JPH1073975A - Device and method for estimating latent image electric potential - Google Patents

Abstract

PROBLEM TO BE SOLVED: To grasp accurate characteristics of a photoreceptor changing with the lapse of time and to form stable images of good quality. SOLUTION: In states where the surface of a photoreceptor is electrified under a given electrifying condition, an exposure controlling section 11 displays on the photoreceptor's surface electrostatic latent images as plural (n) test patches whose gradation is different each other depending on plural (n) values Ln written by a laser into a patch condition storage section 44, and stores the values written by the laser for plural (n) test patches into a storage section 45 of laser written values. A potential sensor 28 measures the surface potential (V) of each test patch and stores it into a surface potential storage section 46. A potential function creating section 47 approximates distribution characteristics of laser written value (L) and surface potential (V) for each test patch to higher order, determines latent image potential function V=f(L) representing characteristics of a photoreceptor, and stores it into a information storage 48. An information processing section 41 grasps characteristics of the photoreceptor by using the stored latent image potential function V=f(L), executes process control of laser written value L or the like of an input image and executes image-forming process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a latent image potential estimating apparatus and a latent image potential estimating method for a photoreceptor used in an image forming apparatus such as a copying machine, a printer, a facsimile machine, etc. using an electrophotographic process system. The present invention relates to improvement of detection accuracy of body characteristics.

[0002]

2. Description of the Related Art There is an increasing demand for higher image quality in image forming apparatuses such as copying machines, and accurate control of an image forming process is becoming important. During the image forming process, it is necessary to always accurately grasp the characteristics of the photoconductor, which constantly fluctuate, and control the surface potential of the photoconductor to an optimum value.
Such a device for controlling the surface potential of the photoconductor to an optimum value is disclosed in, for example, Japanese Patent Publication No. 3-64866 and Japanese Patent Publication No. 4-44270. Japanese Patent Publication No. 3-64866 and Japanese Patent Publication No.
In each of the publications, the target characteristic of the photoconductor is stored in advance, and the optical means is operated with a control input value corresponding to the condition such as the temperature of the photoconductor to expose the surface of the photoconductor to expose the reference latent image. Is formed, the potential of the formed latent image is measured and compared with the target potential to correct the control input value.

[0003]

However, the semiconductor laser writing value L for writing image information on the photosensitive member has 8 bits, that is, 256 gradations, in order to improve image quality. Therefore, ideally, if the correspondence with the surface potential of the photoconductor is measured for every laser writing value L, the characteristics of the photoconductor can be accurately grasped. The characteristics of this photoreceptor are largely temperature dependent. In addition, when a large amount of continuous copying is performed, the influence of the residual potential also occurs. Further, the target value of the charging by the charger is changed by the process control inside the apparatus. Under these various conditions, it is impossible to measure the laser writing value L, that is, the surface potential of the photoconductor for each gradation, and it is difficult to accurately grasp the change in the characteristics of the photoconductor. Met.

SUMMARY OF THE INVENTION The present invention has been made to solve such a disadvantage, and has an object to provide a latent image potential estimating apparatus and a latent image potential estimating method capable of highly accurately estimating a photoconductor surface potential over all gradations. It is intended for.

[0005]

SUMMARY OF THE INVENTION A latent image potential estimating apparatus and a latent image potential estimating method according to the present invention provide electrostatic latent images of a plurality of n test patches with different laser writing values Ln on a photosensitive member surface. When the surface potential Vn of the plurality of n test patches created under constant charging conditions is measured, and the measured surface potential Vn of the plurality of n test patches and the electrostatic latent image of each test patch are created. Of the latent image potential function V
= F (L), and when an event occurs that causes some change in the characteristics of the photoconductor, the latent image potential function V = f
The electrostatic latent images of the number e of patches smaller than the number n of test patches created to determine (L) are written with different laser writing values L.
e, the surface potential Ve of the created e patches is measured, and the measured surface potential Ve of the e patches and the laser writing value Le when the electrostatic latent image of each patch is created are calculated. And updating the coefficient of the latent image potential function V = f (L).

