JPH05224522A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a proper image density by altering image forming conditions in a control state corresponding to the development system of a developing means to be used, in an image forming device using the plural developing means of the different development systems. CONSTITUTION:This device is provided with a control means 18 for controlling a grid bias power source 4b which supplies power with a required voltage to the grid of the primary electrifier 4, and a development bias power source 1a, which applies a required development bias to a developing device 1. An environmental output from an environmental sensor 19 and an output from a potential sensor 20 which detects the surface potential of a photosensitive drum 3 are inputted to the control means 18. When the image forming conditions are altered, the control means 18 judges the development system of a developing unit to be used for development, calculates a grid bias and a development bias in set order corresponding to its development system, and controls the grid bias power source 4b and the development bias power source 1a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine such as an electrophotographic system or an electrostatic recording system or a laser beam printer, and more particularly to a plurality of developing systems having at least two developing systems having different developing characteristics when the environment changes. The present invention relates to an image forming apparatus including a developing unit.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus using, for example, an electrophotographic system, a charging potential of a photosensitive drum as an image carrier and a developing bias applied to a developing device in order to keep the density of a formed image constant. The potential and the like are adjusted to control the image forming conditions such as the development contrast potential and the fog prevention potential. In particular, in a color image forming apparatus that forms full-color or multi-color images, image forming conditions are set according to the characteristics of the developer for each color so that the densities for each color are almost the same.

However, in such a conventional color image forming apparatus, although the image forming conditions for each color of the developer are adjusted, the image density does not change due to the environmental change in which the developer is placed. Not taken into consideration, the change in the image density due to the change in humidity is particularly remarkable, and the density difference due to moisture absorption differs for each color of the developer, that is, the type of developer causes a difference in density. There was a problem that it would end up.

[0004]

In order to solve the above problems, the environmental change in which the developer is placed is measured by an environmental sensor for a certain period of time, and the image forming conditions are determined by the history of this environmental change and the type of the developer. There has also been proposed a color image forming apparatus in which the color difference is changed. Such a color image forming apparatus is a two-component developer in which each color developer (usually yellow, magenta, cyan, and black) is mixed with a magnetic carrier at a predetermined ratio for each color developer (usually yellow, magenta, cyan, and black) from the viewpoint of color developability and color mixing property. Are using.

By the way, the present inventors have used a one-component magnetic toner for a black developer instead of a two-component developer in which a black toner and a magnetic carrier are mixed, and only the black developer is a one-component non-contact jumping developing method. It has been confirmed that there are many advantages as described below.

(1) The image signal does not fluctuate due to a change in the ratio of toner to magnetic particles.

(2) Since the one-component magnetic toner has magnetism, unnecessary toner can be easily collected and scattering in the apparatus can be reduced.

(3) Since the one-component non-contact jumping developing method is non-contact, an image bearing member (photoreceptor) on which a latent image is formed
It is possible to prevent mechanical deterioration due to contact with.

(4) In the one-component non-contact jumping developing method, the number of constituent elements of the developing device is smaller, so that the developing device can be made smaller and the entire apparatus can be made compact.

In the color image forming apparatus having such a construction, the developing characteristics when the environment changes are largely different between the developing means using the two-component developer and the developing means using the one-component magnetic toner. The conventional control, such as changing the constants of moisture absorption and dehumidification for each color toner of the two-component developer, does not adequately deal with environmental changes, and it is not possible to set an appropriate contrast in a leaving environment and to obtain an appropriate image. There was a drawback that the concentration could not be obtained.

Therefore, an object of the present invention is to set the image forming conditions in a control mode corresponding to the developing system depending on which of a plurality of developing means of at least two developing systems having different developing characteristics when the environment changes is used. An object of the present invention is to provide an image forming apparatus capable of always obtaining a stable image having a proper density even if the environmental conditions are changed.

[0012]

The above object can be achieved by a color image forming apparatus according to the present invention. In summary,
The present invention has at least two development characteristics which are different when the environment changes.
An image forming apparatus that includes a plurality of developing units of one developing method and develops a latent image formed on an image bearing member into a visible image by using any one of the developing units. An environment detecting means for detecting an existing environmental condition, and a control means for changing a set image forming condition according to a detection result of the environment detecting means, the control means corresponding to a developing method of a developing means used. The image forming apparatus is characterized in that the set image forming condition is changed in such a control mode.

