JPH0371156A - Image forming device - Google Patents

Abstract

PURPOSE:To automatically correct uneven charge and uneven exposure and to prevent the generation of fogging by controlling the density of the image based upon the detecting result of a surface potential sensor for detecting the unevenness of charged quantity on a photosensitive body. CONSTITUTION:The surface potential sensor 11 is arranged so as to be opposed to an area X5 formed between an exposure area X2 and an erase area based upon an inter-image eraser 5 on the photosensitive drum 3 and the surface potential of the area X5 is detected by impressing the voltage of the prescribed frequency and measuring a change in the returned vibration. Thus, the unevenness of the charged quantity on the surface of the photosensitive body is detected by the sensor 11 and at least one value out of the light quantity of an exposure lamp, the charged quantity of the photosensitive body based upon a charger and a developing bias voltage value is controlled in accordance with the detected result. Even if the potential of an electrostatic latent image formed on the photosensitive body and corresponding to the original image is made uneven due to defective charging or defective exposure, the generation of fogging can be previously prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophotographic image forming apparatus, and more specifically to an apparatus for preventing image deterioration due to charging failure, exposure failure, or the like.

[Prior art]

In copying machines, charging defects may occur on the photoconductor due to soiling of the charger's charging wire, charging grid, etc. due to long-term use, surface deterioration of the charging wire, or uneven characteristics of the photoconductor, or due to optical Exposure defects may occur due to deterioration of the system's exposure lamp or contamination of the lens, etc.

If charging irregularities occur in which the charging potential on the photoconductor is partially higher than the standard due to the charging defect, or if exposure unevenness occurs in which the amount of light is partially insufficient due to exposure defects, the method is applied to that portion. The potential of the electrostatic latent image on the photoreceptor remains high, resulting in a phenomenon in which excess I/toner adheres, a so-called background fog.

In such a case, the operator generally resets the exposure amount to a larger value so that a thinner image is formed, and performs copying again to obtain a copy without background overlap.

(Problem to be Solved by the Invention) However, dealing with the background overlap as described above is not preferable because it not only makes the operator's operations cumbersome, but also wastes paper and paper.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an image forming apparatus in which the image forming apparatus itself automatically corrects charging unevenness and exposure unevenness and prevents background tearing.

[Means for Solving the Problems] An image forming apparatus according to the present invention forms an electrostatic latent image corresponding to an original image on a photoreceptor charged by a charging charger, and applies a developing bias voltage to the electrostatic latent image. In an image forming device that performs development by supplying toner from a developing sleeve, a surface potential sensor detects unevenness in the amount of charge on the photoreceptor, and means for adjusting image density based on the detection result of the surface potential sensor. It is characterized by comprising the following.

[Effect]

If the electrostatic latent image is developed in a state where the potential is higher than the standard due to charging failure by the charger or exposure failure of the optical system, background fogging occurs.

Therefore, the unevenness in the amount of charge on the surface of the photoreceptor after being charged is detected by a surface potential sensor, and the image density is adjusted based on the result.

For example, first, a reflective member having a uniform reflectance is irradiated with an exposure lamp to form an electrostatic latent image corresponding to the reflective member on the photoreceptor. Then, a surface potential sensor detects unevenness in the potential of the electrostatic latent image corresponding to the predetermined area in the electrostatic latent image forming area on the photoconductor, and based on the detection result, at least I is celebrated as the Wordshu Festival. That is, when adjusting the light amount of the exposure lamp, the overall light amount of the optical system is increased by increasing the light amount, thereby lowering the overall potential of the electrostatic latent image formed. As a result, in the case of poor exposure due to insufficient light quantity, the light quantity is compensated and an electrostatic latent image is formed within the standard potential, so that background overlap does not occur. Sometimes, a larger amount of light than usual is set so that an electrostatic latent image is formed within a reference potential, so that background fogging does not occur.

When adjusting the amount of charge on the photoreceptor by the charger, the amount of charge on the photoreceptor before the electrostatic latent image is formed is lowered than usual. As a result, even in the case of a charging failure where the charging potential increases, the charging potential on the photoconductor is corrected to be below the standard, and even in the case of an exposure failure where the amount of light is insufficient, the electrostatic latent image on the photoconductor remains below the standard. Since it is formed at a potential of

When adjusting the developing bias voltage value, by increasing it, the potential difference between the potential of the electrostatic latent image and the developing bias voltage value is reduced. As a result, even if an electrostatic latent image is formed at a potential higher than the reference potential due to poor charging or poor exposure, the potential difference between that potential and the developing bias voltage value becomes smaller than the reference potential difference, and toner adheres to the image. It will be difficult to apply, so skin will not be covered.

