JP2001337494A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of highly accurately obtaining the potential of an electrostatic latent image formed on an image carrier, and capable of obtaining the stable density of the image. SOLUTION: The potential is measured by an electrometer 27 at a timing before the potential of the electrostatic latent image formed on the surface 20 of the photosensitive drum 20 reaches the stable one, and in order to always keep the aimed exposure part potential at the developing position of a developing unit 23, the measured potential is changed by a controller 74 in accordance with the measurement results by a temperature sensor 31 and a photosensitive cycle counter 32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus used for an electrophotographic copying machine, a printer, and the like.

[0002]

2. Description of the Related Art Conventionally, an image bearing member on which an electrostatic latent image is formed by exposure is irradiated with exposure light carrying image information to form an electrostatic latent image on the image bearing member. Develop with toner to form a toner image, and finally, the toner image
2. Related Art An image forming apparatus that forms an image by transferring and fixing on a predetermined recording medium is widely known. In such an image forming apparatus, the potential of the electrostatic latent image formed on the surface of the image carrier is measured by a potentiometer in order to compensate for a decrease in image density due to a decrease in the charge amount due to wear of the image carrier and the like. , And the potential of the image carrier is controlled based on the measured potential. When the potential of an electrostatic latent image formed on the surface of an image carrier is measured by an electrometer, generally, the potential (dark potential) in an image portion of the electrostatic latent image that is not irradiated with exposure light and the exposure light is irradiated. And the potential (bright potential) in the non-image portion to be measured. The light potential is
After a period of time (referred to as a transient time) determined by the characteristics of the image carrier after irradiation of the exposure light, the potential reaches a stable potential. Therefore, the measurement of the light potential is important.

Here, Japanese Patent Application Laid-Open No. 1-315773 proposes three techniques for measuring a light potential. In the first technique, an electrometer is provided at a position where the light potential is stable, and the potential is measured. In the second technique, an electrometer is provided at a position before the bright potential is stabilized, and the rotation of the image carrier is stopped until the bright potential is stabilized to measure the potential. Further, in the third technique, an electrometer is provided at a position before the light potential is stabilized, the potential is measured without stopping the rotation of the image carrier, and the measured potential and the position where the electrometer is provided are measured. The potential to be finally obtained is predicted based on the time.

[0004]

However, in the first technique, an electrometer is provided at a position where the light potential is stable, and therefore, the first technique is to cope with a reduction in the size of the image carrier and an increase in the rotation speed. Is difficult. In the second technique, since the rotation of the image carrier is stopped and the potential measurement is performed, after the potential measurement is completed, the image carrier is rotated and then the image formation is performed. There is a problem that it takes a long time to form an image.

[0005] The transient time until the light potential becomes stable varies depending on various environmental conditions. For this reason, if the potential is simply obtained based on the time from the position where the electrometer is provided as in the third technique, there is a problem that accuracy is lacking.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an image forming apparatus which can obtain the potential of an electrostatic latent image formed on an image carrier with high accuracy and can obtain a stable image density. And

[0007]

An image forming apparatus according to the present invention for achieving the above object irradiates exposure light carrying image information onto an image carrier on which an electrostatic latent image is formed on the surface by exposure. Forming an electrostatic latent image on the image carrier, developing the electrostatic latent image with toner to form a toner image on the image carrier,
In an image forming apparatus that finally transfers and fixes the toner image on a predetermined recording medium to form an image formed of the fixed toner image on the recording medium, the image forming apparatus exposes the surface of the image carrier to light. A latent image forming means for measurement for forming an electrostatic latent image for potential measurement on the surface of the image carrier, and a potential of the electrostatic latent image for potential measurement formed on the surface of the image carrier by the latent image forming means for measurement is exposed. Potential measuring means for measuring at a timing before the potential of the surface of the image carrier changed by the electric potential reaches a stable potential; and the image carrier so that the potential measured by the potential measuring means becomes a predetermined target potential. Condition adjusting means for adjusting at least one of image forming conditions which affect the potential of the electrostatic latent image for potential measurement formed on the surface, and the rate of change of the potential of the image carrier surface after exposure Affect An element measuring means for measuring a single element even without, characterized in that a target potential changing means for changing the target potential in accordance with the measurement result by the element measuring means.

