JPS63177176A - Image forming device - Google Patents

Abstract

PURPOSE:To form an image with invariably optimum density by setting image formation condition which determines image density according to the detection result of an environment detecting means and the kind of a developer. CONSTITUTION:The environment sensor 19 consisting of a humidity sensor and a temperature sensor is arranged at the position where the moisture absorption of toner is well reflected, e.g. nearby a toner hopper or developing device, and a control means 18 is connected to the environment sensor 19 and a potential sensor 20. The density decreases under one and the same condition as humidity is low and increases as the humidity increases. For the purpose, a contrast potential Vcont is found by detecting the humidity and the image formation condition is set according to the value, thereby obtaining a stable image regardless of variation in environmental condition. Further, the image formation condition is set at every color and then even a difference in image density due to a difference among the colors of developer is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer using an electrophotographic method, and particularly to an image forming apparatus capable of forming a multicolor image.

(Prior Art) Conventionally, in an image forming apparatus using an electrophotographic method, in order to keep the density of a formed image constant, the charging potential of a photoreceptor drum, the developing bias potential applied to a developing device, etc. are adjusted. Image forming conditions such as development contrast potential and antifogging potential were controlled. In particular, in multicolor copying machines, image forming conditions are set according to the characteristics of the developer for each color, so that the densities of each color are approximately the same.

(Problems to be Solved by the Invention) However, in such conventional examples, although the image forming conditions for each color of developer are adjusted, the image density changes due to changes in the environment in which the developer is placed. In particular, changes in image density due to changes in humidity are noticeable, and the density difference is noticeable because the rate of density change due to moisture absorption differs depending on the color or type of developer. was there.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and its purpose is to eliminate changes in the density of formed images due to changes in the environment in which the developer is placed, and to It is an object of the present invention to provide an image forming apparatus that can always form images of optimum density by eliminating differences in density of formed images depending on the type.

(Means for Solving the Problems) In order to achieve the above object, in the image forming apparatus according to the present invention, an electrostatic latent image is formed on a uniformly charged photoreceptor, and the electrostatic latent image is An image forming apparatus that forms an image on the same transfer material using at least one type of developer, comprising: an environment detection means for measuring an environment near the development means; It is configured by setting image forming conditions that determine image density based on the detection result and the type of developer.

(Function) The present invention having the above-mentioned configuration is provided with an environment detection means for measuring the environment near the developing means, and is capable of image formation in which the image density is determined based on the detection result of the environment detection means and the type of developer. By setting conditions, image density changes due to environmental changes are corrected for each type of developer, thereby eliminating changes in one image density and density differences between developers.

(Example) The present invention will be explained below based on illustrated embodiments.

FIG. 2 is a block diagram showing an embodiment of the image forming apparatus according to the present invention. In the figure, l is a rotary developing device, and the rotating body includes a yellow developing device IY, a magenta developing device IM, It is equipped with a cyan developer IC and a black developer IBK. 2 is a developer (toner) replenishing device to the developing device 1, 2Y is a yellow hopper, 2M is a magenta hopper, 2C is a cyan hopper, and 2BK is a black hopper.

Regarding the overall operation of this color image forming apparatus.

First, the case of full color mode will be briefly explained 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 3 is uniformly charged by a charger 4. Next, image exposure is performed using the laser light E modulated by the yellow image signal of the original (not shown), and an electrostatic latent image is formed on the photoreceptor drum 3. Developing is performed by a yellow developing device IY.

On the other hand, paper feed guide 5a, paper feed roller 6, paper feed guide 5b
The transfer paper that has advanced through 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 IY is transferred by the transfer charger 10 in the transfer section. The transfer drum 9 continues to rotate and transfers the next color (
In FIG. 1, magenta) is prepared for transfer.

On the other hand, the photoreceptor drum 3 is neutralized by the charger 11,
It is cleaned by the cleaning member 12, charged again by the charger 4, and exposed to the next magenta image signal in the same manner as described above. During this time, the developing device
rotates, and the magenta developer IM is placed at a predetermined development position to perform predetermined magenta development.Subsequently, the same process as above is performed for cyan and black, respectively, to transfer four colors. When this is completed, the four-color developed image on the transfer paper is neutralized by each charger 13 and 14, and the gripper 7 is released and the transfer drum 9 is moved by the one-separation claw 15.
is separated and sent to a fixing device 17 by a conveyor belt 16,
A series of full-color printing operations is completed, and a full-color printed image is formed.

Furthermore, in this embodiment, in addition to the above configuration, an environment sensor 19 consisting of a humidity sensor and a temperature sensor is installed at a position where the moisture absorption of the toner is well reflected, such as near the toner hopper or near the developer. .

FIG. 1 is a block diagram showing one embodiment of the present invention. 4
a is a high-voltage power supply that supplies power to the primary charger.

