JPH01205179A - Image forming device - Google Patents

Abstract

PURPOSE:To form an image with constant density regardless of the condition of humidity by controlling electrification and development based on the moisture absorption state of toner which changes according to the change of humidity. CONSTITUTION:A control means 18 is provided, which recognizes an absolute humidity from data on temperature and humidity detected by an environment sensor 19 and data on air pressure stored in a non-volatile memory 21 and sets an image forming condition fittest for the moisture absorption condition of toner corresponding to the absolute humidity. Therefore, the change of the image density caused by the change of temperature can be corrected and the difference of the change of density for the humidity different every color can be corrected. By varying the data on air pressure used in case of calculating the humidity, the proper image can be always obtained even in a place such as a high land. Thus, the image is formed with constant density regardless of the condition of humidity.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to an image forming apparatus, particularly an electrophotographic method that performs image recording by developing electrostatic Wfft formed on a photosensitive drum with toner and transferring it to a recording medium. The present invention relates to an image forming apparatus.

[Prior Art] Conventionally, electrophotographic image forming devices such as copying machines,
In particular, in image forming apparatuses that perform multicolor recording, in order to obtain a constant density, latent image formation conditions, development conditions, and
Image formation is performed by controlling transfer conditions and the like.

[Problems to be Solved by the Invention] Particularly in the toner development process, it is known that the density changes significantly under the same image forming conditions due to changes in humidity. However, this correction has not been made in the past. Furthermore, since the degree of density change with respect to moisture absorption differs between each color, a method of controlling the development conditions of each color all at once does not provide satisfactory results.

Therefore, there has been a proposal to make the image forming conditions variable by installing a humidity detection means, but it is considered that absolute humidity affects the image, and since general humidity sensors are relative humidity sensors, absolute humidity can be calculated by calculating need to be converted to . Therefore, it is necessary to detect the temperature with a temperature sensor and also take into account the atmospheric pressure. However, providing an atmospheric pressure sensor will increase the cost. Calculations may be used, but good results may not be obtained if the device is installed at high altitudes.

The above problems are common to image forming apparatuses that perform monochrome recording.

In view of the above problems, it is an object of the present invention to provide an image forming apparatus that can form images with good density regardless of humidity conditions.

[Means for Solving the Problems] In order to solve the above problems, the present invention performs image recording by developing an electrostatic latent image formed on a photosensitive drum with toner and transferring it to a recording medium. In an image forming apparatus, a means for detecting temperature and humidity, a nonvolatile memory for storing atmospheric pressure data corresponding to the installation location of the apparatus, and temperature and humidity data detected by the detecting means and atmospheric pressure data stored in the nonvolatile memory. The present invention employs a configuration that includes a control means that recognizes the absolute humidity and sets the optimal image forming conditions for the toner moisture absorption conditions corresponding to the absolute humidity.

[Sakukawa 1] According to the above configuration, charging and development are controlled based on the moisture absorption state of the toner, which changes in response to changes in humidity, so that images can be formed with a constant density regardless of humidity conditions. .

[Example] Hereinafter, the present invention will be described in detail based on the example shown in the drawings.

FIG. 1 is an overall configuration diagram of an electrophotographic full-color printer. The device shown in the figure exposes a photosensitive drum using a laser beam that is digitally modulated with an image signal. Therefore, the image signal of a digitally read document, Image recording is possible by inputting facsimile image signals, etc.
f ability. In addition, the recorded colors are three primary colors by subtractive color mixing,
Full-color recording is performed using cyan, magenta, yellow, and black.

In the figure, reference numeral 1 denotes a rotary developing device, and the rotating body of the developing device 1 includes a yellow developing device 1Y, a magenta developing device IM, a cyan developing device 1G, and a black developing device IBK.
- Code 2 is a toner replenishment device for replenishing toner as a developer from the outside, 2Y is a yellow hopper, 2M is a magenta hopper, 2C is a cyan hopper,
Further, 28 shows a black hopper.

The entire sequence of this color printer will first be briefly explained using the full color mode as an example. Reference numeral 3 denotes a photoreceptor drum that rotates in the direction of the arrow in the figure, and the photoreceptor on the drum is uniformly charged by a primary charger 4 . Next, image exposure of the yellow of the original (not shown) is performed by the laser beam E modulated by the image signal, and an electrostatic latent image is formed on the photosensitive drum 3. Development is performed by the developing device IY.

On the other hand, paper feed guide 5a, paper feed roller 6, paper feed guide 5b
The transfer sheet that has advanced through the gripper 7 is held by the gripper 7 in synchronization with a predetermined timing, and is electrostatically wound around the transfer drum 9 by the contact roller 8 and its opposing pole. The transfer drum 9 rotates in the direction of the arrow shown in the figure in synchronization with the photosensitive drum 3, and the developed image developed by the yellow developer lY is transferred by the transfer+1tF electric device 10 in the transfer section. The transfer drum 9 continues to rotate in preparation for transferring the next color (magenta in FIG. 1).