Here, it is preferable that the element measuring means is a temperature measuring means for measuring a temperature.

It is also preferable that the element measuring means measures an element which indicates the amount of use of the image carrier.

Further, the target potential changing means is configured to maintain the potential of the electrostatic latent image for measuring the potential formed on the surface of the image carrier at the timing of development with toner at a predetermined potential. Changing the target potential is also a preferred embodiment.

[0011]

Embodiments of the present invention will be described below.

FIG. 1 is a schematic configuration diagram showing an embodiment of a copying machine to which the image forming apparatus of the present invention is applied.

As shown in FIG. 1, a copying machine 1 includes a photosensitive drum 20 having an electrostatic latent image formed on the surface thereof, and a charging corotron 21 for previously charging the surface of the photosensitive drum 20.
Scanner unit 22 for reading image information of document 222
A raster scanning device (hereinafter referred to as ROS) 228 for writing an electrostatic latent image including an electrostatic latent image for measuring potential on the surface of the photosensitive drum 20 charged by the charging corotron 21;
The developing device 23 includes a developing device 23 that develops an electrostatic latent image with toner to form a toner image on the photosensitive drum 20 and a transfer corotron 42 that transfers the toner image formed on the photosensitive drum 20 to the recording sheet 30. Have been. The photosensitive drum 20
Corresponds to the image carrier according to the present invention, and ROS 228 corresponds to the measurement latent image forming unit according to the present invention.

The scanner unit 22 includes an exposure lamp 223 for irradiating a light beam to a document 222 set on a platen 221, a carriage 224 for moving the exposure lamp 223 over the area of the document 222, and an exposure lamp 223.
A reflection mirror 225 for guiding a beam from the surface of the original 222 along a predetermined path, a CCD sensor 226 for converting the beam from the surface of the original 222 to a digital signal,
And an image forming lens 227 for forming an image of the beam from the 22 surfaces on the CCD sensor 226.

The ROS 228 includes a semiconductor laser 228a for irradiating a laser beam based on image data captured by the CCD sensor 226, and a polygon mirror 228b for distributing and deflecting the beam from the semiconductor laser 228a in the main scanning direction of the photosensitive drum 20. , Semiconductor laser 228
An imaging lens 228c that forms an image of the beam from a along the main scanning direction line of the photosensitive drum 20, and a reflection mirror 228d that regulates the beam path.

The copying machine 1 has an optical sensor 28 disposed between the developing position and the transferring position. The optical sensor 28 is a reflection type optical sensor that irradiates the photosensitive drum 20 with an LED and measures the amount of reflected light with a photodiode, and measures the toner adhesion amount of the reference patch toner image formed on the photosensitive drum 20. The density of the toner image is measured by the detection.

Further, the copying machine 1 includes a photosensitive drum 20.
Between the writing position A of the electrostatic latent image and the developing position C for
An electrometer 27 for measuring the charged potential of the photosensitive drum 20 is provided. The electrometer 27 changes the potential of the electrostatic latent image for potential measurement formed on the surface of the photosensitive drum 20 by the ROS
The measurement is performed at a timing before the potential of the zero surface reaches the stable potential.

In the copying machine 1, the potential of the electrostatic latent image for potential measurement formed on the surface of the photosensitive drum 20 is set so that the potential measured by the electrometer 27 becomes a predetermined target potential. Is provided with a controller 74 (see FIG. 2) for adjusting at least one of the image forming conditions affecting the image forming conditions. Further, the controller 74 controls the toner supply amount to the developing device 23 based on the detection result of the optical sensor 28. The controller 74 plays a role of a condition adjusting means according to the present invention. Further, the copying machine 1 is also provided with a hygrometer (not shown) for measuring the relative humidity inside the copying machine.

A cleaner 25 for removing residual toner on the photosensitive drum 20 is provided around the photosensitive drum 20.
And an erase lamp 26 for removing the residual charge on the photosensitive drum 20. Further, a sheet transport system 48 for transporting the recording sheets 30 supplied from a sheet supply cassette (not shown) is provided.

