JPH0697356B2 - 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, an image of a copying apparatus or the like that detects a surface state such as a latent image potential on a photosensitive member such as a photosensitive drum and controls the image forming condition based on the result. The present invention relates to a forming device.

2. Description of the Related Art The operation process of an image forming apparatus using a photosensitive drum as described above, particularly a copying apparatus, can be roughly divided into two.
The first is an image forming process in which the photosensitive drum is rotationally driven to perform exposure and development. In this image forming process, an image forming area (hereinafter referred to as an image area) is formed. Before this image forming step, there is a pre-step 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 irrelevant to the original and dark areas of 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 image forming apparatus, it is usual to perform so-called blank exposure during rotation of the photosensitive drum in the non-image area in the previous process 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.

In such a case, since the rise time of the lamp for blank exposure is large and the illuminance of the lamp itself is also large, the non-image portion where the latent image of the original image is not formed is not only the light portion potential but also the light portion potential. Since the dark area potential also becomes distributed, in order to prevent toner adhesion to the entire non-image area, use a blank exposure lamp with a large amount of light (that is, a large power consumption), or use a negative toner. When used, it was necessary to apply a high voltage to the developing bias.

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. 6, the process from the start of copying to the end of copying is roughly divided into three steps.

In the first pre-process, 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 first pre-process, the detected surface potential V _S is 200 V
The added value is applied as the 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.

In the second pre-process, the original image density is measured by the potential sensor. In the second pre-process, a constant value, + 600V, which is not related to the output of the potential sensor is applied as the developing bias, so that wasteful consumption of toner can be suppressed even at this stage.

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

Next, the control flow will be described.

First, when the copy start is performed, the first pre-process starts. In step S1, the number of times is determined through the light portion and dark portion potential measurement in steps S2 to S4 and the charge amount control routine based on the measurement. Here, the charge amount control
N _One time. The number of control times N ₁ is, for example, because the state of the photosensitive drum changes according to the standing time of the copying machine.
The longer the standing time, the more N ₁ .

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.

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.

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

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.

Next, in parallel with the operation of steps S1 to S5, steps S10 to S5 are performed.
Twelve operations are performed. 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, in step S13, it is determined whether to enter the image area and shift to the document density measuring routine (second pre-process) of steps S17 to S19. Actually the above steps
The determination is made based on whether or not the measurement routines of S1 to S5 and S6 to S9 are completed a predetermined number of times. When this step S13 is denied, it returns to step S1.

When step S13 is affirmed, the second pre-process of steps S20 and S17 to S19 is started. In step S20, the developing bias is applied to the developing device 5 as a fixed value, for example, + 600V, prior to the document density measurement in steps S17 to S19.
This is because, as shown in FIGS. 5A and 5B, the potential sensor 7 is located near the opening Z of the case of the photosensitive drum 1.
Since only the upper measuring range X is scanned, if the developing bias is changed only according to the measured value of this region, the toner is not only generated by the reversal development shown in FIG. This is because there is a risk that they will adhere to the photosensitive drum 1.

Next, in steps S17 to S19, final exposure amount correction is performed.

First, in step S17, the optical system described above is driven under the charging and exposure amount conditions obtained as described above to
10 is scanned, a latent image potential due to the reflected light of the original 10 is formed on the photosensitive drum 1, and the latent image potential v _S ′ is measured by the potential sensor 7.

Next, in step S18, the measured amount is sent to the microcomputer 15 as described above, and the microcomputer 15 calculates the average value V _S of the latent image potential v _S ′ during the scanning period of the document.

Next, in step S19, the microcomputer 15 obtains the correction amount ΔV _HL of the lighting voltage of the image area after the document exposure lamp 11 by the following equation based on the average value V _S of the latent image potential which is a function of the document density.

ΔV _HL = 8ΔV _S (3) Here, ΔV _S is the deviation between the average value V _S and the reference value corresponding to the standard document density. In this way, the second pre-process is finished, and the actual image forming process of steps S14 and S15 is started.

In step S14, a value obtained by adding 100 V to the final value of the white background voltage V _L1 obtained as described above is applied to the developing roller 5 as a developing bias, and subsequently, in step S15, a known copy operation is performed.

As shown above, when entering the copy sequence, the first
In the preceding process, the charge amount control and the exposure amount control are performed a predetermined number of times N ₁ and N _2, respectively, in steps S2 to S5 and steps S7 to S9. At that time, in order to prevent toner consumption, in steps S10 to S12 the developing roller is controlled. The developing bias control for No. 5 is performed.

That is, the latent image potential measured at the position of the potential sensor 7 is applied to the developing device 5 after being delayed by the rotation time of the photosensitive drum 1 to the developing device 5, so that the developing bias in the non-image area is on the photosensitive drum. +20 to the surface potential of the surface facing the developing unit
Since the value added with 0V is followed, the surface potential of the photosensitive drum and the potential difference between the developing sleeve can always maintain a constant value (200V) suitable for preventing toner adhesion, and toner on the photosensitive drum in the non-image area can be kept. Will not be consumed and consumed.

Further, during the document density measuring period of the second pre-process, the developing bias of a constant value (+ 600V) is applied. Since the developing bias (+ 600V) is sufficiently higher than the dark portion potential (+ 500V), it is possible to prevent the black portion of the original image other than the detection area of the potential sensor from being developed. Therefore, wasteful toner consumption can be prevented even at this stage.

Effects As is apparent from the above description, according to the present invention, an image having a charging unit, an exposing unit and a developing unit, which forms an image corresponding to a document image by charging, exposing and developing on a photoreceptor An image forming apparatus comprising: a forming unit; a detecting unit that detects a surface potential on the photoconductor; and a control unit that controls an image forming condition of the image forming unit according to a detection result of the detecting unit. In the first pre-process of forming an electrostatic latent image of a light portion and a dark portion region unrelated to the original image, a predetermined value is added to the output of the detecting unit which changes the developing bias of the developing unit every moment. In the second previous step of forming an electrostatic latent image corresponding to the original image and measuring the original density by the detecting means, the developing bias is set to a constant value at which the electrostatic latent image is not developed. Since it is adopted in the previous process, it is possible to prevent the waste toner from adhering to the photoconductor in the previous process, reduce the toner consumption, increase the number of images formed per fixed amount, and extend the life of the cleaner blade. it can. 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 image forming apparatus, FIG. 4 is a flow chart illustrating a control flow in the image forming apparatus of the present invention, and FIGS. 5A and 5B are operations of the image forming apparatus of the present invention. FIG. 6 is a perspective view and a partially cutaway side view for explaining FIG. 6, and FIG. 6 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 unit having a charging unit, an exposing unit and a developing unit for forming an image corresponding to an original image by charging, exposing and developing on a photosensitive member, and a surface potential on the photosensitive member. In the image forming apparatus, the image forming apparatus is provided with a detecting unit for detecting the image forming condition, and a control unit for controlling the image forming condition of the image forming unit according to the detection result of the detecting unit. In the first pre-process of forming the electrostatic latent image, 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, and the electrostatic latent image corresponding to the original image is formed. An image forming apparatus, wherein a developing bias is set to a constant value at which the electrostatic latent image is not developed in a second preceding step of forming an image and measuring the document density by the detecting means.