[0013]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 2 is a schematic sectional view showing the overall construction of a first embodiment in which the present invention is applied to an electrophotographic color image forming apparatus, which is equipped with a developing device called a rotary developing device. The configuration of the electrophotographic color laser beam printer is shown. This type of printer has a photosensitive drum 3 as an image bearing member which is rotatably supported by a shaft and rotates in the direction of the arrow in the figure, and an image forming means is arranged on the outer peripheral portion thereof. This image forming means may be any means, but in the present example, the primary charger 4 for uniformly charging the photoconductor drum 3 and the color-separated light image or the light image E corresponding thereto.
And an exposure unit 26 that forms an electrostatic latent image on the photosensitive drum 3 by, for example, a laser beam exposure device,
The rotary developing device 1 for converting the electrostatic latent image on the photosensitive drum 3 into a visible image.

The rotary developing device 1 includes four developing devices 1Y, 1M for separately storing four color developers, for example, a yellow color developer, a magenta color developer, a cyan color developer and a black color developer. 1C, 1BK and these four developing devices 1
It is composed of a substantially cylindrical casing that holds Y, 1M, 1C, and 1BK and that is rotatably supported. In this embodiment, the yellow color developer, the magenta color developer, and the cyan color developer are two-component developers in which toners of respective colors and magnetic carriers are mixed in a predetermined ratio, and the black color developer is one component. The magnetic toner is used, and only the black developer is used in the one-component non-contact jumping developing method.

The rotary developing device 1 conveys a desired developing device to a position facing the outer peripheral surface of the photosensitive drum 3 by rotation of the housing, develops an electrostatic latent image on the photosensitive drum, and the housing is By rotating once, so-called full-color development for four colors can be performed. Also,
In each developing device, four hoppers 2Y for separately storing four color developers of yellow (color) developer, magenta color developer, cyan color developer and black color developer of the developer (toner) replenishing device 2, Toners of corresponding colors are supplied from 2M, 2C, and 2BK as needed.

Next, the overall operation of the color laser beam printer having the above configuration will be briefly described by taking the case of the full color mode as an example. First, the photosensitive drum 3 is uniformly charged by the primary charger 4. Next, the laser light E modulated by the yellow image signal of the document (not shown)
Image exposure is carried out, and an electrostatic latent image is formed on the photosensitive drum 3, and the electrostatic latent image is developed by the yellow developing device 1Y which is fixed at the developing position in advance.

On the other hand, the transfer paper P fed through the paper feed guide 5a, the paper feed roller 6 and the paper feed guide 5b is held by the gripper 7 in synchronism with a predetermined timing, and is transferred to the contact roller 8. The opposite pole electrostatically transfers the transfer drum 9
It is wound around (recording material carrier). The transfer drum 9 is rotating in the direction of the arrow in the figure in synchronization with the photosensitive drum 3,
The visible image developed by the yellow developing device 1Y is transferred to the transfer paper P by the transfer charger 10 at the transfer portion. The transfer drum 9 continues to rotate in preparation for the transfer of the visible image of the next color (magenta in FIG. 2).

The photoconductor drum 3 is neutralized by the charger 11, cleaned by the cleaning member 12, and then uniformly charged again by the primary charger 4, and is exposed by the next magenta image signal in the same manner as described above. Receive. During this time, the developing device 1 is rotated so that the magenta developing device 1M is fixed at a predetermined developing position, and predetermined magenta development is performed. Then, the same steps as above are performed.
When the transfer for four colors is completed for cyan and black, the four-color image on the transfer paper is changed to the static elimination chargers 13 and 14.
After the charge is removed by, the transfer paper is separated from the transfer drum 9 by releasing the gripper 7 and operating the separation claw 15, and is sent to the fixing device (heat roller fixing device) 17 by the conveyor belt 16. It is fixed and discharged outside the machine. Thus, a series of full-color printing operations are completed, and the required full-color print image is formed.

Further, in this embodiment, in addition to the above-mentioned structure, the toner hoppers 2Y and 2Y in the apparatus are preferably used.
An environment sensor 19 including a humidity sensor and a temperature sensor is provided at a position where the moisture absorption of the toner is well reflected, such as near M, 2C, and 2BK or near the developing device.

Next, a control system of the color laser beam printer having the above structure will be described with reference to FIG.

