JPH05333623A - Digital electrophotographic device - Google Patents

Abstract

PURPOSE:To prevent the sticking of a carrier to the nonimage part of a photosensitive body by executing writing on all regions by means of optical writing. and making the potential by electrification of the photosensitive body low, when the value of output applied to a grid is larger than a rated value, regardless of the value of the output applied to the charger wire of an electrifier. CONSTITUTION:An electrifying charger power source 10 and a grid power source 11 are connected to the charger wire 2b and grid 2c of a sutocorotron electrifier 2, respectively, to apply a voltage and a current. On the other hand, a developing bias power source 12 is connected to a developing roller 4a, to impart a bias voltage and generate a developing potential. When the value of the output applied to the charger wire 2b of the electrifier 2, is larger than the rated value by a prescribed value or more, regardless of the value of the output applied to the charger wire 2b of the electrifier 2, the writing is attained on all regions capable of writing, with a laser writing beam 3, in disregard of original writing data, and the potential by electrification of the photosensitive body 1 can be made low.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a digital electrophotographic apparatus.

[0002]

2. Description of the Related Art In an electrophotographic digital image forming apparatus such as a digital copying machine, a laser printer, a facsimile, etc., a light beam such as a laser beam containing image information is used to perform optical writing on a photoconductor to form it on the photoconductor. The electrostatic latent image is developed to form a toner image, which is transferred to transfer paper and fixed to form an image.

FIG. 6 is a diagram showing a configuration around an image forming unit as an example of a laser printer. This example utilizes a reversal development system that uses a two-component developer containing (-) charged toner as the developer. The photoconductor 1 rotates in the direction of the arrow, is uniformly charged by the charger 2, is optically written by the laser beam 3 containing image information, and an electrostatic latent image of an image corresponding to the image information is formed on the photoconductor 1. It is formed. This electrostatic latent image is developed into a toner image by the developing device 4, and is transferred to the transfer paper 6 under the action of the transfer charger 5, and the transfer paper 6 after transfer is separated by the separation charger 7 into the photoreceptor 1.
The sheets are separated and fixed by a fixing device (not shown) to complete printing. After the transfer, the toner remaining on the photoconductor is removed and cleaned by the cleaning device 8.
The electric charges remaining in the above are eliminated by the elimination lamp 9 to prepare for the next image formation.

As the charger 2 described above, as shown in FIG. 6, a charge wire 2b stretched in a shield case 2a.
And a scorotron charger having a grit 2c provided in the opening of the shield case is often used. A power source is connected to each of the charge wire 2b and the grid 2c, and the charging potential can be adjusted by changing the grid voltage.

Therefore, when the contact of the power supply connection to the charge wire and grit of the scorotron is lost, the charger is forgotten to be set, the grid power supply is set or adjusted incorrectly, the photoconductor is charged to a target potential. I can't. These problems will be explained below.

(1) The charge wire is connected,
If the grid is poorly contacted or disconnected, the grid will float and the photoconductor charge potential will deviate from the standard value and become abnormally large, and the image area written by the laser beam will be developed normally. However, the carrier of the developer adheres to the non-image area. Since only a certain amount of carrier is contained in the developing device, the carrier will continue to decrease when carrier adhesion occurs.

(2) Contrary to the case of (1) above, regardless of whether the grid is connected or not, if the charge wire is poorly contacted or not connected, the charge wire is not discharged. , The photoconductor is not charged,
The potential of the photoconductor does not reach the target value. Then, the toner is spread or adheres to the non-charged portion of the photoconductor after development, resulting in excessive toner consumption.

(3) As will be described later in detail as a measure against the above (1), when the image data is written to the entire area by laser light and the developing bias is applied as usual, the toner is entirely spread. It adheres and leads to excessive toner consumption.

(4) Since the power output of the grid is an output for controlling the electrostatic potential of the photoconductor, if the power output of the grid deviates near the rated value due to a setting or adjustment error or power replacement, A defective image with a lot of background stains.

(5) Regarding prevention of carrier adhesion in an electrophotographic apparatus, see Japanese Patent Laid-Open No. 62-49375.
There is disclosed a device that controls the light amount of an exposure device to be irradiated according to a predetermined light amount change when the charging unit rises and falls. Further, in JP-A-60-238867, the charging means is operated before the reference position of the sheet passes through the charging means, and the entire surface is exposed before the portion corresponding to the charging start position reaches the exposing means. , A device that removes the influence of fluctuations of the charging means and the exposure means at the time of start-up and prevents the carrier adhering machine from being contaminated.

