JP2001005236A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set appropriate electrifying applying voltage in accordance with environmental fluctuation and fluctuation with time by an inexpensive sensor by lowering the developing bias of a developing unit stepwise and detecting the density of a photoreceptor by a reflection type density sensor and setting a developing bias value at the point of time of detecting that it is equal to or above the specified density as developing start voltage. SOLUTION: A patch pattern is prepared by successively shifting down the developing bias Vb on the photoreceptor 1 stepwise, for instance for every 10 V from -100 V to -10 V by a CPU, so that the density is measured by the reflection type density sensor (P sensor) 9. The analog/digital conversion of the output voltage value of the P sensor 9 is executed, and it is successively compared with a developing start density voltage value A. Then, when the output voltage value becomes equal to or below the developing start density voltage value A first, the value of the developing bias Vb corresponding to the output voltage value is set as the developing start voltage Vk. Also, a bias value to obtain appropriate potential by electrification is set in accordance with the developing start voltage Vk detected and the detected value of a humidity sensor 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printer, a copying machine,
The present invention relates to an image forming apparatus such as a facsimile.

[0002]

2. Description of the Related Art Generally, in an electrophotographic image forming apparatus for performing an electrophotographic process, a photosensitive member is uniformly charged by a brush charger or the like and then exposed to form an electrostatic latent image. Is developed by a developing device and transferred to transfer paper by a transfer device. Further, in the electrophotographic process control device described in Japanese Patent Application Laid-Open No. 7-160073, a toner densitometer for measuring a developer concentration in a developing device in order to control a toner supply amount,
A surface potentiometer that measures the potential of the photoconductor for controlling the potential of the photoconductor is mounted, and a good image is obtained by suppressing the fluctuation of the development γ.

[0003]

In the above-described electrophotographic image forming apparatus, the photosensitive member is charged by a brush charger or the like, so that the charging potential of the photosensitive member does not become an appropriate charging potential due to aging or environmental fluctuation. This causes image deterioration such as fog and reverse fog. Then, the above-mentioned JP-A-7-160
In the electrophotographic process control device described in Japanese Patent Application Laid-Open No. 073, a good image can be obtained by mounting a surface potentiometer and a toner densitometer to suppress the fluctuation of development γ. So it will be cost-up.

According to the present invention, an appropriate charging application voltage is set in accordance with environmental fluctuations and aging fluctuations using an inexpensive reflection type density sensor and humidity sensor without using an expensive toner densitometer or surface potentiometer. It is an object of the present invention to provide an image forming apparatus capable of suppressing fogging and reversal fogging and obtaining an image having an appropriate contrast.

[0005]

In order to achieve the above object, according to the first aspect of the present invention, an electrostatic latent image is formed by uniformly charging a photosensitive member with a charging means and exposing the photosensitive member to the photosensitive member. In an image forming apparatus that develops an electrostatic latent image with a developing device, a reflection type density sensor for detecting the density of the photoconductor, a humidity sensor for detecting humidity, and a developing bias of the developing device are gradually lowered. Developing start voltage detecting means for detecting the density of the photoreceptor with the reflective density sensor, and using the value of the developing bias at the time when the reflective density sensor detects a predetermined density or more as a development start voltage. Things.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, an appropriate charging potential is obtained in accordance with a development start voltage detected by the development start voltage detecting means and a detection value of the humidity sensor. Is set.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the density of the photoconductor is reflected while the charging application voltage of the photoconductor is gradually reduced using the bias value. And a charge application voltage determining means for determining a charge application voltage of the photoconductor at a time when the reflection type density sensor detects a density equal to or higher than a predetermined density.

[0008]

FIG. 1 shows an embodiment of the present invention.
This embodiment is an embodiment of the invention according to claims 1 to 3, and is an example of an electrophotographic image forming apparatus. The photoconductor 1 is, for example, a drum-shaped photoconductor, and is rotationally driven by a driving unit (not shown). As the photoconductor 1, a belt-shaped photoconductor or a sheet-shaped photoconductor may be used.

The photoreceptor 1 is uniformly charged by a brush charging charger 2 as charging means, and is then exposed to exposure light 3 from a laser writing optical unit as exposure means to form an electrostatic latent image. The electrostatic latent image on the body 1 is developed by the developing device 4 to become a toner image. on the other hand,
A transfer sheet as a transfer material is fed from a sheet feeding device (not shown). The transfer sheet 5 transfers a toner image on the photoconductor 1 by a transfer charger 5 as a transfer unit, and then fixes the toner image by a fixing unit 6. Is discharged to the outside.