Further, the copying machine 1 is provided with a heating roll 51 having a built-in heater therein, through which the recording sheet 30 having undergone the transfer process is inserted and an unfixed toner image is fixed on the recording sheet 30. A fixing device 50 including a pressure roll 52 that is pressed against the heating roll 51 is provided. The recording sheet 30 is conveyed to the fixing device 50 via a guide plate 53. In addition, the fixing device 5
0, a fuser exit roll 54 that conveys the recording sheet 30 that has passed through, a fuser exit switch 55 for detecting the trailing end of the recording sheet 30 that has passed through the fixing device 50, a discharge tray 56 in which the fixed recording sheet 30 is stored, and Exit roll 5 for sending recording sheet 30 to discharge tray 56
7 are provided.

In the copying machine 1 constructed as described above, when the user operates a copy start switch (not shown), scanning of the original 222 is started, and the electrostatic latent image of the electrostatic latent image is placed on the photosensitive drum 20. Writing is performed. The electrostatic latent image is developed by the developing device 23 with a slight delay from the writing timing. The toner image thus formed on the photosensitive drum 20 is transferred to the recording sheet 30.
The recording sheet 30 is discharged to the discharge tray 56 via the fixing device 50. Thereafter, the above operation is repeated for the set number of copies.

FIG. 2 is a block diagram of a control system in the copying machine according to the embodiment of the present invention.

FIG. 2 shows a block diagram of the scanner unit 11, the image processing unit 12, the optical unit 13, and the image forming unit 14 constituting the control system 10 of the copying machine 1 shown in FIG.

In the scanner section 11, the CCD sensor 2
The image data read at 26 is amplified to an appropriate level by an amplifier 60, converted to an 8-bit digital signal by an A / D converter 61, and after shading correction, by a density converter 62 based on the density data from the reflectance data. The data is converted into data and sent to the image processing unit 12.

The image data sent to the image processing unit 12 is
First, basic image processing as the copying machine 1 is performed by the conversion unit 63,
That is, MTF processing or the like is performed, and the data is converted into image data. Next, the image data is sent to the first gamma correction unit 64, and the gradation is corrected in accordance with the gradation characteristics unique to the ROS 228 and the image forming unit 14.

The image data corrected by the first gamma correction unit 64 is converted into analog image data by a D / A converter 68 and then passed through a second selector 73 to a comparator 69.
The comparator 69 compares the signal with a signal of a predetermined period sent from the triangular wave generator 70 and converts the signal into binary image data by pulse width modulation.

FIG. 3 is an explanatory diagram of binarization processing of image data by the comparator in the present embodiment.

As shown in FIG. 3, the input analog image data A is compared with the triangular wave T generated by the triangular wave generator 70 (see FIG. 2). , The image data is binarized with the small portion as “1”. The binary image data B thus obtained is sent to the laser driver 71 of the optical unit 13 (see FIG. 2), and when the image data is "0", the semiconductor laser 228a of the ROS 228 is turned off and the image data is changed to "1". "
Is turned on at this time, an electrostatic latent image is formed on the photosensitive drum 20.

The image processing section 12 includes a photosensitive drum 2
A patch signal generating means 72 for generating an image signal when the reference patch toner image is formed on
Reference patch data with an image area ratio of 50% is generated. The analog image data and the reference patch data are input to a second selector 73 controlled by a controller 74, and only one of the data is compared with a triangular wave by the comparator 69 to be binarized.

Returning to FIG. 2, the description of the control system 10 will be continued.

The image forming section 14 includes the above-described controller.
A controller 74 is provided.
Based on the signals from the position meter 27 and the optical sensor 28,
Keeping the density of the toner image formed on the optical drum 20 constant
It also plays a controlling role. Also this controller
74, the grid voltage V of the charger 21 according to the control signal _G
Charger controller 75 for changing the
Developing bias applied to the developing device 23 in accordance with the control signal of
Voltage V_BDeveloping bias control unit 76 for changing
ing. A toner supply device 77 is connected to the developing device 23.
The developing device 2 according to the control signal of the controller 74.
3 is supplied with toner. further,
The controller 74 is a laser light amount control unit of the optical unit 13.
Control signal is also sent to the
The semiconductor laser 228a of the ROS 228 is
The amount of light emission is adjusted.

