JPH11184187A - Image forming device and density control method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately control density and to attain a high definition image by detecting reflected light by a detecting means after the output of an irradiating means installed on a density sensor is stabilized, controlling the image density and also continuously rotary-driving an image carrier. SOLUTION: The image carrier 100 is driven by an image carrier drive control part 11 at a timing, that is, before the LED of the density sensor 113 is emitted in accordance with the start of executing a density control. After the image carrier 100 is driven, the LED of the density sensor 113 is emitted. It takes several tens of seconds by the time the output is stabilized just after the LED is energized. Thus, a standby time is arranged. In the case the standby time is not secured, it is allowed to estimate the fluctuation curve of the output and correct the output. Thus, the emitted light quantity of the LED is used in a stable area, besides, the latent image forming effect of the image carrier 100 caused by the continuous irradiation to a fixed point on the image carrier during a power supply standby time is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic process, and more particularly to a technique relating to density control of an image to be formed.

[0002]

2. Description of the Related Art The structure of a multicolor image forming apparatus utilizing an electrophotographic process will be described with reference to FIG.
In the embodiment to which the present invention described later is applied,
A multicolor image forming apparatus having the same configuration as that of the multicolor image forming apparatus is assumed.

The latent images formed for each color by the optical unit 101 on the image carrier 100 are developed by the respective color developing units Dy, Dm,
The toner is developed and visualized by toners of Y (yellow), M (magenta), C (cyan), and K (black) supplied from Dc and Dk, and is transferred to the outer periphery of the transfer belt 102 a plurality of times. A color image is formed. Here, a high voltage is applied to the transfer belt 102 to transfer the toner to the transfer belt 102.
Transcribed above.

[0004] Next, the paper feed unit 103 or the paper feed tray 10
4 is conveyed by a paper conveyance path, and a multicolor image is retransferred from the transfer belt 102. Thereafter, the recording paper 105 is transported by the transport roller 106, is fixed by the fixing unit 107, and is
8 or discharged to the paper discharge unit 109.

Here, each color developing device has a rotating shaft at both ends thereof, each of which is held by the developing device mechanism 110 so as to be rotatable about the shaft. Each developing device is used for selecting a developing device. A rotation is made. Reference numeral 111 denotes a cleaning unit for cleaning the tray on the transfer belt 102; 112, a waste toner unit for holding waste toner from the image carrier 100; and 113, a density sensor.

FIG. 2 shows the structure of the density sensor 113. In FIG. 2, reference numeral 113a denotes a light emitting element as light irradiation means,
113b is a light receiving element for monitoring the irradiation light of the light emitting element 1 from the side, and 113c is a light emission amount control circuit, which monitors the light from the light emitting element 113a with the light receiving element 113b, and outputs the light from the light emitting element 113a by the light emission amount control circuit 113c. The irradiation light quantity is controlled to be constant.

Reference numeral 100 denotes a part of the surface of the image carrier, 113d denotes a light receiving element as a detecting means for monitoring reflected light when the light emitted from the light emitting element 113a is applied to the image carrier 100, and 113e denotes a light receiving element from the light receiving element 113d. Of the received light.

In the above configuration, as shown in FIG. 3, a toner image (hereinafter referred to as a patch) P 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 density sensor 113, the output level of the reflected light is detected, and a difference from a predetermined detection level is stabilized by varying the developing bias to correct the image density. .

[0009]

However, in the above technique, the light emitting element 1 illuminated from the density sensor 113 is used.
The amount of light emitted from the light 13a fluctuates immediately after the start of energization due to the influence of self-heating and the like.

For this reason, processing such as waiting in an energized state until the amount of light emitted from the normal light emitting element 113a becomes stable or performing a correction by predicting a variation curve is performed. 113a to the image carrier 1
If the light is continuously irradiated at the same location of 00, the wavelength band of the light emitting element 1 is close to the sensitivity band of the image carrier, so that the image carrier is slightly charged, causing a phenomenon that the assumed density is disturbed during development.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the above technology, and an object of the present invention is to provide an image forming apparatus capable of performing more accurate density control and a density control method for the image forming apparatus. Is to provide.

[0012]

According to the present invention, in order to achieve the above object, an image which is formed on a surface by a toner image formed by an image forming means using an electrophotographic process and which is rotationally driven is provided. A carrier, light irradiating means for irradiating the toner image formed on the surface of the image carrier or the image carrier with light, and detecting the density of the toner image by detecting reflected light from the toner image An image forming apparatus comprising: a density sensor having a detecting unit; and a density control unit configured to change an image forming process condition of the image forming unit based on a detection result of the density sensor and control a density of a toner image to be formed. In the apparatus, before detecting the reflected light by the detection means, a pre-lighting control means for turning on the light irradiation means, and the light irradiation means being turned on by the pre-lighting control means During that period, characterized by comprising a control means for rotationally driving said image bearing member.

