JPS6380274A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a distinct image without generating ground fogging, color mixture, etc., even at the time of forming a multicolor image, by controlling an electrifying means, and also, controlling a developing means in accordance with the surface potential of a photosensitive body, at the time of forming the image of a second color and thereafter. CONSTITUTION:In the inside of a drum-shaped photosensitive body 200, a temperature detector for measuring the temperature of the photosensitive body 200 is attached, and the temperature detector, a first and second electrifiers 201, 204, a first and second surface potential sensors 202, 205, and a first and second developing devices 203, 206 are controlled by a control part for not only designating the number of print sheets and the size of a transfer member but also executing a density control, etc. In such a case, at the time of forming the image of the second color, in accordance with the surface potential at the time when the photosensitive body 200 is electrified, the electrifying voltage of the second electrifier 204, and also, the developing bias of the second developing device 206 are controlled. Accordingly, even when the drop of the surface potential cannot be covered with only the control of the electrifying voltage due to the fatigue of the photosensitive body 200, fogging and color mixture of an image, or color mixture in the developing device 206 are prevented by controlling the developing bias, and its picture quality can be improved.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Field of Application) The present invention is an image forming process that combines a charging process, an exposure process, and a development process into a single image-bearing process in a copying machine, a laser printer, etc. The present invention relates to an improvement in an image forming apparatus that repeatedly forms a multicolor image on an image carrier.

(Prior Art) In recent years, image forming apparatuses have been using laser beams and light emitted diodes (hereinafter referred to as LEDs) to form multicolor images on image carriers using a plurality of developers.

) or other light-emitting elements, or liquid crystals, optical switching elements such as those using the Faraday effect, etc., to convert digital information into optical information and imprint a latent image onto an image carrier. be. As a preferable example of such an apparatus, an apparatus as shown in FIG. 16 has conventionally been used.

That is, this device charges the photoreceptor 0Φ to a predetermined surface potential by the first charger 0 as it rotates in the direction of the arrow, forms an electrostatic latent image in the first exposure section (b), and then Development is performed by the first developing device O@ having developer (13a). Next, an image formed by the first developer (13a) is produced in the same manner as described above using the second charger (to), the second exposure section 0, and the second developer (b) having the second developer (17a). An image is further formed using the second developer (17a) on the photoconductor θΦ on which the .theta. 13a), (
Control processing is performed to equalize the charge polarity and charge amount of 17a), and the transfer member (A) is
First and second developers (13a) onto which a multicolor image is transferred and which remain on the photoreceptor 0Φ.

By crushing (17a) with a cleaner (2D) and erasing the latent image with a static elimination lamp@, the photoreceptor 0Φ is made capable of forming the next image.In such an apparatus,
Conventionally, the surface potential of the photoconductor 0Φ due to its charging fluctuates due to individual differences in the photoconductor aΦ, fatigue due to continuous printing, and even temperature changes, making the image quality unstable.
In order to maintain the surface potential uniformly, a first surface potential sensor (23) and a second surface potential sensor (24) are provided behind the first and second chargers (2) and (2), and each sensor (23) ,
According to the measurement results in (24), the first charger ■
and controls the charging voltage of the second charger (to). However, in such a device, the first color
When charging with the charger ■, the surface potential of the photoreceptor 0Φ can be controlled relatively easily by simply controlling the charging voltage, and there is no risk of color mixing with other developers. On the other hand, when charging the second color, that is, with the second charger 0◇, the charging process is continuous to the image forming process of the first color, and if the photoreceptor 0Φ is fatigued, simply controlling the charging voltage will not work. Since the necessary surface potential cannot be obtained and the developing bias is always constant, if the developing bias becomes higher than the surface potential during development with the second developing device (b), color mixture will occur in the first color image. On the other hand, if the first color image is too high than the developing bias, the first color toner will get mixed into the second developing device (B), resulting in color mixing, resulting in image deterioration. Problems arise in that the life of the developer is shortened.

(Problems to be Solved by the Invention) Conventionally, even in the second and subsequent colors of multicolor image formation, the only way to make the surface potential of the photoreceptor uniform during charging was to control the charger according to the surface potential of the photoreceptor. Moreover, it is difficult to control the surface potential, and since it is not perfect, there is a problem that the image quality deteriorates due to background fogging and color mixture.