In a second latent image potential estimating apparatus and a latent image potential estimating method according to the present invention, the electrostatic latent images of a plurality of n test patches are fixedly charged on the surface of a photoreceptor with different laser writing values Ln. The surface potential Vn of a plurality of n created test patches is measured under the condition, and the surface potential Vn of the plurality of test patches measured for each section of the laser writing value divided in advance is measured.
The latent image potential function V = f (L) is determined from the laser writing value L when the electrostatic latent image of each test patch is created, and an event occurs that causes some change in the characteristics of the photoconductor. Next, an electrostatic latent image of a number e of patches smaller than the number n of test patches created to determine the latent image potential function V = f (L) is created with a different laser writing value Le, and created e The surface potential Ve of the patches is measured, and the laser writing is performed using the measured surface potential Ve of the e patches and the laser writing value Le when the electrostatic latent image of each patch is created. It is characterized in that the coefficient of the latent image potential function V = f (L) for each section of the value is updated.

[0007] The events that cause some change in the characteristics of the photoreceptor include changes in the ambient temperature, the number of continuous copies, the total number of image formations on the photoreceptor, the elapsed time since the end of the last copy, and information on the charge amount. At least one of them is included.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The control section of an image forming apparatus using an electrophotographic process according to the present invention includes an information processing section including a CPU and a ROM, a drive control section for driving a photosensitive member and the like, and a patch condition storage section. An exposure controller, a charge controller, a laser writing value storage, a surface potential storage, a potential function generator, an information storage, and a coefficient update processor.

During a standby time from when the power of the image forming apparatus is turned on to when the temperature of the fixing unit rises and becomes operable, the information processing unit causes the charging control unit and the exposure control unit to create a test patch. To instruct. When the creation of a test patch is instructed, the charging control unit charges the surface of the photoreceptor under a constant charging condition, and the exposure control unit controls the plurality of n different laser writing values Ln stored in the patch condition storage unit. Thereby, electrostatic latent images of a plurality of n test patches having different gradations are formed on the photoconductor surface. The laser write values L of the formed plurality of n test patches are stored in the laser write value storage unit. On the other hand, the potential sensor measures the surface potential V of each test patch and stores it in the surface potential storage unit. The potential function generator inputs the laser write value L of each test patch stored in the laser write value storage and the surface potential V of each test patch stored in the surface potential storage, and outputs a plurality of test patches. Laser writing value L and surface potential V
Is obtained. Laser writing value L of this test patch
And the distribution characteristics of the surface potential V are higher-order approximation, and the latent image potential function V = f (L) indicating the relationship between the photoreceptor characteristics, ie, the laser writing value L and the surface potential V, is determined and determined. The latent image potential function V = f (L) and each coefficient are stored in the information storage unit. The information processing section has a latent image potential function V = f (L) stored in the information storage section.
Thus, the characteristics of the photoreceptor are grasped, and the process control such as the laser writing value L of the input image is performed to perform the image forming process.

During the image forming process, the information processing unit sends a correction control signal to the charge control unit and the exposure control unit when an event that changes the characteristics of the photosensitive member such as a change in ambient temperature occurs. It instructs creation of a patch and instructs the coefficient update processing unit to perform correction processing. When the creation of a correction patch is instructed, the charging control unit charges the surface of the photoreceptor under a constant charging condition, and the exposure control unit sets a plurality of test patches smaller than the number n of test patches stored in the patch condition storage unit. Of the electrostatic latent image of the correction patch for the laser
Formed on the surface of the photoreceptor. The laser write values L of the plurality of correction patches thus formed are stored in the laser write value storage unit, and the surface potential V of each correction patch detected by the potential sensor is stored in the surface potential storage unit. Remember. The coefficient update processing unit uses the stored laser writing value L and surface potential V of each correction patch to store the latent image potential function V =
Correct and update the coefficient of f (L). The information processing unit accurately grasps the characteristics of the photosensitive member based on the latent image potential function V = f (L) stored in the information storage unit, and performs a process control to form a high quality image.