It is also preferable that the image carrier is driven to rotate while the light irradiating means is on.

[0014] It is also preferable that the pre-lighting control means detects that the image carrier is rotating and turns on the light irradiation means.

It is also preferable that the density control means controls the density of the toner image based on the output of the density sensor after the light irradiation means has been turned on by the pre-lighting control means.

It is also preferable that the density control means sets the detection start timing of the density of the toner image by the density sensor based on the time during which the light irradiation means is turned on by the pre-lighting control means.

The density control means controls the density of the toner image by correcting the output of the density sensor when the pre-lighting control means determines that the time during which the light irradiation means has been turned on is insufficient. Are also suitable.

In the density control method of the image forming apparatus,
A toner image formed by an image forming unit using an electrophotographic process is supported on the surface, and an image carrier that is driven to rotate and light is applied to the surface of the image carrier or the toner image formed on the image carrier. A density sensor having a light irradiation unit for irradiating, a detection unit for detecting the density of the toner image by detecting reflected light from the toner image, and a detection unit for the image forming unit based on a detection result of the density sensor. Density control means for controlling the density of a toner image formed by changing image forming process conditions, and a pre-lighting control means for turning on the light irradiation means before detecting the reflected light by the detection means And control means for rotating the image carrier during the period in which the light irradiation means is lit by the pre-lighting control means. Based on the output of the density sensor after the light irradiating means it is turned on by the lighting control means, and controlling the concentration of toner image.

The density control means may start detecting the density of the toner image by the density sensor at a timing set based on the time during which the light irradiation means is turned on by the pre-lighting control means.

The density control means controls the density of the toner image by correcting the output of the density sensor when the pre-lighting control means determines that the time during which the light irradiation means has been turned on is insufficient. Is also good.

[0021]

(Embodiment 1) An image forming apparatus to which the present invention is applied is, for example, the multicolor image forming apparatus shown in FIG. The same components as the electrophotographic process itself and the electric components such as the density sensor 113 can be used, and the description of the device configuration can refer to the above-described configuration. Therefore, in the present embodiment, the description will be given below mainly on the description of the characteristic configuration.

First, 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. 4 is a block diagram showing a configuration relating to the developing bias control. In FIG. 4, reference numeral 1 denotes an A / D converter, which converts an analog detection signal from the density sensor 113 into a digital signal. Reference numeral 2 denotes a data storage unit that stores detection data.

Reference numeral 3 denotes a data comparing unit which determines whether or not the output value of the density sensor 113 on the surface underlayer of the image carrier is within a predetermined value. Reference numeral 4 denotes an image carrier base calibration unit that calibrates the sensor output when the output value of the density sensor 113 largely deviates from the value of the base of the image carrier due to contamination or deterioration.

Reference numeral 5 denotes an LED light quantity setting unit of the light emitting element 113a (hereinafter, referred to as an LED). The LED light quantity is set at the time of calibrating the background output of the image carrier or measuring a patch whose range is over at the time of patch measurement of the density sensor. Adjust the output value or secure the range. Reference numeral 6 denotes a density sensor output shift setting unit, which is used similarly to the LED light amount setting unit 5.

Reference numeral 7 denotes a density calculator which converts the measured sensor output value of the batch 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.
, The high voltage output unit 10 is connected to the developing bias control unit 9.
Apply the specified output to the developing unit.

Reference numeral 50 denotes a CPU in a DC controller (not shown) installed in the main body of the image forming apparatus, and controls each control block described above. Each of the control blocks 1 to 9 inside the CPU 50 may be arranged inside the DC controller or the density sensor 113 depending on the configuration.

FIG. 5 is a flowchart showing the operation of the developing bias control. In FIG. 5, the base of the image carrier is measured 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 the read value of the base of the image carrier changes due to contamination of the density sensor 113 or deterioration over time, the output calibration of the density sensor 113 is performed in S103. The output calibration of the density sensor 113 is performed by A / D in FIG.
The conversion is performed by each block of the converter 1, the data storage unit 2, the data comparison unit 3, the image carrier base correction unit 4, the LED light amount setting unit 5, and the density sensor output shift setting unit 6.

In step S104, the density of the base surface at the position where the patch on the image carrier is to be printed is measured. And S1
At 05, 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.

In step S106, the value read by the density sensor 113 is converted into a density value, and the flow advances to step S107. How to determine the optimum developing bias value in S107 will be described below.

FIG. 6 shows an example of the measurement patch. 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.

