

According to a third aspect of the present invention, in the density control device according to the first aspect, a plurality of images having different densities are formed on the image carrier, and the density sensor measures the densities of the plurality of images. The first determination unit obtains a sensitivity characteristic curve based on the density measurement results of the plurality of images, and the control unit variably sets the light amount and the output shift level so that the sensitivity curve falls within an allowable range. It is characterized by the following.

According to a fourth aspect of the present invention, a density sensor irradiates a toner image formed on an image carrier by an electrophotographic process with light, and the reflected light is received by the density sensor for photoelectric conversion. By measuring the density of the toner image, based on the measurement result, in a density control method for controlling image forming conditions, it is determined whether or not the sensitivity of the density sensor is within an allowable range. If obtained, the sensitivity correction of the density sensor is performed by variably setting the amount of light emitted from the density sensor and the output voltage shift level of the photoelectric conversion result of the density sensor so as to fall within an allowable range. Features.

According to a fifth aspect of the present invention, in the density control method according to the fourth aspect, the sensitivity correction of the density sensor is performed immediately before image measurement for controlling the image forming conditions. .

According to a sixth aspect of the present invention, in the density control device according to the fourth aspect, a plurality of images having different densities are formed on the image carrier, and the density sensor measures the densities of the plurality of images. And obtains a sensitivity characteristic curve based on the density measurement results of the plurality of images, and variably sets the light amount and the output shift level so that the sensitivity curve falls within an allowable range.

[0025]

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

(Embodiment 1) FIG. 11 shows Embodiment 1 of the present invention.
1 shows a circuit configuration. In FIG. 11, the same portions as those in FIG. 3 of the conventional example are denoted by the same reference numerals, and detailed description thereof will be omitted. In FIG. 11, reference numeral 11 denotes initial setting means.
An initial light amount setting value command is sent to the ED light amount setting means 5. Reference numeral 12 denotes an output shift level setting means, which is a density sensor (light receiving element) 1 according to the result of the data comparing means 4.
A voltage shift is applied to the output voltage from T.13. 50
Is a DC (not shown) installed in the color image forming apparatus main body.
This is the CPU in the controller. Each of the blocks 3 to 11 inside the CPU 50 may be arranged inside the DC controller or the density sensor 113 depending on the configuration.

FIG. 12 is a flowchart for explaining the operation of the first embodiment of the present invention. In FIG. 12, when the sensitivity correction mode is started, first, a reference light amount (P0) for measuring the image carrier is set from the LED light amount setting means 5 according to a command from the initial setting means 11 in S201. S
At 202, the image carrier is measured by the reference light amount P0. Proceeding to S203, the output voltage measured on the image carrier in S202 is sent to the CPU 50, passes through the A / D converter 3, and is compared by the data comparing means 4 to determine whether the output voltage is within an error range with respect to the reference voltage value.

If the comparison result is NG, S20
Proceed to 4. In S204, it is determined whether the transmitted data is within a specified output voltage range. Here, the specified output voltage range indicates the output voltage range of the density sensor 113 and the input voltage range of the CPU 50. If the data is not within the specified output voltage range, the process proceeds to S205, where the output voltage is shifted by the output shift level setting means 12, and this operation is repeated until the output voltage is within the specified output voltage range.
When the data falls within the specified output voltage range, the process proceeds to S206.

In S206, a correction value of v1 / v0 (= α) is calculated from the predetermined reference voltage value (v0) of the image carrier and the actually measured output voltage data (v1). Proceeding to S207, the correction value obtained in S206 is introduced, and the LED light amount setting means is set so as to correct the light emission amount to (P0 / α). Returning to S203 again, if the data comparison results in an error range with respect to the reference value, the sensitivity correction mode ends.

The above processing will be described with reference to the graph shown in FIG. In FIG. 13, the surface of the image carrier 100 is irradiated with light by the density sensor 113, and a voltage value assumed in advance as an output when measuring the reflected light is set to v0. An output voltage curve assumed as an output voltage value of a toner image printed for performing toner image density control on the image carrier based on v0 is represented by (A). Next, the output voltage value on the surface of the image carrier when the sensitivity changes due to the usage durability of the image carrier is represented by v1, and the toner image characteristic curve is represented by (B).

