JPH0421874A - Method for controlling electrostatic potential - Google Patents

Abstract

PURPOSE:To control an electrostatic charge quantity to be a desired value without spending much time for detecting and controlling the electrostatic charge quantity by detecting the electrostatic charge quantity of an image carrier for which specified electrostatic charge is executed and controlling also the output of an electrostatic charge means based on the detected value of the electrostatic charge quantity. CONSTITUTION:When timing that the output of a corona discharger 2 is controlled is attained, a grid bias set value Vgp stored in a Vgp register is read out and a grid bias signal is outputted to a grid bias circuit 2c. Besides, an electrostatic charge area for measuring toner density is formed by the grid bias Vgp and electrostatic charge potential Vp in the electrostatic change area is detected by a surface potential sensor 13. Then, by using the detected value Vp read from an interface 17 and the grid bias set value Vgp, arithmetic operation stored in a ROM is executed. Then, the electrostatic charge is executed by a grid bias value which is newly set. Thus, the respective electrostatic charge quantity is controlled to be the desired value without spending much time.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile machine, and specifically, an image bearing member can be charged with two or more different amounts of charge. The present invention relates to a charging potential control method for an image forming apparatus.

[Conventional technology]

In this type of image forming apparatus, in addition to so-called electrification, in which an area on an image carrier such as a photoconductor or dielectric is charged to a predetermined amount in advance for image exposure according to a document or an image signal, Charging may be performed to form a region for toner concentration measurement, etc. with a different charge amount, or a different charge amount depending on the type of document (for text documents, a thicker layer is used to improve contrast). For photo originals, a small charge amount is applied to improve the gradation, and in full-color image formation, different charge amounts are applied prior to exposure of each color of red, green, and blue. Uniform charging is performed, or image formation is performed at two or more different process speeds, and uniform charging is performed with a different amount of charge depending on the process speed.

[Problem to be solved by the invention]

However, if the amount of charge fluctuates due to aging of the image carrier, etc., the development potential in the development process fluctuates, causing background fog or lack of density in the image. In particular, so-called filming, in which toner, paper dust, or additives contained in paper adhere to the surface of the image carrier in the form of a thin film, is completely removed using an abrasive material (such as felt) or an abrasive fur brush. In the case where the surface of the image carrier itself is polished, the film thickness of the image carrier gradually becomes thinner, and the difference between the film knob of the photoreceptor, etc., which is the image carrier, and the charged potential is expressed by the following equation (1). Because of this relationship, polishing also causes a decrease in the charging potential.

εr° ε.・S (where ■ is the charged potential of the photoconductor, Q is the amount of charge on the photoconductor, d is the photoconductor film thickness, εr is the relative dielectric constant of the photoconductor, ε is the permittivity of vacuum, and S is the photoconductor ) Therefore, conventionally,
It has been mainly used to stabilize and control the amount of charge in uniform charging.
A technique for detecting the amount of charge in a uniformly charged area of the image carrier and controlling the output of the charging means during charging according to the detected value is adopted for charging of all different amounts of charge, It is conceivable to detect and control the amount of charge for each charge.

However, this has the problem that it takes a lot of time to detect and control the amount of charge, which adversely affects other sequence controls of the image forming apparatus. This has become a major problem as there is a demand for charging image carriers with more different charge amounts in response to demands for improved image quality.

The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide a charging system for an image forming apparatus that can charge an image bearing member with two or more different amounts of charge. An object of the present invention is to provide a charging potential control method that controls the amount of each charge to a desired value without spending much time on detecting and controlling the amount of charging.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a charging potential control method for an image forming apparatus in which an image bearing member is charged with two or more different charging amounts. It is characterized by detecting the amount of charge of the charge amount, and controlling the output of the charging means in performing charging with the specific charge amount and charging with at least one other charge amount based on the detected value of the charge amount. It is something.

[Effect]

The present invention configured as described above detects the amount of charge of an image bearing member that has been charged with a specific amount of charge, and based on the detected amount of charge, determines whether the image carrier is charged with the specific amount of charge or at least one other amount. This functions to control the output of the charging means when charging the amount of charge.

〔Example〕

An embodiment in which the present invention is applied to a copying machine, which is an image forming apparatus, will be described with reference to FIGS. 1 and 2.

