JP2641050B2 - 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 such as a copying machine and an LBP (laser beam printer).

[Conventional technology]

2. Description of the Related Art In an electrophotographic copying machine or the like, image forming conditions such as a latent image forming condition, a developing condition, and a transfer condition are appropriately controlled in order to maintain a constant printing density. That is, under various conditions, the charge amount and exposure amount of the photosensitive member or the process conditions during development and transfer are changed to keep the printing density constant. At that time, if the apparatus performs color printing, it is also necessary to adjust the image forming conditions for each color, and in the case of LBP, it is necessary to control the image forming conditions, for example, by changing the emission intensity of the laser beam. Have been proposed, but are very difficult.

It has also been proposed to use a scorotron as a charger for charging the surface of the photoconductor, and to control the charge amount of the photoconductor by changing the grid voltage.

[Problems to be solved by the invention]

However, even when a scorotron is used as the charger, the appropriate value of the charge amount is conventionally estimated from each surface potential of the photoconductor with respect to two kinds of preset grid voltages. However, there is a problem that image fogging may occur and a stable image cannot be obtained.

The present invention has been made in view of such a problem, and provides an image forming apparatus in which a setting error due to an estimated value is small and a stable image is always obtained.

[Means for solving the problem]

The image forming apparatus of the present invention includes at least three types of chargers for charging the surface of the photoreceptor, a bias power supply for applying a voltage to the grid of the charger, and detecting means for detecting the surface potential of the photoreceptor. The detection means detects the surface potential of the photoconductor by the minimum exposure amount and the surface potential of the photoconductor by the maximum exposure amount when a predetermined voltage set in advance is applied to the grid. Control means for controlling a voltage applied to the grid so that a difference between the surface potential of the photoconductor based on the minimum exposure amount and the surface potential of the photoconductor based on the maximum exposure amount becomes a predetermined value. It is like that.

Further, the control means is configured to calculate a surface potential of the photosensitive member based on a minimum exposure amount and a surface potential of the photosensitive member based on a maximum exposure amount when the predetermined value is a middle voltage of the three types of voltages applied to the grid. Is smaller, the smaller of the three types of voltages and the middle voltage are applied to the grid based on the surface potential of the photosensitive member based on the minimum exposure amount and the surface potential of the photosensitive member based on the maximum exposure amount. Controlling the voltage applied to the grid so that the difference between the surface potential of the photosensitive member based on the minimum exposure amount and the surface potential of the photosensitive member based on the maximum exposure amount becomes a predetermined value; When the surface potential of the photosensitive member based on the minimum exposure amount and the surface potential of the photosensitive member based on the maximum exposure amount when the middle voltage of the types of voltages is applied to the grid, the three types of voltages are used. When the threshold voltage and the middle voltage are applied to the grid, based on the surface potential of the photoreceptor by the minimum exposure amount and the surface potential of the photoreceptor by the maximum exposure amount, the surface of the photoreceptor by the minimum exposure amount The voltage applied to the grid is controlled so that the difference between the potential and the surface potential of the photoconductor due to the maximum exposure amount becomes a predetermined value.

Further, there is provided humidity detecting means for detecting humidity, and the control means determines the predetermined value according to the humidity detected by the humidity detecting means.

Further, the control means controls the voltage applied to the grid for each developing color.

[Action]

In the image forming apparatus of the present invention, by the control device,
When an arbitrary voltage is applied to the grid based on each surface potential of the photoconductor by the minimum exposure amount and each surface potential of the photoconductor by the maximum exposure amount when at least three types of preset voltages are applied to the grid of the scorotron The surface potential of the photosensitive member is estimated based on the minimum exposure amount and the maximum exposure amount, and the image forming conditions are controlled in accordance with the estimated values. For this reason, the estimated value is close to the actual characteristics, and the setting error is reduced.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a basic configuration of an image forming apparatus according to the present invention. In the figure, 1 is a drum-shaped photoconductor,
Reference numeral 2 denotes a primary charger for charging the surface of the photoconductor 1,
It is connected to a secondary high voltage power supply 3 and has a scorotron.
4 is a bias power supply for applying a voltage to the grid of the scorotron, 5 is a rotary developing device, 6 is the bias power supply, 7 is a potential sensor for detecting the surface potential of the photoreceptor 1, 8
Is a temperature / humidity detector installed near the developing device 5 and is composed of a temperature sensor and a humidity sensor. Reference numeral 9 denotes a control device for controlling the output of each power supply, and reference numeral 10 denotes a memory for storing data from each sensor taken into the control device 9 for a certain period.