[Examples] Hereinafter, the present invention will be specifically described based on drawings showing examples thereof. FIG. 1 is a schematic diagram showing the general configuration of a copying machine according to the present invention. Below the document platen glass 1 is an exposure unit) 24. An optical system 20 including S-jis 22b to 22d, a lens 23, etc. is provided.

The exposure unit 24 includes an exposure lamp 21 and a ξ 22a which are long in the depth direction of the original glass plate 1, and scans the original M by moving in the direction of the arrow orthogonal to the depth direction of the original glass plate 1 during the copying operation. The light reflected from the document M illuminated by the exposure lamp 21 by the exposure unit 24 is
It is reflected by the 1-ray 22a and sent in the opposite direction to the direction indicated by the arrow, and is then reflected again by the -22b and 22c in the same direction as the direction indicated by the arrow, and is reflected by the ξ 226 via the condenser lens 23. and reaches the photoreceptor drum 3, where an image is formed.

Further, when detecting the electrostatic latent image potential according to the present invention, the exposure unit 24 is moved below the main body 2 part cover 26 provided on the side of the document platen glass 1 and then stopped. ing. At this stop position Z, the exposure unit 24
The reflector sticker 25 attached to the lower surface of the upper cover 26 of the main body is exposed to light.

This seal 25 has a uniform reflectance corresponding to the background portion of a normal document.

A charger 4 is provided below the optical system 20,
The opposing region X on the photosensitive drum 3 is uniformly charged by the charger 4 . The driving force of the main motor 210 is transmitted to the photosensitive drum 3 through gears 31 and 32 (see FIG. 2), and the photosensitive drum 3 rotates in the direction of the arrow a in synchronization with the movement of the exposure unit 24 in the direction of the arrow. do.

Photosensitive drum 3 on the downstream side in the drum rotation direction of the area X1
An exposure area x2 by the optical system 20 is formed above. The scanning light of the original image by the optical system 20 is guided to this region X2 via the optical path B described above, thereby forming an electrostatic latent image corresponding to the original image.

Here, the unnecessary inter-image charge other than the electrostatic latent image corresponding to the original image, that is, the charge in the area between the currently copied image and the next copied image, is L [1] Using an array The image is erased by an inter-image eraser 5. The electrostatic latent image is supplied with toner and visualized in a developing area X3, which is a portion facing the subsequent developing device 6, and a toner image reproducing the original image is formed.

On the other hand, the copy paper is transferred to a portion facing the transfer charger 7 (transfer It is transported to area X4). Here, the toner image is transferred to the copy paper, separated from the photosensitive drum 3 by a separation charger 8, and then conveyed to a fixing device (not shown), where the toner image is fused and fixed onto the copy paper.

After the toner image has been transferred, the surface of the photosensitive drum 3 is cleaned of residual toner by a cleaning device W9, and the residual charge is erased by light irradiation from the eraser lamp 10, and the drum is prepared for the next development.

Next, a mechanism for detecting potential unevenness of an electrostatic latent image, which constitutes the gist of the present invention, will be explained. FIG. 2 is a schematic diagram showing the configuration and arrangement of a surface potential sensor. Surface potential sensor 1
1 is disposed to face the area X between the exposure area X2 on the photosensitive drum 3 and the erase area by the inter-image eraser 5, and applies a voltage of a predetermined frequency to the area X. , the surface potential of region X is detected by measuring the amount of change in the returned vibrations. A drive pulley 44 and a driven pulley 42, which are driven by a motor 40 that can be rotated forward and backward, are provided at positions on the back side and front side of the copying machine from both ends of the photosensitive drum 3, respectively, and the drive pulley 44 and the driven pulley 42 are stretched between these pulleys. The surface potential sensor 11 is attached to the wire 41 . That is, as the drive pulley 44 is rotated by the motor 40, the surface potential sensor 11 moves along a rail (not shown) in the axial direction of the photoreceptor drum 3, and the surface of the area X5.
The potential, ie, the potential of the electrostatic latent image formed in the previously exposed area X2, is measured over the entire length of the image area.

Near the driven boob IJ42, a ladder seat switch 4 flap is provided to set the home position Y1 of the surface potential sensor 4J11, and when the light amount sensor 11 is at the home position Y1, the ladder seat switch 4 flap lever 47
By pressing a, the ξ seat switch 4 outputs a home position detection signal Sp of the surface potential sensor 11 to the CPU 201, which will be described later.

Further, the motor 40 has a built-in pulse generator, and the pulse generator outputs one pulse signal Pm to the CPU 201 for each predetermined amount of rotation.

FIG. 3 is a block diagram of the control system, in which the surface potential sensor 11 is connected via an A/D converter 203 to a predetermined manual port of the CPII 201 that controls the copy operation.