On the other hand, the photosensitive drum 3 is neutralized by the primary charger 11, cleaned by the cleaning blade 12, charged again by the primary charger 4, and exposed to the next magenta image signal as described above. During this time, the developing device 1 rotates, and the magenta developing device IM is fixed at a predetermined developing position to perform predetermined magenta development.

Subsequently, one or more steps are performed for cyan and black, respectively, and when the transfer of the four colors is completed, the four-color developed images on the transfer paper are removed by the respective primary chargers 13 and 14, and the above-mentioned Release the gripper 7 and release the gripper 1 by 1
5 and is separated from the transfer drum 9 by the conveyor belt 16.
The image is sent to the fixing device 17, the -1 full color print sequence is completed, and a required full color print image is formed.

Reference numeral 19 denotes an environmental sensor according to the present invention, which is composed of a humidity sensor and a temperature sensor, and is installed at a position where the moisture absorption of the toner is well reflected, such as near the toner hopper or near the developing unit, as shown in the figure. Now, this environmental sensor 1
The density conditions in the recording process for each color are controlled according to the output of step 9.

FIG. 2 is a block diagram of the main parts of the control system of the apparatus shown in FIG.

In the figure, reference numeral 41 is a high-voltage power supply that supplies power to the single-band electric device, and 42 is a grid bias that is provided in the primary charger and that supplies power to the grid that controls the band @il applied to the photosensitive drum 3 to a predetermined value of ψ. A power supply, reference numeral 1', is a power supply for supplying the developing device with a developing bias obtained by superimposing 00 minutes on a predetermined AC waveform, and reference numeral 18 is a control unit for controlling the output value of each power supply. The control unit 18 is also connected to an environmental sensor 19, a surface potential sensor 20, and the aforementioned storage means. Further, reference numeral 22 denotes means for rewriting memory contents;
For example, it is an input means such as a keyboard.

The present invention will be explained in detail below.

FIG. 3 shows the charging characteristics of the photosensitive drum 3.

The horizontal axis in FIG. 3 is the grid bias voltage of the primary charger 4,
The vertical axis indicates the surface potential, and the symbol VD corresponds to the surface potential of the non-photosensitive area (hereinafter referred to as dark area potential), and VL indicates the surface potential of the photosensitive area (hereinafter referred to as bright area potential).

As shown in the figure, it can be seen that VD, that is, the amount of charge changes in proportion to the grid bias within a certain range. Also, [J]? B y1st place VL has a similar tendency, but the amount of change with respect to the grid bias value, that is, the proportional coefficient is V
The relationship is D>VL. In other words, for the same grid bias conversion, the dark potential changes more than the dark potential.

Therefore, before performing the recording sequence, the control unit 18 sets the grid voltages VG1 and VG24 set in advance.
．． : Yo! J From the data obtained from the surface potential sensor 20 for each VD and VL formed, a charging curve of VD and VL with respect to the grid voltage is assumed as shown in FIG.

After that, when actually forming an image, the image contrast is determined from the charging curve obtained by the above operation, that is, the difference between 00 minutes of the developing bias and VL, or VD-V, which will be described later.
A grid voltage such that L becomes a desired value is calculated and the grid voltage source 42 is controlled.

Further, in order to prevent toner from adhering to the part corresponding to the white background of the image, that is, the part corresponding to VD since this embodiment uses a reversal development method, a developing resistor (IAS) of a value (VB) lower than VD by a certain potential is added. The high-voltage power supply 41 is controlled in order to obtain (this development characteristic is shown as DB in Fig. 3).
.

On the other hand, FIG. 4 shows the characteristics of image density d with respect to humidity when printing under the same image forming conditions.

As shown in the figure, it can be seen that under the same image forming conditions, the density decreases on the low humidity side and increases on the high humidity side. Furthermore, as shown in the figure, it is observed that the density change with respect to humidity differs depending on the toner color.

Therefore, by detecting humidity, determining the contrast potential corresponding to the humidity, and setting image forming conditions for each color based on that value, it is possible to obtain stable images even when environmental conditions change. become.

FIGS. 5A to 5C show the image formation control procedure of the control section 18.

FIG. 5(A) shows a process of detecting humidity and determining the optimum contrast conditions for image formation for each color based on the detected humidity.

In steps S1 and S2, temperature and humidity are measured, for example, once every 30 minutes or average values for 30 minutes, and are stored in the buffer area in the memory 21 for 1, for example, 8 hours by interrupt processing or the like.