As described in the flowchart of FIG. 12, the surface output voltage v when the sensitivity of the image carrier changes.
1 may exceed the upper limit of the output range shown in FIG. In the curve (B), if v1 exceeds the upper limit of the output range, or if the toner image curve seems to exceed the upper limit of the output range, the output voltage is shifted and the curve is output. Be within the range. The output voltage on the surface of the image carrier at this time is represented by v2, and the toner image curve is represented by (C). When the curves (A) and (C) are compared, the characteristics of (A) and (C) do not match because the sensitivity characteristics of the image carrier have changed due to the durability during use. For this reason, v0 and v2 corresponding to the output voltage on the surface of the image carrier
Are compared, and a process of matching two points is performed by changing the amount of emitted light. Thereby, the change in the sensitivity of the image carrier can be corrected.

In the above embodiment, the case where the sensitivity of the image carrier is changed has been described. However, even when the density sensor is soiled by dust such as toner and the amount of emitted light is reduced, the output voltage shift and the amount of emitted light are similarly varied. Corrections can be made.

(Embodiment 2) FIG. 14 shows Embodiment 2 of the present invention.
FIG. Conventional Example in FIG. 3 and Embodiment 1
The same reference numerals as in FIG. 11 denote the same parts, and a detailed description thereof will be omitted. In FIG. 14, reference numeral 13 denotes a toner image bias setting unit for printing a toner image on an image carrier.

FIG. 15 is a flowchart for explaining the operation of the second embodiment of the present invention. The same processing steps as those in FIG. 12 of the first embodiment are denoted by the same reference numerals, and detailed description will be omitted.

In FIG. 15, if the comparison of the output voltage value data on the surface of the image carrier is within the error range in S203, the process proceeds to S301. In S301, a toner image is printed on the image carrier, and measurement is performed by the density sensor 113.
In the present embodiment, the number of toner images having different densities to be printed on the image carrier is three, but any number of at least one or more toner images may be used.

In the present embodiment, the first toner image is a, the second toner image is b, and the third toner image c. Proceeding to S302, if the measurement result of the toner image a is within the output voltage range, the process proceeds to S303. If it is not within the output voltage range, the process proceeds to S305, where the output shift level is set, and this operation is repeated until the output shift level is entered.

In this case, only the toner image a needs to be printed on the image carrier again. In S303, S3
Similarly to 02, if the measurement result of the toner image b is within the output voltage range, the process proceeds to S304. If it is not within the output voltage range, the process proceeds to S305, where the output shift level is set, and this operation is repeated until the output shift level is entered.

In this case, only the toner image b needs to be printed on the image carrier again. In S304, S3
Similarly to the case of 02, if the measurement result of the toner image c is within the output voltage range, it is output that no measurement error occurs during the toner image density control. If it is not within the output voltage range, the process proceeds to S305, where the output shift level is set, and this operation is repeated until the output shift level is entered.

In this case, only the toner image c needs to be printed on the image carrier again.

The above-described processing will be described with reference to the graph shown in FIG. In FIG. 16, after the surface of the image carrier 100 is measured by the density sensor and the sensitivity correction is completed, the density differences 3 that should be on the reference ideal curve (A) are obtained.
The output voltage values of the two toner images are a0, b0, and c, respectively.
Set to 0. Next, the output voltages of the density sensors when the toner image was actually printed on the image carrier were a1, b1,
c1, a curve formed by connecting the respective points is defined as (B). If the actually measured toner image output exceeds the upper limit of the output range, the output shift level is set so as to fall within the output range. The output voltage values at this time are a2, b2, and c2, and the sensitivity characteristic curve of the density sensor is (C). At this time, if the toner image output b2 or c2 is not within the output range, the output shift level may be further reduced.

Further, when the density sensor is stained by dust such as toner and the toner image characteristics are deteriorated, the output shift level may be increased.

The toner image printed on the image carrier described above may be any of yellow, magenta, cyan, and black.

Further, an arithmetic expression showing a sensitivity curve of the density sensor as shown in FIG. 13 can be obtained by a statistical method (for example, a least-power method) based on three toner image output values. When this arithmetic expression is obtained by the arithmetic function of the CPU, an output value (called an expected value or a predicted value) of the density sensor for a density other than the above three image densities, for example, the highest density is obtained. It is determined whether or not is within the allowable range. The light amount and the output shift level may be variably set when a negative determination is obtained. It goes without saying that the same processing may be performed for the lowest density. This makes it possible to keep the sensitivity characteristic curve of the density sensor within an allowable range.

The sensitivity correction of the density sensors of the first and second embodiments is preferably performed immediately before setting image forming conditions such as toner density control described in the conventional example.

[0045]

As described above, according to the first and fourth aspects of the present invention, even if the sensitivity of the density sensor changes, the sensitivity can be corrected. Stable toner image control can be performed with high accuracy, and deterioration of image quality can be prevented.

