JPH0697357B2 - Image forming device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus such as a copying apparatus which detects a surface condition such as a latent image potential on a photosensitive drum and controls an image forming condition based on the result. Is.

2. Description of the Related Art The copying process using a photosensitive drum as described above, particularly the operating process of the copying device, can be roughly divided into two. First
In the image forming process in which the photosensitive drum is rotatably driven to perform the exposure and the development, an electrostatic latent image corresponding to the original is formed in this image forming process. The other is a pre-process for performing a control operation for determining the charge amount, the exposure amount, etc. in preparation for image formation. In this pre-process, non-image areas of light and dark areas unrelated to the original image are formed.

In this non-image area, in a conventional copying machine in which the photosensitive drum and the developing device sleeve are rotationally driven by the same drive source, the photosensitive drum and the developing device sleeve are rotationally driven at the same time. However, there is a problem that the toner is adsorbed on the photosensitive drum and consumed.

In view of this point, in the conventional copying apparatus, it is usual to perform so-called blank exposure during rotation of the photosensitive drum in the non-image area in the previous step to prevent toner adhesion to the photosensitive drum. Attempts have also been made to switch the developing bias to a value at which toner adhesion does not occur.

However, in a copying machine having an automatic control mechanism that detects a latent image potential by a potential sensor to stabilize the image density and controls the image forming condition according to the detection result,
It is necessary to form both the light potential and the dark potential on the photosensitive drum for image density control, the rise time of the blank exposure lamp is long, and the illuminance of the lamp itself also varies widely. Therefore, not only the light potential but also the dark potential is distributed in the non-image area where the latent image of the original image is not formed.Therefore, in order to prevent toner adhesion to the entire non-image area, use a blank exposure lamp. It is necessary to apply a high voltage to the developing bias when using a large amount of light (that is, a large power consumption) or when using a negative toner.

For example, in a copying machine in which CdS is used as the photosensitive member of the photosensitive drum and the dark portion potential is set to + 500V, the developing roller is biased at + 600V in the non-image area to prevent toner adhesion.

On the other hand, the developing characteristics related to the surface potential of the photosensitive drum have the characteristics shown in FIG. That is, this is the development called reversal development, and even if the polarity of the surface potential of the photosensitive drum is in the repulsive direction of the toner charge, when the predetermined value (-500V in FIG. 1) is exceeded, the toner begins to be attracted to the photosensitive drum. (When the developing bias is 0V). Therefore, if the developing bias is fixed to +600 V as described above, there is a drawback that a considerable amount of toner adheres to the photosensitive drum and is consumed in the non-image area in the area corresponding to the low potential or the light portion. there were.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an image forming apparatus capable of preventing wasteful toner consumption in the previous step.

Examples Hereinafter, the present invention will be described in detail based on the examples shown in the drawings. However, in the following embodiments, a copying machine will be described as an example.

FIG. 2 shows a schematic structure of a copying apparatus according to the present invention. The photosensitive drum 1 is composed of, for example, an insulating layer, a photoconductive layer, and a conductive layer from the surface, and is rotatably supported by a main body (not shown) about a shaft 1a.
Around the photosensitive drum 1, the primary charger 2 is arranged in the rotational direction.
A secondary charging device 3, a whole surface exposure lamp 4, a potential sensor 7, a developing roller 5 of a developing device, a transfer charging device 28 and a pre-electrification charging device 29 are arranged.

The surface of the photosensitive drum 1, which has been precharged by the charger 29 prior to each process, is uniformly charged by the primary charger 2 and then the original 10 illuminated by the original exposure lamp 11.
Is exposed on the photosensitive drum 1 via the mirrors 12 and 13. At this time, the secondary charging device 3 removes the charge according to the image of the original, and the whole surface is exposed by the whole surface exposure lamp 4, and then the toner is developed by the developing roller 5. An AC bias voltage is applied to the developing roller 5 as described later, and the gradation of the image is adjusted by jumping development. Then, the transfer charger 28 is operated, and the transfer onto the transfer paper is performed. Also,
A blank exposure lamp 6 that forms a dark portion and a bright portion potential, which will be described later, is arranged above the secondary charger 3.