The output voltage Vv of the surface potential sensor 11 is determined by the A/D converter 20.
3 is converted into a digital signal by the CPU 201
is input to. FIG. 4 is a graph showing the relationship between the output voltage Vv and the latent image potential Vi of the surface potential sensor 11,
In the sensor 11, the latent image potential is appropriate (1! 150
2.5V is output with respect to V.

Further, the CPU 201 receives a pulse signal Pm generated from a pulse generator of the motor 40 for moving the surface potential sensor 11, and a home position detection signal Sp of the limit switch 47, respectively. The CPU 201 recognizes the home position of the surface potential sensor 11 and the position in the measurement area based on the count value of the pulse signal Pm and the home position detection signal Sp. The motor 40 is connected to a predetermined output port of the CI'U 201 via a motor drive circuit 202.
The drive is controlled by the output signal from the CPll 201.

Other output ports of the CPU 201 include an exposure lamp 21, a charging wire 41 of a charging charger 4, and a charging grid 42.
．． Developing sleeve 61 of developing device 6. Ireli lamp 10
．． The inter-image eraser 5, main motor 210, etc. are connected. The exposure lamp 21 is connected to C)'U 201 via a D/A converter 205 and a power supply 204.
The voltage value of the power supply 204 is variably set according to the output signal of the PU 201, and the amount of light is adjusted.

The charging wire 41 and the charging grid 42 are connected to the CIIU 201 via a high voltage transformer 45, as shown in the block diagram of FIG.
A predetermined voltage is applied according to the output signal of II 201.

Additionally, the charging grid 42 is connected to a grid voltage adjustment circuit 206.
It is connected to CPII 201 via. The grid voltage adjustment circuit 206 includes varistors 43a to 43i and a switch 448 between the charging grid 42 and the ground terminal.
~44h are connected in series, and a switch 44a
44h are connected in parallel with varistors 43a to 43h, respectively. Switches 44a to 44h are CPU
It is connected to the 8-bit switch control output of 201.

As a result, when the switches 44a to 44h are selectively turned on by the output signal of the CPII 201, the varistor connected to the switch is short-circuited. In other words, C.P.
II 201 adjusts the grid voltage by selectively turning on the switches 44a to 44h and changing the overall resistance value of the varistors 438 to 43i. The amount can be adjusted.

The developing sleeve 61 is connected to the CPll 201 via a D/A converter 208 and a bias voltage adjustment circuit 207, so that the developing bias voltage applied to the developing sleeve 61 is adjusted according to the output signal of the CPU 201. It has become.

The eraser lamp 10 is connected to the CP (120
1, and the lighting/extinguishing is controlled by the output signal of CPt1201.

1 The inter-image eraser 5 is connected to the CpH 201 via the I10 interface 211, and each L making up the eraser
The ED is controlled to turn on/off.

The main motor 210 is connected to the CPU 201 via a main motor drive circuit 212.
The drive is controlled by the output signal of.

The CPU 201 connects to the CPU 307 via the data bus 214.
It is connected to the 11AM 307 to write and read data such as the detected value of the surface potential sensor 11.

Further, the CPU 201 and the data bus 222. It is connected to an operation panel 21.9 via an I10 interface 221 and a data bus 220, and signals are exchanged with various key switches and displays on the operation panel 219.

Additionally, CPIJ 201 is connected via data bus 218 to on-line controller 217 , which in turn is connected via private telephone line 216 to automatic exchange 215 . The automatic exchange 215 is connected to a telephone line (outside line) 223. These 2 are used to automatically communicate the contents to maintenance personnel in the event that an abnormality occurs in the copying machine.

Next, C
A description will be given based on a flowchart showing the control procedure of Pt1210.

FIG. 6 shows the main routine. When the power of the copying machine is turned on, the CPU 201 returns itself to the initial state (step S2).

In the next step S2, an internal timer is started. This internal timer determines the time required for the I routine of the main routine, regardless of the processing content in each subroutine described below.

In step S3, manual processing of the key matrix of the operation panel, various defect detectors, etc. is performed.

Step S4 is a latent image potential unevenness check routine according to the present invention, and details are shown in FIGS. 7 and 8.

Step S5 is an exposure M adjustment routine for correcting latent image potential unevenness when it is detected, and the details are shown in FIG.

In subsequent steps S6 and S7, a copy operation routine and a communication routine with another CPII (not shown) are sequentially called, and when the processing of all the subroutines is completed, the process waits for the internal timer to end in step S8, and then returns to step S.
Return to 2. This length of time for one routine is used to count various timers used in each subroutine. The various timers determine the end of the timer depending on how many times this one routine has been counted.

7 and 8 show the contents of the latent image potential unevenness check routine in step S4.
In step 1, the contents of the register set according to the circuit state (hereinafter referred to as state ■) are checked. Since stay 1-1 is set to 1 by default, state l-1 is set to 1 at startup.
The process advances to step 5402 of step 2.