Therefore, the present invention eliminates the above-mentioned drawbacks, and provides a highly reliable image forming apparatus that can obtain clear images without causing background fog or color mixture even when forming multicolor images. aim at something.

(Structure of the Invention) (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention, when forming images of the second and subsequent colors, controls the charging means according to the surface potential of the photoreceptor, and also controls the developing device. A control means is provided to also control the means.

(Function) According to the above-mentioned means, the present invention compensates for the non-uniformity of the surface potential of the photoreceptor, which inevitably occurs by controlling the charging means, by controlling the developing means. This prevents fogging and color mixing.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 15.

FIG. 1 is a block diagram showing an outline of the image forming section of the present invention. In this image forming apparatus, temperature detecting means (3
1a), a first charging means (32), a first potential measuring means (33), a first latent image forming means (34), a first developing means (36), and a second Charging means (
37), a second potential measuring means (38), a second latent image forming means (40), and a second developing means (41) are arranged. In addition, the temperature detection means (31a), each charging means (32), (37
), each of the potential measuring means (33), (38), and the second developing means (41) are connected to and controlled by the control means (42). Then, in accordance with the surface potential of the photoreceptor (31) detected by the first potential measuring means (33), the control means (42) generates a correction potential signal such that the photoreceptor (31) has the target surface potential. It outputs to the first charging means (32) and controls the fourth position of charging of the photoreceptor (31) for the first color. Next, the second color is detected by the photoconductor (3) detected by the second potential measuring means (38).
According to the surface potential of 1), the control means (42) outputs a correction potential signal to the second charging means (37) so that the photoreceptor (31) has the target surface potential, and also has the target developing bias potential. The correction potential signal is applied to the second developing means (4
1).

FIG. 2 is a diagram showing a schematic configuration of the entire system of a two-color laser beam printer (hereinafter referred to as LBP) to which the image forming apparatus shown in FIG. 1 is applied.

This two-color LBP 199 is connected to a host system 500 (external devices such as an electronic sieve, a word processor, etc.) via a transmission controller (not shown) (an interface circuit, etc.), and thereby receives two types of dot image data from the host system 500. Upon receiving the data, the two laser beams are respectively modulated to write on the recording medium, and the two types of written dot image data are independently developed and transferred onto the recording paper.

That is, inside this two-color L B P (199), a first section is provided as a basic component for image formation, and (200) in the figure is the image carrier (31) of FIG. It is a drum-shaped photoreceptor corresponding to the photoreceptor (
200) A temperature detector (200a) is attached to measure the temperature. Around the photoreceptor (200), a first charger (201) corresponding to the first charging means (32), a first
Table 1 Hydraulic level sensor (corresponding to potential measuring means (33))
202), a first developing device (203) corresponding to the first developing means (36), and a second developing device (203) corresponding to the second charging means (37).
A charger (204), a second rotational position sensor (205) corresponding to the second potential measuring means (38), a second developing means (
41), a pre-transfer charger (207), a transfer charger (20B), and a peeling charger (
209), cleaner (210), and static eliminator (21)
1) is installed, and the 100 lightning level sensor (20
2) and the first developing device (203), a first loose beam (309) emitted from what corresponds to the first latent image forming means (34) is irradiated onto the photoreceptor (200) to perform the first exposure. A second laser beam (310) emitted from a device corresponding to the second latent image forming means (40) is irradiated between the second table rotation position sensor (205) and the second developing device (206). Then, a second exposure is performed.

In addition, a temperature detector (200a), first and second chargers (20
1) (204), first and second table rotation position sensor (202)
), (205), first and second developing devices (203),
(206) corresponds to the control means (42), and also controls the number of prints, the size of the transfer member, density control, etc.
(not shown).

In addition, this embodiment employs a two-color printing process that operates in two reversal development modes, and at this time, changes in the surface potential of the photoreceptor (200) and
) above toner status etc. are changed as shown in FIG.

That is, as shown in FIG. 3 (2), the first charger (201)
When the photoreceptor (200) is uniformly charged by charging, and reverse exposure is performed by irradiation with the laser beam (309) as shown in υ, only the information area is brought to a low potential and becomes an electrostatic latent image. , areas other than the information area are maintained at a high potential. This electrostatic latent image is made visible with positively charged toner by the first developing device (203) as shown in FIG. 3(C). In this state, the photoreceptor (200) is connected to the second charger (204) as shown in FIG.
), the surface potential of the photoreceptor (200) returns to approximately the first charged state. Next, as shown in FIG. 3(c), the photoreceptor (200)
0), this information area becomes a low-potential electrostatic latent image, and as shown in
), the electrostatic latent image created by the second exposure becomes visible with the positively charged toner, and at this time, since the revealed image created by the first development is formed with the positively charged toner, it affects the second development. Not done.