The control device 9 also functions as the overall control device, and controls the image forming conditions also based on the data stored in the memory 10. Also, an arbitrary voltage was applied to the grid based on each surface potential of the photoconductor with the minimum exposure amount and each surface potential of the photoconductor with the maximum exposure amount when at least three types of preset voltages were applied to the grid. Each surface potential of the photoconductor is estimated based on the minimum exposure amount and the maximum exposure amount, and image forming conditions such as the exposure amount are controlled according to the estimated values.

FIG. 2 is an overall configuration diagram of an electrophotographic full-color printer including the control device 9 described above.

A yellow developing device 5Y, a magenta developing device 5M, a cyan developing device 5C, and a black developing device 5BK are mounted in the rotating body of the rotary developing device 5, respectively. 11 is an external developer (toner) supply device, 11Y is a yellow hopper, 11M
Indicates a magenta hopper, 11C indicates a cyan hopper, or 11BK indicates a black hopper.

First, the sequence of the entire color printer will be briefly described by taking a full color mode as an example. The drum-shaped photoconductor 1 rotating in the direction of the arrow shown in FIG.
It is charged uniformly by the next charger 2. Next, image exposure is performed by a laser beam E modulated by a yellow image signal of a document (not shown), an electrostatic latent image is formed on the photoreceptor 1, and thereafter, the electrostatic latent image is fixed at a developing position in advance. Development is performed by the yellow developing device 5Y.

On the other hand, paper feed guide 12a, paper feed roller 13, paper feed guide 12b
Is transferred by the gripper 14 in synchronization with a predetermined timing, and is electrostatically wound around the transfer drum 16 by the contact roller 15 and its opposite pole. The transfer drum 16 rotates in the direction indicated by the arrow in synchronization with the photoconductor 1, and the developed image developed by the yellow developing device 5Y is transferred by the transfer charger 17 in the transfer section.
The transfer drum 16 continues to rotate, and prepares for transfer of the next color (magenta in FIG. 2).

The photosensitive member 1 is discharged by the charger 18 and is cleaned by the cleaning member 19.
And is exposed as described above by the next magenta image signal. During this time, the developing device 5 rotates,
The magenta developing device 5M is fixed at a predetermined developing position and performs predetermined magenta development. Subsequently, the above process is performed for cyan and black, respectively, and when the transfer for four colors is completed, the four-color visual image on the transfer paper is transferred to each charger.
The electricity is removed by 20, 21 and the gripper 14 is released, separated from the transfer drum 16 by the separation claw 22, separated by the transfer drum 16 by the transfer belt 23, sent to the fixing device 24 by the transfer belt 23, and The full-color print sequence ends, and a required full-color print image is formed.

Here, the control device 9 shown in FIG. 1 controls each image forming condition such as the exposure amount of the photoconductor 1 when obtaining the above-described full-color print image. FIG. 3 and FIG. 4 are characteristic diagrams for explaining the control operation. FIG.
FIG. 4 shows the case of the present embodiment.

In these figures, the horizontal axis corresponds to the grid voltage of the scorotron, the vertical axis corresponds to the surface potential of the photoconductor 1, and
V _D corresponds to the surface potential when light is not irradiated, V _L corresponds to the surface potential when light is irradiated.

As shown in FIG. 3, the surface potential V _D That amount of charge,
Come to limited the scope is proportional to the grid voltage V _G. Also, the potential V _L is also the same tendency, variation ie proportionality coefficient with respect to the grid voltage V _G is the relation of V _D> V _L. Therefore, before performing the print sequence, the control device 9 measures the surface potentials V _D and _VL of the photoreceptor 1 by the preset two grid voltages V _G1 and V _G2 using the potential sensor 7.
From each data, the grid voltage as shown in the figure
The charging curves of V _D and V _L are estimated. Thereafter, when actually forming an image, the image contrast, that is, the developing bias described later, is estimated from the estimated value of the charging curve obtained by the above-described operation.
Difference or V _D -V _L of DC (direct current) component and the surface potential V _L is determined by calculating the grid voltage such that a desired value, and controls the bias current 4.