Here, whether or not the surface potential sensor 11 is at the home position Y is determined based on whether or not the detection signal Sp is input. If the surface potential sensor 11 is not at the Bauhm position Y, a reverse rotation signal is output to the motor drive circuit 202 to drive the motor 40 in the reverse direction in the direction of arrow 3f (see Figure 2). is moved in the direction of the arrow (step 5406) and set to home position Y.

Once the surface potential sensor 11 is set to the home bombardment Y1, the exposure unit 24 of the optical system 20 is then moved to set the temperature to Hz (step 5403).

In the next step 5404, the signal S5, which will be explained next, is
The voltage is output to the A converter 205 and the output voltage of the voltage A 204 is set to 90V, which corresponds to proper exposure. Table 1 is a table showing the relationship between the signals S of S1 to S, including the signal S5, and the output voltage value of the voltage #204 set corresponding to each signal.

Margin below 5 In this embodiment, the power supply 2 corresponds to the signals S1 to S.
The output voltage value of 04 can be set in 9 steps from 82 to 98V at 2V intervals. The CPU 201 receives the signal S,
Several pieces corresponding to each output of ~S (hereinafter ExpSTIi
Equipped with a counter that counts 1 to 9 (referred to as P number), Exp
The count value is updated in accordance with the change in the setting of the number of -5TEPs, and in the first step 5404, as described above, the number of Exp-5TEPs is set to 5, and the signal S
5 is rolled. Note that instead of the method of adjusting the voltage value in stages, a method of continuously adjusting the voltage value without any steps may be used.

When the Exp-3TEP number is set in step 5404,
Proceeding to state 1-2, the process enters the latent image potential creation start routine of step 5407.

FIG. 9 is a flowchart showing the processing contents of the latent image potential creation start routine. First, in step 54014, a signal is output to the main motor drive circuit 212 to drive the main motor 210 and rotate the photosensitive drum 3. Next, after turning on the inter-image eraser 5 and the eraser lamp 10 (Step 540 F2.S, 1073'), 90
Turn on the voltage 6yA204 set to V and turn on the exposure lamp 21.
is turned on (step 54014). Then, in step 54075, signals are output to the high voltage transformer 45 and the Glissode voltage adjustment circuit 206, respectively, to turn on the charger 2. As a result, a sticker 25, that is, an electrostatic latent image corresponding to the background portion of the document, is continuously formed between the exposure area X2 on the photoreceptor drum 3 and the erase area of the inter-image eraser 5, and the area between them is Surface potential sensor 1 in X5
When the creation of an electrostatic latent image facing 1 begins,
Proceed to state 1=8 of the latent image potential unevenness check routine.

In step 5409, a normal rotation signal is output to the motor drive circuit 202 to drive the motor 40 in the normal direction of the arrow e (see FIG. 2) to start moving the surface potential sensor 11 in the direction of the arrow g. (Step S40!).

In the next state 1=8, it is first determined whether or not the pulse signal Pm is input from the pulse generator of the motor 40 (step 5411), and when this is input, 1 is added to the count value n of the internal counter ( step 5412). Then, in step 5413, the pulse signal P
When m is counted up to 20 times, the process advances to state 1=8 (step 3414). When this count value is 20, the surface potential sensor 11 detects the image area (!11!I edge Y).
This is the count value when the count reaches 2.

In step 54L5, similarly to step 5411, the input of the pulse signal Pm is checked. If there is an input, 1 is added to n in step 5416, and then RAM 307
A signal obtained by digitally converting the output voltage Vv of the surface potential sensor 11 by the A/D converter 203 via the data bus 214 is sent to a predetermined area (hereinafter referred to as Vv term) provided corresponding to the count and value n within the data bus 214. Write sequentially as values
(Stenob 5417).

Then, in step 8418, it is determined whether the count value n has reached 229 or not, and if it has reached 229, the status is
Proceeding to I=6, the latent image potential creation end routine is entered, and processing to end the creation of the electrostatic latent image is performed (step 5420).
). In other words, the lengths 21 to 229 correspond to the total lengths Y2 to Y+ of the image area (see FIG. 2), and the measurement of the latent image potential Vv of the entire image area in the longitudinal direction of the photosensitive drum 3 is completed.

FIG. 10 is a flowchart showing the processing contents of the latent image potential creation end routine. First, after turning off the charger 4 in Step 7 54201, the exposure lamp 21. The eraser lamp 10 and the inter-image eraser 5 are turned off (steps 54201 to 54205). Then, the drive of the main motor 210 is stopped to stop the rotation of the photosensitive drum 3 (step 54205).