Since the electrostatic latent images made visible in the two reversal development modes are both toner images of positive polarity, it is not necessary to align them with the same polarity, but the pre-transfer charger (207) is used to charge the toner images. After it is made uniform, it is transferred onto a transfer material.

FIG. 4 is a block diagram showing the entire image forming unit in a two-color LBP according to an embodiment of the present invention.

In this embodiment, the 3e-70
A first charger (201) made of a corotron is sequentially arranged along the rotational direction shown by an arrow around the photoreceptor (200), which consists of layers and has a temperature sensor (201a) attached to its inner surface.
, first front opening cylinder position sensor (202), developing sleeve (
405), a second charger (204) consisting of a scorotron, a second level sensor (205), and a second developing sleeve (406).
A developing device (20B), a pre-transfer charger (207), a transfer charger (208), a peeling charger (209), a cleaner (21()), and a static eliminator (211) are provided.

Also, (212) is the second router beam (309) and the second
A polygon scanner unit that irradiates the photoreceptor (200) with a laser beam (310), (213) a paper feeder, (
214) is an upper paper feed cassette that stores the transfer member A;
215) is the upper paper feed roller, (21&) is the first conveyance path,
(217) is the pre-registration pulse sensor, (21B) is the registration roller, (219) is the second transport path, (220)
(221) is a fixing device, (222) is a paper ejection switch, (223) is a paper ejection roller, and (224) is a paper ejection tray.

In addition, a temperature detector (200a), first and second chargers (20
1) (204), Tables 1 and 2 100 Lightning Level Sensor (202
), (205), first and second developing units (203), (
20&) are controlled by a control section (not shown).

Next, we will discuss the operation. When printing is started based on information from the host system (500), the photoreceptor (20
0), developing device (203), (20&), etc. are driven,
The detection result by the temperature detector (200a) is input to a control unit (not shown), and the photoreceptor (200) whose outer peripheral surface is formed with a 3e-Te layer is rotated to the first position.
It is uniformly positively charged by a charger (201).

Next, the first front cylinder position sensor (202) is connected to the first charger (20
The charging state of the photoreceptor (200) according to step 1) is detected, and the detection result is input to a control section (not shown). On the next stage side of this first front cylinder position sensor (202), the host system (5
00) according to the information from the polygon scanner unit (
The first loser beam (309) reflected by the photoreceptor (212) is irradiated onto the photoreceptor (200) to perform first exposure, and the photoreceptor (200) is exposed to light.
200) An electrostatic latent image is formed by the first exposure. The electrostatic latent image resulting from this first exposure is developed by the first developing device (203), but at this time, the developing sleeve (405) in the first developing device (203) has a relative speed with respect to the photoreceptor (200). The developing sleeve (405) is coated with a toner layer by a coating blade (not shown), and this toner layer is coated with a gap between the photoreceptor and the developing sleeve (405). (200), toner is commanded from a developing sleeve (405) to the electrostatic latent image by application of a developing bias, and development is performed.

Note that the gap provided between the photoreceptor (200) and the developing sleeve (405) differs depending on whether only a DC power source is used as a bias power source (not shown) or when a superimposed power source of an AC power source and a DC power source is used. Appropriate dimensions vary depending on the size. That is,
If using DC power only, select between 50 and 300 JJm, S
- is good, and when using a superimposed power supply, it is good to choose between 80 and 500-. In this embodiment, a gap size of 150-tone was selected for the DC power only, and a gap size of 250-tone was selected for the superimposed power source.

Next, the photoreceptor (200) is recharged by the second charger (204), but in this case, the irregularities in potential that have occurred on the surface of the photoreceptor (200) during the process up to the first development are returned to a uniform level. In this embodiment, a scorotron as shown in FIG. 5 is used. In this scorotron, a voltage of 6KV is applied to the charge wire (160), the shield (159) is at ground potential, and the grid has a voltage of 120KV.
0V is applied. (161).

(IE) 3) is a high voltage power supply and a grid power supply, respectively.