Regarding the prevention of background stain, for example, Japanese Patent Laid-Open No.
In Japanese Patent Laid-Open No. 3-148272, prior to the formation of a visible image pattern, a photoconductor is charged at a potential lower than the charging potential during normal copying, and the visible image pattern is formed by the photoconductor residual stage after the potential is erased. There is disclosed a control device that prevents soiling by doing so.

However, the apparatus of each of the above inventions is for an analog electrophotographic apparatus, and a gridless corotron is used as a charger.

[0013]

SUMMARY OF THE INVENTION The present invention is conceived in view of the above-mentioned problems resulting from a defective power supply connection to a charge wire or a grid in a digital electrophotographic apparatus using a scorotron charger as a charger. Even if there is a connection failure, etc., the carrier adhesion to the photoconductor, the excessive adhesion of the toner, the background stain are different from the above-mentioned means, and the electrophotography solved by the means particularly suitable for the digital electrophotographic apparatus having the scorotron charger. An object is to provide a device.

[0014]

[Means for Solving the Problems] (1) to (4)
In order to solve the above problems, the following inventions are proposed respectively.

The first invention for solving the first problem is to apply the voltage to the grid regardless of the output value applied to the charge wire of the charger in the digital electrophotographic apparatus having the above-mentioned configuration. When the output value exceeds the rated value by a predetermined value or more, the original writing data is ignored by optical writing, and writing is performed in all writable areas to lower the charged position of the photoconductor. Characterize.

In addition, in order to solve the second problem, the second
The invention of, in a digital electrophotographic apparatus of the same configuration,
When the power output is not applied to the charge wire regardless of the output value applied to the charger grid,
It is characterized in that the bias output applied to the developing device is a reverse bias applied so that the toner does not adhere to the photoconductor.

A third invention for solving the third problem is, in addition to the structure of the first invention, applied to the grid regardless of the output value applied to the charge wire of the charger. When the output value becomes larger than a predetermined value, the bias output applied to the developing device is a reverse bias output so that the toner does not adhere to the photoconductor.

A fourth invention for solving the fourth problem is that the output value applied to the grid varies in the vicinity of the rated value regardless of the output value applied to the charge wire of the charger. In this case, the bias output applied to the developing device is shifted according to the power output value to the grid.

[0019]

With the structure of the first aspect of the present invention, the charge potential of the photosensitive member is lowered and the carrier is prevented from adhering.

Further, according to the second aspect of the present invention, since the reverse bias voltage is applied to the portion of the photoconductor which is not charged, the toner is prevented from sticking or sticking after development.

According to the structure of the third invention, in addition to the operation of the first invention, the toner is prevented from sticking or adhering to the whole.

According to the fourth aspect of the present invention, by shifting the output of the developing bias power source in accordance with the output of the grid power source, a good image with less background stain can be obtained.

The problems of the present invention other than the above and means for solving them will become apparent from the description of the embodiments described in detail below with reference to the drawings.

[0024]

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

FIG. 1 shows a power supply for applying a voltage / current to a charge wire 2b and a grid 2c of a charger 2 of an embodiment in which the present invention is applied to the laser printer described with reference to FIG. 6 and a developing roller 4a of a developing device 4. It is a figure explaining the input / output of the developing bias power supply which applies a bias voltage.

A charging charger power source 10 and a grid power source 11 are connected to the charge wire 2b and the grid 2c of the charger 2 configured as a scorotron, respectively.
A current is applied, and a developing bias power source 12 is connected to the developing roller 4a to apply a bias voltage to create a developing potential. These power supplies 10, 11, 12
Are connected to the power supply V _AA (24 V) and the ground GND, and the output is turned on / off by inputting a trigger signal (C trigger, G trigger, B trigger). The output settings are
Pulse width modulation signal (C-PWM, G-PWM, B-PW
The output is changed by the duty by the modulation method by the input of M), and the output value is fed back to the feedback signal (CF).
B, G-FB, B-FB) is output to monitor.