[0011]

FIG. 1 is a block diagram of one embodiment of the present invention.
As shown in the figure, the image forming apparatus is placed on a platen 1,
The light source 4 irradiates the original 3 held by the original cover 2 with light from the light source 4 and reflects the reflected light to a plurality of mirrors 5 a and 5 b and a lens 6.
The image of the document 3 is read by the CCD 7 through the CCD 7. After the image signal read by the CCD 7 is converted into a digital signal by the A / D converter 8, a predetermined image processing is performed by the original image processing unit 9 and sent to the exposure operation value determination unit 10 as an input image signal. The exposure operation value determination unit 10 performs an image signal conversion process on the input image signal sent thereto, determines an output image signal corresponding to the input image signal, and configures the determined output image signal with a semiconductor laser device or the like. It is sent to the exposure control unit 11. The exposure control unit 11 controls the driving of the semiconductor laser element based on the output image signal sent, and exposes the photoconductor 12 with laser light corresponding to the output image signal. A predetermined charge controlled by the charge control unit 13 is charged on the surface of the photoconductor 12 by the charger 1.
4, and forms an electrostatic latent image with the exposed laser light.

Around the photoreceptor 12, a developing section 15 for attaching toner to the electrostatic latent image formed on the photoreceptor 12 to form a visible image, an intermediate transfer section 16 and a photoreceptor cleaning section 1
Seven. The intermediate transfer section 16 includes an intermediate transfer belt 18, a bias applying roller 19, a tension roller 20, and a cleaning section 21. Then, the electrostatic latent image formed on the surface of the photoconductor 12 is visualized by the developing unit 15, and the toner image is transferred to the intermediate transfer belt 18. Intermediate transfer belt 18
Is transferred to the transfer paper 2 sent from the paper supply unit 22.
3 is transferred by the transfer unit 24. The transfer paper 23 onto which the toner image has been transferred is conveyed to the fixing unit 26 by the conveyance unit 25 and fixed there, and is discharged to the discharge tray 27. As a sensor for detecting environmental information when an image is formed as described above, a potential sensor 28 for detecting the potential of the photoconductor 12, an optical sensor 29 for measuring a toner adhesion amount of a toner image on the surface of the photoconductor 12, and a temperature. A sensor 30, a copy counter 31, and the like are provided.

As shown in the block diagram of FIG. 2, the control section of the image forming apparatus includes an information processing section 41 including a CPU and a ROM, and a drive control section for driving the photosensitive member 12, the intermediate transfer section 16, and the like. 42, a condition input unit 43, a patch condition storage unit 44, a laser writing value storage unit 45, a surface potential storage unit 46, a potential function generation unit 47, an information storage unit 48, and a coefficient update processing unit 49. The condition input unit 43 inputs the surface potential detected by the potential sensor 28, the temperature sensor 30, the copy counter 31, the ambient temperature, the number of copies, and the like.
Send to The patch condition storage unit 44 stores the photoconductor 12 at the initial stage.
The number e of test patches formed on the photoreceptor 12 is smaller than the number n of test patches formed on the photoreceptor 12 when an event giving some change to the characteristics of the photoreceptor 12 occurs when different laser write values Ln of a plurality n of test patches formed on the photoreceptor 12 The different laser writing values Le of the patches are stored. The laser writing value Ln for forming a plurality of n test patches is determined by dividing 0 to 255 gradations at substantially equal intervals. When a plurality of n test patches are formed, the laser write value storage unit 45 stores the laser write values Ln of each of the formed test patches and stores a plurality of e.
Is formed, the laser writing value Le of each formed patch is stored. The surface potential storage unit 46 stores the test patches on the surface of the photoconductor 12 and the potential of each patch measured by the potential sensor 28 when a plurality of n test patches and a plurality of e patches are formed. The potential function generation unit 47 detects the light based on the laser writing values Ln of the plurality of n test patches stored in the laser writing value storage unit 45 and the surface potential Vn of each test patch stored in the surface potential storage unit 46. Body 1
And a latent image potential function V = f (L) indicating the relationship between the laser writing value L and the surface potential V.
8 is stored. The coefficient update processing unit 49 is operable to record when an event causing some change in the characteristics of the photosensitive member occurs.
The latent image potential function V stored in the information storage unit 48 from the laser write values Le of the plurality of patches stored in the storage value storage unit 45 and the surface potential Ve of each patch stored in the surface potential storage unit 46. = F (L) is updated.