In this embodiment, the charging means output is used to uniformly charge a photoreceptor, which is an image bearing member, and the charging means output is used to form a region for measuring toner concentration with a different amount of charge from the -like charging. The output of the charging means is controlled.

First, an overview of the entire copying machine will be explained.

In FIG. 2, an original (not shown) on a contact glass 1 is charged by an optical system (not shown) including an illumination means that irradiates the original while moving parallel to the contact glass 1. Already plus 8 with discharger 2
The image is projected onto a drum-shaped photoreceptor 3 that is uniformly charged to 00V, thereby forming an electrostatic latent image on the photoreceptor 3.

This corona discharger 2 has a corona wire 2a and a grid wire 2b, and a grid bias circuit 2c is connected to the grid wire 2b. The electrostatic latent image on the photoconductor 3 is converted into a toner image by toner from a developing device 4 provided on the right side of the photoconductor 3, and this toner image is transferred to a transfer sheet conveyed from a paper feed section (not shown). The image is transferred onto paper by the transfer charger 5. The transfer paper on which the toner image has been transferred is
The paper is separated from the photoreceptor by a separation charger 6, passes through a fixing device (not shown), and is discharged outside the machine as copy paper.

On the other hand, the residual toner on the photoconductor 3 after transfer is removed by a cleaning device 7 provided on the left side of the photoconductor 3, and the residual charge is eliminated by a static elimination lamp 8, and the remaining toner is removed from the photoconductor 3 for the next charging by the corona discharger 2. Be prepared.

Further, a polishing brush 9 serving as polishing means is provided above the cleaning device 7 so as to come into contact with the photoreceptor 3, and is rotationally driven by a motor 10. This polishing by the polishing brush is carried out by rotating the polishing brush 9 for 10 minutes, which is one polishing operation for every 200 copies. This one polishing operation polishes the surface of the photoreceptor 3 by an average thickness of 0.03 μm (the photoreceptor 3 used in this embodiment has an initial film thickness of 25 μm).

In the copying machine of this embodiment, in order to measure toner density, the outside of the original image area on the photoreceptor 3 is charged by the corona discharger 2 to +500 V, which is a different charge amount from uniform charging. After this charged area is divided into required sizes by an eraser 11, it is formed into a toner image using toner from a developing device to form an area for toner density measurement. The toner concentration in this area is detected by an optical sensor 12 having a light emitting element and a light receiving element, and toner replenishment is controlled according to the detected value so that the toner concentration becomes a predetermined concentration.

Such toner density detection and control is performed once every 50 copies.
It will be held twice.

Next, output control of the corona discharger will be explained.

The output of the corona discharger is controlled by controlling the grid bias applied to the grid wire of the corona discharger based on the potential vp of the photoreceptor 3 in the toner concentration measurement area before the toner image is formed, which is detected by the surface potential sensor 13. Do by doing.

The microcomputer 14 that performs this control is mainly composed of a microprocessor (CPU) 15, a memory 16, and an interface (Ilo) 17.

The interface 17 of the microcomputer 14 has a microswitch 18 installed at the document irradiation start position of the illumination device that detects each copy operation and inputs it manually as a digital signal a, as well as the toner density before being converted into a toner image. The charged potential Vp of the photoreceptor 3 in the measurement area is detected by the surface potential sensor 13 and input as a digital signal via an A/D converter (not shown). Further, a grid bias signal is output from the interface 17 to the grid bias circuit 2C via a D/A converter (not shown). A RAM (read/write memory) 16a in the memory 16 includes a gi register for storing a grid bias setting value Vgi for −-like charging, and a register for storing a grid bias setting value Vgi for forming an area for toner density measurement. A Vgp register is provided for recording and storing a grid bias setting value (Vgl). The RAM 16a is also provided with a number register for storing the cumulative number of copies, which is replaced with a larger value one by one by the digital signal a and stored. A ROM (read-only memory) 16b in the memory stores an arithmetic program, which will be described later.