Further, a potential sensor 7 for measuring the surface potential of the photosensitive drum 1 is arranged between the whole surface exposure lamp 4 and the developing roller 5, and the signal from this potential sensor 7 is transferred to the A /
After being input to the D conversion circuit 9 and converted into a digital value,
It is input to the microcomputer 15. The output of the microcomputer 15 is connected to a D / A conversion circuit 16, and the D / A conversion circuit 16 further includes a light amount control circuit 17, a primary high voltage control circuit 18, a secondary high voltage control circuit 19, a transfer control circuit 24, The pre-electrification control circuit 25 and the DC developing bias control circuit 20 are connected. A light quantity control circuit 17 controls the document exposure lamp 11 via a lamp regulator 14, and also primary and secondary high voltage control circuits 18 and 19 are provided.
Are respectively connected to the primary charger 2 and the secondary charger 3 via the primary and secondary high voltage transformers 21 and 22, respectively, and determine the respective charge amounts. Further, the transfer control circuit 24 is connected to a transfer charger 28 via a transfer high voltage transformer 26, and
The pre-elimination control circuit 25 is connected to the pre-elimination charger 29 via the pre-elimination high-voltage transformer 27. DC development bias control circuit
The output of 20 is connected to an AC developing bias control circuit 23, and the output of this AC developing bias control circuit 23 is applied to the developing roller 5.

The DC developing bias control circuit 20 and the AC developing bias control circuit 23 described above are configured as shown in FIG. That is, the sine wave oscillating circuit 30 is connected to the amplifying circuit 31, the AC voltage from the sine wave oscillating circuit 30 is applied to the primary side of the step-up transformer 32, and the voltage generated on the secondary side thereof is the developing roller 5. Applied to.

The other end on the secondary side of the step-up transformer 32 is connected to the DC-DC inverter 33, and is connected to the D / A conversion circuit 16 via the switch 34, and the DC developing bias shown in FIG. Make up the circuit. The switch 34 is a switch for switching between manual exposure and automatic exposure. In the automatic exposure mode, the switch 34 is switched to the side 34a and in the manual exposure mode, the switch 34b is switched to generate different developing bias voltages.

Next, the operation of the above configuration will be described in detail with reference to the flowchart of FIG. 4 and the time chart of FIG.

As shown in FIG. 5, the process from the start of copying to the end of copying is roughly divided into two steps.

In the previous step, the intense bright portion potential V _SL and the dark portion potential V _D are measured to control the charge amount, and the bright portion potential V _L1 is measured to control the exposure amount. In the previous step, a value obtained by adding 200 V to the detected surface potential V _S which changes every moment is applied as a developing bias.

As a result, the potential difference between the surface potential of the photosensitive drum and the developing sleeve is kept constant, so that useless toner is not consumed.

Then, in the actual image forming process, the electrostatic latent image corresponding to the developed image on the photosensitive drum is developed. The developing bias in this image forming step is maintained at a constant value obtained by adding 100 V to the final value of V _L1 measured in the previous step, and the developing operation is actually performed.

Next, the control flow will be described.

First, when the copy start is performed, the previous process is performed. In step S1, the measurement of the potentials in the bright and dark areas in steps S2 to S4 and the number of times the charge amount control routine based on the measurement is performed is determined. Here, the charge amount control
N _One time. Control number N _1, for example the state of the photosensitive drum in accordance with the standing time of the copying machine changes, N ₁ is increased standing time is longer.

If the number of routine passages is N ₁ or more in step S1, the process shifts to the measurement routine of steps S6 to S9 described later,
If it is less than N _1, the process proceeds to step S2 and subsequent steps.

First, in step S2, the original exposure lamp 11 or the blank exposure lamp 6 is made to blink to form a strong bright portion potential V _SL due to strong exposure and a dark portion potential V _D due to lamp extinction on the photosensitive drum. The surface potential is detected by the potential sensor 7, converted into a predetermined level by the potential measuring circuit 8, converted into a digital amount through the A / D conversion circuit 9, and sent to the microcomputer 15.