The patches Pa, Pb, Pc, P shown in FIG.
FIG. 7 shows the relationship between the density values, which are the measurement results of the d and Pe by the density sensor 113, and the developing bias during patch formation.

In FIG. 7, when the target density value to be obtained from the measured densities of the five patches exists between any two points, the optimum developing bias for the target density is obtained by linear interpolation of the two points. Can be.

FIG. 8 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. 9 shows a case where all the measured patches do not reach the target density, and a peak of the density value is found between Pb and Pd. 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 showing 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. 10 shows the relationship between the image data of the halftone density control patch and the density value. Image data shown in FIG.
In the density characteristic curve, since the rise of the density near the center of the image data is remarkable, as shown in FIG. 11, a process for 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.

Next, a characteristic configuration of the first embodiment of the present invention will be described with reference to FIG. 12, the same components as those in FIG. 4 are denoted by the same reference numerals, and detailed description of the configurations with the same reference numerals will be omitted.

In FIG. 12, reference numeral 11 denotes an image carrier drive control unit, 12 denotes an image carrier drive unit, and 13 denotes an LED emission ON / OFF control unit as a pre-lighting control unit.

FIG. 13 is a flowchart for explaining the features of the first embodiment of the present invention. In FIG. 13, when the density control mode is started, the image carrier is first rotated in S201. In FIG. 12, the image carrier is driven at a timing before the image carrier drive control unit 11 causes the LED of the density sensor to emit light in accordance with the start of the density control (see the timing chart of FIG. 14). After the image carrier is driven, the LED of the density sensor is caused to emit light in S202.

FIG. 15 schematically shows changes in the sensor output due to changes in the light output immediately after the LED is turned on. According to FIG. 15, it takes several tens of seconds until the output is stabilized immediately after the LED is turned on. For this reason, the standby time in S203 is desirably performed in an initial check mode when the power of the image forming apparatus main body is turned on, or during a heating period of the fixing device. If the standby time cannot be secured, the output can be corrected by predicting the output fluctuation curve.

Steps S204 to S211 are the same as those shown in FIG.
The same processing as 101 to S107 is performed.

By performing the above operation, the light emission amount of the LED can be used in a stable region. Further, it is possible to prevent an effect of forming a latent image on the image carrier (image memory in a place where a latent image is not originally required) by continuously irradiating a fixed point on the image carrier during the LED power-on standby time. it can.

(Embodiment 2) FIG. 16 shows the configuration of the second embodiment of the present invention, and FIG. 17 shows a flowchart for explaining the operation of the second embodiment. When an initial check immediately after the power of the image forming apparatus is turned on is started, S3
In step 01, it is determined whether or not it is time to start driving the image carrier 100.

Here, if the image carrier 100 is driven, S
Proceed to step 303 to turn on the LED. If the image carrier 100 has not been driven, the process proceeds to S302, and the LED is kept OFF. If the LED is turned on in S303, S30
Proceeding to 4, the sensor output of the concentration sensor 113 is monitored to determine whether the output is stable.

This can be achieved by sequentially comparing the data with the previous extracted data in the data comparing means 3 shown in FIG. FIG. 18 is a timing chart showing the above operation.

It is also possible to judge that the sensor output has been stabilized after the LED is turned on for a certain period of time based on the sensor output fluctuation curve as shown in FIG.

Further, when sufficient time is not required for LED light emission, it is possible to offset the output by predicting the curve of the fluctuation. If the output is determined to be stable in S304, the developing bias control is started.

When the LED is to emit light, the image carrier 100 is driven so that the image carrier 100 is driven.
The above memory effect can be prevented, and density control can be performed in a stable output state of the LED.

[0052]

As described in the embodiment of the present invention, after the output of the light irradiation means provided in the density sensor is stabilized, the reflected light is detected by the detection means to control the density of the image. By rotating and driving the image carrier, accurate density control can be performed, and a high-quality image can be obtained.

The memory effect in forming a latent image on the image carrier can be suppressed by rotating the image carrier while the light irradiating unit is lit by the pre-lighting control unit.

By detecting that the image carrier is rotationally driven and turning on the light irradiation means, it is possible to use the image carrier that is rotationally driven for purposes other than density control.
Control time can be reduced and power can be saved.

The control time can be reduced by setting the timing for starting the detection of the density of the toner image by the density sensor based on the time when the light irradiation means is turned on by the pre-lighting control means.

If the pre-lighting control means determines that the time during which the light irradiation means has been turned on is insufficient, the output of the density sensor is corrected to control the density of the toner image, thereby reducing the control time. And accurate control can be performed.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a configuration of a density sensor.

FIG. 3 is an explanatory diagram of conventional patch measurement.

FIG. 4 is a block diagram illustrating a conventional developing bias control.