Further, the image forming section 14 is provided with a temperature sensor 31 for measuring a temperature, which is one of the factors affecting the speed of change of the surface potential of the photosensitive drum 20 after exposure. The signal from the temperature sensor 31 is input to the controller 74. Further, the image forming unit 14 includes an element (a use cycle) that indicates the usage amount of the photosensitive drum 20 as another one of the elements that affect the change speed of the surface potential of the photosensitive drum 20 after exposure. ) Is provided. The signal from the photoconductor cycle counter 32 is also input to the controller 74. The temperature sensor 31 and the photoconductor cycle counter 32 correspond to an element measuring unit according to the present invention. The controller 74 changes the target potential according to the measurement results of the temperature sensor 31 and the photoconductor cycle counter 32. The controller 74 also plays a role of a target potential changing unit according to the present invention.

FIG. 4 is a diagram showing a potential decay characteristic after exposure of the photosensitive drum shown in FIG.

FIGS. 4 (a), 4 (b) and 4 (c) show the charging potential when a new photosensitive drum 20 is used.
After exposure at 600 V, ambient temperature 20 ° C., 10 ° C., 2
The potential decay characteristic at 8 ° C. is shown. After exposure, the time required for the potential to decay to 95% of the stable level is 80 ms at 20 ° C. shown in FIG.
Is 120 ms at 10 ° C. as shown in FIG. 4 and 28 ° C. as shown in FIG.
Thus, the attenuation of the potential of the photosensitive drum 20 has a temperature dependency, for example, 60 ms.

In this embodiment, the size of the entire copying machine 1 is
In order to reduce the size, the photoconductor drum 20 is reduced in size.
To increase the printing speed.
The rotation speed has also been increased. Therefore, as shown in FIG.
From optical point (writing position) A to position B of electrometer 27
Is 50 ms, and the potential after exposure is 9 at a stable level.
There is not enough time to reach 5%. Ma
In addition, from the exposure point A, the power of the photosensitive drum 20 is actually
The time to the developing position C which is the position for controlling the position is 120.
ms. In the present embodiment, the aim at the developing position C
Exposure part potential (V _{LD_DEVE}) Is always -200V.
Here, the exposed portion potential (V_{LD_DEVE}) Is always -200V
Exposure unit at position B of electrometer 27
The position was measured for each temperature and for the film thickness of the photosensitive drum 20.
Table 1 shows the results.

[0036]

[Table 1]

The thickness of the photosensitive drum 20 is determined by the photosensitive drum.
The ram 20 gradually wears and becomes thinner according to the usage time of the ram 20.
The thinner the film, the shorter the distance that the charge travels
After the exposure until the potential reaches a stable level.
Event time is shorter. That is, from the position B of the electrometer 27
The amount of attenuation up to the developing position C is reduced. Also, if the temperature is high
The same applies to the case where it becomes worse. Therefore, at the developing position C
And the exposed portion potential (V_{LD_D EVE}) Is always controlled at -200V
To do this, the exposure portion potential at the position B of the electrometer 27 is
(Target exposure portion potential V_LS) As shown in Table 1.
Must be set (controlled) to a value.

Therefore, in the present embodiment, a temperature sensor 31 and a photoconductor cycle counter 32 shown in FIG.
The target exposure portion potential V _LS is controlled by the following routine.

FIG. 5 is a flowchart of a routine for _{obtaining the} target exposure portion potential _VLS at the position of the electrometer.

This routine is started before executing a setup mode routine shown in FIG. 6, which will be described later. First, in step ST1, the number of photoconductor cycles (the number of used cycles) P of the photoconductor drum 20 counted by the photoconductor cycle counter 32.
_{R_cyc} (unit: kilocycle) is detected by the control 74. Then, in step ST2, the temperature PR_ the photosensitive drum 20 near measured by the temperature sensor 31 _temp (Unit: ° C.) are also detected by the control 74. Further, in step ST3, the in the target exposed portion potential V _LS, use several cycles minutes of the photosensitive drum 20 correction value _{ΔV LS _ cyc {ΔV LS _} cyc = 100- (PR_
_cyc × 0.2)｝ is calculated. Here, the correction value ΔV _LS
_ _Cyc is the photosensitive drum 20 is new state, i.e. the number of used cycles PR_cor _cyc is 0, becomes 0 at 10, and the addition or the number of 500K cycles thickness is reduced to 10 [mu] m.