Next, the second charger (20
The charging state of the photoreceptor (200) according to step 4) is detected, and the detection result is input to a control section (not shown).

On the next stage side of this table 2 100 lightning level sensor (205), the first
Similarly to exposure, the second laser beam (310) reflected by the polygon scanner unit (212) is applied to the photoreceptor (200).
is irradiated to perform a second exposure, and an electrostatic latent image is formed on the photoreceptor (200) by the second exposure.

The electrostatic latent image resulting from this second exposure is developed by the second developing device (206), but at this time, as in the case of the first developing device (203), the developing sleeve (406) is in contact with the photoreceptor (200). It is moving at such a speed that its relative velocity is almost zero.

A DC bias is applied to the developing sleeve (406) by a bias power source (not shown);
When applying a bias, it is necessary to satisfy the following three conditions. That is, (2) the second image area (exposed area in the second exposure) can be sufficiently developed; (f) the non-image area (unexposed area in the second exposure) should not be smeared by development; It is necessary not to attract the toner of the first image after the second charging.

FIG. 6 schematically shows the state of toner movement in order to show potentials suitable or unsuitable for satisfying these conditions.

First, condition (2) corresponds to the movement of toner from the second developer potential shown as development in FIG. 6 to the second image area potential. This is the second developer potential (developing sleeve potential) and the photoreceptor (second developer potential).
00) and the surface potential of the exposed area, and its development characteristics are as follows:
It has the characteristics as shown in the figure, and in order to obtain sufficient image density, a potential difference of 900 V or more was required.

Next, condition υ occurs when the non-image area potential is lower than the second developer potential, and corresponds to the movement of toner from the second developer potential to the non-image area potential, which is shown as fog in FIG. or is
In order to prevent '
It is necessary that the following is true.

Condition (C) corresponds to the movement of toner from the second developer potential to the first image area potential, which is shown as color mixing in FIG. 6, or vice versa; The relationship with electric potential is the same as the relationship with fog mentioned above in terms of image color mixture.

Developing device color mixing is the opposite movement of toner, and according to experiments, a relationship as shown in FIG. 8 was obtained. As a result, the value obtained by subtracting (second developer potential) from (first image portion potential) needs to be 200V or less.

Therefore, in order to obtain a good overlapping image without color mixture, the following relationship between each potential was required.

(Second developer potential) - (second image portion potential)>900v・
...(D (second developer potential) - (non-image area potential) < 250
V...■ (Second developer potential) - (first image portion potential) <250v.
...(To) (First image area potential) - (Second developer potential) <200v
...■ On the other hand, the surface potential of the photoreceptor (200) when it is charged varies depending on conditions such as (0 photoreceptor individual difference υ, fatigue due to continuous printing (C), temperature change, etc.).

Therefore, in order to eliminate fluctuations in the surface potential of the photoreceptor (200), in this embodiment, surface potential feedback described below is performed.

FIG. 9 shows a change in surface potential due to continuous fatigue, and FIG. 10 shows an example of a change in surface potential due to temperature.

Continuous fatigue generally results in faster dark decay, which lowers the surface potential at the development location.

In general, the higher the temperature, the faster the dark decay, and therefore the surface potential at the development position decreases.

The graphs shown in FIGS. 9 and 10 were measured using a surface potential system located at a development position a predetermined angle away from the charging position determined by the process layout of the machine. The photoreceptor (200) is charged to a certain value at the charging position, and during the time when the photoreceptor (200) rotates from the charging position to the developing position, dark decay occurs and the potential decreases. This potential is generally called a surface potential, and it is greatly related to the development conditions and directly affects the printed image. Therefore, it is important to keep the surface potential at the development position constant.

For this purpose, there are two charging devices (a first charger (201) and a second charger (204)), and each image is visualized by a first developer (203) and a second developer (20B) after exposure. In this embodiment, there are two developing devices (203).

(206) In order to make the surface potential at the respective predetermined values, the first charger (201) and the first developer (203)
) and between the second charger (204) and the second developer (206).
) between surface potential sensors (202) and (205), respectively.
is provided, and the voltage applied to the first charger (201) and the voltage applied to the second charger (204) are controlled by the output thereof, and furthermore, in order to maintain the developing conditions of the above-mentioned (D type to Q type) According to the output of the second front weight sensor (205),
The developing bias of the second developing device (206) is controlled.