Then, the portion corresponding to the white background of the image so as not to adhere toner (here a portion corresponding to V _D since a reversal development), obtains the developing bias constant than V _D potential lower value (V _B), a bias The power supply 6 is controlled.

However, the actual surface potential V _D, V _L, as shown in FIG. 3 in two-dot chain line, not in a linear to the grid voltage V _G. Thus, for example, when it becomes V _G2 higher than the grid voltage V _G, the actual value for the estimated value (V _D) is lowered also it is possible that even V _L is higher than the estimated value. In that case, the contrast ie D _B -V _L becomes low and the developing DC bias value D _B obtained from the estimated value (V _D)
The value of the surface potential V _D approaches, the image fog occurs with.

Therefore, in the present embodiment, the surface potential of the photosensitive member 1 to the control device 9 three grid voltage V _G1, V _G2 and V _G3 set in advance before performing the printing sequence
V _D and V _L are measured by the potential sensor 7 and the surface potential with respect to the grid voltage as shown in FIG.
Estimate the linear charging curves of V _D and V _L. The concept of processing after image formation is the same as that in FIG.

Thus, so far it is approximated by V _D, the charging curve of one of the primary functions of the V _L which is the original curve, inconvenience is caused because it was extrapolated charging curve outside the range of the grid voltage V _G1 ~V _G2 However, in this embodiment, since two types of quadratic functions are used for approximation, a high degree of approximation can be obtained within a practical range, and a small setting error and a stable image can be obtained. It became so.

FIG. 5 shows the image density with respect to humidity when printing is performed under the same image forming conditions. As shown in the figure, under the same image forming conditions, the image density decreases on the low humidity side and increases on the high humidity side. Therefore, if the humidity is detected, the contrast potential corresponding to the humidity is obtained, and the image forming conditions are set based on the value, a stable image can be obtained even if the environmental conditions fluctuate. Become.
Furthermore, since the image density differs for each color with respect to humidity,
If the image forming conditions are changed for each color, it is possible to correct a change in image density due to a difference in color.

FIGS. 6-1 to 6-3 are flowcharts showing the above processing operations.

First, the operation of the process 1 in FIG. 6-1 is a control for the humidity, and the temperature and the humidity are set to, for example, every 30 minutes by an interrupt process or the like.
Measure the average value of times or 30 minutes, for example, memory for 8 hours
It is stored in the buffer area in 10. Then, based on the data, the absolute humidity or a value corresponding thereto (for example, a mixing ratio) is obtained (step 101). This is because the image density is proportional to the absolute humidity, that is, the amount of water.

Next, after calculating the absolute (mixing ratio) humidity for 8 hours, the average values of 2 hours, 4 hours, and 8 hours are obtained (steps 102 and 103). This is to make the following condition determination and to use it as a variable during contrast calculation. That is, first, it is determined whether or not the average value of the mixture for 2 hours is 16.5 g or more (step 104). If so, it is determined that the high humidity state has continued for 2 hours or more, and the contrast flag F is set to CONT.
Set to 1 (step 105). Next, it is determined whether or not the current value is 16.5 g or more (step 106). If so, the flag is set to CONT2 (step 107). At this time, although it was low humidity for 2 hours, it is determined that it is now heading for high humidity. Next, it is determined whether the average value for 8 hours is 9 g or more (step 108), and if so, the flag is set to CONT3 (step 109). At this time, the humidity is determined to be in a moderately humid state for 8 hours or more. Next, it is determined whether the average value for 4 hours is 9 g or more (step 110), and if so, the flag is set to CONT4 (step 111). Thus, it is determined that the vehicle is moving from low humidity to medium humidity. Otherwise, that is, if the average value for 4 hours is <9 g, the low humidity state is determined and the flag is set to CONT5 (step 112).

The above processing is performed when the toner goes from the low humidity state to the high humidity state and when the humidity goes from the high humidity state to the low humidity state.
This is performed because the speed of dehumidification is different. That is, although the image density is proportional to the absolute humidity, the image density is determined not by the humidity of the atmosphere but by how much the toner absorbs moisture. Therefore, the above condition determination is performed.