Next, in step ST4, the temperature component
Correction value ΔV_LS__temp｛ΔV_LS__temp= (30-PR_
_temp) × 1.2｝｝ is calculated. Here, the correction value ΔV
_LS__{te mp}Is 0 when the temperature is 30 ° C or higher, and
For example, it becomes 24 at 10 ° C.

Further, in step ST5, a total correction value is calculated from both correction values.

Total correction value ΔV_LS= ΔV_LS__temp×
(ΔV_LS__cyc/ 100) That is, when the photosensitive drum 20 is new, the total correction is performed.
Value ΔV_LS= ΔV_LS__{te mp}And the correction value ΔV for the temperature_LS
__tempIs applied 100%. Also, the number of cycles used
As the temperature increases, the correction value ΔV for the temperature_LS__tempAdaptation
Rate decreases, and the adaptation rate becomes 0 after 500K cycles or more.
(No correction).

Next, the process proceeds to step ST6, where the developing position C
Exposure potential ΔV _{LS — DEVE} (−200 in the present embodiment)
By setting a value obtained by subtracting the total correction value ΔV _LS from V) as a target exposure portion potential V _LS shown in FIG. 6 described later, the set exposure portion potential ΔV _{LS — DEVE} at the developing position C is always −2.
It can be controlled to 00V.

FIG. 6 is a flowchart of a setup mode routine for setting image forming conditions.

The controller 74 stores in advance a target dark potential V _HS , a target exposure portion potential V _LS , and a fog prevention potential difference V _C from the target dark potential V _HS to the developing bias potential V _B.

First, in step ST11, a non-developed portion on the photosensitive drum 20 is measured by the optical sensor 28, and a reference output V _clean of the optical sensor 28 is obtained. next,
In step ST12, the controller 74 sends a control signal to the charger control unit 75, and the different grid voltage V
_The photosensitive drum 20 is charged by _G1 and _VG2 . Then, the dark potentials V _H1 and V _H2 at that time are measured using the electrometer 27, and then in step ST13, the grid potential V _GS required to obtain the target dark potential V _HS is calculated by the following equation.

[0048]

(Equation 1)

Next, in step ST14, the step
Grid potential V obtained in step ST13 _GSPhotoconductor using
While charging the ram 20, the controller 74
It is necessary for the signal generation means 72 to generate reference patch data.
The second selector 73 sends the reference patch data
Request a choice. This makes the reference patch data binary
And supplied to the laser driver 71, the photosensitive drum
An electrostatic latent image corresponding to the reference patch data is formed on 20
Is done. At this time, the controller 74 controls the laser light amount.
A control signal is sent to the unit 78, and two types of laser light amounts are output.
L_D1, L_D2Drum 2 by ROS 228 using
Expose 0. Then, using the electrometer 27,
Exposure toner potential V_L1, V_L2Measure
Further, in step ST15, the target exposure portion potential V_LS
Laser light amount L required to obtain_DSIs calculated by the following equation.
You.

[0050]

(Equation 2)

Next, in step ST16, the target from the dark potential V _HS by subtracting antifogging potential difference V _C seeking development bias potential V _B, further proceeds to step ST17, the charger control the calculated grid potential V _GS Part 75
To, the amount of laser light L _DS to the laser light quantity control unit 78 sets each of the development bias potential V _B to a developing bias control unit 76.

Next, in step ST18, the controller 74 requests the patch signal generating means 72 to generate reference patch data again, and uses the set grid potential V _GS and laser light amount L _DS to set the photosensitive drum 20. An electrostatic latent image is formed thereon. Then, the electrostatic latent image using a developing bias voltage V _B set in the development bias control unit 76 and developed to form a reference patch toner image on the photosensitive drum 20. In step ST19, the optical sensor 28 detects the density of the reference patch toner image formed on the photosensitive drum 20, and the controller 74 performs development from the toner supply device 77 (see FIG. 2) based on the detection signal of the optical sensor 28. The toner supply amount to the unit 23 is controlled. This routine ends when the toner supply amount control is completed.