In particular, the applied voltage of the second charger (201) and the second developer (
By controlling the developing bias of the second developing device (20B), the second developing device (20B)
In the case of two-color printing, setting the potential at 06) to a predetermined value is necessary to set the potential on the photoreceptor (200) and the second developer sleeve (4) to a predetermined value.
06) It is important to prevent color mixture on the above.

At this time, various methods of controlling the eight chargers (201) and (203) can be considered, but in the present invention, a corotron is used as the first charger (201) and a scorotron is used as the second charger (204). In the corotron, the DC voltage applied to the wire was controlled, and in the scorotron, the grid voltage was controlled. The developing bias of the second developing device (206) is controlled by the second developing device sleeve (406).
The potential applied to was controlled.

Next, the control method will be described.

The first method is to use a charger (2
01), (204) and developing device (203), (20B
) surface potential sensors (202), (205
), and the surface potential is controlled to be constant at that position. Without this control, the surface potential of the photoreceptor (200), which fluctuated greatly due to the difference in dark attenuation while the photoreceptor (200) moves from the charging position to the developing position, can be changed by controlling the surface potential of the photoreceptor (200). The fluctuation occurs due to the difference in dark attenuation during movement from the sensor position to the development position, and since the attenuation time is shortened, the amount of time during which the surface potential fluctuates is reduced.

Therefore, it is possible to reduce fluctuations in the surface potential with this first method, but especially for photoreceptors that undergo many temperature changes and continuous printing fatigue, the fluctuations can vary considerably even in a short period of time, making it impossible to completely Correction becomes difficult. In this case, the tube 2 method can be considered.

It predicts the variation in dark decay that occurs while the photoreceptor (200) moves from the charging position to the development position from the characteristics of the photoreceptor (200), and changes the potential convergence value at the surface potential sensor position in advance depending on the conditions. This is a method to further reduce fluctuations in surface potential at the actually required development position.

First, a method for more accurately correcting variations due to temperature will be explained.

FIG. 12 explains a method of controlling the surface potential in the case of a photoconductor that is suffering from continuous printing fatigue and a photoconductor that exhibits slow dark decay at low temperatures and fast dark decay at high temperatures. As shown by the dotted line Q9,0, the surface potential at the sensor position is set low when the temperature is low and high when the temperature is high, thereby keeping the potential at the developing position device constant. The same thing applies to continuous printing fatigue, and normally dark decay occurs as shown in the actual record (→), but changes in dark decay during continuous printing as shown in actual record 0 are predicted in advance and the potential at the sensor position is calculated. should be controlled.

In other words, if the time taken for the photoreceptor to move between the sensor position and the development position is T, the dark decay Δ■ at time T differs depending on the temperature conditions and continuous copying conditions. , if the required potential at the development position is ``■'', the potential at the sensor position may be ``■÷Δ■''.

In the case of correcting changes in dark attenuation due to changes in temperature, this can be achieved by detecting the temperature of the photoreceptor using a temperature sensing element and automatically changing the value of ΔV.

Correction of changes in dark decay due to continuous printing fatigue can be achieved by counting the number of prints and changing the value of Δ■.

Next, according to the flowchart shown in FIG. 13, potential control during warm-up and potential control before first printing in the control section (not shown) will be described.

For potential control during warming up, the value CHDT1 of the first charging initial control output is read from the table data (step C10I), and the read value is set in the first D/A converter (step C102). Further, the value of the second charging and initial control output (CHDT2) is read from the table data (step C103), and the read value is set in the second D/A converter (step C104).

In the following step (Q105), the first charger (201) turns O.
If N, the first charging potential control is executed as shown in FIGS. 14 and 15 (step 0106).

After the subsequent delay processing (step C107), the second charging potential control is executed as shown in FIGS. 14 and 15 (
Step C109).

Then, step Cll0) increments the potential control number n.
, until the potential control number n reaches 3, steps (C105) to (C111) are repeated, and when it is performed 3 times, the first charger (201) and the second charger (20
4) is turned off (step C112), and this potential control during warming-up is completed.

If the status 1 is not the second color mode (No in step D101), the potential control before the first print is performed in the first color mode.
The charger (201) is turned on (step D102),
As shown in FIGS. 14 and 15, the first charging potential control is executed (step D103), and if only the first color mode is selected (affirmative at step D104), the potential control before first printing ends.

