JPH11160930A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image forming device whose image reproducibility is good and which can adequately take fogging margin by using an existing AIDC sensor without using an expensive potential sensor and without the fear of side effects. SOLUTION: An electrostatic latent image formed on a photoreceptor drum 21 is developed by toner, and transferred on a sheet. In the case of a mode for setting an electrifying voltage for taking the fogging margin, a grid voltage Vg and a developing bias voltages Vb are previously set to a specified value, and the grid voltage Vg is changed by a specified amount, so that toner adhering amount of a test pattern formed on the drum 21 can be optically detected by the sensor 26. At that time, a quantity of exposing light to a test pattern forming area is slightly increased in comparison with the quantity of the exposing light to an area other than the test pattern forming area.

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, and more particularly, to an electrophotographic image forming apparatus in which at least a charging unit, an exposing unit, a developing unit, and a transferring unit are provided around a photosensitive member.

[0002]

2. Description of the Related Art Generally, in an electrophotographic copying machine or printer, extra toner is prevented from adhering to a background portion of an image formed on a photoreceptor (hereinafter, referred to as "fog"). It is necessary to set the surface potential of the photoconductor so that a fogging margin can be obtained. Taking a fog margin means, for example, if fog occurs at a photoconductor surface potential of 400 V, a margin of +100 V is added to control the capability of the charger so that a surface potential of 500 V can be secured. I do. In particular, in a color image forming machine in which it is necessary to improve the gradation of an image, control of a surface potential in consideration of a fog margin is an important issue.

Since the charging efficiency of the photoconductor changes depending on environmental conditions such as temperature and humidity and durability conditions such as the number of formed images, conventionally, a potential sensor is provided in proximity to the photoconductor, and the measurement result is used. Calculate the charging efficiency and calculate the charging efficiency (specifically,
Grid voltage). However, the potential sensor is expensive, which has been one factor in increasing the cost of the color image forming machine.

Therefore, the present inventor has proposed a conventional AIDC (auto i.p.) without using a potential sensor.
Focusing on setting a grid voltage with an appropriate fog margin by using a reflection type optical sensor for detecting the amount of toner adhered to the reference toner pattern in the mage density control). However, in this case, if the surface potential and the developing bias voltage are uniform in the periphery of the detection area (test pattern formation area) of the optical sensor, particularly in the area in the width direction of the photoconductor, a bias phenomenon occurs, and The toner adheres to the end portion and becomes dirty, causing side effects such as image noise and uneven rotation of the photoconductor (pitch unevenness).

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an existing AI without using an expensive potential sensor.
An object of the present invention is to provide an image forming apparatus which can use a DC optical sensor and can secure an appropriate fogging margin without fear of side effects, and has good image reproducibility.

In order to achieve the above object, the image forming apparatus according to the present invention, when in a grid voltage setting mode for obtaining a fog margin, forms a test pattern in which an optical sensor detects a toner adhesion amount. The exposure light amount is slightly increased in the region compared to the other regions. Preferably, the exposure light amount for the test pattern formation region is substantially equal to the bias light amount at the time of image formation, and the drive of the exposure unit is turned off for the other regions.

In the grid voltage setting mode, first, the grid voltage of the charger and the developing bias voltage are set to predetermined values at which a target fogging margin can be obtained. Then, only the test pattern forming area is exposed with a very small amount of light, and the amount of toner attached to the exposed portion is detected by a sensor. Further, the grid voltage is changed by a predetermined amount (development bias voltage is constant), exposure is performed with a very small amount of light, and the amount of toner adhering to the exposed portion is detected by a sensor.
A grid voltage at the time of image formation is set based on the detection results. For example, the charging efficiency is obtained by performing necessary calculations from a grid voltage value at which toner adhesion is detected (fogging has occurred), an initial grid voltage value, a developing bias voltage value, a target fogging margin value, and the like. Then, a grid voltage at the time of image formation is calculated from the charging efficiency.