Further, the photoreceptor 1 is cleaned by the cleaning device 7 after the transfer of the toner image to remove the residual toner, and is discharged by the light 8 from the discharger. Further, a reflection type density sensor (hereinafter referred to as a P sensor) 9 for measuring the amount of toner adhered on the photoconductor 1 (density of the photoconductor 1) between the toner image transfer position and the cleaning position is disposed below the developing device 4. A humidity sensor 10 for measuring the humidity around the photoconductor 1 is disposed below the developing device 4.

FIG. 2 shows a part of the electrical system of this embodiment. The CPU 11 as control means operates based on programs and fixed data stored in the ROM 12. C
The PU 11 performs analog / digital conversion of the output value of the P sensor 9 and the output value of the humidity sensor 10 by an analog / digital converter (A / D) and stores the converted value in the RAM 13.
13 from the analog / digital conversion value stored in photoconductor 1
It is possible to obtain the toner adhesion amount and humidity.

The CPU 11 is connected to a power pack 14 and the like. The power pack 14 is connected to the brush charger 2, the developing device 4 and the transfer charger 5, and the power pack 14 supplies a voltage to the brush charger 2 and the transfer charger 5. Is applied and the power pack 14
, A developing bias is applied to the developing device 4, and the CPU 11 controls the power pack 14 to control the applied voltage of the brush charger 2 and the transfer charger 5 and the developing bias of the developing device 4.

FIG. 3 shows the output characteristics of the P sensor 9.
Since the P sensor 9 has a very high sensitivity at a low concentration, it is suitable for detecting soil pollution. In the output characteristic of the P sensor 9, the toner adhesion amount M / A is 0.05 mg / cm.
An output voltage of 1.2 V of the P sensor 9 which becomes ² is defined as a development start density voltage value (point A in FIG. 4). FIG. 4 shows -10 with respect to the photoreceptor 1 in an uncharged state (depending on time and environment)
The figure shows a change in the output voltage of the P sensor 9 when the developing unit 4 performs development by sequentially shifting down the developing bias from 0 V to 10 V and measuring the density of the developed image with the P sensor 9. In FIG. 4, A indicates a development start density voltage value of 1.2V.

FIG. 5 shows a flow of setting the development start voltage in this embodiment. The CPU 11 sets the development bias selection flag (development bias table selection flag) TableFlag1 and selects the development bias table BiasTable1 because the surface potential of the uncharged photoconductor 1 is 0 V or higher and -100 V or lower. The developing bias table BiasTable1 is set to -1 to -100V.
9 is a table for setting a developing bias every 10 V to 0 V.

Next, the CPU 11 controls the power pack 14 on the uncharged photoreceptor 1 to shift down the developing bias Vb step by step from -100 V to -10 V in steps of 10 V, so that A patch pattern is created, and the P sensor 9 measures the density of the patch pattern. The CPU 11 outputs the output voltage value of the P sensor 9 for the patch pattern (the output voltage value D ₁₀ to the output voltage value D ₁₀ to the developing bias Vb sequentially shifted down every 10 V).
D ₁ ) is converted from analog to digital and stored in the RAM 13, and the output voltage values D _{10 to} D ₁ are used as development start density voltage values A
When sequentially sequentially determines whether or less A compared, corresponding to the output voltage value when either the output voltage value D ₁₀ to D ₁ is equal to or less than the first developing starting concentration voltage value A The value of the developing bias Vb to be performed is defined as a developing start voltage Vk.

[0016] However, the output voltage value D ₁₀ of the density of the patch pattern generated by a developing bias that corresponds already to the output voltage value D ₁₀ in the case was less than developing starting concentration voltage value A exceeds the development start concentration Therefore, it is necessary to lower the developing bias. Therefore, the CPU 11 sets the output voltage value D ₁₀
Is less than the development start density voltage value A, the development bias selection flag (development bias table selection flag) T
riseableFlag2, and the developing bias table Bi
Select asTable2. This developing bias table BiasTable2 is from -200V to -110V.
10 is a table for determining a developing bias at every 10 V up to;

Similarly, the CPU 11 controls the power pack 14 on the uncharged photosensitive member 1 to shift down the developing bias Vb stepwise from -200V to -110V in steps of 10V. The CPU 11 outputs the output voltage value of the P sensor 9 (1
The output voltage values D _{10 to} D ₁ ) corresponding to the developing biases shifted down in steps of 0 V are converted from analog to digital and stored in the RAM 13, and the output voltage values _{10 to} D are stored.
₁ is sequentially compared with the development start density voltage value A, and it is sequentially determined whether the output voltage value is equal to or less than A. Any of the output voltage values D _{10 to} D ₁ becomes the development start density voltage value A or less for the first time. Sometimes, the value of the developing bias Vb corresponding to the output voltage value is set as the developing start voltage Vk. Thus, the CPU 11 constitutes a development start voltage determining unit.