9 In state D-7, first, the motor 40 starts to be driven in reverse, and the surface potential sensor 11 starts moving in the home position Y and in the direction (arrow h) (step 3422
). In step 5423, the home position detection signal Sp
When manually operated, the drive of the motor 40 is stopped and state 1 is reached.
Proceed to =8 (step 5424S425).

In state 1=8, first, the signal value V stored in the Vv term corresponding to the count value n is determined from RAl'l 307.
Read the highest value (IVvma
x and the lowest value Vvmin, respectively, are selected together with their corresponding count values n+&n2 (step 342
6).

Next, in step 5427, the maximum value Vvmax and the minimum value V
The difference from vmin is calculated, and this is compared with a reference value ΔVv stored in advance in the RAM 307 for determining the presence or absence of latent image potential unevenness, and it is determined whether the result is less than the Δshishi value. If Vvmax-Vvmin is less than or equal to .DELTA.Vv, it means that no latent image potential unevenness has occurred, so state I is set to ■ and the process returns to the main routine (step 5428).

On the other hand, if Vv old χ-Vvmin is larger than ΔVv, this means that latent image potential unevenness has occurred, and the process advances to state 1-9 (step 5429).

In state 1=8, a warning display "Cv'" indicating that the latent image potential is inappropriate is displayed on a predetermined display section of the operation panel 219 (step 5430), and the process then proceeds to state 1=80.

In state 1=10, online controller 217
``Cv'' and measured values Vv+nax, Vvm
Issue a command to send the in pig (step 5432
).

As a result, data regarding the abnormality is transmitted to a service base (not shown) via the telephone line 223, and then state I
is set to l and returns to the main routine (step 5233).

FIG. 11 shows the contents of the exposure amount adjustment routine in step S5.A state number is determined in step 5501 and the state number is processed in the same way as the latent image potential unevenness check routine described above. In this subroutine as well, the state is set to 1 by default, so first, it is determined whether the check for latent image potential unevenness has been completed in step 5502 of state 1-1 = 1, and if it has been completed, the state is set to 1. Proceed to 1-1 = 2.

In state l=2, the motor 40 is driven forward in step 5504, and the home position Y of the surface potential sensor 11 is set.
, starts moving in the direction of arrow g.

In state T=3, first, in step 3506, the thing 40
It is determined whether or not there is the human power to read the pulse word pm from the bar suje furek, and each time this large saw is performed, 1 is added to the count value n (Stennob 5507), and in step 5508, n is The maximum latent image potential measured by the image potential unevenness check routine (measured value of l\Vvmax 'W
It is determined whether n + has been reached. Light amount sensor 11
When reaches the measured value 1n, the drive of the motor 40 is stopped (step 5509).

In stay 1-1=4, first, the aforementioned latent image potential creation start routine is processed to form an electrostatic latent image on the photosensitive drum 3 (step 5511). Note that the output voltage of the power supply 204 of the exposure lamp 21 at this time is determined by the following step 5.
Set 82V as described in 512.

Then, in step 5504, by sequentially incrementing the value of the counter from 1 to 9, the signal S to the D/A converter 205 is sent to the D/A converter 205 at predetermined time intervals from S to S as shown in Table 1 above. The output voltage of the power supply 204 is switched from 82V to 98V at 2V intervals. During this time, the output voltage value Vv of the surface potential sensor 11, which is digitally converted by the A/D converter 203, is converted to the IIAM 307.
Each [1x
Write in correspondence with the p-3TEP number. When this is completed, in the next step 5513, the latent image potential creation completion routine, the creation of the electrostatic latent image is completed as described above, and state I--
Proceed to step 5.

In stay 1-1 = 5, the output voltage value Vv of the surface potential sensor 11 measured and stored in step 5512 is read out, and this is set in advance as a target base for adjustment. $ value Vvo
The output voltage value Vv closest to Vvo and the corresponding Exp-5TEP number ne are selected and stored in a counter. This allows A/D from CI”U 201
The signal 5Ila is output to the converter 205 (step 55).
15S516).

When the stay 1-1=6, the surface potential sensor 11 is returned to the home position Y1 in steps 3518 to 5520, and the stay 1-1 is set to 1 in step 5521 to complete the exposure adjustment and return to the main routine. do.

FIGS. 12(a) and 12(b) are relationship diagrams between the latent image potential and the copy image, and FIG. 12(a) shows a state in which latent image potential unevenness has occurred. In the graph in the figure, the vertical axis represents the latent image potential (1), and the horizontal axis corresponds to the image area in the longitudinal direction of the photosensitive drum 3. In this figure, the latent image potential V imax at the highest part of the convex part of the graph is determined by charging failure of the charger 4, uneven electrostatic characteristics of the photoreceptor tram 3, or optical system 2.
This is caused by poor exposure of 0. In other words,
In the charging charger 4, the charging wire 41. Contamination of the charging grid 42 or the stabilizer plate is considered, and in the case of the optical system 20, deterioration or contamination of the exposure lamp 21, or contamination of the lenses 22a to 22d, lens 23, etc. is conceivable. Here, the appropriate latent image potential is Vi1, and background fogging occurs when the latent image potential exceeds Vi2. Therefore, when actual copying is performed, a background overlap 331 occurs on the paper 330.