FIG. 5 is a flowchart illustrating a conventional developing bias control.

FIG. 6 is an example of a patch measured by developing bias control.

FIG. 7 is a schematic diagram for obtaining an optimum developing bias value.

FIG. 8 is a schematic diagram for obtaining an optimum developing bias value.

FIG. 9 is a schematic diagram for obtaining an optimum developing bias value.

FIG. 10 is an image data density characteristic curve in halftone density control;

FIG. 11 is a schematic diagram for obtaining a halftone correction curve.

FIG. 12 is a block diagram showing a characteristic configuration of the first embodiment of the present invention.

FIG. 13 is a flowchart for explaining the first embodiment of the present invention.

FIG. 14 is a timing chart showing the operation of the first embodiment of the present invention.

FIG. 15 is a diagram showing an example of output fluctuation of a density sensor.

FIG. 16 is a block diagram showing a configuration of a second embodiment of the present invention.

FIG. 17 is a flowchart for explaining a second embodiment of the present invention.

FIG. 18 is a timing chart showing the operation of the second embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 1 A / D converter 2 Data storage means 3 Data comparison means 4 Image carrier base calibration means 5 LED light quantity setting unit 6 Density sensor output shift setting unit 7 Density calculation unit 8 Density-development bias comparison unit 9 Development bias control unit 10 High-voltage output unit 11 Image carrier drive control unit 12 Image carrier drive unit 13 LED emission ON / OFF control unit (pre-lighting control unit) 50 CPU 100 Image carrier 101 Optical unit 102 Transfer belt 107 Fixing unit 110 Developing mechanism unit 113 Concentration sensor 113a Light emitting element (LED, light irradiation means) 113d Light receiving element (detection means)

Claims (9)

[Claims] 1. A toner image formed by an image forming means using an electrophotographic process is supported on a surface of the toner image.
An image carrier that is driven to rotate, a light irradiating unit that irradiates light to a surface of the image carrier or a toner image formed on the image carrier, and the toner image by detecting reflected light from the toner image A density sensor having detection means for detecting the density of the image, a density control means for changing an image forming process condition of the image forming means based on a detection result of the density sensor, and controlling a density of a toner image to be formed; In the image forming apparatus, before the reflected light is detected by the detection means, a pre-lighting control means for turning on the light irradiation means, and a period during which the light irradiation means is turned on by the pre-lighting control means An image forming apparatus comprising: a control unit configured to rotationally drive the image carrier. 2. The image forming apparatus according to claim 1, wherein the image carrier is driven to rotate while the light irradiation unit is turned on. 3. The image forming apparatus according to claim 1, wherein the pre-lighting control unit detects that the image carrier is rotating and turns on the light irradiation unit. 4. The density control device according to claim 1, wherein the density control unit controls the density of the toner image based on an output of the density sensor after the light irradiation unit is turned on by the pre-lighting control unit. The image forming apparatus according to claim 1. 5. The method according to claim 1, wherein the density control unit sets a timing to start detecting the density of the toner image by the density sensor based on a time when the light irradiation unit is turned on by the pre-lighting control unit. The image forming apparatus according to any one of claims 1 to 4. 6. The density control means controls the density of the toner image by correcting the output of the density sensor when the pre-lighting control means determines that the time during which the light irradiation means has been turned on is insufficient. The image forming apparatus according to claim 1, wherein: 7. A toner image formed by an image forming means using an electrophotographic process is supported on a surface of the toner image.
An image carrier that is driven to rotate, a light irradiating unit that irradiates light to a surface of the image carrier or a toner image formed on the image carrier, and the toner image by detecting reflected light from the toner image A density sensor having detection means for detecting the density of the toner; density control means for controlling the density of a toner image formed by changing image forming process conditions of the image forming means based on a detection result of the density sensor; A density control method for the image forming apparatus, comprising: a pre-lighting control means for turning on the light irradiation means before detecting the reflected light by the detection means; and a light-emitting means turned on by the pre-lighting control means. And control means for driving the image carrier to rotate, wherein the density control means includes a control unit for controlling the density of the density sensor after the light irradiation unit is turned on by the pre-lighting control unit. A density control method for an image forming apparatus, comprising: controlling a density of a toner image based on an output. 8. The method according to claim 1, wherein the density control means starts the detection of the density of the toner image by the density sensor at a timing set based on a time when the light irradiation means is turned on by the pre-lighting control means. A density control method for an image forming apparatus according to claim 7. 9. The density control unit controls the density of the toner image by correcting the output of the density sensor when the pre-lighting control unit determines that the time during which the light irradiation unit is turned on is insufficient. The density control method for an image forming apparatus according to claim 7, wherein the density control is performed.