Next, the contrast calculation is determined by the contrast flag F. At this time, for example, in the case of CONT1, the variable is an average value X for 3 hours because the state is completely humid. Further, in the case of CONT2, since the state is an intermediate state between the low humidity and the high humidity, the average value of the three-hour average value X is the average value X + W / 2. Then, based on the contrast flag and the color information, the coefficients of the calculation formula are searched and read from the table in the memory (step 113). The general formula of the calculation is V _COMT = a ₁ −b ₁ H, where H is the above-mentioned variable and a ₁ and b ₁ are the above-mentioned coefficients.

Based on the coefficients and variables obtained above, the contrast potential is calculated and stored in the memory (step 114), and this is repeated for each color for four colors (step 115).

FIG. 7 is a plot of the values selected by the above formula. Since the coefficient is changed for each color, the difference in density change can be absorbed and corrected for each color as shown in FIG.

Next, the operation of the processing in FIG. 6-2 will be described. this is,
This is an operation for estimating the charge amount of the photoconductor 1 when an arbitrary grid voltage is supported. First, the photoconductor 1 is rotated to turn on the high-voltage power supply 3 as in a normal copy sequence. Then, the grid voltage is set to a predetermined value _VG1 (step 20).
1) The surface potential V _D1 of the photoconductor 1 is measured and stored in the memory 10 (step 202). Next, the laser is turned on to irradiate the photosensitive member 1 with the maximum amount of light, the surface potential _VL is measured and stored in the memory 10 (step 203). Also, increase the grid voltage by one more.
To two predetermined values V _G2 (step 204), and the surface potential V _LX
Is measured (step 205), and then the laser is turned off to measure the surface potential _VD2 , and each value is stored in the memory 10 (step 206).

Further, the grid voltage is set to a predetermined value V different from V _G1 and V _G2.
G3 is set (Step 207), the surface potential _VD3 is measured (Step 208), then the laser is _{turned on} to measure the surface potential _VL3 , and each value is stored in the memory 10 (Step 209). After that, the laser power is turned off.

As a result, measurement data for calculation described later is obtained. The laser of ON / OFF order and V _G1, V _G2, the timing of V _G3 is the convenience of the sequence, may be made any order.

The processing 1 and the processing 2 are independent of each other, and either processing may be performed first, and the processing timings may not be simultaneous.

Next, the operation of the process 3 in FIG. 6-3 will be described. This control operation is an operation for controlling the grid bias and the developing bias, and is performed after performing the operations of processes 1 and 2.

First, the above-mentioned grid voltages V _G1 , V _G2 , V _G3 and measurement data V _D1 , V _D2 , V _D3 , V _L1 , V _L2 , V _{L3 are converted} to a V _D curve, V _C.
Curve slopes α ₁ , β ₁ and α ₁ −β ₁ and α ₂ , β ₂ , α
Determined by calculating the _{2-beta 2} (step 301). Next, the aforementioned fog removal voltage V _B stored in the buffer memory
And the contrast voltage V _CONT calculated in process 1 is read (step 302). At this time, V _B + V _CONT should be _calculated
The value of V _D -V _L. Therefore V _B + V _CONT is determined whether greater than V _D2 + V _L2 (step _{302), V B + V CONT} <V
_D2 -V _L2 if _{α 1, β 1, V D1} , V D1, using V _G1 V _G,
Find V _D and D _B. (Steps 304, 305, 306). Also, V _B + V
_{If CONT} ≧ V _D2 −V _L2 , V _G , V _D , and D _B are obtained using α ₂ , β ₂ , V _D2 , V _L2 , and V _G2 (steps 307, 308, and 306). Each calculation formula is represented as follows.

_{V D = α k (V G} -V Gk) V Dk D B = V D -V B (k = 1 or 2) grid bias control values in the above calculation (V _G and the developing bias DC control value (D _B) is determined, V _G of four colors by performing repeat this calculation for each color, D _B is obtained (step 309).

Since the grid bias and the developing bias determined by the above operation take environmental conditions into account and also consider differences in environmental conditions for each color, a print image with extremely stable density can be obtained.