FIG. 1 is a block diagram showing a control system of the first embodiment of the present invention, in which a high voltage power source 4a for supplying a required high voltage to the primary charger 4 and an amount of charge given to the photosensitive drum 3 are desired. The grid bias power source 4b for supplying a required bias voltage to the grid of the primary charger 4 which is controlled to the value of, and the development for applying a required developing bias (usually an AC voltage with a DC voltage superimposed) to the developing device 1 Bias power supply 1
A control means 18 such as a microcomputer for controlling each a is provided. A data signal relating to humidity and temperature from the environment sensor 19 is input to the control means 18, and an output signal from a potential sensor 20 that detects the surface potential of the photosensitive drum 3 is also input to the control means 18.

The operation of the control system having the above configuration will be described below.

FIG. 3 is a graph showing the relationship between the grid bias voltage (horizontal axis) and the surface potential of the photosensitive drum 3 (vertical axis). The characteristic curve V _D in the figure shows the surface potential when light is not irradiated. The characteristic curve V _L represents the surface potential when light is irradiated. From the figure, the surface potential V _D , that is, the charge amount is proportional to the grid bias voltage V _G (within the use range) when the range is limited. The surface potential V _L after light irradiation has a similar tendency, but the rate of change of the grid bias voltage V _G with respect to the amount of change, that is, the proportionality coefficient is larger when V _D is V _L (see FIG. 3). As shown
Let α be the proportional coefficient of V _D and β be the proportional coefficient of V _L.
> Β). Therefore, the control means 18 sets the preset grid voltage V before performing the printing sequence.
The voltage values of V _D and V _L at _G1 and V _G2 are measured by the potential sensor 20, respectively, and the charging characteristic curves of V _D and V _{L with} respect to the change of the grid voltage as shown in FIG. 3 are assumed from each measurement data. .. After that, when actually forming an image, from the charging characteristic curve obtained by the above-described operation, the image contrast voltage V _CONT , that is, the difference between the DC component of the developing bias described below and the surface potential V _L after light irradiation is calculated. Alternatively, the grid bias power supply 4b is controlled by calculating a grid voltage such that V _D −V _L becomes a predetermined value. Further, the control unit 18 is constant from the V _D so as not to adhere toner (a portion corresponding to V _D because it uses reverse developing method in the present embodiment) portion corresponding to the white background of the image potential V A developing bias having a value lower by _B is obtained, and the developing bias power source 1a is controlled by this.

Here, the amount of water absorbed by the toner is defined as the amount of water / weight percentage of toner weight. FIG. 4 is a graph showing the correlation between the amount of absorbed water in the toner and the image density when printed under the same image forming conditions. As shown in FIG. 4, two-component developers of yellow Y, magenta M, and cyan C are used. In the case of development, under the same image forming conditions, the lower the toner absorption water content, the lower the density, and the higher the toner absorption water content, the higher the density. Therefore, if the toner absorption water content is detected and the contrast voltage V _CONT corresponding to the detected toner absorption water content is obtained and the image forming condition is set based on the value, the change in the environmental condition is prevented. It becomes possible to obtain a stable image.
In addition, as shown in the figure, since the density with respect to the amount of absorbed water in the toner differs due to the difference in color, if the image forming conditions are made variable for each color, the difference in image density due to the difference in color of the developer is also corrected. can do. FIG. 5 shows the optimum contrast voltage for obtaining a stable image for each toner absorption water content. By varying the image forming conditions for each color as shown by the characteristic curve in FIG. 5, it is possible to correct the difference in image density due to the difference in color of the developer.

On the other hand, in the case of jumping development of a black color developer which is a one-component magnetic toner, as shown in FIG. 4, both the direction and the degree of change of the image density with respect to the amount of moisture absorbed by the toner are yellow. , Which is significantly different from the case of developing with a two-component developer of magenta and cyan. Also, the characteristics of the optimum contrast voltage are greatly different. For this reason, the conventional basic algorithm is the same, but it cannot be handled by the control method in which the coefficient is changed depending on the difference in the characteristics of the developers.

In view of the above points, in the present embodiment, when performing contrast control (changing image forming conditions), it is routine to perform Y, M, and C colors that are two-component development or black colors that are one-component jumping development. And the contrast control methods of the two are made different as shown in FIGS. 6 to 8, for example.

The operation of the control means 18 of this embodiment will be specifically described below with reference to the flow charts shown in FIGS.