According to the present invention, only the test pattern forming region is exposed with a very small amount of light, and has a slightly different potential than the other peripheral regions. Therefore, even if the toner is deposited on the test pattern forming area, the toner hardly covers the peripheral area, and side effects such as smearing the end of the photoconductor with the toner can be avoided as much as possible.

Further, in the present invention, when calculating the grid voltage, environmental conditions (for example, temperature and humidity) and / or endurance conditions (for example, for example) at the time of execution of the setting mode are set.
It is preferable to use (accumulated print number) as a parameter. The amount of toner charge in the developer changes depending on environmental conditions and durability conditions, and the situation where fogging occurs changes. Therefore, when calculating the charging efficiency in the grid voltage setting mode, the detected environmental conditions and endurance conditions are treated as correction values, so that the charging efficiency can be calculated more accurately and with less error. Can be set.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a digital full-color copying machine to which the present invention is applied. The schematic configuration is such that an image reader unit 1 is arranged in an upper section, a full-color image forming section 20 including a laser exposure unit 10 is arranged in a middle section, and a paper feed section 40 is arranged in a lower section. A duplex sorter 70 is provided on the left side of the copying machine.

The image reader unit 1 is for reading an image of a document set on a platen glass 9, and includes a lamp 2, mirrors 3a, 3b, 3c, a lens 4, a color CCD 5, and the like. is there. CC
D5 represents the original image as R (red), G (green), B
It is read as analog electric signals of three primary colors (blue). The analog electric signal is converted into digital print data corresponding to four colors of C (cyan), M (magenta), Y (yellow), and K (black) by the image signal processing unit 6,
In addition, necessary editing processing is performed, and the data is transferred to the laser exposure unit 10.

The laser exposure unit 10 modulates a laser diode (not shown) based on print data to form an electrostatic latent image on the photosensitive drum 21.

The full-color image forming section 20 includes the photosensitive drum 2
1 and the transfer drum 31. Around the photosensitive drum 21, a scorotron-type charging charger 22, a full-color developing unit 23, a residual toner cleaner 24, and a residual charge eraser 25 are provided along the rotation direction (arrow a). Further, a reflection type optical sensor 26 for detecting the amount of toner attached to the surface of the photosensitive drum 21 is provided.

The developing unit 23 includes developing units 23C, 23M, 23Y, and 23K each containing a developer containing cyan, magenta, yellow, and black toners. A latent image of each color is formed on the photosensitive drum 21. Each time the corresponding developing device is driven. Further, a temperature sensor 51 and a humidity sensor 52 are set near the developing unit 23.

The transfer drum 31 is rotatably driven in the direction of arrow b at the same peripheral speed as the photosensitive drum 21 and transfers a toner image onto a recording paper wound around its surface.
The transfer drum 31 includes a chucking claw (not shown) for holding the leading end of the recording paper, a separation claw 32 for separating the recording paper, a charger 33 for adsorbing the recording paper, a transfer charger 34, and a recording paper. Is provided with chargers 35a, 35b and the like for separating the two.

The paper supply unit 40 includes three paper supply cassettes 41 and 4.
2 and 43, and the recording paper is stored in one of the cassettes 41 and 4.
The sheets are fed one by one from 2, 43,
At the same time, the toner is fed to the transfer drum 31 by the timing roller 45 at a predetermined timing.

At the time of full-color image formation, cyan, magenta, yellow, and black images are sequentially formed on the photosensitive drum 21, and the respective toner images are chucked on the outer peripheral surface of the transfer drum 31 by discharge from the transfer charger 34. Is transferred / combined on the recording paper. 4
The recording paper on which the color image has been transferred / combined is separated from the transfer drum 31, sent to a fixing device 46, where the toner is heated and fixed, and sent to a sorter 70 from a discharge roller 47.

The sorter 70 has a function of accommodating the recording paper in a predetermined bin 72 and a function of inverting the recording paper to form an image on the second surface and sending it out to the transport path 44 again.