According to the second and fifth aspects of the present invention, since the sensitivity of the density sensor is corrected immediately before setting the image forming condition using the density sensor, the image forming condition can be set more accurately. it can.

According to the third and sixth aspects of the present invention, not only the surface of the image bearing member but also a toner image can be formed and the output voltage characteristic (sensitivity characteristic) of the density sensor with respect to the toner density can be better measured. At the same time, the sensitivity characteristics can be kept within an allowable range over a wide range from the lowest to the highest density.

[Brief description of the drawings]

FIG. 1 is a sectional view of an image forming apparatus.

FIG. 2 is a configuration diagram illustrating a conventional toner patch measurement.

FIG. 3 is a block diagram for explaining conventional developing bias control.

FIG. 4 is a flowchart showing a conventional developing bias control content.

FIG. 5 is an explanatory diagram illustrating an example of a patch measured by developing bias control.

FIG. 6 is an explanatory diagram for describing a process for obtaining an optimum developing bias value.

FIG. 7 is an explanatory diagram for describing a process for obtaining an optimum developing bias value.

FIG. 8 is an explanatory diagram for describing a process for obtaining an optimum developing bias value.

FIG. 9 is an explanatory diagram showing an image data-density characteristic curve in halftone density control.

FIG. 10 is an explanatory diagram for describing a process of obtaining an intermediate length correction curve.

FIG. 11 is a block diagram illustrating a circuit configuration according to the first embodiment of the present invention.

FIG. 12 is a flowchart showing processing contents of Embodiment 1 of the present invention.

FIG. 13 is an explanatory diagram for explaining the operation of the first embodiment of the present invention.

FIG. 14 is a block diagram illustrating a circuit configuration according to a second embodiment of the present invention.

FIG. 15 is a flowchart showing processing contents of Embodiment 2 of the present invention.

FIG. 16 is an explanatory diagram for explaining the operation of the second embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 light emitting element 2 light receiving element 3 A / D converter 4 data comparing means 5 LED light quantity setting part 6 data storing means 7 density calculating part 8 density-developing bias comparing part 9 developing bias controlling part 10 high voltage output part 11 initial setting means 12 output Shift level setting means 13 Toner image bias setting unit 20 Toner patch 50 CPU 100 Image carrier 101 Scanner unit 102 Transfer belt 103 Feed tray 107 Fixing device 110 Developing device 113 Density center

Claims (6)

[Claims] 1. A toner image formed on an image carrier by an electrophotographic process is irradiated with light by a density sensor, and the reflected light is received by the density sensor.
A density control device that measures the density of the toner image by performing photoelectric conversion and controls image forming conditions based on the measurement result, and determines whether or not the sensitivity of the density sensor is within an allowable range. Means for determining the density of the density sensor by variably setting the amount of light emitted from the density sensor and the output voltage shift level of the photoelectric conversion result of the density sensor so that the density falls within an allowable range if the determination of no is obtained. And a control means for correcting the sensitivity of the image. 2. The density control device according to claim 1, wherein the sensitivity correction of the density sensor by the determination unit and the control unit is performed immediately before an image measurement for controlling the image forming condition. Characteristic concentration control device. 3. The density control device according to claim 1, wherein a plurality of images having different densities are formed on the image carrier, and the density sensor measures the densities of the plurality of images. The means acquires a sensitivity characteristic curve based on the density measurement results of the plurality of images, and the control means variably sets the light amount and the output shift level so that the sensitivity curve falls within an allowable range. Concentration control device. 4. A method of irradiating a toner image formed on an image carrier by an electrophotographic process with light by a density sensor, and receiving reflected light from the density sensor,
By performing photoelectric conversion, the density of the toner image is measured, and based on the measurement result, in a density control method for controlling image forming conditions, it is determined whether or not the sensitivity of the density sensor is within an allowable range, If the determination is no, the sensitivity correction of the density sensor is performed by variably setting the amount of light emitted from the density sensor and the output voltage shift level of the photoelectric conversion result of the density sensor so as to fall within the allowable range. A concentration control method. 5. The density control method according to claim 4, wherein the sensitivity correction of the density sensor is performed immediately before image measurement for controlling the image forming condition. 6. The density control method according to claim 4, wherein a plurality of images having different densities are formed on the image carrier, and the density sensor measures the densities of the plurality of images. A sensitivity characteristic curve based on the density measurement result of the image, and variably setting the light amount and the output shift level so that the sensitivity curve falls within an allowable range.