Since the output value of the power supply is known from the feedback signal and used for various controls, the feedback signal is normally input to the analog port of the CPU.
Since the power supply output is a high voltage, it must be 1/200 to 1/500 of the power supply output to be used as a feedback signal. By performing this inside the power supply, the feedback signal can be directly connected to the analog port of the CPU, and the wiring is simplified.

The charging charger power source 10 is a constant current type, the grid power source 11 is a constant voltage type, and the developing bias power source 1 is used.
2 is preferably a constant voltage type. Charger power supply 10
A stable current can be obtained by using a constant current type as the above, and a constant voltage type can be used as the grid power source 11 to facilitate control of the charging potential and a constant voltage as the developing bias power source 12. By using the voltage type, it is possible to easily control the potential of the developing bias on the photoconductor.

Further, by using the constant voltage type power source as the grid power source and the developing bias power source as described above, the difference (potential) between the grid output voltage and the developing bias output voltage is kept constant, so that the background stain (white background) is further reduced. It is possible to obtain a good image in which a toner particle stain on a portion is less likely to occur.

2 (a), (b), (c), and (d), respectively, normal charge, abnormal grid output, abnormal charge charger output, and defective charge V _D on the photosensitive member during charging failure. , The exposure part potential V _L and the grid output voltage V _GO as the power supply output value
And the development bias output voltage V _{B O} −. The image states in each case are as shown in Table 1.

[0031]

[Table 1]

[0032] is a proper charge _{| V D -V BO - | ≒} 200V
_And | V _BO- −V _L | _≈500 V, which depends on the characteristics of the photoconductor, toner, and carrier (developer), but in this embodiment, V _L = −80 to −100 V, V _BO- =
-600V, is set to V _D = -800V. V _D = -80
In order to charge it to 0V, it is necessary to consider the slight loss (distribution ratio) and set the grid output to about V _GO = −850V. (FIG. 2- (a)).

Next, consider the case where the charging charger load is connected and the grid causes a connection failure for some reason (contact failure, etc.). Even if it is in a floating state, it is pulled by the charger output, and V _GO at the rated time is -85.
It is much larger than 0V. Normal | V _D -V _BO- | ≒ 4
Adhesion of the carrier starts from about 00V, and the larger the amount, the more the amount of the carrier attached to the photoconductor increases (FIG. 2- (b)).

On the contrary, when the grid load is connected and the charging charger load causes a connection failure for some reason, even if the grid output is at the rated value, the charging charger does not generate corona discharge. Since V _D does not rise to the charge level, it becomes the same value as the potential of the exposed area exposed by the exposure means (laser diode, etc.), and toner adheres in all areas of the non-image area and the image area. However, the entire surface becomes solid black (FIG. 2- (c)).

[0035] In _{addition, 0 <| V D -V BO-} | In the <50V about, background contamination occurs in the non-image area, resulting in a poor image quality in appearance (Figure 2- (d)).

Next, FIG. 3 is a flow chart of the process according to the present invention, which can prevent the carrier adhesion to the photoconductor, the abnormal toner adhesion, and the background stain even when the output of these power supplies is abnormal. This will be described in detail based on the flowcharts shown in FIGS. 4 and 5. FIG. 3 is a flowchart of the "copy" operation, and FIGS. 4 and 5 are flowcharts of the subroutine therein.

Table 2 shows the explanation of the flow charts and the symbols appearing in the explanations thereof.

[0038]

[Table 2]

Further, (S1), (S2), ... In the explanations are abbreviations of step 1, step 2 ,.

First, FIG. 3 will be described.

The COPY operation is started by turning on the copy SW after the power is turned on (S1).

At the same time when COPY SW is turned on, the motor and the drive system of the paper feed system are operated, the C trigger and G trigger are turned on,
The charging power source 10 and the grid power source 11 operate (S2).

Considering the timing when the power source rises, C
-By monitoring the FB output (S3), it is determined whether or not the charging charger power supply outputs the rated power (S4).

When it is confirmed by C-FB that the rated current I _C is applied to the charging charger, the G-FB output is monitored next (S5), and the grid power supply outputs the rated voltage V _G. It is determined whether or not (S6).

The rated voltage V _{G is} applied to the grid by the G-FB.
When it is confirmed that is applied, the image forming operation is performed as shown in FIG. 1 (S7), and the C trigger and the G trigger are turned off.
After performing F (S8), the COPY operation ends.

