JPH08106204A - Exposure condition setting method for image forming device - Google Patents

Abstract

PURPOSE: To easily and highly accurately set a proper exposure condition without being received the influence of the fluctuations of photosensitivity of a photosensitive body by calculating new proper values every setting of an exposure condition based on a reference value in which a last calculated proper value is reflected. CONSTITUTION: A last proper laser light emitting strength is preliminarily stored in an arithmetic device 41 of an image forming part in addition to offset amounts for calculating an objective dark potential an objective exposure potential, a fogging preventing potential, the reference value of a grid voltage and the proper laser light emitting strength of a next time. Then, the device 41 calculates a proper grid voltage with which the objective dark potential is obtained by detecting the dark potential at the time of making the grid voltage of an electrostatic charging device 43 as the reference value with a potentiometer 48 and next sets reference values of different two laser light emitting strengths by an offset from the proper laser light emitting strength calculated at the last time and then calculates the proper laser light emitting strength by a linear approximation based on these reference values. Thus, the proper laser emitting strength reflects states immadiately preceding the temp. and the film thickness of the photosensitive body and also is calculated without making the difference between reference values large.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure condition setting method for an electrostatic image forming apparatus, which performs exposure corresponding to an image by exposing means such as a laser.

[0002]

2. Description of the Related Art In an electrostatic image forming apparatus that exposes a photoconductor corresponding to an image by an exposing means such as a laser, the surface potential of the photoconductor corresponding to the image changes according to exposure conditions such as light intensity. However, since the image density changes, it is necessary to set the exposure condition to an appropriate state, and various exposure condition setting methods have been conventionally proposed.

For example, in Japanese Patent Laid-Open No. 3-89269, the exposure conditions of the exposing means are changed to different states, and the surface potential of the photoconductor in each state is measured using a predetermined photoconductor potential measuring means. There is disclosed a method of setting an appropriate exposure condition based on. In this method, as shown in FIG. 5, a photosensitive member charged to a predetermined potential is exposed with two different laser emission intensities LD1 and LD2, and the potential (hereinafter referred to as the exposure partial potential) VL1 in each exposed portion is exposed. And VL2 are measured. Then, the laser emission intensity LDS at which the optimum photosensitive partial potential VLS is obtained is calculated from VL1 and VL2 by linear approximation as shown in the figure.

[0004]

By the way, since the photosensitivity of a photoconductor generally becomes lower as the potential becomes lower,
As shown in FIG. 6, it has a property that the rate of decrease of the potential becomes slower as the laser intensity increases, and becomes saturated when the potential drops to a certain level. Further, it has been known that the photosensitivity of an organic photoconductor, which has been particularly actively used in recent years, greatly changes depending on the temperature of the photoconductor as shown in FIG. 7. For example, a certain target potential (here, 200 V) is used. The amount of light required to obtain the above is 1.05 mW at room temperature, 0.8 mW at high temperature, and 1.4 mW at low temperature. Also,
It is also known that the photosensitivity of the photoconductor is reduced due to the reduction of the film thickness on the surface with repeated use.

When the conventional exposure condition setting method shown in FIG. 5 is applied to the image forming apparatus using the photoconductor having such a property, the following problems occur. That is, in the conventional example of FIG. 5, the two measured potentials VL1,
The laser emission intensity LDS at which the optimum exposure partial potential VLS is obtained was calculated by linearly approximating between VL2. However, as shown in FIG. 6, the reduction rate of the potential becomes slower as the laser intensity increases. , A downward convex curve is formed between the potentials VL1 and VL2. Therefore, if the difference between the two laser emission intensities LD1 and LD2 set as the reference value is made too large, the influence of the curve curvature increases, and the accuracy of the laser emission intensity LDS calculated by linear approximation decreases.

On the other hand, if the difference between the two reference values LD1 and LD2 is set to be too small, the laser emission intensity LDS calculated by linear approximation is out of the range sandwiched by these reference values LD1 and LD2. Will decrease. Therefore, the two reference values LD1 and LD2 are
It is desirable to set the difference as small as possible within a range including the laser emission intensity LDS at which a proper exposure partial potential VLS is obtained, in consideration of variations in assumed devices and photoconductors.

However, as described above, since the photosensitivity of the photoconductor greatly changes in accordance with changes in temperature and film thickness, in the end, a difference between the two reference values LD1 and LD2 is to be expected in consideration of some allowable error. Must be set to a large value. In order to avoid this, a method of increasing the number of reference values can be considered. However, this method requires a lot of time and effort to set the exposure amount, which causes a problem of poor usability. There is also a method of approximating between two reference values by a quadratic function or the like instead of a straight line, but in this case, there is a problem that processing becomes complicated.