In the process of step St, the absolute humidity or a value corresponding thereto (for example, a mixing ratio) is determined based on the detected humidity data, and is stored in the memory. This is because image density is considered to be proportional to absolute humidity, ie, moisture content. By the way, the amount corresponding to absolute humidity, here the mixing ratio H
is expressed by the following formula.

PS H=622・ (□) -P However, P: Vapor pressure PS: Saturated vapor pressure 'f= Relative humidity A: Atmospheric pressure Here, since the saturated vapor pressure PS changes depending on the temperature,
It is necessary to detect the temperature with a temperature sensor.

1. For example, the saturated vapor pressure PS is stored in a table such as ROM.
All you have to do is write down the saturated vapor pressure PS and search for the saturated vapor pressure PS that corresponds to the relevant temperature data.Also, even if the atmospheric pressure A is normally treated as a constant value of 1 atm, it will fluctuate by about 15% throughout the year at the same location. Therefore, it does not have much influence on the humidity calculation result.

However, in areas where the atmospheric pressure is extremely low, such as at high altitudes,
If the calculation is performed assuming 1 atm, the error will be too large, making it impossible to obtain appropriate image forming conditions.

For this reason, a storage means configured such that the contents of the memory 21 are retained even when the power is cut off, such as by a backup battery, is provided to store the atmospheric pressure data and use it for the above calculation. Furthermore, since the atmospheric pressure data can be changed during installation or maintenance using the input means 22, appropriate image forming conditions can be obtained at any location.

Note that the relative humidity type is obtained from the data of the humidity sensor and the value of the temperature sensor based on a high-order approximation formula originally obtained from data given in experiments. This is because the humidity sensor has a nonlinear output with respect to relative humidity and has strong temperature characteristics.

Step S1. After calculating the absolute humidity (mixing ratio) in S2 for 8 hours, in step s3, for 2 hours,
Calculate the average value for 4 hours and 8 hours. This average value is determined after step S4.

First, in step S4, the 2-hour average value is the mixing ratio of 16.
It is determined whether or not it is 5g or more, and if so, the flag is set to C0NT1 in step 2 512. This is determined to mean that the high humidity state continued for two hours or more.

Next, in step S5, it is determined whether the current value is 16.5 g or more, and if so, the flag is set to C0NT2 in step S8.

This indicates that the humidity has been low for two hours, but is now heading towards high humidity.

Next, in step S6, it is determined whether the 8-hour average value is 9 g or more, and if so, the flag is set to C0NT3 in step S9. As a result, the humidity is considered to be in a moderate temperature state for 8 hours or more.

Next, in step S7, it is checked whether the 4-hour average value is 9 g or more, and if so, the flag is set to C0NT4 in step 310. This determines that the temperature is moving from low humidity to medium temperature. Then, steps 54-S
7 is denied if the 54-hour average value is less than 9g,
The flag is set to C0N in step Sit as a low humidity state.
Set it to T5.

The above processing is performed because the rate of moisture absorption and dehumidification of the toner is different when going from low humidity to high humidity and when going from high humidity to low humidity. The flag controlled in the manner described above indicates the moisture absorption state of the toner. Image density is proportional to absolute humidity, but it is determined by how much moisture the toner absorbs, not by the humidity of the atmosphere. It can be seen that concentration control is sufficient.

Next, in step S13, variables for contrast calculation are determined based on the flag. This is because, for example, if the flag is C0NTl, the moisture has been completely absorbed due to high humidity, so the variable will be the 3-hour average value X. Also, C0NT2
In the case of , it is an intermediate state between low humidity and high humidity, so the average value of the 3-hour average value X and the current value W is (X+W)/2.

Furthermore, the coefficients of the calculation formula are searched and read from the table in memory using the contrast flag and color information.
The general formula for calculation is VCONT=al-bl-H-- (1), where H is the variable mentioned above and al, bt are the coefficients mentioned above.

A contrast potential is calculated using the coefficients and variables obtained above, and this is repeated for each color by four colors.

In the manner described above, the contrast potential for obtaining the optimum density condition depending on the humidity condition can be determined for each color.

Figure 6 is a plot of the contrast values calculated by memory calculation based on formula (1).As shown in Figure 0, the coefficients are changed for each color, so The process of absorbing and correcting the differences in density changes due to each color became a process.

FIG. 5(B) shows a sequence of charging control prior to image formation.

First, the drum is rotated in the same manner as in a normal copy sequence, the primary high voltage electric power @41 is turned on, and in step S21, the grid bias is controlled to a predetermined value VGI by the grid bias power supply 42.

In step 322, the potential sensor 20 detects the dark potential VD.
I is measured and the measured value is stored in the memory 21.

Next, the photosensitive laser is turned on to irradiate the drum with the maximum amount of light, and in step S23, the bright area potential VLI is measured and stored in the memory 21.