Next, in step S3, the surface potential converted into a digital amount is processed by the microcomputer 15, and control data to be output to the subsequent stage is formed so that the light portion potential and the dark portion potential each approach the target value.

That is, ΔI ₁ = α ₁ ΔV _D + α ₂ ΔV _SL (1) ΔI ₂ = β ₁ ΔV _D + β ₂ ΔV _SL (2) The current I ₁ and the secondary current I ₂ are obtained. In the above two equations, ΔI ₁ ,
ΔI ₂ is the change, ΔV _D , ΔV _SL are the deviations from the target value,
α ₁ , α ₂ , β ₁ , and β ₂ are control coefficients.

The control data obtained as described above is returned to the analog quantity by the D / A conversion circuit 16 in step S4,
It is input to the secondary and secondary high voltage control circuits 18 and 19. The primary high voltage control circuit 19 controls the primary high voltage transformer 21, which controls the charge amount of the primary charger 2, and the secondary high voltage control circuit 19 controls the secondary high voltage transformer 22. The charge amount of the secondary charger 3 is controlled, and the light portion potential V _SL and the dark portion potential V _D are adjusted so as to approach the target value.

As described above in step S1, the charging control described above is performed through steps S10 to S13, which will be described later, the number of times N ₁ that is different depending on the standing time.

Next, in step S5, the counter indicating the number of times the routine has been passed is incremented by 1, and the process proceeds to step S10.

On the other hand, in step S6, as in step S1, the next step
The number of times of exposure amount control in S7 to step S8 is determined. However, the exposure amount control in steps S7 to S8 is N ₂ here.
Shall be held once. N ₂ can also be set according to the time the copying machine is left unattended. If the routine pass count is less than N _{2 in} step S6, the process proceeds to step S7 and thereafter, and if N ₂ or more, the process directly proceeds to step S10 and later.

In step S7, the blank exposure lamp 6 is turned off, the standard white plate (not shown) provided outside the image area of the document 10 is illuminated using the document exposure lamp 11, and the reflected light is measured.

In the first irradiation, the D / A conversion circuit 16 converts the predetermined data output from the microcomputer 15 into an analog amount, and the lighting voltage V _HL adjusted by the lamp regulator 14 via the light amount control circuit 17 is used as the original. This is performed by giving the exposure lamp 11. The reflected light from the standard white plate due to the first exposure is guided onto the photosensitive drum 1, and the potential (white background potential V _L1 ) corresponding to the white background formed on the surface is passed through the potential sensor 7 and the potential measuring circuit 8. To measure.

This measured potential is converted into digital data by the A / D conversion circuit 9 in step S8, and then introduced into the microcomputer 15, where ΔV _L is a deviation amount γ1 from the target value as a constant ΔV _HL = γ ₁ · ΔV _L The calculation is performed according to.

The calculation result is converted into an analog amount by the D / A conversion circuit 16, and the exposure amount of the document exposure lamp 11 is adjusted via the lamp regulator 14 so that the white background potential V _L1 becomes a target value.
Similar to the charging control, such an exposure amount control is performed with the counter counting in step S9 a different number of times N ₂ depending on the leaving time, and whether or not the exposure control is performed a predetermined number of times N ₂ in step S6. To be judged.

The operations of steps S10 to S12 are performed in parallel with the operations of steps S1 to S9. In step S10, the latent image potential v _S of the photosensitive drum 1 is measured by the potential sensor 7.

In step S11, the rotational movement time from the potential sensor 7 of the photosensitive drum 1 to the developing roller 5 is measured. This is performed, for example, by generating a pulse by an encoder (not shown) attached to the rotary shaft of the photosensitive drum 1 and counting this pulse by the number P of times corresponding to the rotation angle.

Next, +200 V is added to the latent image potential v _S measured in step S12, and this value is applied to the developing roller 5 as the developing bias voltage.

Next, when it is determined in step S13 that the non-image area has not ended, the process returns to step S1.