The present invention has been made under such a background, and even if the photosensitivity of the photoconductor is changed, it is not affected and the proper exposure conditions can be set easily and accurately. It is an object of the present invention to provide an exposure condition setting method for an image forming apparatus that can be performed.

[0009]

In order to solve the above-mentioned problems, the invention according to claim 1 provides a charged photoreceptor,
It is applied to an image forming apparatus which forms a latent image by performing exposure corresponding to an image by a predetermined exposure means, develops the latent image on the surface of the photoconductor, and then transfers it to a printing medium to obtain a printed image. An exposure condition setting method, comprising: a first step of changing a predetermined exposure condition of the exposure means into at least two different states, and detecting a photoconductor surface potential in each state; and a detection result of the first step. On the basis of the second step of calculating an appropriate value of the exposure condition for obtaining the target photoconductor surface potential, and based on the appropriate value of the exposure condition calculated in the second step, the second step is set in the next exposure condition setting. And a third step of setting a reference value for changing the exposure condition in one step.

The invention according to claim 2 is characterized in that, in the invention according to claim 1, the exposing means is a laser beam and the exposing condition is a laser emission intensity.

According to a third aspect of the present invention, in the first aspect of the present invention, the exposure means is a laser beam, and the exposure condition is a pulse width for controlling the on / off time of the laser. It is characterized by that.

[0012]

According to the first aspect of the present invention, each time the exposure condition is set, the reference value reflecting the proper value of the exposure condition calculated last time is set, and based on these reference values, the appropriateness of the new exposure condition is set. The value is calculated.

According to the invention of claim 2, in the invention of claim 1, the laser emission intensity is set as the exposure condition.

According to the invention of claim 3, in the invention of claim 1, a pulse width for controlling on / off of the laser is set as an exposure condition.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing the mechanical structure of a color copying machine to which an embodiment of the present invention is applied, and FIG. 2 is a block diagram showing the electrical structure of the copying machine. As shown in FIG. 1, this color copying machine drives a laser in accordance with a scanner unit 10 for reading a document set on a document table ST, an image processing unit 20 for processing the read image data, and a processed image data. The photoconductor 42 includes a ROS optical unit 30 that irradiates a light beam, and an image forming unit 40 that forms a print image.

As shown in FIG. 2, the scanner unit 1
At 0, the original OS is irradiated with light by the exposure lamp 11, the reflected light is read by the CCD 12, amplified by the amplifier 13 to an appropriate level, and then converted into 8-bit digital image data by the A / D converter 14. . Then, for this image data, shading correction (reference numeral 15),
After performing the gap correction (reference numeral 16), the density conversion unit 17
Then, the reflectance data is converted into density data, which is sent to the image processing unit 20.

The image processing unit 20 performs color signal conversion, black reproduction (UCR), which is basic image processing for a color copying machine, on the density data supplied from the scanner unit 10.
MTF processing or the like is performed (reference numeral 21) to convert into image data of four colors of yellow, magenta, cyan and black. Then, after gamma correction (reference numeral 22), the gradation of each color is corrected in accordance with the gradation of the image forming unit 40, which will be described later, and the D / A converter 23 converts the gradation into analog data. This analog image data is compared in the comparator 24 with the triangular wave signal of the predetermined period supplied from the triangular wave generator 25. Based on the comparison result, the analog image data is pulse-width modulated and converted into binary image data.

That is, as shown in FIG. 3, in the comparator 24, the analog image data AS is compared with the triangular wave TS, and when the analog image data AS is larger than the triangular wave TS, the value is "0", and the analog image data AS is the triangular wave TS. When it is smaller, it is converted into binary image data PS having a value of “1” and output to the ROS optical unit 30. ROS optical section 3
At 0, the laser is turned off when the value of the binary image data PS is “0”, and turned on when the value is “1”.

The patch generator 26 also generates patch data to create a reference latent image patch in a predetermined area outside the image area on the photoconductor 42 when the exposure condition is set. The selector 27 selects either the patch data output from the patch generator 26 or the analog image data output from the D / A converter 23, and supplies it to the comparator 24. That is, in addition to the normal copy operation mode, this copying machine has an exposure condition setting mode in which the exposure condition is set using a predetermined reference latent image patch. Data is selected, and patch data is selected in the exposure condition setting mode. Details of the operation in the exposure condition setting mode will be described later.

The ROS optical section 30 is provided with a laser light quantity varying device 31 and a laser driving circuit 32, which are controlled by the arithmetic unit 41 of the image forming section 40 to change the laser light quantity, and the laser driving circuit 32 is a comparator. Based on the binarized data PS supplied from 24, the laser 33 is on / off controlled. The laser light is deflected by the polygon mirror 34 and guided to the photoconductor 42 of the image forming unit 40 via the f · θ lens 35 and the reflection mirror 36.