When the copy job is actually started, the controller 74 requests the patch signal generation means 72 to generate reference patch data every predetermined number N of copies.
A reference patch toner image is formed on the photosensitive drum 20. Then, the amount of toner adhered to the formed reference patch toner image is detected by the optical sensor 28, and the amount of toner supplied from the toner supply device 77 to the developing unit 23 is corrected based on the detection signal. In the copying machine of the present embodiment, the initial setting is made so that the reference patch toner image is formed with the number of copies N = 10 as a standard interval.

FIG. 7 is a flowchart showing a routine of an image density control program after the start of a copy job.

First, in step ST21, it is determined whether or not a copy job has started. If the copy start switch is turned on and it is determined that the copy job has started, the process proceeds to step ST22, where the controller 74
Counts up the number of copies CNT. Next, the process proceeds to step ST23, where it is determined whether the number of copies CNT has reached the reference patch toner image creation interval N (N = 10 in this embodiment). If it is determined that the number of copies CNT has not reached the reference patch toner image creation interval N, the process proceeds to step ST24, and it is determined whether all copy jobs have been completed. If all copy jobs have not been completed, the steps after step ST22 are repeatedly executed. If it is determined in step ST24 that all copy jobs have been completed, this routine ends.

On the other hand, if it is determined in step ST23 that the number of copies CNT has reached the reference patch toner image creation interval N, the process proceeds to step ST25, where the controller 74 places the reference patch toner image on the photosensitive drum 20. And developing unit 2 for detecting the image density.
3 is corrected. Further, after controlling the image density in step ST25, the process proceeds to step S25.
At T26, the number of copies CNT is reset to 0,
The process proceeds to step ST24 described above.

FIG. 8 is a characteristic diagram of the optical sensor used in this embodiment.

The vertical axis in FIG. 8 represents the optical sensor output RAD.
C, that is, the optical sensor output V from the reference patch toner image
The ratio between the _patch and the optical sensor output _Vclean from the non-developed portion on the photosensitive drum 20 (see FIG. 2), and the horizontal axis is the toner adhesion amount.

As shown in FIG. 8, the output of the optical sensor decreases as the toner adhesion amount increases and the density increases.

FIG. 9 is a flowchart of a general toner supply amount control.

First, in step ST31, a reference patch toner image is formed on the photosensitive drum 20 using the grid potential V _GS , the laser light amount L _DS and the developing bias potential V _B set in step ST17 of the flowchart of FIG. It is developed by the developing device 23. Next, step ST32
In step (2), the amount of toner attached to the reference patch toner image is measured by the optical sensor 28 to obtain the reference patch toner image density V _patch . Further, in step ST33, the ratio between the reference patch toner image density V _patch and the optical sensor output V _clean from the non-developed portion measured in step ST11 of the flowchart of FIG. Get.

RADC = (V _patch / V _clean ) × 1023 Note that “1023” is a coefficient for normalizing the read value of the optical sensor.

Next, in step ST34, the difference between the reference patch density measurement value RADC and the reference patch density target value RADCS is multiplied by a predetermined coefficient K according to the following equation.
The toner supply amount DISP is determined.

DISP = (RADC-RADCS) × K Next, the process proceeds to step ST35, where DISP is set to 0 when DISP is negative, and DISP is set to a predetermined upper limit value DISP_
If it exceeds MAX, DISP is set to DISP_MAX.

As described above, in the general toner supply amount control, the reference patch density measurement value R, which is the measurement result of the optical sensor, is obtained.
If the difference between the ADC and the reference patch density target value RDCS is positive, the density of the reference patch toner image is low. Therefore, the toner replenishment amount, that is, the toner replenishment time is obtained by multiplying the predetermined coefficient K. As a result of this control, the toner adhesion amount of the reference patch toner image becomes constant, and the image density is also kept constant.