FIG. 12(b) shows the state when the exposure amount is adjusted as described above. By increasing the light intensity of the exposure lamp 21, Vimax can be set lower than the level of Vi2. As a result, it is possible to prevent the background overlapping 331 caused by exposure unevenness that occurs in FIG. 12(a).

Note that this correction does not eliminate the latent image potential unevenness itself, so when a halftone image is formed, if there is potential unevenness in the halftone image part, density unevenness will occur, but the character image 332 Since the density is very high and the copy density has almost converged to the maximum density, potential unevenness in the electrostatic latent image hardly appears as density unevenness in the image.

Furthermore, since the image density is not significantly affected by exposure correction, good images can be obtained without any problems when copying general documents.

As described above, in the above embodiment, a method was described in which the exposure amount is adjusted by focusing on the portion where the latent image potential has the highest value, that is, the peak portion of the background breakage. Next, an embodiment will be described in which the exposure amount is adjusted depending on the degree of exposure.

13 to 16 are flowcharts of the exposure adjustment routine showing its contents.

First, in state I=1, it is confirmed that the latent image potential unevenness check described above has been completed, and in the next state I=2, the output voltage value shV of the surface potential sensor 11 measured in the latent image potential unevenness check routine is checked. Average value Vv over the entire length of the image area
is calculated (step 5504).

In the next step 5505, a target reference output voltage value Vvo of the surface potential sensor 11 for adjusting the exposure amount is determined.

This is the difference between the average value Vv and the maximum (1iVvmax) δ
is calculated and determined based on that value.

Table 2 is a table showing the relationship between δ, target reference output voltage value Vvo, and latent image potential.

Table 2: Difference δ between the average value and the highest value Vvmax Vv
.

and the latent image potential are set in advance. This makes δ the second
The rank in the table is determined, and the corresponding target reference output voltage value Vvo is selected.

In state 1-3, run the latent image potential creation start routine described above to create an electrostatic latent image.
), for stay 1-1 = 4, power supply 2 shown in Table 1
Set the Exp-3TEP number of 04 to 1 (step knob 5513), start driving the motor 40 in the normal direction, and first measure the latent image potential Vv over the entire image area by the surface potential sensor 11. It is carried out in the same manner as in the first embodiment shown (step 5
514-5528).

Then, in step 5529 of state I=8, the measured value Vv
The average value Vv of 1Exp− in the RAM 307 is calculated.
5T [Write to iPPI3Vv term.

Similarly, by processing from state T=9 to 48,
Exp-5 Increase TEP number by l until 9, and each Ex
The average value νV of the measured values Vv in the p-3 TEP number is calculated and written in the 99th term of the corresponding Exp-5 IEP number.

Then, in step 5720), execute the latent image potential creation end routine with 1=49, and in step 5725 of state l-50, step from each average value Vv of the output voltage value Vv measured at each Exp-5 TEP number. The average value Vv closest to the target reference output voltage value Vvo selected in 5505 and its corresponding BXp-3TEII
Select number r1e. And in the next step 5726,
By setting the Exp-3TIiP number to the selected ne, the adjustment of the exposure amount is completed and the process returns to the main routine.

That is, in this embodiment, the degree of latent image potential unevenness is determined from the difference δ between the output average value Vv of the surface potential sensor 811 and the maximum value Vvmax, and the target reference output voltage is determined according to the degree. The amount of light from the exposure lamp 21 is adjusted so that the value Vvo is obtained.

In the above embodiment, the average value of the measured values over the entire image area is used as the data for adjustment, but instead, the value with the highest detection frequency in the measurement data may be used as the data for adjustment. good.

Above, we have explained how to prevent background overlap by adjusting the exposure amount.Next, we will explain the control procedure for preventing background overlap by adjusting the amount of charge on the photoreceptor drum 3 by the charger 4. explain.

17 to 19 are flowcharts showing the contents of the latent image potential unevenness check routine in that case.

