JP2631107B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus using a charged image.

[Conventional technology]

In an image forming apparatus such as an electrophotographic copying machine or a printer, controlling image forming conditions and adjusting image density is an important factor for obtaining high image quality.
As a method of adjusting the image density, conventionally, for example, it is possible to detect the surface potential on the photoconductor, control the image forming conditions such as the amount of charge and the amount of exposure, and correct the effects of environmental changes and aging of the photoconductor. In addition, it has been proposed to correct image forming conditions by measuring environmental conditions and the number of copies (prints).

[Problems to be solved by the invention]

However, the charging characteristics of the toner in an electrophotographic apparatus, for example, in a developing process are essentially greatly affected by humidity, and the same is applied to a toner left in a low humidity environment and a toner left in a high humidity environment. A large difference occurs in the image density even under the image forming conditions. For this reason, the conventional image forming apparatus has a problem that it is difficult to appropriately adjust the image density to obtain high image quality.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an image forming apparatus capable of always appropriately adjusting the image density and obtaining high image quality.

[Means for solving the problem]

An image forming apparatus according to the present invention, in an electrophotographic image forming apparatus, comprises: a process unit for forming an image on a photoconductor using a developer; and a first unit for detecting a light portion surface potential and a dark portion surface potential of the photoconductor. Detecting means; controlling means for controlling the process means so that a difference between the light-area surface potential and the dark-area surface potential detected by the first detecting means becomes a target value; Second detecting means for detecting humidity, wherein the control means calculates a history of the water mixing ratio based on a plurality of times of temperature and humidity detected by the second detecting means at predetermined time intervals. Then, the target value is determined according to the calculation result.

The process means is for sequentially forming an image on the photoreceptor using developers of different colors, and the control means is configured to calculate the target value for each color.

[Action]

In the image forming apparatus of the present invention, the control target value of the surface potential of the photoconductor is selected according to the atmospheric conditions in the apparatus,
Image formation is performed by the processing means based on the target value. Thus, the image density is always appropriately adjusted.

〔Example〕

FIG. 1 is a block diagram showing a schematic configuration of an image forming apparatus according to the present invention. In the figure, reference numeral 1 denotes a drum-shaped photosensitive member, and 2 denotes a surface potential measuring device (first detecting means) for detecting a surface state of the photosensitive member 1, and a light portion potential V _L and a dark portion potential on the photosensitive member.
The V _D measured by the detection signal of the surface potential sensor 2a. 3
In primary charger which is powered by the primary high-voltage power supply 4, the grid voltage is controlled so that the grid bias power source 5 by contrast (V _D -V _L) converges to the target value.
Reference numeral 6 denotes a developing device which is energized by a developing bias power supply 7, 8 denotes a temperature near the developing device based on a detection signal of a temperature / humidity sensor 8a,
A temperature / humidity measuring device for measuring humidity, which is provided as second detecting means for detecting an atmospheric condition in the apparatus main body. Then, the target value is selected according to the output of the temperature / humidity measuring device 8. Reference numeral 9 denotes a control device that controls image forming conditions in accordance with the measurement results of the measuring devices, and controls a process unit that forms an image on the photoconductor 1. The control device 9 is constituted by a microcomputer, and a control formula is stored in its memory.

The power of the temperature / humidity measuring device 8 and the control device 9 is supplied directly through a dedicated transformer T without passing through the main switch 10 to each operation and control system as shown in FIG. The transformer T is provided with two windings L ₁ and L _{2. As} soon as the device is installed and the plug 11 is inserted into the outlet, the transformer T is energized. After the output of one winding L ₁ is rectified by the diode stack D _1,
The voltage is stabilized at +5 V by the stabilization circuit 12 and supplied to the control device 9. The output of the other winding L ₂ is rectified by the diode stack D _2, it is supplied as a voltage source of approximately + 24V to temperature and humidity measuring device 8. In the drawing, J ₁ is a connector of the temperature and humidity measurement unit 8 and the temperature and humidity sensor 8a.

FIG. 3 is a block diagram showing a basic configuration of the temperature / humidity measuring device 8. As shown in FIG. 3A, the voltage of about +24 V input from the terminals P ₁ and P ₂ is changed by the power supply circuit 13 to +9 V and −9 V
And supplied as bias power in the measurement circuit. The temperature and humidity sensor 8a is a temperature sensor such as a thermistor.
It consists TH ₁ and polymer resistor output type of the humidity sensor HU ₁ Tokyo, bias supply + 9V through a resistor R ₁ is supplied to the temperature sensor TH _1. In this case, the sensor TH ₁ and the resistor R ₂ is connected in parallel, the value of the resistor R ₂ is a median of (0 to + 50 ° C. to here) is selected (25 ° C. Temperature measurement range and 10kΩ resistance value of the sensor TH ₁₎ of. Then, the temperature sensor output TH ₁ becomes a value of the predetermined voltage range by an operational amplifier (operational amplifier) 14, from the terminal P ₃ of the control device 9 A /
It is sent to the input terminal of a D (analog / digital) converter. The resistance from the oscillator circuit 15 to the humidity sensor HU ₁ R
_3, the amplitude via the capacitor C _1, and the frequency is applied a constant oscillation signal, the value of the resistor R ₃ is a substantially central value of the humidity measuring range is selected. The output of the humidity sensor HU ₁ is sent to an operational amplifier 16 via a capacitor C _2, wherein after being amplified to the value of the predetermined voltage range, a high-precision direct current signal with a linear detection circuit 17. This signal is smoothed further by integrating circuit 18 becomes a low impedance of the signal through the operational amplifier 19 is sent from the terminal P ₄ to the input terminal of the A / D converter of the control unit 9.