Although estimates the appropriate value of the surface potential with respect to any of the grid voltage by measuring each surface potential of the photosensitive member 1 with respect to three of the grid voltage set in advance in the above example, the type of the grid voltage V _G to be measured By further increasing and approximating,
As shown in FIG. 8, an estimated value close to the actual value is obtained. FIG. 8 shows the case of four-point measurement of four kinds of grid voltages V _{G1 to} V _G4 , and a is a for each section of A, B and C in the figure.
Have _1, b ₁ or a _2, b ₂ or a _3, b ₃ coefficients.

In addition, when the second-order and higher-order approximations are used instead of the first-order approximation, a charging curve having a relatively high degree of approximation as shown in FIG. 9 can be obtained.

For example V _D is expressed as follows.

[Effects of the Invention] As described above, according to the present invention, the estimated value of the charge amount is close to the actual value, the setting error is small, there is no image fogging, and an always stable image can be obtained. There is.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the basic configuration of an image forming apparatus according to the present invention, FIG. 2 is an overall configuration diagram of an electrophotographic full-color printer having the control device shown in FIG. 1, and FIG. FIG. 4 is a characteristic diagram for explaining the operation of the control device of the present embodiment, FIG. 5 is a characteristic diagram showing the relationship between humidity and image density, FIG. FIG. 6 is a flowchart showing a control operation for humidity, FIG. 6-2 is a flowchart showing an operation for estimating a charge amount, and FIG.
FIG. 3 is a flowchart showing the control operation of the grid bias and the developing bias, FIG. 7 is an explanatory diagram showing an example of contrast control with respect to humidity, and FIG. 8 is a characteristic when the number of grid voltages for measuring the surface potential is increased. FIG. 9 is a characteristic diagram showing a charging curve when a higher order approximation is made. DESCRIPTION OF SYMBOLS 1 ... Photoconductor 2 ... Primary charger 3 ... Primary high voltage power supply 4 ... Bias power supply 5 ... Developing device 6 ... Bias power supply 7 ... Potential sensor 8 ... Temperature / humidity detector 9 ... Control Device 10 …… Memory

Claims (4)

(57) [Claims] 1. A charging device for charging a surface of a photoreceptor, a bias power supply for applying a grid voltage of the charging device, a detecting unit for detecting a surface potential of the photoreceptor, and at least three kinds of predetermined predetermined values Detecting the surface potential of the photoreceptor based on the minimum exposure amount when the voltage is applied to the grid and the surface potential of the photoreceptor based on the maximum exposure amount by the detection unit. Control means for controlling a voltage applied to the grid so that a difference between the surface potential of the photoconductor according to the exposure amount and the surface potential of the photoconductor according to the maximum exposure amount becomes a predetermined value. Image forming apparatus. 2. The photosensitive drum according to claim 1, wherein said predetermined value is a surface potential of said photosensitive member based on a minimum exposure amount and a photosensitive member based on a maximum exposure amount when said middle value of said three kinds of voltages is applied to said grid. If the surface potential of the photosensitive member is smaller than the surface potential of the photosensitive member, the smaller of the three types of voltages and the middle voltage are applied to the grid, and the surface potential of the photosensitive member according to the minimum exposure amount and the surface potential of the photosensitive member according to the maximum exposure amount Based on the potential, the voltage applied to the grid is controlled so that the difference between the surface potential of the photoconductor by the minimum exposure amount and the surface potential of the photoconductor by the maximum exposure amount becomes a predetermined value. When the value is larger than the surface potential of the photosensitive member based on the minimum exposure amount and the surface potential of the photosensitive member based on the maximum exposure amount when the middle voltage of the three types of voltages is applied to the grid, the three types are used. Based on the surface potential of the photoconductor by the minimum exposure when the higher voltage and the middle voltage are applied to the grid, and the surface potential of the photoconductor by the maximum exposure, the photoconductor by the minimum exposure 2. The image forming apparatus according to claim 1, wherein a voltage applied to the grid is controlled so that a difference between a surface potential of the photosensitive member and a surface potential of the photosensitive member based on a maximum exposure amount becomes a predetermined value. apparatus. 3. The apparatus according to claim 2, further comprising humidity detecting means for detecting humidity, wherein said control means determines said predetermined value in accordance with the humidity detected by said humidity detecting means. 3. The image forming apparatus according to claim 1 or 2. 4. The image forming apparatus according to claim 1, wherein said control means controls a voltage applied to said grid for each developing color.