The operation of determining the latent image potential function V = f (L) indicative of the characteristics of the photoreceptor 12 in the image forming apparatus configured as described above and correcting the coefficient of the determined latent image potential function is described below. A description will be given with reference to the characteristic diagram of the laser write value L and the surface potential V in FIG.

For example, during a standby time until the power of the image forming apparatus is turned on and the temperature of the fixing unit 26 rises and the fixing unit 26 becomes operable, the information processing unit 41 tests the charging control unit 13 and the exposure control unit 11. Instruct creation of a patch. When the creation of a test patch is instructed, the charging control unit 13 charges the surface of the photoreceptor 12 under a constant charging condition, and the exposure control unit 11 sets the plurality of n, for example, eight tests stored in the patch condition storage unit 44. The photosensitive member 1 is changed according to the laser writing value Ln of a different patch.
On the two surfaces, for example, as shown in FIG. 4, electrostatic latent images of a plurality of n test patches 51a to 51n are formed. Since the laser writing values Ln of the test patches 51a to 51n formed on the surface of the photoreceptor 12 are determined by dividing 0 to 255 gradations at substantially regular intervals, as shown in FIG. It will be a different latent image. Here, FIG. 4 shows a test patch 51 on the photoconductor 12.
The test patches 51a to 51n actually formed on the surface of the photoreceptor 12 are obtained by developing the states a to 51n on a plane.
Since this is an electrostatic latent image, the shading is not visible as shown in FIG. 4, but the shading is shown for convenience of explanation.

The formed plurality of n test patches 51
The laser write values Lna to Lnn of a to 51n are stored in the laser write value storage unit 45. On the other hand, the potential sensor 28 measures the surface potential V of the test patches 51a to 51n and stores the measured potential in the surface potential storage unit 46. The potential function generation unit 47 generates the laser writing values Lna to Lnn of the test patches 51a to 51n stored in the laser writing value storage unit 45 and the surface potentials of the test patches 51a to 51n stored in the surface potential storage unit 46. Vna to Vnn are input, and the test patches 51a to 51a shown in FIG.
The distribution characteristics of the laser writing value L and the surface potential V of 51n are obtained. The laser write value L of these test patches 51a to 51n
The distribution characteristics of na to Lnn and surface potentials Vna to Vnn are approximated by a higher order such as the third to sixth order, and the photosensitive member 12 shown in FIG.
, A latent image potential function V = f (L) indicating the relationship between the laser writing value L and the surface potential V is determined, and the determined latent image potential function V = f (L) and each coefficient are stored as information. It is stored in the unit 48. The information processing section 41 stores the characteristics of the photosensitive member 12 based on the latent image potential function V = f (L) stored in the information storage section 48, and controls the process such as the laser writing value L of the input image. And perform image forming processing. During this image forming process, the information processing section 41
The process conditions such as the change in the ambient temperature, the number of continuous copies, the total number of image formations on the photoreceptor 12, the elapsed time from the end of the last copy, etc., are stored in the information storage unit 48.