Here, an image forming mechanism on the photosensitive drum 21 will be described with reference to FIGS. A power source 61 of a voltage Vc is connected to the wire 22a of the charging charger 22, and a Vg generating unit 6 is connected to the grid 22b.
2, a negative grid voltage Vg is applied. The photoconductor surface potential Vo immediately after being charged by the charging charger 22 slightly darkens, but the grid voltage V
can be considered equivalent to g. The surface potential Vo can be controlled by changing the value of the grid voltage Vg. When an image is exposed by the laser exposure unit 10, as shown in FIG. 3, the potential of the image portion is greatly attenuated to Vi, and a latent image is formed. Note that the potential of the background portion slightly attenuates to Vi 'due to the presence of the bias light amount.

In the developing unit 23, a negative developing bias voltage Vb is applied from the Vb generating unit 63 to each developing sleeve 23a. The toner is charged to a negative polarity, and this toner adheres to the image portion attenuated to the low potential Vi. The toner adheres basically under the condition of | Vi | ≦ | Vb |.

During image formation, the potential difference between the surface potential Vo and the developing bias voltage Vb needs to be maintained within a predetermined range. Also, the toner adhesion amount is the developing voltage ΔV
(ΔV = | Vb | − | Vi |). The image portion potential Vi changes with the surface potential Vo if the exposure light quantity is the same. Normally, the exposure light amount is set to be large so that the potential Vi becomes almost 0V. Therefore, the surface potential Vo
When the surface potential Vo (grid voltage Vg) and the developing bias voltage Vb are changed while maintaining a substantially constant potential difference between the developing bias voltage Vb and the developing bias voltage Vb, the developing voltage ΔV changes, and the toner adhesion amount can be changed. . That is, the image reproduction density can be controlled to stabilize the image.

AIDC is processed on the premise of the above-described image forming mechanism. Specifically, for each color, a reference toner pattern serving as a reference for density control is formed under a predetermined grid voltage Vg, a developing bias voltage Vb, and an exposure light amount, and the optical sensor 26 reflects the reflected light amount from the reference toner pattern. Is detected. The detection signal is input to the control unit 65, where the toner adhesion amount (image density) is calculated from the difference between the detection signal of the background portion of the photoconductor and the detection signal of the reference toner pattern.
The relationship between the toner adhesion amount and the sensor detection value is as shown in FIG. 4, and the control unit 65 holds this data in advance.

If the grid voltage Vg and the developing bias voltage Vb are changed according to the calculated toner adhesion amount,
AIDC can be processed for the purpose of keeping the amount of toner attached to the maximum density level constant. Development bias voltage Vb
And the grid voltage Vg are stored in the controller 65 as tables shown in Tables 1 and 2 below. The control unit 65 selects an optimum table number from the toner adhesion amount, and controls the power supply units 62 and 63 with respective output values.

[0025]

[Table 1]

[0026]

[Table 2]

Next, a mode for setting the grid voltage Vg in order to obtain a fog margin will be described. The fog margin is a potential difference ΔVm = | Vg | − | Vb | for preventing the toner from adhering to the image background during image reproduction. In the present embodiment, the target is −100 V (± 30 V). Therefore, first, the grid voltage Vg and the developing bias voltage Vb are set to predetermined values (Vg: -460 V, Vb: -360 V) at which a target margin (-100 V) can be obtained.
Set to. Then, the laser exposure unit 10 emits light with a very small amount of light (see FIG. 5) to form a test pattern (latent image). After the development, the sensor 26 detects the toner adhesion amount. Further, the grid voltage Vg is changed by a predetermined amount (development bias voltage Vb is constant), each is exposed with a very small amount of light to form a test pattern, and the amount of toner adhesion is detected. For example, if the grid voltage Vg is -460
It is assumed that the voltage is changed from V to -445 V, -430 V, and -415 V. Assuming that the grid voltage Vg at which toner fogging is detected by the sensor 26 is -415 V, the grid voltage -415 V and a predetermined developing bias voltage -360 V as a reference are calculated as follows.