The process A shown in FIG. 6 is a flow chart for estimating the present amount of absorbed water in the toner and calculating the optimum contrast voltage V _CONT . First, in the decision block of step S1, the development is performed by the two-component developer Y, M. , C color development or black color jumping development with one-component magnetic toner is determined. In the case of Y, M, and C colors, the initial toner absorption water content x is estimated in the next step S2, and subsequently, in step S3, the temperature and humidity are measured by the environment sensor 19 once every 30 minutes, for example, by interrupt processing. Alternatively, the measurement is performed several times in 30 minutes, the average value thereof is calculated, and the humidity change amount Δα for 30 minutes, the change direction, and the current humidity α ₀ are obtained.

By the way, when the humidity of the toner is adjusted to a certain humidity α, the amount of absorbed water in the toner converges to a certain value x. FIG. 9 is a diagram showing the relationship between the humidity α and the converged toner absorption water content x, and the relationship is expressed by a function of x = f ₁ (α) (or α = f ₁ ^-1 (x) as an inverse function). It represents. The toner absorbed water content in a state where the humidity is sufficiently adjusted to the humidity α _{1 to} α ₅ is x _{1 to} x ₅ , respectively. When the color of the toner changes or the physical properties change, the relationship between the humidity α and the amount x of absorbed water of the toner also changes. For example, as shown in the figure, x = f
_The relationship is represented by a function of ₂ (α) (or its inverse function α = f ₂ ^-1 (x)).

The time during which the toner is conditioned depends on the initial amount of moisture absorbed by the toner and the subsequent change in humidity (current humidity, amount of change in humidity, and whether the humidity has changed to higher or lower humidity). Direction). FIG. 10 is a diagram showing how the amount of absorbed water in the toner changes from the initial value with the lapse of time after the change in humidity. It is assumed that the humidity is switched to the humidity α ₃ at time T ₀ in the state where the initial toner absorption water amount is x ₁ , x ₂ , x ₄ , and x ₅ . Initial values _{x 1, x 2, x 4} , x 5 is the time to converge on the toner absorbed moisture content x ₃ in humidity alpha ₃ (time in which the toner is wet humidity alpha ₃ two tone) Those who dehumidification longer than moisture T ₁ , T ₂ , T ₄ , T ₅ (where T ₂ <T
₁ <T ₄ <T ₅ ). The time for convergence and the amount of absorbed water in the process of convergence are determined by the physical properties of the toner. If the relationship shown in FIG. 10 is used, if the humidity α ₃ continues for a time T ₅ or more, the toner absorption water content at this time is x ₃ regardless of the past toner absorption water content. It can be estimated that

The amount x ′ of toner absorbed water after 30 minutes has passed from the initial stage is the humidity change Δα for 30 minutes, the direction of change,
It can be estimated based on the current humidity α ₀ and the toner absorption water content x ₃ 30 minutes before. An example of the estimation calculation formula is that the relationship of α = f ₁ ⁻¹ (x) as shown in FIG. 9 is used to (1) determine that moisture absorption, that is, α ₀ ≧ f ₁ ⁻¹ (x ₃ )
When (= α ₃ )

[0033]

[Equation 1] (However, k ₁ is a constant proportional to the moisture absorption time constant of the toner.) (2) When it is determined that dehumidification occurs, that is, α ₀ ≤f ₁ ^-1 (x ₃ )
When (= α ₃ )

[0034]

[Equation 2] (However, k ₂ is a constant proportional to the moisture desorption time constant of the toner).

Next, x '= x is set, and the amount of absorbed water in the toner after the next 30 minutes can be similarly estimated.
The calculation of the present toner moisture absorption amount x ′ from the present humidity α ₀ and the toner moisture absorption amount 30 minutes before 30 minutes is generalized to the above equations (1) and (2): (3) α ₀ ≧ f _When ^1-1 (x)

[0036]

[Equation 3] (However, k ₁ is a constant proportional to the water absorption time constant of the toner) (4) When α ₀ ≤f ₁ ^-1 (x)

[0037]

[Equation 4] (However, k ₂ is a constant proportional to the moisture desorption time constant of the toner). In this way, if the toner absorption moisture content is calculated every 30 minutes, the current toner moisture absorption content can be estimated (steps S4 and S5). If the current toner absorption water content can be estimated, the optimum contrast voltage V _CONT for obtaining a stable image can be known from the relationship shown in FIG. 5 (step S7).