Here, first, after setting the surface potential sensor II to the home position Y1 and the exposure unit 24 to the position 1z, the number of Cl-1-3TEPs, which will be explained next, is set to 5 (steps 3602 to 5604). -5T
The EP number is Exp-5TIE of the exposure lamp 21 mentioned above.
Similar to the P number, this is a value counted by a counter built into the CPU 201 in order to adjust the amount of charge on the photoreceptor tram 3 by the charger 4 in stages. In this embodiment, as described above, the switch 44a of the grind voltage adjustment circuit 206 is
By selectively turning on ~44h, the amount of charge can be increased to 9
The number of CM-5TEPs can be set in stages, and the number of CM-5TEPs is determined by the relationship with the number of outputs that turn on the switches 44a to 44h. In other words, when the number of Cll-3TEPs is set to 1, all switches 44a to 44h are turned on to set the charge amount to the minimum, and when the number of Cll-3TEPs is set to 9, all switches 44a to 44h are turned on. When set to OFF, the amount of charge is set to the highest level.

In step 5604, the appropriate amount of charge as a reference is set by setting the C11-5 TIEP number to 5. Cll-3TEP
Once the number is set, an electrostatic latent image is created and the surface potential sensor 11 is moved to adjust the latent image potential around the image area, similar to the latent image potential unevenness check routine shown in FIGS. 7 and 8. Measure (stay 1-1 = 2-7). and state I
=8, the highest value Vvmax and the lowest value Vvmin are selected from the measured values Vv, and the difference therebetween is compared with the reference value ΔVν to determine the presence or absence of latent image potential unevenness.Step 562
7) If latent image potential unevenness has occurred, the process advances to state l=9 (step 5629).

In state I-9, when automatic cleaning of the charging wire 41 is performed, the content of the flag Fch to be sent is determined (step 5630); if this has been reset, automatic cleaning of the charging wire 41 is performed in step 5631). I do. This automatic cleaning is well known, and has a configuration in which, for example, cleaning is performed by moving a cleaning member holding a charging wire in the direction in which the charging wire is stretched. When the automatic cleaning of the charging wire 41 is completed, the flag Fch is set and the process proceeds to step I-2 (steps 5632 and 56).
33) Create an electrostatic latent image again, measure the latent image potential, and check for latent image potential unevenness.

On the other hand, if the flag Fch is set in step 5430, that is, if uneven latent image potential occurs despite automatic cleaning of the charging wire 41 as described above, the process advances to state I=10. 1 Display the warning display Cv'' on the operation panel 219, and transmit the details of the abnormality to the service base in the next state I=11.

FIG. 20 is a flowchart showing the contents of the charge amount adjustment routine. First, when it is determined that the two series of latent image potential unevenness checks are completed (step 570).
2), the motor 40 is driven in state I=2 (step 5704), and the surface potential sensor 1 is driven in state I=3.
1 is moved to the measurement position of the highest latent image potential (1!!Vvmax) and stopped (step 5709).Then, in state I=4, the latent image potential creation start routine is executed to create an electrostatic latent image. 5711), Cll-
5TEII number is changed from 1 to 9 at predetermined time intervals. That is, the amount of charge on the photoreceptor drum 3 by the charger 4 is increased stepwise from the minimum value to the maximum value in the change range, and the electrostatic latent image corresponding to the amount of charge at each stage is formed in the exposed areas X, L and the image. The erase area of the eraser 5 and the erase area of the eraser 5 are sequentially created. During this time, surface potential sensor 1
1 output voltage value Vv in a predetermined area C- in the RAM 307.
The S term 2 is written in correspondence with each C11-5TEP number (step 5712). When this is completed, the creation of the electrostatic latent image is completed (step 5713), and the process proceeds to step 1-1=5.

In state I-5, the output voltage value Vv stored for each C1l-5TEP number is read out, and the output voltage value closest to the target reference value Vvo (iiVv and its corresponding Cll-3TEP value is read out).
Select and set the P number nch (step 5715.S
71.6). Then, in state l=6, surface potential sensor 1
Step 5720 of returning 1 to the home position Y1
), the charge amount adjustment is finished.

When the amount of charge on the photoreceptor drum 3 is adjusted by the charger 3 in this manner, background fogging is prevented by reducing the amount of charge.

In other words, as shown in FIG. 12(a), the background overlap occurs in the part where the potential of the electrostatic latent image is higher than a predetermined potential, so this high part is the target reference value Vvo of the surface potential sensor 11,
Or, the amount of charge before exposure is made lower than the reference value so that the potential is less than or equal to a value close to that value.

In addition, in exactly the same way as when adjusting the exposure amount, when adjusting the charge amount, the maximum value of the latent image potential,
That is, instead of adjusting the amount of charge based on the peak part of the background covering, the latent image potential that is the adjustment target is determined based on the average value of the latent image potential or the value that is measured most frequently, and this value is The amount of charge may be adjusted to achieve this.