FIG. 4 is an external view of the temperature and humidity sensor 8a. FIG. 4 (a) is a front view, and FIG. 4 (b) is a plan view.
Temperature and humidity sensor 8a includes a temperature sensor TH ₁ and humidity sensor HU ₁ is covered by dust-proof filter 20, it is mounted on the printed circuit board 21. The temperature / humidity sensor 8a can be formed as a hybrid IC by printing a thick film on a ceramic substrate and soldering. In addition, as shown in FIG.
That is, the operational amplifiers 22 and 23 may be integrally connected to the output sides of the sensors TH ₁ and HU ₁ . In this case, the sensor unit and the measurement unit can be separated, and the installation location of the sensor 8a can be selected as an optimal location. FIG. 6 shows a specific circuit example of the temperature / humidity measuring device 8 to which the above-mentioned temperature / humidity sensor 8a is connected. Figure J ₁ through J ₃ is connected connector, Q ₁ to Q ₇ is an operational amplifier.

FIG. 7 shows the overall configuration of the apparatus main body. This shows a full-color printer, and a developing device 6
A yellow developing device 6y, a magenta developing device 6m, a cyan developing device 6c, and a black developing device 6bk are mounted in the rotating bodies of the above. The developer (toner) supply device 24 includes a yellow hopper 24y, a magenta hopper 24m, a cyan hopper 24c, and a black hopper 24bk.

Next, the sequence of the entire color printer will be briefly described first taking the case of the full color mode as an example. The photoreceptor 1 rotates in the direction of the arrow shown in FIG.
The secondary charger 3 uniformly charges the battery. Next, image exposure is performed by a laser beam E modulated by a yellow image signal from a document (not shown), and an electrostatic latent image is formed on the photoreceptor 1, and thereafter, is fixed at a predetermined developing position in advance. The development is performed by the yellow developing device 6y.

On the other hand, paper feed guide 25a, paper feed roller 26, paper feed guide 25b
Is transferred by the gripper 27 in synchronism with a predetermined timing signal, and is electrostatically wound around the transfer drum 29 by the contact roller 28 and its opposite pole. The transfer drum 29 rotates in the direction of the arrow in synchronization with the photoreceptor 1, and the developed image developed by the yellow developing device 6y is transferred by the transfer charger 30 in the transfer section. At this time, the transfer drum 29 continues to rotate,
Prepare for transfer of the next color (magenta in the figure).

On the other hand, the photoconductor 1 is discharged by the charger 31 and is cleaned by the cleaning member 32.
And is exposed as described above by the next magenta image signal. During this time, the developing device 6 rotates, and a predetermined magenta development is performed by a magenta developing device 6m fixed at a predetermined developing position. Subsequently, the above-described steps are performed for cyan and black, respectively. When the transfer for four colors is completed, the four-color visual image on the transfer paper is discharged by the chargers 33 and 34, and the grip 27 is turned off. Is released from the transfer drum 29 by the separation claw 35, and is sent to the fixing device 37 by the conveyor belt 36, and a series of full-color print sequences is completed to form a required full-color print image.

Here, in this embodiment, a temperature / humidity measuring device 8 is provided, and the image forming conditions are controlled according to the measurement result. For this reason, the image density is always appropriately controlled so that high-quality prints can be obtained. The details of the control method will be described below.

In FIG. FIG. 8 is showing the characteristics of the humidity sensor HU _1, the horizontal axis represents the mixing ratio of the water vapor, the vertical axis represents the resistance value of the sensor HU _1, the resistance value (1KΩ~10MΩ) voltage values (0V ~ 5V). Further, FIG. 9 is a diagram showing the temperature and humidity characteristics at measuring circuit of Figure 3 (Figure 6), the steep slope of the characteristic curve by inserting a resistor R ₃ As is apparent from FIG. It becomes possible to make it smooth.

The temperature data (T) and the humidity data (V) measured in this way are taken into the microcomputer in the control device 9, and the mixing ratio E is calculated from the following approximate expression based on these data.

FIG. 10 shows an approximate curve and an actual measurement value according to the above-described approximate expression. The solid line indicates the approximate curve, and the black point indicates the actual measurement value. Next, how to correct the target value of the contrast based on the obtained mixture ratio will be described. The data of the mixing ratio obtained as described above is extracted every 30 minutes, and the current measured value and the average values X ₀ , X ₂ , X ₄ , and X _{8 of the} past 2, 4, and 8 hours are obtained, respectively. Contrast (Y _S ) is calculated based on the above data X ₀ , X
₂ , X ₄ and X ₈ are obtained by the following equations.