The charging efficiency T ₁ is calculated based on T ₁ = predetermined reference Vb value / fogged Vg value (1). Specifically, T ₁ = (− 360) / (− 415) = 0.767. The reason why the charging efficiency is obtained by the calculation of the above equation (1) is that fog occurs at a Vg value of -415 V, which means that the photoconductor surface potential Vo when the Vg value is -415 V is obtained.
Means that the battery has been charged to the same potential as the predetermined reference Vb value. Usually, the charging efficiency T ′ is

T ′ = predetermined Vg value, photoconductor surface potential Vo / predetermined Vg value (1 ′) That is, without directly measuring the photoconductor surface potential Vo, the Vg value is lowered, and when the toner fogs out, it can be determined that Vo = Vb. Therefore, the normal charging efficiency calculation formula (1 ′) is as described above. Equation (1) can be used instead. From the charging efficiency T ₁ and the grid voltage Vg at the time of image forming and calculates the combination of the developing bias voltage Vb.

The operation formula is as follows. (Vb−100) / T ₁ = Vg (2) It is possible to calculate a Vg value required to obtain a fogging margin of 100 V by the above equation (2).

First, the developing bias voltage Vb is selected from Table 1 above, Vb is substituted into the above equation (2) to obtain Vg, and the corresponding (closest) table No. is selected from Table 2.

The relationship between the grid voltage setting mode and the AIDC mode is as follows. First, the grid voltage setting mode is executed to determine the combination of the grid voltage Vg and the developing bias voltage Vb in consideration of the fog margin. Next, the AIDC mode is executed with the determined Vg and Vb, and the grid voltage Vg and the developing bias voltage used in the actual image reproduction are determined based on the toner adhesion amount of the reference toner pattern.

As described above, the amount of toner charge in the developer changes depending on the environmental conditions such as temperature and humidity and the durability condition such as the cumulative number of prints, and the photoconductor surface potential Vo at which toner fogging occurs changes. It is assumed that the equation charging efficiency T ₁ (1) is equal to the voltage Vb a Vg value the actual potential Vo when began wearing. However, when the toner charge amount is lower or higher than the normal state, the fogging state of the toner changes. Therefore, it is not possible to substitute the Vb value as the Vo value in the above equation (1 ′). Is not strictly preferred. The fog margin is desirably set in the range of −100 ± 30 V, and it is necessary to minimize the calculation error of the charging efficiency. Therefore, it is preferable to set a correction value using the environmental condition and the durability condition as parameters, and calculate the charging efficiency by correcting the Vb value in the equation (1).

Therefore, if the above equation (1) is replaced by the following equation (3), it is possible to calculate the charging efficiency without error suitable for the actual use environment and use conditions of the apparatus, and to set a more appropriate grid voltage. Becomes possible. T ₂ = (predetermined reference Vb value + correction value) / Vb value at which fogging has occurred (3)

The equation (2) for calculating the Vg value is also replaced by the following equation (4). (Vb-100) / T ₂ = Vg (4)

FIG. 6 shows the change in the toner charge amount with respect to the absolute humidity, and FIG. 7 shows the change in the toner charge amount with respect to the number of prints (when the absolute humidity is 10 g / m ³ ).
If the toner charge amount is high, fogging is unlikely to occur because the electrostatic attraction force with the carrier is increased. On the other hand, when the toner charge amount is reduced, fogging is likely to occur because the electrostatic attraction force with the carrier is weakened.

The correction values corresponding to the absolute humidity and the number of prints are stored in the control unit 65 as a table shown in Table 3 below. Absolute humidity is temperature sensor 51, humidity sensor 5
Based on the detected value of No. 2, the control unit 65 refers to the table shown in Table 4 below. The number of prints is obtained based on the count value of the integration counter 53. For example, the number of prints is 4500 and the absolute humidity is 10 g / m
^{In the case of 3} , +10 V is selected as the correction value.

[0038]

[Table 3]

[0039]

[Table 4]

FIG. 8 shows the grid voltage setting mode and the AID.
The outline of the control procedure in the C mode is shown. Steps S1 to S7
Is a grid voltage setting mode, and steps S8 to S1
0 is the AIDC mode. Note that step S7 is performed by AI
It can be considered to be included in the DC mode.