As described above, even in an image forming apparatus which is small and high-speed, and in which it is difficult to provide an electrometer before the time when the potential after exposure of the photosensitive drum attenuates and reaches a stable potential, Target exposure section potential at the position of the electrometer according to the number of cycles of use of the photoconductor, which correlates with the temperature and the film thickness, which affects the time required for the potential after exposure of the photoconductor drum to attenuate to reach the stable potential By calculating V _LS , the target exposure portion potential V _{LD_DEVE} at the development position can always be obtained. Therefore, it is possible to provide an image forming apparatus capable of obtaining a stable image density.

[0067]

As described above, according to the image forming apparatus of the present invention, the potential of the electrostatic latent image formed on the image carrier can be obtained with high accuracy, and a stable image density can be obtained. .

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a copying machine to which an image forming apparatus of the present invention is applied.

FIG. 2 is a block diagram of a control system in the copying machine according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram of binarization processing of image data by a comparator according to the embodiment.

FIG. 4 is a diagram showing a potential decay characteristic after exposure of the photosensitive drum shown in FIG. 1;

FIG. 5 is a flowchart of a routine for _{obtaining a} target exposure portion potential V _LS at a position of an electrometer.

FIG. 6 is a flowchart of a setup mode routine for setting image forming conditions.

FIG. 7 is a flowchart illustrating a routine of an image density control program after a copy job is started.

FIG. 8 is a characteristic diagram of an optical sensor used in the present embodiment.

FIG. 9 is a flowchart of general toner supply amount control.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Copier 10 Control system 11 Scanner part 12 Image processing part 13 Optical part 14 Image forming part 20 Photoconductor drum 21 Charging corotron 22 Scanner part 23 Developing device 25 Cleaner 26 Erase lamp 27 Electrometer 28 Optical sensor 30 Recording sheet 31 Temperature sensor 32 Photoconductor cycle counter 42 Transfer corotron 48 Sheet transport system 50 Fixing device 51 Heating roll 52 Pressure roll 54 Fuser exit roll 55 Fuser exit switch 56 Discharge tray 57 Exit roll 60 Amplifier 61 A / D converter 62 Concentration converter 63 Conversion Unit 64 first gamma correction unit 68 D / A converter 69 comparator 70 triangular wave generator 73 second selector 74 controller 221 platen 222 document 223 exposure lamp 224 carriage 225 reflection mirror 226 CCD cell Sa 227 imaging lens 228 ROS (raster scanning device) 228a semiconductor laser 228b polygon mirror 228c imaging lens 228d reflecting mirror

Claims (4)

[Claims] An image bearing member on which an electrostatic latent image is formed by exposure is irradiated with exposure light carrying image information to form an electrostatic latent image on the image bearing member. The latent image is developed with toner to form a toner image on the image carrier, and the toner image is finally transferred and fixed on a predetermined recording medium, thereby fixing the toner image on the recording medium. An image forming apparatus for forming an image composed of an image, a latent image forming unit for measurement for forming an electrostatic latent image for potential measurement on the surface of the image carrier by exposure, and Potential measuring means for measuring the potential of the electrostatic latent image for potential measurement formed on the surface of the carrier at a timing before the potential of the surface of the image carrier changed by exposure reaches a stable potential; So that the potential measured by the means becomes a predetermined target potential. Condition adjusting means for adjusting at least one of image forming conditions which affect the potential of the electrostatic latent image for potential measurement formed on the surface of the image carrier, and the potential of the surface of the image carrier after exposure An image, comprising: an element measuring unit that measures at least one element that affects a change speed of the target; and a target potential changing unit that changes the target potential according to a measurement result by the element measuring unit. Forming equipment. 2. An image forming apparatus according to claim 1, wherein said element measuring means is a temperature measuring means for measuring a temperature. 3. An image forming apparatus according to claim 1, wherein said element measuring means measures an element indicating an amount of use of said image carrier. 4. The method according to claim 1, wherein the target potential changing unit is configured to maintain the potential of the electrostatic latent image for measuring potential formed on the surface of the image carrier at a timing of development with toner at a predetermined potential. 2. The image forming apparatus according to claim 1, wherein the target potential is changed.