In the above configuration, the output control of the corona discharger 2 is performed by detecting the charged potential Vp of the photoreceptor 3 and correcting the grid bias setting values Vgi and Vgp based on this detected value every 200 copies. Implemented. In the initial state when the copying machine is shipped, the grid bias such that the charged potential of the photoconductor 3 due to -like charging becomes plus 800 V is set as the set value ■gi to form an area for toner density measurement in the Vgi register. A grid bias such that the charged potential of the photoreceptor 3 becomes plus 500 V due to charging is stored in each Vgp register as a set value Vgp. When the cumulative number of copies increases and the thickness of the photoreceptor 3 becomes thinner due to polishing by the polishing brush 9, the charged potential of the photoreceptor 3 decreases based on the relationship expressed by equation (1). Here, in the scorotron type corona discharger, the following equation (2) exists between the grid bias voltage Vg and the amount of charge Q applied to the photoreceptor.

Q = aVg + β (2) (where α and β are the performance of the charger and the charging time of the photoreceptor (
Constants determined by process speed) Equations (1) and (2)
From this, the following equation (3) can be derived.

V=A (aVg1β)d (3) However, 8-εr・ε. - S In this equation (3), A, α, and β are known constants that can be obtained in advance through experiments, etc., and Vg is a control value and is known to the copying machine, so a certain grid bias Vg
If the photoreceptor charging potential V due to corona discharge is detected at
The photoreceptor film thickness d at that time can be determined by the same formula, and once the photoreceptor film thickness d is determined, by the same formula, an arbitrary
Grid bias Vg to obtain a certain photoreceptor potential V'
′ can be determined.

That is, if the detected value of the photoreceptor charging potential of corona discharge at a certain grid bias Vgt is Vt, the following equation (3) holds true from the above equation (3).

Vt = A (αVgt + β) dt (3).

(In the equation, dt is the photoreceptor film thickness at that time.) The grid bias Vg' for obtaining an arbitrary photoreceptor potential V' satisfies the conditions of the above equation (3) and the lower equation (3)2.

V'=A (αVg'10β)dt (3) 2 equations (
3),, (By dividing the sides of 3L and sorting out the grid bias ■g', the grid bias ■g' can be found as shown in equation (4) below.

In this embodiment, taking advantage of the above, the detected value ■p of the potential of the strip in the area for toner density measurement charged with the grid bias pg is used as Vt, and the desired value is used as Vg'. Using the uniform charging potential plus 800 volts and the charging potential of the area for toner concentration measurement plus 500 volts, the following equation (4), (using 4L as the calculation formula, RO
Let M memorize it.

In these formulas, Vgi' and VgI)' are grids determined by calculations to make the charging potential of the region for measuring the l-ner concentration to be plus 500 volts, respectively, in order to make the charged potential of the region plus 800 volts. bias,
This is stored as a new setting value in the Vg] register and the Vgp register.

The above control will be explained based on FIG. 1.

First, the cumulative number of copies stored in the number register is read out, and it is determined whether it is a multiple of 200 or not to determine whether or not it is time to control the output of the corona discharger 2 (step 2). When it is determined that it is time to control the output of the corona discharger 2, the grid bias setting value VgI) stored in the VgI) register is read out, and the D/
A grid bias signal is output to the grid bias circuit 2C via the A converter, and charging is thereby performed at the grid bias Vgp to form a charged area to form a charged area. The charged potential Vp of the area is detected by the surface potential sensor] 3 (step ①). This detected value Vp read from the interface 17 and the grid bias setting value VgI
) is stored in the ROM using
, (4L calculations are performed (step ■), and the calculation results Vgi' and vgp are respectively set as new Vgj setting values and Vg
I) Store the set values in the gj register and gp register (step ■). Therefore, until the next grid bias correction control, −-like charging and charging for forming a region for toner density measurement are performed using the newly set grid bias value.

In the embodiment described above, the charge amount Vp for forming the area for toner density measurement is detected, but the charge amount Vi for uniform charging may be detected instead.

Next, another embodiment of the present invention will be described.

In this embodiment, the circumferential speed of the photoreceptor 3 is set to a low speed of 120 mm/
Fast process speed of 240 mm 7 seconds
It can be switched at a process speed of 1 second, and each negative charge is performed with different charging amounts of +600V and +800V. Such process speed switching is performed by the operator's selection, such as selecting high-quality copying or high-speed copying with slightly inferior image quality, or by selecting between full-color copying and monochrome copying. Depending on the selection, the copying machine may perform this automatically.

The overall outline of the copying machine can be the same as in the second embodiment.

Let the known constants α and β in the above equation (3) for low process speed and high process speed be β0.
β1, β2. Assuming β2, the above equation (3) becomes the following equation (5)
, (6).