During the image forming process, the information processing unit 41 is operated by the charging control unit 13 and the exposure control unit 11 when an event that changes the characteristics of the photosensitive member 12 such as a change in ambient temperature occurs. To generate a correction patch, and instruct the coefficient update processing unit 49 to perform correction processing. When creation of a correction patch is instructed, the charging control unit 13 charges the surface of the photoconductor 12 under a fixed charging condition, and the exposure control unit 11 stores a plurality of e stored in the patch condition storage unit 44, for example, as shown in FIG. As shown in FIG. 3 (c), the electrostatic latent images of the three patches 52a to 52c are written with different laser writing values Le.
Is formed on the surface of the photoreceptor 12. The laser write values Lea to Lec of the formed patches 52a to 52c are stored in the laser write value storage unit 45. On the other hand, the potential sensor 2
8 measures the surface potentials Vea to Vec of the patches 52a to 52c and stores them in the surface potential storage unit 46. Coefficient update processing unit 4
Reference numeral 9 denotes a laser write value storage unit 45 when a correction process is instructed.
Of the patches 52a to 52c stored in the
Lec and the patches 52a-5 stored in the surface potential storage unit 46
The surface potentials Vea to Vec of 2c are input and the coefficient of the latent image potential function V = f (L) stored in the information storage unit 48 is corrected and updated.

When correcting the coefficient of the latent image potential function V = f (L), V = f (L) is set to αV = f (βL) + γ, and the laser writing values Lea to Lec and the surface potential The coefficients α, β, and γ are determined so as to satisfy Vea to Vec. At this time, V =
Since f (L) includes a higher-order term, the root of a higher-order linear equation is obtained. In this way, as shown in FIG. 3D, the latent image potential function V = f corrected by the patches 52a to 52c.
₁ (L) can be obtained. Where f ₁ (L) = ｛f
(ΒL) + γ｝ / α. The corrected latent image potential function V = f ₁ (L) and each coefficient are stored in the information storage unit 48.
The information processing section 41 grasps the characteristics of the photoconductor 12 from the latent image potential function V = f ₁ (L) stored in the information storage section 48, and controls the process such as the laser writing value L of the input image. To perform image forming processing.

As described above, the change of the ambient temperature and the like
The latent image potential function indicating the characteristics of the photoconductor 12 is corrected when an event that causes some change in the characteristics of the photoconductor 12 occurs, the characteristics of the photoconductor 12 are grasped by the latent image potential function V = f ₁ (L), and the input is performed. Since the process control such as the laser writing value L of the obtained image is performed, the characteristics of the photoconductor 12 can be accurately grasped, and a multi-tone image can be formed stably.

In the above embodiment, the test patch 51 is
The case where the test patches 51 are formed has been described, but the number is not limited to eight, and it is better to increase the number of test patches 51 in order to improve the accuracy. In addition, in order to avoid exposure unevenness and sensitivity unevenness on the photoconductor 12 when creating the test patch 51, it is preferable to shift the position and create a plurality of test patches 51 having the same write value and perform the averaging process. .

In the above embodiment, three correction patches 52 are used.
Although the description has been given of the case in which the laser writing value L is formed, at least two correction patches 52 of the maximum point and the minimum point of the laser writing value L are created to correct the coefficient of the latent image potential function V = f (L). You may do it. In this case, the latent image potential function V = f
(L) is set to αV = f (L) + γ, and the coefficients α and γ are determined so as to satisfy the laser writing value L and the surface potential V of the two correction patches 52. In this case, the correction patch 52
, The calculation process becomes easier because the solution of the higher-order function of the coefficient β does not need to be determined, so that the configuration of the coefficient update processing unit 49 can be simplified and the processing can be simplified. Time can be reduced.