Also, if the second color mode is also executed (step D
After the delay processing (step D105), the second charger (204) is turned on and the second charging potential control and second developing bias potential control are executed as shown in FIGS. 14 and 15 ( In step [>107), potential control before first printing ends.

Further, if the status 1 is the second color mode in the first step (Dlol), only the second color mode is executed, so the second charge 5 (204) is turned on (step D10).
6), as shown in FIGS. 14 and 15, the second charging potential control and the second developing bias potential control are executed (step D107), and the potential control before first printing is completed.

FIGS. 14 and 15 are flowcharts showing details of the charging potential and second development bias potential control processing. 1st
In the subroutine shown in FIG. 4 and FIG. 15, first, the first A/D converter selects the temperature detector (200a) that measures the temperature of the photoconductor (200) (step EIOI), and then selects the temperature detector (200a) that measures the temperature of the photoconductor (200). When the temperature measurement is performed (step E102), either the potential control of the first charger (201) or the potential control of the second charger (204) is selected (step E103), and the ROM (not shown) In the case of potential control of the first charger (201), each process of steps (E104) to (E109) is executed based on the data table of the second charger (201).
204), step (E 113)
) to step (E119) are executed.

Then, step (E110) and step (E12
0), the first target surface potential data (VO31) and the second target surface potential data are respectively set to correspond to the actual temperature of the photoreceptor (200).
The target surface potential data (VO32>) is corrected to obtain corresponding correction data (VO31') and (VO32').

Subsequent steps (E 111) and steps (E 121)
), step (E104) to step (EIIO
) and the six values obtained in steps (E113) to (E120) are stored in a common register, the operations shown in step (E111) and step (E121) are performed. Processing is executed to correct dark attenuation field changes due to temperature changes.

Subsequent steps (E112) and (E122)
Here, the first target potential sensor (202) and the second open position sensor (205) are selected by the first A/D converter, respectively.

Next, whether the potential control of the first charger (201) or the second charger (204) is performed, step (E
123) The subsequent processes are executed.

First, a delay process is executed for a time corresponding to the travel distance between the first and second chargers (201), (204) and the first and second open position sensors (202), (205). The first and second open position sensors (202), (20
5), the surface potential VS is measured (step E1
23°E 124).

In the subsequent steps, processing is performed based on each data shown in step (E 111) and step (E 121).

That is, in step (E125), the surface potential sensor (202), (2
Self-diagnose whether the value read at 05> is greater than or equal to VO30V0)IAX. If it is the above (step E125 affirmative), potential control error processing is executed. (Step E1
26).

If it is the terminal (step E125 negative), step (E
127).

In step (E127), it is determined whether the read value matches the target value and the control width of the error table, according to the arithmetic expression Vs=Vos+Voz. If they do not match (No in step E127), check step by step how much the voltage deviates from the target by, for example, 200V, 100V, or 50V (step E128.
129. E130), a process of setting the control amount to the same size as Δx1 or ΔX2, or twice, four times, and six times, respectively, is executed (steps E131 and E132).
．． E 133. E 134).

After this setting, the process proceeds to step (E135), where the charging output is set, and in the following step (E136), it is checked whether the charging output is larger than the maximum value, and in the following step (E137), the charging output is set. It is checked whether the output is smaller than the minimum value, and if it is too large or too small (step E136 affirmative), (step E13
7 (affirmative), potential control error processing is executed (step E13 &).

If the charging output is within the control range (step E136 negative, step E137 negative), step (E
139), where the actual potential control target is the first charger (
201) or the second charger (204).

If this determination result is the first charger (201), CHDT
After setting l = CHDT (step E140), CHDTl is set to 1st D/
The process of setting the A converter is executed (step E141), and the process advances to step (E149).

Also, if this determination result is the second charger (204), C
HDT2=C) (After setting DT (step E142), set CHDT2 to 2nd D
/A converter is executed (step E143), and the process advances to step (E144).

Step (E144) compares the bias setting value with the sum of the surface potential, drum temperature correction data, and bias allowable range 250 V corresponding to the bias allowable potential α, and if the bias setting value is lower (step (E144 affirmative), proceed to step (E145).

Also, if the bias setting value is higher (step E14
4 (No), proceed to step (E 147).

The meaning of these processes will be described below.