FIG. 7 shows a flow of setting a virtual developing bias for determining an appropriate charging applied voltage in this embodiment. The CPU 11 determines (measures) the development start voltage Vk as described above and detects the detection value Humid of the humidity sensor 10.
The offset voltage corresponding to the development potential and the background potential is set according to the development start voltage Vk and the detection value Humid of the humidity sensor 10.
To obtain a developing bias.

That is, the CPU 11 controls the humidity sensor 10
The detection value Humid is compared with predetermined thresholds Hh and Hl to determine whether the humidity is high, normal humidity, or low,
When the detection value Humid of the humidity sensor 10 is higher high humidity adds the offset voltage H ₁ to the developing start voltage Vk and the developing bias Vb, start developing the offset voltage H ₂ when the detection value Humid of the humidity sensor 10 is normal humidity Voltage V
k and a developing bias Vb, and when the detection value Humid of the humidity sensor 10 is low and low humidity, the offset voltage H ₃
Is added to the development start voltage Vk to obtain a development bias Vb.

As shown in FIG. 6, the inclination of the development γ (development potential vs. image density characteristic) rises when the humidity is high, and the inclination of the development γ changes when the humidity is low. That is, if the developing potential is the same, the image density becomes high at high humidity and becomes low at low humidity. Therefore, the CPU 11
As shown in, when high humidity by adding a small offset voltage H ₁ of 350V to the developing start voltage Vk and the developing bias Vb, when normal humidity by adding conventional offset voltage H ₂ that 400V to the developing start voltage Vk development and bias Vb, at the time of low humidity by adding a large offset voltage H ₃ that 550V to the developing start voltage Vk developing bias V
b. Thus, the CPU 11 constitutes a virtual developing bias setting unit.

FIG. 9 shows that a patch pattern is formed on photosensitive drum 1 by gradually shifting the developing bias from a virtual developing bias value (Vb−50 V) to a virtual developing bias value (Vb + 50 V) in steps of 10 V. 7 shows a change in the output voltage value of the P sensor 9 when the density of the patch pattern is measured by the P sensor 9. In FIG.
A indicates a development start density voltage value of 1.2 V.

FIG. 10 shows a flow of determining the applied voltage value of the present embodiment. In this embodiment, since the charging potential for starting the development is near the virtual developing bias, the charging application voltage table washing flag TableFlag1 is set, and the charging application voltage table ChargeTable1 is set.
Select This charging application voltage table ChargeT
able1 is from (Vb-50V) to (Vb + 50V)
6 is a table for setting a charging application voltage in steps of 10 V every 10 V.

Next, the CPU 11 controls the photosensitive member 1
10 V from (Vb−50 V) to (Vb + 50 V) by the brush charger 2 by controlling the power pack 14.
A patch application pattern is created by applying a charging application voltage to the virtual developing bias Vb in a stepwise manner, and a patch pattern is created. The P sensor 9 measures the density of the patch pattern.

The CPU 11 responds to the patch pattern.
Output voltage value of the P sensor 9 (shifted sequentially every 10 V
Output voltage value D corresponding to each charging applied voltage that has been lowered_Ten
~ D ₁) Is converted to analog / digital and stored in RAM13.
The output voltage value D_Ten~ D₁Is the development start density voltage value
Compare with A sequentially and judge whether it is less than A sequentially
And the output voltage value D_Ten~ D₁Starts development first
Corresponds to the output voltage value when the concentration voltage value becomes less than A
The charging applied voltage to be applied is set as a determined value of the charging applied voltage.

[0025] However, the density of the patch pattern generated by previously charging applied voltage corresponding to the output voltage value D ₁₀ when the output voltage value D ₁₀ of was less developed starting concentration voltage value A exceeds the development start concentration Therefore, it is necessary to lower the charging application voltage. Therefore, the CPU 11 sets the output voltage value D ₁₀
Is less than or equal to the development start density voltage value A, the charging application voltage table selection flag TableFlag2 is set,
Select the charging application voltage table ChargeTable2. This charging applied voltage table BiasTable2
Is 10 from (Vb-150V) to (Vb-50V).
6 is a table for setting a charging application voltage every V.

Similarly, the CPU 11 controls the power pack 14 to charge the photoreceptor 1 in steps from (Vb-150 V) to (Vb-50 V) in steps of 10 V from the (Vb-150 V) to the (Vb-50 V). A patch pattern is created by applying the applied voltage and developing by the developing device 4 with the virtual developing bias Vb, and the P sensor 9 measures the density of the patch pattern.

The CPU 11 responds to the patch pattern.
Output voltage value of the P sensor 9 (shifted sequentially every 10 V
Output voltage value D corresponding to each charging applied voltage that has been lowered_Ten
~ D ₁) Is converted to analog / digital and stored in RAM13.
The output voltage value D_Ten~ D₁Is the development start density voltage value
Compare with A sequentially and judge whether it is less than A sequentially
And the output voltage value D_Ten~ D₁Starts development first
Corresponds to the output voltage value when the concentration voltage value becomes less than A
The charging applied voltage to be applied is set as a determined value of the charging applied voltage.