Vl, = A (α, Vgl - ten β,) d (5) V
l(=A(α2Vgl(+β2)d) (6) (where VgL and VL are the grid bias at low process speed and the resulting surface potential of the photoreceptor, VgH
lVH is the grid bias at high process speed and the resulting surface potential of the photoreceptor) In these equations (5) and (6), A, β1, β1, Ct
2. β2 is a known constant that can be determined in advance through experiments, etc.
Since VgL and VgH are control values and are known to the copying machine, if one of them is detected, for example, the grid bias V at a low process speed, and the photoreceptor charging potential VLt of corona discharge at gLt, the formula can be obtained. The photoreceptor film thickness dt at that time can be determined by (5), and once the photoreceptor film thickness dt is determined, an arbitrary
Grid bias V to obtain a certain photoreceptor potential VL'
Not only can gL' be determined, but also the grid bias Vgll' for obtaining an arbitrary photoreceptor potential VH' can be determined using the other equation (6).

That is, in this case, for low process speeds,
Similarly to the above embodiment, the following equation (7), which corresponds to the above equation (4), holds true.

For high process speed, first, use the above equation (6).
Therefore, the following equation (6), which corresponds to the above equation (3) 2, is established, and Vgll' - A (α2VgH' + β2) dt
(6) + On the other hand, for low process speeds, the following equation (5) 1, which corresponds to the above equation (3) 1, holds true, so dividing the sides of these equations (6) 1 and (5) □, If the grid bias VgH' is rearranged, the grid bias Vgl(' can be found as shown in equation (8) below.

Vl-t=A(α, V gLt+β,)dt (
5L In this example, the detected value ViL of the uniformly charged potential charged with the grid bias VgiL at a low process speed is used as Vl, t, and VgL', VgH
' to obtain the desired uniformly charged potential at each process speed using a uniformly charged potential plus 600 volts at the desired slow process speed and a uniformly charged potential plus 800 volts at the high process speed, respectively. Bias V giL', V gi
In order to obtain H', the following equations (7) 1 and (8) 1 are stored in the ROM as calculation equations.

Then, as in the above embodiment, the uniformly charged potential of the photoreceptor 3 at a low process speed is detected at a certain timing, and using this detected value ViL and the grid bias V giL at that time, the above calculation formula (7) is calculated. 1. (8) The result calculated in 1 is stored as the grid bias setting value during uniform charging at each of the new low process speed and high process speed, and is used during subsequent uniform charging.

In this example, a uniform charging potential at a slow process speed was detected, but a uniform charging potential at a high process speed may also be detected. , a charging potential ■p for forming a region for toner concentration measurement may be detected.

In each of the above embodiments, a scorotron type corona discharger is used as the charging means, but the present invention is not limited to this, and various other charging means may be used.

Furthermore, as long as the charging is performed in a double manner with different amounts of charge, the present invention is not limited to the embodiment described above, and can be applied to image forming apparatuses capable of performing double charging with different amounts of charge for various purposes.

〔Effect of the invention〕

As described above, according to the present invention, in the charging potential control method for an image forming apparatus in which the image bearing member can be charged with two or more different charging amounts, the charging amount of the image bearing member that has been specifically charged is controlled. and, based on the detected value of the amount of charge, control not only the output of the charging means when performing the specific charging but also the output of the charging means when performing at least one other charging. Therefore, there is an excellent effect that the charge amount of each charge can be controlled to a desired value without spending a lot of time on detecting and controlling the charge amount.

[Brief explanation of drawings]

FIG. 1 is a flowchart illustrating output control of a corona discharger according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of the overall configuration of a copying machine according to the embodiment. 2...Corona discharger, 2C...Grid bias circuit, 13.Surface potential sensor 14...Microcomputer-

Claims (2)

[Claims] (1) In a charging potential control method for an image forming apparatus in which an image bearing member can be charged with two or more different amounts of charge, the amount of charge of an image bearing member that has been charged with a specific amount of charge is detected, and the amount of charge is detected. A charging potential control method comprising controlling an output of a charging means when charging a specific charging amount and at least one other charging amount based on a detected value. (2) The charging potential control method according to (1), wherein the image carrier is charged with different amounts of charge depending on two or more different process speeds.