As described above, when entering the copy sequence, the charge amount control and the exposure amount control are performed at predetermined times N ₁ and N _2, respectively, in steps S2 to S5 and steps S7 to S9,
At that time, the developing bias control for the developing device is performed in steps S10 to S12. This developing bias control is repeated until the non-image area ends in step S13 and it is determined to enter the image area in order to prevent toner adhesion in the non-image area. In step S13, the non-image area is actually ended by ending the charge amount and exposure amount control in steps S1 to S9.

When it is determined in step S13 that the non-image area has ended, the image forming process of steps S14 and S15 is started. To the final value of the white background voltage V _L1 obtained as described above in step S14
Apply a value of 100V to the developing device with a developing bias,
Then, in step S15, an actual copy operation is performed.

As described above, the latent image potential measured at the position of the potential sensor 7 is delayed by the rotation time of the photosensitive drum 1 up to the developing device 5 and given to the developing device 5, so that the charging control, the exposure control, and the like are performed. In the pre-process, which is performed, the developing bias changes with the surface potential of the surface of the photosensitive drum facing the developing device.
Since the added value of 200V is followed, the potential difference between the surface potential of the photosensitive drum and the developing sleeve can always maintain a constant value (200V) that is suitable for preventing toner adhesion, and the toner on the photosensitive drum in the non-image area can be kept. Will not be consumed and consumed.

Effects As is apparent from the above description, according to the present invention, an image forming unit having a charging unit, an exposing unit and a developing unit, which forms an image by performing charging, exposure and development on a photoreceptor, In an image forming apparatus including a detection unit that detects a surface potential on a photoconductor and a control unit that controls an image forming condition of the image forming unit according to a detection result of the detection unit, the control unit is independent of an original image. In the previous step of forming an electrostatic latent image of a bright area and a dark area, the developing bias of the developing means is set to a value obtained by adding a predetermined value to the output of the detecting means, which corresponds to the original image. In the image forming process in which the electrostatic latent image is formed and the developing process is performed, the developing bias is maintained at a constant value at which the developing process is performed. Prevents adsorption to the body, reducing the consumption of the toner, increasing the number of image formations per quantification can prolong the life of the cleaner blade. Further, there is an advantage that the blank exposure lamp does not need to have an excessively large light amount to prevent toner adhesion as compared with the conventional apparatus.

[Brief description of drawings]

FIG. 1 is a diagram showing developing characteristics relating to surface potential in an image forming apparatus such as a copying machine, FIG. 2 is a configuration diagram showing an arrangement of the image forming apparatus of the present invention, and FIG. 3 is an image of the present invention. FIG. 4 is a block diagram of a developing bias control circuit in the forming apparatus, FIG. 4 is a flow chart showing the control flow in the image forming apparatus of this embodiment, and FIG. 5 is a control time chart. 1 ... Photosensitive drum, 2 ... Primary charger, 3 ... Secondary charger, 4 ... Full exposure lamp 5 ... Developing roller, 6 ... Blank exposure lamp 7 ... Potential sensor, 10 ... Original 11 …… Original exposure lamp, 28 …… Transfer charger 29 …… Front static eliminator

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuyoshi Takahashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Kunio Yoshihara 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Co., Ltd. (72) Inventor Toshiro Matsui 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Tadashi Ishikawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (1)

[Claims] 1. An image forming means having a charging means, an exposing means and a developing means for forming an image by charging, exposing and developing on a photoconductor, and a detecting means for detecting a surface potential on the photoconductor. And an image forming apparatus including a control unit that controls an image forming condition of the image forming unit according to a detection result of the detecting unit, wherein the control unit is an electrostatic latent image of a bright portion and a dark portion region unrelated to an original image. In the pre-process of forming, the developing bias of the developing means is set to a value obtained by adding a predetermined value to the output of the detecting means, which changes every moment, and the electrostatic latent image corresponding to the original image is actually formed and the development is performed. An image forming apparatus, characterized in that in the image forming step, the developing bias is maintained at a constant value at which development is performed.