Y _S = β ₁ Y ₀ − (α ₀ X ₀ + α ₂ X ₂ + α ₄ X ₄ + α ₈ X ₈ ) where Y ₀ is a predetermined value of contrast, and coefficients β ₁ , α ₀ , α
₂ , α ₄ and α ₈ are weighting factors respectively determined by six cases predetermined according to the magnitudes of the average values X ₀ , X ₂ , X ₄ and X ₈ . The contrast (Y _S ) obtained in this manner becomes a target value of the contrast (y) obtained in the next surface potential measurement, and the grid voltage and the like are controlled.
The following shows the controlled contrast control by the control of the grid voltage (V _G).

ΔV _G = γ (Y _s −y) (γ is a predetermined value) As described above, by using the surface potential control and the correction based on the state of the history of the past environment, highly accurate image density control can be performed. At that time, since the humidity is measured at the same place as the temperature, the mixing ratio can be obtained with high accuracy, and the humidity can be measured in a wide range.

FIG. 11 is a flowchart showing the operation of calculating the contrast based on the above-mentioned mixture ratio. As described above, in step 101, the average values X ₀ , X ₂ , X ₄ , and X ₈ are obtained, and step 102
Then, the coefficients β ₁ , α ₀ , α ₂ , α ₄ , α ₈ of these average values are obtained from a table in the memory of the microcomputer. The table storing the coefficients differs for each filter color. Then, in step 103, the contrast (Y _S ) is calculated.

FIG. 12 is a flowchart showing the operation of contrast control. First, the initial value ( _VG1 ) of the grid voltage is output in step 104, and in step 105, the light portion potential V _L1 and the dark portion potential V _D1 of the photoconductor ₁ are measured. Next, in step 106, the contrast is calculated based on the measured values (y ₁ = V _D1 −V _L1 ).
Is performed, and in step 107, the grid voltage control value ΔV _G = γ
Calculating the (Y _s -y _1). Then, the grid voltage V _G1 is controlled to be a value obtained by adding the control value △ V _G at step 108, to determine if repeated three times, for example, the control number in step 109, the control and if so Finish. As described above, since the fluctuation of the development characteristics with respect to humidity is completely compensated, and the environmental change and the aging change of the photoreceptor 1 are corrected to zero, a pictorial image requiring high-precision multi-tone reproducibility is required. This is an indispensable technology for color copiers and printers.

In the above embodiment, the contrast control is performed by the mixing ratio. However, the control may be performed by the relative humidity or the absolute humidity. It is also possible to control image forming conditions such as DC value, AC amplitude, AC frequency, etc., and it is easy to control transfer conditions.

Further, the microcomputer can also be used for sequence control.

〔The invention's effect〕

As described above, according to the present invention, it is possible to determine whether the current moisture absorption state of the developer is, for example, from a high humidity state to a low humidity state, or whether the high humidity state is continued, and the like. Since the high humidity state of the developer is not determined only from the water mixture ratio, the image density can be controlled with high accuracy, and an effect of obtaining high image quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a circuit configuration diagram showing a temperature / humidity measuring device of FIG. 1 and a power supply system of a control device, and FIG. 4 (a) and 4 (b) are external views of the temperature and humidity sensor, FIG. 5 is a circuit diagram showing an example in which an amplifier is provided in the temperature and humidity sensor,
FIG. 6 is a circuit diagram showing a specific example of a temperature / humidity measuring device, FIG. 7 is an overall configuration diagram of an apparatus main body, FIG. 8 is a characteristic diagram of a humidity sensor,
FIG. 9 is a temperature / humidity characteristic diagram of the measuring instrument circuit of FIG.
FIG. 10 is a characteristic diagram showing the approximate curve of the mixing ratio and the measured values, and FIG.
The figure shows a flowchart illustrating the operation of contrast calculation.
FIG. 12 is a flowchart showing the operation of the contrast control. DESCRIPTION OF SYMBOLS 1 ... Photoreceptor 2 ... Surface potential measuring device 2a ... Surface potential sensor 3 ... Primary charger 6 ... Developer 8 ... Temperature / humidity measuring device 8a ... Temperature / humidity sensor 9 ... Control device

Claims (2)

(57) [Claims] 1. An electrophotographic image forming apparatus, comprising: a process unit for forming an image on a photoreceptor using a developer; a first detecting unit for detecting a surface potential of a light portion and a surface potential of a dark portion of the photoreceptor; Control means for controlling the process means so that the difference between the light part surface potential and the dark part surface potential detected by the first detection means becomes a target value; and detecting the temperature and humidity in the image forming apparatus. A second detecting means, and the control means, based on a plurality of times of temperature and humidity detected at predetermined time intervals by the second detecting means,
An image forming apparatus comprising: calculating a history of a water mixing ratio; and determining the target value according to the calculation result. 2. The method according to claim 1, wherein said process means forms an image sequentially on said photosensitive member using developers of different colors, and said control means calculates said target value for each color. 2. The image forming apparatus according to claim 1.