Next, the process B will be described with reference to FIG. The process B is to measure the relationship between the grid bias voltage V _G and the surface potential V _S shown in FIG. 3 described above when the laser is turned on and when the laser is turned off. Similar to the process A described above, first, in the determination block of step S10, it is determined whether the development is the Y, M, or C color development using the two-component developer or the black jumping development using the one-component magnetic toner. Subsequent to this determination, the photosensitive drum 3 is rotated and the high-voltage power supply 4a is turned on in the same manner as in the normal copy sequence regardless of whether the color is Y, M, C or black.
Next, in the case of Y, M, and C colors, a predetermined grid bias value V _G1 is output from the grid bias power supply 4b in step S11, and the surface potential V _D1 of the photosensitive drum 3 is detected by the potential sensor 20 in step S12. Measure and store in memory. Next, the laser is turned on, the photosensitive drum 3 is irradiated with the maximum amount of light, and the surface potential V _L1 after the laser light irradiation is measured in step S13 and stored in the memory. Next, in order to measure V _D2 and V _L2 in FIG. 3, step S14 is performed.
Then, the grid bias from the grid bias power source 4b is set to another predetermined value V _G2 , and similarly, step S15.
At, V _L2 is measured and stored in memory. Next, V _D2
To turn off the laser to measure
Measure _D2 and store in memory. And the high voltage power supply 4a
Also, the grid bias power supply 4b is turned off to end the operation. As a result, measurement data for the calculation described later is obtained.

The order of turning on / off the lasers and the timing of the grid bias voltages V _G1 and V _G2 may be changed depending on the sequence. Further, in the present embodiment, the potentials when the laser is turned on and off are measured, but it is also possible to measure the potentials of a plurality of sample outputs with a laser output system capable of multi-value output. Further, the processing A and the processing B are independent of each other, whichever may be performed first, and the processing timings may not be the same.

Next, the process C will be described with reference to FIG. The process C must be performed after the processes A and B are performed.

First, in the decision block of step S20, whether the development is Y, M, or C color development using a two-component developer is 1
It is determined whether the black jumping development is performed by the component magnetic toner. In the case of Y, M and C colors, in step S21 V _G1 , V _G2 and measurement data V _D1 , V _D2 , V _L1 , V
The slopes α, β and α-β of the respective charging characteristic curves shown in FIG. 3 for _L2 to V _D and V _L are calculated according to the following equations.

[0042]

[Equation 5] Next, in step S22, the fog removal voltage V _B and the contrast voltage V _CONT calculated in the process A stored in the buffer area of the memory are read. Then, in step S23, the grid bias voltage V _G is set to V _CONT
And V _B is determined to be a voltage that can be obtained. That is, the following calculation is performed.

[0043]

[Equation 6] When the grid bias voltage is obtained by the above formula, V _D is then obtained in step S24. The calculation formula is as follows.

V _D = α (V _G −V _G1 ) + V _D1 Further, in step S25, the DC component V _db of the developing bias is obtained. The calculation formula is as follows.

V _db = V _D -V _{B When} it is judged that the above processing is completed for the three colors (only the two-component developer) (YES in step S26), the processing is completed.

From the above, the grid bias control value V _G ,
The development bias control value V _db is obtained for all two-component development of three colors.

The grid bias and the developing bias thus obtained are extremely stable because they take into consideration not only the humidity condition in which the developer has been placed but also the characteristics of each color of the two-component developer. An image of proper density can be obtained.

Next, when it is judged in the judgment block of step S1 of FIG. 6 that the development is the black color jumping development of the one-component magnetic toner, the following processing is performed.

In the black color jumping development, as shown by the dotted line in FIG. 4, the relationship between the amount of absorbed water in the toner and the image density does not change monotonously as in the case of the two-component development of the other three colors, but the toner. The image density has a maximum value when the amount of absorbed water is a predetermined value. This is probably because the jumping development shows the highest image density when the toner charge amount is a predetermined value. Therefore, the relationship of the optimum contrast voltage with respect to the amount of absorbed water in the toner also has a characteristic having a minimum value as shown by the dotted line in FIG. Therefore, the contrast control algorithm is based on this characteristic.

[0050] Specifically, for example, (1) image density switch the calculation formula for obtaining the optimum contrast voltage to the boundary of x _j as if x _j toner absorption amount of water has a maximum value. (2) Since the characteristics of FIG. 5 are not monotonous, it may be necessary to more accurately estimate the amount of absorbed water in the toner, and the accuracy of estimation of the amount of absorbed water in the toner can be improved by increasing the accuracy of the reading value from the humidity sensor. The humidity sampling interval is shortened from 30 minutes to 10 minutes to increase the humidity. It is achieved by adopting a method such as. In the case of black jumping development, the processing steps are the same as in the case of the other three colors described above, and therefore, the same step numbers are assigned and detailed description is omitted.