In the information recording section 48, all the laser writing values L that can be taken together with the latent image potential function and the coefficient are stored in the latent image potential function V = f (L) or the corrected latent image potential function V = f _1. An LV table converted into a latent image potential V value using (L) may be created and stored. By storing the data in a table as described above, the calculation when the information processing section 41 refers to the characteristics of the photoconductor 12 can be omitted.

Further, since the number of correction patches 52 for updating the latent image potential function is as small as three or two,
The coefficient can be updated while operating the image forming apparatus. For example, at the time of continuous copying, the correction patch 52 may be formed in an area where the input image is not formed on the photoreceptor 12 between prints, or until the last transfer sheet is discharged after all the exposure is completed. The correction process may be performed by forming the correction patch 52 at the time.

In the above embodiment, the case where the latent image potential function V = f (L) is obtained by setting the gradation from 0 to 255 as one section has been described. However, as shown in FIG. Is divided into a plurality of, for example, three, and the divided sections LA and L
Test patches 51a to 51n are formed for each of B and LC to obtain a latent image potential function, and correction patches 52a to 52d are formed for each of the divided sections LA, LB and LC to update the latent image potential function. You may do it. By obtaining and updating the latent image potential function for each of the divided sections LA, LB, and LC, the characteristics of the photoconductor 12 can be accurately grasped, and the influence of the residual potential can be eliminated. .

Although the above embodiment has been described with reference to a monochrome image forming apparatus using one photoreceptor 12, the present invention can also be applied to a color image forming apparatus using four photoreceptors 12. In this case, the latent image potential function may be obtained and corrected for each photoconductor.

[0026]

As described above, according to the present invention, the surface of the photoreceptor is charged under a constant charging condition, and a plurality of n different gradations are formed on the photoreceptor surface by a plurality of n different laser writing values Ln.
The latent image of the test patch is formed, and the characteristics of the photoconductor, that is, the laser write value L and the surface potential are determined from the laser writing value L of each test patch and the distribution characteristics of the surface potential V of each test patch. A latent image potential function V = f (L) indicating the relationship of V is determined, the determined latent image potential function V = f (L) and each coefficient are stored, and the stored latent image potential function V = f (L). As a result, the characteristics of the photoreceptor can be grasped accurately, and thus the characteristics of the photoreceptor that changes with time can be accurately grasped, and high-quality images can be stably formed.

Also, when performing the image forming process,
When an event that changes the characteristics of the photoconductor such as a change in the ambient temperature occurs, the number of test patches n
An electrostatic latent image of a smaller number of correction patches is formed on the photoreceptor surface with different laser writing values Le, and the laser writing values Le of the plurality of correction patches formed and each correction patch are corrected. Latent image potential function V = f stored by patch surface potential Ve
Since the coefficient of (L) is corrected and updated, the changed characteristics of the photoreceptor can be accurately grasped, and a high-quality image can be stably formed even when environmental conditions such as a change in ambient temperature change. Can be.

Further, by dividing the gradation from 0 to 255 into a plurality of sections and obtaining and updating the latent image potential function for each of the divided sections, the characteristics of the photosensitive member can be accurately grasped and the residual The effect of the potential can be eliminated.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a control unit of the embodiment.

FIG. 3 is a characteristic diagram of a laser write value L and a surface potential V showing the operation of the embodiment.

FIG. 4 is an explanatory diagram illustrating a configuration of an electrostatic latent image of a test patch.

FIG. 5 is a characteristic diagram of a laser writing value L and a surface potential V showing an operation of another embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 Exposure operation value determination unit 11 Exposure control unit 12 Photoconductor 13 Charge control unit 28 Potential sensor 30 Temperature sensor 41 Information processing unit 42 Drive control unit 43 Condition input unit 44 Patch condition storage unit 45 Laser write value storage unit 46 Surface potential storage unit 47 Potential function generation unit 48 Information storage unit 49 Coefficient update processing unit

Claims (6)