Finally, a control procedure for preventing background overlapping by adjusting the developing bias voltage value will be described. Second
1 and 22 are flowcharts showing the contents of the latent image potential unevenness check routine in that case. The contents of this procedure are almost the same as the procedure for determining latent image potential unevenness when adjusting the exposure amount shown in FIGS. After the cent (step 5803), immediately move to state 1-2.
All that is required is to start creating a latent image potential at . Thereafter, the highest value Vvma and the lowest value Vvmin are similarly selected from the measured values Vv of the surface potential sensor 11 (step 5825), and latent image potential unevenness is determined based on the difference (step 5826). Then, if there is latent image unevenness, a warning display "Cv" is displayed (step 3829).
, and the details of the abnormality are transmitted (step 5831).

FIG. 23 is a flowchart showing the contents of the developing bias voltage adjustment routine. First, like the Exp-5TEP number or C1l-5TEP number, here the CPU
A counter in 201 is set as a value to be counted in order to adjust the output value of the bias voltage adjustment circuit 207 step by step.
B-5 TEP numbers are available: 1. m (7)VB-
An appropriate VB-5TEP number nvb for the highest value Vvma of the measured potential is selected from the 5TEP numbers (step 5901').

Then, by setting the VB-3TEP number to the selected nvb (step 5902), the adjustment of the developing bias voltage value is completed.

In other words, when the electrostatic latent image on the photosensitive drum 3 is developed with toner from above the developing sleeve 61 in the developing area The larger the difference from the current bias voltage value, the more. Therefore, in the broken background area where a large amount of toner adheres, the latent image potential of that area is high, and the difference between this and the bias voltage value is greater than the standard. Therefore, even if a latent image is formed at a higher potential than usual, the unit area can be reduced by increasing the bias voltage value applied to the developing sleeve 61 so that the potential difference with the high latent image potential does not exceed the standard. By reducing the amount of toner applied, it is possible to prevent background smearing. For this reason, a bias voltage value that provides a reference potential difference with respect to the highest value Vvmax of the measured potential of the electrostatic latent image is selected from among the variable setting values of the bias voltage adjustment time 1% 207, and the bias voltage value corresponding to this value is selected. The number of VB-5TEPs is set.

In addition, when adjusting the above-mentioned developing bias voltage value, the average value or the most frequently measured value is used instead of the highest value of the latent image potential, as in the case of adjusting the exposure amount or charge amount. The developing bias voltage value to be the adjustment target may be selected using the following steps.

Furthermore, in this embodiment, the surface potential sensor is configured to measure the surface potential by moving across the image area, but the structure is not limited to this, and a group of surface potential sensors are arranged in a row across the image area. 6 is also good if you set it up and measure it. Furthermore, although the optical system has been described for slit I exposure, the present invention is also applicable to exposure methods such as flash exposure or exposure using rask scanning.

Furthermore, in this embodiment, an electrostatic latent image of the seal 25 is formed to detect this potential unevenness, but the formation of the latent image that serves as a target for exposure unevenness detection may be performed by other methods.
Furthermore, for example, charging unevenness on the surface of the photoreceptor immediately after being charged by the charging charger 4 may be detected, and the image density may be adjusted based on the detection result.

[Effects] As detailed above, in the image forming apparatus according to the present invention,
A surface potential sensor detects unevenness in the amount of charge on the surface of the photoconductor, and depending on the detection result, at least one of, for example, the amount of light from an exposure lamp, the amount of charge on the photoconductor caused by a charger, and the developing bias voltage value is adjusted. Adjust. As a result, even if the potential of the electrostatic latent image corresponding to the original image formed on the photoreceptor is uneven due to poor charging or poor exposure, it is possible to prevent background overlap and toner and paper. The present invention has excellent effects, such as eliminating wasteful consumption, eliminating operator annoyance, and always obtaining good copy images.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the general configuration of a copying machine according to the present invention;
Fig. 2 is a schematic diagram showing the configuration and arrangement of the surface potential sensor, Fig. 3 is a block diagram of the control system, Fig. 4 is a graph showing the relationship between the latent image potential of the surface potential sensor and the output voltage, and Fig. 4 is a graph showing the relationship between the latent image potential of the surface potential sensor and the output voltage. 5
The figure is a block diagram showing the configuration of the charger, Nos. 6 to 1.
1 and 13 to 23 are flowcharts showing the control procedure of the CPU, and FIG. 12 is a diagram showing the relationship between the latent image potential and the copy image.

Claims (1)

[Scope of Claims] 1. An electrostatic latent image corresponding to the original image is formed on a photoreceptor charged by a charging charger, and this is developed by supplying toner from a developing sleeve to which a developing bias voltage is applied. An image forming apparatus comprising: a surface potential sensor for detecting unevenness in the amount of charge on the photoreceptor; and means for adjusting image density based on the detection result of the surface potential sensor. Device.