Since the output of the charging charger power source in (S4) is a constant current type, it is possible to determine the set state of the load by current detection or voltage detection. In the current detection, the current value flows above a certain value, and in the voltage detection, the load is set when the state in which the output voltage value is below a certain value is detected.

In the case of NO in this judgment, FIG. 2- (C)
Therefore, in order to prevent toner adhesion, a reverse bias V _B + is applied from the bias power source (S
9) If the transfer paper has entered the conveyance path, the transfer paper is discharged, and if not, the processing is instantaneously stopped, and then the charging operation abnormality detection processing is performed (S10).

The judgment of the rated output V _G of the grid power source in (S6) is made based on a certain range of the output voltage V _GO . In addition, since the grid is set to a constant voltage when the power supply is set, the current is detected.

Here, V _{G that} does not hinder the image forming operation
The judgment is made within the range of −50V <V _GO <V _G + 50V.
(G-FB is monitored and judged). For an out-of-rated output outside this range, it is further judged that V _G +200 V <V _GO (S11), and if YES, the state shown in FIG. To prevent carrier adhesion, image data is canceled (S
12) All the data (in the image area) is LD or LED
Full writing by array writing means (S
13), V _D drops from -1000V or more to near -80V. That is, the state of FIG.
Adhering to the carrier can be prevented by setting the state of (c). However, since the toner adheres to the toner only when it is developed, a reverse bias output is further output from the bias power source (S14).

Next, depending on the state of the transfer sheet entering the conveyance path, either transfer sheet discharge or instantaneous stop is carried out to carry out the charging operation abnormality detection processing (S15).

If the determination in (S11) is NO, bias shift processing is performed (S16).

Next, the processing of the "charging operation abnormality detection" subroutine will be described with reference to FIG.

This processing uses two different display methods depending on whether or not the charger is completely set in (S4) and (S6).

First, the set state of the charging charger is detected by the judgment of (S4), the set state of the grid is detected by (S6), and it is checked whether or not both are set (S17).

Therefore, if either of these is not set, the process proceeds to YES, and a display such as "charger is set sale message" is transmitted to the operator by the display means or the like (S18).

Then, the operator opens the main body door and resets the charger according to the troubleshooting manual, closes the main body door, detects it (S19), and then confirms whether the charger is set (S19). S20).

As described above, when the uncharged charger and the grid are not set, the image forming operation is instantly stopped, and the operator is informed by the display means that quick repair can be performed and the loss time of the copying work is lost. Can be reduced.

In (S21), the transfer paper is not conveyed, and the operations of (S4) and (S6) are performed by rotating the transfer paper to check whether both the charger and the grid are set (S21).

After the confirmation operation is judged, if it is not set yet, the process returns to (S18), and if it is set,
The process returns to the determination of the copy SW in (S1).

If it is determined in step S16 that the charging device is completely set, the process proceeds to NO and a display such as "abnormal charging" is transmitted to the operator by the display means (S22).

This is because whether or not the power supply output I _CO deviates from the set value or is not output when the charging operation is abnormal even though the charger is set. In this case, the operator becomes unmanageable, so "Serviceman call" is displayed (S2
3) The operator contacts the repair.

When the display of (S23) is displayed, the copy SW or the like is not accepted at all and the standby state is set (S24).

Next, the "bias shift" process will be described with reference to FIG.

This processing is performed when the grid output voltage V _GO is V _G +200> V _GO in (S11). However, when V _GO is low, the image quality of the copy deteriorates (insufficient contrast, scumming, etc.). Set the lower limit.

[0065] (S25) At V _G -200V <V _GO the lower limit value as 200V is judged whether or not within the range of (<V _G + 200V).

If it is within the range of (S25), the copy image quality is not so affected. Therefore, by keeping the potentials of V _{BO −} and V _GO constant (200 V), it is possible to prevent the carrier adhesion and toner adhesion while developing. The operation is performed (S18).

After the developing bias is shifted and output as in (S16), the process returns to (S7) and the image forming operation is performed as described with reference to FIG.

(S25) If it is not within the range (S25)
Similarly to 26), V _BO- is shifted while maintaining the potential so that carrier adhesion and toner adhesion can be prevented (S
27), the image quality is affected and the standby state is set (S30).