[Claims] 1. An electrostatic latent image of a plurality of n test patches with different laser writing values Ln is formed on the surface of a photoreceptor under a constant charging condition, and the surface potentials of the plurality of n test patches thus formed are formed. Vn is measured, and a latent image potential function V = f (L) is determined from the measured surface potentials Vn of the plurality of n test patches and a laser writing value Ln when an electrostatic latent image of each test patch is created. Then, when an event that causes some change in the characteristics of the photoconductor occurs, an electrostatic latent image of a number e of patches smaller than the number n of test patches created to determine the latent image potential function V = f (L) Are created with different laser writing values Le, the surface potential Ve of the created e patches is measured, and the measured e
Latent image potential function V using surface potential Ve of each patch and laser writing value Le when an electrostatic latent image of each patch is created.
= F (L) coefficient is updated. 2. An electrostatic latent image of a plurality of n test patches with different laser writing values Ln is formed on the surface of a photoreceptor under a constant charging condition, and the surface potentials of the plurality of n test patches thus formed are formed. Vn is measured, and based on the surface potential V of a plurality of test patches measured for each section of the laser writing value divided in advance and the laser writing value L when an electrostatic latent image of each test patch is created. The number of test patches created to determine the latent image potential function V = f (L) and determine the latent image potential function V = f (L) when an event that causes some change in the characteristics of the photoconductor occurs. Electrostatic latent images of a number e of patches smaller than n are created with different laser writing values Le, and the surface potential Ve of the created e patches is measured. Using the laser writing value Le when the electrostatic latent image of each patch was created A latent image potential estimating device for updating a coefficient of a latent image potential function V = f (L) for each section of a laser writing value. 3. An event which causes a change in the characteristics of the photosensitive member is a change in ambient temperature, the number of continuous copies, the total number of image formations on the photosensitive member, the elapsed time since the end of the last copy, and the amount of charge. The latent image potential estimating device according to claim 1, wherein the latent image potential estimating device includes at least one of the information. 4. An electrostatic latent image of a plurality of n test patches with different laser writing values Ln is created on the surface of a photoreceptor under a constant charging condition, and the surface potentials of the plurality of n test patches created are formed. Vn is measured, and a latent image potential function V = f (L) is determined from the measured surface potentials Vn of the plurality of n test patches and a laser writing value Ln when an electrostatic latent image of each test patch is created. Then, when an event that causes some change in the characteristics of the photoconductor occurs, an electrostatic latent image of a number e of patches smaller than the number n of test patches created to determine the latent image potential function V = f (L) Are created with different laser writing values Le, the surface potential Ve of the created e patches is measured, and the measured e
Latent image potential function V using surface potential Ve of each patch and laser writing value Le when an electrostatic latent image of each patch is created.
= F (L) is updated, and the latent image potential estimating method is characterized in that: 5. An electrostatic latent image of a plurality of n test patches with different laser writing values Ln is created on the surface of a photoreceptor under a constant charging condition, and the surface potentials of the plurality of n test patches created are formed. Vn is measured, and based on the surface potential V of a plurality of test patches measured for each section of the laser writing value divided in advance and the laser writing value L when an electrostatic latent image of each test patch is created. The number of test patches created to determine the latent image potential function V = f (L) and determine the latent image potential function V = f (L) when an event that causes some change in the characteristics of the photoconductor occurs. Electrostatic latent images of a number e of patches smaller than n are created with different laser writing values Le, and the surface potential Ve of the created e patches is measured. Using the laser writing value Le when the electrostatic latent image of each patch was created A latent image potential estimating method characterized by updating a coefficient of a latent image potential function V = f (L) for each section of a laser writing value. 6. An event which causes a change in the characteristics of the photosensitive member includes changes in ambient temperature, the number of continuous copies, the total number of image formations on the photosensitive member, the elapsed time since the end of the last copy, and the amount of charge. The latent image potential estimating method according to claim 4 or 5, wherein at least one of the information is included.