As described in the explanation of FIG. 5, development (fogging) from the second developing device (206) to the non-image area, which is the last exposed area of the photoreceptor (200), is caused by the second development bias being at the non-image area potential. 2 more
This occurs when the voltage is higher than 50V. Therefore, the second development bias setting value is (surface potential to be set + 250)
Do not exceed V (to avoid fogging)
It is a calculation.

In step (E145), the bias setting value is compared with the sum of the surface potential/drum temperature correction data, and if the bias setting value is higher (step E145 is affirmative).
Proceed to step (6146). Moreover, if the bias setting value is lower (step E145 negative), step (E
148).

If the developing bias potential is set in this way, the color mixing in the second developing device (206) described in the explanation of FIG. toner flight (the first image area is 200° higher than the second developing bias potential)
This occurs when the voltage is higher than V. ) can be sufficiently prevented.

In step (E147), a constant (ΔY) is subtracted from the developing bias potential control value (VBDT), and in step (E14B), the constant (ΔY) is added to VBDT and set in the third D/A converter. (Step E1
46) Then, proceed to step (E149).

In other words, if the potential is controlled before the first print (step E150 affirmative), the potential control number m is 3 (step E155), and the non-convergence due to potential control ends, and if it is up to 2 times, step (E150 is affirmative). Return to 123).

In addition, if the potential is controlled during warming up (step E151), the potential control number m is 10 times (step 154 is affirmative), and potential control error processing is executed (step E157). Step (E 1
Return to 23).

Furthermore, if status 1 is not in two-color mode (step 154 affirmative), the process returns to step (E 123), but if status 1 is in two-color mode (step 154 is affirmative).
, determine whether the potential control target is the first charger (201) or the second charger (202), and if it is the first color mode, when the potential control is performed five times (step 154 affirmative).
Potential control ends, and in the second color mode, when potential control is performed twice (step 158), potential control ends.

The two-color LBP of this embodiment to which the present invention is applied as described above
199, by controlling the developing bias potential of the second color at the same time as controlling the charging position 4 of the photoreceptor (200), the developing conditions can be kept constant even if the characteristics of the photoreceptor change. It works to maintain it.

Under these conditions, the second developing device (206) further performs development on the photoreceptor (200) on which the first image has already been formed, thereby forming a second image. After this, the photoreceptor (200
) reaches the transfer position after the potentials of the first and second image forming sections are equalized by a pre-transfer charger (207). on the other hand,
At the transfer position, a transfer member (not shown) is attached to the photoreceptor (200).
The image on the photoreceptor (200) is transferred to a transfer member (not shown) by a transfer charger (208). After this, the transfer member is removed by a peeling charger (2
09), it is peeled off from the photoreceptor (200), passes through a fixing device (221), completes a two-color print, and is discharged.

Note that the two-color print image formed in this manner did not cause fogging or color mixture, and a clear and high-quality image could be obtained. On the other hand, after the transfer, the photoreceptor (200) is moved to the cleaner (200).
10) and a static eliminator (211), residual toner and residual charges are removed, and the next printing is made possible, completing one cycle of the image forming process for two-color printing.

With this configuration, when forming the second color image, the photoreceptor (
The second charger (200) is charged depending on the surface potential during charging of the second charger (200).
Since the developing bias of the second developing device (206) can be controlled in addition to the charging voltage in step 4), even if the decrease in surface potential cannot be compensated for by controlling the charging voltage alone due to fatigue of the photoreceptor (200), the developing bias can be controlled. By controlling the bias, it is possible to prevent color mixing in the image or color mixing in the developing device (206), and to improve the image quality.

Note that the present invention is not limited to the above-mentioned embodiments, and can be modified in various ways. For example, the image formed on the photoreceptor may have two or more colors, and in that case, when forming images of the second and subsequent colors, , the charging position and the developing bias are respectively controlled according to the surface potential of the photoreceptor. Further, the method of controlling the charging level and the developing bias is completely arbitrary. Furthermore, the setting position of the surface potential sensor can be set by providing a non-image forming part at the end of the photoconductor and facing it, or by facing the image forming part. This eliminates the need for the non-image forming part of the photoreceptor,
The length of the photoreceptor can be shortened, and the entire device can be made smaller.