In the image forming section 40, a charging device 43, a rotary developing device 44, a transfer device 45 are provided around the photosensitive member 42.
A cleaner device 46, a charge eliminating lamp 47, and an electrometer 48 for measuring the surface potential of the photoconductor are arranged. In addition to the arithmetic unit 41 for controlling the image formation, the arithmetic unit 41
In addition to the charge amount varying device 49 for controlling the charge amount of the charging device 43 controlled by the above, the toner dispensing device 50 for supplying toner to the developing devices of the respective colors of the rotary developing device 44, as shown in FIG. Paper transport device 5
2, a paper tray 53 and the like are provided.

With this configuration, image formation is performed according to the well-known xerographic process. That is, the rotating photoconductor 42 is uniformly negatively charged by the charging device 43, and then the first latent image “black” of the first color is formed by the laser light. This latent image is that black toner negatively charged by the developing device corresponding to the first color “black” of the rotary developing device 44 is attracted to a portion of the photoconductor 42 where the negative charge is removed by the developing bias voltage. To be developed. This developed image is
A transfer corotron 45b transfers the sheet onto a sheet (not shown) conveyed from the sheet tray by the sheet conveying device 52 and wound around the transfer drum 45a. The image that has not been transferred and remains on the photoconductor 42 is removed by the cleaner device 46, the photoconductor 42 is neutralized by the static elimination lamp 47, and is again uniformly negatively charged by the charging device 43. Image formation follows.

In this way, the third color "magenta",
The developed images of four colors up to the fourth color "cyan" are transferred onto the transfer drum 45.
When the sheets are sequentially transferred to the sheet on a, the sheet is peeled from the transfer drum 45a by the peeling corotron 45c, and then the toner is fixed by the fixing device 51 to form a color copy. A static elimination corotron 45d is provided around the transfer drum 45a.
5d removes excess charges on the paper and on the film of the transfer drum 45a after the transfer of each color or the peeling of the paper.

Next, the operation of the photosensitive member potential control in the exposure condition setting mode according to this embodiment will be described with reference to the flow chart shown in FIG. In the present embodiment, the following operation is performed in response to an instruction from the arithmetic unit 41 before the start of copying immediately after the power of the copying machine is turned on and before the start of copying at every predetermined time thereafter. The present invention is not limited to this, and the following operation can be performed during copying or the like according to the sensitivity variation characteristic of the photoconductor 42 to be used.

First, in the initial state, the arithmetic unit 41 of the image forming section 40 has a target dark potential (a target potential of a dark portion on the photoconductor) VHS, a target exposure potential (a target potential of an exposure portion on the photoconductor) VLS, in advance. Target dark potential VHS and developing bias potential V
In addition to the fog prevention potential difference VC which is the potential difference from B, the reference values VG1 and VG2 of the grid voltage, and the offset amount LDoffset for calculating the next proper laser emission intensity, the proper laser emission obtained by the previous photoreceptor potential control The strength LDS is stored.

In step S1, the grid voltage of the charging device 43 is set to the reference value VG by the charging amount varying device 49.
1 and VG2, the dark potentials VH1 and VH2 are detected by the electrometer 48. Furthermore, in step S2, the following equation (1)
Then, an appropriate grid voltage VGS with which the target dark potential VHS is obtained is calculated. VGS = (VG2-VG1) × (VHS-VH1) / (VH2-VH1) + VG1 ……………………………………………… (1)

Next, in step S3, exposure conditions are set. In this embodiment, the reference value LD1 of the laser emission intensity is
LD2 is calculated by the following equations (2) and (3) based on the offset amount LDoffset stored in the arithmetic unit 41 and the proper laser emission intensity LDS obtained in the previous photoconductor potential control. LD1 = LDS-LDoffset ………………………… (2) LD2 = LDS + LDoffset ………………………… (3)

That is, since the reference values LD1 and LD2 are newly set on the basis of the appropriate value LDS of the laser emission intensity of the previous time, the two reference values LD1 and LD2 are set without making the difference between LD1 and LD2 too large. A new proper laser emission intensity LDS can be obtained during the period.

Then, in step S4, the photosensitive member 4 is driven by the proper grid voltage VGS obtained in step S2.
2 is charged, and the selector 27 causes the arithmetic unit 41 to operate.
The patch data from the patch generator 26 is selected in accordance with the instruction of, and this is output to the comparator 24. As a result, the patch data is compared with the triangular wave, and the binarized data is supplied to the laser drive circuit 32 of the ROS optical unit 30.
On the other hand, the laser light amount varying device 31 determines the laser emission intensity of the laser 33 driven by the laser drive circuit 32 in the step S
It is changed to two different values LD1 and LD2 obtained in 3. As a result, each laser emission intensity LD1, LD2
A patch corresponding to is created on the photoconductor 42. Then, the respective patch potentials VL1 and VL2 at this time are detected by the electrometer 48.