4b is a grid bias power supply provided in the primary charger and supplies power to the grid that controls the amount of charge applied to the drum 3 to a desired value; 1' is a developing bias power supply having a DC component superimposed on a predetermined AC waveform to the developer; It is a power source for supplying power, and 18 is a control means such as a microcomputer that controls the output value of each power source. The control means 18 is also connected to an environmental sensor 19 and a potential sensor 20.

The operation of this embodiment will be explained below. FIG. 3 is a graph showing the relationship between the grid bias voltage (horizontal axis) and the surface potential of the photoreceptor drum 3 (vertical axis). In the figure, Vo corresponds to the surface potential when no light is irradiated, and Vt Corresponds to the surface potential when irradiated with light. As can be seen from the figure, the surface potential Vo, that is, the amount of charge is proportional to the grid bias VC in a limited range (in the range of use). Also, the surface potential Vt after light irradiation has a similar tendency, but the grid bias Vt
The ratio of change to the amount of change in G, that is, the proportionality coefficient is VO
The relationship is larger (α>β) in the case of vL than in the case of vL. Therefore, before performing the print sequence, the control means 1
8 is the preset grid voltage VGI, V
Each VD+V due to G2 is measured by the potential sensor 20, and from each data, a charging curve of VDIVL with respect to a change in grid voltage as shown in FIG. 3 is assumed. Thereafter, when actually forming an image, the image contrast, that is, the difference between the DC component of the developing bias and the surface potential vL after light irradiation, or Vo-
A grid voltage such that Vt becomes a predetermined value is calculated and the grid bias power supply 4b is controlled. Further, in order to prevent toner from adhering to the portion corresponding to the white background of the image, in this example, reversal development is performed, a developing bias with a certain potential lower than Vo (Va) is determined, and the developing bias power source 1 ′ is controlled.

Figure 4 is a graph showing the influence of image density on humidity when printing under the same image forming conditions.As shown in the figure, under the same image forming conditions, the lower the humidity, the lower the density, and the higher the humidity. As time goes on, the concentration increases.

Therefore, by detecting the humidity, determining the contrast potential vc0゜t corresponding to the humidity, and setting the image forming conditions based on that value, it is possible to obtain a stable image regardless of changes in environmental conditions. become. Additionally, as shown in the figure, since the density relative to humidity differs depending on the color, if the image forming conditions are made variable for each color, it is possible to compensate for differences in image density due to differences in developer color. .

The operation of the control means 18 of this embodiment will be specifically explained below based on the flowcharts shown in FIGS. 5(a), 5(b), and 5(c).

First, in the 0 interrupt processing etc. explained based on FIG. 5(a) for processing A, the temperature and humidity are measured with the environmental sensor 19, for example, once every 30 minutes or several times every 30 minutes, and the average value is calculated. The humidity is measured and stored in a buffer area in a memory for, for example, 8 hours. In step (2), absolute humidity or a value corresponding thereto (for example, a mixing ratio) is calculated based on the data. This is because image density is considered to be proportional to absolute humidity, that is, the amount of moisture in the air. In step ■, it is determined whether absolute humidity (mixing ratio) has been calculated for 8 hours, and after calculating the absolute humidity (mixing ratio) for 8 hours, in step
Average values of time, 4 hours, and 8 hours x, y, z
seek. These average values x, y, and z serve as variables when calculating contrast by making the following conditional judgments. In step ■, it is determined whether the 2-hour average value
Make it l. This is because it is determined that the high humidity state has continued for more than 2 hours, and then in step 2, it is determined whether the current value is 111t, 5g or more, and if it is 18.5g or more, the flag is set to C6NT2. This has been low humidity for 2 hours, but is now heading towards high temperatures. Next, step ■
Determine whether the 8-hour average value 2 is 9g or more, and
If it is above, set the flag to C0NT3. As a result, the humidity is considered to be in a medium temperature state for 8 hours or more. Next, in step 2, it is compared whether the 4-hour average value y is 9 g or more, and if it is 9 g or more, the flag is set to C0NT4. This determines that the temperature is moving from low humidity to medium temperature. and.

If it is other than the above, that is, the 4-hour average value is <9g, it is assumed that the humidity is low and the flag is set to C0NT5.

Incidentally, 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 from high humidity to low humidity. In other words, image density is proportional to absolute humidity, but atmospheric humidity The condition is determined based on how much moisture the toner has absorbed, rather than on the amount of moisture absorbed by the toner, so the above condition judgment is made.

Next, in step (2), a variable H for contrast calculation is determined using the contrast flag. This is, for example, C0N
In the case of Tl, since the humidity is completely controlled to high humidity, the variable becomes the 2-hour average value X. Further, in the case of C0NT2, since it is in an intermediate state between low humidity and high humidity, the average value of the 2-hour average value X and the current value W is (x + w)/2.