Furthermore, in step S24, the grid bias is set to another predetermined value VG2, and in step S25, VB2 is measured and stored in the memory 21.

Next, in step S26, the laser is turned off and V
B2 is measured and stored in the memory 21, respectively.

As described above, by the control shown in FIGS. 5(A) and 5(B),
Measurement data necessary for image formation control can be obtained. In addition, the on/off order of the photosensitive laser, VGI, VG
The timing of step 2 is as shown in Figure 5 (
B) may be changed in any order other than B).
The processes in FIGS. (A) and CB) are independent of each other, and it does not matter which one is performed first or the timing of the processes may not be simultaneous.

After completing the processing in Figures 5(A) and (B), Figure 5(C)
) image formation is performed.

First, in step S31, grid bias VG1
．． VG2 and surface potential measurement data vni, VB2,
From vLl and VB2, the slope α of the curve of the dark potential VD and the curve of the bright potential VL.

Calculate β and α−β.

Next, in step S32, the bias voltage VB for preventing fog stored in the buffer area and the contrast voltage VCO calculated in the process of FIG.
Read NT.

In step S33, the grid bias VG is set to this VCO.
The voltage obtained is determined by the sum of NT and VB. Here, we perform the following calculations.

Once the grid voltage has been determined, the dark potential VD is calculated in step 534.

VD=a (VG-VGI)+VDl +++ (3
) Further, in step S35, 447,700 minutes of development (D minutes) is determined.

DB=VD-VB (4) In step 336, it is determined whether the above-mentioned calculation has been performed for each color, and when the processing for the four colors is completed, the process shifts to the image forming process similar to the conventional one.

According to the process shown in FIG. 5(C), it is possible to determine the grid bias and developing bias for four colors that can obtain the optimum density according to the moisture absorption state of the toner, and from then on, each color is By forming an image every time, it is possible to always obtain the optimum image density regardless of humidity conditions.

The grid bias and development bias determined in the above example are controlled and taken into account according to environmental conditions, especially absolute humidity, and also take into account differences in environmental conditions for each color, so images with stable density can be obtained. can get.

Furthermore, by rewriting the atmospheric pressure conditions and the like using the input means 22, a constant image density can be obtained regardless of the installation altitude of the apparatus.

Although the apparatus for performing full-color recording using four color toners has been described above, it goes without saying that a similar configuration may be used in a monochrome image forming apparatus.

[Effects of the Invention] As is clear from the above description, the present invention provides an image forming apparatus that performs image recording by developing an electrostatic latent image formed on a photosensitive drum with toner and transferring it to a recording medium. , a means for detecting temperature and humidity, a nonvolatile memory for storing atmospheric pressure data corresponding to the installation location of the device, and absolute humidity from the temperature and humidity data detected by the detection means and the atmospheric pressure data stored in the nonvolatile memory. The system adopts a configuration that includes a control means that recognizes the humidity and sets the optimal image forming conditions for the toner moisture absorption conditions corresponding to the absolute humidity, so changes in image density due to changes in humidity can be compensated for.
In addition, it is now possible to correct differences in density changes due to different humidity for each color, and by making the barometric pressure data used when calculating humidity variable, it is possible to always obtain an appropriate image even in locations such as highlands. Highly reliable image formation! This has the excellent effect of providing Ii placement.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the structure of an image forming apparatus employing the present invention, and FIG. 2 is a block diagram of the control system of the apparatus shown in FIG.
Figure 3 is a diagram showing the surface potential characteristics of the photosensitive drum;
The figure is a diagram of recording density characteristics with respect to humidity, Figure 5 (A) ~
(C) is a flowchart showing the control procedure of the control section of FIG. 2, and FIG. 6 is a diagram showing contrast control according to the state of the control flag. l...Developing device 3...Photosensitive drum 4...
Primary charger 7... Gripper 8... Contact roller 9... Transfer drum 10... Transfer charger 1
1... Charger 12... Cleaning blade 15... Separation claw 16... Conveyor belt 17.
...Fuser 18...Control unit 19...Environmental sensor 20...Surface potential sensor 21...Memory negative/1-LΦsha←-

Claims (1)

[Claims] 1) In an image forming apparatus that records an image by developing an electrostatic latent image formed on a photosensitive drum with toner and transferring it to a recording medium, a means for detecting temperature and humidity;
A nonvolatile memory stores atmospheric pressure data corresponding to the installation location of the device, and absolute humidity is recognized from the temperature and humidity data detected by the detection means and the atmospheric pressure data stored in the nonvolatile memory, and the toner absorbs moisture corresponding to the absolute humidity. An image forming apparatus characterized by comprising a control means for setting image forming conditions optimal to the conditions.