[0069]

As described above, according to the first aspect of the present invention, the carrier is prevented from adhering to the non-image portion of the photoconductor. Further, according to the invention of claim 2, even if the charge wire of the charger has a poor contact, the toner does not stick or adhere to the uncharged portion of the photoconductor, and according to the invention of claim 3, In addition to the effect of the invention of Item 1, the toner is prevented from sticking or adhering to the whole. Also, claim 4
According to the invention described in (1), it is possible to obtain a good image with less background stain.

Further, according to the invention of claim 5, the electrostatic potential,
It is easy to control the potential of the developing bias. or,
According to the invention of claim 6, a good image with less background stain can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view for explaining input / output to / from a charge wire and a power supply to a grid and a developing bias power supply of a charger of a digital electrophotographic apparatus according to an exemplary embodiment of the present invention.

2 (a), (b), (c) and (d) are normal, when the grid output is abnormal, when the charger output is abnormal and when the charging is defective, the charge potential on the photosensitive member and the exposed portion potential. It is explanatory drawing which shows a grid power supply output voltage and a developing bias power supply output voltage.

FIG. 3 is a flowchart of a copy operation according to the present invention.

FIG. 4 is a flowchart of a subroutine of “charge operation abnormality detection”.

FIG. 5 is a flowchart of a "bias shift" subroutine.

FIG. 6 is a cross-sectional view showing a configuration around an image forming unit of an example of a laser printer.

[Explanation of symbols]

 1 Photoconductor 2 Scorotron Charger 2a Shield Case 2b Charge Wire 2c Grid 3 Laser Writing Beam 4 Developer 4a Charger Power Supply 11 Grid Power Supply 12 Development Bias Power Supply

Claims (6)

[Claims] 1. A scorotron charger comprising a charge wire stretched in a shield case and a grid provided in an opening of the shield case, an optical writing means, and a developing device are arranged in this order along the rotation direction of the photoreceptor. In a digital electrophotographic apparatus having a power source for applying a current / voltage to the charge wire and grit of the charger, means for monitoring the output value of the applied current / voltage, and a power source for applying a bias voltage to the developing device. , Regardless of the output value applied to the charge wire of the charger, when the output value applied to the grid exceeds the rated value by a predetermined value or more, the original write data is ignored by the optical writing means. Then, the digital electrophotographic apparatus is characterized in that the charging position of the photoconductor is lowered by writing in all writable areas. 2. A scorotron charger comprising a charge wire stretched in a shield case and a grid provided in an opening of the shield case, an optical writing means, and a developing device are arranged in this order along the rotation direction of the photoreceptor. In a digital electrophotographic apparatus having a power source for applying current / voltage to the charge wire and grid of the charger, means for monitoring the output value of the applied current / voltage, and a power source for applying a bias voltage to the developing device. , When the power supply output is not applied to the charge wire regardless of the output value applied to the charger grid,
A digital electrophotographic apparatus, wherein a bias output applied to a developing device is an output for applying a reverse bias so that toner does not adhere to a photoconductor. 3. The digital electrophotographic apparatus according to claim 1, wherein the output value applied to the grid becomes larger than a predetermined value regardless of the output value applied to the charge wire of the charger. Further, the digital electrophotographic apparatus is characterized in that the bias output applied to the developing device is an output for applying a reverse bias so that toner does not adhere to the photoconductor. 4. A scorotron charger, which comprises a charge wire stretched in a shield case and a grid provided in an opening of the shield case, an optical writing means, and a developing device are arranged along the photosensitive member in the order of its rotating direction. A power supply for applying a current / voltage to the charge wire and grid of the charger, means for monitoring the output value of the applied current / voltage, a power supply for applying a bias voltage to the developing device, and an output applied from the power supply. In a digital electrophotographic apparatus having a means for monitoring, when the output value applied to the grid fluctuates in the vicinity of the rated value regardless of the output value applied to the charge wire of the charger, the power supply to the grid is changed. A digital electrophotographic apparatus, wherein the bias output applied to the developing device is shifted according to the output value. 5. The power output applied to the charge wire of the charger is a constant current type, and the power output applied to the grid and the power output applied to the developing device are constant current types. 5. The digital electrophotographic apparatus according to any one of items 4 to 4. 6. The digital electrophotographic apparatus according to claim 4, wherein the difference between the grid power supply voltage and the developing bias power supply voltage is kept constant.