According to this embodiment, an electrostatic latent image is formed by uniformly charging and exposing the photosensitive member 1 by the charging means 2, and this electrostatic latent image is developed by the developing device 4. In the apparatus, a reflection type density sensor 9 for detecting the density of the photoreceptor 1, a humidity sensor 10 for detecting the humidity, and a density of the photoreceptor 1 while gradually lowering a developing bias of the developing unit 4 are described. A CPU 11 as a development start voltage detecting means for detecting the reflection density sensor 9 and using the value of the development bias at the time when the reflection density sensor 9 detects a predetermined density or more as a development start voltage. Thus, it can be determined that the density of the photoconductor is the density at which development is started.

Further, according to this embodiment, a bias value for obtaining an appropriate charging potential is set according to the development start voltage detected by the CPU 11 as the development start voltage detecting means and the detection value of the humidity sensor 10. Therefore, it is possible to set a virtual developing bias necessary for setting the charging application voltage.

Further, according to this embodiment, the density of the photosensitive member 1 is detected by the reflection type density sensor 9 while the voltage applied to the photosensitive member 1 is gradually lowered using the bias value. A CPU 1 serving as a charge application voltage determining unit that determines a charge application voltage of the photoconductor 1 at the time when the reflection type density sensor 9 detects a predetermined density or more.
1, a suitable charging potential that does not cause fogging or reversal fogging can be applied on the photoreceptor, and a reflection-type density sensor that is less expensive without using an expensive toner densitometer or surface voltmeter, An appropriate charging application voltage can be set in accordance with environmental fluctuations and temporal fluctuations using a sensor, fog and reversal fog can be suppressed, and an image with a more appropriate contrast can be obtained.

[0031]

As described above, according to the first aspect of the present invention, it is possible to determine that the density of the photoconductor is the density at which development is started. According to the second aspect of the present invention, it is possible to set the virtual developing bias necessary for setting the charging application voltage by the above configuration.

According to the third aspect of the present invention, with the above-described structure, it is possible to apply an appropriate charging potential without causing fogging or reversal fogging on the photoreceptor, and use an expensive toner densitometer or surface potentiometer. Without using an inexpensive reflection type density sensor and humidity sensor, it is possible to set an appropriate charging application voltage according to environmental fluctuations and aging fluctuations, and it is possible to suppress fog and reverse fogging, and furthermore, to obtain appropriate contrast Image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing a part of an electrical system of the embodiment.

FIG. 3 is a diagram showing output characteristics of a P sensor in the embodiment.

FIG. 4 shows the output voltage of the P sensor when the development is performed by shifting down the developing bias to the photoreceptor in an uncharged state and the density of the developed image is measured by the P sensor. FIG. 4 is a characteristic diagram showing changes in

FIG. 5 is a flowchart showing a development start voltage setting flow of the embodiment.

FIG. 6 is a characteristic diagram showing the development γ of the embodiment.

FIG. 7 is a flowchart showing a virtual developing bias setting flow for determining an appropriate charging application voltage in the embodiment.

FIG. 8 is a diagram showing a relation between humidity and offset voltage in the embodiment.

FIG. 9 is a characteristic diagram showing a change in an output voltage value of a P sensor with respect to a patch pattern created by changing a developing bias on a photoconductor in the embodiment.

FIG. 10 is a flowchart showing a flow of determining a charging applied voltage according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging means 4 Developing device 9 P sensor 10 Humidity sensor 11 CPU

Claims (3)

[Claims] An image forming apparatus for forming an electrostatic latent image by uniformly charging a photosensitive member with a charging means and exposing the photosensitive member to light, and developing the electrostatic latent image with a developing device. , A humidity sensor for detecting humidity, and a density of the photoreceptor is detected by the reflection type density sensor while gradually lowering a developing bias of the developing device, and the reflection type density is detected. An image forming apparatus comprising: a developing start voltage detecting unit that uses a value of the developing bias at a time when a sensor detects a predetermined density or more as a developing start voltage. 2. An image forming apparatus according to claim 1, wherein a bias value for obtaining an appropriate charging potential is set in accordance with a development start voltage detected by said development start voltage detecting means and a detection value of said humidity sensor. An image forming apparatus comprising: 3. The image forming apparatus according to claim 2, wherein the density of the photoconductor is detected by the reflection type density sensor while the applied voltage of the photoconductor is gradually lowered using the bias value. An image forming apparatus comprising: a charge application voltage determining unit that determines a charge application voltage of the photoconductor at a time when the reflection type density sensor detects a predetermined density or more.