First, in step S1, temperature and humidity information is acquired from temperature and humidity sensors 51 and 52 built in the copying machine. Next, in step S2, predetermined Vg and Vb corresponding to the target fogging margin are determined based on the temperature and humidity information, and in step S3, exposure is performed under a small amount of light under the conditions to form a test pattern, and toner adhesion is performed. Detect the amount. Further, Vg is fixed in a state where Vb is
Is normally switched to four different values, and step S5
Then, each test pattern is created to detect the amount of toner adhesion. Next, in step S6, the charging efficiency is calculated from the grid voltage Vg at which fogging has occurred, and in step S7, a combination of the grid voltage Vg for image formation and the developing bias voltage Vb is determined from the charging efficiency. Although the charging efficiency may be calculated by the above equation (1), it is more accurate to calculate the charging efficiency by the above equation (3) in which a correction value is introduced.

Next, in the AIDC mode, step S is performed.
Under Vg, Vb determined in step 7 and a predetermined exposure light amount,
In step S8, a reference toner pattern is created, and in step S9, the toner adhesion amount is detected. Next, in step S10, a combination of the grid voltage Vg and the developing bias voltage Vb that provides an optimum image density is determined.

As described above, in the grid voltage setting mode for obtaining a fog margin in the present embodiment, as shown in FIG. 5, a test pattern is formed by exposing a very small amount of light, and the formation area is formed. For the other areas, the driving of the laser exposure unit 10 is turned off to set the exposure light amount to zero. Therefore, the toner foggs and adheres to the pattern forming area with a very small amount of light, and the toner hardly adheres to other areas. Therefore, there is no side effect such as soiling the end of the photosensitive drum 21 with toner.

It is preferable that the minute light amount at the time of test pattern creation is such that the pattern forming area has a potential difference Vo-Vi '(see FIG. 3) more than other areas.

It should be noted that the image forming apparatus according to the present invention is not limited to the above-described embodiment, but can be variously modified within the scope of the invention.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a full-color copying machine according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a control system of the copying machine.

FIG. 3 is a chart showing a photoconductor surface potential in a grid voltage setting mode.

FIG. 4 is a graph showing a relationship between a toner adhesion amount and a sensor detection value.

FIG. 5 is a chart showing a grid voltage, a developing bias voltage, and an exposure light amount in a grid voltage setting mode.

FIG. 6 is a graph showing a toner charge amount with respect to an absolute humidity.

FIG. 7 is a graph showing the amount of toner charge with respect to the number of prints.

FIG. 8 is a flowchart showing a control procedure in a grid voltage setting mode and an AIDC mode.

[Description of Signs] 10 ... Laser exposure unit 21 ... Photoreceptor drum 22 ... Charging charger 23 ... Developing unit 26 ... Toner adhesion amount detection sensor 34 ... Transfer charger 51 ... Temperature sensor 52 ... Humidity sensor 53 ... Printed sheet count counter 62 ... Vg generation unit 63 Vb generation unit 65 control unit

Claims (3)

[Claims] 1. An electrophotographic image forming apparatus having at least a charging unit, an exposing unit, a developing unit, and a transferring unit disposed around a photoreceptor, wherein a grid voltage of a charging charger and a developing bias voltage are set to predetermined values in advance. The test pattern formed on the photoreceptor is developed with toner by changing the grid voltage by a predetermined amount, the amount of toner adhesion is optically detected, and the grid voltage at the time of image formation is determined based on the detection result. An image forming apparatus, wherein, when setting, an exposure light amount is slightly increased in a test pattern formation region than in other regions. 2. The image according to claim 1, wherein the amount of exposure light for the test pattern formation area is substantially equal to the amount of bias light for image formation, and the driving of the exposure unit is turned off for other areas. Forming equipment. 3. The method according to claim 1, wherein, when the test pattern is formed and a grid voltage is set at the time of image formation, environmental conditions and / or endurance conditions at the time of executing the setting mode are used as parameters. Item 2
The image forming apparatus as described in the above.