Also for the potential control processing shown in FIGS. 7 and 8, black jumping development is performed differently from the other three colors. Specifically, the values of V _G1 and V _G2 are changed according to the difference in the optimum contrast voltage. For example, other 3
In the case of color two-component development, the grit bias voltage after control is expected to be about -400 V, and V _G1 = -300
V and V _G2 = -500V, whereas the black jumping development has a grit bias voltage after control of-.
It may be expected to be about 500 V, and in this case, V _G1 = -400 V and V _G2 = -600 V are set. Of course, different settings for the three-color two-component development and the black jumping development for realizing the accurate potential control according to the contrast voltage difference are not limited to those described above. Also in this case, the processing steps are the same as in the case of the other three colors, and therefore, the same step numbers are assigned and detailed description thereof is omitted.

The humidity detection contrast control method to which the present invention is applicable is not limited to the above. For example, the method can also be applied to a method of determining the optimum contrast potential by estimating the amount of moisture absorbed by the toner based on a plurality of average values of detected humidity for a certain period (2-hour average, 4-hour average, 8-hour average, etc.).

Further, in the above-mentioned embodiment, 2 having different developing characteristics is used.
Two-component development and one-component jumping development have been shown as examples of one development method, but the present invention is not limited to this, and for example, two-component development and conductive magnetic brush development have different environmental characteristics. The image forming apparatus using a plurality of developing means of the developing system can be applied not only to the color image forming apparatus but also to a normal single color image forming apparatus.

In the above embodiment, the case where the environment sensor measures the humidity has been described. However, in addition to the humidity such as the absolute moisture content and the temperature, the environment sensor measures the factors affecting the toner and controls the image density. Good.

Furthermore, in the above embodiment, the case where the image forming conditions are determined by the charging potential on the photosensitive drum, the potential after light irradiation, and the developing bias potential is described. Other conditions such as the proportion of toner included may be controlled.

[0056]

As is apparent from the above description, the image forming apparatus according to the present invention has at least two different environmental characteristics when changing the image forming conditions according to the environment detection result from the environment detecting means. Since it is determined which developing method of the plurality of developing methods of the developing method is used and the image forming condition is changed in a control mode corresponding to the developing method used, it is possible to change the environment. As a result, there is a remarkable effect that a defect that the image density varies and an extremely stable image having an appropriate density is always obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a control system of a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic sectional view showing the overall configuration of the first embodiment of the present invention.

FIG. 3 is a characteristic diagram showing a relationship between a grid bias voltage and a surface potential of a photosensitive drum.

FIG. 4 is a characteristic diagram showing a change in image density with respect to a toner absorption moisture amount for each color of a developer.

FIG. 5 is a characteristic diagram showing a relationship between an optimum contrast voltage and a toner absorption moisture amount for each color of a developer.

FIG. 6 is a flowchart showing a procedure for setting image forming conditions according to the first embodiment of this invention.

FIG. 7 is a flowchart showing a procedure for setting image forming conditions according to the first embodiment of this invention.

FIG. 8 is a flowchart showing a procedure for setting image forming conditions according to the first embodiment of this invention.

FIG. 9 is a characteristic diagram showing a relationship between humidity and the amount of moisture absorbed by toner that converges with the humidity.

FIG. 10 is a characteristic diagram showing changes over time in the amount of moisture absorbed by the toner when the humidity suddenly changes.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 rotary developing device 1Y yellow developing device 1M magenta developing device 1C cyan developing device 1BK black developing device 1a developing bias power source 3 photoconductor drum 4 primary charger 4a high voltage power source 4b grid bias power source 9 transfer drum 18 control means 19 environment sensor 20 Potential sensor 26 Exposure means

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Claims (2)

[Claims] 1. A latent image formed on an image carrier is visualized as a visible image, comprising a plurality of developing means of at least two developing methods having different developing characteristics when the environment changes. In the image forming apparatus for developing, an environment detecting means for detecting an environmental condition in which the image forming apparatus is placed, and a control means for changing a set image forming condition according to a detection result of the environment detecting means, The image forming apparatus, wherein the control unit changes the set image forming condition in a control mode corresponding to the developing method of the developing unit used. 2. A plurality of developing means of at least two developing systems having different developing characteristics when the environment changes are a developing means using a one-component developer and a developing means using a two-component developer. The image forming apparatus according to item 1.