Note that the exposure means may also be a light emitting element such as an LED array or a light switching element instead of a laser beam. [Effects of the Invention] As explained above, according to the present invention, in the multicolor mode, when forming images of the second and subsequent colors, the charging position and the developing bias potential can be controlled according to the surface potential of the image carrier. , the developing conditions for the second and subsequent colors have been improved, background fog and color mixture that have conventionally occurred have been eliminated, and high-quality images can be produced by 1q.

[Brief explanation of the drawing]

1 to 15 show an embodiment of the present invention, FIG. 1 is a block diagram showing an overview of the image forming section, FIG. 2 is a schematic configuration diagram of the entire LBP system, and FIG. Indicates the surface potential of the photoreceptor in the image forming process, (2)
is during charging by the first charger, ■ during first exposure, (
C) is when developing with the first developing device, Yu is when charging with the second charging device, (e) is during the second exposure, (0 is when developing with the second developing device, Figure 4 is when developing with the second developing device, A schematic explanatory diagram showing the entire image forming unit of LBP, FIG. 5 is a schematic diagram showing a cross section of the scorotron, FIG. 6 is an explanatory diagram showing the developing conditions by the second developing device, and FIG. 7 is the first developing unit. A graph showing the developing characteristics of the developing device, FIG. 8 is a graph showing the reverse adhesion characteristics of the first image to the second developing device, FIG. 9 is a graph showing the photoreceptor characteristics due to continuous fatigue, and FIG. A graph showing the photoreceptor characteristics due to temperature change, FIG. 11 is a graph showing the potential correction of the photoreceptor without considering the temperature, FIG. 12 is a graph showing the potential correction of the photoreceptor considering the temperature, and FIG. FIGS. 14 and 15 are flowcharts showing potential control during warm-up and before first printing; FIGS. 14 and 15 are flowcharts showing 4-position charging control and developing bias potential control; FIG. 16 is a schematic configuration diagram showing a conventional device. Yes. 199...L B P 200...
Photoreceptor 201...First charger 202...First open mold position sensor 203...First developer 204...Second charger 205...Second open mold position sensor 206. ...Second developer 212...Polygon scanner unit 30
9...Second laser beam 310...Second laser beam 500...Host system agent Patent attorney Inoue - Mensu Figure 1 Figure 3 Figure 5 Figure 6 Figure DC bias ['l to π4 & Jiang-Kohshi Kanzui family seven years ago (V') Fig. 7 (:1A14114%:tjf,) (JlePt
Jn) Figure 8: Encounter and Training Figure 9: 5j Multi-purpose It Mechanism: 15th/16th Figure 16 Procedural Amendments (Master) 62.2.5 Showa Year Month Japan Patent Office Commissioner Kuro 1) Mr. Yu Akira■, Indication of the case Patent Application No. 224849 of 1988 2, Name of the invention Image forming device 3, Person making the amendment Relationship with the case Patent applicant (307) Toshiba Corporation 4. Agent: 4-41-11 Kamata, Ota-ku, Tokyo 144 Tsunoda Building Benjo Patent Office Telephone: 736-3558 5. Subject of amendment (1) Detailed description of the invention in the specification Column (2) Drawing 6, contents of amendment (1) 1. In the 11th line of page 13 of the specification, "requisitioned" is corrected to "flying." 2. Correct "from the second developer potential to the first image area potential" in the 11th to 12th lines of page 16 of the specification to "from the second developer to the first image area". 3. Correct "surface potential system" on page 18, line 9 of the specification to "surface potential meter." (2) Figures 5 and 8 will be corrected as shown in the attached sheet. Above/3 days tbD 5th figure 1 coffee O coffee ρD ADD 800

Claims (1)

[Scope of Claims] 1. A plurality of image forming steps each consisting of a charging means, a latent image forming means, and a developing means are arranged around the image carrier, and the arbitrary image formation described above is performed according to the multicolor mode or the monochrome mode. In the device for forming a multicolor or monochrome image on the image carrier by the means, provided at the rear of each set of charging means,
A plurality of potential measuring means for measuring the charged potential on the image bearing member, and the charging level of the image bearing member by each charging means and the developing bias potential of each developing means according to the measurement results from each of these potential measuring means. An image forming apparatus characterized by comprising: a control means for controlling both of the above. 2. The control means controls the charging potential of the charging means and the developing bias of the developing means so that V_B≦V_D_R_U_M+α (where V_B: developing bias potential, V_D_R_U_M: charging potential, α: allowable developing bias potential). An image forming apparatus according to claim 1.