Next, in step S5, the target exposure potential V
The appropriate laser emission intensity LDS for obtaining LS is calculated by linear approximation between the two points shown in FIG. Then, in step S6, the development bias potential VB is obtained by calculating the difference between the target dark potential VHS and the fog prevention potential difference VC. Further, in step S7, the proper grid voltage VGS, the proper laser emission intensity LDS and the developing bias potential VB calculated as described above are stored in the arithmetic unit 41, and thereafter, an image is formed based on these values. In this way, the above-described operation is repeated in the next photoconductor potential control, and a new proper laser emission intensity LDS reflecting the calculated value this time is obtained.

As described above, according to this embodiment, when the laser emission intensity is set as the exposure condition for obtaining the target exposure potential VLS, the linear approximation based on the two different reference values LD1 and LD2 of the laser emission intensity. However, since the two reference values LD1 and LD2 are set by the offset LDoffset from the previously obtained appropriate laser emission intensity LDS, the immediately preceding conditions such as the temperature and the film thickness of the photoconductor are reflected. And two reference values L
Even if the difference between D1 and LD2 is not so large, a new proper laser emission intensity L is obtained between these reference values LD1 and LD2.
The DS can be obtained. As a result, even if the photosensitivity of the photoconductor changes due to the temperature change of the photoconductor or the decrease of the film thickness, it is not affected, and the exposure condition can be set with high accuracy by a simple method using linear approximation. You can

In the above-described embodiment, the laser emission intensity which can be changed by the laser light amount changing device 31 is used as the exposure condition, but the present invention is not limited to this. For example, the pulse width when the laser 33 is on / off controlled. (That is, laser O
The exposure condition may be N time intervals). In this case, the control target is the analog voltage of the patch data (image area ratio 100%) output from the patch generator 26.
As described above, changing the analog voltage input to the comparator 24 changes the pulse width for turning on / off the laser 33. Therefore, in step S3 of FIG. 4, the analog voltages of the two patch data that are reference values are set, in step S4 the patch potentials VL1 and VL2 in the analog voltages of the respective patch data are detected, and then in step S
By calculating the analog voltage of the patch data for obtaining the target exposure potential VLS in 5 by linear approximation between two points and setting the value as the analog voltage with the image area ratio of 100%,
It is possible to obtain the same effect as that of the above embodiment.

[0033]

As described above, according to the present invention, the reference value for calculating the appropriate value of the exposure condition is set based on the previously obtained appropriate value. The state immediately before is reflected, and a new appropriate value can be obtained within the range of these reference values without making the difference between the reference values too large. As a result, even if the photosensitivity of the photoconductor changes due to the temperature change of the photoconductor or the decrease of the film thickness, it is not affected, and the accurate exposure condition can be accurately adjusted by a simple method using linear approximation. Can be set.

[Brief description of drawings]

FIG. 1 is a perspective view showing a mechanical structure of an embodiment of the present invention.

FIG. 2 is a block diagram showing an electrical configuration of the embodiment.

FIG. 3 is a diagram for explaining binarization of image data by pulse width modulation performed in the same embodiment.

FIG. 4 is a flowchart for explaining the operation of the embodiment.

FIG. 5 is a diagram for explaining a conventional exposure condition setting method.

FIG. 6 is a graph showing the relationship between laser intensity and photoreceptor surface potential.

FIG. 7 is a graph showing the relationship between the laser intensity and the photoconductor surface potential in each temperature region.

[Explanation of symbols]

 10 Scanner Section 20 Image Processing Section 30 ROS Optical Section 31 Laser Light Amount Adjusting Device 32 Laser Driving Circuit (Exposure Means) 33 Laser (Exposure Means) 40 Image Forming Section 41 Arithmetic Device 42 Photoconductor 48 Electrometer

Claims (3)

[Claims] 1. A latent image is formed on a charged photoconductor by exposing the charged photoconductor in accordance with an image by a predetermined exposure means, and the latent image on the surface of the photoconductor is developed and then transferred to a print medium. An exposure condition setting method applied to an image forming apparatus for obtaining a printed image by changing a predetermined exposure condition by the exposing means into at least two different states, and detecting a photoconductor surface potential in each state. 1 step and a second step of calculating an appropriate value of an exposure condition for obtaining a target photoconductor surface potential based on the detection result of the 1st step
An image including a step and a third step of setting a reference value for changing the exposure condition in the first step in the next exposure condition setting based on the appropriate value of the exposure condition calculated in the second step Exposure condition setting method for forming apparatus. 2. The exposing means is a laser beam,
The exposure condition setting method according to claim 1, wherein the exposure condition is a laser emission intensity. 3. The exposure means uses laser light,
2. The exposure condition setting method according to claim 1, wherein the exposure condition is a pulse width for controlling a laser on / off time.