Furthermore, the general formula for searching and reading out the coefficients of the calculation formula from the table in the memory using the contrast flag and color information is the contrast potential Vcont = at - t
z Hte, h-chH are the above-mentioned variables, and al and bl are coefficients.

Using the coefficients and variables obtained above, the contrast potential vc
ont is calculated and stored in the memory in step (2).0 or more is repeated for each color for four colors.

Figure 6 is a plot of the above calculation formula.As shown in Figure 0, the coefficients are changed for each color, so the differences in density changes for each color as shown in Figure 4 are absorbed and corrected. It became possible.

Next, processing B will be explained based on FIG. 5(b). First, the photosensitive drum is rotated and the primary high voltage power source 4at-ON is turned on, as in a normal copy sequence. Step 0. Set the grid bias to a predetermined value VGI in o and measure the surface potential of the photoreceptor drum You: Measure and store in memory 0 Next, turn on the laser and irradiate the drum with the maximum light intensity, and in step @ set the surface potential after light irradiation 7 Measure the mouth and store it in memory. Furthermore, in steps [stock] and [phase], the grid bias is set to another predetermined value VG2 to measure the surface potential VL2, and then the laser is turned off and step [
The surface potential VOZ is measured at each phase and stored in memory.

This provides measurement data for later-described calculations. Note that the timing of the laser 0N10FF order VGI and VG2 may be changed depending on the sequence, and processing A and processing B are independent of each other, so it does not matter which one is performed first or even if the processing timings are not simultaneous. good.

Next, processing C will be explained based on FIG. 5(C). Processing C must be performed after processing A and B.

First, in step ■, convert VGI, VG2 and measurement data Vo+, VD2, VLI, Vt2 to VD.
The slopes α, β and α−β of the charging curves of and vL, respectively.
Calculate according to the following formula.

Next, in step [phase], the above-mentioned defogging voltage VB stored in the buffer Nilin and the contrast voltage VCOnt calculated in process A are read out, and in step 0, the grid bias VG is obtained as the sum of this vcont and v8. determined by the voltage. That is, the following calculation is performed.

Once the grid voltage is determined in step (2), VD is then determined by calculation.

Vo = α(VG - VGI) +vDI Furthermore, in step [phase], the developing bias DC component (DB) is determined.

D B = Vo −We When it is determined in step [phase] that the above processing has been completed for the four colors, the processing is ended.

As described above, the grid bias control value vG and the developing bias control degree value DB were determined.

The grid bias voltage obtained as above,
Since the developing bias D6 is a value that takes into consideration not only the humidity conditions under which the developer is stirred, but also the characteristics of each color of the developer, an extremely stable image with an appropriate density can be obtained.

Incidentally, the above embodiment can form a multicolor image fJML=7-2
Although described above, the present invention is not limited thereto, and can also be applied to a normal monochrome image forming apparatus.

Further, in the above embodiment, the case where the environment detection means measures the absolute humidity has been described, but the image density may be controlled by measuring elements that color the developer in addition to temperature and humidity.

Furthermore, in the above embodiment, the image forming conditions are determined by the charging potential on the photoreceptor drum, the potential after light irradiation, and the developing bias potential, but the conditions such as the charging potential of the developer are controlled. You may.

(Effects of the Invention) The present invention has the configuration and operation described above, and by setting image forming conditions based on the detection result of the environment detection means and the type of developer, it is possible to change the image density due to environmental changes. This has the effect of eliminating density differences due to differences in developer types, and making it possible to always form images with appropriate density.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an image forming apparatus according to the present invention, and FIG. 2 is a block diagram of the embodiment. Fig. 3 is a graph showing the relationship between grid bias voltage and drum surface potential, Fig. 4 is a graph showing density changes with respect to humidity for each color of developer, and Figs. 5 (a), (b), (C
) are flowcharts showing the procedure for setting the image forming conditions in the same embodiment, and FIG. 6 is a graph showing the relationship between the set contrast potential and humidity. Explanation of symbols 1... Developing device (developing means) 3... Photoreceptor drum 4...-Next charger (charging means) 18... Control means 19... → [T'A boo (environment) Detection means) Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 1b)

Claims (3)

[Claims] (1) An electrostatic latent image is formed on a uniformly charged photoconductor, the electrostatic latent image is visualized by a developing means, and an image is formed on the same transfer material using at least one type of developer. The image forming apparatus includes an environment detecting means for measuring an environment near the developing means, and setting image forming conditions for determining image density based on the detection result of the environment detecting means and the type of developer. Features of the image forming device. (2) The image forming apparatus according to claim 1, wherein the environment detection means detects absolute humidity. (3) The image forming condition is determined by the charging potential of the photoconductor, the electrostatic latent image potential of the photoconductor, and the developing bias potential of the developing means. The image forming apparatus described in .